The effects of 8-OH-DPAT on medulllary 5-HT neurons and sympathetic activity in baroreceptor-denervated animals

The effects of the 5HT_1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on medullary 5-hydroxytryptamine (5-HT) neuronal firing and inferior cardiac sympathetic nerve activity were simultaneously determined in baroreceptor-denervated cats. 5-HT neuronal firing was inhibited by 50% at a 1 μg/kg i.v. dose of 8-OH-DPAT in the baroreceptor-denervated animal. Unit firing was completely inhibited by a 3 μg/kg dose. In contrast, 8-OH-DPAT inhibited inferior cardiac nerve activity between 10 and 100 μg/kg i.v. A similar relationship between the 8-OH-DPAT-induced inhibition of 5-HT unit activity and sympathetic nerve activity was observed in sham-operated control animals. These data suggest that the sympatholytic effects of 8-OH-DPAT cannot be explained on the basis of an autoreceptor effect of the drug.