EFFECT OF VAGOTOMY ON HYPERACTIVITY AND INCREASED DOPAMINE TURNOVER INDUCED BY INTRAPERITONEAL ADMINISTRATION OF THYROTROPIN-RELEASING-HORMONE

Thyrotropin-releasing hormone (TRH) injected intraperitoneally at dose s of 10 mg/kg and 20 mg/kg induced marked hyperactivity in rats. Altho ugh regional levels of brain dopamine and its metabolites (DOPAC and H VA) in vagotomized rats did not differ from those in sham-operated con trols, the (DOPAC + HVA)/dopamine ratio, an indicator of dopamine turn over, was significantly higher in the nucleus accumbens of TRH-treated sham-operated rats than that in untreated sham-operated controls. TRH injection induced hyperactivity only in sham-operated rats and not in subdiaphragmatic bilaterally vagotomized rats. Similarly, bilateral v agotomy completely abolished the TRH-induced increase in dopaminergic turnover in the nucleus accumbens. These results suggest that the dopa minergic system in the nucleus accumbens is involved in hyperactivity induced by TRH, and that TRH mainly affects peripheral receptors. The vagal nerve may be the major pathway from the visceral organs to the b rain involved in the etiology of hyperactivity.