Activation of lateral hypothalamic neurons stimulates brown adipose tissue thermogenesis

The lateral hypothalamic area, containing orexin neurons, is involved in several aspects of autonomic regulation, including thermoregulation and energy expenditure. To determine if activation of lateral hypothalamic area neurons influences sympathetically-regulated thermogenesis in brown adipose tissue, we microinjected bicuculline (120pmol, 60nl, unilateral) into the lateral hypothalamic area in urethane/chloralose-anesthetized, artificially-ventilated rats. Disinhibition of neurons in lateral hypothalamic area evoked a significant increase (+1309%) in brown adipose tissue sympathetic nerve activity accompanied by parallel increases in brown adipose tissue temperature (+2.0°C), in expired CO₂ (+0.6%), in heart rate (+88 bpm) and in mean arterial pressure (+11 mm Hg). Subsequent microinjections of glycine (30nmol, 60nl) to inhibit local neurons in raphe pallidus or in dorsomedial hypothalamus or of glutamate receptor antagonists into dorsomedial hypothalamus promptly reversed the increases in brown adipose tissue sympathetic nerve activity, brown adipose tissue temperature and heart rate evoked by disinhibition of neurons in lateral hypothalamic area. We conclude that neurons in the lateral hypothalamic area can influence brown adipose tissue sympathetic nerve activity, brown adipose tissue thermogenesis and heart rate through pathways that are dependent on the activation of neurons in dorsomedial hypothalamus and raphe pallidus.