Intra-ventrolateral preoptic nucleus injection of γ-aminobutyric acid induces sedation in rats

The ventrolateral preoptic nucleus (VLPO) plays a critical role in regulating and maintaining sleep-awake cycle. It receives both excitatory and inhibitory inputs and regulates the activity of tuberomamillary nucleus and other monoaminergic nuclei, which in turn determines the alternation between wakefulness and non-rapid eye movement sleep. Although a previous study has shown that systematic administration of GABAergic anesthetic agents activated VLPO neurons, which is believed to be responsible for the sedative effects of these agents, it is unknown whether a direct administration of γ-Aminobutyric acid (GABA) into the VLPO can induce sedation. Here we report that rats that received intra-VLPO infusion of GABA demonstrated sustained reduction in locomotion, most significantly during the 10-40th min period after infusion. Conversely, rats that received intra-VLPO infusion of noradrenaline demonstrated a sustained increase in locomotion from 20 ^th min after infusion. By contrast, no appreciable change was observed in rats that received intra-VLPO infusion of glycine. This result demonstrates that exogenous GABA may activate sleepactive neurons in the VLPO and promote sedation.