The active electrogenesis of the command neurons in the defensive behavior of the mollusk during conditioning]

In the paper changes of active electrogenesis of the command neurones of defensive closure of snail pneumostome at elaboration, extinction and repeated elaboration of classic conditioned defensive reflex to tactile stimulus was described; the tactile stimulation of other point of the body served as a differentiating stimulus. During the increase of biological significance of conditioned stimulus as a result of learning the stimulation of the command neurones in response to this stimulus was raised. At the same time the neurones showed decreased excitability in response to differentiating stimulus. Possible mechanisms of quick reconstruction of neurones excitability and functional value of PA generation threshold changes were discussed.     

The neuronal organization of a focus of conditioned excitation in the cat sensory-motor cortex]

The activity of single units in the focus of conditioned excitation was studied during defensive conditioning to direct electrical stimulation of the cat sensorimotor cortex. Reorganizations of spike activity set in during the period of reflex elaboration, were manifest in the increased number of excited neurones and those which respond both to the conditioned and unconditioned stimuli. In the course of elaboration, the inhibitory phase of unit responses to direct electrical stimulation of the sensorimotor cortex was reduced, while the frequency of background unit spike activity was enhanced. Acute extinction of the reflex restored the initial duration of the inhibitory phase and reduced the frequency of the background activity.     

Effect of the microiontophoretic application of acetylcholine on the formation of conditioned reactions in motor cortex neurons

In alert rabbits the activity of the motor cortex neurones was recorded with simultaneous application of acetylcholine to them in the process of defensive conditioning. Conditioned reorganization, mainly of activation type, were found in 60% of neurones. In most cases conditionally reacting cells were sensitive to acetylcholine. Ionophoretic application of the transmitter promoted the formation of conditioned neuronal responses and increased them in comparison with conditioned reactions evoked in absence of acetylcholine. It is supposed that the influence of acetylcholine on conditioned cellular process is realized due to its action on the state of excitability of the cortical neurones.     

Several mechanisms of acetylcholine participation in the processes of formation and fixation of temporary connections

Microphoretic application of acetylcholine (ACH) to the neurones of the rabbit sensorimotor cortex elicits changes of spontaneous and evoked activity which do not correlate with one another and which persist up to two minutes after the end of ACH application. Following the formation of a defensive conditioned reflex to sound, the reactions to ACH in units involved in the formation of the temporary connection are intensified as compared with their reactions before conditioning and with reactions of those neurones which did not elaborate a temporary connection. The possible mechanisms of ACH participation in the processes of elaboration and fixation of temporary connections are discussed.     

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.     

Interaction between neurons of the visual and sensomotor areas of the neocortex during elaboration and extinction of a conditioned defense reflex

Cooperation in activities of pairs of neurones situated in projection cortical areas of conditioned and unconditioned stimuli was studied in rabbits during intertrial intervals at different stages of elaboration and extinction of conditioned defensive response by means of auto- and crosscorrelation analysis of impulse fluxes. At the stage of generalization the number of pairs of neurones discharging in correlation was shown to increase a little (64 per cent) in comparison to that at the initial stage of conditioning (50 per cent) and pseudoconditioning (54 per cent). At the stage of stabilization and during extinction the number of pairs of neurones discharging in correlation decreased correspondingly to 34 and 32 per cent. Parallel analysis of correlation in neuronal discharges and simultaneously recorded electroencephalogram allowed to suppose that excitatory synchronizing influences and inhibitory cortical system play a great part in synchronization of activities of cortical neurones. Participation of these two systems is not the same at different stages of conditioning and extinction.     

Conditioned reactions to time of hypothalamic neurons. The perifornical nucleus]

In 40% of the 52 neurones of the hypothalamic perifornical nucleus in alert rabbits conditioned trace reactions of the activational (52%) and inhibitory (48%) type were recorded in the course of elaboration of a conditioned motor reflex to time. The sign and pattern of the trace responses were determined by the nature of cell reactions to actual paired stimuli. After 50 to 70 pairings, the unit trace conditioned reaction to time persisted for a period of 10 to 15 successive omissions. Trace responses were observed most frequently in the 5th of 8th omissions. In some cases conditioned enhancement of cell activity coincided with the conditioned motor response to time. This fact together with the maximal development of a summery trace cellular response at the moment of formation of conditioned motor reactions attests the participation of neurones of the perifornical nucleus in maintaining conditioned motor activity.     

Conditioned reactions of hippocampal neurons during amphetamine poisoning and its counteraction with haloperidol

Activity of 144 neurones of the dorsal part of the rabbits hippocamp was recorded during elaboration of motor conditioned reflex to time. Chronic amphetamine intoxication lowered the ability of hippocampal neurones to form conditioned reactions in response to pairings of sound stimuli with electrocutaneous reinforcement and fully suppressed mechanisms of reproduction by cells of engrams of previous pairings in series of their omissions Single administration of haloperidol to intact animals somewhat increased the number of neurones reacting to the pairing and their omissions in conditioned reflex to time without significantly influencing the intensity and dynamics of reproduction of endogenous cellular reactions in the series of consecutive omissions of pairing. Haloperidol administration during amphetamine intoxication elicited shifts towards normalization of conditioned activity of neurones, eliminating the suppressing action of amphetamine on mechanisms of reproduction of engrams of combined stimuli. Such "therapeutic" effect of haloperidol in many cases did not depend on the character of its psychotropic action. The properties of amphetamine and haloperidol action on the cells of the hippocamp are discussed as compared to their action on the neurones of other brain structures, previously studied in an analogous experimental situation.     

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.     

Projections and actions of tachykininergic, cholinergic, and serotonergic neurones in the intestine of the Atlantic cod

The native tachykinins cod neurokinin A and cod substance P, serotonin and acetylcholine have excitatory effects on the circular smooth muscle of the cod intestine. Furthermore, immunoreactivities to the cod tachykinins, serotonin and two markers for cholinergic neurones, viz. choline acetyltransferase and vesicular acetylcholine transporter, have been demonstrated in myenteric neurones of the cod intestine. In order to elucidate whether the neurones containing these substances project orally and thus might be involved in the ascending excitatory reflex of peristalsis, myotomy operations have been performed on the cod intestine. The immunoreactive areas of the myenteric plexus immediately oral and anal to the myotomy operations have been measured by using confocal laser scanning microscopy. Large accumulations of immunoreactivity to the tachykinins are found on the anal side of the myotomies, indicating oral projections of tachykininergic neurones. The areas immunoreactive to serotonin and choline acetyltransferase are of equal size on the oral and anal sides. Since the tachykinin containing neurones of the intestine project orally, and since cod neurokinin A and cod substance P have excitatory effects on circular smooth muscle, we conclude that tachykininergic neurones are involved in the ascending excitatory reflex of peristalsis in the cod intestine. Received: 6 March 1997 / Accepted: 15 September 1997     

Tonic component of the conditioned reflex process and its functional role

Tonic background activity of 266 neurones in the hippocampus and different neocortical areas was studied in freely moving rabbits in the process of defensive and food instrumental conditioned performance and during switching-over of instrumental and classical food and defensive reflexes. Associations of CS and reinforcement evoke background activity changes in most of recorded cortical neurones preceding the development of other conditioned manifestations. Conditioned reflex was performed only after reaching the background firing rate of almost every examined neurone optimal for its realization. The performance of different conditioned reflexes was associated with different background activity levels of cortical neurones. The above mentioned data form the experimental basis for the identification of the tonic component in conditioned process which reflects tonic character of temporary connection formation and function.     

Arachidonic acid and its acyclic derivatives regulate the short-term plasticity of the cholinoreceptors of the neurons in the edible snail]

On identified Helix neurones RPa3 and LPa3 using the method of double-electrode clamp technique on the membrane the influence was shown of eicosanoids on the dynamics of inward current extinction caused by the repeated ionophoretic applications of acetylcholine to soma. Extracellular influence of arachidonic acid (50-100 microM) increased the extinction. Phospholipase A2 inhibitor quinacrine hydrochloride (100-600 microM) decreasing the content of arachidonic acid in the cell acted differently. Inhibitor of lipoxygenase oxidation of arachidonic acid (nordihydraquiaretic acid) (3-10 microM) weakened the extinction. Blockader of cyclooxygenase oxidation of arachidonic acid--indomethacin (10-50 microM) did not influence the extinction. All the studied composition decreased the amplitude of input current caused by acetylcholine. The obtained results allowed to suppose that arachidonic acid and its acyclic metabolites formed as a result of lipoxygenase oxidation regulated short-term plasticity of snail neurones cholinoreceptors. Cyclic eicosanoids formed at cyclooxygenase oxidation of arachidonic acid had no regulating influence on cholinoreceptors plasticity.     

Responses of somatic cortical neurons during the conditioned placing reflex in cats

Unit activity was studied in areas 3 and 4 during the conditioned placing reflex in cats. Responses of somatic cortical neurons in this case were shown to develop comparatively late — 80–100 or, more often, 200–450 msec after the conditioned stimulus. In the motor cortex responses preceded movement by 50–550 msec, whereas in the somatosensory cortex they usually began simultaneously with or after the beginning of the movement. Judging from responses of somatic cortical neurons, the placing reflex is realized by the same neuronal mechanism as the corresponding voluntary movement. The differential stimulus and positive conditioned stimulus, after extinction of the conditioned placing reflex, evoked short-latency spike responses lasting 250–350 msec in the same neurons as took part in the reflex itself. In these types of internal inhibition, responses of the neurons were thus initially excitatory in character. Participation of the neurons in the conditioned placing reflex and its extinction, disinhibition, and differentiation, is the result of a change in the time course of excitatory processes and is evidently connected with differential changes in the efficiency of the various synaptic inputs of the neuron.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 392–401, July–August, 1982.     

The effect of acetylcholine and atropine on the temporal connection in the neuronal populations of the motor cortex]

On alert non-immobilized rabbits the activity of neurones in the sensorimotor cortex was studied at pair combination of brain structures stimulations. During omission of the reinforcing stimulus at the place of its expected presentation a complicated complex develops of neurones impulses reconstructions, consisting in reproduction of responses and activity changes which by their configuration differ from them and usually appear in later terms. Direct acetylcholine application on the cortex promotes manifestation of both types of neurones activity reconstructions. But atropine application depresses mainly the second type of reconstructions. Besides, acetylcholine increases the general duration of the given conditioned effects, but atropine decreases it.     

Neuronal activity of the cerebral cortex in cats with conditioned inhibition

Unit activity of the somatosensory cortex was studied in chronic experiments on cats during alimentary instrumental conditioned reflex performance and elaboration of conditioned inhibition (CI). First presentations of the CI signal at the beginning of CI formation caused, due to orienting reaction to a new stimulus, a levelling of the response of the neurones to the positive conditioned signal included into the CI complex. At the stage of consolidated CI, this depression proceeded gradually during the development of conditioned inhibition caused by consecutive presentations of the nonreinforced CI combination. Two groups of neurones were involved in the process of the CI performance: one of them being the same which was activated also in response to positive stimulation during performance of the conditioned response, and the second one being areactive to the positive conditioned stimulus but reducing the frequency of the background activity.     

Conjugation of unit activity in the visual and sensomotor areas of the rabbit neocortex during a conditioned reflex to sound and light

Conjugation of unit activity in the visual and sensorimotor neocortical areas was studied by means of histograms of cross- and autocorrelation in rabbits with conditioned reflex to light (1st group) and sound (2nd group). Relative number of neurones pairs acting in correlation in the areas remote from each other, in intersignal intervals both before and after stimuli did not differ in the 1st and 2nd groups. At the same time delays in neuronal discharges in one area after the other were different. In the 1st group animals there was a predominance of the number of visual area neurones discharging after sensorimotor with a delay up to 125 ms, in comparison with the number of sensorimotor area neurones discharging after the visual one. In the 2nd group rabbits the number of visual area neurones with such a delay of discharges after sensorimotor was less and, on the contrary, a predominance of sensorimotor area neurones was observed discharging after the visual one. The obtained results allow to suggest that neurones of the visual and sensorimotor neocortex areas form a single functional system in cases when conditioned and unconditioned stimuli are addressed to these areas and when only one of the studied areas is the projection zone for the combined stimuli. Organization of the neurones activity in systems in these two cases is different.     

The organization of the network characteristics of the cells in local and distributed neuronal networks of the cat brain]

In cats with elaborated alimentary instrumental reflexes to light net characteristics of neurones of visual, motor cortex and the hypothalamus lateral nucleus were studied on the basis of revealed interneuronal interactions by means of cross-correlation method of analysis. Different organization of net properties of the cortical neurones in organization of local and distributed neuronal networks was shown, namely: predominance of the divergent characteristics over the convergent ones for cells in local networks and levelling of these relations in distributed nets. Neurones of the lateral hypothalamus nucleus had equal presentation of divergent and convergent properties in organization of local and distributed networks. Net characteristics of neurones of the cortical and subcortical structures were manifested in the background after the elaboration and the extinction of conditioned reflexes. Only small cells of the visual cortex were functionally dependent and changed correlation of net characteristics in local networks at CR extinction.     

Plastic changes in the spontaneous activity of pond snail neurons during rhythmic and associated intracellular electrostimulation

In experiments on spontaneously active neurones of the isolated CNS of pond snail, under contingent stimulation with selective auto-reinforcement of interpulse intervals longer than their mean background value, 70 per cent of neurones were capable of adaptive rearrangements of the initial firing frequency, leading to frequency minimization or maximization of influences applied to them. After control rhythmic stimulation, usually no substantial changes of spontaneous activity were observed. The detected phenomena of initial transformation of the spontaneous impulse activity are considered as a cellular analogue of the instrumental conditioned reflex.     

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.     

Comparison of the effect of serotonin administered into the dorsal hippocampus on conditioned passive and active avoidance in rats

It has been established that intrahippocampal bilateral injection of 5-HT in a dose of 2 micrograms prolonged the time of passive avoidance reflex retention, inhibiting the retrieval of active avoidance reflex and facilitating its extinction. The data obtained show the dependence of 5-HT effect on reinforcing and triggering properties of spatial-environmental and phasic conditioned stimuli. It is suggested that intrahippocampal 5-HT administration was responsible for the retrieval of traces of conditioned reinforced stimuli.