Remote effects of short-term neonatal hyperthermia in Krushinsky-Molodkina rats prone to audiogenic seizures strain.

Using the audiogenic seizure prone Krushinsky-Molodkina rat strain, it was demonstrated that short-term (5 min) exposure of 14-day-old pups to an elevated temperature (42°C) resulted in a significant decrease in audiogenic seizure severity at the age of 1 month. Presumably, this effect is determined by the activation of the heat-shock protein system (stress proteins).

[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 RV 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.

[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.

[Behavioral impairments in Morris water maze in rats selectively bred for audiogenic seizure susceptibility (Krushinsky-Molodkina strain)]. / Povedenie v vodnom teste Morrisa krys linii Krushinskogo-Molodkinoi, selektirovannykh na povyshennyiu sudorozhnuiu gotovnost'.

Krushinsky-Molodkina rats (KM strain) with genetically determined seizure susceptibility (clonic and tonic seizures in response to the sound of an electric bell, Krushinsky, 1960) were tested in two versions of Morris water maze and compared with normal albino rats (Sprague-Dawley and Wistar). The tests revealed a learning deficit in KM rats. They showed slow acquisition in both the spatial version of the test and the version with the platform, less efficient strategy of searching for target platform, and high scores of floating and thigmotaxis. However, males of KM rats (not females) did not differ significantly from Wistar strain in the probe trial in the spatial variant of the Morris test. No preference for searching for the platform at the place of its previous localization was observed in KM females. Together with our previous findings of the low scores in Revecz-Krushinsky test and data of other authors (Batuev et al., 1983) concerning a working memory deficit in the radial maze, the results suggest the of complex cognitive deficit combined with possible increased stress reactivity in KM rats.

[The solving of the Revecz-Krushinskii test by rats of different genotypes]. / Reshenie testa Revesha-Krushinskogo krysami raznykh genotipov.

Brown Norway rats bred from the original wild stock, KM (Krushinskii-Molodkina) albino rats selectively bred for audiogenic seizure susceptibility, and Wistar albino rats were subjected to Revecz-Krushinskii reasoning test. It determines whether rats can anticipate regular yet invisible shifts of food bait positions. A bait was placed under one of 12 opaque cylinders (arranged in a line) to be tipped by a rat in order to obtain food. In the first trial the cylinder 1 was baited, in the second trial the cylinder 2 was and so on up to 12th one. The correct strategy of this problem solving is a choice "one cylinder ahead" of the previous bait location. Rats appeared to be unable to realize this algorithm accurately. However, in some cases their performance was significantly different from chance. They apparently realized another strategy: to choose recently baited cylinders with shifting a zone of search. It was typical for brown and Wistar rats but not for KM which preferred to choose the cylinders baited in the previous trials, but their preference was not specified by recently baited positions. In the second experiment (learning of an accurate choice of one target cylinder with a fixed position in the line) the worst performance was found also in KM rats. The strain differences in Revecz-Krushinskii test performance are supposed to be caused by the level of spatial working memory.

[A model of audiogenic epilepsy--rats of the Krushinskii-Molodkina strain. Proof of genetic homogeneity]. / Model' audiogennoi épilepsii--krysy linii Krushinskogo--Molodkinoi. Dokazatel'stvo geneticheskoi odnorodnosti.

Genetical homogeneity of Krushinskii-Molodkina (KM) stock was studied by the method of reciprocal transplantation of skin. The rats were selected inside genealogic card from 5 different substrains of the 20th generation of brother-sister crossing (F 20). The tail-to-tail transplantation was made by the scheme of double reciprocal ring in 9 females from the KM stock. Observations within 314 days showed a good condition of the transplants. The obtained data suggest that Krushinskii-Molodkina rats are an inbred strain.

[The solving of the Revecz-Krushinskii test by Norway rats]. / Reshenie testa Revesha--Krushinskogo krysami pasiukami.

Reasoning abilities of Norway rats were studied in Revecz-Krushinskii test. In this test 12 opaque plastic cylinders were placed in a row. Rats obtained the bait (sunflower seeds) after tipping the goal cylinder (from the feeder situated under it) independently of the number of one tipped before. Positions of the baits were changed in the following order: the cylinder No 1 in the first trial, No 2--in the second and so on up to the twelfth one. Rats were tested 3 times (12 trials, once a week) in a rectangular box with a starting chamber and a working part with a special device which excluded the influence of olfactory stimuli. Solution scores demonstrated that rats chose cylinders in the nonrandom manner and their behaviour scores were similar to those of crows and monkeys. Analysis of errors and strategies of behaviour of rats showed that quick improvement of feeding was at least partly determined by easy acquisition of recent food positions (i.e., the algorithm of shifting).