Neonatal scopolamine or antidepressant treatment: effect on development of hamster circadian rhythms

Chronic treatment of young rodents with drugs altering monoamine metabolism has been reported to produce lasting effects on behavior that resemble human affective disorders. To test the generality of this finding, scopolamine, imipramine, or clomipramine was injected daily between the ages of 8 and 21 days in golden hamsters. Wheel-running rhythms were monitored continuously from the age of 4 to 20 weeks of age to test the hypothesis that neonatal treatments would lower the amplitude of biological activity rhythms in adults. Of these three neonatal treatments only scopolamine altered running rhythms, significantly increasing the amplitude of running rhythms in adult hamsters under both entrained and free-running conditions. Hamsters treated neonatally with scopolamine were also more sensitive to the hypothermic effects of the muscarinic agonist, oxotremorine, as adults. These data indicate that neonatal exposure to cholinergic receptor blockade may produce long-lasting changes in biological rhythm characteristics related to upregulation of muscarinic receptors.