RETROGRADE LABELING OF RAT DORSOLATERAL SEPTAL NUCLEUS NEURONS FOLLOWING INTRASEPTAL INJECTIONS OF WGA-HRP

Projection neurons in the rat dorsolateral septal nucleus (DLSN) were retrogradely labeled following intraseptal injection of wheat germ agg lutinin conjugated horseradish peroddase (WGA-HRP). Injections of WGA- HRP centered in the medial septum (MS) and parts of the intermediate a nd ventrolateral subdivisions of the lateral septum retrogradely label ed only a few centrally scattered multipolar-shaped neurons. In contra st, injections placed in the nucleus of the diagonal band of Broca (DB B) consistently resulted in labeling of DLSN neurons of all sizes and shapes. Large injections in rostral DBB appeared to retrogradely label every DLSN neuron, while similar injections in caudal DBB only labele d neurons in restricted regions of the nucleus. A collection of small cells forming the ventricular border of caudal DLSN and a group of lar ger cells situated in the dorsolateral tip of rostral DLSN were consis tently labeled following each DBB injection. The pattern of retrograde ly labeled neurons in the DLSN appeared in a complementary fashion to that seen in the other lateral septal nuclei. Our findings support the conclusion that the DLSN is a morphologically heterogeneous nucleus c onsisting almost entirely of projection neurons. The pattern of retrog rade labeling in the lateral septum suggests that these projection neu rons may be topographically organized since distinct subpopulations of cells were labeled following different injections in the MS/DBB compl ex. (C) 1996 Wiley-Liss, Inc.