Alterations in glutamatergic signaling in the brain of dopamine supersensitivity psychosis and non-supersensitivity psychosis model rats

The Underlying Neurobiological Mechanisms of Psychosis: Focus on Neurotransmission Dysregulation, Neuroinflammation, Oxidative Stress, and Mitochondrial Dysfunction

Psychosis, defined as a set of symptoms that results in a distorted sense of reality, is observed in several psychiatric disorders in addition to schizophrenia. This paper reviews the literature relevant to the underlying neurobiology of psychosis. The dopamine hypothesis has been a major influence in the study of the neurochemistry of psychosis and in development of antipsychotic drugs. However, it became clear early on that other factors must be involved in the dysfunction involved in psychosis. In the current review, it is reported how several of these factors, namely dysregulation of neurotransmitters [dopamine, serotonin, glutamate, and γ-aminobutyric acid (GABA)], neuroinflammation, glia (microglia, astrocytes, and oligodendrocytes), the hypothalamic-pituitary-adrenal axis, the gut microbiome, oxidative stress, and mitochondrial dysfunction contribute to psychosis and interact with one another. Research on psychosis has increased knowledge of the complexity of psychotic disorders. Potential new pharmacotherapies, including combinations of drugs (with pre- and probiotics in some cases) affecting several of the factors mentioned above, have been suggested. Similarly, several putative biomarkers, particularly those related to the immune system, have been proposed. Future research on both pharmacotherapy and biomarkers will require better-designed studies conducted on an all stages of psychotic disorders and must consider confounders such as sex differences and comorbidity.

Upregulation of heat-shock protein HSP-70 and glutamate transporter-1/glutamine synthetase in the striatum and hippocampus in haloperidol-induced dopamine-supersensitivity-state rats

BACKGROUND

The excessive blockade of dopamine D2 receptors (DRD2s) with long-term antipsychotic treatment is known to induce a dopamine supersensitivity state (DSS). The mechanism of DSS is speculated to be a compensatory up-regulation of DRD2s, but an excess blockade of DRD2s can also cause glutamatergic neuronal damage. Herein, we investigated whether antipsychotic-induced neuronal damage plays a role in the development of DSS.

METHODS

Haloperidol (HAL; 0.75 mg/kg/day for 14 days) or vehicle was administered to rats via an osmotic mini-pump. Haloperidol-treated rats were divided into groups of DSS rats and non-DSS rats based on their voluntary locomotion data. We then determined the tissue levels of glutamate transporter-1 (GLT-1)/glutamine synthetase (GS) and heat shock protein-70 (HSP-70) in the rats' brain regions.

RESULTS

The levels of HSP-70 in the striatum and CA-3 region of the DSS rats were significantly higher than those of the control and non-DSS rats, whereas the dentate gyrus HSP-70 levels in both the DSS and non-DSS rats were increased versus the controls. The levels of GLT-1/GS in the CA-3 and nucleus accumbens were increased in the DSS rats.

CONCLUSIONS

These results suggest that the DSS rats experienced striatal neuronal damage and indicate that a HAL-induced upregulation of HSP-70 and the GLT-1/GS system in the CA3 may be involved in the development of DSS. It remains unknown why the non-DSS rats did not suffer neuronal damage. In view of the need for therapeutic strategies for treatment-resistant schizophrenia, dopamine supersensitivity psychosis, and tardive dyskinesia, further investigations of our findings are warranted.

Effects of repeated electroconvulsive shocks on dopamine supersensitivity psychosis model rats

While the long-term administration of antipsychotics is known to cause dopamine supersensitivity psychosis (DSP), recent studies revealed that DSP helps form the foundation of treatment resistance. Electroconvulsive shock (ES) is one of the more effective treatments for treatment-resistant schizophrenia. The objective of this study was to examine whether repeated ES can release rats from dopamine supersensitivity states such as striatal dopamine D2 receptor (DRD2) up-regulation and voluntary hyperlocomotion following chronic administration of haloperidol (HAL). HAL (0.75 mg/kg/day) was administered for 14 days via mini-pumps implanted in rats, and DRD2 density and voluntary locomotion were measured one day after drug cessation to confirm the development of dopamine supersensitivity. The rats with or without dopamine supersensitivity received repeated ES or sham treatments, and then DRD2 density was assessed and a voluntary locomotion test was performed. Chronic treatment with HAL led to the up-regulation of striatal DRD2 and hyperlocomotion in the rats one day after drug cessation. We thus confirmed that these rats experienced a dopamine supersensitivity state. Moreover, after repeated ES, locomotor activity and DRD2 density in the DSP model rats fell to the control level, while an ES sham operation had no effect on the dopamine supersensitivity state. The present study suggests that repeated ES could release DSP model rats from dopamine supersensitivity states. ES may be helpful for patients with DSP.

Reduction of dopamine and glycogen synthase kinase-3 signaling in rat striatum after continuous administration of haloperidol

BACKGROUND

Some individuals with schizophrenia present with a dopamine supersensitivity state (DSS) induced by a long-term administration of excessive antipsychotics; this is recognized as dopamine supersensitivity psychosis (DSP). The mechanisms underlying DSP are not established. Here, we investigated dopamine signaling in DSS rats.

METHODS

Haloperidol (HAL; 0.75 mg/kg/day for 14 days) or vehicle was administered to rats via an osmotic mini-pump. We then screened DSS rats from HAL-treated rats by a voluntary locomotion test. The striatal levels of dopamine (DA) and its metabolites 3,4-hydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined, as were the levels of protein kinase v-akt murine thymoma viral oncogene homolog (AKT), glycogen synthase kinase-3 (GSK-3), and phosphorylated GSK-3 in the striatal regions.

RESULTS

In the DSS rats, the DA, DOPAC, and HVA levels were significantly decreased. In a western blot analysis, the DSS rats exhibited a significant decrease in GSK-3α/β and an increase in the pGSK-3β/GSK-3β ratio, whereas AKT was not changed.

CONCLUSIONS

Our results indicated that the DSS rats had hypofunction of the basal dopamine release and AKT/GSK-3 signaling even at 7 days after the antipsychotic was discontinued. Protracted reductions in pre- and post-dopamine D2 receptor signaling might cause prolonged DSS.

Tardive Dyskinesia: New Treatments Available

Tardive dyskinesia (TD), the choreoathetoid movements of fingers, arms, legs, and trunk and irregular stereotypical movements of the mouth, face, and tongue, has been the scourge of antipsychotic medications since the approval of chlorpromazine. TD tends to occur late in treatment and sometimes remains after discontinuation of the antipsychotic medication. With the recent approval of two medications, valbenazine (Ingrezza^®) and deutetrabenazine (Austedo^®), there are now treatments for this disfiguring consequence of dopamine-blocking medications. The current article distinguishes the movement disorder adverse effects of dopamine antagonists, explains the putative mechanism of action, and describes how best to treat TD with the new vesicular monamine transporter 2 (VMAT2) medications now approved by the U.S. Food and Drug Administration. [Journal of Psychosocial Nursing and Mental Health Services, 57(5), 11-14.].