Inga Igorevna Poletaeva

The understanding of the object permanence rule (the notion that an object that has disappeared from view continues to exist) is an important issue for animal cognition studies. This ability has been tested in laboratory rodents, but no studies have been conducted using wild rodent species. The aim of this study was to compare the ability to use the object permanence rule in three species of wild rodents and to identify plausible interspecific behavioral differences. The wood mouse (Sylvaemus uralensis), the striped field mouse (Apodemus agrarius), and the bank vole (Clethrionomys glareolus) were used as subjects in the puzzle-box, in which an animal is motivated to escape from a brightly lit environment into the darkness. Test stages 2, 3 and 4 required an understanding that the underpass which leads from light into the dark part of a box still exists, although it is not seen any longer. The test difficulty gradually increased: at first, the passage to the dark was unobstructed; then, it was covered with sawdust; and, finally, it was blocked using a cardboard plug. Interspecific differences were found. Wood mice and striped field mice demonstrated consistently high success rates at all stages of the test, including the most difficult one (when the passage was blocked by a plug), indicating a well-developed ability to operate the object permanence rule. In contrast, the proportion of bank voles who solved the test decreased as the test complexity increased. Bank voles were also characterized by prolonged periods of immobility and lower levels of locomotion. The data suggest that interspecies variability in object permanence task solutions is associated not only with different levels of cognitive ability per se - but also with species-specific behavioral traits, which could be linked to the ecological specialization of these species.

The review summarizes the main peculiarities of rodent audiogenic epilepsy (seizures in response to loud sound), which is related to brain neurochemistry and morphology as well as to the disturbances of muscle tone regulation. The Krushinsky–Molodkina rat strain selectively bred for audiogenic epilepsy is the valuable genetic model of human seizure states. The pattern of neurochemical disturbances in this strain is similar to those in other rodent strains with audiogenic epilepsy, which permit to suggest the non-random nature of these phenomena. The postictal catalepsy and cataleptic states of other types are discussed in relation with audiogenic seizure fits. Brain anomalies in these animals emerge, presumably, during early ontogeny.

This investigation included an analysis of the nootropic effects of a dimeric dipeptide, substance GK-2, a nerve growth factor mimetic, in a cognitive test (object permanence, by J. Piaget) in mice of two strains selected for their large and small relative brain weights (strains LB and SB). The influences of the dipeptide (0.5 mg/kg, injected i.p., subchronically, 5 days) on cognitive test solution in mice of different genotypes were opposite, mice of both strains escaped more quickly in the comfortable dark part of the box, but in cases of the obstacles (the underpass being masked by wood shavings) this effect was significant for 8-month-old LB strain mice, while in SB mice no effect was found. The proportions of mice that solved the task successfully when the underpass was blocked by a plug were lower in LB and higher in SB (the small sizes of groups permitted us to obtain only the tendency in differences from controls). Neophagophobia test performance show that the dipeptide infusion induced more active reaction to the novel food with LB reactions being clearer. The age interstrain differences in solution of this test were also found, both in dipeptide and in the control groups. The data on genotype–dependent changes in behavior after GK-2 infusion are important for more extensive characteristic of GK-2 pharmacological properties as a possible therapeutic drug.

Mice of two strains, selected, respectively, for successful solution of puzzle-box test (addressed to “object permanence” rule operation) and for non-solution of this test, were tested for short term memory, attention to moving object and neophagia. The data obtained demonstrated, that mice, selected for successful “object permanence” test solution demonstrated higher scores in recent memory and attention indices. It was suggested, that interstrain differences discovered should be addressed to differences in the “executive functions” expression.

Mice of two strains selected for successful solution of “object permanence” test and for lack of such solution demonstrated the differential reaction to injections of two drugs. The effects of injections of atomoxetine. which blocks the noradrenaline reuptake, and of ‘non-benzodiazepine” anxiolytic afobazol was different. The success of solutions increased in mice selected for this test “non-solution”: and decreased or was inefficient in mice, selected for successful solution of object permanence cognitive test.

The study provides a review of experimental research on selection of mice that yields positive results. The selection of mice was high (the task required mice to understand that an object which has become invisible, still exists and could be found) and poor performance in a cognitive test. The results obtained revealed better short term memory in mice, selected for high performance scores, and that these mice also showed higher performance in tests for novelty and attention. This suggests that differences between mice used in the experiment are associated not only with cognitive abilities in tests, but also with more pronounced “executive functions”.

This study provides a review of experimental research on selection in mice, which yielded positive results. The selection of mice was high (the task required mice to understand that an object that has become invisible still exists and can be found) and poor performance occurred in a cognitive test. The results we obtained revealed better short term memory in mice selected for high performance scores and that these mice also had higher performance in tests for novelty and attention. This suggests that differences between the mice used in the experiment are associated not only with cognitive abilities in tests, but also with more pronounced “executive functions.”

In this paper, the data are presented concerning different reactions to seven daily injections of atomoxetine in two mouse strains differing in relative brain weight. Atomoxetine affected the performance in a puzzle-box cognitive test in a complicated way—the large brain mice were less successful at task solutions (presumably because they were not afraid of the brightly lit test box), while the small brain strain of atomoxetine treated mice solved the task more successfully. The behavior of all atomoxetine treated animals was more active in an aversive situation (an unescapable slippery funnel, (analogous to the Porsolt test) and the time of immobility decreased significantly in all atomoxetine treated mice. The general patterns of behavioral reactions to atomoxetine in the cognitive test and other interstrain differences demonstrated in these experiments made it possible to suggest that differences in ascending noradrenergic projections between the two strains used exist. Further analysis of the noradrenergic system in these strains is needed (and further analysis of the effects of drugs which affect noradrenergic receptors).