ABSTRACT
Objective To examine whether microinjectlon of morphine into the rat thaiamle nucleus submedlus (Sin) could depress the bee venom (BV)-induced nociceptive behaviours. Methods In inflammatory pain model induced by BV subcutaneous injection into rat unilateral hind paw, the inhibitory effects of morphine microinjection into thalamic nucleus suhmedius (Sin) on the spontaneous nociecptlve behavior, heat hyperalgesia and tactile ailodynia, and the influence of naioxone on the morphine effects were observed in the rat. Results A single dose of morphine (5.0 μg, 0. 5μL) applied into the Sm ipsilaterni to the BV injected paw significantly depressed the spontaneous paw flinching response. Morphine also significantly increased the heat paw withdrawal iateneies in the bilateral hind paw and the tactile paw withdrawal threshold in the ipsilnteral hind paw 2 hours after BV injection. All these depressive effects could be effectively antagonized by pre-treatment with the opiuld receptor antagonist naloxone (1.0μg, 0. 5μL) in the Sm 5rain prior to morphine administration. Naloxone alone injected to the Sm had no effect on the BV-induecd nociceptive behavior. Conclusion These results suggest that Sm is involved in opioid receptor-mediated antt-nociception in the rat with the BV-induced inflammatory pain. Together with results from previous studies, it is likely that this effect is produced by activation of the Sm-ventrolateral orbital cortex-periaqueductal gray pathway, leading to activation of the brainstem descending inhibitory system and depression of the nodceptive inputs at the spinal cord level.
ABSTRACT
Objective To investigate whether the μ- and δ-opioid receptors were involved in mediating the a ntinociceptive effect of opioid injection into the nucleus submedius (Sm). Methods Nociceptive behavior produced by subcutaneous injection of formalin (65 mmol/L, 50 μL) into the hind paw of the rat was assessed quantitatively using an automated movement detection system. The effects of morphine and selectiveμ- and δ-opioid receptor antagonists microinjected unilaterally into the Sm were determined in the awake rats. Results Morphine (31 mmol/L, 0. 5 μL) depressed the nociceptive behavior elicited by formalin, and this effect was antagonized completely by the selective μ-receptor antagonist β-funaltrexamine (β-FNA, 0. 4 mmol/L, 0. 5 μL) and naloxonazine (0.8 mmol/L, 0.5 μL), and partly by the δ-receptor antagonist naltrindole (0.4 mmol/L, 0.5μL).Administration of morphine into thalamic regions more than 0. 5 mm dorsal to the Sm had no effect on the nociceptive behavior. Conclusion Antinociceptive effects produced by opioid acting on Sm neurons are mediated mainly by μ-opioid receptors, and partly by δ-receptors.
ABSTRACT
Objective To observe and compare the analgesic effects of electro-acupuncture(EA)of “Tsusanli point” (St. 36) with various stimulation parameters. Methods Single wide dynamic range (WDR) and nociceptive specific (NS) neurons were recorded extracellularly in the dorsal horn of the rat lumbar spinal cord. The late train discharges (C-response) of the neurons evoked by intense electrical stimulation of the skin were used as a nocicepive response. The inhibitory effects of EA stimulation of the “Tsusanli point” (St. 36) with various intensities (1 and 6 mA) and frequencies (5, 20, 50 and 100 Hz) on the C-response were observed, respectively. Results A lower frequency (5 Hz) was appropriate to the high-intensity EA, while a higher frequency (50 Hz) was proper for the low-intensity EA. Conclusion The effect of EA on the spinal nociceptive transmission is both intensity- and frequency-dependent.
ABSTRACT
Standard electrical quantity (a), chronaxie (?), rheobase (Rh), "b" in Weiss' formula and intensity threshold of duration being 40 ?s and 300 ?s (T_(?) and T_(200)) were measured on peroneus nerves in rabbits. The results show that "a" is an actual index for measuring the excitability of various groups of fibers. The larger fibers, the higher excitability and the smaller "a" values. "b" does not indicate excitability. "?" , "Rh" , "T_(40)" and "T_(200)" are not actual indexes for measuring excitability because they are influenced by "b" in Weiss' formula.
ABSTRACT
A total of 100 neurons were recorded from the nucleus raphe magnus (NRM), of which 59 were identified as noxious-exaitation neurons; 30 as noxioes-inhibition neurons; 5 as non-noxious neurons; and 6 as non-responsive neurons Seventy neurons were further tested with electro-acupuncture (EA). 69.77% of the noxious-excitation neurons were excited and 68.42% of the noxious -inhibition neurons inhibited by EA. Stimulation of the periaqueductal gray (PAG) could activate the majority of the EA-response neurons. Systemic morphine could also affect the EA-response neurons through the following three patterns: excitation, inhibition and no-effect. No signilicant correlation between the response patterns of EA and morphine was found. The results indicate that the effect of NRM in EA and morphine analgesia is only partially overlapped.