PHENOTYPE OF INTRAADRENAL GANGLION NEURONS DURING POSTNATAL-DEVELOPMENT IN RAT

The postnatal development of intraadrenal ganglion neurons was studied in rat by using indirect immunohistochemistry and in situ hybridizati on. The large neuropeptide tyrosine (NPY)-expressing ganglion neurons (type I ganglion neurons) matured postnatally, with marked increases i n acetylcholinesterase (AChE)-, neurofilament 10 (NF10)-, and tyrosine hydroxylase (TH)-like immunoreactivities (LIs) paralleled by increasi ng levels of mRNAs encoding NPY, low-affinity neurotrophin receptor (L ANR), and tropomyosin kinase receptor (trk). The smaller vasoactive in testinal polypeptide (VIP)-immunoreactive (IR) ganglion neurons (type II ganglion neurons) expressed increasing levels of VIP mRNA postnatal ly and also contained immunoreactive nitric oxide synthase (NOS) and i ts mRNA. These type II ganglion neurons appeared to be relatively matu re already at postnatal day (P2) and did not express detectable levels of LANR or trk mRNAs. The cell size of both the type I and type II ga nglion neurons increased about 2.5-fold postnatally. The type I gangli on neurons formed more densely packed clusters with increasing age, wh ereas the type II ganglion neurons were spread out in small groups or individually, mainly in the peripheral parts of the medulla, and appea red to fulfill their migration into the medulla and/or to the inner re gions of the cortex early postnatally, possibly after establishing con tact with their cortical targets. We suggest that the type I ganglion neurons represent sympathetic ganglion neurons of the same origin as t he chromaffin cells and that they mature mainly postnatally. The devel opment of the type II (VIP/NOS) ganglion neurons takes place earlier; however, their phenotype remains more uncertain. (C) 1996 Wiley-Liss, Inc.