Tinnitus has been associated with increased spontaneous and evoked activity, increased neural synchrony, and reorganization of tonotopic maps of auditory nuclei. However, the neurotransmitter systems mediating these changes are poorly understood. Here, we developed an in vitro assay that allows us to evaluate the roles of excitation and inhibition in determining the neural correlates of tinnitus. To measure the magnitude and spatial spread of evoked circuit activity, we used flavoprotein autofluorescence (FA) imaging, a metabolic indicator of neuronal activity. We measured FA responses after electrical stimulation of glutamatergic axons in slices containing the dorsal cochlear nucleus, an auditory brainstem nucleus hypothesized to be crucial in the triggering and modulation of tinnitus. FA imaging in dorsal cochlear nucleus brain slices from mice with behavioral evidence of tinnitus (tinnitus mice) revealed enhanced evoked FA response at the site of stimulation and enhanced spatial propagation of FA response to surrounding sites. Blockers of GABAergic inhibition enhanced FA response to a greater extent in control mice than in tinnitus mice. Blockers of excitation decreased FA response to a similar extent in tinnitus and control mice. These findings indicate that auditory circuits in mice with behavioral evidence of tinnitus respond to stimuli in a more robust and spatially distributed manner because of a decrease in GABAergic inhibition.T innitus, the persistent perception of a subjective sound in the absence of an acoustic stimulus (ringing of the ears), is often a debilitating condition that reduces the quality of life for many of those chronically affected. Estimates of the number of people experiencing tinnitus range from 8% to 20% of the general population (1). Despite the prevalence and growing incidence of tinnitus, the mechanisms underlying the induction and maintenance of tinnitus remain poorly understood.Animal models of tinnitus have contributed significantly to the understanding of the pathophysiology of tinnitus (2-8). An emerging pattern associated with tinnitus pathology indicates that intense noise exposure leads to cochlear damage and hearing loss, which often is not clinically detected. Decreased cochlear input leads to hyperactive, more responsive central auditory circuits, which is evidenced by functional MRI (fMRI) studies in patients with tinnitus and in vivo recordings in animal models of tinnitus (9-13). Increased spontaneous firing rates, increased evoked responses, and reorganization of tonotopic maps are consistent with decreased inhibition (disinhibition) (1, 14). However, direct evidence that disinhibition mediates these changes is still lacking. In addition, the alternative hypothesis that predicts increased excitation as a potential mechanism in mediating these changes has not been tested (15). Addressing these unexamined questions could lead to pharmacological approaches for treating tinnitus patients.We used flavoprotein autofluorescence (FA) imaging in brain slices prepared from...

α-Synuclein (a-Syn), a protein implicated in Parkinson disease, contributes significantly to dopamine metabolism. a-Syn binding inhibits the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. Phosphorylation of TH stimulates its activity, an effect that is reversed by protein phosphatase 2A (PP2A). In cells, a-Syn overexpression activates PP2A. Here we demonstrate that a-Syn significantly inhibited TH activity in vitro and in vivo and that phosphorylation of a-Syn serine 129 (Ser-129) modulated this effect. In MN9D cells, a-Syn overexpression reduced TH serine 19 phosphorylation (Ser(P)-19). In dopaminergic tissues from mice overexpressing human a-Syn in catecholamine neurons only, TH-Ser-19 and TH-Ser-40 phosphorylation and activity were also reduced, whereas PP2A was more active. Cerebellum, which lacks excess a-Syn, had PP2A activity identical to controls. Conversely, a-Syn knock-out mice had elevated TH-Ser-19 phosphorylation and activity and less active PP2A in dopaminergic tissues. Using an a-Syn Ser-129 dephosphorylation mimic, with serine mutated to alanine, TH was more inhibited, whereas PP2A was more active in vitro and in vivo. Phosphorylation of a-Syn Ser-129 by Polo-like-kinase 2 in vitro reduced the ability of a-Syn to inhibit TH or activate PP2A, identifying a novel regulatory role for Ser-129 on a-Syn. These findings extend our understanding of normal a-Syn biology and have implications for the dopamine dysfunction of Parkinson disease.