Lateral hypothalamic lesions impair flavour-nutrient and flavour-toxin trace learning in rats.

Food-restricted rats with ibotenic acid lesions of the lateral hypothalamus (LHx) learned to prefer a flavour paired with concurrent intragastric (i.g.) infusions of maltodextrin, although their preference was weaker than that displayed by sham controls. Unlike controls, the LHx rats failed to acquire a flavour preference when the i.g. maltodextrin infusion was delayed by 15 min. The same rats learned to avoid flavours paired with i.g. lactose or lithium chloride over short delays (15-30 min), but were impaired, relative to controls, at a long conditioned-unconditioned stimuli delay (2 h). These data indicate that the LH is critical for the formation of flavour-postingestive consequence learning over a delay, particularly with nutrient reinforcement. Lateral hypothalamus lesions might specifically impair the processing of nutrient-generated unconditioned stimuli and, more generally, could interfere with the maintenance of flavour memories.