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Abstract: Previous studies have revealed that 5-HT1A agonists ameliorate antipsychotic-induced extrapyramidal symptoms (EPS) through postsynaptic 5-HT1A receptors. Here, we conducted an intracerebral microinjection study of (±)-8-hydroxy-2-(di-n-propylamino)-tetralin ((±)8-OH-DPAT) to determine the action site of the 5-HT1A agonist in alleviating EPS. Bilateral microinjection of(±)8-OH-DPAT (5µg/1µL per side) either into the primary motor cortex (MC) or the dorsolateral striatum (dlST) significantly attenuated haloperidol-induced catalepsy in rats. The anticataleptic action of (±)8-OH-DPAT was more prominent with the MC injection than with the dlST injection. WAY-100135 (a selective 5-HT1A antagonist) completely antagonized the reversal of haloperidol-induced catalepsy both by intracortical and intrastriatal (±)8-OH-DPAT. Furthermore, lesioning of dopamine neurons with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (30mg/kg/day, i.p., for 4days) did not alter the anti-EPS actions of (±)8-OH-DPAT in a mouse pole test. The present results strongly suggest that 5-HT1A agonist alleviates antipsychotic-induced EPS by activating postsynaptic 5-HT1A receptors in the MC and dlST, probably through non-dopaminergic mechanisms. [Copyright &y& Elsevier]

We previously demonstrated that 5-HT stimulants, including selective serotonin reuptake inhibitors (SSRIs), potentiated antipsychotic-induced extrapyramidal symptoms (EPS) by stimulating 5-HT2A/2C, 5-HT3 and 5-HT6 receptors. Here, we studied the effects of the 5-HT1A agonist (±)-8-hydroxy-2-(di-n-propylamino) tetralin ((±)-8-OH-DPAT) on the fluoxetine enhancement of EPS (i.e., bradykinesia and catalepsy) to determine if the 5-HT1A agonist can counteract the serotonergic potentiation of EPS. Fluoxetine did not induce EPS signs by itself, but significantly potentiated haloperidol-induced bradykinesia in mice. (±)-8-OH-DPAT (0.1–1mg/kg, i.p.) significantly attenuated the fluoxetine enhancement of haloperidol-induced bradykinesia in a dose-dependent manner. A selective 5-HT1A antagonist (s)-WAY-100135 completely reversed the anti-EPS action of (±)-8-OH-DPAT. Microinjection studies using rats revealed that local application of (±)-8-OH-DPAT into the dorsolateral striatum or the motor cortex significantly diminished fluoxetine-enhanced catalepsy. In contrast, (±)-8-OH-DPAT injected into the medial raphe nucleus failed to affect EPS induction. The present results illustrate that 5-HT1A agonist can alleviate the SSRI enhancement of EPS by activating postsynaptic 5-HT1A receptors in the striatum and cerebral cortex. [ABSTRACT FROM AUTHOR]

Abstract: Previous studies showed that 5-HT1A and 5-HT2 receptors play an important role in controlling the extrapyramidal motor disorders. However, the functions of other 5-HT receptor subtypes remain elusive. To elucidate the role of 5-HT receptors, specifically of 5-HT3∼5-HT7 subtypes, in modifying antipsychotic- induced extrapyramidal side effects (EPS), we studied the effects of the 5-HT stimulant 5-hydroxytryptophan (5-HTP) and various 5-HT receptor antagonists on haloperidol (HAL)-induced bradykinesia and catalepsy in mice and rats. Pretreatment of mice with 5-HTP (25–100mg/kg, i.p.) dose-dependently enhanced HAL (0.3mg/kg, i.p.)-induced bradykinesia and catalepsy. The potentiation of HAL-induced EPS by 5-HTP (50mg/kg, i.p.) was significantly inhibited by ritanserin (5-HT2 antagonist, 0.3-3mg/kg, i.p.), ondansetron (5-HT3 antagonist, 0.1–1mg/kg, i.p.), or SB-258585 (5-HT6 antagonist, 1–10mg/kg, i.p.) in a dose-dependent manner. However, neither WAY-100135 (5-HT1A antagonist, 1–10mg/kg, i.p.), GR-125487 (5-HT4 antagonist, 1–10mg/kg, i.p.), SB-699551 (5-HT5A antagonist, 1–10mg/kg, i.p.) nor SB-269970 (5-HT7 antagonist, 1–10mg/kg, i.p.) reduced the 5-HTP and HAL-induced bradykinesia or catalepsy. In addition, both ondansetron (0.1–1mg/kg, i.p.) and SB-258585 (3 and 10mg/kg, i.p.) also alleviated bradykinesia and catalepsy induced by HAL (0.5mg/kg, i.p.) alone in mice. Furthermore, bilateral microinjection of ondansetron (5μg (13.7nmol) per side) or SB-258585 (5μg (8.92nmol) per side) into the dorsolateral striatum (dlST) attenuated haloperidol-induced catalepsy in rats. These results suggest that serotonergic stimulation augments extrapyramidal motor disorders by activating the striatal 5-HT3 and 5-HT6 receptors and the antagonism of these receptors effectively alleviates antipsychotic-induced EPS. [Copyright &y& Elsevier]

Abstract: Blonanserin is a novel antipsychotic agent that preferentially interacts with dopamine D2 and 5-HT2A receptors. To assess the atypical properties of blonanserin, we evaluated its propensity to induce extrapyramidal side effects (EPS) and to enhance forebrain Fos expression in mice. The actions of AD-6048, a primary metabolite of blonanserin, in modulating haloperidol-induced EPS were also examined. Blonanserin (0.3–10mg/kg, p.o.) did not significantly alter the pole-descending behavior of mice in the pole test or increase the catalepsy time, while haloperidol (0.3–3mg/kg, p.o.) caused pronounced bradykinesia and catalepsy. Blonanserin and haloperidol at the above doses significantly enhanced Fos expression in the shell (AcS) region of the nucleus accumbens and dorsolateral striatum (dlST). The extent of blonanserin-induced Fos expression in the AcS was comparable to that induced by haloperidol. However, the striatal Fos expression by blonanserin was less prominent as compared to haloperidol. Furthermore, combined treatment of AD-6048 (0.1–3mg/kg, s.c.) with haloperidol (0.5mg/kg, i.p.) significantly attenuated haloperidol-induced bradykinesia and catalepsy. The present results show that blonanserin behaves as an atypical antipsychotic both in inducing EPS and enhancing forebrain Fos expression. In addition, AD-6048 seems to contribute at least partly to the atypical properties of blonanserin. [Copyright &y& Elsevier]