IDENTIFICATION OF HYPOTHALAMIC VASOPRESSIN AND OXYTOCIN NEURONS ACTIVATED DURING THE EXERCISE PRESSOR REFLEX IN CATS

Blood pressure and heart rate reflexly increase during static muscle c ontraction in anesthetized cats. Previous studies have demonstrated th at vasopressin (AVP) and oxytocin (OT) may act as neuromodulators to r egulate cardiovascular responses elicited by contraction of skeletal m uscle. In this study, we tested the hypothesis that neurons containing AVP and OT in the paraventricular nucleus (PVN) and the supraoptic nu cleus (SON) of the hypothalamus are activated during static muscle con traction. A laminectomy was performed to expose the spinal cord and th e peripheral cut ends of L7 and S1 ventral roots were stimulated elect rically to induce muscle contraction. Hypothalamic neurons activated d uring the muscle contraction were identified by Fos-like immunoreactiv ity (FLI). Static muscle contraction significantly increased FLI in th e PVN and SON, compared with sham-operated cats. Double-staining of ne urons in the PVN for AVP and OT showed that 22 +/- 4% of the AVP and 2 6 +/- 3% of the OT neurons in the PVN expressed FLI. in contrast, only 4 +/- 1% of the AVP and 3 +/- 1% of the OT neurons in the PVN were la beled with FLI in sham-operated animals. These results indicate that n eurons in the PVN and SON of the hypothalamus were activated during st atic muscle contraction. Furthermore, as FLI was present in AVP and OT neurons, this suggests these neurons may constitute a part of the neu ral pathway involved in cardiovascular regulation during static muscle contraction. (C) 1997 Elsevier Science B.V.