TARGET-INDEPENDENT CHOLINERGIC DIFFERENTIATION IN THE RAT SYMPATHETICNERVOUS-SYSTEM

Chemical coding in the sympathetic nervous system involves both noradr energic and, for a minority of neurons, cholinergic neurotransmission. The expression of the cholinergic phenotype in the developing sympath etic nervous system was examined to determine if coding for cholinergi c transmission occurs before or after innervation of peripheral target organs. The vesicular acetylcholine transporter (VAChT) and choline a cetyltransferase, the products of the ''cholinergic gene locus'' deter mining the cholinergic phenotype, were expressed in principal cells of the paravertebral, but only rarely in prevertebral, sympathetic chain s as early as embryonic day 14. A subpopulation of VAChT- and choline acetyltransferase-positive sympathetic ganglion cells persisted throug hout development of the stellate and more caudal paravertebral ganglia into anatomically distinct cell groups, and into adulthood. The forep aw eccrine sweat glands, innervated exclusively by the stellate gangli on, received VAChT-positive nerve terminals at least as early as poste mbryonic day 4, coincident with the development of the sweat glands th emselves. These terminals, like the VAChT-positive cell bodies of the developing stellate ganglion, have some noradrenergic traits including expression of tyrosine hydroxylase, but did not express the vesicular monoamine transporter, and are therefore not functionally noradrenerg ic. Development of the cholinergic phenotype in principal cells of the sympathetic paravertebral ganglia apparently occurs via receipt of in structive cues, or selection, within the sympathetic chain itself or p erhaps even during migration of the cells of the neural crest from whi ch the paravertebral ganglia arise.