氟哌啶醇对MK-801致小鼠高活动性与前脉冲抑制损害的作用

目的观察氟哌啶醇对谷氨酸功能低下小鼠模型表现出的高活动性及前脉冲抑制(prepulse inhibition,PPI)损害的作用。方法昆明种小鼠152只分组(n=8或n=10)进行下述对照观察:观察不同剂量氟哌啶醇(0.03、0.1、0.3 mg/kg)腹腔注射对昆明种小鼠探究行为和自主活动的影响;以0.25 mg/kg MK-801诱导小鼠自主活动增加,观察上述剂量氟哌啶醇对MK-801致小鼠高活动性的影响;以0.5 mg/kg MK-801诱导小鼠PPI损害,观察氟哌啶醇(0.1、0.3、1 mg/kg)对基线水平PPI以及MK-801损害后PPI的作用。结果与对照组比较,氟哌啶醇剂量为0.1 mg/kg和0.3 mg/kg时,小鼠的探究行为及自主活动总路程减少(P<0.05);但剂量为0.03 mg/kg时,对小鼠的探究行为及自主活动均无影响(P>0.05)。氟哌啶醇剂量为0.1~0.3 mg/kg时,呈剂量依赖性抑制由MK-801引起的自主活动增加(F=27.23,P<0.01),0.1mg/kg的氟哌啶醇的抑制程度为22%(P<0.01),0.3 mg/kg的氟哌啶醇的抑制程度为65%(P<0.00...     

氯氮平对谷氨酸功能低下精神分裂症小鼠模型的作用

目的 观察氯氮平对地卓西平马来酸盐（MK-801）所致谷氨酸功能低下精神分裂症小鼠模型的高活动性及刻板行为的作用。方法 昆明种小鼠130只。（1）取34只小鼠分为4组：溶媒空白对照组（腹腔注射溶媒，以下简称对照组）；3种氯氮平剂量（1．0，1．5，2．0mg／kg体质量，腹腔注射）组；每组8～10只，观察氯氮平对小鼠探究行为和自主活动的影响。（2）取46只小鼠分为5组，分别为对照组、MK-801模型组（溶媒＋MK-801，0．25mg／kg体质量，腹腔注射）及3种剂量（同上）氯氮平组分别加MK-801（0．25mg／kg体质量，腹腔注射），每组8～10只，观察氯氮平对MK-致801小鼠自主活动增加的影响。（3）取50只小鼠，每组10只，给药方案同“（2）”，观察氯氮平对MK-801引起的刻板行为的影响。结果 （1）与对照组比较，氯氮平剂量为1．5mg／kg体质量和2．0mg／kg体质量时，小鼠的探究行为及自主活动总路程减少（P均〈0．001）；但剂量为1．0mg／kg时，对小鼠的探究行为及自主活动均无影响（P均〉0．05）。（2）氯氮平剂量为1．0～2．0mg／kg体质量时，呈剂量依赖性抑制由MK-801引起的自主活动增加（均P〈0．05）。（3）氯氮平剂量为1．5～2．0mg／kg体质量时，呈剂量依赖性抑制MK-801引起的刻板行为（均P〈0．05）。但低剂量（1．0mg／kg体质量）氯氮平对MK-801引起的刻板行为无明显影响（P〉0．05）。结论 氯氮平对MK-801所致谷氨酸功能低下精神分裂症小鼠模型不同脑区的作用有选择性，低剂量时抑制由中脑边缘、中脑皮质系统介导的高活动性，较高剂量时抑制由中脑边缘、中脑皮质系统及黑质纹状体系统控制的高活动性及刻板行为。     

利培酮对谷氨酸功能低下的精神分裂症小鼠模型的作用

目的 观察第二代抗精神病药利培酮对地卓西平马来酸盐（MK-801）所致谷氨酸功能低下精神分裂症小鼠模型的作用。方法 昆明种雄性小鼠122只。（1）取32只小鼠，分为溶媒（腹腔注射溶媒）和不同剂量利培酮（腹腔注射0．025，0．050，0．075mg／kg）4组，每组8只，观察利培酮对小鼠探究行为和自主活动的影响。（2）取50只小鼠分为5组，每组10只，分别为空白对照组（溶媒＋溶媒）、MK-801模型组（腹腔注射溶媒＋MK-801 0．25mg／kg）和3个不同剂量的利培酮（方法同前）组（3组均含0．25mg／kg的MK-801），观察利培酮对MK-801致小鼠自主活动增加的影响。（3）取40只小鼠分为5组，每组8只。给药方案同前，观察利培酮对MK-801引起的刻板行为的影响。结果 （1）与溶媒组比较，利培酮剂量为0．050mg／kg和0．075mg／kg时，小鼠的探究行为和自主活动总路程减少（均P〈0．05和（0．001）；但低剂量（0．025mg／kg）对小鼠的探究行为（P=0．093）和自主活动（P=0．263）的影响未达统计学意义。（2）利培酮（0．025-0．075mg／kg）呈剂量依赖性地抑制由MK801引起的自主活动增加和刻板行为（均P〈0．05）。结论 利培酮能特异性地抑制MK-801引起的行为改变。     

地卓西平马来酸盐对雄性大鼠自发活动和前脉冲抑制及再认记忆的影响

目的 观察急性腹腔注射N-甲基-D-天冬氨酸(NMDA)受体拮抗剂地卓西平马来酸盐(MK-801)刘大鼠自发活动、感觉运动门控和物体再认记忆的影响,探讨MK-801模拟精神分裂症不同内表现型的适宜剂量.方法 成年雄性SD大鼠共104只,按照体质量采用分层随机化方法进行分组.(1)取SD大鼠48只,分为MK-801小剂量组、MK-801中剂量组、MK-801高剂量组和对照组,每组12只,观察不同剂量MK-801 (0.1、0.2、0.4 mg/kg)对大鼠自发活动的影响;(2)取SD大鼠32只,分为MK-801小剂量组、MK-801中剂量组、MK-801高剂量组和对照组,每组8只,观察不同剂量MK-801(0.1、0.2、0.4 mg/kg)对大鼠前脉冲抑制(PPI)的影响;(3)取SD大鼠24只,分为MK-801小剂量组和对照组,每组12只,观察小剂量MK-801 (0.1 mg/kg)对大鼠物体辨别测试的影响.结果 (1)中高剂量MK-801 (0.2,0.4 mg/kg)呈剂量依赖性诱导大鼠自发活动的增加以及PPI的损害(P＜0.05或P＜0.01),小剂量(0.1 mg/kg)组在自发活动和PPI上与对照组差异无统计学意义(P＞0.05).(2)小剂量MK-801组在物体辨别测试中对新物体的偏爱指数显著低于对照组[(57.79±10.66)％比(73.34±18.52)％,P＜0.05].结论 中高剂量MK-801可引起自发活动和感觉运动门控功能异常,而小剂量在排除运动系统异常的前提下可特异性地破坏大鼠的再认记忆,提示MK-801模拟精神分裂症的不同内表现型时应根据研究目的选择适宜剂量.     

MK-801建立精神分裂症的感觉运动门控障碍的小鼠模型研究

目的 观察N-甲基-D-天冬氨酸(NMDA)受体拮抗剂地革西平马来酸盐(MK-801)对小鼠感觉运动门控功能的影响,确定建立精神分裂症的感觉运动门控障碍小鼠模型的适宜剂量.方法 采用不同剂量(0.125 mg/kg、0.25mg/kg、0.50 mg/kg)的MK-801建立感觉运动门控障碍的小鼠模型,用SR-LAB惊反射测试系统测定小鼠前脉冲抑制(PPI)、惊反射幅度和习惯化等行为学指标以比较不同剂量的药理作用.结果 ①前脉冲刺激的强度高于背景12 dB时,MK-801 0.125 mg/kg、0.25 mg/kg、0.50 mg/kg各剂量组PPI的数值分别为(28.7%±4.8%)、(27.6%4±5.6%)、(9.2%±4.0%).与对照组(53.6%±4.5%)的差异均有统计学意义(P<0.01),呈剂量依赖性破坏了小鼠的PPI.②MK-801剂量为0.5 mg/kg时,惊反射的幅度明显大于对照组(P＜0.001),增加的幅度为53%.③MK-801 0.5 mg/kg剂量组的习惯化为(-2.6%±10%),与正常对照组(43.7%±7.6%)相比,引起了习惯化明显损害(P＜0.001).结论 MK-801能够引起小鼠PPI的缺失,且能增加小鼠对惊反射刺激的反应性.0.50 mg/kg的MK-801可作为建立精神分裂症的感觉运动门控障碍的小鼠模型的适宜剂量.     

急慢性注射地卓西平马来酸盐对小鼠额叶microRNA-181b表达的影响

目的研究急慢性注射地卓西平马来酸盐(MK-801)对小鼠额叶中与精神分裂症相关的微小RNA(microRNA,miRNA)-181b表达的影响,探讨其参与精神分裂症病理学的可能机制。方法急性注射实验中40只小鼠随机分成四组,分别腹腔注射不同剂量(0.125 mg/kg,0.25 mg/kg,0.50 mg/kg)的MK-801和生理盐水(简称急性对照组),15 min后用实时荧光定量PCR(real-time PCR)技术检测额叶miRNA-181b的相对表达量;慢性注射实验中22只小鼠随机分成两组,分别腹腔注射0.25 mg.kg-1.d-1的MK-801和生理盐水(简称慢性对照组),连续14 d,然后检测miRNA-181b的相对表达量。结果急性注射0.125 mg/kg、0.25 mg/kg、0.50 mg/kgMK-801的各组小鼠额叶miRNA-181b的相对表达水平分别为0.65±0.05、0.61±0.05和0.91±0.08。前两个剂量组miRNA-181b的表达明显低于对照组(1.00±0.13),P<0.05,而0.5 mg/kg的MK-801则对miRNA-181b表达无影响(P>0.05)。慢性MK-801注射组miRNA-181b的相对表达量为1.86±0.19,显著高于慢性对照组(1.00±0.10),P<0.05。结论急性和慢性MK-801对额叶中miRNA-181b表达的影响不同,结合miR-181b的分子功能,提示miRNA-181b在急性和慢性模型鼠的构建中起到不同的作用。     

MK-801建立谷氨酸功能低下精神分裂症小鼠模型的研究

目的用谷氨酸N-甲基-D-天冬氨酸(NMDA)受体非竞争性拮抗剂地卓西平马来酸盐(MK-801)建立谷氨酸功能低下精神分裂症小鼠模型,评价MK-801不同剂量时对这种模型的行为学改变,探讨其适宜剂量。方法根据文献及预试验,确定MK-801的实验剂量,用DigBehv自发活动视频分析系统测定腹腔注射MK-801不同剂量组小鼠的自发活动,用评分量表评价小鼠的刻板行为,并与注射生理盐水组比较。结果MK-801(0．125～0．50 mg／kg)呈剂量依赖性增加小鼠的自发活动和刻板行为。MK-801剂量为0．25 mg／kg时能显著增加小鼠的自发活动和刻板行为,而且从行为学方面评定,没有明显的神经毒性作用。0．50 mg/kg剂量组出现了后肢肌力障碍和明显的共济失调等神经毒性表现。结论0．25 mg／kg的MK-801可作为谷氨酸功能低下小鼠模型的最适宜剂量,引起的行为学改变能够客观量化。     

帕利哌酮对地卓西平马来酸盐引起大鼠自发活动增加及感觉门控功能异常的作用

目的探讨利培酮及其活性代谢产物帕利哌酮对地卓西平马来酸盐(dizocipline maleate,MK-801)引起的大鼠自发活动增加及感觉门控功能异常的作用,分析二者药理学作用的异同。方法成年雄性Sprague-Dawley(SD)大鼠共96只。选取SD大鼠48只,根据体重分层随机分为对照组、MK-801模型组、帕利哌酮0.10 mg/kg组、帕利哌酮0.50 mg/kg组、帕利哌酮1.00mg/kg组及利培酮组,每组8只,观察不同剂量帕利哌酮及利培酮(0.1 mg/kg)对MK-801(0.40 mg/kg)引起的大鼠自发活动增加的影响;选取SD大鼠48只,根据体重分层随机分组,每组8~10只,观察不同剂量帕利哌酮(0.10、0.50和1.00 mg/kg)及利培酮(0.5 mg/kg)对MK-801(0.25 mg/kg)引起大鼠前脉冲抑制(prepulse inhibition,PPI)功能异常的影响。结果利培酮及帕利哌酮均不同程度地逆转MK-801引起的大鼠自发活动增加(P0.05),而帕利哌酮的对抗作用随着给药剂量的增加而减弱;帕利哌酮各剂量组均不同程度地提高大鼠基线PPI,组间差异具有统计学意义(P0.05),但未能逆转MK-801引起的PPI减低效应,组间差异无统计学意义(P0.05);而利培酮(0.5 mg/kg)可逆转MK-801对大鼠PPI的破坏作用(P0.05)。结论利培酮和帕利哌酮不同程度地逆转了MK-801引起大鼠自发活动增加及感觉门控功能异常,说明帕利哌酮虽为利培酮活性代谢产物,但二者药理学作用不尽相同。     

奥氮平对谷氨酸功能低下的精神分裂症小鼠模型的作用

Objective To investigate the effects of olanzapine on hyperlocomotion and deficient prepusle inhibition (PPI) of hypoglutamatergic schizophrenia model in mice produced by dizocilpine maleate (MK-801), an N-methyl-D-aspartate (NMDA)antagonist.Methods (1) To investigate the effects of olanzapine on explorative behavior and spontaneous activity, three doses of olanzapine ( 0.1, 0.2, 0.3 mg/kg, i.p.) or vehicle was injected 30 min before the test.Locomotor activity was recorded for 30 min with an automated video tracking system, in which the components of the locomotor activity were divided into exploration (the first 10 min) and spontaneous activity (the second 20 min).(2) To examine the effects of olanzapine on MK-801-induced hyperlocomotion, mice were administered with olanzapine (0.1, 0.2 and 0.3 mg/kg) or vehicle 5 min before administration of MK-801 (0.25 mg/kg).After the second injection, locomotor activity was recorded for 90 min by the video tracking system.( 3 ) To explore the effects of olanzapine on intact and MK-801-disrupted sensorimotor gating, olanzapine (0.3, 1,3 mg/kg, i.p.) or the vehicle were injected 35 min before the start of the experiment, MK-801 (0.5 mg/kg, i.p.) or the same volume of saline was administered 5 min before the PPI experiment.Results ( 1 ) Olanzapine (0.2 and 0.3 mg/kg) significantly inhibited the explorative behavior and spontaneous activity (P ＜ 0.05 ) .Olanzapine at 0.1 mg/kg did not affect exploration ( P = 0.363 ) and spontaneous activity ( P = 0.196 ).Olanzapine (0.1 - 0.3 mg/kg) dose-dependently antagonized MK-801 -induced hyperlocomotion.(2) None of the olanzapine doses tested had a significant effect on baseline PPI.Olanzapine ( 1 - 3 mg/kg) dosedependently restored the MK-801-induced deficits in PPI.Conclusion Olanzapine specifically inhibited the MK-801-induced hyperlocomotion and deficits in PPI in mice and the results are also consistent with clinical findings.     

奥氮平对谷氨酸功能低下的精神分裂症小鼠模型的作用

Objective To investigate the effects of olanzapine on hyperlocomotion and deficient prepusle inhibition (PPI) of hypoglutamatergic schizophrenia model in mice produced by dizocilpine maleate (MK-801), an N-methyl-D-aspartate (NMDA)antagonist.Methods (1) To investigate the effects of olanzapine on explorative behavior and spontaneous activity, three doses of olanzapine ( 0.1, 0.2, 0.3 mg/kg, i.p.) or vehicle was injected 30 min before the test.Locomotor activity was recorded for 30 min with an automated video tracking system, in which the components of the locomotor activity were divided into exploration (the first 10 min) and spontaneous activity (the second 20 min).(2) To examine the effects of olanzapine on MK-801-induced hyperlocomotion, mice were administered with olanzapine (0.1, 0.2 and 0.3 mg/kg) or vehicle 5 min before administration of MK-801 (0.25 mg/kg).After the second injection, locomotor activity was recorded for 90 min by the video tracking system.( 3 ) To explore the effects of olanzapine on intact and MK-801-disrupted sensorimotor gating, olanzapine (0.3, 1,3 mg/kg, i.p.) or the vehicle were injected 35 min before the start of the experiment, MK-801 (0.5 mg/kg, i.p.) or the same volume of saline was administered 5 min before the PPI experiment.Results ( 1 ) Olanzapine (0.2 and 0.3 mg/kg) significantly inhibited the explorative behavior and spontaneous activity (P ＜ 0.05 ) .Olanzapine at 0.1 mg/kg did not affect exploration ( P = 0.363 ) and spontaneous activity ( P = 0.196 ).Olanzapine (0.1 - 0.3 mg/kg) dose-dependently antagonized MK-801 -induced hyperlocomotion.(2) None of the olanzapine doses tested had a significant effect on baseline PPI.Olanzapine ( 1 - 3 mg/kg) dosedependently restored the MK-801-induced deficits in PPI.Conclusion Olanzapine specifically inhibited the MK-801-induced hyperlocomotion and deficits in PPI in mice and the results are also consistent with clinical findings.     

Spontaneous alternation behaviour in rats: kynurenic acid attenuated deficits induced by MK-801

The present study was undertaken to investigate the effects of pharmacological modulation of the NMDA receptors on spontaneous alternation behaviour. The performance of rats treated with MK-801 and kynurenic acid (KYNA) was assessed in the cross-arm-maze. We evaluated: (a) the total number of arm entries representing locomotor activity, (b) spontaneous variation of different arms thought to reflect alternation performance. In the first experiment, MK-801 (0.01, 0.025, 0.05, 0.1 and 0.2 mg/kg, i.p.) was given 30 min prior to the testing. Beginning the dose of 0.05 mg/kg the drug increased locomotion and impaired alternation performance. An ability of animals to enter subsequently three or four different arms was reduced significantly. In the second experiment, the dose of 0.05 mg/kg was chosen as the lowest possible dose of MK-801 producing marked behavioural impairment. KYNA (0.3, 3 and 30 mg/kg, s.c.) was administered 60 min prior to the MK-801. While all KYNA doses prevented hyperlocomotion, only the highest dose (30 mg/kg) maintained alternation score at the control levels, i.e. the KYNA plus MK-801 treated animals alternated regularly three or four different arms. The results suggest different sensitivity of the two behavioural systems, i.e. locomotion and space orientation, towards pharmacological insult. In conclusion, the study confirmed protective behavioural effects of KYNA given in sufficient amounts and sufficiently long prior MK-801.     

Olanzapine and risperidone block a high dose of methamphetamine-induced schizophrenia-like behavioral abnormalities and accompanied apoptosis in the medial prefrontal cortex

This study aims to propose a comprehensive new model for schizophrenia, which shows PPI disruption at baseline state as an endophenotype, the development of cross-sensitization to an NMDA receptor antagonist, MK-801 as a clinical phenotype of the progression into treatment-resistance, and accompanied induction of apoptosis in the medial prefrontal cortex as a critical possibility during the progression. Repeated administration of a high dose of methamphetamine (METH) (2.5 mg/kg), which could increase glutamate levels in the medial prefrontal cortex (mPFC), induced TUNEL-positive cells in this region, accompanied development of behavioral cross-sensitization to MK-801 in response to a challenge injection of MK-801, and PPI disruption at baseline state without a challenge injection. Olanzapine (OLZ) (1.0 mg/kg) and risperidone (RIS) (0.1 mg/kg), which inhibited and remarkably attenuated METH (2.5 mg/kg)-induced increases in glutamate levels, respectively, blocked not only the induction of TUNEL-positive cells in the mPFC but also the accompanied development of above behavioral abnormalities. These findings suggest that repeating the METH-induced glutamate release produces behavioral abnormalities as a clinical phenotype of schizophrenia, accompanied apoptosis as a critical possibility during the progression, and suggest that sufficient dose of olanzapine and risperidone can block the development of these behavioral abnormalities and accompanied apoptosis during the progression.     

Neonatal exposure to the glutamate receptor antagonist MK-801: effects on locomotor activity and pre-pulse inhibition before and after sexual maturity in rats

Neonatal lesions of the ventral hippocampus in rats lead to post- but not pre-pubertal behavioral changes suggesting adolescent onset of dopaminergic hypersensitivity and providing an animal model of schizophrenia. Neonatal exposure to glutamate receptor antagonists produces accelerated apoptosis leading to neuronal loss in central nervous system structures including the hippocampus. This suggested that neonatal MK-801 might lead to behavioural changes like those reported following ventral hippocampal lesions. Thus, rats received MK-801 (0, 0.5, 1.0 mg/kg ip) on postnatal day 3 (P3) and were tested pre- (P35) and post-pubertally (P56). MK-801 produced an increase in TUNEL staining in the hippocampus and other forebrain structures, confirming the induction of apoptosis. Results showed little difference in locomotor activity between neonatal saline- and MK-801-treated groups during habituation or following saline injection but increased activity was seen in the 0.5 mg/kg MK-801 group following amphetamine (1.5 mg/kg i.p.) at P35 but not P56. In tests of pre-pulse inhibition (PPI), neonatal saline and MK-801 groups showed stable startle amplitudes, minimal responding to the pre-pulse stimuli alone, an increase in PPI with increases in pre-pulse intensity, and reduced PPI with apomorphine (0.1 mg/kg s.c.). At P56, neonatal MK-801 groups tested following vehicle showed less sensitivity to changes in pre-pulse intensity. It was concluded that neonatal MK-801 increases apoptotic cell loss in the hippocampus but does not produce behavioural effects like those seen after neonatal ventral hippocampal lesions. However, neonatal MK-801 did lead to increases in locomotor activity in juveniles but not adults and reduced sensitivity to pre-pulse intensity in PPI tests in adulthood.     

D-Serine and a glycine transporter inhibitor improve MK-801-induced cognitive deficits in a novel object recognition test in rats

Compounds enhancing N-methyl-d-aspartate (NMDA) glutamate receptor function have been reported to improve cognitive deficits. Since cognitive deficits are considered to be the core symptom of schizophrenia, enhancing NMDA receptor function represents a promising approach to treating schizophrenia. In the present study, we investigated whether d-serine or a glycine transporter inhibitor N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine (NFPS), both of which enhance NMDA receptor function, could improve MK-801-induced cognitive deficits in rats, and compared their effects with those of the atypical antipsychotic clozapine and of the typical antipsychotic haloperidol. To assess cognitive function, we used a novel object recognition test in rats that measured spontaneous exploratory activity of a novel object when paired with a familiar object. We then evaluated the effects of the compounds on cognitive deficits induced by treatment with MK-801, the NMDA receptor antagonist. Pretreatment with clozapine (1, 5 mg/kg, i.p.) but not haloperidol (0.03, 0.1 mg/kg, i.p.) significantly improved MK-801-induced cognitive deficits. Pretreatment with D-serine at 800 mg/kg (i.p.) or NFPS (0.3, 1 mg/kg, i.p.) significantly improved MK-801-induced cognitive deficits under this test paradigm. These findings suggest that impaired preference for novel objects induced by MK-801 in the novel object recognition test could be a useful animal model for evaluating the efficacy of compounds targeting the cognitive deficits observed in schizophrenic patients. The results also suggest that enhancing NMDA receptor function is an effective way for treating the cognitive deficits associated with schizophrenia.     

Non-NMDA excitatory amino acid receptors in the ventral tegmental area mediate systemic dizocilpine (MK-801) induced hyperlocomotion and dopamine release in the nucleus accumbens

This study investigated the putative role of non-NMDA excitatory amino acid (EAA) receptors in the ventral tegmental area (VTA) for the increase in dopamine (DA) release in the nucleus accumbens (NAC) and behavioral stimulation induced by systemically administered dizocilpine (MK-801). Microdialysis was utilized in freely moving rats implanted with probes in the VTA and NAC. Dialysates from the NAC were analyzed with high-performance liquid chromatography for DA and its metabolites. The VTA was perfused with the AMPA and kainate receptor antagonist CNQX (0.3 or 1 mM) or vehicle. Forty min after onset of CNQX or vehicle perfusion of the VTA, MK-801 (0.1 mg/kg) was injected subcutaneously. Subsequently, typical MK-801 induced behaviors were also assessed in the same animals by direct observation. MK-801 induced hyperlocomotion was associated with a 50% increase of DA levels in NAC dialysates. Both the MK-801 evoked hyperlocomotion and DA release in the NAC was antagonized by CNQX perfusion of the VTA in a concentration-dependent manner. None of the other rated MK-801 evoked behaviors, e.g. head weaving or sniffing, were affected by CNQX perfusion of the VTA. By itself the CNQX or vehicle perfusion of the VTA alone did not affect DA levels in NAC or any of the rated behaviors. These results indicate that MK-801 induced hyperlocomotion and DA release in the NAC are largely elicited within the VTA via activation of non-NMDA EAA receptors, tentatively caused by increased EAA release. Thus, the locomotor stimulation induced by psychotomimetic NMDA receptor antagonists may not only reflect impaired NMDA receptor function, but also enhanced AMPA and/or kainate receptor activation in brain, e.g., in the VTA. In view of their capacity to largely antagonize the behavioral stimulation induced by psychotomimetic drugs, such as MK-801, AMPA, and/or kainate receptor antagonists may possess antipsychotic efficacy. J. Neurosci. Res. 51:583–592, 1998. © 1998 Wiley-Liss, Inc.     

NC-1900, an arginine-vasopressin analogue, ameliorates social behavior deficits and hyperlocomotion in MK-801-treated rats: therapeutic implications for schizophrenia

We previously reported that chronic administration of N-methyl-D-aspartate (NMDA) antagonists reduced the density of vasopressin V1a receptors in several brain regions in rats that demonstrated social interaction deficits and increased locomotor activity. These observations indicate the ability of arginine-vasopressin (AVP), or its analogues, to modulate behavioral abnormalities associated with blockade of NMDA receptors. The present study was performed to investigate the effect of NC-1900, an AVP analogue, on social behavior and locomotor activity in rats treated with MK-801, a non-competitive NMDA receptor antagonist. Male Wistar rats were administered MK-801 (0.13 mg/kg/day ip) or saline for 14 days. Social behavior and locomotor activity were measured 45 min after the injection of NC-1900 (10 ng/kg sc) or saline together with the last MK-801 or vehicle administration. Social interaction was quantified by an automated video-tracking system, and stereotyped behavior and ataxia were manually measured. Acute administration of NC-1900 partially reversed MK-801-induced hyperlocomotion and deficits in social interaction, while NC-1900 itself did not affect these behavioral measures in animals chronically treated with vehicle saline. These results suggest that the central AVP system may interact with glutamatergic and dopaminergic transmissions, and indicate potential therapeutic effects of AVP analogues on positive and negative symptoms of schizophrenia.     

Behavioural supersensitivity following neonatal 6-hydroxydopamine: Attenuation by MK-801

Male rat pups were administered 6-hydroxydopamine (6-OHDA, 75 microg, intracisternally, 30 min after desipramine, 25 mg/kg, s.c.) on Days 1 or 2 after birth, or were sham-operated (receiving vehicle). In four experiments, the acute effects of apomorphine, with or without pretreatment with MK-801 (0.03 mg/kg), upon motor activity in test chambers was measured. Acute treatment with apomorphine (0.1 mg/kg) increased locomotor, rearing and total activity markedly compared to both the acute saline administered 6-OHDA rats and the sham-operated rats administered saline. Acute MK-801 (0.03 mg/kg) co-administered shortly before (5 min) apomorphine (0.3 or 1.0 mg/kg) reduced markedly locomotion and total activity in 6-OHDA-treated and sham-operated rats. Rearing behaviour was increased in both the 6-OHDA groups of rats. Acute MK-801 increased activity in the 6-OHDA-treated rats, which was not observed in sham-operated rats. At the 0.3 and 1.0 mg/kg doses of apomorphine, neonatal 6-OHDA treatment increased all three parameters of motor activity. Acute treatment with apomorphine (0.1 mg/kg) induced different effects on the motor activity of 6-OHDA-treated and sham-operated mice. In sham-operated rats apomorphine reduced motor activity during the 1st 30-min period but increased locomotion and total activity, but not rearing, during the 2nd and 3rd periods, whereas in 6-OHDA-treated rats, apomorphine increased locomotor, rearing and total activity markedly. Dopamine loss and serotonin elevation in the striatum and olfactory tubercle were confirmed. The present findings confirm the influence of non-competitive glutamate antagonists in attenuating the behavioural supersensitivity to dopamine antagonists.     

Rodent data and general hypothesis: antipsychotic action exerted through 5-HT2A receptor antagonism is dependent on increased serotonergic tone

Summary. The locomotor stimulation induced by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (dizocilpine) in mice was regarded as a model of at least some aspects of schizophrenia. The serotonin synthesis inhibitor dl-p-chlorophenylalanine (PCPA) was used to evaluate the involvement of endogenous serotonin in (a) the induction of MK-801-induced hyperlocomotion in NMRI mice, and (b) the inhibition of MK-801-induced hyperlocomotion by each of five monoaminergic antagonists (M100907, clozapine, olanzapine, raclopride, SCH23390). Further, brain monoaminergic biochemistry was characterised in rats and mice after various drug treatments. PCPA pretreatment did not significantly reduce MK-801-induced hyperlocomotion in any of the experiments performed; however in a meta-analysis of six experiments, the locomotion displayed by MK-801-treated animals was diminished 17% by PCPA pretreatment. The selective 5-HT2A receptor antagonist M100907 exerted a dose-dependent inhibition of MK-801-induced hyperlocomotion. This effect was abolished in mice pretreated with PCPA, but could be restored in a dose-dependent manner by restitution of endogenous 5-HT by means of 5-hydroxytryptophan (5-HTP). On the other hand, the inhibition of MK-801-induced hyperlocomotion exerted by the selective dopamine D-2 receptor antagonist raclopride or the dopamine D-1 receptor antagonist SCH23390 was unaffected by PCPA pretreatment. The antipsychotics clozapine and olanzapine displayed a split profile. Hence, the inhibitory effect on MK-801-induced hyperlocomotion exerted by low doses of these compounds was diminished after PCPA pretreatment, while inhibition exerted by higher doses was unaffected by PCPA. These results suggest that (1) MK-801-induced hyperlocomotion is accompanied by an activation of, but is not fully dependent upon, brain serotonergic systems. (2) In the hypoglutamatergic state induced by MK-801, endogenous serotonin exerts a stimulatory effect on locomotion through an action at 5-HT2A receptors, an effect that is almost completely counterbalanced by a concomitant inhibitory impact on locomotion, mediated through stimulation of serotonin receptors other than 5-HT2A receptors. M100907, by blocking 5-HT2A receptors, unveils the inhibitory effect exerted on locomotion by these other serotonin receptors. (3) Dopamine D-2 receptor antagonistic properties of antipsychotic compounds, when they come into play, override 5-HT2A receptor antagonism. Possible implications for the treatment of schizophrenia with 5-HT2A receptor antagonists are discussed. It is hypothesized that treatment response to such agents is dependent on increased serotonergic tone. Accepted February 9, 1998; received December 16, 1997