Effects of Capsaicin on the Primary Sensory Neurons in Rat / 대한마취과학회지

BACKGREOUND: Capsaicin acts specifically on a subset of primary sensory neurons involved in nociception. In addition to its excitatory actions, capsaicin can have subsequent antinociception and anti-inflammatory effects due to pharmacological, functional desensitization and axonal degeneration. Because capsaicin has selective actions on unmyelinated C and thinly myelinated Adelta primary sensory neurons, it can be speculated that intrathecally adminstered capsaicin results prolonged analgesia without adverse effects related to the destruction of the nonnociceptive nerve fibers. METHODS: We performed experiments to investigate the effects of capsaicin on electrophysiological responses of acutely dissociated rat dorsal root ganglion neurons and pain-like behaviors, such as tail flick responses to hot water (53 degrees), formalin-induced hyperalgesic responses and allodynic responses induced by peripheral nerve injury. RESULTS: Capsaicin affects preferentially small- to medium-diameter rat dorsal root ganglion neurons. In capsaicin responsive cells, superfusion with capsaicin evoked membrane potential depolarization and large inward currents. Cellular excitablity was continuously suppressed even after 3 min wash-out. Intrathecally administered capsaicin had no effect on tail withdrawal latencies, but flinching responses induced by subcutaneous formalin and allodynic responses induced by peripheral nerve injury were suppressed by capsaicin. CONCLUSIONS: The results suggest that capsaicin which acts on primary sensory neurons carrying nociceptive information is effective in managing pain induced in a pathological condition, such as inflammatory and neuropathic pain. The data may also be applicable for seeking novel pharmacological strategies for managing intractable pain, i.e. chemical neurolysis.

The Effects of Intrathecal Ketamine Isomers on Formalin-Evoked Behavior and Spinal c-fos Expression in Rat / 대한마취과학회지

BACKGROUND: This study was designed to investigate the different analgesic potency and the action mechanism of the intrathecal isomers of ketamine. For these purpose, we evaluated the effect of intrathecal ketamine isomers on the behavioral response and the spinal c-fos expression in the formalin tested rats. METHOD: The subjects were divided into 2 groups(NF group, Fgroup). The NF group was designed for the purpose of the drug itself's effect on the induction of c-fos. Saline(NF/saline group), S(+) ketamine(NF/SK group), R(-) ketamine(NF/RK group) and ketamine(NF/K group) were administered intrathecally to be examined by immunocytochemical method. Same drugs were administered in the F group(F/saline, F/SK, F/RK, F/K) and formalin was injected into right hind paw of the rats after 30 minutes of intrathecal drug administration. The number of flinching was counted at intervals of 5 minutes for 60 minutes. In NF and F group, Fos immunoreactive neurons was counted after 2 hours of formalin injection and intrathecal drug injection respectively. RESULTS: In F/saline group, flinching was developed immediately after formalin injection and revealed biphasic response. The number of flinching in F/SK group, F/RK group, F/K group was significantly smaller than that of F/saline group. The number of flinching of F/SK group by comparison of F/SK vs F/RK was significantly smaller, and that of F/K group by comparison of F/RK vs F/K was significantly smaller. There was no significant difference among NF group on the total number of Fos immunoreactive neurons. In F group, Fos immunoreactive neurons increased significantly in comparison with NF group. The total number of Fos immunoreactive neurons in F/SK group, F/RK group and F/K group were significantly smaller than that of F/saline group. Of F group, the number of Fos immunoreactive neurons of F/SK was the smallest and F/K, F/RK followed increasing order. Attenuation of Fos induction by the ketamine isomers was observed in the whole spinal cord of F/SK group and F/K group but in the superficial and deep laminae of F/RK group. CONCLUSION: This study suggests that intrathecal ketamine isomers have an inhibitory effect on pathologic pain and c-fos expression in the rats and different analgesic effect which is lamina specific.