Inhibition of median preoptic area neurons inhibits brown adipose tissue sympathetic outflow

The rostral raphe pallidus (rRPa) contains sympathetic premotor neurons controlling brown adipose tissue (BAT) thermogenesis and energy expenditure that are excited during cold-defense responses to skin cooling. Cutaneous thermal cold afferent signals are transmitted via the dorsal horn and lateral parabrachial nucleus to provide a glutamatergic drive to median preoptic area (MnPO) neurons that mediate skin-cooling evoked increases in BAT sympathetic nerve activity (SNA) and BAT temperature. The present study sought to determine whether there is a level of tonic discharge in MnPO neurons that contributes to the excitability of BAT sympathetic premotor neurons in the rRPa. In chloralose/urethane-anesthetized, artificially-ventilated Wistar rats, nanoinjection of GABA (9 nmol in 30 nl) into the midline MnPO elicited a long-lasting reduction in the amplitudes of the BAT SNA and heart rate responses (a) to nanoinjections of NMDA into the rRPa and (b) to episodes of skin cooling. We conclude that the MnPO contains a population of neurons whose tonic discharge supports the excitability of BAT and cardiac sympathetic premotor neurons in rRPa. Supported by a grant from NINDS: NS040987(SFM).