Extrapyramidal side-effects and dopamine D(2/3) receptor binding in substantia nigra

Treatment of Symptom Clusters in Schizophrenia, Bipolar Disorder and Major Depressive Disorder With the Dopamine D3/D2 Preferring Partial Agonist Cariprazine

Cariprazine is currently approved for the treatment of patients with schizophrenia (USA and EU), and for manic, depressive, and episodes with mixed features in bipolar I disorder (USA): several randomized controlled studies have also explored its efficacy in patients with major depressive disorder. This review summarizes its current therapeutic uses and potential advantages for treating the main symptoms of schizophrenia, bipolar I and major depressive disorder, considering its pharmacodynamic properties, efficacy, and tolerability. Its predominantly D3 receptor preferring affinity, with functional selectivity according to the prevailing neuronal environment, contributes to its efficacy across a wide array of psychopathological symptoms (including reality distortion, disorganized thought, negative symptoms, mood disturbance, anhedonia, and cognitive impairment), and to a favorable side effect profile. Cariprazine may be a "drug of choice" in patients with predominant negative and cognitive symptoms of schizophrenia, as well as those with metabolic syndrome. Further investigation of its relative efficacy when compared to aripiprazole or other active comparators is warranted. Its effectiveness in the treatment of bipolar mania, bipolar I depression and bipolar I episodes with mixed features, with minimal accompanying metabolic changes is well-established. The longer half-life and delayed time to relapse in patients diagnosed with schizophrenia when compared to other second-generation antipsychotics represent other advantages, given the high rates of non-adherence and frequent relapses seen in clinical practice. Its efficacy in overlapping symptom domains in other major psychiatric disorders appears promising.

Dopamine-receptor blocking agent-associated akathisia: a summary of current understanding and proposal for a rational approach to treatment

Dopamine-receptor blocking agent-associated akathisia (DRBA-A) is an adverse effect that can significantly limit the use of these important medications for the treatment of a variety of psychiatric diseases, yet there is no unifying theory regarding its pathophysiology. This knowledge gap limits clinicians' ability to effectively manage DRBA-A and mitigate negative outcomes in an already vulnerable patient population. Based on a review of the current literature on the subject, it is hypothesized that dopaminergic and noradrenergic signaling is perturbed in DRBA-A. Accordingly, it is proposed that the optimal agent to manage this extrapyramidal symptom should increase dopamine signaling in the affected areas of the brain and counteract compensatory noradrenergic signaling via antagonism of adrenergic or serotonergic receptors.

Polymorphisms in Dopaminergic Genes in Schizophrenia and Their Implications in Motor Deficits and Antipsychotic Treatment

Dopaminergic system dysfunction is involved in schizophrenia (SCZ) pathogenesis and can mediate SCZ-related motor disorders. Recent studies have gradually revealed that SCZ susceptibility and the associated motor symptoms can be mediated by genetic factors, including dopaminergic genes. More importantly, polymorphisms in these genes are associated with both antipsychotic drug sensitivity and adverse effects. The study of genetic polymorphisms in the dopaminergic system may help to optimize individualized drug strategies for SCZ patients. This review summarizes the current progress about the involvement of the dopamine system in SCZ-associated motor disorders and the motor-related adverse effects after antipsychotic treatment, with a special focus on polymorphisms in dopaminergic genes. We hypothesize that the genetic profile of the dopaminergic system mediates both SCZ-associated motor deficits associated and antipsychotic drug-related adverse effects. The study of dopaminergic gene polymorphisms may help to predict drug efficacy and decrease adverse effects, thereby optimizing treatment strategies.

Tardive Dyskinesia, Oral Parafunction, and Implant-Supported Rehabilitation

Oral movement disorders may lead to prosthesis and implant failure due to excessive loading. We report on an edentulous patient suffering from drug-induced tardive dyskinesia (TD) and oral parafunction (OP) rehabilitated with implant-supported screw-retained prostheses. The frequency and intensity of the movements were high, and no pharmacological intervention was possible. Moreover, the patient refused night-time splint therapy. A series of implant and prosthetic failures were experienced. Implant failures were all in the maxilla and stopped when a rigid titanium structure was placed to connect implants. Ad hoc designed studies are desirable to elucidate the mutual influence between oral movement disorders and implant-supported rehabilitation.

A comparative review of escitalopram, paroxetine, and sertraline: Are they all alike?

It is known that newer antidepressants, such as the selective serotonin reuptake inhibitors (SSRIs), provide advantages in tolerability over antidepressants such as the tricyclics. However, even within the SSRI class, differences in efficacy or tolerability exist between the individual drugs. Among the three most widely prescribed SSRIs are paroxetine, sertraline, and escitalopram. Escitalopram is commonly referred to as an SSRI, but also has well-documented allosteric properties, and thus can be further classed as an allosteric serotonin reuptake inhibitor. All three antidepressants are efficacious compared with placebo, but there is evidence that escitalopram is more effective than a range of other antidepressants. There are no direct data to regard either paroxetine or sertraline as a superior antidepressant. Escitalopram is superior compared with paroxetine, which has a less favorable tolerability profile. Paroxetine is associated with cholinergic muscarinic antagonism and potent inhibition of CYP2D6, and sertraline has moderate drug interaction issues in comparison with escitalopram. Overall, as an allosteric serotonin reuptake inhibitor that is somewhat different from classical SSRIs, escitalopram is the first choice judged by combined efficacy and tolerability, and nonclinical data have offered possible mechanisms through which escitalopram could be more efficacious, based on its interaction with orthosteric and allosteric binding sites at the serotonin transporter.

[123I]Epidepride neuroimaging of dopamine D2/D3 receptor in chronic MK-801-induced rat schizophrenia model

PURPOSE

[(123)I]Epidepride is a radio-tracer with very high affinity for dopamine D(2)/D(3) receptors in brain. The importance of alteration in dopamine D(2)/D(3) receptor binding condition has been wildly verified in schizophrenia. In the present study we set up a rat schizophrenia model by chronic injection of a non-competitive NMDA receptor antagonist, MK-801, to examine if [(123)I]epidepride could be used to evaluate the alterations of dopamine D(2)/D(3) receptor binding condition in specific brain regions.

METHOD

Rats were given repeated injection of MK-801 (dissolved in saline, 0.3mg/kg) or saline for 1month. Afterwards, total distance traveled (cm) and social interaction changes were recorded. Radiochemical purity of [(123)I]epidepride was analyzed by Radio-Thin-Layer Chromatography (chloroform: methanol, 9:1, v/v) and [(123)I]epidepride neuroimages were obtained by ex vivo autoradiography and small animal SPECT/CT. Data obtained were then analyzed to determine the changes of specific binding ratio.

RESULT

Chronic MK-801 treatment for a month caused significantly increased local motor activity and induced an inhibition of social interaction. As shown in [(123)I]epidepride ex vivo autoradiographs, MK-801 induced a decrease of specific binding ratio in the striatum (24.01%), hypothalamus (35.43%), midbrain (41.73%) and substantia nigra (37.93%). In addition, [(123)I]epidepride small animal SPECT/CT neuroimaging was performed in the striatum and midbrain. There were statistically significant decreases in specific binding ratio in both the striatum (P<.01) and midbrain (P<.05) between the saline and MK-801 group.

CONCLUSION

These results suggest that [(123)I]epidepride is a useful radio-tracer to reveal the alterations of dopamine D(2)/D(3) receptor binding in a rat schizophrenia model and is also helpful to evaluate therapeutic effects of schizophrenia in the future.