SYMPATHETIC AND RESPIRATORY CONTROL BY HYPOTHALAMIC PERIFORNICAL AREA: ROLE OF HYPOCRETIN NEURONS

Abstract

Hypocretin (orexin) neurons within the hypothalamic perifornical area (PeF) are believed to contribute to the cardiorespiratory responses associated with stress or arousal. In this study we first showed that microinjections of bicuculline into the PeF of urethane-anesthetised rats evoked increases in renal sympathetic nerve activity and phrenic nerve activity burst rate that were significantly greater than the increases in these variables evoked from regions dorsal, ventral and lateral to the PeF. Systemic administration of almorexant (a hypocretin receptor antagonist) significantly reduced the increases in these variables evoked by bicuculline microinjection into the PeF, but had little effect on the sympathetic and respiratory response to stimulation of peripheral chemoreceptors. The results indicate that blockade of central hypocretin receptors powerfully inhibit the respiratory and sympathetic response evoked by activation of PeF neurons.