褪黑素对颞叶癫痫大鼠海马BDNF表达的影响及意义

目的探讨褪黑素(melatonin,Mel)在匹罗卡品(pilocarpine,PILO)致痫大鼠模型中的抗癫痫作用机制。方法采用匹罗卡品诱导大鼠慢性颞叶癫痫模型,用原位杂交、免疫组化技术检测海马脑源性神经营养因子(BDNF)基因和蛋白表达水平;用Ti mms染色评价苔藓纤维发芽(mossy fiber sprouting,MFS),动态观察了Mel对癫痫大鼠海马BDNF基因、蛋白表达水平的影响及其与MFS的关系。结果(1)PILO诱导大鼠癫痫持续状态(SE)后6h,海马BDNF基因和蛋白表达水平均明显增强;SE后7~14d,BDNF蛋白表达仍维持较高水平,尤其在齿状回处BDNF蛋白高表达可持续至SE后28d。PILO Mel组大鼠海马BDNF基因和蛋白表达与PILO组有着类似变化趋势,但在SE后各时相点BDNF基因和蛋白表达水平均低于PILO组,尤其在SE后6h~7 d表现最为明显(P<0.05)。(2)SE后14 d,PILO组大鼠Ti mms染色密度开始增强,至SE后28 d Ti mms染色密度进一步增强,与PILO Mel组比较差异有统计学意义(P<0.05)。结论Mel对癫痫发作大鼠海马BDNF基因和蛋白表达具有一定的调节作用,这可能是其抑制MFS而发挥抗癫痫作用的机制之一。     

褪黑素鼻粘膜吸收规律的研究

目的 :研究褪黑素鼻粘膜吸收规律。方法 :观察褪黑素在大鼠鼻腔洗出液中的稳定性 ,在此基础上 ,以大鼠在体鼻循环为实验模型 ,研究褪黑素鼻粘膜吸收规律。 结果 :褪黑素在鼻粘膜洗出液中稳定性良好 ,在鼻粘膜吸收符合一级动力学方程 ,褪黑素鼻粘膜吸收常数不随药物浓度发生变化。结论 :褪黑素在鼻粘膜的吸收机制为被动扩散 ,其在鼻粘膜平均吸收速率常数为 1.0 5 4× 10 -2 min-1     

人胚胎中枢神经系统褪黑素受体的鉴定及生物学特性

目的：证实人胚胎脑及脊髓组织是否存在褪黑素（Mel)受体（MR）,阐明Mel生物学行性及对神经系统作用的机制。方法：应用放射配体结合法检测人胚胎脑及脊髓组织^125I-Mel特异结合情况。结果：视网膜^125I-Mil特异结合量最高,视交叉及嗅球次之,其次为下丘脑、海马、脑干;动力学分析表明Mel与其受体的结合为可逆性结合;特异性结合分析提示对Mel呈高度特异性;10和50umol/LGTPγS使^125I-Mel特异结合降低。结论：人胚胎脑和脊髓组织均存在^125I-Mel特异结合位点,GTPγS对^125I-Mel特异结合及亲和力均有一定的影响。支持MR与抑制性G蛋白偶联的观点。     

褪黑素抑制由17—β—雌二醇诱发的垂体催乳素瘤的生长

目的：观察整体条件下褪黑素（melatonin,MLT)抑制由17－β－雌二醇（E2）诱发的垂体催乳素（prolactin,PRL)瘤的生长,并初步探讨其作用机制,方法：以雄性Sprague-Dawley大鼠皮下埋植E2药泵,诱发PRL瘤,实验组大鼠分5组,在诱瘤之前每日定时分别皮下注射0．05,0．25,0．50,1．00和2．00mgMLT,共90d,对照组大鼠皮下注射等体积4％乙醇－生理盐水。结果（1）给予0．05,0．25,0．50,1．00和2．00mg MLT处理组PRL瘤重量分别较对照组降低25．91％（P＞0．05）,48．78％（P＜0．01）,36．78％（P＜0．05）,31．04％（P＞0．05）和35．22％（P＜0．05）,（2）Northern Blot分别表明,注射0．05,0．25,0．50mg MLT组PRL瘤细胞PRL mRNA表达水平分别比对照组降低33．67％（P＜0．05）,25．51％（P＜0．05）和41．84％（P＜0．01）,原代培养的PRL瘤细胞原位杂交实验也获得类似结果;（3）激光扫描共聚焦显微镜检测结果显示,0．05,0．25和0．50mg MLT组PRL瘤细胞DNA的相对含量分别较对照组降低40．73％（P＜0．001）,51．15％（P＜）．001）和60．23％（P＜0．001）;（4）紫外分光光度法测定显示,0．05,0．25,0．50,1．00和2．00mg MLT组血浆过氧化脂质水平分别比对照组降低26．45％（P＜0．05）,23．97％（P＜0．05）,47．11％（P＜0．001）,66．12％（P＜0．001）和64．46％（P＜0．001）。其量－效关系的相关系数为－0．8257（P＜0．05）。结论一定剂量的MLT对E2诱发PRL瘤生长由于显著的抑制作用,MLT的这种抑瘤作用可能是通过其抑制RL基因由高达和DNA合成实现的。     

褪黑素对大鼠体温及活动度昼夜节律的影响

目的　了解外源性褪黑素对大鼠体温及活动度昼夜节律的影响及其可能的调节机制。方法　正常光照条件下,24h连续记录大鼠的体温及活动度的变化,以不同剂量褪黑素在不同的昼夜时间给药观察体温和活动度节律的变化。结果　大鼠的体温及活动度存在昼夜节律性,给药后昼夜节律性不消失;但体温振幅减小,中值降低。黑暗中期给药后,峰值位相显著延迟;活动度振幅增加,中值显著降低,峰值位相延迟。结论　外源性褪黑素不能使体温或活动度的昼夜节律消失,而只是改变昼夜节律的参数。褪黑素可分别调节体温和活动度的昼夜节律,但对活动度的调节作用更为明显。     

血清褪黑素水平与儿童哮喘关系的临床研究

目的:研究支气管哮喘患儿在不同病情时的血清褪黑素水平变化,探讨影响哮喘患儿血清褪黑素水平变化的因素。方法:收集哮喘急性发作期患儿血清样品45例,其中轻度15例、中度15例、重度15例、临床缓解期患儿15例、健康对照组15例,应用ELISA法测定血清样品的褪黑素水平。结果:血清褪黑素水平轻度发作组为(22.76±5.16pg/ml),中度发作组(16.79±3.35pg/ml),重度发作组(11.54±1.45pg/ml),缓解期组(22.06±3.36pg/ml),对照组(28.72±4.32pg/ml)。五组间进行多重比较,除缓解组与轻度发作组无显著差别外,其余各组间差别显著(P<0.05),且随着病情的加重,褪黑素的水平逐渐降低。结论:哮喘患儿血清褪黑素水平明显降低,它的降低可能与患儿睡眠紊乱,机体处于应激状态有关。     

中医"肾应冬"调控机制与褪黑素受体关系的研究

目的通过观察性腺轴褪黑素受体的季节性变化,从而深入揭示“肾应冬”的调控机制。方法采用放射性配基饱和法,检测雄性SD大鼠性腺轴褪黑素受体的最大结合量(Bm ax)和解离常数(Kd值)的冬夏变化。结果在正常生理条件下,下丘脑(P<0.05)和垂体(P<0.05)Bm ax值均表现为冬高夏低。下丘脑(P<0.05)和垂体(P<0.01)Kd值均表现为冬高夏低。摘除松果腺后,冬季手术组下丘脑(P<0.01)、垂体(P<0.01)Bm ax值都明显高于正常组,夏季手术组下丘脑(P<0.01)Bm ax值明显高于正常组。冬、夏手术组下丘脑(P<0.01)、垂体(P<0.01)Kd值都明显高于相应的正常组。而睾丸的褪黑素受体的Bm ax值和Kd值因含量极少而无法测出。结论“肾应冬”调控机制与性腺轴褪黑素受体的季节性变化有关,松果腺在此过程中起了重要的高位调节作用。     

Possible involvement of GABAergic mechanism in protective effect of melatonin against sleep deprivation–induced behaviour modification and oxidative damage in mice

Sleep is an important physiological process responsible for the maintenance of physical, mental and emotional health of a living being. Sleep deprivation is considered risky for several pathological diseases such as anxiety and motor and cognitive dysfunctions. Sleep deprivation has recently been reported to cause oxidative damage. This study has been designed to explore the possible involvement of the GABAergic mechanism in protective effects of melatonin against 72‐h sleep deprivation‐induced behaviour modification and oxidative damage in mice. Mice were sleep‐deprived for a period of 72 h using the grid over water suspended method. Animals were divided into groups of 6–8 animals each. Melatonin (5 and 10 mg/kg), flumazenil (0.5 mg/kg), picrotoxin (0.5 mg/kg) and muscimol (0.05 mg/kg) were administered for 5 days starting 2 days before 72‐h sleep deprivation. Various behavioural tests (plus maze, zero maze, mirror chamber, actophotometer) and body weight assessment followed by oxidative stress parameters (malondialdehyde level, glutathione, catalase, nitrite and protein) were carried out. The 72‐h sleep deprivation caused significant anxiety‐like behaviour, weight loss, impaired locomotor activity and oxidative damage as compared with naïve (without sleep deprivation). Treatment with melatonin (5 mg/kg and 10 mg/kg, ip) significantly improved locomotor activity, weight loss and antianxiety effect as compared with control (sleep‐deprived). Biochemically, melatonin treatment significantly restored reduced glutathione, catalase activity, attenuated lipid peroxidation and nitrite level as compared with control animals (72‐h sleep‐deprived). Flumazenil (0.5 mg/kg) and picrotoxin (0.5 mg/kg) pretreatments with a lower dose of melatonin (5 mg/kg) significantly antagonized the protective effect of melatonin. However, muscimol (0.05 mg/kg) pretreatment with melatonin (5 mg/kg, ip) potentiated the protective effect of melatonin which was significant as compared with their effect per se. This study suggests that GABAergic modulation is involved in the protective action of melatonin against sleep deprivation‐induced anxiety‐like behaviour and associated oxidative damage.     

Melatonin-induced modulation of glucose metabolism in primary cultures of rabbit kidney-cortex tubules

The effect of melatonin on glucose metabolism in the presence and absence of insulin has been investigated in the primary cultures of renal tubules grown in a defined medium. In the absence of glucose in the medium containing 5 microg/mL of insulin and 2 mm alanine + 5 mm glycerol + 0.5 mm octanoate, 100 nm melatonin stimulated both glucose and lactate synthesis, while in the medium devoid of insulin melatonin action was negligible. Melatonin-induced increase in glucose and lactate synthesis was accompanied by an enhancement of alanine and glycerol consumption. In view of measurements of [U-14C]L-alanine and [U-14C]L-glycerol incorporation into glucose, it is likely that melatonin increased alanine utilization for glucose production, while accelerated lactate synthesis was because of an enhanced glycerol consumption. As (i) 10 nm luzindole attenuated the stimulatory action of melatonin on glucose formation and (ii) the indole induced a decrease in intracellular cAMP level, it seems likely that in renal tubules melatonin binds to ML1 membrane receptor subtype. In view of a decline of intracellular fructose-1,6-bisphosphate content accompanied by a significant rise in hexose-6-phosphate and glucose levels, melatonin might result in an acceleration of flux through fructose-1,6-bisphosphatase probably because of an increase in the active, dephosphorylated form of this enzyme. Thus, the administration of melatonin in combination with insulin might be beneficial for diabetic therapy because of protection against hypoglycemia.     

Physiological concentrations of melatonin inhibit the nitridergic pathway in the Syrian hamster retina

In the present work, the effect of melatonin on the hamster retinal nitridergic pathway was examined. When the retinas were incubated in the presence of low concentrations (1 pM-10 nM) of melatonin for 15 min, a significant decrease of nitric oxide synthase (NOS) activity was observed. However, when crude retinal homogenates were preincubated with melatonin for 15 min, no changes in NOS activity were detected, despite the fact that under the same conditions trifluoperazine, a calmodulin inhibitor, significantly decreased enzymatic activity. Kinetic analysis showed that melatonin decreased the V(max) of retinal NOS without changes in the K(m). On the other hand, low concentrations (100 pM) of melatonin significantly reduced retinal L-arginine influx. A decrease in the V(max) of L-arginine uptake was observed in the presence of melatonin, whereas the K(m) remained unchanged. Melatonin significantly inhibited the accumulation of cyclic guanosine monophosphate (cGMP) levels induced by both L-arginine and sodium nitroprusside (SNP). In summary, the present results indicate that melatonin could be a potent inhibitor of the retinal nitridergic pathway.