Accumulating evidence suggests that
insulin acts within the hypothalamus to alter sympathetic nerve activity (SNA) and baroreflex function. Although
insulin receptors are widely expressed across the hypothalamus, recent evidence suggests that neurons of the arcuate nucleus (
ARC) play an important role in the sympathoexcitatory response to
insulin. The purpose of the present study was to determine whether circulating
insulin acts directly in the
ARC to elevate SNA. In anesthetized male Sprague-Dawley rats (275-425 g), the action of
insulin was neutralized by microinjection of an anti-
insulin affibody (1 ng/40 nl). To verify the efficacy of the affibody,
ARC pretreatment with injection of the anti-
insulin affibody completely prevented the increase in lumbar SNA produced by
ARC injection of
insulin. Next,
ARC pretreatment with the anti-
insulin affibody attenuated the lumbar sympathoexcitatory response to intracerebroventricular injection of
insulin. Third, a hyperinsulinemic-euglycemic clamp increased lumbar, but not renal, SNA in animals that received
ARC injection of a control affibody. However, this sympathoexcitatory response was absent in animals pretreated with the anti-
insulin affibody in the
ARC. Injection of the anti-
insulin affibody in the adjacent ventromedial hypothalamus did not alter the sympathoexcitatory response to
insulin. The ability of the anti-
insulin affibody to prevent the sympathetic effects of
insulin cannot be attributed to a general inactivation or nonspecific effect on
ARC neurons as the affibody did not alter the sympathoexcitatory response to
ARC disinhibition by
gabazine. Collectively, these findings suggest that circulating
insulin acts within the
ARC to increase SNA.