LATERAL HYPOTHALAMIC-STIMULATION INHIBITS DENTATE GRANULE CELL LTP - DIRECT CONNECTIONS

We discovered that angiotensin II (Ang II) applied directly to the den tate gyrus inhibited LTP induction in medial perforant path-dentate gr anule cell synapses and that the inhibition can be blocked by losartan , an Ang II AT(1) receptor specific antagonist. In the first part of t his study we found that electrical stimulation of the lateral hypothal amus (LH) inhibits LTP in these synapses and the inhibition can be blo cked by pretreating the animals with losartan, indicating that LH angi otensin-containing neurons project to the dentate gyrus. Results of th e second part of the study demonstrate clearly that some angiotensin-c ontaining LH neurons project directly to dentate granule cells. LH neu rons were identified by retrograde tracers applied to the granule cell layer. Double-labeled neurons containing angiotensin and HRP were spa rsely distributed and both fusiform and multipolar LH neurons appeared in a smart cluster lateral and ventral to the fornix at the level of the paraventricular nucleus. Large numbers of angiotensin staining neu rons were observed in the hypothalamus. Results support our hypothesis that some angiotensin containing LH neurons project directly to the d entate gyrus. (C) 1997 Elsevier Science Inc.