Substance P immunoreactivity in the superior cervical ganglia of normotensive and genetically hypertensive rats.

Substance P-like immunoreactivity (SPI) was investigated in the superior cervical ganglion of normotensive and genetically hypertensive (GH) Otago Wistar rats aged 1, 2, 8-10 and 50-60 weeks, by used of an indirect immunoperoxidase method. SPI was not seen in neuronal cell bodies but a subpopulation of ganglion cells was supplied by SP-positive terminals which closely invested the cell surface. This subpopulation showed no particular topographical distribution. The number of SP-positive terminal varicosities per unit area was several times higher in GH rats than in normotensive rats at all ages over 2-60 weeks. The proportion of neurons supplied by SP-positive terminals (sampled in 8-10 week-old rats) was also greater in GH than in normotensive rats. Decentralization of the ganglion or chronic capsaicin treatment removed all SP-immunoreactive terminals around the cell bodies, indicating that the SP-positive terminals are collaterals of thoracic sensory afferents. As SP has been reported to have an excitatory effect in sympathetic ganglia, intraganglionic release of SP might contribute to the development of hypertension in the GH strain.