ACTIVIN ANTISERUM INFUSED INTO THE LATERAL HYPOTHALAMIC AREA AFFECTS OPERANT-BEHAVIOR OF RATS FED LYSINE-DEFICIENT DIET

Rats were trained to maintain a high rate of bar pressing to receive 5 0-mg pellets of a complete diet when given a lysine-deficient (Lys-def ) diet ad libitum, This bar-pressing behavior was significantly inhibi ted when rats were also allowed ad libitum access to 0.4 M Lys to drin k. A brain activin system may modulate motivation to engage in bar-pre ssing behavior, since previous work has established that antagonism of activin by infusion of inhibin or follistatin, but not activin, into the lateral hypothalamic area (LHA) also inhibits bar-pressing behavio r. The present study sought to clarify whether the effect of inhibin o r follistatin might be mediated by antagonism of endogenous activin or by a separate direct effect of inhibin or follistatin. Thus, we infus ed an antiserum, which specifically inhibits activin A activity, into the LHA, Infusion of antiserum greatly inhibited bar-pressing behavior of rats fed a Lys-def diet and was additive with Lys consumption furt her to decrease bar pressing. Ad libitum Lys consumption was unchanged from control levels, indicating that it is likely that an endogenous activin system in the LHA mediates behavioral responsiveness when rats are fed a Lys-def diet but does not appear specifically to affect app etite for Lys.