Showing papers in "The Journal of Neuroscience in 1981"

Activity of norepinephrine-containing locus coeruleus neurons in behaving rats anticipates fluctuations in the sleep-waking cycle

Abstract: Spontaneous discharge of norepinephrine-containing locus coeruleus (NE-LC) neurons was examined during the sleep-walking cycle (S-WC) in behaving rats. Single unit and multiple unit extracellular recordings yielded a consistent set of characteristic discharge properties. (1) Tonic discharge co-varied with stages of the S-WC, being highest during waking, lower during slow wave sleep, and virtually absent during paradoxical sleep. (2) Discharge anticipated S-WC stages as well as phasic cortical activity, such as spindles, during slow wave sleep. (3) Discharge decreased within active waking during grooming and sweet water consumption. (4) Bursts of impulses accompanied spontaneous or sensory-evoked interruptions of sleep, grooming, consumption, or other such ongoing behavior. (5) These characteristic discharge properties were topographically homogeneous for recordings throughout the NE-LC. (6) Phasic robust activity was synchronized markedly among neurons in multiple unit populations. (7) Field potentials occurred spontaneously in the NE-LC and were synchronized with bursts of unit activity from the same electrodes. (8) Field potentials became dissociated from unit activity during paradoxical sleep, exhibiting their highest rates in the virtual absence of impulses. These results are generally consistent with previous proposals that the NE-LC system is involved in regulating cortical and behavioral arousal. On the basis of the present data and those described in the following report (Aston-Jones, G., and F. E. Bloom (1981) J. Neurosci.1: 887-900), we conclude that these neurons may mediate a specific function within the general arousal framework. In brief, the NE-LC system may globally bias the responsiveness of target neurons and thereby influence overall behavioral orientation.

Nonrepinephrine-containing locus coeruleus neurons in behaving rats exhibit pronounced responses to non-noxious environmental stimuli

Abstract: The effect of sensory stimulation on discharge in norepinephrine- containing locus coeruleus (NE-LC) neurons was studied in unanesthetized behaving rats. Single unit and multiple unit extracellular recordings demonstrated consistent patterns of response. (1) Short latency (15-to 50-msec), transient, biphasic changes in discharge were elicited predictably by non-noxious auditory, visual, and somatosensory stimuli; individual recordings typically exhibited polysensory responsiveness. (2) Sensory-evoked field potentials (FPs) were synchronized with unit responses simultaneously recorded from the same electrodes. (3) The magnitudes of sensory-evoked response varied as a function of vigilance, so that the largest responses occurred for stimuli which awakened animals and the least responsiveness was exhibited during uninterrupted sleep. (4) Sensory responsiveness decreased during grooming and sweet water consumption, similar to the results for sleep. (5) Characteristic response properties were topographically homogeneous throughout the NE-LC. (6) Discharge was synchronized markedly among neurons in multiple unit populations during phasic robust responses. These results are interpreted in light of the preceding report (Aston-Jones, G., and F.E. Bloom (1981) J. Neurosci. 1: 876–886) and studies of the postsynaptic effects of NE to indicate that the NE-LC system may function more in phasic processes than in modulation of the tonic arousal level. We propose that pronouced NE-LC discharge may enhance activity within target cell systems primarily concerned with processing salient external stimuli and suppress cental nervous system activity related more to tonic, vegetative functions. Thus, the NE-LC system may bias global behavioral orientation between stimuli in the external versus internal environments.

Invariant characteristics of a pointing movement in man

Abstract: Simple arm movements involving forward projection of the hand toward a target were studied by measuring simultaneous wrist position in three-dimensional space and changes in elbow angle. An attempt was made to identify those features of the movement which exhibit invariant characteristics under the hypothesis that such invariances may reflect the operations by which central processes participate in the organization of the movement. The first such invariance to be identified was that the trajectory in space is independent of movement speed. Secondly, the movement can be viewed as consisting of two phases, an acceleratory phase and a deceleratory one, with the movement during the acceleratory phase being so organized as to maintain the ratio of elbow angular velocity to shoulder angular velocity invariant with respect to target location in the deceleratory phase. It is suggested that proprioceptive information is used to control the movement and that the latter invariance may result from a negative feedback of force involving tendon organ afferents.

An autoradiographic study of the projections of the central nucleus of the monkey amygdala

Abstract: The efferent connections of the central nucleus of the monkey amygdala have been studied using the autoradiographic method for tracing axonal projections. Small injections of 3H-amino-acids which are largely confined to the central nucleus lead to the labeling of several brainstem nuclei as far caudally as the spinomedullary junction. Specifically, in the forebrain, the central nucleus projects heavily to the bed nucleus of the stria terminalis, the basal nucleus of Meynert, the nucleus of the horizontal limb of the diagonal band, and more lightly to the substantia innominata and the preoptic area. In the hypothalamus, label is found over the dorsomedial nucleus, the perifornical region, the lateral hypothalamus, the supramammillary area, and most heavily in the paramammillary nucleus. In the thalamus, all components of the nucleus centralis medialis and the nucleus reuniens receive fibers from the central nucleus and there is a light projection to the medial pulvinar nucleus. In the mesencephalon, there is heavy labeling dorsal to the substantia nigra ad over the peripeduncular nucleus and lighter labeling within the substantia nigra pars compacta and the ventral tegmental area; the midbrain central gray is also labeled. More caudally, fibers from the central nucleus travel in the lateral tegmental reticular fields and contribute collaterals to the raphe nuclei, the cuneiform nucleus, and the central gray substance. Perhaps one of the heaviest terminal zones is the parabrachial region of the pons, both the lateral and the medial nuclei of which receive a prominent central nucleus projection. Only the ventral aspect of the adjacent locus coeruleus appears to receive a substantial input, but there is labeling also over the area of the nucleus subcoeruleus. Finally, there is heavy labeling around the dorsal motor nucleus of the vagus and over the parvocellular component of the nucleus of the solitary tract. A number of intra-amygdaloid connections between the basal and lateral nuclei of the amygdala and the central nucleus are also described. The present findings, taken together with recently reported widespread projections from the temporal association cortex to the amygdala, point out a potentially trisynaptic route between neocortical association regions and a variety of brainstem nuclei, many of which are related to autonomic function.

The functional properties of the light-sensitive neurons of the posterior parietal cortex studied in waking monkeys: foveal sparing and opponent vector organization.

Abstract: We describe in this paper the results of a new study of the inferior parietal lobule in 10 waking monkeys combining the methods of behavioral control, visual stimulation, and single neuron analysis. In this study, 1682 neurons were identified; 804 were studied in detail. Neurons insensitive to visual stimuli comprise the fixation, oculomotor, and projection-manipulation classes thought to be involved in initiatives toward action. The largest group of the light-sensitive (LS) neurons were activated from large and frequently bilateral response areas that excluded the foveal region; we term this foveal sparing. The remaining cells subtended areas including the fovea, when tested with large stimuli (6 degrees X 6 degrees), but only 8 of 216 cells studied in detail responded to the small fixation target light. We propose that a dynamic central neural process associated with the acts of fixation and visual attention suppresses responses to foveal stimuli. Parietal LS neurons are sensitive to stimulus movement and direction over a wide range of velocities. The vectors point either inward toward the center or outward toward the perimeter of the visual field, and for neurons with bilateral response areas, the vectors commonly point in opposite directions in the two half-fields; we term this opponent vector organization. The functional properties of area 7 LS neurons are such that they could signal motion in the immediate surround and the apparent motion accompanying head movements and forward locomotion. We surmise that they contribute to a central neural image of immediately surrounding space and to the perceptual constancy of that space obtaining during bodily movement. These properties are suitable for the attraction of gaze and attention to objects and events in the peripheral visual fields. It is this system, together with the classes of parietal neurons concerned with action initiatives, whose destruction is thought to account for the hemi-inattention and neglect of the parietal lobe syndrome in primates.

Neuronal death in the spinal ganglia of the chick embryo and its reduction by nerve growth factor.

Abstract: In the spinal ganglia of the chick embryo, two neuronal populations can be distinguished: large, early differentiating ventrolateral (VL) cells and small, late differentiating dorsomedial (DM) cells. It was found that, beginning with stage 25, the DM cells originate from a narrow band of small, immature cells at the medial border of the ganglion, extending to the dorsolateral border. We have designated this band as the inner and outer marginal zone. Neuronal death was investigated in thoracic ganglion 18 and brachial ganglion 15 by counting degenerating cells, separately for the VL and DM populations, at every stage from stage 24 (4% days) to stage 38 (12 days). In both ganglia, separate degeneration periods were found for the VL and DM populations which do not overlap. The peaks of degeneration are: stage 27 (5% days) for the VL population in ganglion 18, stage 30 (6% to 7 days) for VL in ganglion 16, and stage 35 (8% days) for DM in both ganglia. Daily injections of 6 pg of nerve growth factor, (NGF) in 6 to 12 ~1 of 0.9% sterile salt solution into the yolk sac from stage 21 (3% days) to the day of sacrifice resulted in a significant reduction of neuronal death in the VL population of ganglion 18 and in the rescue of practically all VL neurons in ganglion 15 and all DM neurons in both ganglia, which normally would have died. This is the first demonstration of an NGF effect on VL neurons. In the analysis of the multiple effects of nerve growth factor (NGF), the sympathetic ganglia have played the dominant role; the sensory ganglia which are the other target of NGF have attracted much less attention. Yet, if one entertains the notion that NGF might be the natural trophic maintenance agent for these two neuron types (i.e., that NGF is actually produced by their target organs), then one approach to the testing of this hypothesis would be to engage in in viva experiments. For this

Autoradiographic localization of muscarinic cholinergic receptors in rat brainstem

Abstract: We have localized muscarinic cholinergic receptors in the rat brainstem by a light microscopic autoradiographic method. Initially, we examined the kinetics and specificity of the binding of radiolabeled quinuclidinyl benzilate ([3H]QNB) in slide-mounted, frozen tissue sections to determine that we were labeling the muscarinic cholinergic receptors as they had been described previously in biochemical pharmacological studies. Subsequently, using optimal binding parameters to obtain high specific to nonspecific ratios, we labeled tissue sections and generated autoradiograms by the apposition of emulsion- coated coverslips. We found high concentrations of autoradiographic grains associated with many nuclei in the brainstem including the superior colliculus, nuclei of the lateral lemniscus, pontine nucleus, parabrachial nucleus, trigeminal nerve nucleus (V), the tegmental nuclei, nucleus of the facial nerve (VII), the locus coeruleus, the medial vestibular nucleus, cochlear nucleus, of the tractus solitarius, and nucleus of the hypoglossal nerve (XII). We conclude that muscarinic cholinergic effects of acetylcholine and important in the normal function of both the sensory and motor systems. We speculate on the possible mechanisms of action of certain cholinergic agents, such as the mechanism of anticholinergic compounds when used to treat motion sickness or anticholinesterase poisoning.

Coexistence of neuronal and glial precursor cells in the cerebral ventricular zone of the fetal monkey: an ultrastructural immunoperoxidase analysis

Abstract: The cytological composition of the proliferative zones in the fetal monkey occipital lobe was examined at the light and electron microscopic levels by immunoperoxidase localization of glial fibrillary acid protein (GFA), a protein that is present in astrocytes and radial glial cells but not neurons. During the peak of neurogenesis at embryonic day 80, two distinct classes of proliferative cells, GFA-positive and GFA-negative, are intermixed in the ventricular and subventricular zones. Both cell types are readily recognized in different phases of the mitotic cycle along the ventricular surface. The results indicate that, contrary to prevailing views, (1) glial and neuronal cell lines coexist within the fetal proliferative zones and (2) the onset of glial phenotypic expression occurs prior to the last cell division.

The influence of attentive fixation upon the excitability of the light- sensitive neurons of the posterior parietal cortex

Abstract: We describe the effect of behavioral state upon the excitability of light-sensitive (Ls) neurons of the inferior parietal lobule, area 7a, studied in waking monkeys. The responses of parietal LS neurons to visual stimuli are facilitated during the state of attentive fixation of a target light as compared to their responses to physically and retinotopically identical test stimuli delivered during the eye pauses of alert wakefulness. Seventy percent of the neurons tested (n = 55) showed significant increments in responses in the state of attentive fixation; the median value of the increments was 3.5 times. Only 4 of the 55 cells examined completely showed the reverse relation. Three sets of control experiments were done. The facilitation occurred when the responses evoked during the trials of a reaction task with attentive fixation of a target were compared with those evoked by identical stimuli delivered to the same retinotopic locations at the end of each intertrial interval: the facilitation of attentive fixation is not due to a shift in the general level of arousal. The facilitation occurred when the animal maintained attentive fixation of a spot of the tangent screen without a target light or when an additional light mimicking the target light was presented along with testing stimuli in the state of alert wakefulness without attentive fixation: the facilitation is not produced by a sensory-sensory interaction between target and testing lights. Finally, the facilitation was observed whether or not the test stimuli were behaviorally relevant. We conclude that the act of attentive fixation exerts a specific and powerful effect upon the excitability of the neural systems linking the retinae and the inferior parietal lobule and that the facilitation plays an important role in visually guided behavior.

Hormonal control of cell form and number in the zebra finch song system

Abstract: Administration of testosterone (T), 17 beta-estradiol (E2), or 5 alpha- dihydrotestosterone (DHT) to female zebra finch chicks (Poephila guttata) at hatching exerts effects on brain sexual differentiation. Within a telencephalic station (the nucleus robustus archistriatalis, RA) of the neural pathway which participates in the efferent control of song, masculinization of several indices of neuronal size is induced by exposure to T or E2. Within RA, a sensitive assay of a single neuron's sexually differentiated state is the diameter of its soma. By this criteria, all of the neurons within RA can be masculinized with a sufficient dose of T. As the dose of T is progressively decreased, the proportion of RA neurons which undergo the transition from female to male falls, while the magnitude of the change in soma size remains basically unaltered. Administration of T or DHT masculinizes the number of neurons in RA.

Immunocytochemical localization of vasoactive intestinal polypeptide- containing cells and processes in the suprachiasmatic nucleus of the rat: light and electron microscopic analysis

Abstract: The distribution of vasoactive intestinal polypeptide-like (VIP) immunoreactivity in neurons and processes within the suprachiasmatic nuclei (SCN) of the rat was investigated with light and electron microscopic immunocytochemical techniques These studies utilized well characterized antisera directed to synthetic vasoactive intestinal polypeptide Specificity was established by absorption of the antisera with synthetic vasoactive intestinal polypeptide Neurons and dendrites exhibiting specific VIP immunoreactivity are concentrated in the ventral half of the nucleus, with the greatest concentration of immunoreactive perikarya occurring in the ventral SCN immediately adjacent to and within the optic chiasm (OC) Thin varicose axons containing VIP immunoreactivity are present throughout the SCN A large number of immunoreactive axons leave the dorsal aspect of the SCN to reach the periventricular hypothalamic nucleus and continue dorsally to form an extensive plexus along the ventral border of the paraventricular hypothalamic nucleus Other immunoreactive axons project upon the contralateral SCN via the OC Ultrastructurally, VIP- containing neurons in the SCN are characterized by a spherical to slightly elongated soma and an invaginated nucleus that fills the majority of the cell body In the soma, peroxidase reaction product is localized on the outer membrane of all cellular organelles The reaction product of immunoreactive boutons is related primarily to vesicles, and some of these boutons establish axodendritic synaptic contacts in the SCN The demonstration of VIP-containing neurons in the SCN provides further evidence that this nucleus is composed of a heterogeneous population of neurons which form distinct subfields within it

Neuronal and behavioral sensitivity to binaural time differences in the owl

Abstract: We demonstrated that ongoing time disparity (OTD) was a sufficient cue for the azimuthal component of receptive fields of auditory neurons in the owl (Tyto alba) midbrain and that OTDs were sufficient to mediate meaningful behavioral responses. We devised a technique which enabled us to change easily between free field and dichotic stimuli while recording from single auditory neurons in the owl mesencephalicus lateralis pars dorsalis (MLD). MLD neurons with restricted spatial receptive fields (“space-mapped neurons”) showed marked sensitivity to specific ongoing time disparities. The magnitudes of these disparities were in the behaviorally significant range of tens of microseconds. The ongoing time disparities were correlated significantly with the azimuthal center of receptor fields. Space-mapped neurons were insensitive to transient disparities. MLD neurons which were not space- mapped, i.e., were omnidirectional, did not show any sensitivity to specific OTDs. We confirmed the behavioral relevance of OTD as a cue for localizing a sound in azimuth by presenting OTD differences to tame owls. Using head turning as an assay, we showed that OTD was a sufficient cue for the azimuth of a sound. The relationship between azimuth and OTD obtained from our neurophysiological experiments matched closely the relationship obtained from our behavioral experiments.

Presynaptic inhibitory effect of acetylcholine in the hippocampus.

Abstract: (1) In order to investigate the effects of acetylcholine (ACh) on synaptic transmission in the rat hippocampus, extracellular and intracellular recordings were made from pyramidal neurons in an in vitro slice preparation while synaptic inputs to the cell population were stimulated. ACh was applied ionophoretically into somatic and dendritic layers of the slice. (2) ACh applied into the apical dendritic layer of the CA1 region reduced the size of the locally evoked field excitatory postsynaptic potential (EPSP) without altering the size of the afferent fiber volley. Likewise, dendritically applied ACh reduced the size of intracellularly recorded EPSPs. This effect of ACh appeared to be muscarinic since it was not affected by hexamethonium (up to 3 X 10-5 M) but was antagonized by atropine in a dose-dependent manner. (3) The distribution of Ach-sensitive sites matched closely the spatial distribution of activated synapses on the pyramidal cell dendrites as shown by ionophoretic mapping experiments. (4) In contrast to the effects of dendritic applications of ACh, ionophoresis of ACh into the cell layer resulted in an increase and prolongation of EPSPs and a transient decrease in the size of recurrent somatic inhibitory postsynaptic potentials (IPSPs). These effects on synaptic potentials could not be explained by the observed changes in membrane potential and input resistance following somatic application of ACh. (5) Short dendritic applications of ACh had no consistent effect on the membrane potential or slope conductance of pyramidal neurons and did not attenuate the depolarization evoked by brief dendritic applications of glutamate. In addition, the time course of ACh-reduced EPSPs was not different from control. (6) We conclude that ACh exerts a presynaptic inhibitory effect on both excitatory and inhibitory afferents to hippocampal pyramidal neurons. This effect of ACh is widespread, occurring in all regions of Ammon's horn tested as well as in stratum moleculare of fascia dentata.

Local circuit synaptic interactions in hippocampal brain slices

Abstract: The hypothesis that recurrent inhibition in the hippocampus is mediated by interneurons was tested with simultaneous intracellular recordings from the CA1 region of guinea pig hippocampal slices in vitro. In recordings from 101 pairs of pyramidal cells, no interactions were detected in 87% of the pairs. In 13% of the pyramidal cell pairs, spike trains induced in one cell caused inhibitor postsynaptic potentials (IPSPs) in the second cell. No excitatory interactions were detected. In recordings from 43 pairs of cells, where one cell was a pyramidal cell and the other cell was an interneuron, no interactions were detected in 53% of the pairs. In 30% of the interneuron-pyramidal cell pairs, spike trains elicited from the interneuron caused IPSPs in the pyramidal cell. In 28% of the pairs, spike trains elicited from the pyramidal cell caused excitatory postsynaptic potentials (EPSPs) in the interneurons. In 4% of these pairs, reciprocal interactions were seen, with the pyramidal cell exciting the interneuron and the interneuron inhibiting the pyramidal cell. These results support the hypothesis that inhibitory mediate recurrent inhibition in the hippocampus. However, the data also suggest that the interneurons from which these results were recorded were a subset of inhibitory interneurons distinct from the classical basket cell. These interneurons may mediate both feed-forward and recurrent inhibition in the hippocampus.

Glycine receptor: light microscopic autoradiographic localization with [3H]strychnine

Abstract: Glycine receptors have been localized by autoradiography in the rat central nervous system (CNS) using [3H]strychnine. The gross distribution of receptors is in excellent accord with the distribution determined by filtration binding assays. Specifically, the density of glycine receptors is greatest in the gray matter of the spinal cord and decreases progressively in regions more rostral in the neuraxis. Glycine receptors were found to be associated with both sensory and motor systems in the CNS. Moreover, there is a striking correlation between areas of high strychnine binding site density and areas in which glycine has been found to be electrophysiologically active. Finally, the anatomic localization of strychnine binding sites may help explain many of the signs and symptoms of strychnine ingestion. For example, individuals consuming subconvulsive doses of strychnine frequently experience altered cutaneous and auditory sensation. We have localized strychnine receptors in areas of the acoustic system known to influence discriminative aspects of audition and in areas of the spinal cord and trigeminal nuclei which modulate discriminative aspects of cutaneous sensation. The alteration of visceral functions (e.g., blood pressure and respiratory rate) associated with strychnine ingestion may be accounted for in a similar manner.

The visual claustrum of the cat. I. Structure and connections

Abstract: The cat's dorsocaudal claustrum was studied in Golgi preparations, by electron microscopy, and by anterograde and retrograde tracer techniques. It receives a convergent retinotopic projection from several visual cortical ares, including areas 17, 18, 19, 21a and PMLS (posteromedial lateral suprasylvian area). The projection arises from spiny dendrite cells (pyramidal and fusiform) in the middle of cortical layer VI. As shown by a double label experiment, they form a separate population from those projecting to the lateral geniculate nucleus. There are also inputs from the lateral hypothalamus, from the nucleus centralis thalami, and probably from the locus coeruleus, but not from the sensory nuclei of the thalamus. Non-visual cortical areas do not project to the visual claustrum, but many of them are connected to other parts of the nucleus. For example, the splenial (cingulate) gyrus projects to a claustral zone just ventral to the visual area, and regions anterior to the visual area are connected with somatosensory and auditory cortex. The commonest cell type in the claustrum is a large spiny dendrite neuron whose axon leaves the nucleus after giving off local collaterals. Small spine-free cells, with beaded dendrites and a locally arborizing axon, are found also. Electron microscopy of the claustrum after ablation of the visual cortex showed degenerating type 1 axon terminals synapsing on spines and beaded dendrites, suggesting a direct cortical input to both cell types. The visual claustrum projects back to the visual cortex, to the same areas from which it receives an input. The return projection is predominantly ipsilateral, but there is, in addition, a small crossed projection. The claustrocortical axons terminate in all cortical layers but most heavily in layers IV and VI. The majority of the cells in the visual claustrum project to the cortex, and retinotopy is maintained throughout the entire corticoclaustral loop. No subcortical projections from the claustrum could be identified.

Plasticity in the spinal cord sensory map following peripheral nerve injury in rats.

Abstract: The medial part of the L4 and 5 dorsal horn in adult rats is dominated by afferents from the toes and foot. After transection of the sciatic and saphenous nerves, virtually all cells in this region are left without any peripheral receptive field. Beginning 4 to 5 days after nerve section, however, many peripherally deafferented cells take on a novel receptive field on the thigh, lower back, or perineum. The new receptive fields are served by intact nerves ending in proximal skin rather than by misdirected sprouts of cut toe-foot nerves. Thus, peripheral axotomy results in synaptic reorganization in the spinal cord proper. Receptive field reorganization occurs after nerve transection, ligation, or ligation with distal transection but does not occur if the nerve is crushed. If a cut nerve is sutured and regeneration is permitted, spinal reorganization is reversed and the toe-foot afferents regain exclusive dominance of the medial dorsal horn.

Classical conditioning in a simple withdrawal reflex in Aplysia californica

Abstract: The ability of Aplysia and other gastropod molluscs to exhibit complex behaviors that can be modified by associative learning has encouraged us to search for an elementary behavior controlled by a simple and well analyzed neural circuit that also can be modified by this type of learning. Toward that end, we have now produced classical conditioning in the defensive siphon and gill withdrawal reflex of Aplysia. We used as a conditioned stimulus (CS) a light tactile stimulus to the siphon, which produces weak siphon and gill withdrawal. As the unconditioned stimulus (US), we used a strong electric shock to the tail, which produces a massive withdrawal reflex. Specific temporal pairing of the CS and US endowed the CS with the ability of triggering enhanced withdrawal of both the siphon and the gill. Random or unpaired presentations of the CS and US, as well as presentations of the CS or US alone, produced either no enhancement or significantly less enhancement than paired presentations of the CS and US. The conditioning is acquired rapidly (within 15 trials) and is retained for several days. The conditioned response is abolished completely by removal of the abdominal ganglion and many of the neurons involved in the conditioning have been identified in this ganglion previously. These include the sensory neurons and several interneurons in the CS pathway and the siphon and gill motor neurons of the conditioned and unconditioned response pathways. Moreover, the sensory neurons of the US pathway have been identified in the pleural ganglia. As a result of its simplicity, it should be possible in this reflex to specify neurons that are causally related to the conditioned response. Since this reflex also exhibits nonassociative learning, it also may be possible to compare associative and nonassociative learning on a mechanistic level.

Ontogenesis of olivocerebellar relationships. I. Studies by intracellular recordings of the multiple innervation of Purkinje cells by climbing fibers in the developing rat cerebellum

Abstract: The establishment of the adult innervation of Purkinje cells (PCs) by climbing fibers (CFs) was studied in the cerebellar vermis of the developing rat. Excitatory postsynaptic potentials (EPSPs) evoked in PCs by activation of the climbing fibers (CF-EPSPs) were recorded intracellularly from a total of 310 cells in young rats aged from 3 to 15 postnatal days. The CF system was activated by electrical stimulation of either the inferior olive (IO) nucleus or the region near the fastigial nucleus (juxtafastigial or JF stimulation). A given PC at each age was considered to be innervated by more than one CF when the amplitude of the spontaneous or evoked CF-EPSPs fluctuated in a stepwise manner. On the other hand, innervation of a PC by a single CF was established on the basis of the all-or-none character of CF-EPSPs. Two parameters were followed throughout development, the percentage of multiply innervated PCs and the mean number of steps in the evoked CF- EPSPs. The data presented confirm the transient multiple innervation of PCs by CFS on postnatal days 8 and 9 (Crepel, F., J. Mariani, and N. Delhaye-Bouchaud (1976) J. Neurobiol. 7: 567–578) and strongly suggest its existence at earlier stages (from postnatal day 3). Moreover, it is shown that the multiple innervation was maximal on postnatal day 5 and then decreased until the innervation by a single CF was established on day 15.

Evidence for collateral projections by neurons in Ammon's horn, the dentate gyrus, and the subiculum: a multiple retrograde labeling study in the rat

Abstract: Although it has been recognized for some years that each cytoarchitectonic field of Ammon's horn and the subiculum gives rise to a specific pattern of cortical and subcortical projections, it has not been clear whether these various projections arise from different populations of neurons within each field or whether they arise as collaterals from an essentially homogeneous population of cells. We have examined this problem, and the related issue of the origin of the commissural and ipsilateral associational projections of the dentate gyrus, by injecting retrogradely transported fluorescent dyes into two or more of the relevant projection fields in adult rats and subsequently examining the brains for doubly or triply labeled neurons. It is clear from these experiments that at least two of the known efferent projections of field CA1 (to the septum and to the entorhinal cortex) arise from the same pyramidal neurons and also that the commissural, ipsilateral associational, septal, and subicular projections of the other major field of Ammon's horn--field CA3--similarly are due to collaterals. Double-labeling experiments also indicate that at least 80% of the cells in the deep hilar region of the dentate gyrus give rise to both an ipsilateral (associational) and a crossed (or commissural) projection to the dentate granule cells. In contrast, the projection neurons in the dorsal part of the subiculum form a quite heterogeneous population; cells that project to both the septum and the entorhinal area are intermingled with others that project to one or the other area but not to both. The cortical and cortico-subcortical connections of the hippocampal formation thus appear to be quite different from those of the neo-cortex, and the existence of such an extensive system of collateral projections clearly has important consequences for studies of the development of the hippocampus and of its response to selective deafferentation.

Two components from eye tissue that differentially stimulate the growth and development of ciliary ganglion neurons in cell culture

Abstract: Survival and development of chick ciliary ganglion neurons in vivo appear to depend on information from the embryonic eye structure that contains the postsynaptic targets of the neurons. We have tested embryonic eye extracts on ciliary ganglion neurons in dissociated cell culture for stimulation of growth and development. Control conditions were chosen that permitted the long term maintenance of the neurons in the absence of tissue extracts of conditioned medium. The conditions included coating the culture substratum with fibroblast material and increasing the K+ concentration in the culture medium to 25 mM. Neurons survived for at least 3 weeks in control conditions. Two major components were resolved in eye extracts that stimulated growth and development of the neurons above the basal levels obtained with control conditions. One component, with an apparent molecular weight of about 2 X 10(4) by gel filtration analysis, stimulated neuronal growth without increasing the levels of choline acetyltransferase activity per neuron. The second component, with an apparent molecular weight of about 5 X 10(4), increased development of choline acetyltransferase levels per neuron but had no effect on neuronal growth. Both components were effective in normal K+ as well as 25 mM K+. These components may represent mechanisms by which the postsynaptic target tissue acts in vivo to direct the growth and development of ciliary ganglion neurons.

Effects of serotonin on the generation of the motor program for swimming by the medicinal leech

Abstract: I have examined the effects of serotonin on the generation of the motor program for swimming by the medicinal leech, Hirudo medicinalis, using both intact animals and isolated nerve cords. In normal saline, isolated nerve cords rarely produced episodes of the motor program for swimming except in response to electrical stimulation of swim-initiating interneurons or of segmental nerves; saline containing micromolar concentrations of serotonin caused isolated nerve cords to produce episodes of the swim motor program in the absence of electrical stimulation. Stimulation of serotonin-containing neurons also caused isolated nerve cords to produce the swim motor program but only if the volume of saline around the ganglia containing the stimulated neurons was small (less than 50 ~1); under such conditions, serotonin was detected in the saline bathing the stimulated neurons. Serotonin also was found in blood from the sinus that contains the nerve cord of the leech. The concentrations of serotonin were correlated with the behavior of the animals whose blood was sampled; animals with the highest levels swam significantly more than did animals with low or intermediate levels; animals with the lowest levels of serotonin in their blood swam very little and were generally inactive. The concentrations of serotonin found in leech blood (10 to 100 nM) were similar to the lowest concentrations of serotonin that elicited swimming from isolated nerve cords. Experimentally elevating the concentration of serotonin in leech blood caused increased swimming activity. These observations suggest that serotonin is a modulator of neuronal control of swimming by the medicinal leech. Biogenic amines influence the control of motor systems in many organisms. Motor areas of vertebrate brains, such as the basal ganglia, receive rich aminergic innervation, degeneration of which results in such motor abnormalities as parkinsonism (Hornykiewicz, 1966, 1973). In spinal cords, aminergic pathways may activate pattern generators for locomotion (Grillner, 1975). Invertebrate nervous systems, in which amines also activate motor programs (Granzow and Kater, 1977; Anderson and Barker, 1977; Livingstone et al., 1980), are useful for analyzing the cellular basis of aminergic actions. For example, studies of identified neural pathways in Aplysia have allowed detailed analyses of the mechanisms by which serotonergic neurons cause long term changes in synaptic transmission (Klein and Kandel, 1978; Kupfermann, 1979). ’ This work was supported by National Institutes of Health Grant NS14410 and National Science Foundation Grant BNS75-23567 to Dr. William B. Kristan, Jr. and by National Institutes of Health Postdoctoral Fellowship NS 06182-01 to A. L. W. I thank Dr. Kristan for his support, advice, and enthusiasm; Philip Lloyd for advice on the bioassay for serotonin; and Janis Weeks for her helpful criticism of this manuscript. This paper presents a study of the effects of serotonin on the neuronal generation of the motor program for swimming by the leech.” The nervous system of the leech is useful for studying the effects of serotonin on a central pattern generator for several reasons: the motor program for swimming can be produced by isolated chains of ganglia (Kristan and Calabrese, 1976), a number of the motor and interneurons that participate in the control of swimming have been identified (Stent et al., 1978; Weeks, 1980), interneurons that elicit swimming in response to sensory stimuli have been identified (Weeks and Kristan, 1978; Weeks, 1980, 1981), and each segmental ganglion contains a small number (9 in ganglia 1 to 3, 7 in ganglia 4 to 21) of identifiable serotonin-containing neurons (Lent et al., 1979; Marsden and Kerkut, 1969; Rude, 1969). Although intact leeches often initiate swims in the apparent absence of external stimuli, isolated nerve cords ’ Present address and that to which all reprint requests should be ,’ Terms such as “swim” and “swimming” will be used as shorthand sent: Department of Neurobiology, Harvard Medical School, 25 Shatfor longer phrases such as “motor program for swimming.” SII will be tuck Street, Boston, MA 02115. used as an abbreviation for swim-initiating interneuron. The

Aspartate and glutamate as possible neurotransmitters in the visual cortex.

Abstract: To identify possible neurotransmitters in the visual cortex, high pressure liquid chromatography was used to measure the release of endogenous compounds from a tissue slice preparation of the visual cortex of the rat. When synaptic release was induced, either by raising the K+ concentration in the medium or by adding veratridine, of the compounds measured, marked increases (6- to 35- fold) in release rate were observed for aspartate, glutamate, and gamma-aminobutyric acid (GABA). This increased release was blocked either with a low Ca2+/high Mg2+ or a tetrodotoxin-containing medium. To label possible aspartate or glutamate pathways, D-[3H]aspartate and D-[3H]glutamate were injected in the lateral geniculate nucleus (LGN), superior colliculus, and visual cortex. Following injections in the LGN, labeling was observed in the pyramidal cells in cortical layer 6 and in a diffuse band in layer 4, whereas no cortical cells were labeled after injections in the superior colliculus. When D-[3H]aspartate was injected in the cortex, the uptake again was concentrated in the layer 6 cells, but not labeled cell bodies were seen in the LGN, confirming the specificity of the uptake and retrograde filling process. Diffuse labeling was present in the LGN, however, presumably produced by anterograde filling process. Diffuse labeling was present in the LGN, however, presumably produced by anterograde transport from the layer 6 cells. These results suggest that layer 6 cells in the cortex, which are the source of the recurrent projection to the thalamus, may use aspartate or glutamate as their transmitter. Analysis of the function of the corticothalamic pathway may be facilitated by these findings.

Concurrent discrimination learning of monkeys after hippocampal, entorhinal, or fornix lesions.

Abstract: Ablations of anterior inferotemporal cortex in monkeys are known to impair learning when discriminations between members of several pairs of objects are taught concurrently. This deficit has been attributed to a loss of visual mnemonic functions. But ablations of hippocampus have also been shown to impair retention, and this impairment transcends the visual modality. Therefore, in the first of two experiments, we compared the behavioral effects of inferotemporal cortical lesions with those of either hippocampus, entorhinal area, or fornix, using a visual concurrent discrimination task. Monkeys with either hippocampal or entorhinal ablations were impaired, while those with fornix sections were not. However, ablations of hippocampus included inadvertent damage of the inferotemporal cortex. Therefore, in the second experiment, behavioral effects of inferotemporal lesions were compared with those of hippocampus (without additional inferotemporal damage) on the concurrent task in both visual and tactual modalities. In the visual mode, monkeys with hippocampal removals were as impaired as those with inferotemporal ablations. In the tactual mode, however, hippocampal, but no inferotemporal, ablations were followed by a deficit. Our results, taken together with other existing evidence, emphasize the role of the hippocampus in mediating associative learning in more than one modality. These results, obtained with non-human primates, are in line with clinical findings.

The growth and organization of the optic nerve and tract in juvenile and adult goldfish

Abstract: The optic nerves, tracts, and tecta of goldfish, 1 to 5 years old, have been studied anatomically using light and electron microscopy, horseradish peroxidase (HRP), and tritiated proline radioautography. The aims were to document an earlier inference that fibers are added to the nerve continually and to describe the growth and organization of the pathway. (1) The numbers of optic fibers were counted in electron micrographs of the nerve. There were about 120,000, 165,000 and 180,000 in 1-, 3-, and 5-year-old fish, respectively. (2) In young fish, there are a few thousand nonmyelinated fibers which exit the retina together and cluster together in the nerve and tract. When the axons of only the newest (peripheral) ganglion cells were cut intraretinally, fibers in and around the bundles of nonmyelinated fibers degenerated. The nonmyelinated fibers are, therefore, the new ones. (3) Fibers from ventral or dorsal hemiretinas were backfilled selectively with HRP introduced into one of the brachia of the optic tract. Behind the optic papilla, where the cross-section of the optic nerve was trapezoidal, the new fibers were found in a strip along the narrow base of the two flanking zones. Closer to the brain, the fibers from the two hemiretinas intermingled before being segregated again at the origin of the brachia. (4) Small groups of ganglion cells were labeled by intraretinal injection of HRP and their fibers were traced in sections of the nerve and tract. The labeled fibers were clustered, but the positions of the fibers in the cross-section of the nerve were defined less precisely than the positions of the somata in the retina. (5) Hemisection of the nerve in the orbit, followed by intraocular injection of tritiated proline, produced radioautographs with an unlabeled annular zone of tectum. Since the retina projects topographically to the tectum, the severed fibers must have originated from an annular region of the retina. We infer that new fibers are added to the nerve continually and that the retinal origins of fibers are correlated with their positions in the cross-section of the nerve. These rules of order change with distance from the retina; the strict order at the optic papilla changes gradually to an equally strict but different, order at the level of the brachia.

Specific changes in rapidly transported proteins during regeneration of the goldfish optic nerve.

Abstract: Double labeling methods were used to identify changes in the complement of proteins synthesized in the retinal ganglion cells and transported down the optic nerve during the process of axonal regeneration. Eight to 62 days after goldfish underwent a unilateral optic nerve crush, one eye was labeled with [3H]-, the other with [14C]proline. Control and regenerating optic nerves were dissected out and homogenized together after 5 hr, a time which allowed us to examine selectively membrane- bound components which migrate in the rapid phase of axoplasmic transport. Proteins from the two sides were so-purified and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Analysis of the 3H and 14C incorporation patterns along the gels revealed a radical shift away from the normal labeling spectrum during regeneration, with selective changes in labeling at particular molecular weights varying over a 3-fold range. Eight days after crushing the optic nerve, the greatest increases in labeling were seen for material with apparent molecular weights of 24,000 to 27,000, 44,000, and 210,000 daltons. These peaks declined thereafter, and on days 29 to 39, the most prominent increases were at 110,000 to 140,000 daltons. These studies indicate a continuously changing pattern in the synthesis and/or degradation of proteins that are rapidly transported down the optic nerve during regeneration and point to molecular species potential significance in the establishment of the visual map upon the brain.

Neurite outgrowth in molluscan organ and cell cultures: the role of conditioning factor(s)

Abstract: Isolated neurons from adult central ganglia of the snail Helisoma were cultured in vitro in modified Liebowitz L-15 medium. Such neurons displayed electrical excitability comparable to that in acutely dissected ganglia. Isolated neurons remained spherical in defined medium throughout culture durations up to 2 weeks. This static morphology was contrasted by the significant neuritic outgrowth which occurred from neurons maintained in medium with co-cultured intact Helisoma brains or in brain conditioned medium. A morphological sequence of growth cone formation and neurite extension occurred only in the presence of a conditioning factor(s) with a mode of action which included tight binding of the conditioning factor to the substratum. Under these conditions, the two primary neuronal phenotypes, electrical excitability and complex neuronal architecture, could be affected independently in adult molluscan neurons cultured in vitro.

Metabolic effects of unilateral lesion of the substantia nigra

Abstract: Regional brain glucose utilization following unilateral lesion of the substantia nigra in rat was studied by [14C]-2-deoxyglucose autoradiography. Substantia nigra lesions were performed by perinigral injections of 6-hydroxydopamine (6-OHDA) . HBr, 6 microgram, in rats pretreated 30 min earlier with desmethylimipramine (DMI), 25 mg/kg, subcutaneously. The lesion produced extensive destruction of the ipsilateral substantia nigra pars compacta and a greater than 99% reduction in dopamine concentration in the ipsilateral striatum. Pretreatment with DMI prevented any reduction in the concentration of norepinephrine in ipsilateral forebrain structures. Glucose utilization was increased in the ipsilateral globus pallidus at 11, 21, 53, and 104 days after substantia nigra lesion with the largest increase (about 140% of control) occurring at 21 days post-lesion. In addition, glucose utilization in ipsilateral lateral habenular nucleus was increased at each of the above time points. No changes in glucose utilization were noted in frontal cortex, striatum, subthalamic nucleus, entopeduncularis, or ventral tier nuclei of the thalamus. These results suggest that lesion of the substantia nigra with depletion of striatal dopamine content results in disinhibition of some striatal, and perhaps olfactory cortical, efferents producing increased metabolism and glucose utilization in terminal fields within the globus pallidus and lateral habenular nucleus.

The influence of gonadectomy, androgen exposure, or a gonadal graft in the neonatal rat on the volume of the sexually dimorphic nucleus of the preoptic area

Abstract: Although the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of the adult rat has been shown to be modified by the hormone environment early in postnatal life, the present study was performed to clarify several fundamental questions related to this process. This study was designed to evaluate the ability of exogenous testosterone propionate (TP), or a gonadal graft, to influence SDN-POA volume in rats which were gonadectomized as neonates. Orchidectomy on day 1 resulted in an approximately 50% decrease in adult SDN-POA volume; however, the influence of the testes on their resulting SDN-POA volume was replaced affectively by the administration of 100 micrograms or 1 mg of TP on postnatal day 2 or by a testicular (but not ovarian) graft on the day of castration. In the female, ovariectomy on postnatal day 1 failed to alter SDN-POA volume relative to that of sham-operated females. Exogenous TP, but neither testicular nor ovarian grafts, resulted in a larger SDN-POA volume when observed in the adult female. Thus, the development of the SDN-POA of the neonatal male is significantly influenced by the hormonal activity of the testes at this time period. While the SDN-POA of the neonatal female is potentially responsive to androgen, the role played by the ovaries in the development of the SDN-POA remains unclear. In addition, the different response of the developing male and female SDN-POA to a testicular graft suggests that the hormonal sensitivity of this nucleus may differ in the two sexes.