Role of GABA pathway in motor and non-motor symptoms in Parkinson's disease: a bidirectional circuit.

Parkinson's disease (PD) is a progressive neurodegenerative disease as a result of the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The fundamental features of PD are motor and non-motor symptoms. PD symptoms develop due to the disruption of dopaminergic neurotransmitters and other neurotransmitters such as γ-aminobutyric acid (GABA). The potential role of GABA in PD neuropathology concerning the motor and non-motor symptoms of PD was not precisely discussed. Therefore, this review intended to illustrate the possible role of GABA in PD neuropathology regarding motor and non-motor symptoms. The GABA pathway is essential in regulating the inhibitory tone to prevent excessive stimulation of the cerebral cortex. Degeneration of dopaminergic neurons in PD is linked with reducing GABAergic neurotransmission. Decreasing GABA activity promotes mitochondrial dysfunction and oxidative stress, which are highly related to PD neuropathology. Hence, restoring GABA activity by GABA agonists may attenuate the progression of PD motor symptoms. Therefore, dysregulation of GABAergic neurons in the SNpc contributes to developing PD motor symptoms. Besides, PD non-motor symptoms are also related to the dysfunction of the GABAergic pathway, and amelioration of this pathway may reduce PD non-motor symptoms. In conclusion, the deregulation of the GABAergic pathway in PD might be intricate in developing motor and non-motor symptoms. Improving this pathway might be a novel, beneficial approach to control PD symptoms.