Five different methods for the estimation of the binding potential, a measure of Bmax/Kd, of [11C]raclopride in human striatum were compared using data from a dose ranging study of the neuroleptic CP-88,059-01. Binding potential was estimated indirectly, from distribution volumes in striatum and cerebellum, using both single- and two-tissue compartment models with a metabolite-corrected plasma curve as input function. The two-tissue compartment model was also used for a direct estimate of the binding potential. In addition, a direct estimate was obtained from the reference tissue compartment model using the cerebellum as indirect input function. Finally, an estimate of binding potential was calculated from the ratio of striatum over cerebellum counts at late times after injection. The estimates of striatum binding potential from all methods, except the direct determination using a two-tissue compartment model with metabolite-corrected plasma input function, correlated with each other. Use of an average metabolite correction resulted in only a small reduction in accuracy in this series of normal subjects. The reference tissue model provided estimates of the binding potential with the same sensitivity for detecting changes as those methods that required a metabolite-corrected plasma input function. This indicates that for routine analysis of clinical [11C]raclopride studies, no arterial cannulation is required. The range of normal values was significantly less variable with the reference tissue method than when simple striatum-to-cerebellum ratios were used.

Positron emission tomography (PET) and 11C-raclopride were used to assess the time course of binding to central dopamine D2 receptors by the novel neuroleptic ziprasidone. In a third party blind study, six healthy male control subjects received a predose of 40 mg ziprasidone and were scanned at an interval of between 4 and 36 h post-dose. One additional subject was assigned to placebo predose and was scanned at 4 h post-dose. Binding potential (BP) was compared with that seen in the subject predosed with placebo and with that seen in nine unmedicated normal volunteers. Subjects studied up to 12 h post-dose had BPs that were greater than 2 SD less than the mean BP, indicative of extensive D2 receptor binding by ziprasidone. With increasing time between dosing and PET scanning there was a curvilinear increase in BP, so that all studies performed at or after 18 h post-dose gave BPs in the normal range (mean +/- 2 SD). Elevated prolactin levels returned to within the normal range by 18 h post-dose. PET measures of binding potential correlated significantly with serum levels of ziprasidone at the time of scanning and less significantly with absolute prolactin levels at the same time.

Abstract. Positron emission tomography (PET) and 11C. raclopride were used to measure the occupancy of central dopamine D2 receptors by a new neuroleptic, CP-88,059-1. In a double blind dose escalation study, seven healthy male subjects received a predose of between 2 mg and 60 mg CP-88,059-1, 5 h before PET scanning. One additional subject was assigned to placebo predose. Receptor occupancy was defined as the percentage reduction in binding potential compared with that seen in the subject predosed with placebo and with that seen in seven unmedicated normal volunteers previously studied. Binding of 11C-raclopride decreased in a dose dependent manner, and 85 % dopamine D 2 receptor occupancy was achieved with the highest dose of CP-88,059-1. The findings confirm that brain dopamine D 2 receptors are blocked by CP-88,059-1 and suggest that an effective antipsychotic dose will be between 20 mg and 40 mg. The study highlights the potential of positron emission tomography in the preclinical evaluation of new drugs.

In a double-blind multicentre study of outpatients with DSM-III-R major depressive disorder, 129 sertraline and 129 placebo patients were evaluated over a 6-week period. Sertraline exhibited a significantly greater (P < 0.001) antidepressant effect compared to placebo as measured by the HAM-D, MADRS, CGI-S and CGI-I. In the subset of patients with severe depression (baseline HAM-D >/= 25), sertraline was also significantly more effective than placebo (P < 0.05). Side effects were more commonly reported in sertraline (59%) compared to placebo (38%) patients; the most common being nausea, headache and insomnia. A subset of 107 patients (66 sertraline; 41 placebo) who were defined as responders (CGI-I of 1 or 2) after 6 weeks treatment were entered into a 20-week continuation phase. In this responder subset, there was continuing improvement in both groups of patients, but with no significant differences in mean HAM-D or MADRS between the groups. However, a higher number of sertraline patients were associated with a persistent pattern of improvement relative to placebo (P < 0.05). The incidence of side effects was similar in sertraline (52%) and placebo (49%) treated patients in the continuation period.

with the reported ability of al antagonists to suppress raphe neuronal activity. Desipramine did not reverse the inhibitory effect of ziprasidone. Oral (PO) 3.2 mg/kg ziprasidone and clozapine had no effect on dopamine release in the striatum (STR) of awake rats, but increased dopamine release in the prefrontal cortex (PFC) to 160%-180% of basal levels. Ziprasidone enhanced STR dopamine release after doses of :::: IO mg/kg PO, but still preferentiaIly increased PFC dopamine release. Olanzapine produced similar increases in PFC and STR dopamine release. Pre-treatment with WAY-100635 (0.1 mg/kg subcutaneous; SC) inhibited the PFC dopamine release induced by 10 mg/kg PO ziprasidone by 80% and that induced by 3 mg/kg SC c10zapine by 60%, but had no effect on olanzapineinduced PFC dopamine release. These results show that ziprasidone and clozapine, unlike olanzapine, act as 5HTIA agonists in vivo. 5HTlA agonist effects may contribute to the beneficial clinical effects seen in patients and could offer advantages over agents for the treatment of schizophrenia that do no activate 5HTlA receptors.