NHBA isolated from Gastrodia elata exerts sedative and hypnotic effects in sodium pentobarbital-treated mice

The rhizomes of Gastrodia elata have been used for the treatment of insomnia in oriental countries. N⁶-(4-hydroxybenzyl) adenine riboside (NHBA) was originally isolated from G. elata. For the first time we report a detailed study on the effects and mechanisms of NHBA on its sedative and hypnotic activity. Adenosine, an endogenous sleep factor, regulates sleep-wake cycle via interacting with adenosine A₁/A(2A) receptors. Using radioligand binding studies and cAMP accumulation assays, our results show that NHBA may be a functional ligand for the adenosine A₁ and A(2A) receptors. NHBA significantly decreases spontaneous locomotor activity and potentiates the hypnotic effect of sodium pentobarbital in mice. Sleep architecture analyses reveal that NHBA significantly decreases wakefulness time and increases NREM sleep times. However, NHBA does not affect the amount of REM sleep. Pretreatment with the adenosine A₁ receptor antagonist DPCPX or the A(2A) receptor antagonist SCH 58261 significantly reverses the increase in sleeping time induced by NHBA in sodium pentobarbital treated mice. Immunohistochemical studies show that NHBA increases c-Fos expression in GABAergic neurons of the ventrolateral preoptic area (VLPO), which suggests that NHBA activates the sleep center in the anterior hypothalamus. Altogether, these results indicate that NHBA produces significant sedative and hypnotic effects. Such effects might be mediated by the activation of adenosine A₁/A(2A) receptors and stimulation of the sleep center VLPO.