Ketamine treatment reverses behavioral and physiological alterations induced by chronic mild stress in rats

Several studies have supported the idea that ionotropic glutamate N-methyl-d-aspartate receptor (NMDA) is an important player in the etiology of psychopathologies, such as anxiety disorders and major depression. Additionally, studies have shown that ketamine induces antidepressant effects in humans as well as in rodents subjected to animal models of depression. In this context, the present study was aimed to evaluate behavioral and physiological effects of acute and chronic administration of ketamine, a NMDA receptor antagonist, in rats exposed to chronic mild stress (CMS). After 40 days of CMS, rats were treated with ketamine (15 mg/kg) and sweet food consumption, body and adrenal gland weight, corticosterone and adrenocorticotropic (ACTH) hormone levels, and hippocampal BDNF protein levels were assessed. Our findings demonstrated that CMS evoked anhedonia, induced hypertrophy of adrenal gland, impaired gain of body weight and increased corticosterone and ACTH circulating levels in rats. Acute and chronic treatment with ketamine reversed the increase in adrenal gland weight, promoted regain of body weight, and normalized corticosterone and ACTH circulating levels. Repeated, but not acute, administration of ketamine reversed anhedonia-like behavior, although the treatment with ketamine per se increased sweet food consumption in non-stressed rats. Finally, acute and chronic ketamine treatment did not alter hippocampal BDNF protein levels in stressed rats. In conclusion, these findings support the idea of a putative role of NMDA receptors in mood-related symptoms, and rapid and robust effects of ketamine in reverting mainly physiological alterations induced by chronic mild stressful situations in rats.     

A novel class of amino-alkylcyclohexanes as uncompetitive,fast, voltage-dependent,N-methyl-D-aspartate (NMDA) receptor antagonists – <Emphasis Type="Italic">in vitro</Emphasis> characterization

The fact that potent NMDA receptor channel blockers produce phencyclidine-like psychotropic symptoms in man and rodents implies that uncompetitive antagonism of NMDA receptors may not be a promising therapeutic approach. However, recent data indicate that agents with moderate affinity such as memantine and neramexane (MRZ 2/579) are useful therapeutics due to their strong voltage-dependency and rapid unblocking kinetics. Merz has developed a series of novel uncompetitive NMDA receptor antagonists based on an amino-alkylcyclohexane structure. These compounds displaced [(3)H]-MK-801 binding to rat cortical membranes with K(i) values between 1 and 100 microM and inward current responses of cultured hippocampal neurons to NMDA were antagonized in a strongly voltage-dependent manner with rapid blocking/unblocking kinetics. Three of these compounds, with similar biophysical properties to memantine, were chosen for development. MRZ 2/759 (1-ethenyl-3,3,5,5-tetramethyl-cyclohexylamine), 2/1010 (1,3,3,5-tetramethyl-6-azabicyclo[3.2.1]octane) and 2/1013 (8,8,10,10-tetramethyl-1-azaspiro[5.5] undecane) displaced [(3)H]-MK-801 binding with K(i) values of 1.18, 2.59 and 3.64 microM, respectively. They were similarly potent against NMDA-induced currents in hippocampal neurons - IC(50) values of 1.51, 3.06 and 2.20 microM, respectively. In line with their moderate affinity, all were voltage-dependent (delta = 0.86, 0.96 and 0.89, respectively) and fast, open-channel blockers (k(on) 7.90, 1.70 and 2.60 x 10(4) M(-1) sec(-1), k(off) 0.13, 0.12 and 0.24 sec(-1), respectively). These compounds are also NMDA receptor antagonists in the CNS following systemic administration and have good therapeutic indices in a variety of in vivo behavioural models where glutamate is known to play a pivotal role. In view of their relatively low affinity and associated rapid kinetics, they should prove to be useful therapeutics in a wide range of CNS disorders.     

Dual effects of 3, 4-methylenedioxymethamphetamine （ecstasy） on survival and apoptosis of primary hippocampal neurons

BACKGROUND： 3, 4-methylenedioxymethamphetamine （MDMA, also known as ＂ecstasy＂） has been shown to exhibit neurotoxic effects on the hippocampus. However, exposure to sub-lethal insults of MDMA has been reported to result in neuroprotection. OBJECTIVE： To investigate the effects of MDMA on hippocampal neuronal viability, caspase-3 activity, and mRNA expression of the N-methyI-D-aspartate （NMDA） receptor 2B （NR2B） subunit. DESIGN, TIME AND SETTING： A cytological, in vitro experiment was performed at the Department of Anatomy, School of Medicine, and Department of Toxicology-Pharmacology, Faculty of Pharmacy Tehran University of Medical Sciences in 2008. MATERIALS： MDMA was extracted from ecstasy tablets, which were kindly supplied by the Pharmacology-Toxicology Department, Faculty of Pharmacy, Tehran University of Medical Sciences, Iran. METHODS： Hippocampal neurons were isolated from Wistar rats at gestational day 18. Following primary culture, hippocampal neuronal viability was detected by MTT assay. Varying concentrations of MDMA （100-5 000 μmol/L） were used to determine lethal concentration 50 （LC50）, which was around 1 500 μmol/L. Five concentrations of MDMA below 1 500 μmol/L （100, 200, 400, 800, and 1 050 μmol/L） were used for the remaining experiments. After 24 hours of MDMA treatment, NR2B mRNA expression was detected by RT-PCR, and caspase-3 relative activity was determined by colorimetric assay. MAIN OUTCOME MEASURES： Hippocampal neuronal viability, caspase-3 activity, and NR2B mRNA expression. RESULTS： MDMA-induced neurotoxicity in hippocampal neuronal cultures was dose-dependent. In high concentrations （1 000-5 000μmol/L） of MDMA, neuronal viability was decreased. However, with a 500 μmol/L dose of MDMA, neuronal viability was significantly increased （P 〈 0.01）. Low concentrations of MDMA （200 and 400μmol/L） significantly decreased caspase-3 activity （P 〈 0.01）, whereas high concentrations of MDMA significantly increased caspase-3 activity （P 〈 0.01）. NR2B subunit mRNA expression was not significantly altered after 100 -1 050 μmol/L MDMA exposure. CONCLUSION： MDMA exhibits dual effects on hippocampal neuronal viability and caspase-3 activity. These effects are independent from NR2B subunit expression levels.     

东莨菪碱与氯胺酮对幼鼠海马乙酰胆碱酯酶和NMDA受体2B亚基mRNA的相互影响

目的 探讨东莨菪碱与氯胺酮对幼鼠海马乙酰胆碱酯酶(AchE)和NMDA受体2B亚基mR-NA(NR2BmRNA)的相互影响.方法 1月龄筛选合格SD大鼠40只随机分为正常对照组(C组)、东莨菪碱组(S组)、氯胺酮组(K组)、东莨菪碱加氯胺酮组(SK组).S组、SK组腹腔注射东莨菪碱0.8mg/kg;30min后K组、SK组腹腔注射氯胺酮50mg/kg,随后每30 minK组、SK组腹腔注射氯胺酮25mg/kg,共追加2次;C组腹腔注射等体积的生理盐水.采用Y型迷宫进行学习能力测试,测试结束后处死大鼠分离大鼠海马取右侧海马应用比色法测定AchE活性,取左侧海马应用RT-PcR测定NR2BmRNA的表达.结果 东莨菪碱加氯胺酮组大鼠学习障碍加重,训练时间和训练次数分别为(45.3±2.9)min、(39.4±3.2)次,高于东莨菪碱组[(41.3±2.9)min、(35.0±4.5)次]和氯胺酮组[(40.5±2.3)min、(36.0±3.7)次];东莨菪碱加氯胺酮组AchE活性测定和NR2BmRNA的表达分别为2.46±0.30,0.72±0.05,高于东莨菪碱组(1.98±0.25,0.52±0.04)和氯胺酮组(1.91±0.28,0.60±0.04);均差异有显著性(P<0.05).结论 东茛菪碱与氯胺酮合用后对幼鼠海马AchE和NR2BmRNA产生相互作用,抑制学习呈协同作用.     

Labeling in vivo of sigma receptors in mouse brain with [3H]-(+)-SKF 10,047: Effects of phencyclidine, (+)- and (−)-N-allylnormetazocine,and other drugs

The sigma receptor, so named because of the distinct pharmacolgical profile produced by its prototypic agonist SKF 10,047 (N-allynormetazocine), is believed to mediate mania and psychotomimetic effects in man. While this sigma receptor has received extensive biochemical and pharmacological characterization in vitro, little information is available on the nature of the sigma site in vivo. In the present study, we examined the binding of [³H]-(+)-SKF 10,047 to sigma receptors in mouse brain in vivo and to sigma receptors in mouse and guinea pig brain in vitro and determined the relative potencies of various drugs in displacing this ligand. Mice were injected with 5 μCi of [³H]-(+)-SKF 10,047 into the tail vein. After various time intervals, the mice were decapitated; their brains were rapidly removed, weighed, and homogenized in 50 mM Tris-HCI buffer, pH 7.7; and total and particulate bound radioactivity were determined. Specifically bound [³H]-(+)-SKF 10,047 in the particulate fraction was defined as the difference in total radioactivity in the particulate fraction obtained from vehicle-injected mice minus the radioactivity in the particulate fraction from haloperidol (2 mg/kg i.p.)-injected mice. Specifically bound [³H]-(+)-SKF 10,047 in the particulate fraction reached peak levels of 30 min after i.v. injection and constituted 90–95% of the total particulate radioactivity. Labeling of the sigma sites could be blocked in vivo by injecting mice i.p. with the drug 30 min before the i.v. injection of the ³H-ligand. Under these conditions, (+)-SKF 10,047, (+)-3-PPP, cyclazocine, pentazocine, and haloperidol were found to be the most potent compounds in reducing specific [³H]-(+)-SKF 10,047 binding. Neuroleptics such as thioridazine and chlorpromazine had good potency, while clozapine, spiperone, and sulpiride were very weak inhibitors in vivo. Specific [³H]-(+)-SKF 10,047 binding was also reduced in vivo by imipramine, dl-propranolol, bupropion, rimcazole, and phenoxybenzamine, but was not reduced by apomorphine and naloxone at doses of 50 mg/kg i.p. Phencyclidine, m-NH₂-PCP and (?)-3-PPP were only weak inhibitors of (+)-SKF 10,047 binding in vivo. The relative potencies of these agents obtained in vivo correspond well with their relative affinities obtained in vitro in mouse and guinea pig brain for displacing [³H]-(+)-SKF 10,047 but not with their relative affinities for displacing TCP in guinea pig brain. Comparison of the dose-response curves for the drug revealed the presence of perhaps two sites labeled by [³H]-(+)-SKF 10,047 in vivo.     

Interactive effects of subanesthetic ketamine and subhypnotic lorazepam in humans

 Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist with psychotogenic and dissociative effects in healthy humans. These cognitive and perceptual effects in humans are reportedly reduced by benzodiazepine premedication. This study assessed the interactive effects of a ketamine (IV bolus of 0.26 mg/kg followed by an infusion of 0.65 mg/kg per hour) and lorazepam 2 mg., PO, in humans. Twenty-three healthy subjects completed 4 test days involving the oral administration of lorazepam or matched placebo 2 h prior to the IV infusion of ketamine or placebo. Ketamine: 1) produced behaviors similar to the positive and negative symptoms of schizophrenia as assessed by the Brief Psychiatric Rating Scale (BPRS); 2) evoked perceptual alterations as measured by the Clinician-Administered Dissociative States Scale (CADSS); 3) impaired performance on the Wisconsin Card Sorting Test (WCST) and other tests sensitive to frontal cortical impairment; and 4) had amnestic effects. Lorazepam produced attention impairments, concrete proverb interpretations, and recall impairments. Lorazepam reduced ketamine-associated emotional distress and there was a non-significant trend for it to decrease perceptual alterations produced by ketamine. However, it failed to reduce many cognitive and behavioral effects of ketamine, including psychosis. Further, lorazepam exacerbated the sedative, attention-impairing, and amnestic effects of ketamine. There was no evidence of pharmacokinetic interaction between these medications. These data suggest that subhypnotic lorazepam and ketamine show a spectrum of interactive effects, ranging from antagonism to potentiation. Received: 1 April 1996/Final version: 20 May 1997     

Chronic treatment with the uncompetitive NMDA receptor antagonist memantine influences the polyamine and glycine binding sites of the NMDA receptor complex in aged rats

Summary Receptor binding studies on rat cortical membranes were used to characterize the NMDA receptor in aged rats (22 months) treated for 20 months with a memantine containing diet delivering 30 mg/kg/day in comparison to aged and young/adult rats treated with control-diet. Spatial memory impairing effects of (+)-MK-801 (0.16 mg/kg) in the radial maze was not altered within the course of memantine-treatment (up to 16 months). However, chronic memantine-treatment significantly increased the number of [³H]MK-801 binding sites and the affinity of [³H]glycine. A non-significant trend to such changes was also seen in aged-control rats. Glycine-dependent [³H]MK-801 binding (functional binding under non-equilibrium conditions at a fixed L-glutamate concentration) revealed that a decreased ability of glycine to stimulate channel opening in aged rats was partially attenuated by the long-term memantine treatment. Furthermore, an increased ability of spermidine to enhance [³H]MK-801 binding in aged-control rats was even more pronounced in the aged memantine-treated group. Together these findings may indicate that changes in functional receptor-channel properties during the process of aging occur prior to a detectable loss of binding sites and that memantine enhances an endogenous compensatory mechanism triggered by glutamatergic hypofunction which is suggested to take place in aging.     

炎性痛诱导的大鼠背根节及脊髓后角NMDAR1表达变化的研究

目的 观察炎性痛条件下NMDA受体亚型R1(NR1)的表达变化。方法 采用福尔马林试验，在大鼠一侧足背皮下注射5％福尔马林50μL制备局部炎性痛病灶，利用痛行为测定结合组织化学方法检测大鼠背根节及脊髓后角NR1的表达变化。结果 炎症组大鼠背根节中、小型细胞及脊髓背角的NR1表达较生理盐水组显著增加，表明福尔马林刺激导致的炎症痛及痛过敏可能是通过上调NR1受体的表达而实现的。结论 NMDA受体的激活在痛觉过敏的产生和维持中起着至关重要的作用。     

组胺对N-甲基-D-天门冬氨酸诱发的神经元损伤的改善作用

目的:在细胞水平探讨组胺对N-甲基-D-天门冬氨酸 (NMDA) 诱发的神经元损伤的改善作用及初步机制.方法:采用原代新生大鼠皮层培养的方法,以形态学和二苯基四氮唑溴盐染色为指标观察神经元的损伤和药物的改善作用.结果:组胺在10-4、10-6、10-7、10-8 mol/L浓度时能显著改善NMDA 50 μmol/L作用3 h引起的神经元死亡,并在10-4和10-7 mol/L浓度时分别呈现保护双峰.组胺10-7 mol/L的改善作用只被组胺H2受体西米替丁逆转,而组胺10-4 mol/L的改善作用只被H1受体吡拉明逆转.结论:组胺能减弱NMDA诱发的神经元兴奋性死亡,其保护作用在低浓度时可能与H2受体有关,在高浓度时可能与H1受体有关.