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Pharmacology Studies on the intrathecal effect of endorphin in primate
394
Studies on the in~ath~a1 effect of endorphin in primate. - T.L. Yaksh, K.E. Gross and Choh Hao Li (Departments of Neurosurgery and Pharmacology. Mayo Foundation, Rochester, Minn. 55905, U.S.A.), Brain Res., 241 (1982) 261-269. The intrathecal administration of /3-endorphin in the primate through an indweliing spinal catheter, produced a significant elevation in the nociceptive threshold as measured by the discrete trial shock titration task. The time of onset, duration of effect and magnitude of effect were all dose dependent over a range of 150- 750 pg. The effects were antagonized in a dose-dependent fashion by the systemic administration of naioxone. Aside from the elevations in the shock titration threshold produced by intrathecal ,&endorphin, no untoward effect on the animal’s motor function or behavioral reactivity was noted. There was no change in mean blood p0, and pCO,, heart rate and blood pressure measured immediately before and at 1, 3 and 6 h after intrathecal injection of /?-endorphin. The intrathecal administration was unaccompanied by any signs of irritation, agitation, retching or changes in pupil size. Significantly, unlike morphine, intrathecal ~-endo~hin failed to produce any signs of scratching behavior at the doses used in these experiments. Once daily administration of intrathecal /3-endorphin (500 pg) showed a significant progressive decline in the ~tinociceptive effect over an 8 day period. Animals made tolerant to /3-endorphin in this fashion showed a significantly reduced response to an otherwise active dose of intrathecal morphine, indicating evidence for cross-tolerance.
STOMATOLOGY is a selective stimulation of the rat incisor tooth pulp possible? -
P. Engstrand, B.-C. Shyu and S.A. Andersson, Pain, 15 (1983) 27-34. Stimulation of the tooth pulp in animals is commonly used as an exclusive source of noxious stimulation. Nevertheless there is considerable debate whether the rat incisor tooth pulp can be selectively stimulated. By recording compound action potentials from the mandibular nerve, these authors have provided data confirming Hayashi’s finding (Exp. Neurol., 67 (1980) 438) that such stimulation always activates nerve fibers outside the tooth pulp. The recorded compound action potential had the same threshold and Iatency before and after apical tooth pulp removal. Similarly, transection of the nerve fibers at the root apex and connecting the tooth pulp with the alveolar nerve, resulted in compound action potentials of the same size, shape and latency recorded from the intact mandibular nerve. Transection further away from root apex abolished the response. It appears that rat incisor tooth pulp stimulation is an inadequate stimulus for activating tooth pulp afferents in isolation and not useful for the study of nociceptive input. Analgesia for orofacial nociception produced by morphine microinjection into the spinal trigeminal complex.. - J.P. Rosenfeld, C. Pickrel and J,G. Broton, Pain, 15
(1983) 145-155. Although there is considerable evidence that opiates have an analgesic action when injected directly into the spinal cord, previously there was no evidence that a
Studies on the in~ath~a1 effect of endorphin in primate. - T.L. Yaksh, K.E. Gross and Choh Hao Li (Departments of Neurosurgery and Pharmacology. Mayo Foundation, Rochester, Minn. 55905, U.S.A.), Brain Res., 241 (1982) 261-269. The intrathecal administration of /3-endorphin in the primate through an indweliing spinal catheter, produced a significant elevation in the nociceptive threshold as measured by the discrete trial shock titration task. The time of onset, duration of effect and magnitude of effect were all dose dependent over a range of 150- 750 pg. The effects were antagonized in a dose-dependent fashion by the systemic administration of naioxone. Aside from the elevations in the shock titration threshold produced by intrathecal ,&endorphin, no untoward effect on the animal’s motor function or behavioral reactivity was noted. There was no change in mean blood p0, and pCO,, heart rate and blood pressure measured immediately before and at 1, 3 and 6 h after intrathecal injection of /?-endorphin. The intrathecal administration was unaccompanied by any signs of irritation, agitation, retching or changes in pupil size. Significantly, unlike morphine, intrathecal ~-endo~hin failed to produce any signs of scratching behavior at the doses used in these experiments. Once daily administration of intrathecal /3-endorphin (500 pg) showed a significant progressive decline in the ~tinociceptive effect over an 8 day period. Animals made tolerant to /3-endorphin in this fashion showed a significantly reduced response to an otherwise active dose of intrathecal morphine, indicating evidence for cross-tolerance.
STOMATOLOGY is a selective stimulation of the rat incisor tooth pulp possible? -
P. Engstrand, B.-C. Shyu and S.A. Andersson, Pain, 15 (1983) 27-34. Stimulation of the tooth pulp in animals is commonly used as an exclusive source of noxious stimulation. Nevertheless there is considerable debate whether the rat incisor tooth pulp can be selectively stimulated. By recording compound action potentials from the mandibular nerve, these authors have provided data confirming Hayashi’s finding (Exp. Neurol., 67 (1980) 438) that such stimulation always activates nerve fibers outside the tooth pulp. The recorded compound action potential had the same threshold and Iatency before and after apical tooth pulp removal. Similarly, transection of the nerve fibers at the root apex and connecting the tooth pulp with the alveolar nerve, resulted in compound action potentials of the same size, shape and latency recorded from the intact mandibular nerve. Transection further away from root apex abolished the response. It appears that rat incisor tooth pulp stimulation is an inadequate stimulus for activating tooth pulp afferents in isolation and not useful for the study of nociceptive input. Analgesia for orofacial nociception produced by morphine microinjection into the spinal trigeminal complex.. - J.P. Rosenfeld, C. Pickrel and J,G. Broton, Pain, 15
(1983) 145-155. Although there is considerable evidence that opiates have an analgesic action when injected directly into the spinal cord, previously there was no evidence that a