Rationale: Tardive dyskinesia is a syndrome of abnormal and involuntary movements which occurs as a complication of long-term neuroleptic therapy especially classical neuroleptics such as haloperidol and chlorpromazine. Dysfunction of GABA receptor mediated inhibition, and increased glutamatergic neurotransmission has been implicated in the development of orofacial dyskinesia in rats and tardive dyskinesia in humans. Neurosteroids modulate both GABAergic as well as glutamatergic neurotransmission in various brain areas.
Objective: The objective of the present study was to elucidate the role of various neurosteroids in neuroleptic-induced vacuous chewing movements and related behaviors in rats by using behavioral, biochemical, and neurochemical parameters.
Materials and methods: Animals chronically treated with haloperidol (1 mg/kg i.p.) for a period of 21 days exhibited marked increase in vacuous chewing movements, tongue protrusions, and facial jerkings as compared to vehicle-treated controls. It also resulted in increased superoxide anion levels and lipid peroxidation, whereas decreased levels of endogenous antioxidant enzymes (catalase and superoxide dismutase) in rat brain striatum homogenates. Neurochemical studies revealed that chronic administration of haloperidol resulted in significant decrease in the levels of dopamine, serotonin, and norepinephrine in rat brain striatum homogenates, whereas urine biogenic amines metabolite levels were increased. In a series of experiments, rats co-administered with allopregnanolone (0.5, 1, and 2 mg/kg i.p.) and progesterone (5, 10, and 20 mg/kg i.p.), both positive GABA-modulating [negative N-methyl-D-aspartate (NMDA)-modulating] neurosteroids prevented, whereas pregnenolone (0.5, 1, and 2 mg/kg i.p.) and dihydroxyepiandrosterone sulfate (0.5, 1, and 2 mg/kg i.p.) both negative GABA-modulating (positive NMDA-modulating) neurosteroids aggravated all the behavioral, biochemical, and neurochemical parameters.
Conclusions: These results suggest that neurosteroids may play a significant role in the pathophysiology of vacuous chewing movements and related behaviors by virtue of their action on either the GABA or NMDA modulation. Furthermore, neurosteroids showing selectivity for positive GABA modulation and/or negative NMDA modulation may be particularly efficacious as novel therapeutic agents for the treatment of tardive dyskinesia and deserve further evaluation.