TRK-IMMUNOREACTIVITY IN THE MONKEY CENTRAL-NERVOUS-SYSTEM - FOREBRAIN

Neurotrophins such as nerve growth factor (NGF) mediate their effects through interactions with high-affinity tropomycin-related kinase (trk ) receptors. The present study employed a polyclonal antibody to chara cterize the distribution of trk-immunoreactive neurons within the nonh uman primate brain. Both young adult and aged cebus and rhesus monkeys displayed trk-immunoreactive neurons within all subdivisions of the b asal forebrain. Colocalization studies revealed that between 66% and 7 6% of trk-immunoreactive basal forebrain neurons also expressed immuno reactivity for the low-affinity p75 NGF receptor, an excellent marker for cholinergic basal forebrain cells. In this experiment, most single -labeled basal forebrain neurons contained only trk immunoreactivity, whereas 4% of basal;forebrain neurons expressed only the low-affinity p75 NGF receptor. Scattered trk-immunoreactive neurons also were obser ved within the caudate nucleus and putamen. Although dual-localization studies with choline acetyltransferase (ChAT) were not performed, str iatal neurons codistributed with ChAT-immunoreactive cells, and both t ypes of cells were similar in size and morphology. This suggests that trk immunoreactivity is expressed within cholinergic interneurons with in the primate striatum. Finally, lightly stained trk-immunoreactive n eurons were observed within the stratum oriens of the hippocampal form ation and within the hypothalamus. These data indicate that both choli nergic and, possibly, noncholinergic forebrain neurons express the pro tein for the high-affinity trk. receptor, which transduces the signal mediating the trophic effects of neurotrophins. In addition, the patte rn of trk immunoreactivity was preserved in two aged (26 and 29 years old) rhesus monkeys, suggesting that the expression of trk, for the mo st part, is sustained throughout the lifetime of the organism. (C) 199 4 Wiley-Liss, Inc.