Effect of Dehydroepiandrosterone on Avoidance Behavior of Adult Male Rats

We studied the effect of repeated intraperitoneal treatment with dehydroepiandrosterone in doses of 0.1 and 0.7 mg/kg on conditioned-response activity and behavior of adult male rats. The effect of dehydroepiandrosterone on learning was estimated in conditioned active and passive avoidance response paradigms. Chronic administration of dehydroepiandrosterone in low and high doses had no effect on retention of conditioned passive avoidance response in adult male rats 24 h after learning. However, chronic administration of dehydroepiandrosterone in low dose impaired acquisition of the conditioned active avoidance response. It should be emphasized that chronic administration of dehydroepiandrosterone in high dose did not modulate acquisition and retention of this reaction.     

Effects of nucleus basolateralis amygdalae neurotoxic lesions on aversive conditioning in the rat

After bilateral stereotaxic administration of ibotenic acid on the n. basolateralis amygdalae, male adult rats were tested in the light-dark box apparatus to measure the time-course of the acquisition and retention of passive and active avoidance responses. The results show that after the lesions both passive avoidance and active avoidance acquisition were impaired. Passive avoidance responses were retained quite well, while active avoidance responses disappeared quickly. Conditioned freezing was almost completely absent. Thus it appears that the n. basolateralis plays a facilitatory role in all the conditioned responses which were investigated.     

The effects of the hormones of peripheral endocrine glands on the processes of behavior, learning, and memory

The effects of systemic administration of thyroid, adrenal cortex, and sex hormones on learning ability, memory trace retention, and behavior were compared in male rats. These studies showed that thyroid, corticosteroid, and sex hormones had no effect on passive learning. Excess quantities of sex hormones disrupted active learning and subsequent reproduction of received information; an excess of thyroid hormone improved the acquisition and retention of the active avoidance habit. Increases in the levels of adrenal cortex hormones worsened active learning and the retention of memory traces, and also increased the level of behavioral activity. Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 48, No. 6, pp. 980–988, November–December 1998.     

Comparative characteristics of learning and behavior processes in conditions of elevated sex hormone levels

The effects of elevated levels of sex hormones resulting from systemic administration of hormone preparations on the abilities to learn and retain memory traces and on behavior were studied in rats of both sexes. Experiments were performed using models of conditioned active and passive avoidance reflexes and in the “open” field test. Increases in testosterone and estradiol levels had no effect on passive learning. Increases in testosterone levels in male rats led to derangement of active learning but had no effect on animal behavior. Elevated estradiol levels in female rats accelerated active learning and increased the animals' behavioral activity. Translated from Problemy éndokrinologii, Vol. 44, No. 6, pp. 47–69, November–December, 1998.     

Effect of Noopept and Afobazole on the Development of Neurosis of Learned Helplessness in Rats

We studied the effects of new psychotropic preparations noopept and afobazole on acquisition of the conditioned active avoidance response and development of neurosis of learned helplessness in rats. Noopept in doses of 0.05-0.10 mg/kg accelerated acquisition of conditioned active avoidance response and reduced the incidence of learned helplessness in rats. Afobazole in a dose of 5 mg/kg produced an opposite effect, which is probably related to high selective anxiolytic activity of this preparation.     

Neuroprotective and antiamnesic effects of Semax during experimental ischemic infarction of the cerebral cortex

Semax had a pronounced neuroprotective and antiamnesic effect during focal photoinduced ischemia of the prefrontal cortex. Intranasal administration of Semax for 6 days decreased the volume of cortical infarction and improved retention and performance of conditioned passive avoidance response. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 12, pp. 618–621, December, 2006     

Impairment of Latent Inhibition in Adult Rats after Blockade of Dopaminergic Terminals in the Ventral Hippocampus during the Period of Pubertal Development

Wistar rats aged 32 days were given bilateral injections of the neurotoxin 6-hydroxydopamine in the area of the ventral hippocampus. After four weeks, “latent inhibition,” which is widely used in studies of selective attention in the context of reinforcement training, was assessed. In the present experiments, latent inhibition was formed in two classical conditioned reflex tasks – passive and active avoidance. Before acquisition of the passive avoidance reaction, animals were given 20 presentations of the conditioned contextual stimulus without reinforcement (pre-exposure stage). The active avoidance reaction was developed after pre-exposure to the conditioned light stimulus (100 presentations without reinforcement). In both behavioral tasks, the formation of latent inhibition was impaired in the operated rats as compared with the corresponding sham-operated animals. At the same time, administration of neurotoxin had no effect on acquisition of the two conditioned reactions in the absence of a pre-exposure stage. The contribution of dopamine terminals in the ventral hippocampus to the development of the neural networks responsible for suppressing attention to unimportant information in the brain is discussed.     

Sustained aftereffect of the amnestic action of scopolamine in rats and its elimination by piracetam

Experiments were carried out on male Wistar rats to assess (1) the effect of chronically administered (for 20 days) scopolamine on their learning capacity and memory 10 days after its last administration and (2) the influence of the nootropic piracetam, given for 10 days after scopolamine and before learning a conditioned passive avoidance response, on cognitive functions of the brain altered as a result of the M-cholinergic receptors being blocked by scopolamine. Scopolamine-dosed rats showed poor reproduction of the conditioned passive avoidance response when tested for this response at 24 h and 30 days after learning it, whereas those treated with piracetam after scopolamine retained the response well both at 24 h and at 30 days. Piracetam also restored the scopolamine-impaired acute extinction of orienting/exploratory activity in the rats. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 4, pp. 372–374, April, 1995 Presented by S. B. Seredenin, Member of the Russian Academy of Medical Sciences     

Impairment of learning and memory after photothrombosis of the prefrontal cortex in rat brain: effects of Noopept

Experiments were performed on rats trained conditioned passive avoidance response. Acquisition and retention of memory traces were impaired after photothrombosis of the prefrontal cortex. The acyl-prolyl-containing dipeptide Noopept facilitated retention and retrieval of a conditioned passive avoidance response, normalized learning capacity in animals with ischemic damage to the cerebral cortex, and promoted finish training in rats with hereditary learning deficit. These results show that Noopept improves all three stages of memory. It should be emphasized that the effect of Noopept was most pronounced in animals with impaired mnesic function.     

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. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 3, pp. 342–350, March, 2006.     

Postnatal Development of Conditioned Reflex Behavior: Comparison of the Times of Maturation of Plastic Processes in the Rat Hippocampus

The formation of conditioned reflex fear, escape responses, and conditioned avoidance responses during acquisition of a conditioned two-way avoidance reflex was studied in rats of different ages. Rats aged 16–17 days acquired the conditioned reflex but not the escape reaction or the conditioned avoidance response; acquisition efficiency was higher than in adult rats. Escape responses appeared from postnatal day 18. The ability to acquire this type of learning was complete by age 3–4 weeks. Maturation of the mechanisms of the “classical” (the fear phase) and operant (transfer to another sector in response to the unconditioned stimulus) components did not facilitate acquisition of the conditioned two-way avoidance reflex until the middle of postnatal week 4. Learning efficiency in four-week-old rats was lower than in adults. It is suggested that the maturation of different types of memory may be associated with the periods at which plastic processes develop in the hippocampus. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 54, No. 5, pp. 666–672, September–October, 2004.     

Improvements in the selective perception and training of rats using an original analog of the C-terminal fragment of vasopressin

This report presents studies on the effects of intranasal administration of five doses (0.001, 0.01, 0.1, 1, and 10 μg/kg) of a new analog of arginine-vasopressin fragment AVP_(6–9), i.e., D-MPRG, on the learning ability of rats with positive and negative reinforcement. All doses of the peptide improved learning. The most effective dose was 0.01 μg/kg, at which the peptide accelerated the acquisition of a conditioned active avoidance reflex both when given 1 h before and when given immediately after training sessions. The peptide had greater effects when animals were trained with negative reinforcement. Analysis of the results suggests that the action of D-MPRG is mainly on perception processes, i.e., extraction of the conditioned stimulus from the environmental surroundings and evaluation and enhancement of its biological significance. In addition, this peptide prevented extinction of the acquired habit and improved the processes of consolidation, though this effect was weaker than its effect on perception. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni. I. M. Sechenova, Vol. 84, No. 12, pp. 1363–1369, December, 1998.     

Antiamnestic Effects of Antibodies to Glutamate in Experimental Alzheimer’s Disease

Experiments on rats showed that neurodegenerative brain damage caused by administration of neurotoxic fragment of β-amyloid protein Aβ_25-35 in a dose of 2 μg into Meynert giant cell nucleus leads to long-term memory impairment in rats. Intranasal administration of antibodies to glutamate in a dose of 300 μg/kg 1 h after damage restores learning capacity of the experimental animals in the conditioned passive avoidance paradigm.     

Sex hormones and behavioral reactions

The paper provides a comparative analysis of the effects of imbalance of gonadal hormones on behavioral processes in rats of both sex. Learning was assesses in active and passive avoidance paradigms, behavior was evaluated in the "open field" test. Hemigonadectomy in male rats or hemiovariectomy in female rats was found to fail to modify the dynamics of acquisition and reproduction of active avoidance and passive reactions as compared to the controls, but to affect the pattern of animal behavior in the "open field" test. Castration of rats of both sex impaired the acquisition and retention of active avoidance performance. Excess of testosterone in male rats significantly inhibited the ability of the animals to form an active avoidance response. Excessive estradiol levels in female rats accelerated the acquisition of active avoidance performance and greatly attenuated extinction of this performance. Gonadal hormonal treatment did not alter the reproducibility of passive avoidance performance. The lack of estrogens resulted in amnesia of passive avoidance performance while that of androgens failed to destroy passive avoidance performance. Excessive estradiol in female rats or its lack in male rats significantly modified the pattern of animal behavior in the "open field" test. The absence of estrogens or their excess did not affect the behavior of rats with exception of individual components.     

Ratio between the contents of 11-dehydrocorticosterone and corticosterone after acute and repeated stress: Effect of dehydroepiandrosterone sulfate

Acute stress was accompanied by reduction of 11-dehydrocorticosterone to corticosterone in male rats. The reverse reaction predominated during repeated stress and increased after administration of dehydroepiandrosterone sulfate. Treatment with μ-opioid receptor antagonist naltrexone in a dose of 0.1 mg/kg 20 min before administration of dehydroepiandrosterone sulfate abolished this effect. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 138, No. 8, pp. 158–161, August, 2004     

Modulatory Effect of 8-OH-DPAT on Behavior of Ovariectomized Female Rats

Behavior of ovariectomized rats was studied after chronic administration of serotonin 1A receptor agonist 8-OH-DPAT alone or in combination with 17beta-estradiol for 14 days. The effect of 8-OH-DPAT on learning was evaluated in the conditioned passive avoidance task. Behavioral activity in elevated plus-maze and open field was recorded. Administration of 8-OH-DPAT to ovariectomized female rats increased the number of entries into open arms of the maze and the time spent there. Combination treatment of ovariectomized animals with 8-OH-DPAT and 17beta-estradiol decreased total locomotor and emotional activity in the open field. Administration of 8-OH-DPAT alone or in combination with 17beta-estradiol improved performance of the conditioned passive avoidance response.     

Age effects in the acquisition and retention of active and passive avoidance learning by rats

Three groups of 8 male albino rats within each of the age ranges 24, 50, and 100 days were trained on an active avoidance task to a criterion of 10 successive avoidances. The number of trials to criterion was found to be a monotonic function of age. One group at each age was tested immediately thereafter for passive avoidance of the conditioning chamber, another group was tested for passive avoidance after 25 days, and the third was tested for retention of active avoidance after 25 days. Groups at 50, 75, and 125 days were used as controls for the active avoidance retention groups. All animals took significantly fewer trials to relearn the active avoidance after 25 days than did controls on the acquisition of the original learning task. On passive avoidance 24-day olds performed less efficiently than the older groups and failed to show any retention after 25 days.     

Lipid peroxidation in the brain and liver of rats during acute stress and melatonin treatment

We studied the effects of acute stress and exogenous melatonin in various doses on the intensity of lipid peroxidation in emotiogenic structures of the brain and liver of rats with different activity in the open field. Stress had no effect on the content of malonic dialdehyde in the hypothalamus, sensorimotor cortex, and liver of active and passive rats receiving physiological saline. The influence of melatonin on malonic dialdehyde content depended on the dose of this substance. The amount of malonic dialdehyde in brain structures (active and passive rats) and liver (active rats) increased after administration of exogenous melatonin in doses of 0.5 and 2 mg/kg, but decreased after treatment with the hormone in a dose of 1 mg/kg. Melatonin in various doses decreased malonic dialdehyde content in the liver of passive rats. The effects of melatonin are partly related to modulation of lipid peroxidation in central and peripheral tissues of the organism. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 138, No. 7, pp. 19–23, July, 2004     

Differential effects of electrical stimulation of amygdala, caudate-putamen or substantia nigra pars compacta on taste aversion and passive avoidance in rats

The effect of unilateral, low-intensity subseizure electrical stimulation of the basolateral nucleus of the amygdala (ABL), caudate-putamen (CD) or substantia nigra pars compacta (SNC) on the acquisition and retention of a conditioned taste aversion and a step-down passive avoidance response were compared in two separate experiments. In Experiment 1 electrical stimulation of the ABL while rats were drinking saccharin prior to poisoning with LiCl disrupted conditioned taste aversion. Stimulation of the CD or SNC had no disruptive effect on taste aversion. In contrast, stimulation at all 3 brain loci disrupted the retention of a passive avoidance response in Experiment 2. The implications of these data for the hypothesis of dual neural control systems for shock avoidance behavior and taste aversion, are discussed.     

Effects of an Agonist and an Antagonist of 5-HT1A Serotonin Receptors on Learning in Female Rats during the Ovarian Cycle

The experiments reported here addressed comparative analysis of the role of 5-HT_1A serotonin receptors in the mechanisms mediating cognitive processes during natural cyclical changes in sex hormone levels in adult female rats. The effects of chronic (14 days) administration of the 5-HT_1A serotonin receptor agonist 8-OH-DPAT (0.05 mg/kg, s.c.) and the 5-HT_1A serotonin receptor antagonist NAN-190 (0.1 mg/kg, i.p.) to females at different phases of the ovarian cycle on conditioned reflex responses were studied. A conditioned passive avoidance reaction and the Morris water maze were used as behavioral tests. Chronic administration of NAN-190 to females led to the appearance of the conditioned passive avoidance response in the proestrus and estrus phases, in contrast to control females, but had no effects on the dynamics of spatial learning in the Morris water test. Chronic administration of 8-OH-DPAT consistently impaired the processes of non-spatial and spatial learning in females regardless of the phase of the ovarian cycle. The results obtained in these experiments evidenced the modulatory role of 5-HT_1A serotonin receptors in learning processes in rats in key phases of the ovarian cycle.