Comparative analysis of early neurodegeneration signs in a mouse model of Alzheimer's disease-like pathology induced by two types of the central (Intracerebroventricular vs. Intrahippocampal) administration of Aβ25-35 oligomers

Animal models of Alzheimer's disease (AD) induced by intracerebroventricular (ICV) or intrahippocampal (IH) administration of amyloid-beta (Aβ) are widely used in current research. It remains unclear whether these models provide similar outcomes or mimic pathological mechanisms of AD equally. The aim of the work was to compare two models induced by ICV or IH administration of Aβ25-35 oligomers to C57BL/6 mice. Parameters characterizing cognitive function (passive avoidance test), protein expression (IBA1, Aβ, LC3-II) and expression of genes for neuroinflammation (Aif1, Lcn2, Nrf2), autophagy (Atg8, Becn1, Park2), or markers of neurodegeneration (Cst3, Insr, Vegfa) were analyzed. Сognitive deficits, amyloid accumulation, and neuroinflammatory response in the brain evaluated by the microglial activation were similar in both models. Thus, both ways of Aβ administration appear to be equally suitable for modelling AD-like pathology in mice. Our findings strongly support the key role of Aβ load and neuroinflammatory response in the hippocampus and frontal cortex for the progression of AD-like pathology and development of cognitive deficits. There were certain minor differences between the models in the mRNA level of genes involved in the processes of neuroinflammation, neurodegeneration, and autophagy. Modulating effects of the central administration of Aβ25-35 on the mRNA expression of Aif1, Lcn2, Park2, and Vegfa genes in different brain structures were revealed. The effects occurred to be more pronounced with the ICV method compared with the IH method. These findings give insight into the processes at initial stages of Aβ-induced pathology depending on a primary location of Aβ oligomers in the brain.

Neuroprotective Effects of Ceftriaxone Involve the Reduction of Aβ Burden and Neuroinflammatory Response in a Mouse Model of Alzheimer's Disease

Ceftriaxone (CEF) is a safe and multipotent antimicrobial agent that possesses neuroprotective properties. Earlier, we revealed the restoration of cognitive function in OXYS rats with signs of Alzheimer's disease (AD)-like pathology by CEF along with its modulating the expression of genes related to the system of amyloid beta (Aβ) metabolism in the brain. The aim of this study was to determine the effects of CEF on behavior, Aβ deposition, and associated neuroinflammation using another model of an early AD-like pathology induced by Aβ. Mice were injected bilaterally i.c.v. with Aβ fragment 25-35 to produce the AD model, while the CEF treatment (100 mg/kg/day, i.p., 36 days) started the next day after the surgery. The open field test, T-maze, Barnes test, IntelliCage, and passive avoidance test were used for behavioral phenotyping. Neuronal density, amyloid accumulation, and the expression of neuroinflammatory markers were measured in the frontal cortex and hippocampus. CEF exhibited beneficial effects on some cognitive features impaired by Aβ neurotoxicity including complete restoration of the fear-induced memory and learning in the passive avoidance test and improved place learning in the IntelliCage. CEF significantly attenuated amyloid deposition and neuroinflammatory response. Thus, CEF could be positioned as a potent multipurpose drug as it simultaneously targets proteostasis network and neuroinflammation, as well as glutamate excitotoxicity, oxidative pathways, and neurotrophic function as reported earlier. Together with previous reports on the positive effects of CEF in AD models, the results confirm the potential of CEF as a promising treatment against cognitive decline from the early stages of AD progression.

Methylated arginine analogues: their potential role in atherosclerosis and cognition using the poloxamer-407-induced mouse model of dyslipidemia

An experimental mouse model of dyslipidemia and atherosclerosis was utilized to study the generation of methylarginines in vivo, as well as any potential behavioral changes in mice associated with the production of excess methylarginines. Following 14 weeks of poloxamer 407 treatment, mice developed atherosclerosis and the plasma concentrations of monomethylarginine and asymmetric dimethylarginine were found to be significantly greater than corresponding concentrations in control mice. This finding may have contributed to the development of aortic atherosclerotic lesions in poloxamer-treated mice by interfering with nitric oxide availability and, hence, normal function of vascular endothelium. Poloxamer-407-treated mice also showed a significant decrease in locomotor and exploratory activity, together with signs of emotional stress and anxiety relative to controls. Passive avoidance testing to assess learning and memory provided suggestive evidence that poloxamer-treated mice could potentially be characterized as having undergone a disruption in the process of forgetting about an aversive event, specifically, a foot shock, when compared with control mice. Thus, it is also suggested that the increase in both plasma monomethylarginine and asymmetric dimethylarginine in poloxamer-407-treated mice may somehow influence learning and memory, because endothelial dysfunction caused by reduced nitric oxide availability has been hypothesized to negatively influence cognitive function.

[GABA-Receptors in Modulation of Fear Memory Extinction]

GABA is the major inhibitory neurotransmitter in the central nervous system determining the efficacy of neuronal interaction. GABA-receptors play a key role in different aspects of fear memory--acquisition and consolidation, retention, reconsolidation and extinction. Extinction is an important behavioural phenomenon which allows organism to adapt its behavior to a changing environment. Extinction of fear memory is a form of new inhibitory learning which interferes with expression of the initial acquired fear conditioning. Resistance to extinction is symptom of depression and posttraumatic stress disorder. The aim of the present review was to summarize own and literary data about GABAergic modulation of fear extinction and pharmacological correction of extinction impairment at influences on GABA(A)- and GABA(B)- receptors.

[BEHAVIOR, MEMORY AND IMMUNOLOGICAL STATUS IN MICE MODEL OF DESYNCHRONOSIS]

Interstrain differences in behavior and parameters of the immune system of CBA and C57BL/6 mice with round the clock coverage (KO) were investigated. Open field, light/dark, acoustic startle response, forced swimming, elevated plus-maze, passive avoidance were used for measuring emotional behavior and memory. The number of lymphocyte subpopulations CD3+, CD4+8-, CD4-8+, CD4+8+, CD19+, CD3+hi spleen and thymus, the ratio of cells in different phases of the cell cycle was determined by flow cytometry. C57BL/6J mice strictly increased anxiety in response to the KO compared to CBA mice. Moreover, KO-treated C57BL/6J mice impaired the passive avoidance learning. We found that KO evoked significant changes in the cellular composition of the thymus and decrease of thymocytes proliferation in C57BL/6J mice. In opposite KO-treated CBA mice showed change of splenic cellular structure with increased % CD19+ cells and the proliferation of splenocytes. Our study demonstrated genotype-dependent reactions of the nervous and immune systems in response chronic constant light.

[Latent inhibition and extinction of passive avoidance in mice C57BL/6J AND DBA/2J]

The study was carried out in mice C57BL/6J and DBA/2J for comparative analysis of two interference processes: latent inhibition and extinction of passive avoidance produced with an unconditioned aversive stimulus of different parameters (0.5 and 0.25 mA). With a strong training to new stimulus, impairment of extinction has been detected only in mice DBA/2J. Reduction in the strength of punishment during training was accompanied by acceleration of extinction in mice C57BL/6J and its appearance in mice DBA/2J. The learning of passive avoidance in strong and weak reinforcement was the same for both strains of mice. Interline differences were found also in the analysis of latent inhibition. With strong and weak training to conditional stimulus, lost of novelty by repeated an 8-fold pre-exposures to the experimental chamber, in DBA/2J mice, in contrast to C57BL/6J, latent inhibition was disrupted. In addition, DBA/2J mice showed impairment of extinction with weak training to non-relevant stimulus.

[Fear memory extinction accelerated by simultaneous activation of GABA(B) and NMDA receptors]

Effects of the N-methyl-D-aspartate (NMDA) agonist (D-cycloserine) and GABA(B) agonist (baclofen) on the fear memory extinction as manifested in the passive avoidance reaction in C57Bl/6J mice with "behavioral despair" (model of depression) and without previously developed stress have been studied. The positive acceleration of the fear memory extinction was observed in depressive mice upon the simultaneous administration of D-cycloserine and baclofen.

[Interaction of N-methyl-D-aspartate and Dopamine D1 receptors in modulation of passive avoidance extinction at mice with depressive-like state]

The effect of activation of N-methyl-D-aspartate (D-cycloserine) and dopamine D1 (SKF 38393) receptors on learning and extinction of the passive avoidance response in mice under normal conditions and after formation of "behavioural despair" is studied. The data on ineffectiveness of D-cycloserine and SKF 38393 on training a conditional reflex were obtained. In mice with the normal state, SKF 38393 did not alter the dynamics of extinction, and D-cycloserine facilitated a more rapid decline in retrieval of memory trace when testing without penalty. On exposure to D-cycloserine + SKF 38393 injection, dynamics of extinction was similar to that under the action of D-cycloserine. In mice with the reaction of "behavioral despair", D-cycloserine and SKF 38393 reduced the deficit of the passive avoidance extinction typical for "depressed" animals without drugs. With simultaneous activation of NMDA and D1 receptors we observed acceleration of the extinction start and development of complete extinction of the memory trace about pain impact as compared with single injections of D-cycloserine and SKF 38393.

[Extinction of fear memory in experimental models of depression]

The review contains the materials of scientific literature, research results of the author with colleagues about important cognitive symptom of depression--impairment of fear memory extinction. Experimental models of depressive-like state and behavior involved in the development of depression are reviewed. Special attention is focused on data that demonstrates genetic determination to the emergence of deficit of fear memory extinction as factor of risk to occurrence of depression.

[Extinction of passive avoidance response in various mouse strains]

Dependence of the passive avoidance extinction dynamics on a mouse strain was shown. Mice C57BL/6J and AKR/J extinguished more quickly relative to DBA/2J, CBA/Lac and BALB/c, and this extinction was stable. Individual instability of extinction was characteristic of C3H/HeJ mice. Extinction of the passive avoidance in mice CBA/Lac and BALB/c was slower: with a delay in the beginning and prolonged retention of memory trace of the shock exposure. In DBA/2J mice, the extinction was impaired. These data suggest that DBA/2J, CBA/Lac and BALB/c mice constitute groups of risk with high predisposition to impairment of extinction of memory of aversive events, which is thought to be a symptom of a depressive-like state.

Involvement of different types of dopamine receptors in the formation of latent inhibition of a conditioned passive avoidance reaction in rats

The effects of systemic injections of dopaminergic agents on normal and weak latent inhibition of a conditioned passive avoidance reaction were studied in rats. Formation of normal latent inhibition was induced using 20 pre-exposures to a contextual conditioned stimulus prior to training. Weak latent inhibition was modeled using 10 pre-exposures. The effects of the D(2)/D(3) receptor agonist quinpirole (1 mg/kg) and the D(1) receptor agonist SKF 38393 (1 mg/kg) separately and in combination with haloperidol (0.5 mg/kg) were tested. Quinpirole induced the expression of normal latent inhibition but had no effect on weak latent inhibition. Activation of D(1) receptors with SKF 38393 had no effect on the formation of latent inhibition regardless of the number of pre-exposures. Haloperidol significantly strengthened weak latent inhibition but impaired normal latent inhibition. Administration of haloperidol in combination with SKF 38393 prevented this impairment. These results suggest that while D(1) receptors have no influence as an independent substrate on the formation of latent inhibition, activation of these receptors is required for the complete manifestation of D(2)-mediated modulation of this process.

Effects of activation and blockade of dopamine receptors on the extinction of a passive avoidance reaction in mice with a depressive-like state

Learning and extinction of a conditioned passive avoidance reaction resulting from neuropharmacological actions on dopamine D(1) and D(2) receptors were demonstrated to be specific in intact mice and in mice with a depressive-like state. Learning was degraded only after administration of the D(2) receptor antagonist sulpiride and was independent of the initial functional state of the mice. In intact mice, activation of D(2) receptors with quinpirole led to a deficit of extinction, consisting of a reduction in the ability to acquire new inhibitory learning in conditions associated with the disappearance of the expected punishment. In mice with the "behavioral despair" reaction, characterized by delayed extinction, activation of D(1) receptors with SKF38393 normalized this process, while the D(2) agonist was ineffective. A positive effect consisting of accelerated extinction of the memory of fear of the dark ("dangerous") sector of the experimental chamber was also seen on blockade of both types of dopamine receptor.

[Flumazenil restores amnesic trace of memory in mice with depression-like state]

Experiments on C57BL/6J mice of submissive stereotype and behavioral despair response and ASC/Icg mice with high predisposition to catalepsy, which served as depression-like state models, were used to study the influence of benzodiazepine receptor antagonist flumazenil on the restoration of a passive avoidance reaction learned under conditions of the amnesic effect of animal detention in a dark compartment. It is established, that flumazenil (10 mg/kg) reactivated retrieval of the amnesic memory trace in mice of submissive stereotype with the behavioral despair response, while being ineffective in ASC mice.

Learning and extinction of a passive avoidance response in mice with high levels of predisposition to catalepsy

This report presents results obtained from comparative analysis of learning and the dynamics of extinction of a conditioned passive avoidance response in ASC mice, which were bred for a high level of predisposition to catalepsy, and in CBA and AKR mice. The following findings were obtained: 1) impairments to the extinction of the memory of fear represent an important symptom of depression in ASC mice; 2) extinction is delayed in CBA mice; and 3) new inhibitory learning occurs quickly in AKR mice. Prolonged retention of the fear memory in ASC mice appears to be related to increased anxiety on prolonged testing without a punishment. The deficit of inhibition of the fear reaction in ASC mice allows this strain to be regarded as a genetic model of depression.

[Involvement of dopamine receptors of different types in formation of latent inhibition of passive avoidance reaction in Wistar rats]

The effect of the intraperitoneal injection of dopaminergic agents on normal and weak latent inhibition of step-through passive avoidance task was studied in rats. Normal latent inhibition was caused by 20-fold preexposure (four times daily) of environmental conditional stimulus before training. For modeling of the weak latent inhibition 10-fold preexposure was used. Effects of D2 agonist quinpirole (1 mg/kg) and selective D1 agonist SKF 38393 (1 mg/kg) injected individually and in combination with haloperidol (0.5 mg/kg) were tested. Quinpirole caused a significant potentiation of the normal latent inhibition (20-fold preexposures) but did not affect the weak latent inhibition. Haloperidol reinforced the weak latent inhibition but reduced the normal latent inhibition. The agent SKF 38393 was not able to affect the latent inhibition independently of the preexposure number. Injected in combination with haloperidol, SKF 38393 prevented the normal latent inhibition from being impaired by haloperidol. These findings suggest that D1 receptors do not appear to participate in the modulation of the latent inhibition as an independent substrate, but D1 receptors are essential for the full manifestation of the D2-mediated modulation of the latent inhibition.

[Effects of activation and blockade of dopamine receptors on extinction of passive avoidance response in mice with depressive-like state]

Selectivity of training and extinction of passive avoidance response caused by pharmacological influences on D1 and D2 dopamine receptors in intact mice and mice in depressive-like state was shown. Training was impaired only by administration of D2 receptor antagonist sulpiride and did not depend on the initial functional condition of mice. In intact mice, activation of D2 receptors by quinpirole evoked deficiency of extinction, i.e., impairment of the capability of new inhibitory training under conditions of disappearance of the expected punishment. In mice with reaction of "behavioral despair" characterized by a delay of extinction, activation of D1 receptors by SKF38393 normalized this process (as distinct from the inefficiency of D2 agonist). The positive effect of acceleration of fear memory extinction was revealed also under conditions of blockade of D1 and D2 dopamine receptors.

[Learning and extinction of passive avoidance in mice with high predisposition to catalepsy]

The passive avoidance learning and extinction in mice strain ASC with high predisposition to catalepsy as compared with mice of CBA and AKR strains were analyzed. Impairment of fear extinction as a major symptom of depression was revealed in ASC mice, whereas a delay of extinction in CBA mice and fast formation of new inhibitory learning in AKR mice were found. It is suggested that the long persistence of fear in ASC mice results from increased anxiety during the repeated presentation of a context in the absent of aversive stimulus. Defect of fear inhibition in ASC mice makes it possible to use this strain of mice as genetic model of depression.

[Contribution of GABA receptors in extinction of memory trace in norm and depressive-like state]

The dependence of activation and blockade of GABA receptors influences on extinction of passive avoidance response from a type of receptors and initial psychoemotional state of mice is shown. The activation of GABAA receptors by muscimol disrupted extinction in norm and did not influence on delay of this process at mice with "behavioral despair". The activation of GABAB receptors by baclofen accelerated extinction of fair memory at mice with depressive-like state. The blockade of GABAA receptors by bicuculline was ineffective in modification of extinction. The blockade of GABAB receptors by phaclofen promoted retention of fear expression at intact mice and facilitation of extinction at "depressive" mice.

Comparative analysis of the persistence of a conditioned passive avoidance reflex in rats with different forms of inherited hypertension

The characteristics of anxiety behavior and reproduction of a conditioned passive avoidance reflex acquired in response to a single combination with an unconditioned aversive stimulus were studied in NISAG rats with inherited stress-sensitive arterial hypertension and spontaneously hypertensive SHR rats. SHR rats were characterized by hyperactive behavior, very low levels of anxiety, and poor reproduction of the conditioned reflex as compared with NISAG and control Wistar and WAG rats. Intermediate-anxiety NISAG rats showed no difficulties in acquiring and subsequently retaining the conditioned reflex. These differences in the ability to undergo single-combination learning in rats with different forms of hypertension suggest that memory processes are independent of elevated arterial blood pressure. The effects of the genetic characteristics of behavior and emotional status of these animals on memory are discussed.

Effects of activation and blockade of NMDA receptors on the extinction of a conditioned passive avoidance response in mice with different levels of anxiety

The effects of an agonist (D-cycloserine) and an antagonist (dizocilpine) of N-methyl-D-aspartate (NMDA) receptors on the learning and extinction of a conditioned passive avoidance response were studied in mice with low, intermediate, and high levels of anxiety. In intermediate-anxiety mice, D-cycloserine (30 mg/kg) had no effect on learning but accelerated extinction, while dizocilpine (0.15 mg/kg) degraded acquisition of the reflex but delayed extinction. In high-anxiety mice, with good learning and no extinction, D-cycloserine had no effect, while dizocilpine decreased learning and facilitated retention of performance of the memory trace at the ongoing level in conditions promoting extinction. In low-anxiety mice, D-cycloserine degraded learning and accelerated extinction, while dizocilpine completely blocked learning and the retention of the passive avoidance response.

[Learning to solve a spatial task in a water maze in aggressive and submissive mice]

Learning and retention of the spatial memory were studied in mice with alternative under conditions of various experimental protocols. Visible and hidden platform acquisition in a simple model of the water maze was similarly fast both in aggressive and submissive mice, but extinction differed. Retention of the platform location preference persisted in aggressive mice in four testing trials. In submissive mice, extiction of the spatial memory was accompanied with a prolongation of search with parallel production of episodes of "passive drift". Differences in spatial learning between aggressive and submissive mice were revealed in a water maze complicated with partitions. In this case, aggressors were able to learn the position of a hidden platform (in contrast to submissive mice with the dominant response of "passive drift"). During testing the response, aggressive mice longer retained the spatial preference without extinction.

Characteristics of extinction of a conditioned passive avoidance reflex in mice with different levels of anxiety

The relationship between the extinction of a conditioned passive avoidance reflex and the initial anxiety level was studied in mice. The time spent in the open arms of an elevated cross maze was used to classify the mice into high-, intermediate-and low-anxiety individuals. Each level of anxiety was found to correspond to a defined extinction dynamic. Highly anxious mice were characterized by the absence of extinction of the conditioned passive avoidance reflex and stability of good reproduction of the memory trace on testing to as long as 15 days. In intermediately anxious individuals, a deficit in performance of the avoidance reflex appeared from day 7 of extinction. In low-anxiety mice, memory trace reproduction deteriorated from test day 11.

[GABA(B) receptors and amnesia in mice withalternative stereotypes of behavior]

The influence of agonists and antagonists of GABA(B) receptors on the development of amnesia has been studied using the passive avoidance test in C57Bl/6J mice with previously generated aggressive and submissive behavioral stereotypes. It is established that baclofen in a dose of 1 mg/kg produces amnesia in aggressive mice and imparts stability with respect to the amnestic influence in submissive mice. Phaclofen in a dose of 5 mg/kg prevents the development of amnesia that is most strongly pronounced in submissive mice.

[Extinction of a passive avoidance response of mice with a depressive-like state]

The analysis of a behaviour and memory of mice with depressive state is conducted. The mice with "behavioral despair" obtained by forced swimming and mice with submissive stereotype generated by 20 confrontations were used. They were characterized by increased anxiety and reduced exploratory activity in tests of the elevated plus-maze and light/dark apparatus. It is shown that for want of behavioral differences in manifestation of a depressive state the process of extinction was opposite. Mice with "behavioral despair" revealed retention of a high level of memory trace retrieval down to the 21st day of testing reflecting essential delay of extinction. Submissive mice displayed fast extinction begining with the 5th day of testing.

[Effects of dehydroepiandrosterone sulfate and dizocilpine on memory trace extinction in aggressive and submissive mice]

It was shown that injections of NMDA receptor antagonist dizocilpine and neurosteroid dehydroepiandrosterone sulfate (DHEAS) and sequential injections of these substances had different effects on learning and extinction of passive avoidance in aggressive and submissive mice. In aggressive mice, dizocilpine impaired and DHEAS did not change learning and retention. However, being injected after dizocilpine, DHEAS blocked the defect of memory trace retrieval induced by dizocilpine. In submissive mice, dizocilpine impaired learning and prolonged extinction of the learned habit. Injection of DHEAS prolonged the extinction in a similar way. Under conditions of sequential injections, DHEAS did not change the suppressive effect of dizocilpine on learning and was not effective in prolongation of extinction.

Effects of activation of D1 dopamine receptors on extinction of a conditioned passive avoidance reflex and amnesia in aggressive and submissive mice

The studies reported here demonstrate the relationship between the effect of activation of D1 dopamine receptors on the reproduction of a conditioned passive avoidance reflex during extinction and amnesia and the aggressive and submissive behavioral stereotypes. During extinction, the D1 receptor agonist SKF 38393 at a dose of 5 mg/kg given before acquisition of the conditioned reflex and on test day 12 suppressed the reproduction of the conditioned skill in aggressive mice and improved reproduction in submissive mice. The effects of activation of D1 receptors were also opposite relative to the stereotype in amnesia. In aggressive mice, SKF 38393 significantly decreased the resistance to amnesia characteristic of these animals; in submissive mice, SKF 38393 weakened the amnestic effects of the delay in the "dangerous" sector and restored memory traces. The possible mechanisms of the selectivity of the actions of D1 receptors in mice with alternative behavioral stereotypes in retaining memory traces related to aversive stimulation during extinction and amnesia are discussed.

Acquisition and extinction of a conditioned passive avoidance reflex in mice with genetic knockout of monoamine oxidase A

We report here the results obtained from comparative analysis of learning and the dynamics of extinction of a conditioned passive avoidance response in mice with genetic knockout of monoamine oxidase A (MAO A) and the progenitor line C3H. Mice of both lines acquired the conditioned passive avoidance reaction efficiently. Mice with genetic knockout of MAO A were characterized by prolonged retention of reproduction of the memory trace, as compared with rapid extinction in C3H mice. Smaller numbers of transfers, and vertical rearings on days 7-13 and the numbers of glances into and rom the dark sector on days 11-13 of extinction in MAO A-knockout mice appear to reflect their more marked fear reactions when confronted with the "dangerous" sector, along with increased anxiety, these facilitating longer-lasting retention of the memory trace.

[Comparative analysis of conditioned passive avoidance retention in rats with different forms of inherited arterial hypertension]

Comparing behavioral traits of anxiety in elevated plus-maze and retention of passive avoidance response in two rat strains with hereditary arterial hypertension ISIAH (inherited stress induced arterial hypertension) and SHR (spontaneously hypertensive rats) has shown the following. The SHR rats demonstrate impairment in retrieval of passive avoidance, hyperactivity and low anxiety. ISIAH rats showned better avoidance performance, average level of anxiety and activity. The interdependence of two pathologies: hypertension and memory impairment is discussed.

[The influence of dehydroepiandrosterone sulfate on the extinction of passive avoidance in aggressive and submissive mice]

The effects of dehydroepiandrosterone sulfate (DHEAS) on the extinction of passive avoidance was studied on C57Bl/6J mice with aggressive and submissive behavioral stereotypes. Administered in a single dose 30 mg/kg one day or one hour before training, DHEAS selectively blocked the extinction of the conditioned habit in submissive mice, thus favoring its retrieval. The probable mechanism of this phenomenon can be related to a decrease in the level of inhibiting control in the GABAergic system.

[Influence of activation and blockade of NMDA receptors on extinction of passive avoidance response in mice with different levels of anxiety]

Influence of agonist (D-cycloserine) and antagonist (dizocilpine) N-methyl-D-aspartate receptors on learning and extinction of passive avoidance response in medium-, high-, and low-anxious mice was studied. In medium-anxious mice, D-cycloserine (30 mg/kg) although not changing learning accelerated development of extinction, whereas dizocilpine (0.15 mg/kg), while impairing passive avoidance learning, detained the extinction. In high-anxious mice with good retrieval of memory trace and absence of extinction, D-cycloserine was ineffective, whereas dizocilpine reduced learning and promoted retention of memory trace retrieval at the generated level on extinction. In low-anxious mice, D-cycloserine impaired learning and accelerated extinction, whereas dizocilpine completely blocked learning and retention of passive avoidance response.

[Features of a passive avoidance extinction of mice with a different level of anxiety]

The dependence of the passive avoidance extinction from a level of mice initial anxiety is investigated. Mice were classified as high-, medium- and low-anxious by time spent in the open area of the elevated plus-maze. It is revealed that to each from levels of anxiety there corresponds certain dynamics of extinction. The high-anxious mice are characterized absence of the passive avoidance extinction and stability of good retrieval of memory trace for want of testing down to 15 days. At medium-anxious mice the deficit of avoidance habit performance developed since the 7th day of extinction. At low-anxious mice since the 11th day of testing the deterioration of retrieval was observed.

[Influence of D1 dopamine receptor activation on extinction of passive avoidance and amnesia in aggressive and submissive mice]

In mice with aggressive and submissive behavioral stereotypes, passive avoidance retrieval in extinction and amnesia was shown to be differently dependent on the activation of D1 dopamine receptors. In extinction, agonist of D1 receptors SKF 38393 injected before training or on 12-th day of testing in a dose of 5 mg/kg impaired the retrieval of a conditioned habit in aggressive mice and improved the retrieval in submissive mice. The opposite effects of D1 receptor activation depending on stereotype were also observed in a procedure of amnesia. In aggressive mice, SKF 38393 essentially reduced the resistance to amnesic effects characteristic of this stereotype. In submissive mice, SKF 38393 attenuated the amnesic effect of a detention in a dangerous compartment and restored the amnesic memory trace. Possible mechanisms of selective involvement of D1 receptors in retention of memory trace of aversive stimuli during extinction and amnesia in mice with different stereotypes of behavior are discussed.

[Training and extinction of passive avoidance in mice lacking monoamine oxidase A]

The passive avoidance learning and memory trace retention in mice lacking monoamine oxidase A (MAO A) and control C3H strain were analyzed. It is shown that mice of both strains were well the passive avoidance learners. A delay of the memory trace extinction was found in lacking MAO A mice as compared with control C3H strain. Mice with a genetic MAO A knockout showed decreased amounts of transitions, rearings, looking to a dark compartment and appearing from it. These findings seem to reflect more expressed fear reaction to a dangerous compartment and increased anxiety promoting longer retention of memory trace on a high level of retrieval.

The Effects of the Duration of Adaptation to Laboratory Conditions on the Formation of a Passive Avoidance Reflex in Rats

The level of adaptation of rats to their new living conditions was studied during formation of a passive avoidance habit using a single combination. A short acclimation period (3 days) had positive influences on the ability of rats to retain a memory trace. There was a negative correlation between step-through latency and measures of anxiety behavior in the elevated cross maze. A change in the adaptation period to nine days decreased the state of anxiety and the level of performance of the conditioned response. There were no correlations between these measures. The modulating role of the level of adaptation to living conditions, associated with different levels of anxiety, in a passive one-session avoidance learning model was assessed.

The effects of novelty and behavioral stereotype on the development of amnesia in mice

The aim of the present study was to analyze the significance of the interaction between the basic behavioral strategy, the extinction of the novelty of information, and the efficacy of amnesia-inducing influences. Using a combination of training to passive avoidance with holding the animal in the unsafe sector of the apparatus, comparative analysis was performed of the reproduction of a memory trace in aggressive and submissive mice of line C57BL/6J with and without six sessions of familiarization with the apparatus. These experiments showed that preliminary habituation prevented the development of amnesia in submissive but not aggressive individuals. The cause of these differences in the effects of preexposure on the development of amnesia involves the selectivity of the process of extinction of information novelty characteristic for the behavioral stereotype.

[Typological features of behavior and memory in Norway rats selected for absence of aggression toward a man]

Features of behavior and retrieval of passive conditioned avoidance on a new and forgotten stimuli were compared in Wistar rats and Norway rats bred for the absence of aggression toward a man. As distinct from white rats, grey rats were characterized by low anxiety and high locomotor exploratory activity in the elevated plus maze and dark-light chamber. Norway rats demonstrated better avoidance performance with active defensive behavioral strategy than Wistar rats. Latent inhibition during conditioning with a previously forgotten situational stimulus was the same in both rat strains. The results are discussed in terms of the use of grey rats as a model for an in-depth analysis of the mechanisms of memory optimization.

[Extinction and amnesia in aggressive and submissive mice with various terms of agonistic interaction]

Dependence of the passive avoidance retrieval on the duration of agonistic interactions was analyzed in C57BL/6J mice in procedures of extinction and amnesia during formation of aggressive and submissive behavioral stereotypes. The resistance to amnestic stimulation was lower in aggressive mice with 10-day experience of victories than in aggressive animals after 20 daily confrontations. Prolongation of extinction in aggressive mice and fast extinction in submissive animals did not depend on the number of agonistic interactions.

[Effect of forced swimming on the memory track retention in mice with various behavioral stereotypes]

The effects of forced swimming on retrieval of the passive avoidance during its extinction were found to depend on aggressive and submissive behavior. In mice without generated behavioral stereotypes, swim stress applied before or after training stabilized retention of the memory trace retrieval. The similar improved influence of forced swimming on memory storage is revealed in submissive, but not aggressive mice. The increase of resistance against extinction under the swim stress can be connected to facilitation of emotional processes.

[Comparative analysis of haloperidol effects on passive avoidance retention in aggressive and submissive mice]

The effects of haloperidol on retention of avoidance during its extinction in C57BL/6J mice were shown to depend on a behavioral stereotype (aggressive or submissive). In submissive mice, haloperidol (0.5 mg/kg) injected an hour before training stabilized retrieval of the conditioned reflex in repeated testings (up to 17 days) as compared to its fast extinction in control animals. In aggressive mice, on the contrary, haloperidol reduced the retention of the memory trace retrieval. It is suggested that divergent haloperidol effects on extinction of passive avoidance in mice with alternative behavioral strategies are determined by the features of organization of the mesolimbico-cortical dopaminergic system and emotional state, in particular, anxiety.

[Effect of haloperidol on development of amnesia in aggressive and submissive mice]

The effect of haloperidol on the passive avoidance habit retrieval upon amnesia was studied in C57BL/6J mice with aggressive and submissive behavioral stereotypes formed under agonist confrontation conditions. In the control (untreated) group, the efficacy of the amnesic action of detention in the dangerous compartment on the learning day was reduced for the aggressive stereotype as compared to the submissive one. In the aggressive mice, the administration of haloperidol (0.5 mg/kg) one hour before learning deteriorated the conditional reaction retrieval between 2nd and 13th days of test. In the submissive mice, the administration of haloperidol produced a prolonged antiamnesic effect. Thus, the effect of haloperidol on the violated memory trace reproduction depends on the individual behavioral state.

Studies of the interaction between behavioral stereotypes and the effects of activation of presynaptic dopamine receptors during extinction and amnesia in mice

The involvement of presynaptic dopamine receptors in the retention of a conditioned passive avoidance reflex through extinction and amnesia was studied in C57BL/6J mice selected in a 20-day aggressive conflict test for aggressive and submissive behavioral stereotypes. These experiments showed that in aggressive mice, activation of presynaptic receptors with the agonist (+)3-(3-hydroxyphenyl)-N-n-propylpiperidine [(+)3PPP] at a dose of 2 mg/kg degraded learning, significantly decreased the retention time of the acquired conditioned habit in extinction, and increased the effect of an amnesia-inducing treatment. Mice showing submissive behavior in daily confrontations with aggressors responded to administration of (+)3PPP with long-lasting reproduction of the conditioned passive avoidance reaction during extinction and showed no changes in the development of amnesia. These data on the relationship between the effects of activating presynaptic dopamine receptors in reproduction of the memory trace in conditions of trace disruption on the one hand and behavioral status on the other are assessed from the point of view of different basal levels of dopaminergic system operation in aggressive and submissive mice.

[The effect of the duration of adaptation to laboratory conditions on the passive avoidance reflex in rats]

Influence of adaptation degree in new conditions on the passive avoidance was studied. The short period of habituation (3 days) positively influenced the rats' ability for memory trace retrieval. A negative correlation between the step through latency and anxiety in the elevated plus-maze, was shown. Prolongation of adaptation up to 9 days reduced levels of anxiety and retrieval of conditioned response. Modulating role of adaptation degree causing various anxiety levels in passive avoidance, is discussed.

[Effect of novelty and behavioral stereotype on development of amnesia in mice]

The research was aimed at analysis of interaction of basic behavioural strategy, extinction of information novelty and efficiency of amnesic influence. It is shown that preliminary habituation to the task apparatus prevented development of amnesia, induced detention of the animal in a dangerous compartment in submissive rather than aggressive mice C57BL/6J. The findings suggest that revealed distinctions in effects of pre-exposure on development of amnesia are essentially predetermined by selectivity of extinction of the information novelty specific to a stereotype of behaviour.

[Retention of a memory trace of learning induced by a new and extinctive stimulus in C57BL/6J and BALB/c mice]

Influence of preliminary habituation to the experimental box on passive avoidance learning was studied in mice of C57BL/6J and BALB/c strains. The 20-fold preexposure of mice to the environmental stimulus inhibited the acquisition and consequent retention of a memory trace in BALB/c mice and did not affect the acquisition in C57BL/6J mice. Subsequent retention in this strain was facilitated. The interstrain differences are discussed with respect to detected genetically determined types of behavior and exstinctive inhibition at the habituation stage.

[Effects of pre-exposure to an experimental chamber on memory trace retrieval in aggressive and submissive mice during extinction of conditioning]

Mice with a submissive stereotype of behaviour developed a fast habituation to novelty of environment. A subsequent training revealed a deficit of passive avoidance learning and prolongation of the memory trace extinction. Aggressive mice are characterised by a delay of the habituation and absence of any significant changes in the memory trace retrieval. The findings suggest that responses to environmental novelty and use of its estimation in learning and retention of memory traces are essentially predetermined by the basic strategy of behaviour.

[Interaction of stereotypic behavior in mice and effects of activation of presynaptic dopaminergic receptors in extinction and amnesia]

Using the methods of agonistic confrontations of C57BL/6J mice for formation of aggressive and submissive types of behavior and passive avoidance training we investigated the influence of activation of dopamine presynaptic receptors on retention of a memory trace during extinction and amnesia. Autoreceptor agonist (+)3PPP (2 mg/kg, intraperitoneal injection) impaired learning and retention of a memory trace during extinction and strengthened the amnestic influence of animal detention in a dangerous compartment on the training day only in aggressive mice. In submissive mice, (+) 3PPP improved the retrieval of passive avoidance during extinction but did not change the development of amnesia. This work was the first to demonstrate that the effects of dopamine autoreceptor activation on the passive avoidance retrieval depend on behavioral stereotype (aggressive or submissive). It is suggested that different basic states of the dopaminergic system in aggressive and submissive mice are responsible for different (+) 3PPP effects.

[Compensating and reactivating effects of quinpirole on extinction of conditioned response and amnesia in mice with alternative behavioral stereotypes]

The effect of quinpirole on the passive avoidance habit retention in male C57BL/6J mice with aggressive and submissive behavioral strategies was studied during the habit extinction and amnesia. It was found that the activation of D2 dopamine postsynaptic receptors by quinpirole injections (1 mg/kg, i.p.) prolonged the passive avoidance retrieval during extinction in the submissive mice, while not affecting the basically high memory retrieval level in the aggressors. Under the amnesia conditions, quinpirole reactivated the passive avoidance retrieval irrespective of the base initial behavior status (aggressive versus submissive). It is concluded that the different basic state of the dopaminergic activity in mice predetermines the compensating-reactivating effect of quinpirole.

[Effect of the activation of GABA A, benzodiazepine, and D2 dopamine receptors on the passive avoidance extinction in submissive and aggressive mice]

The effect of activation of GABAA, benzodiazepine, and D2 dopamine receptors on extinction of passive avoidance and their dependence on the initial state of aggressive and submissive C57BL/6J mice were studied. It was found that in mice with the submissive stereotype of behavior produced by experience of defeats in daily agonistic confrontations, extinction of the conditioned reaction occurred faster than in control mice. The activation of D2 receptors by quinpirole and of benzodiazepine receptors by medasepam before training restored the retrieval of the memory trace. A prolongation of extinction was observed in aggressive mice in comparison with control and submissive animals, and activation of GABAA by muscimol and benzodiazepine receptors by medazepam led to acceleration of extinction. Activation of D2 receptors was ineffective. Thus, the difference in initial behavioral strategy determined both the development of extinction of the passive avoidance and variability of participation of D2, GABAA, and benzodiazepine receptors in the maintenance of availability of the memory trace to retrieval.