Differences in acquisition of discrete lever-press and shuttle avoidance responses in 6 strains of mice

Differential Neurosensitivity to the Discriminative Stimulus Properties of Ethanol in C57BL/6J and C3H/He Mice

BACKGROUND

A large body of evidence suggests that the interoceptive cue associated with ethanol intoxication is complex and dependent on a number of environmental and biological factors. Despite the fact that mice have been widely used to study genetic influences on sensitivity to various actions of ethanol, few studies have used mice to examine sensitivity to the discriminative stimulus effects of ethanol. The purpose of this study was to compare sensitivity to the discriminative stimulus effects of ethanol in two inbred mouse strains, namely C57BL/6J and C3H/He mice.

METHODS

Adult male C57BL/6J and C3H/He mice were trained to discriminate between ethanol and saline using a two-lever food reinforcement operant procedure. Once criterion discrimination performance was achieved, dose-response functions were determined from generalization tests. Additional experiments were conducted to determine whether differences in discrimination performance were related to differential blood/brain ethanol levels in the two mouse strains.

RESULTS

A greater proportion of C57BL/6J mice acquired the discrimination and required fewer trials to achieve criterion performance compared with C3H/He mice with a 1.0 g/kg ethanol training dose. This deficit in acquisition was overcome when the training dose was increased to 2.0 g/kg for C3H/He mice. In a second experiment, a 1.5 g/kg training dose of ethanol was used for both strains. Again, a greater proportion of C57BL/6J mice acquired the discrimination and required fewer training trials to achieve criterion performance compared with C3H/He mice. Blood ethanol levels did not differ between the strains after administration of the 1.5 g/kg training dose. However, blood and brain ethanol levels did differ between the strains after doses of ethanol were administered that produced equivalent discrimination performance.

CONCLUSIONS

Results indicate that ethanol discrimination was more readily acquired and maintained in C57BL/6J mice than C3H/He mice. Ethanol dose-response functions generated from generalization tests also clearly demonstrated greater sensitivity to the discriminative stimulus properties of ethanol in C57BL/6J mice compared with the C3H/He strain. This differential sensitivity to the interoceptive cue produced by ethanol does not seem to be related to learning or pharmacokinetic differences between the two inbred strains.

Structural and functional characterization of gastric mucosa and central nervous system in histamine H2 receptor-null mice

To examine the physiological role of the histamine H(2) receptor, histamine H(2) receptor-null mice were generated by homologous recombination. Histamine H(2) receptor-null mice, which developed normally and were fertile and healthy into adulthood, exhibited markedly enlarged stomachs and marked hypergastrinemia. The former was due to hyperplasia of gastric gland cells (small-sized parietal cells, enterochromaffin-like cells and mucous neck cells which were rich in mucin), but not of gastric surface mucous cells, which were not increased in number as compared with those in wild-type mice despite the marked hypergastrinemia. Basal gastric pH was slightly but significantly higher in histamine H(2) receptor-null mice. Although carbachol but not gastrin induced in vivo gastric acid production in histamine H(2) receptor-null mice, gastric pH was elevated by both muscarinic M(3) and gastrin antagonists. Thus, both gastrin and muscarinic receptors appear to be directly involved in maintaining gastric pH in histamine H(2) receptor-null mice. Interestingly, gastric glands from wild-type mice treated with an extremely high dose of subcutaneous lansoprazole (10 mg/kg body weight) for 3 months were very similar to those from histamine H(2) receptor-null mice. Except for hyperplasia of gastric surface mucous cells, the findings for gastric glands from lansoprazole-treated wild-type mice were almost identical to those from gastric glands from histamine H(2) receptor-null mice. Therefore, it is possible that the abnormal gastric glands in histamine H(2) receptor-null mice are secondary to the severe impairment of gastric acid production, induced by the histamine H(2) receptor disruption causing marked hypergastrinemia. Analyses of the central nervous system (CNS) of histamine H(2) receptor-null mice revealed these mice to be different from wild-type mice in terms of spontaneous locomotor activity and higher thresholds for electrically induced convulsions. Taken together, these results suggest that (1) gastrin receptors are functional in parietal cells in histamine H(2) receptor-null mice, (2) abnormal gastric glands in histamine H(2) receptor-null mice may be secondary to severe impairment of gastric acid production and secretion and (3) histamine H(2) receptors are functional in the central nervous system.

Aspects of animal experiments for evaluation of cognitive enhancers: in particular, the behavioral characteristics of Mongolian gerbils

1. The step-through passive avoidance response and discrete lever-press avoidance response of Mongolian gerbils were evaluated to point out the basic problems in the learning and memory tests in this species. 2. Mongolian gerbils exhibited extremely poor acquisition and maintenance of the passive avoidance response. 3. In contrast to the result under the passive avoidance situation, Mongolian gerbils demonstrated an excellent performance under the discrete lever-press avoidance situation. 4. A 5-min brain ischemia elicited a severe morphological damage of the pyramidal cells in hippocampal CA1 region. 5. A small part of such ischemic animals showed a deficit of acquisition of the discrete lever-press avoidance. 6. These results suggest that there is merit and demerit of the acquisition dependent on the type of tasks, and that the brain function of Mongolian gerbils may be maintained even after the ischemic operation.

Differences in one-way active avoidance learning in mice of three inbred strains

DBA/2J, C57BL/6J, and C3H/HeJ mice were given 10 one-way avoidance training trials per day, using an unconditioned stimulus intensity that provided equivalent motivation for learning to mice of all three strains, and were found to differ in their abilities to learn and retain the response. DBA/2J mice acquired the response in fewer days than did the mice of the other two strains, although C57BL/6J mice eventually reached a level of performance similar to that of DBA/2J mice. Both the rate of acquisition and the level at which avoidance performance stabilized were significantly lower in C3H/HeJ, than in DBA/2J or C57BL/6J, mice. In addition, DBA/2J mice showed a significantly greater task retention from one testing day to the next than did C57BL/6J or C3H/HeJ mice.

Effects of ceruletide, administered singly and in combination with central-acting drugs, on discrete shuttle avoidance response in mice

The single administration of ceruletide at 10-300 micrograms/kg, i.p., slightly but significantly decreased the response rate (frequency of shuttles) under a discrete avoidance task in mice. Over 10 micrograms/kg of ceruletide attenuated the increase in the response rate induced by methamphetamine (0.5 mg/kg, s.c.). However, ceruletide, at 1-300 micrograms/kg, did not significantly enhance the response- and/or avoidance-decreasing effects of chlorpromazine (1 mg/kg, s.c.), haloperidol (0.1 mg/kg, s.c.), pilocarpine (4 mg/kg, s.c.) and N6-(L-2-phenylisopropyl)-adenosine (0.1 mg/kg, s.c.), but rather tended to reduce the avoidance-decreasing effect of chlorpromazine and pilocarpine at 1-100 micrograms/kg.

Facilitating effect of oxiracetam and piracetam on acquisition of discrete two-way shuttle avoidance in normal mice

Effects of oxiracetam and piracetam on acquisition of the discrete two-way shuttle avoidance response were investigated in normal mice of the dd strain. When oxiracetam or piracetam was administered only once immediately before the training session, the mice showed a greater number of avoidance responses in comparison with the saline-treated control mice, with the maximum effect at 30 mg/kg of oxiracetam and 100 mg/kg of piracetam. These results suggest that oxiracetam and piracetam facilitate the avoidance acquisition in normal mice.