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  • Title: [The effect of morphine on the input neuronal system of the spinal cord, participating in the formation of nociceptive pressor reflexes].
    Author: Beliantseva IA, Lukoshkova EV.
    Journal: Biull Eksp Biol Med; 1991 Oct; 112(10):365-8. PubMed ID: 1804344.
    Abstract:
    Effect of morphine applied to the spinal cord segments L4-S2 or C6-tI on pressor reflexes evoked by supramaximal stimulation of radial and tibial nerve with low frequency (I-2 Hz) was studied in anesthetized cats. Only pressor reflexes elicited by excitation of the tibial nerve afferents were suppressed by morphine applied to the L4-S2 segments. This effect was characterized by diminution of amplitude and steepness of the reflexes and by augmentation of their latency. Both the degree and the rate of the reflex suppression were found to enhance with increasing of morphine concentration from 0.02 to 0.5%. When applied to C6-tI segments, morphine did not suppress the pressor reflexes to the tibial nerve stimulation while reflexes to the radial nerve signals were decreased considerably. In addition to this local action of morphine, the effects resulting from it's distant action, namely, some reduction in systemic arterial pressure and an increase of pressor reflexes evoked by afferent signals entering into the spinal cord segments remote from the application region, were found to occur. All these effects were reversed by naloxone (0.2 mg/kg i. v.). It is concluded that along with attenuation of different withdrawal components of the defence reaction, action of morphine on the opiate receptors of some neurons situated near the entrance of afferent signals into the spinal cord results in suppression of the circulatory components of this reaction.
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