['In animal models of reduced dopamine transmission, such as haloperidol-induced catalepsy or monoamine-depleted animals, serotonin (5-hydroxytryptamine; 5-HT) 5-HT(1A) agonists appear to enhance motor activity. However, the exact mechanism remains unclear.', 'The objective of the present study was to demonstrate that 5-HT(1A) agonists can increase locomotor activity by activation of postsynaptic 5-HT(1A) heteroreceptors without the involvement of somatodendritic 5-HT(1A) autoreceptors which are known to regulate 5-HT neuronal activity.', 'The effects of the 5-HT(1A) full agonist R-(+)-8-hydroxy-2-(di- n-propylamino)tertralin ( R-(+)-8-OHDPAT) on locomotor activity in reserpinized (i.e., monoamine-depleted) rats were studied.', 'The present data demonstrate that R-(+)-8-OHDPAT significantly increased locomotor activity in monoamine-depleted animals at a dose as low as 0.01 mg/kg. The partial 5-HT(1A) agonist/D(2) antagonist buspirone (3 mg/kg) also elevated locomotor activity. The effects of these 5-HT(1A) compounds were found to be similar to the locomotor-stimulating effect of the dopamine precursor 3,4-dihydroxyphenylalanine (150 mg/kg, 15 min after 50 mg/kg benserazide). The 5-HT(1A) antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarboxamide maleate (WAY 100635; 0.2 mg/kg) blocked the R-(+)-8-OHDPAT (0.03 mg/kg)-mediated increase in locomotion. Blockade of 5-HT synthesis with DL- p-chlorophenylalanine (pCPA), a tryptophan hydroxylase inhibitor, prior to reserpinization did not affect R-(+)-8-OHDPAT-induced locomotion.'] Do postsynaptic 5-HT ( 1A ) receptors mediate an increase in locomotor activity in the monoamine-depleted rat?