INFLUENCES OF THE BED NUCLEUS OF THE STRIA TERMINALIS AND OF THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS ON THE EXCITABILITY OF HIPPOCAMPAL-LATERAL SEPTAL SYNAPSES IN MICE

Previous experiments have shown that conditioning in aversive situatio ns is associated with specific changes in excitability of hippocampal- septal synaptic transmission and that these changes might be related t o a modulation of this synaptic transmission by afferents originating from the bed nucleus of the stria terminalis (BNST) and from the parav entricular nucleus (PVN) of the hypothalamus. Accordingly, the aim of the present experiment was to assess changes in excitability of hippoc ampal-septal synapses by varying the interval between the application of a conditioning pulse in either the BNST or the PVN, and a test puls e in fimbria fibers (FF). Electrical stimulation of FF, induces in the lateral septum (LS) a field potential characterized by two negative w aves (N2 and N3) the magnitude of which is an index of excitability of two populations of target cells located in the ventral and dorsal lat eral septum, respectively. Results showed that prestimulation of both the BNST and the PVN produced an increase in the amplitude of the N3 w ave, although the optimal interpulse interval required for producing m aximal increase was different as a function of the two structures. Onl y prestimulation of the BNST induced a significant increase in the amp litude of the N2 wave. These results suggest that the PVN projects mai nly to the dorsal aspect of the LS, while the BNST projects to both do rsal and ventral parts of the LS. Together with results from previous experiments conducted in behaving mice exposed to conditioned aversive stimuli, it is concluded that these projections might play a role in the relief of contextual conditioned fear. (C) 1998 Published by Elsev ier Science Ireland Ltd.