[Changes of the neuronal membrane excitability as cellular mechanisms of learning and memory].

In the presented review given literature and results of own studies of dynamics of electrical characteristics of neurons, which change are included in processes both an elaboration of learning, and retention of the long-term memory. Literary datas and our results allow to conclusion, that long-term retention of behavioural reactions during learning is accompanied not only by changing efficiency of synaptic transmission, as well as increasing of excitability of command neurons of the defensive reflex. This means, that in the process of learning are involved long-term changes of the characteristics a membrane of certain elements of neuronal network, dependent from the metabolism of the cells. see text). Thou phenomena possible mark as cellular (electrophysiological) correlates of long-term plastic modifications of the behaviour. The analyses of having results demonstrates an important role of membrane characteristics of neurons (their excitability) and parameters an synaptic transmission not only in initial stage of learning, as well as in long-term modifications of the behaviour (long-term memory).

[The effect of serotonin precursor 5-hydroxytryptophan and neurotoxic analogue 5,7-dihydroxytryptamine on defensive conditioning in a snail].

This study is devoted to investigation of the influence of precursor of serotonin 5-hydroxytryptophane (5-HTP) and neurotoxic analogue 5,7-dihydroxytryptamine (5,7-DHT) on defensive conditioning and electrical characteristics of command neurones of defensive behaviour after learning. Snails injected with 5-HTP learned faster as compared to control group injected with physiological solution. After the 5,7-DHT injection, snails failed to form the conditioned reflex. Injection of 5-HTP after the preliminary injection of neurotoxin 5,7-DHT restored the capability of snails for learning. Injections of 5-HTP prevented the effect of 5,7-DHT at the behavioural level, but not at the level of electrical characteristics of the command neurones.

Electrophysiological studies of the effects of chronic administration of caffeine on the formation of a conditioned defensive reflex in the common snail.

Chronic administration of caffeine to common snails increased the rate of formation of a conditioned defensive reflex. When daily caffeine injections were given immediately after the training procedure, the conditioned defensive reflex was acquired more quickly than when caffeine injections were given before the training procedure started. Chronic caffeine administration to both trained and untrained snails led to depolarization changes in the membrane potential and reductions in the threshold potential of defensive behavior command neurons in common snails. Comparative studies showed that addition of caffeine to the solution bathing the mollusk nervous system resulted in decreases in the threshold potential of command neurons in both intact and trained snails; there was, however, no change in the membrane resting potential.

Changes in electrical properties of command neurons during protective effect of low doses of antibodies to S100 protein on the development of long-term sensitization in Helix lucorum.

We studied the effect of antibodies to Ca(2+)-binding protein S100 in a dilution of 10(-12) (LAT-S100) on the development of long-term sensitization in Helix lucorum, a neurobiological model of anxious and depressive states. After administration of LAT-S100 preventing the development of long-term sensitization before training, the membrane and threshold potentials in command neurons regulating defense behavior decreased less markedly than during long-term sensitization. It is assumed that the "protective" effect is associated with mechanisms of long-term potential maintenance and changes in intra- and extracellular balance of Ca(2+)-binding protein S100.

Effects of preliminary administration of haloperidol in low doses on the effects of haloperidol on behavioral reactions and command neuron membrane potential in edible snail.

We studied the effects of preliminary administration of haloperidol in low doses on changes in motor activity of edible snail and in electrical properties of defensive behavior command neurons induced by chronic administration of haloperidol. The rate of locomotion decreased after injections of haloperidol preparations (C6, C12, C30, C200 and a mixture C12+C30+C200) for 3 days. Similar changes were observed after 3 days of haloperidol administration. Haloperidol preparations in low doses produced a modulating effect on the decrease in locomotion rate and hyperpolarization of command neurons in edible snails caused by chronic exposure to haloperidol: the decrease in locomotion rate caused by chronic haloperidol treatment was prevented by preliminary injection of haloperidol in low doses C6, C12 and C30; the depolarizing shift of command neuron membrane potential was also abolished after consecutive injection of the same haloperidol preparations C6, C12 and C30.

[Electrophysiological study of effects of chronic injection of caffeine on defensive reflex conditioning in grape snail].

It was found that chronic injection of caffeine to grape snail increases a velocity of elaboration of conditioned defensive reflex. It was shown that after daily injection of caffeine immediately after procedure of learning the conditioned defensive reflex elaborated faster than daily injection before procedure of learning. It has been shown, that chronic injection of caffeine both in naive as well as learned snails led to depolarizing shift of membrane potential and to decrease of threshold potential of command neurons of the defensive behaviour of grape snails. It was also found that addition of caffeine in bath solution led to decrease of threshold of generation of action potential of command neurons both in intact and learned snails. The resting membrane potential of command neurons was not changed.

Investigation of changes in NO content during long-term sensitization in edible snail using EPR-spectroscopy: effects of antibodies to calcium-binding protein S-100.

EPR-spectroscopy experiments (electron paramagnetic resonance) demonstrated a decrease in NO production in the nervous system and heart of edible snail Helix lucorum after formation of long-term sensitization, a neurobiological model of anxiety and depression. The protective effect of antibodies to Ca(2+)-binding protein S-100 in dilution of 10(-12) on the formation of long-term sensitization was accompanied by partial recovery of NO synthesis in the nervous system and heart. These findings indicate that the imbalance in Ca(2+)-binding protein S-100 can lead to inhibition or modulation of some processes during plastic reorganization in the body and especially during pathological processes.

Protective effect of low-doses of antibodies to S-100 protein on the formation of long-term sensitization in helix lucorum.

Injection of antibodies to Ca-binding protein S-100 in a dilution of 10(-12) before the formation of long-term sensitization in Helix lucorum (10 min before the first electric shock) prevented the increase in defense reactions of pneumostome closure and ommatophore withdrawal. Thus, we demonstrated a protective effect of low-dose antibodies to S-100 on the formation of long-term sensitization as a neurobiological model of anxiety and depression.

Comparative studies of the effects of chlorpromazine and 5,6-dihydroxytryptamine on locomotion, defensive reactions in the snail Helix lucorum, and command neuron excitability in long-term sensitization.

The actions of the neuroleptic chlorpromazine (CPZ) and the neurotoxin 5,6-dihydroxytryptamine (5,6-DHT) on defensive reactions, locomotion, formation of long-term sensitization, and the electrical characteristics of command neurons in the common snail were compared. Prolonged (chronic) treatment with CPZ led to a significant increase in the pneumostoma closure time, as well as changes in motor behavior, with a decrease in the rate of locomotion. Administration of 5,6-DHT in small daily doses for one week was accompanied by gradual decreases in the rate of locomotion of the snails, which persisted for one week. A similar effect was seen after administration of the same total dose of neurotoxin, 30 mg/kg, as a single injection. Administration of CPZ prevented the formation of long-term sensitization, as did treatment with 5,6-DHT. The procedures of treatment with CPZ, long-term sensitization, long-term sensitization followed by CPZ, and acquisition of long-term sensitization on the background of treatment with CPZ gave a locomotion speed which was directly proportional to the length of the sole. No such relationship was seen during the acquisition of long-term sensitization on the background of treatment with 5,6-DHT. Electrophysiological studies showed that chronic CPZ led to a depolarization shift in the membrane potential and a decreased action potential generation threshold in command neurons, which also occurred on treatment with 5,6-DHT. It is concluded that the actions of the neuroleptic CPZ on defensive behavior and locomotion in the common snail, as well as on the electrical characteristics of identified neurons, were similar to the toxic actions of serotonin.

The effects of changes in extracellular calcium concentrations on the electrical properties of command neurons after acquisition of a defensive conditioned reflex in snails.

Studies of the electrical characteristics of the command neurons of a defensive reflex showed that the membrane potential showed no significant changes in response to changes in the calcium concentration in the perfusing solution in either intact or trained snails. Increases in the calcium ion concentration in intact snails were accompanied by increases in the threshold potential, from 14 +/- 0.7 mV at 2.5 mM Ca2+ to 21.8 +/- 0.9 mV at 20 mM Ca2+. The threshold potential in trained snails decreased in response to both increases and decreases in calcium concentrations, from 16.8 +/- 0.6 mV (physiological saline containing 10 mM Ca2+) to 13.3 +/- 0.6 mV at 20 mM Ca2+ and 11.8 +/- 0.8 mV at 2.5 mM Ca2+. The critical depolarization level changed correspondingly: in intact snails, this decreased with increases in calcium concentration, while in trained snails it increased in response to both increases and decreases in the calcium concentration.

Protein synthesis-dependent reactivation of a contextual conditioned reflex in the common snail.

We report here a study of the effects of blockade of protein synthesis with anisomycin during reactivation of a contextual conditioned reflex in the common snail. The amplitudes of the defensive reactions of snails to standard tactile stimulation before training were identical in two conditions: 1) testing of responses of snails fixed by the shell to a plastic ball floating in water and 2) on the surface of the terrarium glass. After applying electric shocks to the snails' skin for 5 days, a significant difference in responses reflecting the formation of a contextual conditioned reflex was seen in only one of the contexts. Placing trained snails in the same context (reminding) two days after training with simultaneous injection of anisomycin led to significant weakening of training, while control injections of physiological saline produced no such changes. These data suggest that the mechanisms of memory consolidation after training and reminding are not identical.

Modulatory action of combined treatment with antibodies against S100 protein and low doses of this protein on membrane effects of quinine.

Antibodies against calcium-binding protein S100 (AB-S100) 1.5-fold increased, while quinine 2-fold decreased the frequency of action potential generation in B4 and B6 neurons. Application of quinine against the background of AB-S100 treatment returned this parameter to the initial level. Pretreatment with AB-S100 in low doses prevents changes the frequency of action potential generation induced by application of AB-S100 in the initial dilution. The duration of action potential increased by 1.6 times after application of AB-S100 and quinine, while after application of quinine increased this parameter by more than 6 times. AB-S100 decreased maximum inward current by 20%. Our experiments demonstrated a modulating effect of combined administration of AB-S100 and its low doses on the membrane effects of quinine.

[Comparative investigation of influence of injections of chlorpromazine and 5,6-dihydroxytryptamine on locomotion, defensive reactions of snall helix lucorum and excitability of command neurons in long-term sensitization].

Comparative analysis of the action of chlorpromazine (CPZ) and neurotoxin 5,6-dihydroxytryptamine (5,6-DHT) on defensive reactions and locomotion of grape snail and elaboration of long-term sensitization (LTS), was carried out. Long-term (chronic) injection of chlorpromazine led to significant increasing of a pneumostome closing time and to changing of motor behaviour towards decrease of the velocity of the locomotion. Daily injections of 5,6-DHT in small doses within a week were accompanied by the gradual decrease of the velocity of snails locomotion, which was kept for a week. Similar effect was observed in injection of neurotoxin (30 mgs/kg). Injections of CPZ prevents elaboration of LTS, as well as injections of 5,6-DHT. After the action of CPZ, LTS, LTS followed by CPZ, and also during elaboration of LTS after injection of CPZ, the velocity of locomotion directly depended on the length of leg. During elaboration of LTS after injection of 5,6-DHT, such dependency is not retained. Electrophysiological study revealed that chronic injections of CPZ led to depolarizing shift of membrane potential and decrease of the threshold of action potential generation in command neurons as after injection of neurotoxin 5,6-DHT. Therefore, the action of neuroleptic drug CPZ on the defensive behaviour, locomotion of grape snail and electrical characteristics of identifying neurons is comparable with the action of toxic analogue of serotonin.

Effect of chronic administration of chlorpromazine on electrical parameters of command neurons in edible snail.

Electrophysiological experiments showed that chronic administration of neuroleptic chlorpromazine depolarized plasma membrane and decreased the threshold of action potential generation in command neuron of defense behavior of edible snail and motoneurons of pneumostome closure reflex. The effects of chlorpromazine on electrical parameters of the identified neurons can be explained by its serotonin-depleting action.

The effects of 6-hydroxydopamine on the electrical characteristics of snail neurons in long-term sensitization.

The effects of the neurotoxin 6-hydroxydopamine on the formation of long-term sensitization and changes in the membrane characteristics of identified neurons were studied. Injections of the neurotoxin 6-hydroxydopamine blocked the acquisition of long-term sensitization; when neurotoxin injections were given after the formation of long-term sensitization, they had no subsequent effect on conduction parameters. At the cellular level, recording of the electrical characteristics of common snail defensive behavior command neurons (LPa3, RPa3, LPa2, and RPa2) showed that the effects of 6-hydroxydopamine consisted of a small depolarization shift in the membrane potential and a change in the action potential generation threshold. Formation of long-term sensitization after injections of 6-hydroxydopamine did not lead to further decreases in the membrane and threshold potentials of command neurons as compared with snails only given injections of 6-hydroxydopamine. The changes in electrical measures of command neurons induced by administration of the neurotoxin 6-hydroxydopamine lasted at least two weeks.

[Protein synthesis-dependent reactivation of environmental conditioned reflex in terrestrial snails]. / Zavisimaia ot belkovogo sinteza reaktivatsiia obstanovochnogo uslovnogo refleksa u vinogradnoi ulitki.

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.

[Effect of changes in extracellular calcium concentration on electrical characteristics of command neurons after defensive reflex conditioning in snail]. / Vliianie izmeneniia kontsentratsii vnekletochnogo kal'tsiia na élektricheskie kharakteristiki komandnykh neironov posle vyrabotki oboronitel'nogo uslovnogo refleksa u ulitki.

Studies of electrical characteristics of command neurons of the defensive reflex have shown that membrane potential does not reliable differ for both naive and learned snails with changing of the calcium concentrations in external solution. With increasing of the concentrations of calcium ions it is observed the increases of threshold potential from 14 + 0.7 mV in 2.5 mM Ca2+ to 21.8 + 0.9 mV in 20 mM Ca2+ for naive snails. Threshold potential decreases from 16.8 + 0.6 mV (saline solution for snail--10 mM Ca2+) to 13.3 + 0.6 mV in 20 mM Ca2+ with increasing of calcium concentrations for learned snails, and under its reduction it is also decreased, but less remarkably, than for naive, to 11.8 + 0.8 mV in 2.5 mM Ca2+. On the same scheme it is changed a critical level of depolarization: for naive snails it decreases with increasing of the calcium concentrations, and for learned snails it increases either with increasing of the calcium concentrations, and so with its reduction.

Effect of chronic haloperidol on electrical parameters of command neurons in Helix Lucorum.

We studied the effects of neuroleptic haloperidol on electric characteristics (resting potential, action potential threshold, and critical level of depolarization) of command neurons LPa3, RPa3, LPa2, and RPa2 responsible for defense behavior in edible snail Helix Lucorum. Chronic administration of haloperidol led to hyperpolarization shift of the membrane potential and increased the threshold of action potential in these neurons. The data indicate a new possible mechanism of sedative action of neuroleptics based on hyperpolarization of some cerebral neurons, in particular, neurons responsible for some behavioral functions.