Flight induced by infusion of bicuculline methiodide into periventricular structures

Microinjections of different doses of bicuculline methiodide (BM) were performed into the mesencephalic central gray (CG), the medial hypothalamus (MH) and lateral hypothalamus (LH). Flight reactions could be induced by microinjections of BM into either the CG or the MH. However, the type of flight behavior was different whether the injection was made in the CG or the MH. Furthermore, microinjections of 35 ng of BM in either structure produced an increase in locomotor activity whose time course differed according to the injected structure, and an increase in rearings was induced at MH but not at CG sites. At lateral hypothalamic sites, BM produced an increase in locomotor activity and rearings but no jump. These effects were antagonized in a dose-dependent manner by a local pretreatment with 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP), a GABA agonist. These results suggest that (1) at the level of both the MH and the CG, a GABAergic link is involved in the inhibition of a substrate whose activation produces aversive effects, and (2) the aversive effect induced by CG BM microinjection seems to be different from that induced by MH BM microinjection.