The paraventricular nucleus of the hypothalamus (PVH) plays an important role in energy homeostasis, regulating neuroendocrine, behavioral and autonomic functions. However, the role of the PVH in regulating thermogenesis and energy expenditure in brown adipose tissue (BAT) is unclear. The present study investigated the effect of activating neurons within the PVH on BAT thermogenesis. In urethane-chloralose anesthetized, artificially ventilated rats maintained at a core body temperature of 37.0 -38.0 °C, microinjection of N-methyl-D-aspartate (NMDA, 12 pmol in 60nl) into the PVH did not increase BAT sympathetic nerve activity (SNA) or BAT thermogenesis. In contrast, the increase in BAT SNA evoked by body cooling was completely reversed by microinjection of NMDA into the PVH. Additionally, the increases in BAT SNA evoked by body cooling, by microinjection of prostaglandin E₂ (170 pmol in 60nl) into the medial preoptic area or by microinjection of bicuculline (30 pmol in 60nl) into the dorsomedial hypothalamus were completely reversed by microinjection of bicuculline (30 pmol in 60nl) into the PVH. Although the increases in BAT SNA and thermogenesis evoked by microinjection of NMDA (12 pmol in 60nl) into the raphe pallidus (RPa) was markedly attenuated following microinjection of bicuculline (30 pmol) into the PVH, the increases in BAT SNA and thermogenesis evoked by microinjection of bicuculline (30 pmol in 60nl) into the RPa was unaffected by microinjection of bicuculline into the PVH. These results demonstrate that disinhibition of neurons in the PVH inhibits BAT SNA likely via activation of a GABAergic input to BAT sympathetic premotor neurons in the RPa.