Schedule-induced polydipsia was used to determine the effects of selective serotonin re-uptake inhibitors on adjunctive water consumption. Polydipsia was induced in food deprived rats by exposure to a fixed time feeding schedule (FT = 60 s) for 150 min per day for 22 days. Selected polydipsic rats consumed 3-4 times greater volume of water compared to food deprived control rats. Chronic administration of the selective serotonin re-uptake inhibitors fluoxetine and clomipramine (CMI) at 5 mg/kg per day and fluvoxamine at 10 mg/kg twice a day significantly decreased schedule-induced polydipsia (SIP) on day 15 and throughout the remainder of the study compared to control rats. The noradrenergic re-uptake inhibitor, desipramine (DMI), only decreased SIP behavior on day 1. The neuroleptic, haloperidol (0.03 and 0.1 mg/kg), and the benzodiazepine, diazepam (2.5 mg/kg), failed to alter SIP behavior. Since obsessive-compulsive disorder (OCD) and polydipsic behavior both involve excessive expression of a normal behavior, the polydipsia model may be relevant for the prediction of compounds useful in the treatment of OCD.

A series of 3-[[(aryloxy)alkyl]piperidinyl]-1,2-benzisoxazoles was synthesized and evaluated as potential antipsychotic D2/5-HT2 antagonists. Most of these compounds showed potent antipsychotic-like activity in an apomorphine-induced climbing mouse paradigm, with many also showing preferential mesolimbic activity, as indicated by their weaker effects in an apomorphine-induced stereotypy model. In receptor binding assays, many displayed a moderate affinity for the D2 receptor coupled with a significantly greater affinity for the 5-HT2 receptor: a property that has been suggested as necessary for atypicality. From this series, compound 45, 1-[4-[3-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1- piperidinyl]propoxy]-3-methoxyphenyl]ethanone (iloperidone, HP 873), was further evaluated in a battery of in vivo and in vitro assays. This compound showed a 300-fold greater potency in inhibition of climbing than in inhibition of stereotypy or induction of catalepsy, and when evaluated chronically in an electrophysiological model, 45 caused a depolarization blockade of dopamine neurons in the A10 area of the rat brain but not in the A9 area. Additionally, it showed positive activity in a social interaction paradigm, suggesting potential efficacy against asociality, a component of the negative symptoms of schizophrenia. In chronic ex vivo studies, 45, similar to clozapine, caused a down regulation of 5-HT2 receptors but had no effect on the number of D2 receptors. Compound 45 is currently undergoing clinical evaluation.

The synthesis of a series of 9-amino-1,2,3,4-tetrahydroacridin-1-ols is reported. These compounds are related to 1,2,3,4-tetrahydro-9-acridinamine (THA, tacrine). They inhibit acetylcholinesterase in vitro and are active in a model that may be predictive of activity in Alzheimer's disease--the scopolamine-induced impairment of 24-h memory of a passive dark-avoidance paradigm in mice. Two compounds, (+/-)-9-amino-1,2,3,4-tetrahydroacridin-1-ol maleate (1a, HP-029) and (+/-)-9-(benzylamino)-1,2,3,4-tetrahydroacridin-1-ol maleate (1p, HP-128), were also active in reversing the deficit in 72-h retention of a one-trial dark-avoidance task in rats, induced by ibotenic acid lesions in the nucleus basalis magnocellularis. In addition, compound 1 p showed potent in vitro inhibition of the uptake of radiolabeled noradrenaline and dopamine (IC50 = 0.070 and 0.30 microM, respectively). Compounds 1a and 1p, which showed less acute toxicity in both rats and mice than THA, are in phase II and phase I clinical trials, respectively, for Alzheimer's disease.

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