Effects of moderate and intensive training on functional activity of central 5-HT1B receptors in the rat substantia nigra

The efficacy of the selective 5-HT_1B receptor agonist CP 93,129 in inhibiting the forskolin-stimulated adenylyl cyclase activity in the rat substantia nigra was reduced by both moderate and intensive prolonged training compared with sedentary resting rats. The concentration–response curves of the agonist were shifted to the right with a sixfold increase of the half-maximal inhibitory concentration. A difference was observed between the two training exercises in regard to further changes in 5-HT_1B receptor sensitivity induced by an acute restraint stress. This manipulation did not affect the functional response of the 5-HT_1B receptors further in moderately trained rats, whereas an additional desensitization of the 5-HT_1B receptors was observed in intensively trained rats. These results strongly suggest the existence of regulation mechanisms altering the functional efficacy of 5-HT_1B receptors and, accordingly, affecting the serotonergic activity, since 5-HT_1B receptors modulate the neuronal release of the amine.