The distribution of neurons coexpressing immunoreactivity to AMPA-sensitive glutamate receptor subtypes (GluR1-4) and nerve growth factor receptor in the rat basal forebrain.

The regional distribution of neurons containing alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor (GluR1-4) subunit immunoreactivity, relative to the distribution of cholinergic neurons within the basal forebrain of rats, was assessed using single- and dual-antigen immunocytochemistry. Analysis of serial sections stained with antibodies to nerve growth factor receptor (NGFr) and antibodies against each of the AMPA receptor subunits, GluR1-4, revealed a regional codistribution between NGFr- and GluR1- and GluR4-immunoreactive neurons in the medial septum, diagonal band nuclei and nucleus basalis magnocellularis. Quantitative dual-labelling immunocytochemistry using NGFr in combination with each of the GluR antibodies revealed > 65% colocalization between NGFr and GluR4 in each of the major cholinergic nuclei in the basal forebrain and 10-15% colocalization between NGFr, GluR1 and GluR2-3. The reticular nucleus of the thalamus, a structure known to be highly susceptible to AMPA-induced neurotoxicity, expressed GluR4 immunoreactivity exclusively. The observation that cholinergic neurons of the basal forebrain are also highly sensitive to AMPA and express the GluR4 subunit suggests that GluR4 may be important in AMPA receptor-mediated excitotoxicity.