Combined treatment with a selective PDE10A inhibitor TAK-063 and either haloperidol or olanzapine at subeffective doses produces potent antipsychotic-like effects without affecting plasma prolactin levels and cataleptic responses in rodents.

Activation of indirect pathway medium spiny neurons (MSNs) via promotion of cAMP production is the principal mechanism of action of current antipsychotics with dopamine D2 receptor antagonism. TAK-063 [1-[2-fluoro-4-(1H-pyrazol-1-yl)phenyl]-5-methoxy-3-(1-phenyl-1H-pyrazol-5-yl)pyridazin-4(1H)-one] is a novel phosphodiesterase 10A inhibitor that activates both direct and indirect pathway MSNs through increasing both cAMP and cGMP levels by inhibition of their degradation. The activation of indirect pathway MSNs through the distinct mechanism of action of these drugs raises the possibility of augmented pharmacological effects by combination therapy. In this study, we evaluated the potential of combination therapy with TAK-063 and current antipsychotics, such as haloperidol or olanzapine after oral administration. Combined treatment with TAK-063 and either haloperidol or olanzapine produced a significant increase in phosphorylation of glutamate receptor subunit 1 in the rat striatum. An electrophysiological study using rat corticostriatal slices showed that TAK-063 enhanced N-methyl-D -aspartic acid receptor-mediated synaptic responses in both direct and indirect pathway MSNs to a similar extent. Further evaluation using pathway-specific markers revealed that coadministration of TAK-063 with haloperidol or olanzapine additively activated the indirect pathway, but not the direct pathway. Combined treatment with TAK-063 and either haloperidol or olanzapine at subeffective doses produced significant effects on methamphetamine- or MK-801-induced hyperactivity in rats and MK-801-induced deficits in prepulse inhibition in mice. TAK-063 at 0.1 mg/kg did not affect plasma prolactin levels and cataleptic response from antipsychotics in rats. Thus, TAK-063 may produce augmented antipsychotic-like activities in combination with antipsychotics without effects on plasma prolactin levels and cataleptic responses in rodents.

Short- and long-term effects of risperidone on catalepsy sensitisation and acquisition of conditioned avoidance response: Adolescent vs adult rats.

The effects of antipsychotic drugs (APDs) on the adolescent brain are poorly understood despite a dramatic increase in prescription of these drugs in adolescents over the past twenty years. Neuronal systems continue to be remodeled during adolescence. Therefore, when given in adolescence, antipsychotic drugs (APDs) have the potential to affect this remodeling. In this study we investigated the effects of chronic 22-day risperidone treatment (1.3mg/kg/day) in both adolescent and adult rats. We examined short- and long-term changes in behaviour (catalepsy, locomotion and conditioned avoidance response (CAR)), and dopaminergic and serotonergic neurochemistry in the striatum and the nucleus accumbens. Here, we report that, both during chronic treatment and after a lengthy drug-free interval, risperidone induced a sensitised cataleptic response regardless of the age of exposure. Selectively in adolescents, risperidone-induced catalepsy was inversely correlated with striatal dopamine turnover immediately after chronic treatment. After a drug-free interval, a significant proportion of rats with prior adolescent risperidone treatment also failed to acquire CAR to a defined criterion. Our data provide evidence that the same chronic risperidone treatment regimen can induce contrasting short- and long-term neural outcomes in the adolescent and adult brains.

Early life stress causes refractoriness to haloperidol-induced catalepsy.

The use of classic antipsychotic drugs is limited by the occurrence of extrapyramidal motor symptoms, which are caused by dopamine (DA) receptor blockade in the neostriatum. We examined the impact of early-life stress on haloperidol-induced catalepsy using the rat model of prenatal restraint stress (PRS). Adult "PRS rats," i.e., the offspring of mothers exposed to restraint stress during pregnancy, were resistant to catalepsy induced by haloperidol (0.5-5 mg/kg i.p.) or raclopride (2 mg/kg s.c.). Resistance to catalepsy in PRS rats did not depend on reductions in blood or striatal levels, as compared with unstressed control rats. PRS rats also showed a greater behavioral response to the DA receptor agonist, apomorphine, suggesting that PRS causes enduring neuroplastic changes in the basal ganglia motor circuit. To examine the activity of this circuit, we performed a stereological counting of c-Fos(+) neurons in the external and internal globus pallidus, subthalamic nucleus, and ventral motor thalamic nuclei. Remarkably, the number of c-Fos(+) neurons in ventral motor thalamic nuclei was higher in PRS rats than in unstressed controls, both under basal conditions and in response to single or repeated injections with haloperidol. Ventral motor thalamic nuclei contain exclusively excitatory projection neurons that convey the basal ganglia motor programming to the cerebral cortex. Hence, an increased activity of ventral motor thalamic nuclei nicely explains the refractoriness of PRS rats to haloperidol-induced catalepsy. Our data raise the interesting possibility that early-life stress is protective against extrapyramidal motor effects of antipsychotic drugs in the adult life.

[Some neuroendocrinological changes in rats of cataleptic strain GC. Influences of ontogenesis and generation of breeding].

The content of biogenic amines: dopamine, noradrenaline and serotonine, in rats of cataleptic strain GC as compared with the control strain Wistar at the age of 1 and 5 months is decreased, the maximal decrease being found in the so-called "nervous" animals. The aldosterone content was decreased at 5 month age in the GC rats. The testosterone content at the age of 1 month in GC rats does not differ from that in Wistar rats, but at the age of 5 months it was decreased as compared to Wistar, the maximal decrease being found again in "nervous" GC rats. The data obtained point to peculiarities of ontogenetic regulation and to commonness of mechanisms of catalepsy and "nervousness" in GC rats.

[The physiological characteristics of genetic predisposition to catalepsy in rats depending on the stage of selection]. / Nekotorye fiziologicheskie kharakteristiki geneticheskoi predraspolozhennosti k katalepsii u krys v zavisimosti ot stadii selektsii.

Male rats with a genetic predisposition to cataleptic reactions revealed a reduced motor activity and a diminished activation of mineralocorticoid and testosterone synthesis in response to a mild stress as compared with the Wistar rats. The reactions, however, were exactly opposite in the Wistar rats with signs of cataleptic features. The data obtained suggest that, when creating genetic animal models of human diseases, the initial stages of breeding should correspond to early stages of the disease whereas advanced stages of breeding are similar to later, chronic phases of the disease.