EFFECT OF INTRACEREBROVENTRICULAR AND INTRAVENOUS INSULIN ON FOS-IMMUNOREACTIVITY IN THE RAT-BRAIN

The potential central neural substrate for the sympathoexcitatory effe ct of insulin was investigated in conscious rats using Fos expression as an index of neural activity. Fos immunoreactivity in the hypothalam us and brainstem was compared in rats infused with intracerebroventric ular (i.c.v.) insulin or saline for 60 min. The insulin had no effect on Fos expression in any brain nuclei. Likewise, a 90-min intravenous infusion of insulin (euglycemic) had no effect on brain Fos immunoreac tivity. However, when blood glucose was allowed to decrease, Fos expre ssion did increase in the arcuate nucleus and in the brainstem. These data do not provide any evidence to support the idea that insulin can act within the central nervous system to increase sympathetic nervous outflow. (C) 1997 Elsevier Science Ireland Ltd.