The role of spinal cholecystokinin B receptors in thermal allodynia and hyperalgesia in diabetic mice

We examined the tail-flick response to various heat intensities in diabetic and non-diabetic mice. Heat intensities were set to one of six values by adjusting the source of voltage for a 50-W projection bulb to 20, 25, 35, 50, 65 and 80 V. Tail-flick latencies at source voltages of 35 and 50 V in diabetic mice were significantly shorter than those in non-diabetic mice. However, tail-flick latencies at 25, 65 and 80 V in diabetic mice were not significantly altered. Although tail-flick latencies in non-diabetic mice were not affected by i.t. pre-treatment with CI-988, a selective cholecystokinin B (CCK(B)) receptor antagonist, those at 35 and 50 V in diabetic mice were significantly increased. In non-diabetic mice, i.t. pre-treatment with cholecystokinin octapeptide (CCK-8), at a dose of 0.3 ng, decreased tail-flick latencies at 35 and 50 V. Furthermore, the attenuation of tail-flick latencies induced by i.t. pre-treatment with CCK-8 in non-diabetic mice was reversed by i.t. pre-treatment with CI-988. Protein kinase C (PKC) activator phorbol-12, 13-dibutyrate (PDBu)-induced reduction in the tail-flick latencies at heat intensities of 35 and 50 V in non-diabetic mice was dose-dependently and significantly reversed by i.t. pre-treatment with CI-988. On the other hand, the CCK-8-induced thermal hyperalgesia and allodynia at heat intensities of 35 and 50 V in non-diabetic mice were inhibited when PKC activity was inhibited by i.t. pre-treatment with calphostin C. These results indicate that the thermal allodynia and hyperalgesia in diabetic mice may be due, at least in part, to the activation of CCK(B) receptors followed by the activation of PKC in the spinal cord.     

CCK(B) receptor antagonist L365,260 potentiates the efficacy to and reverses chronic tolerance to electroacupuncture-induced analgesia in mice

Cholecystokinin octapeptide (CCK-8) is a physiological antagonist of endogenous opioids in the central nervous system (CNS). Our previous work has shown that CCK-8 plays an important role in the development of tolerance to morphine analgesia and electroacupuncture (EA) analgesia in the rat. The present studies were designed to examine whether the CCK(B) receptor is involved in the modulation of EA analgesia and the development of EA tolerance in mice. The latency to flick the tail in the radiant heat was used as index to assess the efficacy of EA analgesia. Subcutaneous (s.c.) injection of the CCK(B) receptor antagonist L365,260 produced a dose-dependent (0.125-2.0 mg/kg) potentiation of the analgesia induced by 100 Hz EA, with a maximal effect occurred at 0.5 mg/kg. In addition, L365,260 (0.5 mg/kg) significantly reversed chronic tolerance to 100 Hz EA in mice. These results suggest that the CCK(B) receptor might play a role in the tonic inhibition of 100 Hz EA-induced analgesia and in the mediation of chronic tolerance to 100 Hz EA in mice. The results opened a way for further investigation of the function of CCK-8 in pain modulation using inbred strains of mice.     

在尾核痛反应神经元和整体甩尾反射水平上研究CCK-8对抗电针的镇痛作用

目的 研究八肽胆囊收缩素（CCK-8）对抗电针（EA）对大鼠尾核（Cd）中痛反应神经元放电和甩尾潜伏期（TFL）痛阈的同时影响。方法 采用同步记录大鼠Cd中痛兴奋神经元（PEN）或痛抑制神经元（PIN）电变化与辐射热照大鼠尾所引起TFL的方法。结果 （1）辐射热照大鼠尾可使PEN诱发放电增加或PIN诱发放电减少的同时发生甩尾反射，表现出辐射热致疼痛效应。（2）EA双侧“足三里”15min，可抑制PEN的电活动或加强PIN的电活动，同时使TFL延长，即呈现出EA的镇痛效应。（3）脑室（icv）注射CCK-8（10ng／10μl）能同时对抗EA所引起的PEN或PIN和TFL的镇痛作用。结论 CCK-8的抗EA镇痛作用，在中枢痛反应神经元电活动和整体行为反射水平上是协调一致的。揭示，PEN和PIN的电活动作为疼痛和镇痛指标是确实可行的。     

A comparative study on characterization and distribution of cholecystokinin binding sites among the rat, mouse and guinea pig brain

Using the in vitro quantitative receptor autoradiographical technique, [propionyl-3H]propionylated cholecystokinin octapeptide ([3H]pCCK-8) binding sites were investigated in tissue sections of rat, mouse and guinea pig brains. In all the tested animals, [3H]pCCK-8 bound very slowly to the tissue sections. Dissociation was also slow, and had a biphasic profile suggesting CCK-8 binding sites are heterogeneous. Dissociation rate constants were, however, unequal among these species. In the saturation binding studies, both Bmax and (Kd)app values varied among the animal species. The autoradiograms revealed marked species differences in [3H]pCCK-8 binding sites in the brain among 3 closely related species of rodents. [3H]pCCK-8 binding sites were undetectable in the nucleus accumbens/caudate-putamen and the amygdaloid complex of the mouse brain, and scarcely found in the ventromedialis of the hypothalamus of the mouse and guinea pig brain. Furthermore, moderate-to-high densities of [3H]pCCK-8 binding sites were observed in the cerebella of the mouse and guinea pig, whereas in the rat cerebellum the binding sites were undetected. The above-mentioned observations suggest the existence of species differences in the binding pattern of CCK-like peptides among closely related animal species. Furthermore, it would appear that CCK-like peptides in the brain may play different physiological roles among animal species.     

Brain cholecystokinin and β-endorphin systems may antagonistically interact to regulate tissue DNA synthesis in rat pups

Previously, we have shown that intracisternal (i.c.) administration of β-endorphin suppresses brain and liver DNA synthesis in rat pups. This finding is consistent with the view that endogeneous CNS β-endorphin plays an important role in controlling postnatal growth. Recent evidence suggests that brain CCK₈, the sulfated carboxyterminal octapeptide fragment of cholecystokinin, may function physiologically as an endogenous opioid antagonist. We now report that CCK₈ injected i.c. together with β-endorphin effectively prevented β-endorphin from inhibiting brain and liver DNA synthesis in 10-day-old rats. CCK₈ blocked the liver DNA effect of β-endorphin via actions within the brain, as subcutaneous administration of CCK₈ was ineffective. In contrast to CCK₈, i.c. administration of CCK_8U (the unsulfated form of CCK₈) together with β-endorphin did not prevent β-endorphin from inhibiting liver DNA synthesis, and only slightly reversed the brain DNA effect.The results obtained support a role for endogenous brain CCK₈ in the modulation of tissue DNA responses to CNS β-endorphin and possibly to other endogenous opioids. If so, interference with brain CCK function could disrupt tissue growth. Thus, normal mammalian development may require a close functional interaction between the cholecystokinin and β-endorphin systems in the brain.     

Resistance to diet-induced obesity is associated with increased proopiomelanocortin mRNA and decreased neuropeptide Y mRNA in the hypothalamus

Mechanisms mediating genetic susceptibility to diet-induced obesity have not been completely elucidated. Elevated hypothalamic neuropeptide Y (NPY) and decreased hypothalamic proopiomelanocortin (POMC) are thought to promote the development and maintenance of obesity. To assess the potential role of hypothalamic neuropeptide gene expression in diet-induced obesity, the present study examined effects of a high-fat diet on hypothalamic NPY and POMC mRNA in three strains of mice that differ in susceptibility to develop diet-induced obesity. C57BL/6J, CBA, and A/J mice were fed either normal rodent chow or a high-fat diet for 14 weeks after which hypothalamic gene expression was measured. On the high-fat diet, C57BL/6J mice gained the most weight, whereas A/J mice gained the least weight. On the high-fat diet, NPY mRNA significantly decreased as body weight increased in CBA and A/J mice, but not in C57BL/6J mice. In addition, POMC mRNA significantly increased as body weight increased in A/J mice, but not in CBA and C57BL/6J mice. Since decreased NPY mRNA and increased POMC mRNA would presumably attenuate weight gain, these results suggest that a high-fat diet produces compensatory changes in hypothalamic gene expression in mice resistant to diet-induced obesity but not in mice susceptible to diet-induced obesity.     

针刺穴位对重度颅脑损伤患者脑脊液中IL-8、sICAM-1含量的影响

目的观察针刺治疗对重度颅脑损伤患者脑脊液中白细胞介素-8( IL-8)、可溶性细胞粘附分子-1(sICAM-1)含量的影响,并探讨针刺治疗的脑保护作用机制.方法 50例重度颅脑损伤患者随机分为对照组和治疗组.对照组(24例)应用常规治疗,治疗组(26例)在常规治疗基础上于入院后第1 d起针刺涌泉和历兑穴(时间为30 min,1次/d,共7 d),采用酶联免疫吸附方法(ELISA)检测患者伤后1、2、3、5、7 d脑脊液中IL-8、sICAM-1含量.结果①对照组脑脊液中IL-8、sICAM含量在伤后1 d升高,2 d达高峰,3 d开始下降, 5 d进一步下降,7 d下降到正常水平;②治疗组脑脊液中IL-8、sICAM-1含量在伤后1 d升高,2 d下降,3 d继续下降, 5 d下降到正常水平;③治疗组伤后2、3、5 d脑脊液中IL-8、sICAM-1含量均低于对照组相应时相点脑脊液中IL-8、sICAM-1含量( P <0.05).结论针刺治疗能减轻重度颅脑损伤后脑内炎症反应,从而减轻因炎症反应引起的继发性脑损害,为重度颅脑损伤后的脑保护治疗提供了新途径.