Effects of excitatory amino acid lesions upon neurokinin B and acetylcholine neurons in the nucleus basalis of the rat.

The nucleus basalis magnocellularis (NBM) contains cholinergic neurons that project to the neocortex and is densely innervated by excitatory amino acid-containing terminals. A dysfunction in the balance of excitatory inputs or an alteration in the sensitivity of NBM cells to glutamate may underlie the selective vulnerability to aging. Some large NBM neurons contain neurokinin B (NKB) mRNA. The present study investigated whether alpha-2-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) or N-methyl-D-aspartate (NMDA) differentially destroy NKB-containing, NKB-receptive, or cholinergic NBM cells, and whether this vulnerability is altered by aging. Injections of AMPA or NMDA significantly decreased neocortical ChAT activity, as compared to control levels, across all three age groups, with no interaction between lesion and age group. The results of in situ hybridization histochemistry and NKB receptor studies suggest that NKB-containing neurons in the NBM, and the neurons they innervate, are not vulnerable to NMDA or AMPA in either young or old rats. While NKB mRNA-positive cells were diffusely distributed throughout the basal forebrain, only a small proportion of the large NBM cells contained NKB mRNA. The results suggest that NKB does not extensively colocalize with acetylcholine within the basal forebrain of rats and that NBM NKB neurons do not directly innervate cholinergic cells.