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 agglutinin conjugated horseradish peroxidase (WGA-HRP). Injections of WGA-HRP centered in the medial septum (MS) and parts of the intermediate and ventrolateral subdivisions of the lateral septum retrogradely labeled only a few centrally scattered multipolar-shaped neurons. In contrast, injections placed in the nucleus of the diagonal band of Broca (DBB) 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 labeled neurons in restricted regions of the nucleus. A collection of small cells forming the ventricular border of caudal DLSN and a group of larger cells situated in the dorsolateral tip of rostral DLSN were consistently labeled following each DBB injection. The pattern of retrogradely 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 consisting almost entirely of projection neurons. The pattern of retrograde labeling in the lateral septum suggests that these projection neurons may be topographically organized since distinct subpopulations of cells were labeled following different injections in the MS/DBB complex.