Final answer:
The degeneration of dopaminergic neurons leads to an imbalance in neurotransmitters, specifically glutamate and GABA, in Parkinson's disease. Additionally, disruptions in other neurotransmitter systems have been observed in PD. GABA is the main inhibitory neurotransmitter in the CNS and is involved in Huntington's disease.
Step-by-step explanation:
In Parkinson's disease, the degeneration of dopaminergic neurons in the Substancia Nigra (SN) and consequent loss of dopamine (DA) leads to alteration in the neurotransmitters in the basal ganglia circuitry, particularly an imbalance in glutamate and GABA neurotransmission in the nigrostriatal pathway, resulting in an increased excitation in the SN promoting excitotoxicity and cell death.
Loss of DA neurons in the SNc (and also in the VTA) and consequent reduction of dopaminergic innervation is a hallmark of Parkinson Disease (PD). Various other studies have also shown disruptions in components of serotonergic, noradrenergic, cholinergic and glutamatergic systems in PD patients.
GABA is the main inhibitory neurotransmitter in the central nervous system (CNS). It is synthesized by the enzyme glutamic acid descarboxylase (GAD) which catalyzes the decarboxylation of glutamate. GABAergic dysfunction has been observed in Huntington's disease, an inherited degenerative disorder.