The effects of acute and chronic antidepressant treatments on temperature and locomotor activity responses to 8-OHDPAT, clonidine and apomorphine

Chronic antidepressant administration has previously been shown to alter the sensitivity of 5-HT(1A), a₂-adrenoceptors and dopamine autoreceptors. The purpose of the present study was to examine the effect of pretreatment with acute and chronic antidepressants (5 mg/kg paroxetine, 7.5 mg/kg dispramine, 3 mg/kg and 30 mg/kg fluvoxamine, p.o.) on the locomotor activity and temperature changes following acute challenges with either the 5-HT(1A) receptor agonist, 8-OHDPAT, the α₂ agonist clonidine and the dopamine agonist, apomorphine. Administration of 8-OHDPAT (0.05 mg/kg, s.c.) caused a significant hypothermic response which was attenuated by chronic (but not acute) administration of paroxetine and desipramine. Clonidine (0.2 mg/kg, s.c.), caused a significant reduction in colonic temperature and in locomotor activity. Chronic, but not acute, pretreatment with all the antidepressants tested significantly attenuated the hypothermic effect of clonidine; however there was no reversal of the hypoactive response. A single injection of apomorphine (0.05 mg/kg, s.c.) caused a reduction in locomotor activity. Chronic paroxetine and fluvoxamine administration slightly, but not significantly, reversed this apomorphine induced hypoactive response. These data suggests that chronic treatment with antidepressants from the different pharmacological classes cause different adaptive changes in 5-HT(1A), α₂-adrenoceptors and dopamine and autoreceptor function.