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KMID : 0377619630050030232
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Korean Jungang Medical Journal
1963 Volume.5 No. 3 p.232 ~ p.233
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Experimental studies concerning the effects of serotonin on sense of pain
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Kim, Hei Sung
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Abstract
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Since the discovery of serotonin by Rapport in 1948, it has been reported by numerous investigators that serotonin plays an important role in the function of central nervous system. Schneider and Rein reported that reserpine which is a serotonin releaser inhibits the analgesic action of morphine. Emele, using hot plate method, demonstrated that MAO inhibitors such as JB516 have about the same potency of analgesic action as that of codeine. However, no direct evidence is available to indicate that serotonin produces analgesic activity. This experiment is, therefore, undertaken to evaluate analgesic activity of serotonin.
Materials and Methods :
Albino rats weighing about 150 g were employed. Analgesic activity of drugs was measured by determining the withdrawal time of tail (pseudopain sense reflex)using the Automatic Thermostimulator (author´ s device) at the fixed temperature of 65°C. Sleeping time of rats was determined by measuring the time from disappearance of orthostatic reflex to the moment of its recovery. The serotonin content in brain was determined by Aminco-Bowmann´s spectrophoto-fluorometer according to the method of Bogdanski et al.
Results :
1) Intraperitoneal injection of serotonin in a dose of 5 mg/kg produced no appearent effects in rats. But a dose of 15 mg/kg of serotonin decreased the voluntary movement and produced a sleep and a significant delay in the onset of pseudopain sense reflex 30 min. after the administration. The injection of 30 Mg/kg resulted in a deep sleeping within 5 min., lasting for 90 min. The onset of pseudopain sense reflex in rats treated with serotonin of 30 mg/kg was also markedly delayed and the mean onset time of this reflex was 147 sec. which was statisti cally significant compared with that observed in normal animals (P<0. 01).
2) The inhibitory effect of morphine on the pseudopain sense reflex of rats was significantly enhanced by the administration of serotonin.
3) Antipyretic analgesics such as antipyrine, arninopyrine and salicylates produced no effects on the pseudopain sense reflex of normal and serotonin-treated rats.
4) i\´lean serotonin content in rat´s brain was 0.53 ± 0.01 ug/g 30 min. after intraperitoneal injection of serotonin 30 mg/kg. This value is not significantly different from the mean brain serotonin content of 10 normal rats of 0.55±0.04 fag/g.
5) The inhibitory activity of morphine on the pseudopain sense reflex of rats was affected by pretreamtent neither with JB516 which elevates the brain serotonin content not with reserpine which depletes the brain serotonin.
6) Intraperitoneal injection of pentobarbital sodium 20 mg/kg produced a deep sleep as well as an inhibition of pseudopain sense reflex in rats. The inhibitory activity of morphine on the pseudopain sense reflex was markedly enhanced by pre-treatment with pentobarbital sodium.
7) The administration of serotonin prolonged the sleeping time induced by previous injection of pentobarbital sodium and vice versa.
8) Serotonin or pentobarbital sodium markedly depressed the convulsion of rats induced by the administration of strychnine 1 mg/kg.
From the above results, it may be concluded that serotonin produces inhibition of the pseudopain sense reflex as judged by Automatic Thermostimulator, and suggests that it may posses an analgesic activity. It appears that the inhibitory activity of serotonin on the pseudopain sense reflex of rats is associated with its sleeping activity and related partially to the decreasing of the spinal. reflex excitability. On the basis of the fact that the inhibitory activity of morphine on the pseudopain sense reflex is intensified by the aministration of serotonin, it may be concluded that serotonin may enhance the analgesic ation of morphine. The mechanims of this enhancement remains obscure but seems to be the same as that by which pentobarbital enhances the analgesic action of morphine.
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KEYWORD
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