A LATERAL HYPOTHALAMIC D1 DOPAMINERGIC MECHANISM IN CONDITIONED TASTE-AVERSION

The aim of this study was to elucidate the role of the neuropil locate d in the LHA in the acquisition of the association between a taste (co nditioned stimulus = saccharin) and a visceral distress (unconditioned stimulus = lithium chloride) leading to long delayed learning of a co nditioned taste aversion (CTA). In 82 male rats guide-cannulae were di rected bilaterally into the basolateral LHA where bilateral microinjec tions were made after the conditioned stimulus and before the uncondit ioned stimulus. We found that: (1) tetrodotoxin, a non-specific blocke r of neuronal activity disrupted the acquisition of the CTA; (2) SCH 2 3390, a specific D1 receptor blocker also disrupted learning of the CT A, while sulpiride, a D2 receptor blocker, did not; (3) neither the sp ecific blockade of D1 nor of D2 receptors could prevent the visceral d istress-induced decrease in water intake, showing that the visceral di stress was actually experienced; and (4) the sham taste aversion learn ing (i.e. without visceral distress) revealed that neither the D1 nor the D2 receptors blockade induced by themselves either a taste prefere nce or a taste aversion towards saccharin, indicating that the impaire d acquisition of the CTA was not due to a superimposed taste preferenc e that could have been induced by the intra-LHA D1 receptors blockade. It is concluded that the neuropil in the LHA is necessary in the proc ess of the acquisition of long delayed learning and that it uses a D1 receptor specific mechanism.