Original Articles

Effect of CNS monoamine transmitters upon the pain and analgesia

Shi-lan Ren, Guo-ju Zhao, Guang-gou Luo


1. The evoked potentials (EP) was induced in the sensorimotor cortex central tegmenal fasciculus (CTF) of the midbrain and nuclei medialis group (NMG) of the thalamus by electrical stimulation of the sciacic nerve in mice, rats and rabbits. Intracerebral microinjection of 5-HT induced depression of EP. There was no obvious change in NA. Injection of morphine into NMG yielded significant depressions of EP.
2. The pain threshold (screech from electrical stimulation to the tail) in mice was reduced 24 h after reserpine 1 mg/kg ip. Then, the mice of reduced pain threshold were given microinjections of NA, 5-HT or DA to complement the monoamines which were depleted in CNS by reserpine. Only 5-HT produced a significant restoration of the pain threshold.
3. Injection of 5-HT into the brain of mice to elevate CNS 5-HT levels has effected a rise in the pain threshold, particularly at 5 and 60 min (P<0.01). l-Try ip had no obvious effects on the pain threshold of the mice.
4. The morphine analgesic action was reduced, but not abolished, by resperpine.
To summarize, the CNS 5-HT level runs parallel to the pain threshold in electrophysiologic response and pain behavior. No significant effects were noted when the levels of other monoamines were altered in brain.

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