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 hybridization. The large neuropeptide tyrosine (NPY)-expressing ganglion neurons (type I ganglion neurons) matured postnatally, with marked increases in acetylcholinesterase (AChE)-, neurofilament 10 (NF10)-, and tyrosine hydroxylase (TH)-like immunoreactivities (LIs) paralleled by increasing levels of mRNAs encoding NPY, low-affinity neurotrophin receptor (LANR), and tropomyosin kinase receptor (trk). The smaller vasoactive intestinal polypeptide (VIP)-immunoreactive (IR) ganglion neurons (type II ganglion neurons) expressed increasing levels of VIP mRNA postnatally and also contained immunoreactive nitric oxide synthase (NOS) and its mRNA. These type II ganglion neurons appeared to be relatively mature 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 ganglion neurons increased about 2.5-fold postnatally. The type I ganglion neurons formed more densely packed clusters with increasing age, whereas the type II ganglion neurons were spread out in small groups or individually, mainly in the peripheral parts of the medulla, and appeared to fulfill their migration into the medulla and/or to the inner regions of the cortex early postnatally, possibly after establishing contact with their cortical targets. We suggest that the type I ganglion neurons represent sympathetic ganglion neurons of the same origin as the chromaffin cells and that they mature mainly postnatally. The development of the type II (VIP/NOS) ganglion neurons takes place earlier; however, their phenotype remains more uncertain.