SUBSTANCE P LIKE IMMUNOREACTIVE NEURONS IN THE CHOLINERGIC CORTICAL PROJECTION NEURON AREAS OF THE BASAL FOREBRAIN IN THE CAT

The distribution of the substance P like immunoreactive (SP LI) neurons in the basal forebrain cholinergic corticopetal neuron areas in the cat was studied and compared with that of the choline acetyltransferase like immunoreactive (ChAT LI) neurons in the paired consecutive sections of the corresponding areas.A continuum of ChAT LI neurons were distributed in the medial septal nucleus (MS),nuclei of diagonal band,vertical and horizontal divisions (NDBV/H),nucleus basalis of Meynert (NBM),subcommissural ventral pallidum (sVP),and the areas of interstitial elements of Ch4,e.g.the internal capsule (ic) and nucleus of anterior commissure (Nac).The distribution of the SP LI neurons closely resembled that of the ChAT LI neurons with similar shape and size in the corresponding areas of the MS NDB NBM continuum.However,no perikarya in the paired surfaces of two adjacent sections could be really identified as bisected neurons being SP and ChAT LI respectively.The number of the SP LI neurons,compared with that of the ChAT LI neurons was more in MS,almost the same in NDBV/H,much less in NBM,and only a few in the interstitial elements of Ch4 areas and sVP.The results demonstrated that the majority of the SP LI neurons in the MS NDB NBM were mainly contained in the MS NDB and most of the SP LI neurons in the cholinergic neuron areas belonged to a subdivision with different chemical property.We suggested that the SPergic neurons in the MS NDB might be one of the main components,in addition to the cholinergic and GABAergic neurons,in the septohippocampal projection system and might play an important role in modulation of the memory functioning neocortex hippocampus neocortex circuit.