Potentiation of valproate-induced anticonvulsant response by nigella sativa seed constituents: the role of GABA receptors

ABSTRACT

This study investigated antiepileptic effects of the main constituents of Nigella sativa [NS] seed [i.e. aqueous extract [AE], fixed oil [FO], volatile oil [VO]] and the main components of its VO [i.e. thymoquinone, alpha-pinene and p-cymene] using pentylenetetrazole [PTZ] and maximal electroshock [MES]-induced convulsions. The potential of these constituents to induce minimal neurological deficit [MND] was also evaluated by using chimney test. Except for the FO, all of the NS seed constituents protected mice effectively against PTZ-induced convulsions. The activity of the VO in this model maybe attributed mainly to its content of thymoquinone and p-cymene and to a lesser extent, alpha-pinene. VO and its component p-cymene effectively suppressed convulsions induced by MES. The contents of p-cymene present in the effective dose of the VO maybe partially responsible for its anti-seizure effects. All of the NS seed constituents induced varying degrees of MND in the chimney test. MND induced by VO may pertain to its contents of thymoquinone [63%], p-cymene [23%] and alpha-pinene [<14%]. Protective indices of p-cymene and thymoquinone were closer to one, but only in PTZ model. Exploration on the role of receptors suggests that picrotoxin and bicuculline-sensitive GABA receptors, most probably GABAA receptors, mediate an increase in GABAergic response. In the part dealing with the interaction of valproate with thymoquinone, it can be mentioned that thymoquinone increased the potency of valproate in both PTZ and MES models