Contribution of presynaptic dopaminergic receptors to the mechanism of the reactivating effects of blockade of the GABA-benzodiazepine-ionophore complex

Changes in the reactivating efficiency of blockade of components of the GABA-benzodiazepine-ionophore complex were analyzed in conditions of preliminary activation and inhibition of dopamine autoreceptors using (+)ZRRR and haloperidol respectively. A conditioned passive escape reflex was used, along with amnesia produced by detaining mice in the danger sector of a chamber immediately after imposition of a painful stimulus. Doses of bicuculline (1 mg/kg), picrotoxin (1 mg/kg), and flumazenil (10 mg/kg) given before testing restored performance of the conditioned response without altering the neurochemical background. Reductions and increases in dopaminergic activity during the training period prevented restoration of the conditioned passive escape response by blockade of GABAa and benzodiazepine receptors and chloride channels. It is suggested that the neurochemical mechanisms involved in restoring the damaged memory trace are based on the formation of te optimal balance in the activities of the various components of the GABA-benzodiazepine-ionophore complex and the dopaminergic system.

[The effects of medazepam on memory trace reproduction during learning and amnesia in aggressive and submissive C57Bl/6J mice]

Experiments were conducted on C57B1 mice to study the role of the social status on the reproduction of a conditioned reaction of passive avoidance and the effect of medazepam on the processes of reproduction. Aggressive and submissive animals were selected according to the test for agonistic confrontations. No effect of the animals' social status on the formation of a conditioned habit was revealed, but a significant increase in the level of defecation was recorded in the aggressive mice. Medazepam administration before the test reduced the reproduction of the conditioned reaction only in the control mice. An amnestic effect blocked reproduction in control and submissive mice but did not change it in the aggressors. Medazepam restored the amnestic memory trace only in submissive individuals. In aggressive mice it reduced the emotional response but did not change reproduction. The data obtained suggest that variations of the social status determine both the behavioral responsiveness to training and the changes in reproduction in response to medazepam.

[The mechanisms of the emotiogenic regulation of memory]

The determining mechanism of memory regulation is a system involving the right temporal region and two anterior frontal regions. This is a cortical part of the integral system of the emotional regulation of memory. The dopaminergic mechanism forms the basis for fortifying the emotiogenic memory system, promoting the facilitation of retrieval. The selective emotional set of aggressive and submissive mice determines both the processes of extinction, development of amnesia, and subsequent reactivation of a memory trace induced by neuropharmacological agents. The GABA system is shown to enter the mechanism that controls the activity of dopamine system--dopamine release from the terminals of the nigrostriatal and mesolimbic dopaminergic systems is stimulated. The neurochemical background in the development of amnesia or forgetting determines the subsequent retrieval of a memory trace. The dopamine and GABA systems are common links in the retrieval of amnestic and forgetting memory traces, respectively. A substantial rise of met-enkephaline levels along with the maximum increase of D2-receptor density in the frontal cortex, amygdala, striatum, and hippocampus were observed in rats after learning. In vitro experiments indicated that met-enkephaline and beta-endorphine stabilized the kinetics of dopamine-receptor interactions.

[The contribution of presynaptic dopaminergic receptors to the mechanism of the reactivating influences of blockade of the GABA-benzodiazepine-ionophor complex]

The changes in reactivating efficiency of the GABA-benzodiazepine-ionophore complex blockade were examined in mice after preliminary activation or inhibition of dopamine autoreceptors by (+)3PPP (2 mg/kg) and haloperidol (0.01 mg/kg). The passive avoidance learning task and amnesia produced by detention of a mouse in the dangerous compartment were used. The pretest injections of bicuculline (1 mg/kg), picrotoxin (1 mg/kg), and flumazenil (10 mg/kg) recovered the passive avoidance response in mice injected with saline before training. Pretreatment with the dopamine autoreceptor agonist and antagonist prevented from the recovery of amnestic memory trace induced by blockade of GABA-benzodiazepine-ionophore complex components. The results imply the involvement of dopamine/GABA-dependent mechanism in the modulation of memory trace retrieval.

Dopamine and opioid regulation of the memory retrieval recovery in mice

The reactivation effects of the delta-opioid receptor blockade and D2 dopamine receptor activation on the detention-induced memory deficit in mice were investigated, in order to study possible interactions between opioid and dopamine systems in memory retrieval. Animals were trained in a one-trial passive-avoidance task. Pretesting treatment with ICI 174,864 (1, 3 or 5 mg/kg, i.p.) or quinpirole (0.5, 1 or 2 mg/kg, i.p.) facilitated retrieval of memory trace in saline-pretreated mice. Pretraining injection of the dopamine autoreceptor agonist, (+)-3PPP (2 mg/kg), having no effect alone in learning, prevented the ability of ICI 174,864 to produce the memory-enhancing effect. It is suggested that the normal functioning of the dopamine system was critical for the facilitation of retrieval by delta-antagonist. Quinpirole-induced reactivátion of memory retrieval was enhanced by pretreatment with Leu-enkephalin (0.2 mg/kg), inducing increased retention. We discuss these results in the context of an important interactions between D2 dopamine and delta-opioid receptors.

Memory retrieval enhancement by kappa opioid agonist and mu, delta antagonists

The present study sought to identify specific opioid receptor subtypes involved in the modulation of reactivation of amnesic or forgotten memory traces by use of a one-trial inhibitory avoidance training procedures in mice. The effects of naloxone, ICI 174,864 (mu and delta opioid receptor antagonists, respectively) and dynorphin (kappa agonist) were investigated. The results indicated that preretention test administration of naloxone (2 mg/kg) or ICI 174,864 (3 mg/kg) attenuated the amnesia and forgetting as indicated by prolongation of step-through latency. On the other hand, the activation of kappa opioid receptors by dynorphin (1 mg/kg) also showed reactivating effects both after amnesia and forgetting. On the basis of the parallelism of the effects for mu and delta opioid receptor antagonists and kappa agonist, and on the finding that all three opioids demonstrated a different degree of reactivation of amnesic and forgotten memory traces, it was concluded that mu, delta, and kappa opioid receptors contribute to the modulation of amnesia and forgetting by independent mechanisms.

[The interaction of dopamine and opioid receptors in the re-establishing of an amnesic and forgotten memory trace by quinpirole]

The present study evaluated the contribution of delta and kappa opioid receptors to the dopamine-mediated reestablishment of an amnestic and forgotten memory trace. Using passive avoidance as a memory index, the pretraining injection of leukephalin was determined to enhance the efficiency of quinpirole, a selective dopamine D-2 receptor agonist, to reactivate the memory retrieval in amnesia and forgetfulness. In contrast, pretreatment with dynorphin attenuated the retrieval by enhancing the effect of the pretesting injection of quinpirole in amnesia. Quinpirole was found to be more effective in attenuating amnesia than forgetfulness.

Effect of Leu-enkephalin on the memory reactivation produced by blockade of the benzodiazepine/GABA-chloride ionophore receptor complex

This investigation sought to characterize the interaction between GABA/benzodiazepine and opioid systems in memory retrieval deficit induced by detaining an animal in the training apparatus after acquisition. Mice pretreated with saline or Leu-enkephalin (0.2 mg/kg) were trained in one-trial passive avoidance test with following detention. Pre-testing administration of bicuculline (1 mg/kg), picrotoxin (1 mg/kg), or flumazenil (10 mg/kg) produced the memory-enhancing effect in the saline-pretreated mice. Pretraining treatment with Leu-enkephalin blocked the reactivation of memory produced by bicuculline and picrotoxin, but not flumazenil. The present investigation suggest that both benzodiazepine/GABA and opioid systems are important modulators of memory retrieval and that a specific interaction between these systems is responsible for the observed recovery of impaired memory trace.

[GABA-opioid interaction during the recovery of a passive avoidance conditioned reaction]

The modulating influence of preliminary activation of the delta-opiate receptors on retrieval and retention of the memory trace during the blockade of various components of GABA-benzodiazepine-ionophore complex in a passive avoidance paradigm was studied in mice. The psychogenic amnesia was caused by a detention of a mouse in the dangerous compartment. Bicuculline (1 mg/kg), picrotoxin (1 mg/kg) and flumazenil (10 mg/kg) injected prior to testing attenuated the retrieval deficit caused by amnesia. Pretraining administration of leu-enkephalin (0.2 mg/kg) facilitated the efficiency of the action of the blockade of benzodiazepine receptors on the retrieval of the passive avoidance response whereas the blockade of GABA-A receptors and chloride channels was non-effective. These experiments provide additional support for the hypothesis that "neurochemical set" plays an important role of a regulator determining the neurochemical interaction between opiate receptor and GABA-benzodiazepine-ionophore complex in modulating memory processes.

Neurochemical mechanisms of memory control

Modulation of memory trace retrieval in emotiogenic brain structures, cortex and brainstem reticular formation by postsynaptic noradrenergic and dopaminergic drugs was found. At the initial stage of latent inhibition-a most significant mechanism of information selection-memory trace retrieval is retarded in all structures and in the cortex and the zona incerta later on. A haloperidol model of latent inhibition was obtained. Most important role of dopaminergic system in latent inhibition was shown. Inhibition of the GABA-benzodiazepine-ionophore complex by the blockade of GABA-receptors induced by bicuculline, the chloride channels by picrotoxin, the benzodiazepine receptors by flumazenil (R015-1788) and R015-3505 facilitates the memory trace retrieval damaged by amnesic agent. The dopaminergic activation enhances the dominant state and developes conditions for switching on the interferential GABA-ergic inhibition.

[GABAergic modulation of amnesic trace reproduction by activation of the dopaminergic system]

Features of amnesia trace reactivation by activation of different links of dopaminergic system synaptic apparatus following the change of benzodiazepine, GABAA and GABAB receptors activity are found in experiments in mice. Diazepam pretreatment increases bupropion effectiveness, prolongs duration of enhanced passive avoidance response retrieval during D-1 and D-2 receptors activation by (+)3-PPP and decreases both characteristics under selective D-2 receptor activation by quinpirole. Activation of GABAA and GABAB receptors induces the attenuation of quinpirole effect and the duration of (+)3-PPP action.

The role of GABAA and GABAB receptors in the development of amnesia

It has been demonstrated that a gradual spontaneous recovery of a previously unreproducible memory trace and the prevention of the antiamnesic effect of the blockade of the GABAA receptor, but not of the blockade of the benzodiazepine receptor or the chloride channel, take place with the development of amnesia against the background of the activation of the GABAB receptor by baclofen. The "neurochemical set" created by the activation of the GABAA receptor by muscimol in a dose of 1 mg/kg prevents the antiamnesic effect of the blockade of any component of the benzodiazepine-GABA-ionophore complex, while at a dose of muscimol of 0.5 mg/kg, the retrieval of the amnestic trace takes place only by blockade of the benzodiazepine receptor. Thus, the development of amnesia is determined by the functional state of inhibitory GABAergic systems of the brain, which governs the subsequent correction of the amnestic memory trace.

[The role of the dopaminergic system and GABA-benzodiazepine- ionophore complex in the regulation of memory retrieval]

The spontaneous forgetting model has been used to demonstrate the possibility of the memory forgetten trace extraction under the dopamine reuptake blockade by nomifensine and bupropion, increase of its quantity by amfonelic acid, activation of the postsynaptic dopaminergic receptors by (+)3-PPP, blockade of the latter by (-)3-PPP, and under the blockade of separate links of the GABA-benzodiazepine-ionophore complex by bicuculline, picrotoxin, flumazepil and R015-3505. Effectiveness of the neuropharmacological actions improving the memory forgotten trace retrieval is shown to depend upon the duration of the spontaneous forgetting process. The presynaptic receptors are involved in the retrieval process control--improvement of the conditioned habit performance after forgetting due to the activation of presynaptic dopaminergic receptors by specific agonist (-)3-PPP is clearly correlated with the initial retrieval level. The above facts underlie a hypothesis about the neurochemical forgetting mechanisms.

Influence of changes in the effectiveness of blockade of the benzodiazepine-GABA ionophore complex on the reproduction of the amnestic memory trace in mice after preliminary administration of diazepam

A comparative analysis was carried out in experiments on mice, using the methodology of the conditioned passive avoidance reaction, of the effectiveness of the blockade of the BD-GABA ionophore complex and its individual components in the recovery of a memory trace following "psychogenic" amnesia developing against the background of preliminary activation of BD-receptors by diazepam. It was shown that an improvement in the reproduction of the conditioned reaction was observed on the second day under conditions of "neurochemical tuning" only with the blockade of the GABAA receptor by bicuculline. Flumazepil and picrotoxin did not elicit an improvement in the reproduction of the reaction. A similar relationship of the effectiveness of the pharmacological actions was observed on the 21st day after training and "psychogenic" amnesia. The facts presented permit the hypothesis that the development of "psychogenic" amnesia is determined by the functional state, which governs the possibility of retrieving the memory trace, of the mediator systems of the brain during learning and the amnestic influence.

[The role of GABA-A and GABA-B receptors in the development of amnesia]

The paper deals with analysis of the influence of blockade of separate components of benzodiazepine-GABA-ionophore complex on the recovery of memory trace amnesia under GABA-A and GABA-B receptors activation in the experiments with conditioned reaction of passive avoidance of mice. Activation of GABA-A receptors did not change the behavioural amnesia manifestation at all terms of testing. Activation of GABA-B receptors before learning and amnestic influence caused spontaneous recovery of avoidance reaction. Blockade of chloride channel by picrotoxin and of benzodiazepine receptor by flumazepil restored the reproduction of the memory trace disturbed against the background of GABA-B receptors activation. Systemic flumazepil administration contributed to the memory trace reproduction against the background of GABA-A receptors activation by muscimol in the dose of 0.5 mg/kg. In conditions of amnesia development against the background of muscimol in the dose of 1 mg/kg the blockade of any component of benzodiazepine-GABA-ionophore complex was not effective. The obtained data testify that activation of GABA-A and GABA-B receptors changes the amnesia development and correction of amnesia memory trace by the blockade of separate components of benzodiazepine-GABA-ionophore complex.

[Effect of a change in the effectiveness of a benzodiazepine-GABA-ionophore complex blockade on the reproduction of an amnesic memory trace in mice after preliminary diazepam administration]

The paper deals with the results of analysis of the influence of blocked of BD-GABA-ionophore complex and its separate components on recover of memory trace amnesia during BD-receptors activation in experiments on elaboration of CR of passive avoidance in mice. It is shown that at "neurochemical tuning" the improvement of conditioned reaction reproduction on the 2-nd and 21-st day after learning and amnestic action was observed only at GABAA receptor blockade by bicuculline, while the blockade of BD-receptor by flumazepil and of chlorine channel by picrotoxin was ineffective. Simultaneous blockade of all BD-GABA-ionophore complex components was not more effective in comparison with the blockade of its separate links in the recovery of conditioned reaction reproduction. The presented data allow to suppose that "psychogenic" amnesia development is determined by the functional state of neurotransmitter brain systems at learning and amnestic action which stipulates subsequent possibility of memory trace retrieval.

[Effect of quinpirole on the retrieval of a memory trace in amnesia]

In experimental studies on mice it was shown that quinpirole, a selective agonist of dopaminergic postsynaptic D-2 receptors, possessed a pronounced antiamnestic activity. Administration of quinpirole before testing on 2nd and 22nd days reactivated the retrieval of passive avoidance impaired by an amnestic agent. The drug effect depended on the duration of "psychogenic" amnesia. It is suggested that the postsynaptic dopaminergic D-2 receptors are actively involved in the neurochemical mechanisms of memory trace retrieval.

[Comparative analysis of the antiamnesic action of a blockade of the benzodiazepine-GABA-ionophore complex and of an activation of the dopaminergic system in the brain of mice]

In experiments on mice by the method of conditioned reaction of passive avoidance and amnesia elicited by the animal delay in the dangerous compartment immediately after electrocutaneous stimulation, antiamnestic effect is demonstrated of pharmacological influences, changing the activity of benzodiazepine-GABA-ionophore complex and dopaminergic system. Comparative analysis of the efficiency of neuropharmacological substances of different actions on synaptic apparatus of the studied transmitter systems in amnesia reduction showed that the greatest effect of improving the reproduction of the conditioned habit was that of the bupropion, the highly specific blockator of dopamine reverse absorption. The obtained results testify that amnesia development is based on activation of the inhibitory GABAergic brain processes and disturbance of dopaminergic system functioning.

[Bupropion activation of memory trace retrieval in amnesia and forgetting]

The effect of a new antidepressant bupropion on the processes of retrieval of the conditioned response of passive avoidance in mice under amnesia of different genesis and spontaneous forgetting was studied. The drug was shown to exert the antiamnesic effect and to facilitate retrieval of amnesia-affected or forgotten memory trace. The maximal effect of bupropion was observed at the dosage of 30 mg/kg. At the use of bupropion on the 2nd day after exertion of amnesic influences there was registered the tendency to prolongation of preservation of the conditioned habit enhanced retrieval as compared with greater time periods. The drug effect under memory trace retrieval impaired by cycloheximide-induced amnesia was similar in the action but more pronounced than that under "psychogenic" amnesia. The data obtained testify in favour of an active involvement of the brain dopaminergic system in the processes of memory trace retrieval.

[Reproduction of a memory trace in amnesia and forgetting following alteration in the activity of pre- and postsynaptic dopamine receptors]

The paper deals with analysis of the action of enantiomers 3-PPP on memory trace reproduction disturbed by amnestic effects and spontaneous forgetting in mice. A considerable antiamnestic effect is shown of (+)3-PPP and (-)3-PPP in 10 mg/kg doze changing the activity of postsynaptic dopamine receptors. The influence of drugs in 2 mg/kg doze changing the activity of presynaptic receptors consisted in recovery of conditioned habit only in situation of a weak amnestic effect and at forgetting, when the level of reproduction was like a weak amnesia. The range of enantiomers 3-PPP action on reproduction processes disturbed by amnesia or forgetting is determined by the possibility of specific activation of pre- and postsynaptic receptors at different depth of disturbances of memory trace reproduction causing differentiation of 3-PPP effects.

[Effect of activation and blocking of the GABA-ergic system during disorders of memory trace reproduction]

Analysis of the effects of activation and blocade of GABA-ergic system showed significant changes in the level of reproduction of conditioned reaction of passive avoidance in mice--lowering under administration of muscimol and baclopfen and increase under administration of picrotoxin and bicucullin in a dose of 1 mg/kg. Sharp lowering was observed of the efficiency of activating influence of drugs depressing the activity of GABA-ergic system at a long interval from the moment of administration of "psychogenic" amnestic agent. Dependence was established of the drugs influence on the type of memory disturbance: higher value of bicucullin and picrotoxin in retrieval of memory trace disturbed by cycloheximide in comparison to "psychogenic" amnesia. On the basis of the obtained results a suggestion is made on the significance of GABA-ergic mechanisms in regulation of reproduction processes.

[Facilitation of memory trace retrieval by the action of amfonelic acid]

Amfonelic acid exerting the central dopaminergic effect was studied on mice by the passive avoidance conditioned response method under amnesia induced by leaving the animals in a dark chamber following electrocutaneous stimulation and different terms of natural forgetting. Amfonelic acid was shown to prevent the amnesic effect, to improve retrieval of the conditioned response decreased as a result of amnesia or prolonged forgetting.

[Effect of benzodiazepine receptor blockade on memory processes in the mouse]

The results of study testify to a stimulating effect of benzodiazepine receptors blocators RO15-1788 and RO15-3505 on reproduction of conditioned reaction of passive avoidance in mice disturbed as a result of various procedures-"psychogenic" and cycloheximide amnesia, extinction and forgetting. A considerable antiamnesic effect of the drugs on cycloheximide amnesia models is noted, in comparison with the "psychogenic" one. RO15-3505 is more effective in the processes of extraction of memory traces under amnesia. The obtained results testify to an important contribution of benzodiazepine-GABA-ergic brain systems in inhibitory regulation of the processes of stored memory traces reproduction.

[Effect of diazepam on interference processes]

It has been found in experimental behavioral interference during training in two conditioned reflexes, rapidly following each other, that intraperitoneal injection of diazepam (2 mg/kg) 30 min before training potentiates the inhibitory effect of the defensive reaction to the drinking one. Electrophysiological analysis of the modulating effect of amygdaloid stimulation on the peripheral signal transmission via the central gray matter has demonstrated that in the majority of the neurons, diazepam produced a longer and pronounced inhibition of the excitatory reactions in response to electrocutaneous stimulation after conditioning stimulation of the amygdaloid. The data obtained allow an assumption that inhibitory processes determined by the activity of the GABAergic amygdalofugal system underlie the interference interrelations.

[Effect of transmeridional flights and mountainous conditions on different kinds of memory]

The effect of transmeridional flights and highland exposures on memory processes was studied. During 21-day observation following an environmental change memory processes were activated: short-term memory storage increased, proceptive and retroactive interference decreased, fixation of memory track improved, number of reminiscences grew, and forgetfulness lessened. These processes were especially active during 11th though 21st days of adaptation. Improvement of short-term memory was found in verbal and nonverbal tests, nonverbal short-term memory being changed more significantly. These findings point to the leading role of memory in the development of adaptive behavioral programs. The conclusions can be applied to the selection of optimal mental tasks given to the man after his transmeridional flight or transfer to highlands.

[Changes in human reaction time during adaptation to mountainous conditions]

In studies on human adaptation to mountain environment (Altai, 2.600 m) the following psychophysiological characteristics were measured: latency of simple motor reaction (RT), time of reaction to a moving object (RMO) and estimations of time intervals. It has been shown that during the first days of adaptation, RT of right and left hands significantly increases by 10% as compared to the control data (Novosibirsk), as well as weighted dispersion of these parameters. Deviations in RMO in 11--20th subsequent measurements and their dispersion increase significantly. This testifies to a destabilization of functions, due to rapid fatigue, impairment of mobility and functional efficiency of nervous centres. Further stay in mountains leads to an optimization of human time reactions: RT is shortened, deviations in RMO decrease, subjective estimation of time intervals becomes more precise. Of special interest is that improvement of psychophysiological parameters is accompanied by a sharp decline of their dispersion. Such increase in adaptability and narrowing of variations range are typical of the state of tension of regulatory systems.

Layer by layer analysis of commissural hippocampal evoked potentials during glutamate microiontophoresis

Commissural evoked potentials (EP) in hippocampal area CA1 were investigated during microiontophoretic application of sodium glutamate (SG) in experiments on unanesthetized rats immobilized with diplacin. EP were recorded by the central barrel of a five-barreled microiontophoretic microelectrode before and during application of SG. The effect of SG in the region of EP reversal was characterized by depression of the initial positive phase of the response and an increase in negativity. In the radial layer SG caused a substantial increase in the commissural response recorded at a depth. At a distance of 100 mu from the tip of the iontophoretic pipet no changes in EP were found. An increase in the intensity of transhippocampal stimulation was accompanied by a marked increase in the amplitude and a change in shape of the individual phases of EP and it abolished the effect of the microiontophoretically applied SG. During paired stimulation with an interval of 20--200 msec different effects of SG on the testing response were recorded depending on the length of the interval.

[Laminar analysis of commissural evoked potentials of the hippocampus following microiontophoretic administration of glutamate]

The hippocampal commissural evoked potentials (EP) were studied by means of microiontophoretic application of glutamate in unanesthetized immobilized rats. Near the reversion level, glutamate strongly decreased the primary positive component of the commissural EP, with a parallel enhancement of the negativity. An increase in the stimulus intensity restored the EP shape. In the stratum radiatum, glutamate considerably increased the deep commissural response. Using paired microelectrodes, the effect of glutamate disappeared at a distance more than 100 m from the phoretic electrode tip. When delivering paired stimuli with 20-200 msec interval, the second EP was changed under the glutamate effect.