Oxidative Stress Contributes to Status Epilepticus Associated Mortality.

Status epilepticus is a common manifestation of nerve agent toxicity and represents a serious medical emergency with high rates of mortality and neurologic injury in those that survive. The aim of the current study was to determine if targeting oxidative stress with the catalytic antioxidant, AEOL10150, would reduce pilocarpine-induced mortality and attenuate neuronal death and neuroinflammation. We found that treatment with AEOL10150 in conjunction with scopolamine and diazepam following pilocarpine-induced SE was able to significantly reduce mortality compared to treatment with just scopolamine and diazepam. Mortality was further reduced when AEOL10150 was used in conjunction with atropine and diazepam which is considered the standard of care for nerve agent exposures. Both treatment paradigms offered significant protection against SE-induced oxidative stress. Additionally, treatment with scopolamine, AEOL10150 and diazepam attenuated SE-induced neuronal loss and neuroinflammation. Taken together, the data suggest that pharmacological targeting of oxidative stress can improve survival and attenuate secondary neurological damage following SE induced by the nerve agent surrogate pilocarpine.

Age-dependent differences in dopamine transporter and vesicular monoamine transporter-2 function and their implications for methamphetamine neurotoxicity.

The abuse of methamphetamine (METH) is a serious public health problem because METH can cause persistent dopaminergic deficits in the brains of both animal models and humans. Surprisingly, adolescent postnatal day (PND)40 rats are resistant to these METH-induced deficits, whereas young adult PND90 rats are not. Studies described in this report used rotating disk electrode voltammetry and western blotting techniques to investigate whether there are age-dependent differences in monoamine transporter function in PND38-42 and PND88-92 rats that could contribute to this phenomenon. The initial velocities of dopamine (DA) transport into, METH-induced DA efflux from, and DA transporter (DAT) immunoreactivity in striatal suspensions are greater in PND38-42 rats than in PND88-92 rats. DA transport velocities into vesicles that cofractionate with synaptosomal membranes after osmotic lysis are also greater in PND38-42 rats. However, there is no difference in vesicular monoamine transporter-2 (VMAT-2) immunoreactivity between the two age groups in this fraction. This suggests that younger rats have a greater capacity to sequester cytoplasmic DA into membrane-associated vesicles due to kinetically upregulated VMAT-2 and also have increased levels of functionally active DAT. In the presence of METH, these may provide additional routes of cellular efflux for DA that is released from vesicles into the cytoplasm and thereby prevent cytoplasmic DA concentrations in younger rats from rising to neurotoxic levels after drug administration. These findings provide novel insight into the age-dependent physiological regulation of neuronal DA sequestration and may advance the treatment of disorders involving abnormal DA disposition including substance abuse and Parkinson's disease.

Methylphenidate-induced increases in vesicular dopamine sequestration and dopamine release in the striatum: the role of muscarinic and dopamine D2 receptors.

Methylphenidate (MPD) administration alters the subcellular distribution of vesicular monoamine transporter-2 (VMAT-2)-containing vesicles in rat striatum. This report reveals previously undescribed pharmacological features of MPD by elucidating its receptor-mediated effects on VMAT-2-containing vesicles that cofractionate with synaptosomal membranes after osmotic lysis (referred to herein as membrane-associated vesicles) and on striatal dopamine (DA) release. MPD administration increased DA transport into, and decreased the VMAT-2 immunoreactivity of, the membrane-associated vesicle subcellular fraction. These effects were mimicked by the D2 receptor agonist quinpirole and blocked by the D2 receptor antagonist eticlopride. Both MPD and quinpirole increased vesicular DA content. However, MPD increased, whereas quinpirole decreased, K(+)-stimulated DA release from striatal suspensions. Like MPD, the muscarinic receptor agonist, oxotremorine, increased K(+)-stimulated DA release. Both eticlopride and the muscarinic receptor antagonist scopolamine blocked MPD-induced increases in K(+)-stimulated DA release, whereas the N-methyl-d-aspartate receptor antagonist (-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) was without effect. This suggests that D2 receptors mediate both the MPD-induced redistribution of vesicles away from synaptosomal membranes and the MPD-induced up-regulation of vesicles remaining at the membrane. This results in a redistribution of DA within the striatum from the cytoplasm into vesicles, leading to increased DA release. However, D2 receptor activation alone is not sufficient to mediate the MPD-induced increases in striatal DA release because muscarinic receptor activation is also required. These novel findings provide insight into the mechanism of action of MPD, regulation of DA sequestration/release, and treatment of disorders affecting DA disposition, including attention-deficit hyperactivity disorder, substance abuse, and Parkinson's disease.