Non-cholinergic effects of paraoxon on [3h]-GABA release from rat cerebellar giant synaptosomes

Diethyl p-nitrophenyl phosphate (paraoxon) is the active toxic metabolite of parathion. Some evidences indicate that OPs affect the GABA system via noncholinergic mechanisms. The purpose of this study was to investigate the effects of paraoxon on K+-evoked [3H]-GABA release from cerebellar synaptosomes. Adult male rats (200 ± 30 g; 3-4 months old) were sacrificed by decapitation and the cerebellum was removed immediately and homogenized. Homogenate was centrifuged twice at 1000 × g for 5 min (all in 0-4 ?C). Synaptosomes were incubated with [3H]-GABA (S.A 99 Ci/mmol, 0.1 µm). Then, aliquots of the synaptosomal suspension were layered on microporous filters at the bottom of superfusion chambers (14900 Superfusion System, Raiteri,s Method, UGO BASILE, Italy). Following 34 minutes of superfusion (time required to equilibrate the system, t = 0), fractions were collected every minute and the radioactivity in the different samples was quantified by liquid-scintillation counting. At t = 8 (s1) and t = 28 (s2), synaptosomes were depolarized with KCl (30 mM). Paraoxon was added to the superfusion medium concomitantly with the second stimulus (s2) and the ratio of s2 /s1 release was compared between the control and test groups. Present data indicate that paraoxon increases spontaneous and K+-evoked [3H]-GABA release from rat cerebellar giant synaptosomes, possibly via noncholinergic mechanisms.