Malonate-induced degeneration of basal forebrain cholinergic neurons: attenuation by lamotrigine, MK-801, and 7-nitroindazole.

Abstract

Previously, we have reported that intranigral infusions of malonate, an inhibitor of mitochondrial function, lead to the degeneration of the dopaminergic neurons of the nigrostriatal pathway that is mediated, at least in part, through NMDA receptor activation and nitric oxide formation. In the present study, unilateral focal infusions of malonate into the nucleus basalis magnocellularis (nbM) of male Sprague-Dawley rats (weighing 250-300 g) resulted in a dose-related depletion in ipsilateral cortical and amygdaloid choline acetyltransferase (ChAT) activity. Infusion of a 3 mumol dose of malonate into the nbM of vehicle-treated animals resulted in a 41 and 54% decrease in cortical and amygdaloid ChAT activity, respectively. Systemic pretreatment with lamotrigine (16 mg/kg, i.p.) and MK-801 (5 mg/kg, i.p.) attenuated the depletions in cortical and amygdaloid ChAT activity that resulted from an infusion of this dose of malonate into the nbM. Acetylcholinesterase (AChE) histochemistry of the nbM following focal infusion of malonate (3 mumol) showed a marked decrease in the number of AChE-positive neurons that was partially prevented by MK-801 pretreatment. Before examining the role of nitric oxide formation in malonate-induced toxicity, the ability of systemic administration of N omega-nitro-L-arginine (L-NA) to inhibit nitric oxide synthase (NOS) activity in the nbM and cerebellum was investigated. L-NA (2, 10, and 20 mg/kg, i.p.) produced a dose-related inhibition of nbM and cerebellar NOS activity that was maximal following a dose of 10 mg/kg L-NA. This level of NOS inhibition persisted for at least 13 h following L-NA (10 mg/kg) administration. Subsequently, the effect of L-NA pretreatment on malonate toxicity was evaluated. Following pretreatment with L-NA (2 and 10 mg/kg, i.p.), the toxic action of malonate on cortical and amygdaloid ChAT activity was not altered. In addition, infusion of a lower dose of malonate (2 mumol) into the nbM resulted in decreases in cortical and amygdaloid ChAT activity that were not altered by pretreatment with L-NA (2 and 10 mg/kg, i.p.). In 7-nitroindazole (7-NI; 25 and 50 mg/kg, i.p.)-pretreated animals, malonate (3 mumol) produced decreases in cortical and amygdaloid ChAT activity that were attenuated by both doses of 7-NI. Thus, malonate-induced destruction of the basal forebrain cholinergic neurons was attenuated by systemic pretreatment with lamotrigine, MK-801, and 7-NI but not by L-NA.