We report that half striatal cholinergic interneurons are dual transmitter cholinergic and GABAergic interneurons (CGINs) expressing ChAT, GAD65, Lhx7, and Lhx6 mRNAs, labeled with GAD and VGAT, generating monosynaptic dual cholinergic/GABAergic currents and an inhibitory pause response. Dopamine deprivation increases CGINs ongoing activity and abolishes GABAergic inhibition including the cortico-striatal pause because of high [Cl−]i levels. Dopamine deprivation also dramatically increases CGINs dendritic arbors and monosynaptic interconnections probability, suggesting the formation of a dense CGINs network. The NKCC1 chloride importer antagonist bumetanide, which reduces [Cl−]i levels, restores GABAergic inhibition, the cortico-striatal pause-rebound response, and attenuates motor effects of dopamine deprivation. Therefore, most of the striatal cholinergic excitatory drive is balanced by a concomitant powerful GABAergic inhibition that is impaired by dopamine deprivation. The attenuation by bumetanide of cardinal features of Parkinson’s disease paves the way to a novel therapeutic strategy based on a restoration of low [Cl−]i levels and GABAergic inhibition.
The brain-derived neurotrophic factor (BDNF) is synthesized as a precursor, namely proBDNF, which can be processed into mature BDNF (mBDNF). Evidences suggest that proBDNF signaling through p75NTR may account for the emergence of neurological disorders. These findings support the view that the relative availability of mBDNF and proBDNF forms is an important mechanism underlying brain circuit formation and cognitive functions. Here we describe novel insights into the proBDNF/p75NTR mechanisms and function in vivo in modulating neuronal circuit and synaptic plasticity during the first postnatal weeks in rats. Our results showed that increased proBDNF/p75NTR signaling during development maintains a depolarizing γ-aminobutyric acid (GABA) response in a KCC2-dependent manner in mature neuronal cells. This resulted in altered excitation/inhibition balance and enhanced neuronal network activity. The enhanced proBDNF/p75NTR signaling ultimately led to increased seizure susceptibility that was abolished by in vivo injection of function blocking p75NTR antibody. Altogether, our study shed new light on how proBDNF/p75NTR signaling can orchestrate the GABA excitatory/inhibitory developmental sequence leading to depolarizing and excitatory actions of GABA in adulthood and subsequent epileptic disorders.
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