LATERAL TEGMENTAL FIELD INVOLVEMENT IN THE CENTRAL SYMPATHOINHIBITORYACTION OF 8-OHDPAT

This study examined the effects of kainic acid and NMDA microinjection s into the lateral tegmental field on the sympatholytic effect of the 5-HT1A agonist 8-OH-DPAT. Kainic acid has been reported to destroy cel l bodies while leaving fibers of passage intact while NMDA excites the cell bodies but not the axons of neurons. Microinjection of kainic ac id was found to block the usual sympatholytic effect of 8-OH-DPAT but not the sympathoinhibition produced by the alpha2 agonist clonidine. M icroinjection of NMDA elicited profound pressor responses related to a n increase in sympathetic activity. Sympatholytic effects of 8-OH-DPAT and clonidine were transiently overridden by microinjections of NMDA, but not glutamate. A role for the lateral tegmental field in the gene ration of sympathetic tone and in the sympatholytic mechanism of 8-OH- DPAT is supported by the chemical lesion and stimulation studies.