PubMed · 8977691
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L Juhlin, M J Olsson. 1996. Vitiligo.. https://doi.org/10.1111/j.1365-2133.1996.tb03901.x
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Behavioural and plasma cortisol changes were recorded for groups of eight Suffolk x Greyface lambs subjected to castration or tail docking using rubber rings with and without local anaesthetic treatment. Immediately after application of the rubber ring, local anaesthetic (2 x 0.2 ml 2% lignocaine) was administered either by needle and syringe or by high-pressure needleless injection into each side of the neck of the scrotum or tail at the site of the ring, or by high pressure needleless injection into the testes before ring application. In other groups, the innervation to the scrotum or tail was disabled by crushing with a powered bloodless castrator just proximal to the ring. Measurements were recorded in groups of control (handled) lambs, with and without local anaesthetic treatment. Application of local anaesthetic by high pressure needleless injection had little effect on either plasma cortisol values or behaviour of control lambs. For castration, application of the bloodless castrator and/or local anaesthetic at the ring site reduced the peak plasma cortisol concentration by 50% (P < or = 0.01), the incidence of active behavioural responses by 80 and 64% (P < or = 0.01) respectively, and the time spent in abnormal postures by 68 and 59% (P < or = 0.01) respectively. Both methods were effective in reducing pain for tail docking [active behavioural responses reduced by more than 80% (P < or = 0.01) and abnormal postures by 56% (P < or = 0.01)], although local anaesthetic was more effective, reducing the peak cortisol by 60% (P < or = 0.01) [crushing by 44% (P > 0.05)]. Injection of local anaesthetic into the testes was less effective than injection into the neck of the scrotum at the site of the ring [reduction in abnormal lying postures (P < or = 0.05), 45 vs 71%, respectively]. The rapid action, effectiveness, and ease of application of these experimental methods may provide the basis for commercially viable methods for reducing the acute pain produced by rubber ring castration and tail docking of lambs.
BACKGROUND: It has been proposed that the measure of noxious stimulus-induced Fos (the protein product of the immediate early gene c-fos) expression in the spinal cord dorsal horn of laboratory animals may provide an estimate of the potential of specific treatments to produce preemptive analgesia. The present study examined this hypothesis by comparing the effects of intrathecal lidocaine given before and after hindpaw formalin injection on persistent nociceptive responses and Fos expression in spinal cord dorsal horn of rats. METHODS: Formalin-induced nociception and Fos expression in the spinal cord, in response to a 50-microl injection of 2.5% formalin into the hind paw, were assessed in rats given an intrathecal injection of 50 microl 2% lidocaine by lumbar puncture between the L5 and L6 vertebrae, either 3 min before (pretreatment) or 5 min after (post-treatment) formalin injection. RESULTS: Pain behaviors (hindpaw licking, elevation, and favoring) in the second phase of the formalin test were significantly reduced by pretreatment, but were unaffected by post-treatment. The number of immunocytochemically stained Fos-positive cells and the immunoprecipitation of the Fos antibodies were reduced by pretreatment, and were also reduced, to a lesser extent, by post-treatment. CONCLUSIONS: The finding that persistent nociceptive behaviors and Fos expression were suppressed by intrathecal lidocaine pretreatment suggests that nociception in the second phase of the formalin test depends on increases in central hyperexcitability generated during the first phase. On the other hand, the finding that the intrathecal injection of lidocaine after formalin treatment reduced Fos expression but not nociceptive responses indicates an uncoupling of the behavioral and Fos protein responses to formalin and suggests that changes in Fos expression may not be a good predictor of the ability of agents to produce preemptive analgesia.
BACKGROUND: The dorsal horn of the spinal cord is a pivotal point for transmission of neuronal pain. During spinal and epidural anesthesia, the neurons of the dorsal horn are exposed to local anesthetics. Unfortunately, little is known about the action of local anesthetics on the major ionic conductances in dorsal horn neurons. In this article, the authors describe the effects of bupivacaine, lidocaine, and mepivacaine on voltage-gated Na+ and K+ currents in the membranes of these neurons. METHODS: The patch-clamp technique was applied to intact dorsal horn neurons from laminae I-III identified in 200-microm slices of spinal cord from newborn rats. Under voltage-clamp conditions, the whole-cell Na+ and K+ currents activated by depolarization were recorded in the presence of different concentrations of local anesthetics. RESULTS: Externally applied bupivacaine, lidocaine, and mepivacaine produced tonic block of Na+ currents with different potencies. Half-maximum inhibiting concentrations (IC50) were 26, 112, and 324 microM, respectively. All local anesthetics investigated also showed a phasic, that is, a use-dependent, block of Na+ channels. Rapidly inactivating K+ currents (KA currents) also were sensitive to the blockers with IC50 values for tonic blocks of 109, 163, and 236 microM, respectively. The block of KA currents was not use dependent. In contrast to Na+ and KA currents, delayed-rectifier K+ currents were almost insensitive to the local anesthetics applied. CONCLUSIONS: In clinically relevant concentrations, local anesthetics block Na+ and KA currents but not delayed-rectifier K+ currents in spinal dorsal horn neurons. The molecular mechanisms of Na+ and K+ channel block by local anesthetics seem to be different. Characterization of these mechanisms could be an important step in understanding the complexity of local anesthetic action during spinal and epidural anesthesia.