Expression of nerve growth factor (NGF) receptors in the brain and retina of chick embryos: comparison with cholinergic development.

The expression of nerve growth factor receptor (NGFR) transcripts was investigated with in situ hybridization techniques in the CNS of chick embryos from 3 days of incubation (E3) to 14 days posthatch (P14). The time course and distribution of NGFR expression was compared with the development of the cholinergic phenotype. Cholinergic properties were assessed by immunolabeling for choline acetyltransferase (ChAT) and histochemistry for acetylcholinesterase (AchE) activity. NGFR transcripts are expressed transiently in the inner plexiform layer and ganglion cell layer of the retina (E4-P1), neostriatum and hippocampus (E18), infundibular hypothalamus (E7-18), spiriform complex (E9-15), layers 2, 3 (E9-18), and 10 (E11-18) of the optic tectum, nucleus mesencephalicus profundus, pars ventralis (E9-18), parvicellular isthmic nucleus (E7-P1), magnocellular isthmic nucleus (E9-E18), nucleus semilunaris (E7-18), isthmo-optic nucleus (E7-P14), rostral motor nuclei (E5-18), developing cerebellum (E7-15), internal granule cell layer (E11-18) and Purkinje cell layer (E15-P14) of the cerebellar cortex, and the inferior olivary nucleus (E9-15). A small number of neuronal populations with embryonic expression of NGFR remain strongly NGFR-positive in the posthatch animal:habenular nuclei (labeled after E5), nucleus subrotundus (after E9), mesencephalic trigeminal nucleus (after E5), caudal parts of locus ceruleus and nucleus subceruleus (after E7), medullar reticular nuclei (after E11), and motor nuclei IX, X, and XII (after E9). The majority of neuronal populations with NGFR expression show cholinergic properties in development, and NGFR expression always precedes the onset of ChAT immunoreactivity. Postnatal expression of growth factor receptors is largely confined to neurons of the reticular type. NGFR expression in avian CNS nuclei differs from that in mammals. Early loss of NGFR expression in the cholinergic basal forebrain (which remains strongly NGFR positive in mammals) and persistent NGFR expression in parts of the avian locus ceruleus indicate changes of growth factor receptor expression and growth factor requirements in phylogeny. Knowledge of the time and distribution of NGFR expression in the chick embryo will facilitate the assessment of specific functions of NGF and NGF-like molecules in an embryonic model with easy access for experimental manipulations.(ABSTRACT TRUNCATED AT 400 WORDS)