Showing papers on "Cuneate nucleus published in 1978"

Anatomical observations on the dorsal column nuclei, their thalamic projection and the cytoarchitecture of some somatosensory thalamic nuclei in the monkey.

Abstract: The results of the present anatomical study on macaque monkeys concern some aspects of the dorsal column nuclei, their projection to the thalamus and the cytoarchitecture and topography of the recipient areas in the thalamus for the somatosensory pathways. Some observations regarding the cytoarchitecture of the dorsal column nuclei are reported; the gracile nucleus differs cytoarchitectonically over the rostrocaudal dimension in a way similar to the feline nucleus; the cuneate nucleus has a distinct pars rotunda (Ferraro and Barrera, '35) which might be analogous to a similar structure in the raccoon shown to be activated by afferents from the volar side of the hand and digits (Johnson et al., '68). Cytoarchitectonic observations and other arguments suggesting the presence of the nucleus Z in the monkey are presented. In Nissl stained frontal sections, cut in the stereotaxic frontal plane as well as in sections cut perpendicular to the long axis of the brain stem the cytoarchitecture and topography of the posteromedial, ventroposterior and centrolateral thalamic nuclei of the macaque were analysed. The posteromedial nucleus (POm) has been found to include portions of Olszewski's ('52) magnocellular medial geniculate, suprageniculate and pulvinar nuclei. The nucleus ventralis posterolateralis (VPL) corresponds to the main portion of Olszewski's VPLc, whereas most of his VPLo corresponds to the nucleus ventralis intermedius of Hassler ('59) and Mehler ('71). Electrolytic lesions were used to study the projection from the gracile and cuneate nuclei to the thalamus. With postoperative survival periods of 6 to 14 days the resulting degeneration was studied in frontal sections stained according to the Wiitanen modification of the Fink-Heimer method. Both the gracile and cuneate nuclei project profusely to the contralateral nucleus ventralis posterolateralis and more sparsely to the contralateral posteromedial nucleus and the zona incerta. A distinct somatotopic organization exists in the projection to the ventroposterior nucleus, but not in that to the other target areas. The projection to the ventroposterior nucleus is very dense and evenly distributed except rostrally and dorsally, where it is more scattered. It is concluded that the posteromedial and the ventroposterior thalamic nuclei are very similar in monkeys and cats regarding cytoarchitecture, topography and afferent projections from the dorsal column nuclei.

PRESYNAPTIC ACTIONS OF β-AMINOBUTYRIC ACID AND SOME ANTAGONISTS IN A SLICE PREPARATION OF CUNEATE NUCLEUS

Abstract: 1 A slice preparation of the rat cuneate nucleus is described which is suitable for electrophysiological studies on the presynaptic action of drugs. 2. Superfusion of a slice with gamma-aminobutyric acid (GABA) depolarized the afferent nerves in a concentration-related manner. The responses were Cl-dependent. Depolarizations to high concentrations of GABA often faded. Glycine and L-glutamate had little effect. 3 (+)-Bicuculline antagonized GABA in an apparently competitive manner (pA2 = 5.35) at low response levels. Strychnine was 10 times less potent. Responses to high concentrations of GABA were sometimes potentiated by (+)-bicuculline and strychnine. 4 Bemegride and leptazol both antagonized GABA, but with low potency and in a manner which was clearly not competitive.

Coding of information about tactile stimuli by neurones of the cuneate nucleus.

Abstract: 1 The responses of cuneate neurones to controlled tactile stimulation of the foot pads were examined in unanaesthetized, decerebrate cats The neurones were divided into three functional classes; one sensitive to steady tactile stimuli, and two dynamically sensitive classes which could be readily differentiated by their responsiveness to cutaneous vibration Each class appeared to receive an exclusive input from only one of the three known groups of tactile receptors associated with the foot pads, namely the Pacinian corpuscles, the Merkel endings and the intradermal, encapsulated endings known as Krause or Meissner corpuscles 2 Cuneate neurones responsive to steady indentation of the skin displayed approximately linear or sigmoidal stimulus-response relations over indentation ranges up to approximately 15--2 mm Response variability at a fixed stimulus intensity was relatively low and showed little systematic change over the full range of the stimulus-response curves 3 One class of dynamically sensitive cuneate neurones responded to cutaneous vibration over a range of approximately 5-80 Hz with maximal responsiveness around 30 Hz The other class, the Pacinian neurones, responded over a range of approximately 80- greater than 600 Hz with maximal responsiveness at 200-400 Hz The thresholds and combined band width of vibratory sensitivity of these populations were comparable with known subjective thresholds and range of cutaneous vibratory sensibility 4 Responses of cuneate neurones were phase-locked to the vibratory stimulus suggesting that information about vibration frequency could be coded by the patterns of impulse activity Quantitative measures indicated that maximal phase-locking occurred in responses to vibration frequencies of 10-50 Hz with a progressive decline at higher frequencies Above 400 Hz, impulse activity occurred almost randomly throughout the vibratory stimulus cycle and therefore carried little further signal of vibratory frequency The decline, with increasing frequency, in the ability of cuneate neurones to signal information about vibratory frequency parallels the known subjective capacities for frequency discrimination 5 A switch-over occurred at approximately 80 Hz in the population of cuneate neurones able to provide the more reliable signal of vibratory frequency; above 80 Hz, the Pacinian neurones; below 80 Hz, the neurones receiving intradermal, rapidly adapting receptor input from the pads 6 The observed properties of cuneate neurones are compatible with a role in signalling information which could contribute to subjective tactile abilities

Projections of the ascending somesthetic pathways to the cat superior colliculus visualized by the horseradish peroxidase technique.

Abstract: Projections of the somesthetic ascending pathways to the superior colliculus (SC) of the cat have been demonstrated by means of the horseradish peroxidase (HRP) tracing technique. Following HRP injection in one SC, marked neurons were found in the contralateral dorsal horn and in the contralateral dorsal column nuclei, mainly the cuneate nucleus. Moreover, in the contralateral trigeminal complex, the sub-nucleus caudalis of the spinal nucleus of the Vth nerve, and the subnucleus oralis plus the main sensory trigeminal nucleus were labeled. Thus, the anterolateral system and the lemniscal system subserving face and forelimb sensation send afferent fibers to the contralateral SC.

Facilitation of synaptic transmission by general anaesthetics.

Abstract: 1. The actions of five structurally different intravenous and inhalation anaesthetics (alphaxalone/alphadolone, halothane, ketamine, methohexitone, and pentobarbitone) have been studied on synaptic transmission through the cuneate nucleus of the dorsal column-lemniscal afferent pathway in the decerebrate cat. 2. Synaptic input and output were estimated from antidromic and orthodromic potentials, which were evoked by either afferent volleys from the periphery or micro-electrode excitation of the presynaptic fibre terminals in the cuneate and recorded at forelimb nerves and the medial lemniscus. 3. Each of the anaesthetic agents potentiated the efficiency of synaptic transmission, as shown by the elevation of input-output curves constructed from the integrals of the potentials evoked by varying intensities of either peripheral or cuneate stimulation. 4. The excitability of the afferent terminals, as measured at the peripheral nerves by the antidromic responses to micro-electrode stimulation, was depressed by the anaesthetics. Post-synaptic excitability, which was assessed from the direct lemniscal response to intra-nuclear stimulation, did not appear to change. 5. Hypotensive states (mean arterial levels less than 60 torr) produced depolarization of presynaptic terminals and depression of synaptic efficiency and transmission; these changes opposed the primary effects of the general anaesthetics. 6. It is concluded that anaesthetics do not depress activity at all synapses of the central nervous system. Their facilitatory action on cuneate transmission is attributed to an enhanced release of excitatory transmitter; the underlying mechanism may be hyperpolarization of the primary afferent terminals, secondary to an increase in K+ conductance.

Properties of the pyramidal tract neuron system within the precentral wrist and hand area of primate motor cortex.

Abstract: 1. To obtain basic anatomical data that will be useful in interpreting the results of studies of primate pyramidal tract neurons (PTNs), extracellular, single-unit recording techniques were used to determine a number of the properties of the PTN population within the electrically defined, precentral wrist zone of the monkey's motor cortex. 2. Recordings were obtained from a total of 1,375 antidromically identified PT and corticospinal tract (CST) cells. A mathematical model was then used to correct the statistics of the sample for variations in the probability of unit detection, which arise from variations in neuronal size and extracellular field dimensions. 3. Both the experimentally observed and theoretically corrected results suggest that the PT projection from this cortical zone is derived principally from slowly conducting, and presumably small to medium-sized cells (an estimated 85% of the resident PTN population). 4. Both the fast and slow cell subpopulations were found to be concentrated within cortical layer V, where they tend to congregate in small, mixed clusters of 2 to 5 neurons. Estimates of the total packing density of PTNs within layer V of this cortical zone suggest that they account for only 10-20% of the neurons within this major efferent layer. 5. 70% of the slow and 82% of the fast PT neurons within this cortical area were found to send their axons into the contralateral, lateral corticospinal tract. Thus, in futur functional studies of PTNs in this cortical area, it can be assumed that three of every four neurons will in fact influence segmental cells of one category or another directly. 6. Extensive data are also presented on the incidence of axon collateral branching from PT and CST cells to the red nucleus, the medial medullary reticular formation and the cuneate nucleus. 7. Some general implications of these findings for the design of future functional studies of anatomically identified motor cortex cell systems are then discussed.

EFFECTS OF γ‐AMINOBUTYRIC ACID ON NERVE TERMINAL EXCITABILITY IN A SLICE PREPARATION OF CUNEATE NUCLEUS

Abstract: 1 Superfusion of a slice preparation of the rat cuneate nucleus with gamma-aminobutyric acid (GABA) depolarized the afferent nerve fibres and increased their excitability. However, before the depolarization had reached its peak the increased excitability reversed to a decreased excitability, an effect which outlasted the depolarization. 2 Both components of the GABA excitability response were dose-related Cl--dependent and antagonized by bicuculline. 3 Possible mechanisms underlying the sequence of excitability changes are discussed.

Interaction of minor tranquillizers with synaptic processes mediated by gaba

Abstract: Benzodiazepines selectively enhance GABA-mediated pre-synaptic inhibition in the spinal cord and preand post-synaptic inhibition in the cuneate nucleus. Field potentials in the substantia nigra and in Deiters' nucleus elicited by stimulation of GABA-ergic striato-nigral neurons and cerebellar Purkinje cells, respectively, are abolished by Picrotoxin and bicuculline. Benzodiazepines reduce the effect of these GABA receptor blockers. Activation of dopamine neurons by neuroleptics is reduced by benzodiazepines. Benzodiazepines reduce the spontaneous firing rate of cerebellar Purkinje cells with GABA-ergic input. Phenobarbitone similarly facilitates GABA-ergic inhibition but in addition depresses excitatory mechanisms. Meprobamate does not affect GABA-ergic transmission.

Dorsal column nuclei in a prosimian primate (Galago senegalensis). II. Cuneate and lateral cuneate nuclei: morphology and primary afferent fibers from cervical and upper thoracic spinal segments.

Abstract: The morphology and brachial cord primary afferent projections of the cuneate and lateral cuneate nuclei have been studied in the lesser bushbaby. The cuneate nucleus was divided into three regions. From caudal to rostral these were the large cell, cell column and rostral regions. Primary afferents from C2, C4, C6, C7, C8, T1 and T3 terminated within distinct partially overlapping terminal zones in the ipsilateral large cell and cell column regions of the cuneate nucleus (CN) and the lateral cuneate nucleus (LCN). Segmentotopic was the greatest in the rostal region of the CN due to a more diffuse projection pattern. In the LCN, the transverse terminal fields appeared as curved mediolaterally oriented laminae. In each case, ascending fibers of passage from C4, C6, and C7 in the cuneate fasciculus were organized so that two distinct fiber laminae were present. The separation of fibers and the formation of the two ascending laminae were completed either within two segments rostral to their respective level of entry (for C6 and C7 lesions) or in the caudal medulla (for C4 lesion). For each of these segments, the laminae consisted of a small dorsomedial one and a large lateral one. The organization of primary afferents from one segment into two ascending fiber laminae in the cuneate fasciculus was reflected in a differential termination pattern within both the CN and LCN. The results of this study were discussed relative to earlier anatomical and physiological studies on the DCN in other animals.

The fine structural organization of the cuneate nucleus in the monkey (Macaca fascicularis).

Abstract: The fine structure of the cuneate nucleus of the monkey (Macaca fascicularis) has been studied. The neurons were classified into three groups according to their nuclear morphology, the arrangement of the rough endoplasmic reticulum (RER) and the appearance of the Golgi complexes. Group I neurons had a regular nucleus and contained abundant cytoplasm in which were found well-developed RER and Golgi complexes. Group II neurons had a slightly irregular nucleus and a variable arrangement of the RER and Golgi complexes. Group III neurons were characterized by a deeply indented nucleus, and scanty cytoplasm in which the cytoplasmic organelles were poorly developed. Group II neurons were the most commonly encountered while Group I neurons were the rarest. Axon terminals contained either round of flattened vesicles. Axon terminals and dendrites commonly formed synaptic complexes. In one type the axon terminal, containing round vesicles, formed the central element, which is presynaptic to the dendrites surrounding it; in addition it is postsynaptic to axon terminals containing flattened vesicles. In another type a large dendrite formed the central element which is postsynaptic to axon terminals containing round or flattened vesicles.

Efferent Oxytocinergic Projections from the Hypothalamus to the Hindbrain in Rats and Pigeons

Abstract: It has been confirmed by fluorescence- and light-microscopic techniques that the neurosecretory system of the rat and the pigeon comprises exohypothalamic pathways besides the fibers of the hypothalamo-neurohypophyseal tract. The targets of the exohypothalamic pathways are the habenular region, the subfornical organ, and the reticular formation. We were able to demonstrate, by the immunohistochemical technique and by the pseudoisocyanine technique, that the hypothalamus-hindbrain connection known from lower vertebrates is also present in the pigeon and the rat. These fibers follow known pathways through the mesencephalic reticular formation to the hindbrain. Most of the fibers are found in the medial cuneate nucleus and in the gracile nucleus. Fewer fibers are seen in the lateral cuneate nucleus, in the nucleus solitarius and also in the area postrema. Using the electron microscope, the neurosecretory fibers in the dorsal-columns region are seen to contain neurophysin vesicles that are of the same type as the neurophysin vesicles of the classic neurosecretory system. First, the diameter of these vesicles ranged from 90 to 150 nm in the pigeon and from 130 to 200 nm in the rat. Secondly, using the method of NAUMANN and STERBA (1976) we were able to show that the content of these vesicles is indeed neurophysin. Furthermore, synaptic terminals of such oxytocinergic fibers were shown to exist.