Elsevier

Neuropharmacology

Volume 27, Issue 6, June 1988, Pages 603-609
Neuropharmacology

Serotonin-2 receptor-mediated regulation of release of acetylcholine by minaprine in cholinergic nerve terminal of hippocampus of rat

https://doi.org/10.1016/0028-3908(88)90181-5Get rights and content

Abstract

5-Hydroxytryptamine (5-HT) inhibited the K+-induced release of [3H]acetylcholine ([3H]ACh) from slices of the hippocampus of the rat, dose-dependently. Minaprine (3-(2-morpholinoethylamino)-4-methyl-6-phenylpyridazine, Fig. 1) had no effect on the release of [3H]ACh. However, it inhibited the

Fig. 1. Chemical structure of minaprine dihydrochloride. attenuation of the release of [3H]ACh by 5-HT dose-dependently. The 5-HT2 receptor antagonists, mianserine, methysergide and spiperone, prevented the inhibitory effect of the 5-HT, as well as did minaprine. The attenuating effect of 5-HT was not mimicked by the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and was not prevented by a 5-HT1A and 5-HT1B mixed receptor antagonist, propranolol, or by the 5-HT3 receptor antagonists, cocaine and metoclopramide.

Minaprine inhibited the bindings of [3H]5-HT, [3H]8-OH-DPAT and [3H]ketanserin in the hippocampus. The inhibitory effect of minaprine on the binding of [3H]ketanserin was more marked than on the binding of [3H]5-HT and [3H]8-OH-DPAT, and was non-competitive. The K1 value of minaprine for the binding of [3H]ketanserin was 2.9 μM.

The inhibitory effect of 5-HT on the release of [3H]ACh was observed in the presence of tetrodotoxin. By electrolytic lesioning of the medial septum, the K+-induced release of [3H]ACh from the slices of hippocampus was significantly reduced and the release was no longer inhibited by 5-HT. The lesioning significantly decreased the binding of [3H]ketanserin in the hippocampus, with hardly any reduction in the binding of [3H]5-HT and [3H]8-OH-DPAT.

These results suggest that minaprine suppresses the inhibitory effect of 5-HT on the release of ACh in the hippocampus through inhibition of the binding of 5-HT at the 5-HT2 receptor site on the nerve ending of cholinergic neurons, which come from the medial septum.

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