The effects of iontophoretically applied opiates were tested on 24 spinothalamic tract cells in 12 anesthetized monkeys. The drugs used were chosen because of their agonist actions on different classes of opiate receptors (mu, morphine; kappa, dynorphin; delta, methionine enkephalinamide; sigma, N-allylnormetazocine or SKF 10047 and phencyclidine). The actions of the opiate drugs were generally inhibitory, although excitatory or mixed effects were sometimes seen, especially with morphine and dynorphin. Drug effects could change, depending on the position of the iontophoretic electrode array or on the current employed. Naloxone sometimes antagonized the action of the opiate drugs used, but naloxone did not seem to be a drug suited for iontophoretic application. A number of explanations are discussed to explain the variable actions of the opiate drugs.
SUMMARY1. Systemic arterial blood pressure changes in response to stimulation of the distal stump of the cut spinal ventral root were investigated in anaesthetized, vagotomized, and carotid sinus-denervated cats.2. Low intensity electrical stimulation (< 20 T, where T is threshold intensity) of the ventral root caused a rise in blood pressure. This elevation was abolished by paralyzing the muscles with gallamine. This pressor response has been reported previously, and it is likely to be evoked by afferents excited by the contracting muscle.3. High intensity electrical stimulation (500 T) of the ventral root caused a second and marked pressor response. This was not affected by muscular paralysis or by cutting the sciatic nerve, but it was abolished by cutting the dorsal root.4. Threshold intensity for the second component of the pressor response was within the same range as the intensity needed for activation of C fibres in the ventral root, ranging between 200 T and 300 T. This response was graded with increasing stimulus intensity, and it showed both spatial and temporal summation.5. From the above results, we conclude that non-myelinated fibres in feline spinal ventral root course distally to the dorsal root ganglion and then enter the spinal cord via the dorsal root. Activation of these fibres results in a marked elevation of the systemic arterial blood pressure as in other somato-sympathetic reflexes induced by peripheral C fibre activation.
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