C-fos expression in vasopressin and oxytocin neurons of hypothalamus induced by static muscle contraction

Static muscle contraction reflexly Increases blood pressure and heart rate in anesthetized cats. Vasopressin (AVP) and oxytocln (OT) have been Implicated as neuromodulators that play a role In cardiovascular regulation. The activity of AVP and OT are regulated by the paraventricular nucleus (PVN) and supraoptlc nucleus (SON) of the hypothalamus. We tested the hypothesis that neurons containing AVP and OT In the PVN were activated during static muscle contraction. We stimulated the L7 and S1 ventral roots of the spinal cord to Induce muscle contraction. Hypothalamlc neurons activated during the muscle contraction were Identified by Fos-llke ImmunoreactMty (FLJ). Static muscle contraction Increased FU In PVN and SON, (mean number of FU Increased 74% and 65%, respectively) compared with sham-operated cats. Double staining of neurons in the PVN for AVP and OT revealed that 14% AVP neurons and 23% OT neurons were labeled with FU. In contrast, only 3% AVP and 4% OT neurons In the PVN expressed FU in sham-operated animals. These results Indicate that neurons In the PVN and SON of hypothalamus were activated during the static muscle contraction. Furthermore, as FU was present in AVP and OT neurons this suggests these neurons may constitute part of neural pathway involved in the cardiovascular regulation during static muscle contraction. (Supported by NIH HL-06296).