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In dopaminergic neurons, free radicals are likely produced via dopamine metabolism by monoamine oxidase or via its auto-oxidation, a process facilitated by transition metals. In this study we examined the effect and possible mechanisms of apomorphine to reduce iron- and dopamine-induced 2,3-dihydroxybenzoic acid (2,3-DHBA) formation by microdialysis. We have shown that (1) FeSO(4).7H(2)O reduced both the release of dopamine and the output of dihydroxyphenylacetic acid (DOPAC); (2) apomorphine may reduce FeSO(4).7H(2)O-induced increases of 2,3-DHBA formation; (3) apomorphine has substantially reduced DOPAC output in early phase and blocked dopamine-induced increase of 2,3-DHBA levels. It is concluded that apomorphine is a potent hydroxyl radical scavenger in vivo, especially for the dopamine formation.

The amplitude of the acoustic startle reflex is normally reduced when the startling stimulus is preceded by a weak click or "prepulse'. Prepulse inhibition (PPI) of acoustic startle has been used as an operational measure of sensorimotor gating or inhibition, and is reduced in schizophrenia patients and in rats with central dopamine (DA) activation. The DA agonist-induced disruption of PPI in rats may thus offer a useful animal model to study impaired sensorimotor gating in schizophrenia. We have previously reported that DA-glutamate interactions in the nucleus accumbens (NAC) regulate PPI. The NAC has at least two major subregions-the core and shell-that have distinct anatomical and neurochemical properties. In this study, we compared changes in PPI after manipulations of DA-glutamate activity in these two NAC subregions. Consistent with previous findings, infusion of the non-NMDA agonist AMPA into the NAC core subregion significantly reduced PPI, and this effect was opposed by systemic administration of the D2 antagonist haloperidol. Also consistent with previous reports, infusion of the non-NMDA antagonist CNQX into the NAC core subregion did not alter PPI, but its co-infusion with D-amphetamine (AMPH) attenuated the AMPH-disruption of PPI. In contrast, while PPI was reduced after AMPA infusion into the NAC shell subregion, this effect of AMPA could not be blocked by pretreatment with haloperidol. Infusion of either AMPH or CNQX into the NAC shell subregion reduced PPI independently. The PPI-disruptive effects of intra-shell CNQX infusion were not blocked by haloperidol. The present results suggest striking differences between the NAC core and shell subregions in their neurochemical modulation of sensorimotor gating of acoustic startle in the rat.