FOS-LIKE IMMUNOREACTIVITY (FLI) IN THE MEDULLA OF CATS INDUCED BY STATIC MUSCLE CONTRACTION 1051

Abstract

Induced static muscle contraction reflexly increases both blood pressure and heart rate. A number of sites in the medulla have been implicated for the complete expression of this pressor response. In order to identify which sites may be involved in the cardiovascular responses to static muscle contraction, we stimulated the L7 and S1 ventral roots in anesthesized cats and measured FLI in multiple regions within the medulla. The results show a distinct distribution of FLI in the following areas: lateral reticular nucleus, lateral tegmental field, nucleus of solitary tract, A1 region, vestibular nucleus, and subretrofacial nucleus (SRF). Numbers of FLI labeling neurons induced by static muscle contraction increased 65%, 46%, 63%, 67%, 47% and 67%, respectively, when compared with the same stereotaxic level of those areas in control animals (no electrical stimulation delivered to the ventral roots, p<0.05 in each region). Double labeling showed that 66% of the neurons which stained with phenylethanolamine-N-methyltransferase (PNMT) in the SRF also were labeled with FLI. By contrast, only 24% PNMT neurons in the SRF were FLI positive in control animals (p<0.01). No distinct FLI double labeling with PNMT was observed in the other areas of the medulla. The results support the hypothesis that the ventrolateral medulla is an important region of integration for the cardiovascular responses induced during static muscle contraction. Further, adrenergic neurons in the SRF are likely involved in these responses.