Plasticity in the phenotypic expression of catecholamines and vasoactive intestinal peptide in adult rat superior cervical and stellate ganglia after long-term hypoxia in vivo

Sympathetic ganglia in the adult rat contain various populations of nerve cells which demonstrate plasticity with respect to their transmitter phenotype. The plasticity of the neuronal cell bodies and of the small intensely fluorescent cells in the superior cervical and stellate ganglia in response to hypoxia in vivo (10% O 2 for seven days) was assessed by studying the expression of catecholamines and vasoactive intestinal peptide. The levels of norepinephrine, dopamine, 3,4-dihydroxyphenylacetic acid and vasoactive intestinal peptide immunoreactivity were determined. In addition, the density of the immunohistochemical staining of cells for tyrosine hydroxylase and vasoactive intestinal peptide was evaluated. In the intact superior cervical ganglion, hypoxia increased the dopamine level as well as the density of small intensely fluorescent cells immunolabelled for tyrosine hydroxylase and vasoactive intestinal peptide. In the axotomized ganglion, hypoxia elicited a twofold rise in the level of the vasoactive intestinal peptide as well as enhancing the density of neuronal cell bodies immunostained for this peptide. Thus, the effect of hypoxia on the expression of vasoactive intestinal peptide expression in neurons was dependent on neural interactions. In the intact stellate ganglion, hypoxia alone induced a 1.5-fold increase in the density of neuronal cell bodies immunostained for vasoactive intestinal peptide. Thus, ganglia-specific factors appeared to play a role in determining changes in neuronal phenotype in response to hypoxia. The present study provides evidence for the involvement of dopamine and vasoactive intestinal peptide in ganglionic responses to long-term hypoxia as well as for differential responses by the two ganglionic cell populations, i.e. neuronal cell bodies and small intensely fluorescent cells. Changes in the expression of the vasoactive intestinal peptide during long-term hypoxia may be of energetic, trophic and/or synaptic significance. Hypoxia may be considered to be a vasoactive intestinal peptide-inducing factor in sympathetic ganglia.