Antiamnesic effect of metoprine and of selective histamine H1 receptor agonists in a modified mouse passive avoidance test

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Abstract

The aim of this study was to elucidate the effect caused by the inhibition of histamine catabolism by means of metoprine and the activation of histamine H1 receptors by selective agonists on learning and memory processes, using a modified method of the mouse passive avoidance test. The administration of scopolamine 1 mg/kg (i.p.) immediately after the training session caused statistically-significant amnesia during the retention trial performed 24 h later. Piracetam (30 mg/kg (i.p.)), used as a positive control, and administered 20 min before the training session, prevented scopolamine-induced memory impairment. The histamine-N-methyltransferase inhibitor, metoprine, (2 and 5 mg/kg (s.c.)) had effects similar to those of this nootropic drug. The highly-selective H1 receptor agonist, 2-(3-trifluoromethylphenyl)histamine (FMPH) (2.65 and 6.5 μg/mouse (i.c.v.)) and the less selective agonist, 2-thiazolylethylamine (2-TEA) (0.1 and 0.3 μg/mouse (i.c.v.)) both antagonized the scopolamine-induced amnesia significantly and in a dose-related manner. The selective H1 receptor antagonist, pyrilamine (20 mg/kg (i.p.)), revealed no effect by itself, but significantly prevented the antiamnesic action both that of the H1 receptor agonists, and that of endogenous histamine, released by metoprine, thus suggesting a cognitive improvement via the activation of H1 receptors.

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Acknowledgements

The authors wish to thank SmithKline Beecham for the generous gift of 2-thiazolylethylamine. This work was supported by grants from the MURST 60 and 40%.

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