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.     

Changes in the cholinosensitivity of sensomotor cortex neurons during conditioned reflex extinction]

Characteristics of neuronal responses of the sensorimotor cortex to ionophoretically administered neuromediators (acetylcholine, L-glutamate) were studied in rabbit in the course of extinction of conditioned defensive reflex. In the majority of neurones the extinction of the conditioned reflex is accompanied by a drop of cholinosensitivity. In a number of neurones the extinction of reflexes either does not change the reaction to acetylcholine, or enhances it. The analysis of these reactions permits to assume the existence of a group of neurones directly involved in the formation, fixation and storage of the temporary connection.     

Effect of microelectrophoretic application of GABA on the formation of a cellular analog of a conditioned reaction

Influence of GABA application on ability of sensorimotor cortical neurones to form conditioned cellular reactions was studied in chronic experiments on rabbits. Neuronal reactions were analysed at the initial stage of eye-lid conditioning. GABA application in a period of presentation of paired conditioned and unconditioned stimuli disturbed formation of inhibitory conditioned cellular reactions and did not influence elaboration of activating responses. Plastic changes underlying the process of formation of inhibitory conditioned neuronal reactions are supposed to be of intracortical nature.     

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.     

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.     

Changes in the configuration of conditioned reactions of visual cortex neurons during changes in reinforcement parameters]

In order to study the influences of controlled changes of defensive integration on the activity of visual cortical units their responses to a conditioned light flash and electric cutaneous stimulation with a 600 msec interval between them were recorded in experiments on alert rabbits. It has been shown that in a third of the neurones the types of reaction to light flashes and electric stimuli coincide. The changes in parameters of the reinforcing shock led to a changed response of most cells to the conditioned photic stimulus and electric stimulation. The changes may have affected units which produce any activation phase, including cells with activity characteristic of detectory ("simple" and "complex") visual neurones. The data obtained suggest that the special function of the visual cortex is used in different ways in systemic mechanisms of conditioned and unconditioned defensive acts and that the integrated system of a behavioral act exerts control both on the use of the unit in a certain systemic process and on its receptive field.     

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.     

Changes in the chemosensitive properties of the central neurons of the snail Helix pomatia and of the mouse as affected by opioid peptides

In experiments on neurones of the isolated ganglia of the snail and surviving hippocampal slices from mice, studies have been made of the effect of Met- and Leu-enkephalins on neuronal sensitivity to acetylcholine and norepinephrine. It was shown that in some cases the enkephalins do not affect bioelectrical activity of the neurones, but changed their responses to acetylcholine and norepinephrine. It is concluded that during investigation of the effect of enkephalins on the nervous cells, alongside with changes in the bioelectrical activity, special attention should be paid to changes in chemoreceptive properties of the neurones.     

The dependence of the neuronal reactions of the sensorimotor cortex to a simultaneous complex stimulus on the level of the differentiation of its components]

On alert animals the change was studied of the neuronal activity of the sensorimotor cortical area of cats brain in dependence on the level of differentiation of the components of simultaneous heteromodal complex stimulus. According to the character of this dependence and a number of other parameters two groups of neurones were singled out in the sensorimotor cortex. It was shown that parameters of reactions of all recorded neurones of the sensorimotor cortex to the positive conditioned signal were the first established after consolidation of the animal conditioned motor activity. In the course of elaboration following parameters changed: expressiveness, intensity, duration and value of latency. Reactions of neurones of both groups to the inhibitory stimuli were stabilized only after consolidation of the habit of differentiation. Responses of the first group neurones changed only by the pattern of discharge, while the responses of the second group neurones could change by expressiveness of response, its sign, duration and value of latency. Oscillations of the differentiation level after finishing of the elaboration of inhibitory conditioned reactions affected only the responses of the second group neurones to complex components.     

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.     

Cholinergic regulation of the activity of somatosensory cortex neurons during early postnatal ontogeny of the cat

In 11-14 days kittens, about 20% of neurones in the somatosensory cortical zone react to stimulation of subpallidal region which is a source of cholinergic projections to the cerebral cortex. The effect of subpallidal region stimulation is reproduced in case of microiontophoretic acetylcholine application and blocked by atropine what points to its cholinergic nature. Cholinergic stimulation causes inhibition of the background and evoked activities of the cortical neurones while, as it is known, in adult cats, acetylcholine mainly stimulates a reaction of activation. It is postulated that in kittens at the end of the second week of postnatal development, cholinergic innervation of the cortex significantly differs from the definitive one by its quantitative and functional parameters.     

Reactions of neurons in the sensory-motor cortex on different amounts of administered acetylcholine

As a result of acetylcholine iontophoresis with different currents 3-fold increase of transmitter compared with the threshold one for reaction has been shown not to result in change of a type of reaction pattern more than in 80.3% of neurones. Such increase of action force is quite enough for the significant lengthening of the reaction excitatory components in the most of investigated neurones. After the following repeated application of smaller quantity of transmitter the number of neurones with growth of frequency of excited impulsive activity recovers as well as the level of firing frequency decrease in the course of repetitive administration of transmitter. The effect of large doses of transmitter results in aftereffect expressed by increasing probability of excitatory component reduction during the repetitive applications of acetylcholine.     

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.     

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.     

Cholinergic transmission at mechanosensory afferents in the crayfish terminal abdominal ganglion

Electrical stimulation of mechanosensory afferents innervating hairs on the surface of the exopodite in crayfish Procambarus clarkii (Girard) elicited reciprocal activation of the antagonistic set of uropod motor neurones. The closer motor neurones were excited while the opener motor neurones were inhibited. This reciprocal pattern of activity in the uropod motor neurones was also produced by bath application of acetylcholine (ACh) and the cholinergic agonist, carbamylcholine (carbachol). The closing pattern of activity in the uropod motor neurones produced by sensory stimulation was completely eliminated by bath application of the ACh blocker, d-tubocurarine, though the spontaneous activity of the motor neurones was not affected significantly. Bath application of the acetylcholinesterase inhibitor, neostigmine, increased the amplitude and extended the time course of excitatory postsynaptic potentials (EPSPs) of ascending interneurones elicited by sensory stimulation. These results strongly suggest that synaptic transmission from mechanosensory afferents innervating hairs on the surface of the tailfan is cholinergic.Bath application of the cholinergic antagonists, dtubocurarine (vertebrate nicotinic antagonist) and atropine (muscarinic antagonist) reversibly reduced the amplitude of EPSPs in many identified ascending and spiking local interneurones during sensory stimulation. Bath application of the cholinergic agonists, nicotine (nicotinic agonist) and oxotremorine (muscarinic agonist) also reduced EPSP amplitude. Nicotine caused a rapid depolarization of membrane potential with, in some cases, spikes in the interneurones. In the presence of nicotine, interneurones showed almost no response to the sensory stimulation, probably owing to desensitization of postsynaptic receptors. On the other hand, no remarkable changes in membrane potential of interneurones were observed after oxotremorine application. These results suggest that ACh released from the mechanosensory afferents depolarizes interneurones by acting on receptors similar to vertebrate nicotinic receptors.Abbreviations ACh cetylcholine - mns motor neurones - asc int ascending interneurone     

Dynamics of the reactivity of cortical neurons to repeated electrophoretic application of acetylcholine

Dynamics of reactivity was studied in 50 neurones of the rat sensorimotor cortex to repeated acetylcholine microiontophoresis. By the parameter of response plasticity the neurones are distributed into three groups--unchanging, decreasing and increasing the excitatory component of the reaction. A connection has been established of the type and rate of tonic and evoked activities dynamics with the duration of the excitatory component of neuronal reactions to acetylcholine. The highest probability of these dynamic activity changes manifestation is observed in cholinoceptive neurones with duration of excitatory reaction components to acetylcholine equal to 3.2, 8.1 and 13.5 s.     

The action of Avermectin (MK 936) on identified central neurones from Helix and its interaction with acetylcholine and gamma-aminobutyric acid (GABA) responses

Intracellular recordings were made from identified neurones in the suboesophageal ganglionic mass of the snail, Helix aspersa. Avermectin, MK 936, 0.01-1.0 microM, induced an outward current in certain neurones. The size of this current varied from one cell type to another. This direct effect of Avermectin occurred irrespective of whether the neurones were sensitive to GABA or not and was generally irreversible. Avermectin, 0.1 microM, reduced the chloride mediated inhibitory GABA response and potentiated the largely sodium mediated excitatory GABA response. Avermectin, 0.1 microM, reduced the chloride mediated acetylcholine inhibitory response and potentiated the sodium mediated excitatory acetylcholine response. In neurones which showed a biphasic response to acetylcholine, Avermectin enhanced the excitatory and depressed the inhibitory component. It is concluded that Avermectin can interact with chloride ionophores to induce an outward current and can reduce chloride mediated responses associated with acetylcholine and GABA.     

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.     

Differential accessibility to two insect neurones doe not account for differences in sensitivity to α-bungarotoxin

The nicotinic acetylcholine receptor probe α-bungarotoxin (1.0 × 10^?7 M) blocks the depolarising response to ionophoretic application of acetylcholine onto the cell body membrane of the fast coxal depressor motoneurone (D_f) of desheathed cockroach (Periplaneta americana) metathoracic ganglia, but at the same concentration is completely ineffective in blocking the depolarising action of acetylcholine on dorsal unpaired median (DUM) neurones in the same ganglion. The possibility that this is due to differences in accessibility of the toxin to the neurones has been tested by a combination of ionophoretic injection of horseradish peroxidase into single neurones with a study of the distribution of the exogenous tracer lanthanum, which is of similar effective size to α-bungarotoxin. The peripherally located cell body membranes and the fine axonal processes of D_f and DUM neurones of desheathed metathoracic ganglia are equally accessible to lanthanum. Differential accessibility to the two cell types does not account therefore for the differences in sensitivity to α-bungarotoxin.     

Pharmacological and electrophysiological characteristics of neurones in the paramedian reticular nucleus.

1. Neurones in the paramedian reticular nucleus of decerebrate, unanaesthetised cats have been identified by microelectrode recording combined with antidromic activation of their axons in the ipsilateral inferior cerebellar peduncle. Most paramedian reticular neurones were not influenced by somatic stimulation. 2. When applied by iontophoresis from multibarrelled micropipettes acetylcholine and 5-hydroxytryptamine excited all but a few paramedian reticular neurones while l-noradrenaline inhibited almost all the neurones investigated. The excitatory response to acetylcholine could be antagonised by gallamine. 3. The paramedian reticular nucleus appears to be a relatively homogeneous group of neurones, pharmacologically as well as anatomically.