Enhanced dopaminergic tone impairs GABAergic homeostasis in the striatum of dopamine transporter knockout rats

Dopamine Transporter (DAT) regulates the dopaminergic transmission and homeostasis by reuptaking dopamine from the synaptic cleft and filling dopaminergic vesicles for subsequent release. Psychostimulants can target DAT, leading to neurochemical and behavioral alterations that can be reproduced in DAT knockout (DAT-/-) rats. Indeed, they show hyperactive behaviors, due to the high elevation of striatal extracellular dopamine, and display cognitive and locomotor deficits. Decreased striatal volume loss observed in DAT-/- rodents, which may account for the hyperactive behavior, could be related to a loss of GABAergic interneurons. Thus, taking advantage of DAT-/- rats, we investigated whether the GABAergic striatal homoeostasis is modulated by a condition of dopaminergic hyperactivity, measuring several GABAergic markers. Adult male DAT-/- rats created in the outbred Wistar Han background were housed by genotype in groups of three or four with free access to tap water and standard pellet food. Striata were rapidly dissected after decapitation and stored at -80°C. Protein levels were measured by means of Western Blot in the whole homogenate, cytosolic and post-synaptic fractions. DAT-/- rats showed reduced protein levels of vGAT and GAD67, indexes of synthesis and release of GABA, paralleled by decreased expression of Parvalbumin, Reelin and PGC1a, markers of abundance and functionality of GABAergic interneurons. Concomitantly, we observed reduced GAT1 and GAT3 protein levels, transporters responsible for GABA reuptake from the synaptic cleft, suggesting reduced GABA reuptake. In addition, protein levels of GABAA a1, GABAA a2, GABAA b1 and GABAB R1 subunits, of scaffolding protein Gephyrin and of postsynaptic adhesion GABAergic molecule NLGN-2 were reduced, potentially contributing to a decreased GABAergic tone. Overall, our findings suggest a hyperdopaminergic-induced impairment of GABAergic homeostasis in the striatum, defined by insufficient synthesis, vesicular storage, release and reuptake of GABA and altered GABAergic post-synaptic signal transduction. These data might help paving the way to a better understanding of the role of the GABAergic neurotransmission in pathological conditions characterized by enhanced dopaminergic tone. Beatrice Rizzi is supported by cycle XXXVIII of the PhD programme in Theoretical and Applied Neuroscience, DM351 (Finanziamenti PNRR).