Showing papers in "Acta Neurobiologiae Experimentalis in 1980"

An exploration of the ability of macaques to detect microstimulation of striate cortex.

Abstract: With its head steadied within a form-fitting mask, a macaque was first taught to signal when it detected the application of 0.2-ms electrical pulses at 50 Hz through electrodes chronically implanted within its striate cortex. Stimuli were then applied via a movable microelectrode and the threshold for the animal’s detection determined at intervals of 50-250 micrometers. With permanently implanted 130- 200-micrometers diameter electrodes such thresholds range between 50 and 250 microamperes (and are highly stable), whereas with the microelectrodes sites were encountered, estimated to be primarily within cortical layers V-VI, where the monkey could reliably detect as little as 2-4 microamperes. The threshold at most sites within striate cortex with the microelectrode, however, was 15-25 microamperes. Background unit activity recorded with the microelectrode varied greatly in different laminae and survived the microstimulation, but has so far provided no clear basis for predicting threshold. It is tentatively hypothesized that the relatively rare points where the threshold is as much as 10 times less than that in the surround arise because the giant, solitary cells of Meynert provide the exclusively effective output for the behavioral response. This hypothesis would also explain the singular uniformity of sensation (a "phosphene") evoked in human subjects by such stimuli, and the equivalence of all such stimuli in striate cortex found for the macaque.

Effects of pyramidal lesions on forelimb movements in the cat.

Abstract: The effects of uni- and bilateral transections of the medullary pyramids on movements requiring differential use of distal forelimb muscles were studied. The pyramidotomy abolished for more than one year the ability to solve tasks which required flexion and adduction of the digits involved in grasping, e. g. to extract food from narrow horizontal and vertical tubes; unilateral and bilateral pyramidal lesions had comparable effects. In other tasks, involving primarily movements of more proximal muscles, e. g. in retrieving food from behind vertical bars or from between vertical walls, the impairment was both less pronounced and shorter lasting; unilateral pyramidal lesions produced in these movements smaller deficits than bilateral lesions.

Relationships of precentral premotor and prefrontal cortex to the mediodorsal and intralaminar nuclei of the monkey thalamus.

Abstract: The projections of precentral, premotor and prefrontal cortical areas to the mediodorsal and intralaminar thalamic nuclei have been reexamined by means of the anterograde labelling technique in 21 macaque monkeys. Three principles which have been already mentioned in previous reports could be confirmed within limits: (i) The dichotomy of agranular and granular frontal cortices related to lateral and medial thalamic nuclear division respectively, (ii) the reciprocity of fronto-thalamic connections and (iii) the thalamic matrix consisting of longitudinally arranged cell columns (Kievit and Kuypers 1977) from which the cortical connections originate and where they end. One main exception to these principles involves the intralaminar and paralaminar nuclear continuum which seems to disrupt the nearly parallel system of thalamically relayed information channels by forming complex patterns of converging and diverging connectivities with cortical, subcortical and possibly intrathalamic regions. Another exception concerns the partial bilaterality of fronto-thalamic projections which is not reciprocated as far as we know by the thalamo-cortical counterparts. Major emphasis is laid upon the fact that agranular frontal cortex, i.e., precentral and premotor (including supplementary motor) areas not only project to the ventrolateral nuclear complex and to intralaminar nuclei but in addition to MD (paralaminar zone) whose efferent connections are known to be directed mainly towards the frontal eyefield and the caudate nucleus and to a lesser degree to the agranular frontal cortex.

Spatial memory and instrumental conditioning.

Abstract: Short-term spatial memory of rats was studied in a 12-arm radial tubular maze. Correct performance does not depend on maze structure which affects, however, the rat’s trajectory through the maze. Rats overtrained in the 12-arm radial maze show considerable transfer of the habit to a maze consisting of 12 parallel alleys entered from a common choice area. When isolated maze channels equipped with one way doors on both ends are randomly scattered over an enclosed area of 2 square meters the rats are capable of visiting them sequentially, even when they encounter this particular configuration for the first time. Rats which were allowed 6 choices in the 12-arm radial maze and were then transferred to linear configuration of the same maze channels do not show significant preference for the yet unvisited channels. This indicates that in absence of spatial cues other sensory properties of the different channels cannot guide the choice behavior of the animal. An essential prerequisite of spatial memory tests is elimination of cues which would allow direct sensory location of the baited alleys. Smelling the food hidden in the food-cups may significantly improve the rats performance unless the maze channels are saturated with food odor. It is concluded that a prerequisite for the striking performance of rats in the tasks of the above type is their thorough familiarization with the list of choices. The spatial location of an item is an important cue for the recognition of the choices already made.

Utility of the neurological examination in rats.

Abstract: This study presents general observations of neurological examination in rats after various CNS manipulations. The examination consisted of neurologic reactions as described in Bures and co-workers. Subjects studied were controls, hippocampal irradiates, and animals with cerebellar lesions or midline cerebellar transplants. Utility of the procedure as an adjunct to more detailed testing is discussed.

Effects of red nucleus lesions on forelimb movements in the cat.

Abstract: The effects of uni- and bilateral lesions of the red nucleus on the ability to retrieve food with a forepaw from food wells of different shape were analyzed. Movements which required the use of distal muscles, e.g. retrieving food from narrow horizontal and vertical tubes, were more affected than movements primarily involving more proximal muscles. A decrease in the digital skill occurred during at least 4 months after the surgery, even in the case of subtotal lesions of the red nucleus. The effects of uni- and bilateral rubral lesions appeared to be essentially similar.

Interaction of cholinergic and dopaminergic influences on yawning behavior

Abstract: The possible interaction between cholinergic and dopa- minergic influences in the induction of yawning behavior in the rat is explored resorting to several experimental approaches: comparison of the ontogeny of yawning behavior induced by physostigmine (0.15 mglkg) and apomorphine (0.05 mglkg); simultaneous injection of both drugs; "crossed blocking" experiments, in which the action of the cho- linomimetic agent is examined after injection of spiroperidol (0.05 mglkg) and that of apomonphine after scopolamine (0.25 mglkg). While phy- sostigmine-elicited yawning is highest in early postnatal days and tends to decline from the 7th day onwards, reaching its lowest level around 3 wk, yawning induced by apomorphine begins around the 9th day and increases thereafter to a plateau that is reached in the third week. No synergism on yawning behavior is observed by simultaneous inject- ion of optimal or suboptimal doses of physostigmine and apomorphine. Scopolamine blocks apomorphine-induced yawning; spiroperidol blocks apomorphine- but potentiates physostigmine-induced yawning, both in 15-day-old and young adult rats. Two 5-HT uptake blockers, citalo- pram (10-20 mglkg) and fluoxetin (10-20 mglkg) potentiate physostig- mine- but not apomorphine-elicited yawning. On the basis of these results a tentative model of "in series" organization of dopaminergic and cholinergic influences on yawning behavior is proposed. ,

Motivational role of social reinforcement in dog-man relations.

Abstract: Lesions of dorsomedial amygdala (DMA) or lateral hypothalamus (LH) produced prominent impairment of the alimentary behavior in dogs. Besides, various behavioral responses, including social, were depressed. To evaluate whether these changes were either specific for alimentary disturbances or dependent on changes in the general reward system, another type of reward, i.e. social contact with experimenter as a reinforcement for several motor responses was introduced. Damage of amygdalo-hypothalamic system, which produced a syndrome of depression, also impaired socially reinforced responses. This impairment lasted much longer then decrease of food intake. Therefore it was assumed that DMA and LH damage produced impairment not limited to alimentary mechanisms, but involving various aspects of positive motivational system and in particular including the social behavior during man-dog relations. Taking into account various theories of reinforcement in instrumental learning the authors are inclined towards a hedonistic theory of reward.

The postural support of movement in cat and dog

Abstract: The postural adjustment which accompanies single limb movement in the standing cat and dog was analyzed. Four trays equipped with strain gauges were used for measuring the vertical forces exerted by each limb before and during movement performance. Three types of movements were analyzed: flexion movements elicited by motor cortex stimulation, placing movements, conditioned movements of either forelimb or hindlimb (lift-off in cat, flexion with maintained final position in dog). In both cats and dogs the postural adjustment during movement consists of a bipedal stance on two diagonally opposite limbs. Large quantitative differences were observed depending on the type of movement. Cortical stimulation elicited an adjustment where changes of forces exerted by the forelimb a hindlimb were nearly equal. During conditioned fore- and hindlimb lift-off in the cat there was a tendency to use only forelimbs for the postural adjustment associated with forelimb movement and hindlimbs for the adjustments associated with hindlimb movement. For placing in the cat and conditioned movement in the dog, the adjustment was intermediate, that is a predominant contribution of forelimb support with forelimb movements but nevertheless an associated contribution from hindlimbs. The general significance of the results with respect to the mechanism of postural adjustment associated with movement is analyzed.

Structures involved in acquisition and performance of visually guided movements in the cat.

Abstract: Cats were trained to press on a lever either fixed or moving at different speeds from left to right or right to left at random. In the first series of animals, the following bilateral lesions were performed after reaching criterion on the moving lever: (1) deep cutting of cortico-cortical fibers connecting visual and frontal cortex; (2) subtotal electrolytic destruction of n. ventralis lateralis of the thalamus (nVL); (3) ablation of the anterior (3a) or middle (3b) suprasylvian cortex. No postoperative deficits were noticed after lesions (1), (2), (1 + 2) or (3b). On the other hand, impairment was found after lesion (3a), strongly suggesting the role of the anterior suprasylvian cortex in visual guidance of the forepaw movement in cat. The second group of animals was first trained to press the fixed lever and then underwent bilateral n. VL lesions. After lesion, performance with fixed lever remained normal while the animals displayed a deficit with the moving lever. The conclusion is that the n. VL is essential only during the acquisition phase of the tested visuomotor performance.

Mechanisms of motivation in avoidance behavior

Abstract: The mechanisms involved in avoidance behavior are dis- cussed. It is assumed that the conditioned stimulus (CS) activates the memory pattern of associations related to the former applications of the unconditioned stimulus (US) and, as a result, produces an u.ndesir- able sensory state. This activates another memory pattern of associations related to the avoidance response and the postrponement of the US. The performance of the avoidance response disco,ntinues the CS, result- ing in inactivation of the first memory pattern; this leads to a removal of the undesirable sensations, i.e., to an improvement in the sensory state. It is suggested that avoidance behavior obeys the same general rules which apply to approach (appetitive) behavior. I,n both alpproach and avoidance behavior the instrumental response provides a desirable sensory change (due to obtaining of the desired US in approach behavior and the postponement of the undesired US together with the disconti- nuation of CS i,n avoidance behavior). In 'both cases the reslponse gradually extinguishes when its performance no longer provides the sensory "better-being".

Subcortical connections of the prefrontal cortex in dogs: afferents to the proreal gyrus.

Abstract: Afferent subcortical connections to the proreal gyrus of the prefrontal cortex (PFC) in the dog were investigated using the horseradish peroxidase retrograde transport method. The afferent projections derive mainly from dorsal-intermediate and caudal regions of the mediodorsal nucleus (MD), from $he ventral as well as from the lateral thalamic nuclei. In the ventral nuclei, the distribution of labeled cells showed a topography correlated with injections localized in the anteroposterior direction. Furthermore, single cells were labeled in midline and intralaminar thalamic nuclei as well as some extrathalamic structures. The data obtained in behavioral and anatomical experiments with dog and monkey are discussed. The distribution of afferent projection from MD and the functional division on particular subfields of PFC seems to be in accordance in both species.

Sex hormone influences on yawning behavior.

Abstract: Young male albino rats yawn significantly more than females or castrated males when injected with physostigmine (0.10 mg/kg). Treatment with testosterone (100 pg daily) during seven days restores cholinomimetically induced yawning in castrated males, and increases yawning in normal and androgenized females. Treatment with estradiol (200 pg daily) during one week does not modify physo- stigmine induced yawning behavior in castrated males nor in andro- genized females.

Recent experiments testing an opponent-process theory of acquired motivation.

Abstract: There are acquired motives of the addiction type which seem to be non-associative in nature. They all seem to involve affective phenomena caused by reinforcers, unconditioned stimuli or innate releasers. When such stimuli are repeatedly presented, at least three affective phenomena occur: (1) affective contrast effects, (2) affective habituation (tolerance), and (3) affective withdrawal syndromes. These phenomena can be precipitated either by pleasant or unpleasant events (positive or negative reinforcers). Whenever we see these three phenomena, we also see the development of an addictive cycle, a new motivational system. These phenomena are explained by an opponent-process theory of motivation which holds that there are affect control systems which oppose large departures from affective equilibrium. The control systems are strengthened by use and weakened by disuse. Current observations and experiments testing the theory are described for: (1) the growth of social attachment (imprinting) in ducklings; and (2) the growth of adjunctive behaviors. The findings so far support the theory.

Respiratory responses to stimulation of afferent vagal fibres in rabbits.

Abstract: In the experiments with 43 paralyzed rabbits ventilated artificially under general anaesthesia with halothane the effect of electrical stimulation of the central end of the vagus nerve on respiratory pattern was investigated. The analysis of respiratory responses to varying parameters of stimulation, and comparison of results with the experiments in which stimulation of pulmonary receptors was used, confirmed the view that the activities transmitted along the thick myelinated fibres of the vagus nerve exerted an inhibitory effect on the generation of inspiratory activity, while the activities transmitted along thin myelinated fibres accelerated the respiratory rate. The integrative processes transforming the activity of thick fibres had a time constant shorter by two orders than the integration of responses to stimulation of thin fibres.

Acquisition of the escape reflex in cats after the nucleus centralis of the amygdala lesions.

Abstract: Three groups of 6 cats were trained in bar-press escape responses from unsigmlled shock. Lesions of dorsolateral part of the amygdaloid nucleus centralis were made ,either 10 days or 35 days before training in two groups of subjects. The remaining 6 cats served as intact control ,group. The lesions resulted in a lengthening of instru- mental response latencies especially in the final period of training. This was not caused by any changes in animals sensitivity and re- activity to paBnful sti,mulation since no differences between control and lesioned groups were observed at earlier stages of training. Fur- ther, no group effects were observed in threshold reactivity to shock. However in contrast to the control cats, both lesioned groups performed escape responses to low intensity stimuli with very long latencies.

Cortical mechanisms of goal-directed motor acts in the rhesus monkey.

Abstract: Multineuronal activity from the frontal cortex (s. principalis) and the motor cortex (g. precentralis) in the Rhesus monkey during the goal-directed performance was recorded. The experimental sequence comprised a chain of signals securing adequate behavioral performance. The sequence began with an anticipatory signal, then the conditioned signal was switched on, a lamp in either the right or the left key, and after a 5-10 s delay, a trigger signal opening a screen followed. Then the monkey had to press the key indicated by light and grasp the food from a box. Differences in the average firing rate and in the patterns of response were observed by comparing the unit activity during the CS expectancy with the trigger signal expectancy (delay). A mathematical treatment of the unit firing pattern allowed us to select specific firing pattern rearrangements likely to be involved in the short-term memory mechanisms, i.e. intracortical reverberation and successive recruitment of neuronal populations. Unit activity of s. principalis in one hemisphere depended on the CS right vs. left location. Similar differences were found for the delays. During the delay, information about the CS spatial location is probably stored as short-term traces in the units of s. principalis. The frontal cortex unitary responses elicited by the trigger signal depended on the direction of the subsequent movement. The motor cortex units provided less pronounced differences in .response to the trigger. In contrast to the motor cortex units, some frontal cortex units reacted only to the presence of food reward.

Mathematical modelling of reaction latency: the structure of the models and its motivation.

Abstract: The basic structural assumptions concerning the dynamic models of the reaction latency are presented. The linear dynamic stochastic model of the reac- tion latency is considered as a special case of dynamic model. The biological moti- vation for using these models are outlined. These models express the reaction latency as a first access time of the random threshold of a certain stochastic process. This approach was used in modelling the reaction latency in escape and avoidance expe- riments (the results will be presented in subsequent papers).

Effects of reversible elimination of some bulbar structures on the generation of respiratory pattern in rabbits.

Abstract: The regions of (i) nucl. n. VII (N. VII), (ii) nucl. retrofacialis (N. r. VII), (iii) nucl. Ambiguus (A.c) and (iv) nucl. ret. parvocellularis (n.rp) were explored with microelectrodes and then the active sites were injected with 5 microliters of lignocaine. The activity of both phrenic nerves, blood pressure and end-tidal CO2 percent were recorded throughout the experiment. Blockade of the n.VII region elicited apneustic discharge in both phrenic nerves; blockade of N.r.VII gave variable frequency responses but always reduced phrenic amplitude of discharges; microinjection of lignocaine into the region of A.c. invariably accelerated central respiratory rhythm, the amplitude of discharges being reduced predominantly contralaterally to the injection site; blockade of the R.pc elicited a dramatic prolongation of expiratory pause, decrease in amplitude and rate of rise of phrenic activity. All effects disappeared within 30 min after injection and histological examinations revealed only minor lesions at the sites of injections. It is concluded that the respiratory neurons of the medulla form a complex, strongly interconnected network.

Emotionality and exploratory behavior following cortico-basomedial amygdala lesion in rat.

Abstract: Twelve rats with amygdaloid lesion (CBM group) and 20 sham operated (Control group) were tested. Emotional reactivity evaluated by six category scale showed transient decrease in CBM group with respect to Control one. The CBM lesion enhanced the locomotor activity in electromagnetic activity meter in the initial phase of confinement in the apparatus. Open-field ambulation was higher in CBM rats than in controls on the first day of examination, while on the second day both groups showed similar locomotor activity. No between group differences were found in response to introduction of novel object. Both groups preferred to stay in box placed in open-field than move around the field. However, CBM rats were engaged in box exploration, whereas controls spent major proportion of time sitting motionless. These results indicate that CBM lesion increases some components of response to novelty. The pattern of changes and their transitory character suggest that cortico-basomedial region of the amygdala is involved in the control of processes underlying the initial phase of responding to novel environment.

Emotional reactivity after frontomedial cortical, neostriatal or hippocampal lesions in rats.

Abstract: Emotional reactivity following lesions in structures corre- sponding to the main components of dorsal prefrontal system of the mon- key was evaluated in a total of 165 rats by a six-categorial rating scale. Frontomedial cortical damage- (FM) and 1,esions in anterodorsal (DH) or posteroventral (VH) hippocampal regions elicited marked increases in emotional reactivity, relative to sham operated controls. The most profound effect was observed in FM rats. VH rats were somewhat more emotional than DH ones. Anteromedial neostriatal lesions (NC) evoked increased emotionality only on the first day of testing. Damage to diffe- rent structures differentially affected the various categories examined. The magnitude of overall reactivity and the pattern of changes indicate a similarity of effects from frontomedial and hippocampal lesions. This similarity was stronger between FM and VH than DH lesions. The ne- gligible eff.ect of NC damage on emotional reactivity suggests a functio- nal dissociation between the enteromedial neostriatum and the anato- mically related frontomedial cortex.

Intermediate stage of sleep and acute cerveau isolé preparation in the rat.

Abstract: The acute cerveau is016 rat shows spindle bursts of large amplitude alternating with low voltage activity in the frontal cortex and continuous theta rhythm in the dorsal hippocampus. These patterns closely resemble an "intermediate" stage of sleep-waking cycle, when the forebrain structures seem to be functionally disconnected from the brainstem. In the rat, paradoxical sleep is preceded and often followed by a short stage characterized by spindles of large amplitude (up to 700 pV, 6-13, c/s) in the frontal cortex and a theta activity (up to 250 pV, 4-7 c/s) in the dorsal hippocampus and the occipital cortex (7, 8, 22). Before the paradoxical sleep, this transitionnal or intermediate stage is presumably due to low level of activatory influences from the brain- stem (principally midbrain); these influences progressively diminish as slow sleep developes, while the pontine ascending influences responsible for paradoxical sleep are still absent or at a low level. After the end of paradoxical sleep, the intermediate stage would be in the inverted order, due to the suppression or very reduced dorso-pontine activation, while the activatory ascending influences are still absent or at very low level. Thus, the intermediate stage of sleep with its high cortical spindles may correspond to a state of cerveau is016 (4, 8, 10). In the present paper this hypothesis was tested in cerveau is016 rats. Up to now, this prepa- ration was studied only in cats (2, 3, 16, 20, 21) and in dogs (1). Twenty four male Wistar rats underwent a complete intercollicular

Inspiratory facilitatory and inhibitory vagal influences during apnoea in rabbits.

Abstract: During hyperventilation apnoea in vagotomized, anaesthetized rabbits, paralyzed and artificially ventilated, the effects of electrical afferent stimulation of the vagus nerve on the provocation and inhibition of inspiratory activity were investigated. The experiments were repeated using hyperinflation or short-lasting inflation in nonvagotomized animals. It was found that the possibility of observing inspiratory facilitatory phenomena depended on the interrelationship between the frequency of impulses transmitted separately through the thick and thin myelinated fibres. The time constants of central summation of vagal information and the possibility of observation of the phenomena of inspiratory facilitation depended on the central respiratory drive changed by CO2 and temperature.

Tegmental afferents of the amygdaloid body in the rat.

Abstract: Horseradish peroxidase (HRP) was injected to various parts of the amygdala in 50 rats. Retrograde axonal transport revealed that tegmental areas containing biogenic amines: dorsal and median raphe nuclei, locus coeruleus and ventral tegmental area, project diffu- sely to various amygdaloid areas. Morewer, HRP labeled cells were found in the parabrachial nucleus (following injection of the lateral amygdaloid nucleus) and in tegmental dorsolateral nucleus (after in- jection of the central nucleus of amygdala).

Carotid baroreceptor reflex in man, its modulation over the respiratory cycle

Abstract: Carotid baroreceptors were stimulated in 40 healthy volunteers by a rapid increase of the carotid transmural pressure due to subatmospheric pressure applied to a tight neck chamber (neck suction). Heart rate, arterial blood pressure and respiratory response were recorded. Reflex vagal inhibition of the sinus node preceded a blood pressure fall. Cardiac response adapted in a few seconds during prolonged baroreceptor stimulation, whereas reflex hypotension was maintained over the whole stimulation period applied up to 30 s. Augmented inspiratory movements were observed during neck suction. Short-lasting baroreceptor stimuli produced much less cardiac inhibition if applied during the early inspiratory than during the expiratory phase. On the peak and on the plateau of the voluntarily sustained deep inspirations, a spontaneous sinus bradycardia and a facilitation of the baroreceptor-cardiac reflex appeared. Voluntarily delayed expiration following deep and sustained inspiration coincided with cardioacceleration and baroreflex inbibition. Thus voluntarily Imposed, breathing patterns may reverse both respiratory sinus arrhythmia and cyclical modulation of the baroreflex responsiveness over the respiratory cycle.

Microelectrode analysis of the cellular mechanisms of conditioned reflex in rabbits.

Abstract: Spikes and postsynaptic potentials (PSPs) were recorded in the sensorimotor cortex of awake rabbits (1) A cellular analog of cortico-cortical conditioned reflex (CR) was studied Direct cortical stimulation of a remote point (conditional stimulus - CS) was paired with the stimulation near the microelectrode insertion (unconditional stimulus - UCS) The most neurons showed response facilitation when short intertrial intervals and strong UCS were used These changes were short-lasting (up to 30 s) and were explained by posttetanic potentiation Of 21 units tested with long (7 to 120 s) intertrial intervals, 9 showed significant response modification of longer duration (2) The analog of cortico-cortical CR was modified using stimulation of homolateral cortex as the CS The UCS was complimented by lateral hypothalamic reinforcement (LHR) in instrumental or classical paradigm Of 37 units tested, 5 showed an increase in the probability of short-latency ( less than 25 ms) spike (3) Extracellular activity of 17 neurons was followed through the entire cycle of elaboration and extinction of a "local conditioned startle response" established by pairing click CS with cortical UCS and LHR Responses of 7 neurons showed significant modifications The latency distributions of averaged PSPs were compared for naive (N), conditioned (C) and extinguished (E) states Latencies in N and E groups were similar but were different from those in C group Of 41 C group neurons, 26 responded at a latency of less than 17 ms; and 9 responded after less than or equal to 7 ms A pathway for this simple CR may pass through the cortex Thus PSP changes were observed in all models Augmentation of short-latency EPSPs support the idea that an increase in efficacy of excitatory synapses underlies the conditioning Interneuronal excitatory connections within the sensorimotor cortex are, presumably changed during elaboration of simplest motor CRs These connections can be analyzed with intracellular recordings triggered by spikes of a neighbouring neuron

Qualitative and quantitative effects of ACTH, piromen, cytoxan and isobutyl-2-cyanoacrylate treatments following spinal cord transection in rats.

Abstract: Adult, male, Long-Evans hooded rats were subjected to a spinal cord transection in the mid-thoracic region. Following surgery, animals were divided into groups for treatments with ACTH, Piromen, isobutyl-2-cyanoacrylate and Cytoxan. Animals were sacrificed at varying intervals from 7-180 days. Horizontal sections of the lesion site were stained with the Bodian silver and Gomori trichrome techniques and numbers of nerve fibers counted within the lesion. Statistical analysis of the quantitative data indicated that Piromen and Cytoxan, respectively, were significantly more effective than the other treatments in promoting regeneration of nerve fibers into the scar. Microcysts appeared adjacent to the lesion in all animals early in the postoperative period and coalesced to form large cavitations which continued to enlarge throughout the postoperative period. Although nerve fibers appeared to traverse the lesion, no return of function was observed.

Locus coeruleus lesions and avoidance behavior in rats.

Abstract: Bilateral electrolytic lesions of the locus coeruleus were performed in rats. In comparison with controls, lesioned rats showed decreased acquisition of two-way avoidance response, less intertrial responses, longer latency of avoidance responses on the first day of training, and needed more trials to reach the extinction criterion. It is suggested that locus coeruleus, contrary to the ventral noradrenergic bundle, facilitates avoidance behavior in rats.

Protection from extinction by a conditioned inhibitor.

Abstract: The phenomenon of protection from extinction (PFE) of a conditioned stimulus (CS) by a conditioned inhibitor (CI) has not been yet unequivocally demonstrated for the CS-CI compound in which the CS precedes the onset of the CI. Preliminary data from a project ad- dressed to this problem strongly indicate that PFE is a real and robust phenomenon. Moreover, the protection is demonstrated not only for' the CS duration overlapping with the CI but also for the early part of the CS which is not prevented by the CI from eliciting a conditioned res- ponse. The review of a few theories of conditioning suggests that the phenomenon of PFE is theoretically acceptable and predicted within the framework of any hypothetical mechanism which allows for post-trial "processing" or "consolidation" of information acquired during the trial.

Avoidance responding in dogs trained in symmetrical or asymmetrical go, no-go differentiation.

Abstract: The acquisition and the consolidation processes of avoidan- ce responding in go, (no-go differentiation with asymmetrical and sym- metrical reinforcement procedures were studied in 49 male mongrel dogs. Differentiation training procedures with asymmetrical and sym- metrical reinforcement were contrasted by the occurrence of painful shock on negative trials. The quality of conditioned stimuli and their relative saliency exerted strong effects on the rapidity of learning and the number of commision errors when the "asymmetrical" procedure was used, whereas these effects were strongly attenuated under "sym- metrical" procedure of reinforcement. Dogs trained in "symmetrical" go, no-go differentiation showed characteristic responses executed with shorter latencies and larger percentages of errox on negative trials and numerous extra-and intertrial responding in early stages of differentia- tion learning. Retention tests showed a greater stability of acquired differential responding trained under "symmetrical" than under "asym- metrical" procedure of reinforcement. The data indicate that the strength of the secondary punishing effect of CS ;prolongation is directly related to the saliency of the stimulus. The relations between the pri- mary and secondary punishing effects in the two types of differentia- tion task, and problem of signalling and arousing properties of stimuli used in training, were discussed.