Post-session sulpiride infusions within the perifornical region of the lateral hypothalamus enhance consolidation of associative learning

Whilst neurons within the lateral hypothalamus are well known to be respons ive to the presentation of previously learned associative stimuli, the cons olidation of a Pavlovian association is thought to depend in large part upo n other brain regions, including the amygdala. The present study addressed this assumption directly, by examining the effect of postsession infusions of sulpiride within the lateral hypothalamus upon the acquisition of a cond itioned approach response in an appetitive differential conditioning task. Subjects were exposed to an initially neutral stimulus (CS+), which immedia tely preceded the availability of a 10% sucrose reward (US). A second. cont rol stimulus (CS-) was also presented, but never in close temporal proximit y to the US. The number and duration of alcove approaches were recorded. Im mediately following each training session, subjects were infused bilaterall y with sulpiride (0, 0.5, 5 mu g) in the vicinity of the perifornical regio n of the lateral hypothalamus. Sulpiride dose-dependently enhanced the rate of acquisition of a conditioned approach response to presentation of the C S+, but was without affect upon approach behaviour during CS- or US present ations. Thus, 0.5 mu g sulpiride facilitated at an early stage (session 2 o nwards) the number of alcove approaches to the CS+ while 5 mu g sulpiride e nhanced to a greater extent the duration of conditioned approach, particula rly during later sessions. A subsequent locomotor test using 0.5 mg/kg d-am phetamine indicated that repeated infusions of the higher dose sulpiride (5 mu g), but not the lower dose (0.5 mu g), resulted in behavioural sensitis ation to administration of the psychomotor stimulant. Acquisition of a nove l conditioned instrumental response was not affected by previous exposure t o sulpiride. These data suggest that dopamine-sensitive neurons within the lateral hypothalamus may play a significant role in the acquisition of appe titive Pavlovian associations.