Dual effect of N-methyl-N-(1-methyl-4-pyrolidino)-2-butyl)acetamide on release of (3H)-acetylcholine from the rat hippocampal slices

Modulation of release of acetylcholine from the striatum by a proposed excitatory amino acid antagonist U-54494A: Comparison with known antagonists, diazepam and phenytoin

The effect of (U-54494A) cis-3,4-dichloro-N-methyl-N-[2-(1-Pyrrolidinyl)- cyclohexyl] benzamide monohydrochloride, an excitatory amino acid antagonist, on N-methyl-D-aspartic acid (NMDA)- and K(+)-evoked release of [3H]acetylcholine [( 3H]ACh) from slices of striatum was investigated. For the purpose of comparison, MK 801, PCP, CGP 37849, CPP, phenytoin and diazepam were investigated under identical conditions. Both U-54494A and the excitatory amino acid antagonists blocked NMDA-evoked release of [3H]ACh but these compounds failed to inhibit K(+)-evoked release of this neurotransmitter. Phenytoin blocked both NMDA and K(+)-evoked release of [3H]ACh, whereas diazepam was ineffective under similar conditions. These observations indicate that excitatory amino acid antagonists, including U-54494A, may mediate their anticonvulsant effect by blocking the activity of NMDA receptors, diazepam by activating the benzodiazepine receptors and phenytoin by inhibiting the activity of various depolarizing agents.

Stereoselective binding and activity of oxotremorine analogs at muscarinic receptors in rat brain

The activities of the enantiomers of BM-5 were examined to measure muscarinic cholinergic selectivity in the central nervous system. Autoradiographic studies assessed the ability of each enantiomer to inhibit the binding of [3H]-(R)-quinuclidinyl benzilate ([3H]-(R)-QNB) to muscarinic receptors in the rat brain. (+)-(R)-BM-5 inhibited [3H]-(R)-QNB binding to rat brain sections at concentrations below 1.0 microM, while 100-fold higher concentrations of (-)-(S)-BM-5 were required for comparable levels of inhibition. Analysis of the autoradiograms indicated that both stereoisomers had a similar distribution of high affinity binding sites. Each enantiomer displayed higher affinity for muscarinic receptors in the superior colliculi and lower affinity for receptors in the cerebral cortex and hippocampus. (+)-(R)-BM-5 and oxotremorine inhibited adenylyl cyclase activity in the cerebral cortex with efficacies comparable to that for acetylcholine. (+)-(R)-BM-5 was 26-fold more potent than (-)-(S)-BM-5 in inhibiting adenylyl cyclase. Oxotremorine-M and carbamylcholine stimulated phosphoinositide turnover in the cerebral cortex. Oxotremorine had lower activity and (+)-(R)-BM-5 was essentially inactive at comparable concentrations. The difference in activity of the two enantiomers indicates a remarkable stereochemical selectivity for muscarinic receptors. The stereoselectivity index is comparable for both the autoradiographic assays (48) and measures of adenylyl cyclase activity (26) in the cerebral cortex.

An improved synthesis of the enantiomers of BM-5 and their effects on the central in vivo release of acetylcholine

Racemic N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide (BM-5), a putative postsynaptic agonist and presynaptic antagonist at muscarinic receptors, was resolved into the enantiomers by a new method suitable for large scale preparation. The method involves a chemoselective N-debenzylation as the key step. The enantiomers of BM-5 were obtained after six separate steps in 25% overall yield. The ability of the enantiomers to release acetylcholine was evaluated in vivo by use of brain dialysis. (R)-BM-5 was the more potent enantiomer in this assay.

Effect of irreversible loss of muscarinic receptors on (3H)-acetylcholine release from the hippocampus

The role of muscarinic receptors in the regulation of (3H)-acetylcholine (3H-Ach) release from the hippocampus was investigated with the irreversible cholinergic agonist BM-123 (N-[4(2-chloroethylmethylamino)-2-butynyl]2-pyrrolidone). Pretreatment with BM-123 had no significant effect on spontaneous (3H)-Ach release at 12, 24, 72, and 144 hr. However, this treatment significantly reduced the inhibitory effect of oxotremorine (10 microM) on (3H)-Ach release at 12, 24, and 72 hr (p less than 0.02). At these time intervals, there was a significant loss in muscarinic receptors as determined by (3H)-oxotremorine-M binding. The maximum loss of both oxotremorine-induced inhibition of (3H)-Ach release and muscarinic receptors occurred at 12 hr. Both parameters returned to normal by 144 hr. There was a linear relationship between the recovery of (3H)-Ach release and (3H)-oxotremorine-M binding sites. These results indicate that muscarinic receptors play a significant role in the regulation of (3H)-Ach release in hippocampus, and that this receptor system may lack spare receptors.