I. I. Poletaeva

A comparison of wild-caught wood mice and bank voles in the Intellicage: assessing exploration, daily activity patterns and place learning paradigms

Our previous work has revealed very high baseline neurogenesis in the dentate gyrus of wood mice as compared particularly to bank voles; a difference which may be related to learning capacity. This study explored whether the newly-developed Intellicage system could be used to compare these species in simple spatial learning paradigms. The Intellicage is essentially a group-housing cage that also allows continuous automatic recording of each individuals behaviour. Seven wild-caught bank voles (Clethrionomys glareolus) were compared with seven wild-caught long-tailed wood mice (Apodemus sylvaticus) in the Intellicage system over 9 days. During the first 90 min after entering the cage, the wood mice were substantially more exploratory than the bank voles (P = 0.003). Over subsequent days, both species showed nocturnal activity increases with voles being 3.7 times more active overall. In the spatial learning paradigms, there were significant species-by-time interactions with wood mice outperforming bank voles on both place learning (P = 0.027) and subsequent reversal (P = 0.006). Conclusions are firstly that the wood mice show superior learning abilities in this paradigm, and secondly that the Intellicage serves as a valuable cognitive testing arena for small wild rodents, or for circumstances where cognition must be compared independent of different responses to handling or novel environments.

Lab Mice in the Field: Unorthodox Daily Activity and Effects of a Dysfunctional Circadian Clock Allele

Daily patterns of animal behavior are potentially of vast functional importance. Fitness benefits have been identified in nature by the association between individual timing and survival or by the fate of individuals after experimental deletion of their circadian pacemaker. The recent advances in unraveling the molecular basis of circadian timing enable new approaches to natural selection on timing. The investigators report on the effect and fate of the mutant Per2Brdm1 allele in 4 replicate populations of house mice in a seminatural outside environment over 2 years. This allele is known to compromise circadian organization and entrainment and to cause multiple physiological disturbances. Mice (N = 250) bred from Per2Brdm1 heterozygotes were implanted subcutaneously with transponders and released in approximately Mendelian ratios in four 400 m2 pens. An electronic system stored the times of all visits to feeders of each individual. The study first demonstrates that mice are not explicitly nocturnal in this natural environment. Feeding activity was predominantly and sometimes exclusively diurnal and spread nearly equally over day and night under the protective snow cover in winter. The effect of Per2Brdm1 on activity timing is negligible compared to seasonal changes in all genotypes. Second, the Per2Brdm1 allele did not have persistent negative effects on fitness. In the first year, the allele gradually became less frequent by reducing survival. New cohorts captured had the same Per2Brdm1 frequency as the survivors from previous cohorts, consistent with an absence of an effect on reproduction. In the second year, the allele recovered to about its initial frequency (0.54). These changes in selective advantage were primarily due to female mice, as females lived longer and the sex ratio dropped to about 25% males in the population. While it is unknown which selective advantage led to the recovery, the results caution against inferences from laboratory experiments on fitness consequences in the natural environment. It also demonstrates that the activity of mice, while strictly nocturnal in the laboratory, may be partially or completely diurnal in the field. The new method allows assessment of natural selection on specific alleles on a day-today basis.

Behavioral screening of two mouse lines selected for different brain weight

1. Several behavioral tests were used to compare two lines of mice selected for large (LB) and small brain (SB) weight on the basis of brain/body weight ratio values. 2. An elevated pain sensitivity as well more intense startle response was shown in SB mice in comparison with LB mice. 3. In inescapable situations of slip funnel and tail suspension tests, analogues of the Porsolt swim test, higher immobility scores in SB mice suggest an increased level of fear and/or anxiety the stress situations. 4. The SB mice demonstrated higher levels of locomotion in open field and cross-maze tests. In the latter test, the SB mice also showed increased tendency for stereotyped alternation of two arms during maze exploration. 5. Acute administration of a moderate dose of ethanol (3 g/kg) had opposite effects on the total time of cross-maze exploration: this measure increased in the SB and decreased in the LB line. By contrast, the tendency for stereotypy was similarly increased and the efficacy of maze exploration decreased in both lines.

Pentylenetetrazol and strychnine convulsions in brain weight selected mice

The seizure sensitivities to pentylenetetrazol (Ptz, 25-100 mg/kg) and strychnine (S, 2 mg/kg) were tested in two mice lines selected for large (LB) and small (SB) brain weight (brain weight difference being approximately 75 mg). The selection was based on a regression line connecting body and brain weight. SB mice were more sensitive to both drugs-their seizure latencies were shorter and lethality higher than in LBs. The seizures generated by Ptz and S are known to affect different neurotransmitter systems. The interstrain differences in seizure susceptibility are probably determined by SB mice nervous system traits rather than by differences in the particular neurochemical trait. The data on neocortical cytoarchitectonics obtained during our previous brain selection experiment could serve as the indirect evidence favouring such a suggestion.

[Laboratory rat selection for the trait "the absence of audiogenic seizure proneness"].

The hybrids between Krushinsky-Molodkina (KM) inbred strain, selected for high predisposition to audiogenic epilepsy (AE), and Wistar rats non-prone to audiogenic seizure were the initial population for selection. Rats were selected for the trait “the absence of audiogenic seizure proneness”. The creation of such strain in which the significant proportion of animals develop no AE in response to sound and share partly the genetic background of the KM strain is very important for the correct use of KM strain as the laboratory model of seizure states. As alleles which determine the AE proneness are recessive the selection for the “opposite” trait proceeds necessarily slow.

Dipeptide preparation Noopept prevents scopolamine-induced deficit of spatial memory in BALB/c mice

The effect of original nootropic preparation Noopept on learning and long-term memory was studied with BALB/c mice. Scopolamine (1 mg/kg) impaired long-term memory trace, while Noopept (0.5 mg/kg) had no significant effect. Noopept completely prevented the development of cognitive disorders induced by scopolamine (blockade of muscarinic cholinergic receptors). Our results confirmed the presence of choline-positive effect in dipeptide piracetam analogue Noopept on retrieval of learned skill of finding a submerged platform (spatial memory). We conclude that the effectiveness of this drug should be evaluated in patients with Alzheimer’s disease.

[Genetic analysis of the predisposition to audiogenic seizure fits in Krushinsky-Molodkina rat strain].

The expression of audiogenic seizure fits has been studied in F1 hybrids between audiogenic seizure-prone Krushinsky-Molodkina rat strain and Wistar rats not prone to audiogenic seizures, as well as in two backcross generations. Only 10% of F1 hybrids exhibit audiogenic seizure fits, whereas the frequency of this character in two generations of their backcrosses with Krushinsky-Molodkina rats is about 50%. A digenic model with incomplete penetrance has been put forward to explain the control of audiogenic seizure fits. This model fits the data obtained: the theoretically expected distributions of the character in offsprings of different crosses do not differ significantly from those observed in experiments. The model explains why the distribution of the character is the same in the first and second backcross offsprings.

[The interstrain differences in the effects of D-amphetamine and raclopride on dorsal striatum dopaminergic system in KM and Wistar rats (microdialysis study)].

The levels of dopamine (DA) was determined by intracerebral microdialysis in vivo in KM rats selected for high audiogenic epilepsy, and in Wistar rats selected for nonsusceptibility to loud sound. The basal level of dopamine was 25% higher in the KM rats (P < 0.05). A single amphetamine injection (1 mg/kg body weight, intraperitoneously) caused a significant increase in the DA basal level up to 250-260% in animals of both genotypes. However, in Wistar rats, the level of DA reached maximum as soon as 20 min after amphetamine administration, whereas in KM rats, this happened only after 120 min. After a single injection of the D2/D3 dopamine receptor antagonist raclopride (1.2 mg/kg of body weight, intraperitoneously), an increase in the level of DA was similar in amplitude in rats of both genotypes (up to about 210%); however, this occurred 20-30 and 100 min after raclopride administration to Wistar and KM rats, respectively. This evidence suggests that the genetic defect of KM rats, namely, the high level of audiogenic epilepsy, is caused by abnormalities of the neurotransmitter brain systems and presumably accompanied by the regulatory gene dysfunction.

Exploratory behavior of F2 crosses of mouse lines selected for different brain weight: a multivariate analysis.

Principal component analysis of behavioural measures together with body and brain weight of hybrid F2 mice crosses between two lines selected for large (LB) and small (SB) brain weight yielded eight-factor solution explaining 75.1% of total variance. Two of eight factors had sufficient loading on brain weight and several behavioural measures. The factor analysis showed that, among F2 hybrids, mice with larger brain weight were characterised, in open-field test, by higher scores of locomotion in the periphery of arena and of rearing, as well as less frequent grooming and freezing than mice with smaller brain weight. F2 hybrids with larger brain weight moved faster and displayed stereotyped behaviour in the cross-maze test more frequently. In general, this diversity is in accord with the behaviour differences between parent LB and SB lines. The results show that, in mice fear-anxiety and stereotypic behaviours, which are known to interfere with normal exploration and learning of the environment, are causally connected with brain weight.

Selection of mice for high scores of elementary logical task solution

52 Genetic studies on the capacity of laboratory rodents for solving cognitive tasks are mainly based on the estimation of differences between the strains [8] and the changes in this ability after manipulations with the genome of laboratory mice [7]. In spite of much interest in studies on the role of the genotype in deter mination of cognitive capacities in rodents, no attempts have been made to select animals for higher capacity of performing these tasks. Among the cogni tive tests is the ability to perform the extrapolation task. This task estimates whether the animal can find a food reinforcement that has disappeared from its’ view by “extrapolating” the future position of the food rein forcement and, for this purpose, move in the appropri ate direction and approach the food. This ability revealed intraspecific variability [3]; however, an attempt to select rats for higher expression of this capacity was unsuccessful due to increased anxiety in these rats, which prevented their use for testing.