AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 3 636-R644, Copyright © 1996 by American Physiological Society
Central trigeminal effects of somatostatin and etorphine on adrenal and autonomic function in the cat
D. A. Bereiter, A. P. Benetti, D. F. Bereiter and C. B. Hathaway
Department of Neuroscience, Brown University/Rhode Island Hospital, Providence 02903, USA.
The influence of somatostatin and the potent mu-opiate receptor agonist
etorphine on adrenal and autonomic responses mediated by trigeminal neurons
was examined in chloralose-anesthetized cats. Microinjections of
somatostatin (100 pmol) into laminae I-II of trigeminal subnucleus caudalis
(Vc) evoked increases in the adrenal secretion of catecholamines and
adrenal blood flow without affecting arterial pressure, heart rate, or
plasma adrenocorticotropic hormone. Injections of somatostatin into laminae
III-IV of Vc had no effect. Microinjections of etorphine (500 pmol) into
laminae I-II of Vc had no effect, whereas injections into laminae III-IV
caused small increases in total adrenal blood flow and peripheral
concentrations of norepinephrine. To assess local effects of these drugs on
peripheral trigeminal nociceptor-evoked autonomic responses, corneal
stimulation was presented before and after topical application of
somatostatin or etorphine on the dorsal brain stem surface. Somatostatin
did not affect the adrenal and autonomic responses evoked by noxious
thermal or chemical irritant stimulation of the cornea. Topical etorphine
blocked completely the increase in adrenal blood flow, arterial pressure,
and heart rate after noxious thermal stimulation of the cornea. These
results suggest that somatostatin and mu-opiate receptor agonists act by
different mechanisms at the level of the spinal trigeminal complex to
affect adrenal and autonomic function.
