Endogenous oxidized indoles share inhibitory potency against [3H]isatin binding in rat brain

Ability to delay neuropathological events associated with astrocytic MAO-B increase in a Parkinsonian mouse model: implications for early intervention on disease progression

We previously demonstrated that elevation of astrocytic monoamine oxidase B (MAO-B) levels in adoxycycline (dox)-inducible transgenic mouse model following 14 days of dox induction results in several neuropathologic features similar to those observed in the Parkinsonian midbrain (Mallajosyula et al., 2008).These include a specific, selective and progressive loss of dopaminergic neurons of the substantia nigra (SN),selective decreases in mitochondrial complex I (CI) activity and increased oxidative stress. Here, we report that the temporal sequence of events following MAO-B elevation initially involves increased oxidative stress followed by CI inhibition and finally neurodegeneration. Furthermore, dox removal (DR) at days 3 and 5 of MAO-B induction was sufficient to arrest further increases in oxidative stress as well as subsequent neurodegenerative events. In order to assess the contribution of MAO-B-induced oxidative stress to later events, we compared the impact of DR which reverses the MAO-B increase with treatment of animals with the lipophilic antioxidant compound EUK-189. EUK-189 was found to be as effective as DR in halting downstream CI inhibition and also significantly attenuated SN DA cell loss as a result of astrocytic MAO-B induction. This suggests that MAO-B-mediated ROS contributes to neuropathology associated with this model and that antioxidant treatment can arrest further progression of dopaminergic cell death. This has implications for early intervention therapies.

Melatonin has membrane receptor-independent hypnotic action on neurons: an hypothesis

Melatonin, which is known to have sleep-promoting properties, has no morpho-physiological barriers and readily enters neurons and their subcellular compartments from both the blood and cerebrospinal fluid. It has multiple receptor-dependent and receptor-independent functions. Sleep is a neuronal function, and it can no longer be postulated that one or more anatomical structures fully control sleep. Neurons require sleep for metabolically driven restorative purposes, and as a result, the process of sleep is modulated by peripheral and central mechanisms. This is an important finding because it suggests that melatonin should have intracellular sleep-inducing properties. Based on recent evidence, it is proposed that melatonin induces sleep at the neuronal level independently of its membrane receptors. Thus, the hypnotic action of melatonin and the mechanisms involving the circadian rhythms are separate neurological functions. This is contrary to the presently accepted view.

Ability to delay neuropathological events associated with astrocytic MAO-B increase in a Parkinsonian mouse model: implications for early intervention on disease progression

We previously demonstrated that elevation of astrocytic monoamine oxidase B (MAO-B) levels in a doxycycline (dox)-inducible transgenic mouse model following 14 days of dox induction results in several neuropathologic features similar to those observed in the Parkinsonian midbrain (Mallajosyula et al., 2008). These include a specific, selective and progressive loss of dopaminergic neurons of the substantia nigra (SN), selective decreases in mitochondrial complex I (CI) activity and increased oxidative stress. Here, we report that the temporal sequence of events following MAO-B elevation initially involves increased oxidative stress followed by CI inhibition and finally neurodegeneration. Furthermore, dox removal (DR) at days 3 and 5 of MAO-B induction was sufficient to arrest further increases in oxidative stress as well as subsequent neurodegenerative events. In order to assess the contribution of MAO-B-induced oxidative stress to later events, we compared the impact of DR which reverses the MAO-B increase with treatment of animals with the lipophilic antioxidant compound EUK-189. EUK-189 was found to be as effective as DR in halting downstream CI inhibition and also significantly attenuated SN DA cell loss as a result of astrocytic MAO-B induction. This suggests that MAO-B-mediated ROS contributes to neuropathology associated with this model and that antioxidant treatment can arrest further progression of dopaminergic cell death. This has implications for early intervention therapies.