Brainstem systems mediate the enhancement of palatability by chlordiazepoxide.

Previous studies have indicated that the benzodiazepine receptor complex is involved in enhancing taste palatability after chlordiazepoxide (CDP) administration. Positive, palatability-dependent ingestive reactions elicited by orally infused tastes are facilitated in rats by CDP (10 mg/kg), and this effect is reversible by benzodiazepine antagonists. In contrast, the rats' more neutral or aversive reactions are not facilitated by CDP. Because benzodiazepine receptors exist in highest density in the forebrain, it has seemed plausible to posit forebrain structures as the locus of CDP action. However, benzodiazepine receptors do exist in the caudal brainstem (albeit in lesser density), and the isolated decerebrate brainstem has been demonstrated to possess considerable taste processing and response capacity. The present study examined the effects of CDP on taste reactivity in chronic mesencephalic decerebrate rats. The results show that CDP can act on the subdiencephalic brainstem to enhance positive ingestive reactions even in the absence of communications with the forebrain. This indicates that both the relevant benzodiazepine receptors and the minimal neural circuit needed to modulate taste reactivity exist within or below the mesencephalon.