The re-formation of connections in the nervous sytem of Lymnaea stagnalis after nerve injury.

Changes in the tentacle reflex pathway of the pond snail Lymnaea stagnalis induced by peripheral nerve injury were studied with behavioural and electrophysiological techniques. After nerve injury regeneration of sensory axons is obtained in 6-12 days, suggesting an axonal outgrowth at a rate of 1 mm per day. Recovery of the tentacle reflex takes much more time indicating that synaptic efficacy is affected considerably by the period of sensory deprivation following nerve injury.     

Age and individual differences in infants' learning abilities.

To assess age and individual differences in infants' learning abilities the method of conditioned head turning toward the source of milk was applied to 20 infants at two different age periods - one month and four months. The results indicate that with increasing age the conditioned reflex is established more speedily in the first six months of life with a corresponding shortening of the mean latency. Extinction, however, occurs more speedily in one-month-old infants than in four-month-old infants. There are no differences in the mean latency of positive reaction during extinction and establishment of the conditioned reflex in both age categories. Considerable individual differences were ascertained in the rate of establishment and extinction of the conditioned reflex. Differences in the rate of extinction of the conditioned reaction appeared to be relatively stable.     

Widespread anatomical projections of the serotonergic modulatory neuron,CB1, inAplysia

Although sensitization-related changes in the neural circuitry of withdrawal reflexes inAplysia are well studied, relatively few studies address the organization of the modulatory components of sensitization. In particular, it is not known whether individual modulatory loci can simultaneously influence multiple reflex circuits. There is, however, evidence that a single modulatory transmitter, serotonin, plays a pivotal role in facilitating different reflex circuits during sensitization. Furthermore, it is known that activation of a pair of serotonergic neurons, the CB1s, produces heterosynaptic facilitation of the sensorimotor connections of one of these reflex circuits. These data together raise the possibility that the CB1s may produce sensitizing changes in the neural elements of multiple reflex systems simultaneously. In the present study, we utilized immunocytochemistry and intracellular labeling to obtain anatomical evidence of CB1's possible role in modulating multiple reflex circuits. We found that two distinct neurons satisfy previously published physiological criteria for CB1. One of these, CB1, is immunoreactive to serotonin. The second cell, here named CB2, has a different neuroanatomy and is not serotonin immunoreactive. Focusing on CB1, we found (1) profuse fine processes given off by its axons in the posterior neuropil of the cerebral ganglion, (2) extensive branching and fine processes in the pleural ganglion, and (3) a branch of CB1 that projects into the pedal ganglion. These three observations are consistent with the hypothesis that, in addition to its already established role in modulating the siphon withdrawal circuit, CB1 may also modulate synaptic connections between (1) the sensory and motor neurons of the tentacle withdrawal reflex (2) the sensory neurons and interneurons of the tail and tail-elicited siphon withdrawal reflex, and (3) the sensory and motor neurons of the tail withdrawal reflex. These observations support further physiological investigations of a possible global role of CB1 in modulating the tail and tentacle withdrawal reflexes.     

Nociceptive inputs to C3, a motoneuron of the tentacle withdrawal reflex in Helix aspersa

The tentacle withdrawal reflex of snails is perhaps the fastest, most sensitive reflex in the animals' repertoire. We have investigated the sensory inputs to a major motoneuron (C3) mediating the reflex. The cell C3 is sensitive to both chemical and mechanical stimulation, but there is little or no discrimination of quality in chemical stimuli. Small increments in the concentration of chemical stimuli produce large changes in neuronal responses. When chemicals are applied to the afferent nerve, the effects are comparable to those caused by applications to the olfactory epithelium, suggesting that the transducing elements are unspecialized. The afferent pathway is independent of the procerebrum, which is the primary olfactory lobe. Two excitatory synaptic inputs are identified, both of which originate in the tentacle, propagate centrally and synapse directly onto C3. A small, low threshold input is assigned to dendritic sites distant from the soma. A larger, higher threshold input is assigned to proximal dendritic sites. The latter input is largely responsible for the strong activation of C3 following noxious stimulation of the tentacle. The sensory inputs to C3 have properties similar to those of fibres in the nasal branch of the vertebrate trigeminal nerve.     

Reversal of signal significance of stimuli in the avoidance reflex]

The course of reversal learning in go -- no go avoidance reflex differentiation in both cats and dogs was analysed in terms of interrelations between drive and instrumental reflex activity. When signalling properties of the conditioned stimuli were reversed, marked changes in the drive state of experimental animals occurred. The increase of the fear drive influenced both the transfer of the instrumental response to the new positive conditioned stimulus and the extinction of the response to the previously positive stimulus. The quality of the conditioned stimuli and their reflexogenic strength exerted clear effects on the fear drive and on the course of reversal learning. Prefrontal lesions affected the drive state and the conditioned reflex activity of the animals during the reversal learning.     

Significance of the relative position in space of associated stimuli for formation and performance of motor conditioned reflexes

In experiments on cats the rate of formation of conditioned reflexes to sound (running to the feeding trough) depended on the spatial interrelations of the paired stimuli: the closer the source of the conditioned signal to the feeding trough, the sooner the formation of the conditioned reflex. It has been assumed that during formation of a conditioned reflex the closing of connection between conditioned and unconditioned stimuli is also attended with the closing of connection between the spatial parameters of the paired stimuli. Experiments with inactivation through cold of the temporal area (cortical representation of the vestibular system) of one hemisphere have shown that such a connection is formed in central parts of the vestibular analyser. When the conditioned reflex is elaborated to one feeding trough, the connection is duplicated by both hemispheres; in reflexes to two feeding troughs (i.e. spatial choice) such connections are lateralized in each hemisphere.     

Protein synthesis-dependent reactivation of environmental conditioned reflex in terrestrial snails

We investigated influence of anisomycine injection on reconsolidation of contextual memory after development of environmental conditioned reflex in terrestrial snail Helix. Testing the amplitude of behavioral reactions (tentacle withdrawal) in response to standard tactile stimulation of the skin in two contexts: a) when the snail was fixed by the shell and was moving on the surface of the ball floating in water, or b) was moving on the flat surface of glass terrarium, has shown no difference in response amplitudes. After a session of electric shocks (5 days) in one context only (ball) the associative learning was clearly observed as the significant difference of response amplitudes in two contexts. On the other day following testing was performed a session of "reminding", immediately after which the snails were injected by anisomycine (control snails were injected by saline solution). Testing has shown that injection of anisomycine led to impairment of the context conditioning. Results suggest that the mechanisms of consolidation of new memory and memory reconsolidation after retrieval are not identical.     

Level of neuroactive steroids in the brain, and gender-related differences in formation and decrease of conditioned reflex in rats

We investigated gender-related differences in dynamics of the brain sexual steroids during learning and the decrease of conditioned reflex in the modeling experiment. It was revealed that, before training to conditioned reflexes, females manifested a greater anxiety than males. Significant differences between males and females in formation of the conditioned reflex of passive avoidance were not revealed, whereas the conditioned response decrease were by 2-3 days faster in male rats than in females. It was revealed that there was an increase of testosterone content in various structures of the brain, especially in hippocampus and frontal cortex with its constant level in the blood plasma in learning conditioned response of passive avoidance in male adult rats. Also an increased estradiol concentration was found in females' amygdale, while increased value of estradiol was detected in hippocampus and the singular cortex in decrease of the conditioned response of passive avoidance. In blood plasma, the testosterone level was not changed, and the estradiol concentration was reduced significantly after the decreased conditioned reflex. Different dynamics of changes in the levels of sex steroids in the brain and the blood plasma can indicate a probability of their formation in nervous tissue. The correlation analysis confirms the conception about selective involvement of the brain's testosterone and estradiol in the specific structures in realization ofthe learning and memory processes in adult male and female rats.     

Level of neuroactive steroids in the brain and sex-related peculiarities of formation and extinction of conditioned reflex in rats

Sex-related peculiarities of dynamics of brain sex steroids in the process of learning and extinction of the conditioned reflex of passive avoidance have been studied in model experiment. Prior to learning of the conditioned reflex, female rats were found to be distinguished by manifestation of anxiety and fear as compared with male rats. At formation of the conditioned reflex, no significant sex-related differences were detected between males and females, whereas extinction of the conditioned reaction of passive avoidance in males occurred by 2–3 days faster than in females. At learning of conditioned reaction of passive avoidance, in sexually mature male rats there was revealed an increase of the testosterone content in various brain structures, especially in hippocampus and frontal cortex, while its level in blood plasma remained unchanged. Also shown was an elevation of estradiol concentration in female amygdale, whereas at extinction of the conditioned reaction of passive avoidance, a rise of estradiol values was noted in hippocampus and cingular cortex. At the same time, the testosterone level in blood plasma did not change, whereas after extinction of the conditioned reflex the estradiol concentration decreased statistically significantly. Different dynamics of changes of the sex steroid levels in brain and blood plasma can indicate a possibility of their formation in the nervous tissue. The performed correlation analysis confirms the concept of selective involvement of testosterone and estradiol of individual brain structures in realization of processes of learning and memory in sexually mature male and female rats.     

The biochemical-genetic mechanisms of learning. II. Selection for high and low rate of acquiring a motor conditioned reflex]

Using the model of feeding motor conditioned reflex, polymorphism for the rate of the formation of this response was found in a population of laboratory animals. Selection for high and low rate of the formation of this reflex resulted in significant differences inthis character between two strains already in the second generation. These differences are maintained in subsequent generations. The existing henerogeneity for the rate of the formation of conditioned rsponse in the population is shown to be genetically determined.     

Effect of adaptation to central highlands conditions on active avoidance conditioning and its retention after emotional pain stress

The generation of conditioned reflex of active avoidance (CRAA) and its retention after emotional stress were studied in different groups of rats. The degree of conditioned reflex of active avoidance in pre-adapted rats was higher than in non-adapted animals. However, the degree of CRAA maintenance was independent of the character of CRAA fixation and the rats' adaptability after 1 and 3 exposures to emotional stress. In a usual degree of conditioned reflex fixation its maintenance was higher in rats living on the plain than in low-mountain rats (adapted and non-adapted).     

Recognition of chemical stimuli by guppy, Poecilia reticulata Peters

An alimentary conditioned reflex to beta-phenylethanol and a subsequent differentiation of cumarine were elaborated in conditions of simultaneous paired choice in guppies. It was shown that beta-phenylethanol in a concentration not over 7 X 10(-6) M is perceived through olfaction. The conditioned reflex persists for a long time: twenty five to fifty days after section of the olfactory nerves (the conditioned reflex is restored after their regeneration) and at least seventy days in intact fishes.     

Various neurochemical mechanisms for the production of conditioned reflexes of various biologicals modalities at the level of the caudate nucleus]

Microinjection of noradrenaline in to the head of the caudate nucleus failed to influence the latent time of the conditioned reaction of avoidance and the muscle tone, but limited the motor activity and considerably increased the value and the latent time of the food-procuring reflex. Serotonin failed to influence the latent time of the conditioned defence reflex and did not alter the motor activity of rats; however, it shortened the latent period of the conditioned motor-food reflex and markedly stimulated the food-procuring reaction. Dopamine inhibited the conditioned food and defence reflex, but markedly stimulated the spontaneous motor activity of rats. The data obtained pointed to differences in the neurochemical mechanisms realizing the conditioned reflex reactions of different biological modality at the level of the caudate nucleus of rats.     

Neuronal response in the cat parietal association cerebral cortex (area 5) during performance of conditioned reflex motion

Responses in 160 neurons of the cat parietal cortex were investigated during the performance of instrumental food reflex (lever pressing) during experiments involving presentation of a conditioned acoustic stimulus. Discharge rate changed in 49% of neurons during the period preceding the conditioned reflex movement. Three basic types of cell with an excitatory response pattern were discovered apart from a small group showing suppression of activity, each differently involved in the process of conditioned reflex movement performance. Excitation arose in neurons of the first type 200±52.9 msec (average) before the onset of the conditioned reflex movement, reaching its peak discharge rate as the animal placed its paw on the lever. The former parameter was 605±54.2 msec for the second type of neuron, with firing rate peaking between the start of electromyographic response and the completion of lever pressing. The same parameter measured 1,000–2,000 msec in the third type and activation took the form of a diffuse increase in discharge rate without a clear-cut peak occurring during performance of the instrumental reflex. Findings would suggest the involvement of the parietal cortex neuronal system in the triggering as well as the follow-through of conditioned reflex motion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 223–231, March–April, 1987.     

Effects of whole body vibration on motor unit recruitment and threshold

Whole body vibration (WBV) has been suggested to elicit reflex muscle contractions but this has never been verified. We recorded from 32 single motor units (MU) in the vastus lateralis of 7 healthy subjects (34 ± 15.4 yr) during five 1-min bouts of WBV (30 Hz, 3 mm peak to peak), and the vibration waveform was also recorded. Recruitment thresholds were recorded from 38 MUs before and after WBV. The phase angle distribution of all MUs during WBV was nonuniform (P < 0.001) and displayed a prominent peak phase angle of firing. There was a strong linear relationship (r = -0.68, P < 0.001) between the change in recruitment threshold after WBV and average recruitment threshold; the lowest threshold MUs increased recruitment threshold (P = 0.008) while reductions were observed in the higher threshold units (P = 0.031). We investigated one possible cause of changed thresholds. Presynaptic inhibition in the soleus was measured in 8 healthy subjects (29 ± 4.6 yr). A total of 30 H-reflexes (stimulation intensity 30% Mmax) were recorded before and after WBV: 15 conditioned by prior stimulation (60 ms) of the antagonist and 15 unconditioned. There were no significant changes in the relationship between the conditioned and unconditioned responses. The consistent phase angle at which each MU fired during WBV indicates the presence of reflex muscle activity similar to the tonic vibration reflex. The varying response in high- and low-threshold MUs may be due to the different contributions of the mono- and polysynaptic pathways but not presynaptic inhibition.     

Neuronal response in the cat parietal association cortex to conditioned and non-conditioned acoustic stimuli

Neuronal response in the cat association cortex (area 5) to conditioned and non-conditioned acoustic stimulation was investigated. Numbers of neurons responding to a conditioned acoustic stimulus according to the traditional reflex pattern were twice as high. Numbers of inhibitory neuronal responses to the stimulus increased when instrumental reflex occurred. Neurons were found which only reacted to a conditioned acoustic stimulus in the absence of conditioned reflex movement occurring with instrumental food reflex. Although findings do not exclude the possibility of this cortical area contributing to the analysis of sensory signals and evaluation of their biological significance, it might be supposed that its main functional property lies in its involvement in the process of initiating behavioral response to a conditioned response.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 637–645, September–October, 1988.     

Analysis of the formation of systems of conditioned reflexes to time in rabbits]

Experiments on rabbits carried out by the food-procuring conditioned reflex method have shown that conditioned reflex systems to "pure" time can be elaborated, provided that conditioned stimulus is presented at regular, though different time intervals, following one another in a fixed sequence. The complexity of elaborating such systems to time is determined by the number of signal time intervals in the system, their different length, and their sequence. The formation of conditioned reflex systems to time is characterized by definite stages.     

New data on the correlation of the cardiac and motor components of the instrumental conditioned defensive reflex in dogs

Correlation of heart rate (HR) and conditioned motor reaction (CMR) was studied in dogs with conditioned avoidance reflex by the V. P. Petropavlovski? method. An increase of HR was shown in response to presentation of conditioned sound stimulus reaching maximum directly before CMR beginning. Immediately after the beginning of CMR and further against the background of continuous keeping of the paw in the safety zone, CMR greatly decreases. The CMR changes testify to a heavy weakening of classical conditioned reflex of fear as a result of kinesthetic afferentation signalling about successful keeping of the paw in the safety zone.     

Conditioned reflex analysis of functional connections between the hippocampus and limbic system structures

Instrumental defensive conditioned reflex elaborated in dogs to stimulation of the dorsal and ventral hippocampus, also appeared, due to generalization, in response to stimulation of a number of limbic structures. Two types of changes in the generalization effects (estimated by parameters of motor conditioned reaction) were observed in the course of conditioned reflex stabilization: enhancement (in response to stimulation of the lateral hypothalamus, lateral nucleus of septum, limbic cortex) and weakening toward complete disappearance (in response to stimulation of the medial nucleus of amygdala and medial hypothalamus). Manifestation of the generalization phenomenon from the brain structures, which are not involved initially into conditioned activity, suggests the existence of close functional connections between these structures and the hippocampus.     

Characteristics of the function of the higher portions of the central nervous system of rats subjected to acute hypoxia in the antenatal period]

A reduction of motor activity, and of the orientative reflex, its more rapid extinction in comparison with control were seen in the sexually mature rats which sustained acute hypoxia during the antenatal period. The experimental animals displayed disturbances of the conditioned reflex activity indicating a worse fixation of the temporary association, weakening of the inhibitory process and reduction of the nervous process mobility. Epileptiform convulsions occurred in presentation of "difficult" experimental tasks. There was also noted an increase in convulsioness after the administration of threshold doses of carasol.