Investigation of the effects of oxotremorine on learning and memory in the forced swimming test and on convulsions induced by scopolamine and food intake after fasting

Increased immobility has been considered to reflect behavioral depression in the forced swimming test in which cholinergics display depressant and anticholinergics exhibit antidepressant effects. It has been also suggested that immobility can be a coping strategy to stressful situations or an indicator of learning. Antimuscarinic administration and subsequent food supply after fasting cause convulsions in mice and rats. It has been shown that M1 and M2 muscarinic receptor expression is increased in the brain regions during fasting. Oxotremorine, a muscarinic agonist, can increase immobility in the forced swimming test with its learning and memory enhancing effect and prevent convulsions with its cholinergic activity. In the present study, discrimination index and immobility time were measured in rats given oxotremorine (0.05, 1 mg/kg) before the test session in the novel object recognition test and before the pretest session in the forced swimming test. Immobility time was determined in the forced swimming test in animals given oxotremorine (0.1 mg/kg) alone or with amitriptyline before the test session. Mice fasted for 24 h were administered with oxotremorine twice (0.1 mg/kg) during fasting or once (0.05, 0.1 mg/kg) after fasting and were treated with scopolamine and given food. The memory enhancing effect of oxotremorine was not demonstrated in the novel object recognition test. However, increased immobility in the forced swimming test produced evidence for its learning enhancing effect. Oxotremorine did not cause an effect in the same test when given alone, but prevented the immobility decreasing effect of amitriptyline and supported the suggestion that anticholinergic system contributes to the antidepressant-like or memory impairment effect. Oxotremorine administration during fasting did not prevent the development of convulsions, whereas oxotremorine after fasting decreased the frequency of convulsions. Present findings showing the relationship between immobility duration and learning and memory formation in the forced swimming test, and the role of muscarinic receptors in convulsions induced by antimuscarinic administration and food intake in fasted animals provided novel data for further studies.