Dopamine Receptor Blockade in Nucleus Accumbens or Caudate Nucleus Differentially Affects Feeding Induced by 8-OH-DPAT Injected into Dorsal or Median Raphe

The 5-hydroxytryptamine (5-HT)1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) elicits a variety of behaviours including feeding in rats. These effects are accompanied by a reduction in 5-HT neurotransmission resulting from activation of somatodendritic 5-HT receptors located in the midbrain raphe nuclei. Previous work showing that dopamine receptor antagonists attenuate 8-OH-DPAT-induced feeding indicates that a facilitation of dopamine activity, secondary to reduced 5-HT activity, is involved in the expression of this effect. Microinjection studies were conducted to explore further the nature of this 5-HT-dopamine interaction. Injection of 8-OH-DPAT (0.125-2 micrograms) into either dorsal or median raphe induced dose-dependent increases in 1 h food intake in non-deprived rats. Pretreatment with haloperidol (0.05 and 0.1 mg/kg s.c.) attenuated the effect induced by median raphe 8-OH-DPAT (0.5 microgram) complementing previous results with dorsal raphe 8-OH-DPAT. The feeding resulting from dorsal raphe (1 microgram) or median raphe (0.5 microgram) 8-OH-DPAT was attenuated by alpha-flupenthixol (1.25 and 2.5 micrograms) injected into the nucleus accumbens. alpha-Flupenthixol in either the dorsolateral or ventrolateral aspects of the caudate nucleus attenuated also the feeding response to dorsal raphe, but not median raphe, 8-OH-DPAT. However, alpha-flupenthixol in the dorsomedial caudate failed to alter feeding resulting from dorsal raphe 8-OH-DPAT.(ABSTRACT TRUNCATED AT 250 WORDS)