Glutamate Injection into the Suprachiasmatic Nucleus Stimulates Brown Fat Thermogenesis in the Rat

Injection of glutamate (100 mM to 1 M, in 0.25 micrograms saline) into the hypothalamic suprachiasmatic nucleus (SCN) dose-dependently increased interscapular brown adipose tissue (IBAT) and core temperatures in the urethane-anaesthetized rat. This effect was more pronounced in rats tested during the light-off period than in animals tested during the light-on period. Prior injection of the local anaesthetic, procaine (5% in 0.5 microliter saline), into the ipsilateral ventromedial hypothalamic nucleus (VMH) attenuated the increases in IBAT and core temperatures induced by intra-SCN glutamate. The VMH has previously been implicated in the central regulation of BAT thermogenesis; the present results suggest the pathway arising in the SCN exerts an excitatory influence on VMH neurons involved in the control of BAT function.