[Role of the somatic monoaminergic systems in the mechanisms of regulation of pain sensitivity during reflex stimulation].

Experiments on rats were performed to study the role of the monoaminergic systems in the mechanisms of analgesia produced by stress (foot shock) and auricular electroacupuncture (AEA). Analgesia was measured by the hot-plate (HP) and the tail-flick (TF) tests. Inhibition of catecholamine synthesis with alpha-methyl-p-tyrosine (alpha-MPT) antagonized the AEA-induced analgesia measured by the TF test. alpha-MPT did not influence the HP test latency after AEA, and HP or TF tests after stress. Inhibition of dopamine receptors by haloperidol produced a decrease in the stress- and AEA-induced analgesia. The similar effects were demonstrated in propranolol treated rats after AEA. P-chlorophenylalanine (an inhibitor of serotonin synthesis) suppressed the stress-induced analgesia measured by the HP test and AEA-induced analgesia measured by the HP or TF tests. The data indicate that the monoaminergic systems are involved in the stress- and AEA-induced analgesia. Apart from the monoaminergic systems, other neurochemical mechanisms are also involved in the stress- and AEA-induced analgesia.