Preclinical neurochemical and electrophysiological profile of 1192U90, a potential antipsychotic.

11192U90 was submitted to receptor binding and monoamine uptake assays. It bound potently at serotonin 5-HT2, dopaminergic D2, serotonin 5-HT1A, and adrenergic alpha 1 and alpha 2 receptors. It also bound to dopaminergic D1, serotonin 5-HT3, serotonin 5-HT4, and sigma sites, albeit with lower affinity. It was essentially inactive at 22 other sites, including those for cholinergic M1 and M2. It weakly inhibited uptake of 3H-norepinephrine, 3H-serotonin and 3H-dopamine. Acute doses of 1192U90 (5 and 20 mg/kg P.O.) increased whole-brain levels of dopamine metabolites but did not affect levels of norepinephrine, dopamine, and serotonin. Subcutaneous injection of 1192U90 (0.8 mg/kg/day) and clozapine (20 mg/kg/day) for 28 days preferentially decreased the number of spontaneously active dopamine cells in the ventral tegmental area (VTA) but not the substantia nigra (SN) of rats, as measured by population sampling. This outcome is characteristics of atypical antipsychotics like clozapine. Acute injections of 1192U90 reversed the rate-inhibiting effects of microiontophoretically applied dopamine and intravenously injected apomorphine and d-amphetamine on dopamine cell firing. Intravenous injection or iontophoretic application of 1192U90 or the 5-HT1A agonist (+/-)8-OH-DPAT inhibited the firing rates of dorsal raphe nucleus (DRN) neurons in rats, and the effects of both compounds were blocked by iontophoretically applied S(-) propranolol, a 5-HT1A antagonist. The results suggest that 1192U90 is a preferential dopamine D2 antagonist as well as a 5-HT1A agonist that may prove to be an atypical antipsychotic.

High expression of nitrobenzylthioinosine-insensitive dipyridamole binding sites in postmortem human ependymal tissue.

The presence of both nitrobenzylthioinosine-sensitive and nitrobenzylthioinosine-insensitive dipyridamole binding sites in postmortem human ependymal tissue is reported. Displacement studies using 15 nM [3H]dipyridamole revealed 50-60% of the sites were sensitive to nitrobenzylthioinosine. Non-linear analysis of binding isotherms to estimate the density of nitrobenzylthioinosine-sensitive and -insensitive sites revealed a maximum number of nitrobenzylthioinosine-sensitive binding sites (Bmax) of 395 +/- 19 fmol/mg protein and a nitrobenzylthioinosine-insensitive Bmax of 3910 +/- 700 fmol/mg protein (corresponding Kd values of 0.1 nM and 114 nM respectively). Thus there are approximately 10 times as many nitrobenzylthioinosine-insensitive sites as nitrobenzylthioinosine-sensitive [3H]dipyridamole binding sites in human ependymal membranes.

The novel anticonvulsant lamotrigine prevents dopamine depletion in C57 black mice in the MPTP animal model of Parkinson's disease.

The effect of the novel anticonvulsant Lamotrigine (LTG) was studied on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced dopamine depletion in C57BL/6 mouse brain. Whole brain dopamine levels were measured by HPLC-ED 2 days after treatment with MPTP (15 mg/kg s.c.). While LTG alone had no direct effect on dopamine levels at two hours or two days after treatment, MPTP induced dopamine depletion was significantly less in mice pretreated with LTG (approximate ED50: 6 mg/kg). LTG (38 mg/kg) was shown to completely protect against dopamine depletion when given 1 or 2 hours prior to MPTP administration. The effect of LTG (38, 100 mg/kg) on MPTP toxicity was compared to the effects of the anticonvulsants phenytoin (67 mg/kg), carbamazepine (156 mg/kg), and riluzole (33 mg/kg) and the Ca++ channel blocker nicardipine (0.1 mg/kg). Only phenytoin and LTG showed significant protection against MPTP. Results suggest LTG prevents MPTP induced dopamine depletion via a novel mechanism.