ROLE OF CENTRAL DOPAMINERGIC AND 5-HYDROXYTRYPTAMINERGIC PROJECTIONS IN THE BEHAVIORAL-RESPONSES ELICITED BY THYROTROPIN-RELEASING-HORMONE IN RATS

The systemic administration of thyrotropin-releasing hormone (TRH) to rats elicits locomotor activation wet dog shakes, jaw movements, paw l icking and tail rattle. Central dopamine (DA) and 5-hydroxytryptamine (5-HT) systems and peripheral vagal afferents have been implicated in these responses. To define this circuitry further, the effects of lesi ons of these pathways on the behavioral responses elicited by intraper itoneal (IF) injections of TRH were assessed in rats. Lesions of the D Aergic innervation of the nucleus accumbens did not affect the locomot or activation, wet dog shakes, paw licking, jaw movements or tail ratt le elicited by TRH. This is consistent with our in vivo microdialysis finding that TRH did not affect the release of DA in the nucleus accum bens at a dose that strongly increased locomotor activity. Depletion o f spinal 5-HT significantly decreased the wet dog shakes induced by TR H, while depletion of forebrain 5-HT had no effect on any behavior. Bi lateral vagotomy did not affect the locomotor response to TRH or any o f the other behaviors measured. Taken together, these results suggest that the DAergic mesolimbic, the 5-HTergic projections to the forebrai n and vagal afferent systems are not mediators of the behavioral respo nses to systemic TRH. In contrast, the raphe-spinal 5-HTergic projecti on system may serve to modulate the wet dog shakes elicited by this pe ptide.