The central efferent mechanism of brown adipose tissue thermogenesis induced by preoptic cooling

Abstract

This study was performed to investigate central efferent mechanisms for brown adipose tissue thermogenesis. In unanesthetized rats, the effects of local anesthesia of the ventromedial hypothalamus, anterior hypothalamus, and lateral hypothalamus were observed on the brown adipose tissue thermogenesis induced by preoptic cooling. Rats had a thermode, thermocouple, and bilateral injection cannulae chronically implanted in the hypothalamus and a thermocouple beneath the interscapular brown adipose tissue. The experiments were done at an ambient temperature of 24–25 °C. Preoptic cooling increased brown adipose tissue and colonic temperatures without shivering. Injecting lidocaine bilaterally into the ventromedial hypothalamus during preoptic cooling reduced brown adipose tissue temperature (T_bat). The mean maximum decrease of T_bat was 0.51 ± 0.26 °C and occurred 5–8 min after lidocaine injection. When lidocaine was injected into the anterior hypothalamus, T_bat increased. The mean maximum increase of T_bat was 0.85 ± 0.29 °C and occurred 4–9 min after lidocaine injection. In the lateral hypothalamus, lidocaine had no effect on T_bat∙T_bat was not influenced by injection of saline into the ventromedial, anterior, or lateral hypothalamus. The efferent pathway from preoptic to brown adipose tissue may thus traverse the medial part of hypothalamus. The ventromedial hypothalamus facilititates and anterior hypothalamus inhibits brown adipose tissue thermogenesis induced by preoptic cooling.