Expression of c-Fos-like immunoreactivity in the feline brainstem in response to isometric muscle contraction and baroreceptor reflex changes in arterial pressure

This study compared whether activation of muscle ergoreceptor afferents cau sed by isometric muscle contraction, activation of baroreceptor afferents i nduced by i.v. infusion of phenylephrine, or baroreceptor afferent inactiva tion, caused by carotid artery occlusion, elicit similar patterns of c-Fos induction in brainstem areas. Adult cats were anesthetized with ol-chloralo se, and in each case, the experimental intervention caused an increase in t he arterial blood pressure. There were two sets of control experiments: in both, animals underwent the same surgical procedures but then either remain ed at rest for the entire study, or the tibial nerve was stimulated, as in the contraction group, following muscle paralysis with tubocurarine. Follow ing the procedures, animals rested for 90 min to allow neuronal expression of c-Fos. Control cats showed very little c-Fos immunoreactivity (c-Fos-ir) in the brainstem. Muscle contraction induced c-Fos-ir expression mainly in the nucleus tractus solitarius, lateral reticular nucleus, lateral tegment al field, vestibular nucleus, subretrofacial nucleus, spinal trigeminal tra ct and in a lateral region of the periaqueductal grey (P 0.5-1.0). The majo rity of the c-Fos-ir was found in brainstem areas contralateral to the cont racted muscle. In addition, muscle contraction induced c-Fos-ir in the dors al horns of spinal segments L-6-S-1 on the ipsilateral side of the spinal c ord. Phenylephrine infusion caused c-Fos-ir expression in the nucleus tract us solitarius, spinal trigeminal tract, solitary tract, and dorsal motor nu cleus of the vagus. No c-Fos-ir was apparent in the periaqueductal grey. Ca rotid occlusions induced c-Fos-ir expression in the area postrema, nucleus tractus solitarius, solitary tract, and spinal trigeminal tract. Expression was bilateral. Areas that exhibited c-Fos-ir correspond to sites previousl y reported to release various neuropeptides in response to muscle contracti on or carotid occlusions. These results indicate that the exercise presser reflex and baroreflex activate similar, but not completely identical, sites in the brainstem. (C) 2000 Elsevier Science B.V. All rights reserved.