TRANSIENT AND PERMANENT PATTERNS OF EXPRESSION OF THE LOW-AFFINITY NEUROTROPHIN RECEPTOR IN THE INTERPEDUNCULAR NUCLEUS OF THE RAT

There is a prominent cholinergic projection from the medial habenular to the interpeduncular nucleus (IPN) which develops postnatally. In th is study we examined the developmental course of expression of the low -affinity neurotrophin receptor (LANR), a receptor that binds to all m embers of the neurotrophin family, in the IPN. Three systems express L ANR in the IPN. The cholinergic habenular axons that project to the in termediate and central subnuclei of the IPN are immunoreactive only du ring the time that the axons are growing and forming characteristic cr est synapses in the intermediate subnuclei. The dorsomedial (DM) subnu clei, which are neither cholinergic targets nor contain cholinergic ne urons, develop LANR immunoreactivity postnatally and the expression re mains high in the adult. The walls of the prominent system of arteriol es and venules that penetrate the IPN and ascend through the intermedi ate subnuclei are strongly immunoreactivity during the time of active angiogenesis and retain detectable but diminished levels of immunoreac tivity in the adult. The LANR immunoreactivity seen in the vessels is likely to be associated with the peripheral sympathetic axons that inn ervate the smooth muscle in the vessels. These three systems within th e same nucleus, which differ in phenotype, develop neurotrophin recept or immunoreactivity contemporaneously but their levels of expression d iffer in the adult, suggesting that they are regulated in different wa ys, possibly by different members of the neurotrophin family. (C) 1994 Academic Press, Inc.