In vivo microdialysis and liquid chromatography/thermospray mass spectrometry of the novel anticonvulsant 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (topiramate) in rat brain fluid.

The concentration of a novel anticonvulsant, 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (topiramate), was determined in the extracellular fluid of rat brain by in vivo microdialysis combined off-line with liquid chromatography/thermospray mass spectrometry. A microdialysis probe was stereotaxically implanted in the nucleus accumbens region of the rat brain. The maximum concentration of topiramate in the brain dialysate for a dose of 50 mg kg-1 i.v. was approximately 10 microM and occurred 45 min post-injection. The detection limit of topiramate in the extracellular fluid of rat brain was in the 0.1 microM range using selected ion monitoring techniques. The base peak, which was the ammonium adduct ion [M + NH4]+, was used for detection. An internal standard of d12-labeled topiramate was utilized for quantitation by isotope dilution analysis.

N-aryl-N'-benzylpiperazines as potential antipsychotic agents.

N1-(2-Alkoxyphenyl)piperazines additionally containing an N4-benzyl group bearing alcohol, amide, imide, or hydantoin functionalities were prepared and evaluated in the conditioned avoidance response (CAR) test predictive of clinical antipsychotic activity and in in vitro receptor-binding assays. Certain of the compounds display high affinity for the D2, 5-HT1A, and alpha 1-adrenergic receptors. Structures bearing acyclic amide, lactam, and imide functionalities display good biological activity, with a preference for the 1,3-disubstituted phenyl ring relative to the 1,4- and 1,2-congeners (7 vs 10 and 12). Every possible position of hydantoin attachment was investigated (e.g., substitution at N1, N3, and C5). The hydantoin involving attachment to N1 (24) was found to have good biological activity, whereas those hydantoins with attachment to N3 or C5 (22, 23, and 25) were inactive. Several of the smaller acetylated derivatives (30 and 33) have fair in vivo activity, which was lost in the case of the larger benzoyl analog 31. Uracil congener 34 had modest affinity for the D2 receptor (65 nM) as well as excellent in vivo activity. Benzylamino compounds display (viz. 27 and 35-38) moderate CAR activity but have surprising receptor affinity, often greater than those of comparable structures bearing a carbonyl (36 vs 7). Benzyl and benzhydryl alcohol compounds 40-48 are more active than amino structures 27 and 35-38 and also exhibit excellent in vivo activity in the CAR test with modest D2 and 5-HT1A receptor binding.

In vivo demonstration of the enhancement of MK-801 by L-glutamate.

MK-801 infused bilaterally into the nucleus accumbens of rats produced a dose-related increase in locomotor activity that was not blocked by intra-accumbens infusion of haloperidol (2.5 micrograms). Intra-accumbens infusion of L-glutamate (1.0 microgram) was without effect when administered alone, but significantly enhanced the increase in locomotor activity produced by MK-801 (5.0 micrograms). The inactive isomer of MK-801 did not produce hypermotility and L-glutamate did not enhance amphetamine(intra-accumbens)-induced hypermotility. These results extend to an in vivo model electrophysiological and radioligand binding studies demonstrating an enhancement of MK-801 activity by L-glutamate. The results also reinforce the concept that such an enhancement would occur during an escalation of excitatory amino acid levels accompanying pathological overload and, thus, would trigger a compensatory neuronal protection by MK-801.

Reciprocal hindlimb scratching and putative subtype-selective muscarinic agents.

We have previously proposed that the reciprocal hindlimb scratching (RHS) of mice elicited by intrathecal injection of muscarinic agents is mediated by M1 muscarinic receptors. In this study, benzhexol potently inhibited pilocarpine-induced RHS (ID50 = 0.5 ng), methoctramine did not fully block RHS and RS 86 neither produced nor blocked RHS. These data (1) differentiate the three muscarinic agents using this in vivo endpoint, (2) substantiate binding studies characterizing benzhexol and methoctramine as putative M2 and M2 antagonists, respectively, and (3) further support using RHS for studying muscarinic agents.