New insights on the effects of Withania somnifera on the motivational properties of addictive drugs

Introduction: Withania somnifera Dunal, known as Ashwagandha or Indian ginseng, has long been used in Ayurvedic medicine for its anti-inflammatory and immunomodulatory properties. Recent studies demonstrated its neuroprotective effects in experimental models of neurodegenerative disorders, including Parkinson disease and the standardized methanolic extract of Withania somnifera Dunal roots (WSE) has been shown to interact with some of the psychopharmacological effects of morphine and ethanol. In particular, WSE prevents the acquisition and expression of morphine-elicited conditioned place preference (CPP) and, in mice chronically treated with morphine, could prevent the development of tolerance and dependence. In addition, chronic administration of WSE during chronic treatment with morphine could prevent the drastic reduction of dendritic spine density in the rat nucleus accumbens (NAc) shell upon spontaneous and naloxone-precipitated withdrawal. Moreover, WSE may also reduce ethanol withdrawal-induced anxiety, potentiate ethanol-induced anxiolysis and impair acquisition and maintenance of ethanol self-administration under both fixed and progressive ratios and acquisition and expression of ethanol-elicited CPP. Morphine and ethanol increase dopamine (DA) transmission and elicit Extracellular signal Regulated Kinase phosphorylation (pERK) in the NAc, effects that have been suggested as neurochemical and molecular measures of their addictive properties. The aim of the present research was to characterize the effects of WSE on morphine- (5 mg/kg) and ethanol- (1 g/kg) and elicited DA transmission in the NAc shell of male Sprague-Dawley (SD) rats as well as on those of morphine (10 mg/kg)- and ethanol (2 g/kg) elicited ERK phosphorylation in the NAc shell and core of CD-1 mice. Methods: DA transmission in the NAc shell of SD rats (280-320 g) was monitored by in vivo brain microdialysis technique; standard pERK immunodetection assay was applied to 40 µm-thick sections of mice forebrain (NAc). Results: WSE (75 mg/kg) administration significantly reduces morphine (5 mg/kg)- and completely blocks ethanol (1 g/kg)-elicited increases of DA transmission in the NAc shell. Furthermore WSE administration (50 mg/kg) significantly reduces morphine (10 mg/kg)- and ethanol (2 g/kg)-elicited ERK-phosphorylation in the NAc shell and NAc core. Conclusions: The observation that WSE significantly affects the increases of DA transmission in the NAc shell of SD rats induced by morphine and ethanol confirms the ability of WSE to interfere with their central effects and suggests a possible mechanism by which WSE impairs morphine and ethanol motivational properties. This interpretation is further supported by the observation that WSE also significantly affects morphine- and ethanol-elicited ERK-phosphorylation in the same area. Taken together these results point to Withania somnifera as an interesting plant for further studies aimed at characterizing its potential application for prevention and/or treatment of drug dependence.