VASOCONSTRICTION INDUCED BY INHALATION OF IRRITANT VAPOR IS ASSOCIATED WITH APPEARANCE OF FOS PROTEIN IN C1 CATECHOLAMINE NEURONS IN RABBIT MEDULLA-OBLONGATA

The medulla oblongata was examined with Fos and tyrosine hydroxylase (TH) immunohistochemistry after 2 h of intermittent nasopharyngeal stimulation with formaldehyde vapour in the conscious rabbit. The stimulation caused apnoea, bradycardia and a rise in blood pressure known to be associated with vigorous vasocontriction. Fos-positive neurons occurred in the spinal trigeminal nucleus, the nucleus tractus solitarius, the raphe nuclei and the ventrolateral medulla. In the rostral ventolateral medulla, 68% of the Fos-positive neurons were TH-positive C1 cells. Our data indicate that nasopharyngeally-evoked peripheral vasoconstriction is associated with activation of C1 neurons.