Utility of an elevated plus-maze for dissociation of amnesic and behavioral effects of drugs in mice

N-Acetylcysteine reverses mitochondrial dysfunctions and behavioral abnormalities in 3-nitropropionic acid-induced Huntington's disease

Mitochondrial dysfunction is a major event involved in the pathogenesis of Huntington's disease (HD). The present study evaluates the role of N-acetyl-L-cysteine (NAC) in preventing mitochondrial dysfunctions in a 3-nitropropionic acid (3-NP)-induced model of HD. Administration of 3-NP to rats (Wistar strain) resulted in significant inhibition of mitochondrial complexes II, IV and V in the striatum. However, no significant effect on complex I was observed. Increased generation of reactive oxygen species and lipid peroxidation was observed in mitochondria of 3-NP-treated animals. Endogenous antioxidants (thiols and manganese-superoxide dismutase) were lowered in mitochondria of 3-NP-treated animals. 3-NP-treated animals showed increased cytosolic cytochrome c levels and mitochondrial swelling. Increased expressions of caspase-3 and p53 were also observed in 3-NP-treated animals. Histopathological examination of the striata of 3-NP-treated animals revealed increased neural space, neurodegeneration and gliosis. This was accompanied by cognitive and motor deficits. NAC treatment, on the other hand, was found to be effective in reversing 3-NP-induced mitochondrial dysfunctions and neurobehavioral deficits. Our findings suggest a beneficial effect of NAC in HD.

Role of gonadal hormones in anxiety and fear memory formation and inhibition in male mice

Recent research investigating Pavlovian fear conditioning and fear extinction has elucidated the neurocircuitry involved in acquisition and inhibition of fear responses. Modulatory factors that may underlie individual differences in fear acquisition and inhibition, however, are not well understood. Testosterone is known to affect anxiety-like behavior and cognitive processing. In this study, we hypothesized that castration would increase anxiety and reduce memory for contextual fear conditioning in an age-dependent manner. In addition, castration would reduce the rate of extinction to context, as high levels of testosterone correlate with reduced PTSD-like symptoms. We compared behaviors in male mice that were castrated at one of two different time points, either before puberty (at 4 weeks) or after puberty (at 10 weeks) to sham-operated control mice. The behaviors investigated included: anxiety, cued and contextual fear conditioning, and extinction of the fear memory. An interaction of hormone status and age and a significant effect of age were measured in the elevated plus maze, a measure of anxiety. Castration caused a significant reduction of contextual fear memory, but no effect on cued fear memory. There was no significant effect of castration on extinction. Interestingly, a significant effect of age of the mouse at the time of testing was observed on extinction. These results suggest that endogenous androgens during puberty are important for anxiety and fear memory formation. In addition, these results define a late post-adolescent developmental time point for changes in anxiety and fear extinction.

Nootropic, anxiolytic and CNS-depressant studies on different plant sources of shankhpushpi

CONTEXT

Shankhpushpi, a well-known drug in Ayurveda, is extensively used for different central nervous system (CNS) effects especially memory enhancement. Different plants are used under the name shankhpushpi in different regions of India, leading to an uncertainty regarding its true source. Plants commonly used under the name shankhpushpi are: Convolvulus pluricaulis Chois., Evolvulus alsinoides Linn., both from Convolvulaceae, and Clitoria ternatea Linn. (Leguminosae).

OBJECTIVE

To find out the true source of shankhpushpi by evaluating and comparing memory-enhancing activity of the three above mentioned plants. Anxiolytic, antidepressant and CNS-depressant activities of these three plants were also compared and evaluated.

MATERIALS AND METHODS

The nootropic activity of the aqueous methanol extract of each plant was tested using elevated plus-maze (EPM) and step-down models. Anxiolytic, antidepressant and CNS-depressant studies were evaluated using EPM, Porsolt?s swim despair and actophotometer models, respectively.

RESULTS

C. pluricaulis extract (CPE) at a dose of 100 mg/kg, p.o. showed maximum nootropic and anxiolytic activity (p < 0.001). E. alsinoides extract (EAE) and C. ternatea extract (CTE) showed maximum memory-enhancing and anxiolytic activity (p < 0.001) at 200 and 100?mg/kg, respectively. Amongst the three plants, EAE and CTE showed significant (p < 0.05), while CPE did not exhibit any antidepressant activity. All the three plants showed CNS-depressant action at higher dose levels.

DISCUSSION AND CONCLUSIONS

The above results showed all the three plants possess nootropic, anxiolytic and CNS-depressant activity. The results of memory-enhancing activity suggest C. pluricaulis to be used as true source of shankhpushpi.

Protective effect of lycopene on oxidative stress and cognitive decline in rotenone induced model of Parkinson's disease

Evidence from clinical and experimental studies indicate that oxidative stress is involved in pathogenesis of Parkinson's disease. The present study was designed to investigate the neuroprotective potential of lycopene on oxidative stress and neurobehavioral abnormalities in rotenone induced PD. Rats were treated with rotenone (3 mg/kg body weight, intraperitoneally) for 30 days. NADH dehydrogenase a marker of rotenone action was observed to be significantly inhibited (35%) in striatum of treated animals. However, lycopene administration (10 mg/kg, orally) to the rotenone treated animals for 30 days increased the activity by 39% when compared to rotenone treated animals. Rotenone administration increased the MDA levels (75.15%) in striatum, whereas, lycopene administration to rotenone treated animals decreased the levels by 24.33%. Along with this, significant decrease in GSH levels (42.69%) was observed in rotenone treated animals. Lycopene supplementation on the other hand, increased the levels of GSH by 75.35% when compared with rotenone treated group. The activity of SOD was inhibited by 69% in rotenone treated animals and on lycopene supplementation; the activity increased by 12% when compared to controls. This was accompanied by cognitive and motor deficits in rotenone administered animals, which were reversed on lycopene treatment. Lycopene treatment also prevented release of cytochrome c from mitochondria. Collectively, these observations suggest that lycopene supplementation along with rotenone for 30 days prevented rotenone-induced alterations in antioxidants along with the prevention of rotenone induced oxidative stress and neurobehavioral deficits. The results provide an evidence for beneficial effect of lycopene supplementation in rotenone-induced PD and suggest therapeutic potential in neurodegenerative diseases involving accentuated oxidative stress.

Modulation of dopaminergic system and neurobehavioral functions in delayed neuropathy induced by organophosphates

Acute exposure to organophosphate pesticides (OPs) is associated with the development of a syndrome called organophosphate-induced delayed neuropathy (OPIDN) which is not mediated through hyper-cholinergic crisis. The present study has been designed to examine the role of alterations in dopaminergic system and neurobehavioral deficits in OPIDN. Rats were administered an acute dose of monocrotophos (MCP, 20 mg/kg body weight, orally) or dichlorvos (DDVP, 200 mg/kg body weight, subcutaneously), 15-20 min after treatment with antidotes (atropine (20 mg/kg body weight) and 2-pralidoxime (100 mg/kg body weight) intraperitoneally) to induce OPIDN. At biochemical level, an increase in dopamine, norepinephrine, and homovanillic acid levels were observed in brain of MCP- or DDVP-treated animals compared to controls. This was accompanied by increased intracellular calcium levels and lipid peroxidation in the cerebral cortex of OP-exposed animals. In addition, deficits in locomotor activity and spatial memory were observed in animals exposed to either MCP or DDVP. These results clearly suggest the role of dopaminergic system in memory and motor deficits observed in delayed neuropathy induced by OPs.

Protective effects of selective and non-selective cyclooxygenase inhibitors in an animal model of chronic stress

OBJECTIVE

Cyclooxygenase isoenzyme is known to be expressed in different regions of brain, and is mainly used for the treatment of pain and inflammation. Recently, it is proposed that cyclooxygenase isoenzyme may also play a key role in the pathophysiology of various brain-related disorders. The present study was aimed to explore the protective effect of cyclooxygenase inhibitors on stress by using an animal model of chronic stress.

METHODS

The animals were forced to swim individually for a period of 6 min every day for 15 d. Then, the behavior (locomotor activity, anxiety and memory) and biochemical (lipid peroxidation, nitrite level, reduced glutathione, and catalase) alterations were assessed.

RESULTS

Forced swimming for 15 d caused impaired locomotor activity, anxiety-like behavior and decreased percentage of memory retention, as compared to naive mice (without chronic fatigue treatment). Biochemical analysis revealed significant increases in lipid peroxidation and nitrite level, while levels of reduced glutathione and catalase activity were both decreased. Chronic treatment with naproxen (14 mg/kg, i.p.), rofecoxib (5 mg/kg, i.p.), meloxicam (5 mg/kg, i.p.), nimesulide (5 mg/kg, i.p.) and valdecoxib (10 mg/kg, i.p.) significantly attenuated these behavioral and biochemical (oxidative damage) alterations in chronic-stressed mice.

CONCLUSION

The cyclooxygenase inhibitors could be used in the management of chronic fatigue-like conditions.

Anti-amnesic effect of Ficus religiosa in scopolamine-induced anterograde and retrograde amnesia

CONTEXT

Ficus religiosa Linn (Moraceae) is a variety of fig tree. Its figs are known to contain a high serotonergic content, and modulation of serotonergic neurotransmission plays a crucial role in the pathogenesis of amnesia. Thus, the present study was envisaged.

OBJECTIVE

To investigate the effect of the methanol extract of figs of Ficus religiosa (FRFE) on scopolamine-induced anterograde and retrograde amnesia in mice.

MATERIALS AND METHODS

Transfer latency (TL) to the preferred niche in the elevated plus-maze (EPM) and learning avoidance of passive behavior to avoid punishment in the modified passive avoidance paradigm (MPA) served as behavioral models for the assessment of memory. Scopolamine (1 mg/kg, i.p.) was administered before training for induction of anterograde amnesia and before retrieval for induction of retrograde amnesia in both models. TL in the EPM, step down latency (SDL), number of trials, and number of mistakes in the MPA were determined in vehicle control, FRFE treated (10, 50, and 100 mg/kg, i.p.), and standard groups (piracetam 200 mg/kg, i.p.). Cyproheptadine, a non-selective 5-HT(1/2) blocker (4 mg/kg, i.p.), was administered along with the FRFE to investigate the involvement of serotonergic pathways in the anti-amnesic effect of FRFE.

RESULTS AND DISCUSSION

FRFE resulted in a significant improvement of memory, as its treatment attenuated the scopolamine-induced anterograde and retrograde amnesia dose-dependently. Further, cyproheptadine pretreatment significantly reversed the anti-amnesic effect of FRFE.

CONCLUSION

FRFE has anti-amnesic activity against scopolamine-induced amnesia, in a dose-dependent manner. Inhibition of the anti-amnesic effect of FRFE by cyproheptadine substantiates the involvement of serotonergic pathways for its activity.

Impaired mitochondrial functions in organophosphate induced delayed neuropathy in rats

Acute exposure to organophosphates induces a delayed neurodegenerative condition known as organophosphate-induced delayed neuropathy (OPIDN). The mechanism of OPIDN has not been fully understood as it does not involve cholinergic crisis. The present study has been designed to evaluate the role of mitochondrial dysfunctions in the development of OPIDN. OPIDN was induced in rats by administering acute dose of monocrotophos (MCP, 20 mg/kg body weight, orally) or dichlorvos (DDVP, 200 mg/kg body weight, subcutaneously), 15-20 min after treatment with antidotes [atropine (20 mg/kg body weight) and 2-PAM (100 mg/kg body weight) intraperitoneally]. MDA levels were observed to be higher and thiol content was lower in mitochondria from brain regions of OP exposed animals. This was accompanied by decreased activities of the mitochondrial enzymes; NADH dehydrogenase, succinate dehydrogenase, and cytochrome oxidase. In addition, mitochondrial functions assessed by MTT reduction also confirmed mitochondrial dysfunctions following development of OPIDN. The spatial long-term memory evaluated using elevated plus-maze test was observed to be deficit in OPIDN. The results suggest impaired mitochondrial functions as a mechanism involved in the development of organophosphate induced delayed neuropathy.

Fetal effects of psychoactive drugs

Psychoactive drug use by pregnant women has the potential to effect fetal development; the effects are often thought to be drug-specific and gestational age dependent. This article describes the effects of three drugs with similar molecular targets that involve monoaminergic transmitter systems: cocaine, methamphetamine, and selective serotonin re-uptake inhibitors (SSRIs) used to treat maternal depression during pregnancy. We propose a possible common epigenetic mechanism for their potential effects on the developing child. We suggest that exposure to these substances acts as a stressor that affects fetal programming, disrupts fetal placental monoamine transporter expression and alters neuroendocrine and neurotransmitter system development. We also discuss neurobehavioral techniques that may be useful in the early detection of the effects of in utero drug exposure.

The role of calsenilin/DREAM/KChIP3 in contextual fear conditioning

Potassium channel interacting proteins (KChIPs) are members of a family of calcium binding proteins that interact with Kv4 potassium (K(+)) channel primary subunits and also act as transcription factors. The Kv4 subunit is a primary K(+) channel pore-forming subunit, which contributes to the somatic and dendritic A-type currents throughout the nervous system. These A-type currents play a key role in the regulation of neuronal excitability and dendritic processing of incoming synaptic information. KChIP3 is also known as calsenilin and as the transcription factor, downstream regulatory element antagonist modulator (DREAM), which regulates a number of genes including prodynorphin. KChIP3 and Kv4 primary channel subunits are highly expressed in hippocampus, an area of the brain important for learning and memory. Through its various functions, KChIP3 may play a role in the regulation of synaptic plasticity and learning and memory. We evaluated the role of KChIP3 in a hippocampus-dependent memory task, contextual fear conditioning. Male KChIP3 knockout (KO) mice showed significantly enhanced memory 24 hours after training as measured by percent freezing. In addition, we found that membrane association and interaction with Kv4.2 of KChIP3 protein was significantly decreased and nuclear KChIP3 expression was increased six hours after the fear conditioning training paradigm with no significant change in KChIP3 mRNA. In addition, prodynorphin mRNA expression was significantly decreased six hours after fear conditioning training in wild-type (WT) but not in KO animals. These data suggest a role for regulation of gene expression by KChIP3/DREAM/calsenilin in consolidation of contextual fear conditioning memories.

Involvement of serotoninergic 5-HT1A/2A, alpha-adrenergic and dopaminergic D1 receptors in St. John's wort-induced prepulse inhibition deficit: a possible role of hyperforin

Prepulse inhibition (PPI) of acoustic startle response is a valuable paradigm for sensorimotor gating processes. Previous research showed that acute administration of St. John's wort extract (500 mg/kg, p.o.) to rats caused significant disruption of PPI while elevating monoamines levels in some brain areas. The cause-effect relationship between extract-induced PPI disruption and augmented monoaminergic transmission was studied using different serotoninergic, adrenergic and dopaminergic antagonists. The effects of hypericin and hyperforin, as the main active constituents of the extract, on PPI response were also tested. PPI disruption was prevented after blocking the serotoninergic 5-HT1A and 5-HT2A, alpha-adrenergic and dopaminergic D1 receptors. Results also demonstrated a significant PPI deficit after acute treatment of rats with hyperforin, and not hypericin. In some conditions manifesting disrupted PPI response, apoptosis coexists. Electrophoresis of DNA isolated from brains of hyperforin-treated animals revealed absence of any abnormal DNA fragmentation patterns. It is concluded that serotoninergic 5-HT1A and 5-HT2A, alpha-adrenergic and dopaminergic D1 receptors are involved in the disruptive effect of St. John's wort extract on PPI response in rats. We can also conclude that hyperforin, and not hypericin, is one of the active ingredients responsible for St. John's wort-induced PPI disruption with no relation to apoptotic processes.

Neuroprotective effect of N-acetylcysteine in the development of diabetic encephalopathy in streptozotocin-induced diabetes

Diabetic encephalopathy is characterized by impaired cognitive functions that involve neuronal damage triggered by glucose driven oxidative stress. The objective of the present study was to determine whether N-acetylcysteine (NAC) supplementation ameliorates learning and memory deficits caused by hyperglycemia-induced oxidative stress in experimental diabetes. Male Wistar rats (200-250 g) were rendered diabetic by a single intraperitoneal injection of streptozotocin (50 mg/kg). Cognitive deficits were observed in diabetic animals assessed using elevated plus maze test after 8 weeks of induction of diabetes. Acetylcholinesterase activity, a marker of cholinergic function, was decreased by 15.6% in the cerebral cortex, 20.9% in cerebellum and 14.9% in brain stem of diabetic rats compared to control rats. There was an increase in lipid peroxidation in cerebral cortex (21.97%), cerebellum (20.4%) and brain stem (25.5%) of diabetic rats. This was accompanied by decrease in glutathione and total thiol content along with decrease in the activities of superoxide dismutase, catalase and glutathione reductase. However, glutathione peroxidase activity increased by 11.2%, 13.6% and 23.1% in cerebral cortex, cerebellum and brain stem respectively, while the activity of glutathione-s-transferase decreased only in cerebral cortex (21.7%). Supplementation with NAC (1.4 g/kg/day in drinking water) significantly attenuated cognitive deficits and oxidative stress in diabetic rats. Our results emphasize the involvement of increased oxidative stress in cognitive impairment in diabetic animals and point towards the potential beneficial role of NAC as an adjuvant therapy to conventional anti-hyperglycemic regimens for the prevention and treatment of diabetic encephalopathy.

Protective effects of Punica granatum seeds extract against aging and scopolamine induced cognitive impairments in mice

Dementia is one of the age related mental problems and characteristic symptom of various neurodegenerative diseases including Alzheimer's disease. This impairment probably is due to the vulnerability of the brain cells to increased oxidative stress during aging process. Many studies have shown that certain phenolic antioxidants attenuate neuronal cell death induced by oxidative stress. The present work was undertaken to assess the effect of ethanolic extract of Punica granatum seeds on cognitive performance of aged and scopolamine treated young mice using one trial step-down type passive avoidance and elevated plus maze task. Aged or scopolamine treated mice showed poor retention of memory in step-down type passive avoidance and in elevated plus maze task. Chronic administration (21 days) of Punica granatum extract and vitamin C significantly (p < 0.05) reversed the age induced or scopolamine induced retention deficits in both the paradigms. Punica granatum extract also significantly lowered lipid peroxidation level and increased antioxidant glutathione level in brain tissues. Punica granatum preparations could be protective in the treatment of cognitive disorders such as dementia and Alzheimer's disease.

Nasal Colivelin treatment ameliorates memory impairment related to Alzheimer's disease

Humanin (HN) and its derivatives, such as Colivelin (CLN), suppress neuronal death induced by insults related to Alzheimer's disease (AD) by activating STAT3 in vitro. They also ameliorate functional memory impairment of mice induced by anticholinergic drugs or soluble toxic amyloid-beta (Abeta) in vivo when either is directly administered into the cerebral ventricle or intraperitoneally injected. However, the mechanism underlying the in vivo effect remains uncharacterized. In addition, from the standpoint of clinical application, drug delivery methods that are less invasive and specific to the central nervous system (CNS) should be developed. In this study, we show that intranasally (i.n.) administered CLN can be successfully transferred to CNS via the olfactory bulb. Using several behavioral tests, we have demonstrated that i.n. administered CLN ameliorates memory impairment of AD models in a dose-responsive manner. Attenuation of AD-related memory impairment by HN derivatives such as CLN appears to be correlated with an increase in STAT3 phosphorylation levels in the septohippocampal region, suggesting that anti-AD activities of HN derivatives may be mediated by activation of STAT3 in vivo as they are in vitro. We further demonstrate that CLN treatment inhibits an Abeta induced decrease in the number of choline acetyltransferase (ChAT)-positive neurons in the medial septum. Combined with the finding that HN derivatives upregulate mRNA expression of neuronal ChAT and vesicular acetylcholine transporter (VAChT) in vitro, it is assumed that CLN may ameliorate memory impairment of AD models by supporting cholinergic neurotransmission, which is at least partly mediated by STAT3-mediated transcriptional upregulation of ChAT and VAChT.

7-Nitroindazole, a neuronal nitric oxide synthase inhibitor, impairs passive-avoidance and elevated plus-maze memory performance in rats

The role of nitric oxide (NO) on cognitive performance in a modified elevated plus-maze (mEPM) and passive-avoidance (PA) task was investigated by using the NO synthase (NOS) inhibitor 7-nitroindazole (7-NI) and an NO precursor l-arginine. The interaction between the activation of N-methyl-d-aspartate (NMDA) receptors and NO synthesis on memory retention was also studied. 7-NI, l-arginine or MK-801, a non-competitive NMDA receptor antagonist were injected intraperitoneally (i.p) to male Wistar rats 30 min before the first training session of the PA test or 30 min before on the first day testing (acquisition session) of mEPM task. Transfer latency, the time rat took to move from the open arm to the enclosed arm, was used as an index of learning and memory in a mEPM test. The retention session was performed 24 h after the acquisition one. In the PA task, the retention test was carried out 24 h after training and reduction of retention latency was used to evaluate the acquisition of learning and memory. Blood glucose level and locomotor activity of the rats was also evaluated. 7-NI (10, 20, 25, 50 mg/kg) and MK-801 (0.15 mg/kg) significantly prolonged the transfer latency on retention session in a mEPM test and shortened step-through latency in PA test. 7-NI-induced impairment in memory and learning was partly reversed by l-arginine (200 mg/kg), a competitive substrate for NOS. However subeffective doses of 7-NI (5 mg/kg) and MK-801 (0.075 mg/kg) given in combination significantly impaired plus-maze and PA performances in rats. Thus NMDA receptor mediated NO pathways may be implicated in the PA and mEPM behaviours in rats. Since 7-NI does not affect blood pressure and did not alter blood glucose level and locomotor activity in conscious rats, 7-NI-induced impairment of memory is not due to either hypertension, changes in blood glucose level or effects on locomotor activity.

Reversal of Memory Deficits by Atorvastatin and Simvastatin in Rats

The present study was undertaken to investigate the beneficial effects of Atorvastatin and Simvastatin in cognitive dysfunctions of rats. Alprazolam, Scopolamine and high fat diet (HFD) induced amnesia served as interoceptive memory models where as, Water-maze and Elevated plus-maze served as exteroceptive models. A total of 38 groups of rats were used in this investigation. Escape latency time (ELT) recorded during acquisition trials conducted from day 1 to day 4, in water maze was taken as an index of acquisition, where as mean time spent in target quadrant during retrieval trial on day 5, was taken as the index of retrieval (memory). On elevated plus-maze, transfer latency (TL) measured on 1st d served as the index of acquisition and TL recorded on 2nd d was taken as the index of retrieval (memory). Alprazolam (0.5 mg kg(-1) intraperitoneally), Scopolamine (0.4 mg kg(-1) intraperitoneally) and HFD treated (for 90 days) rats exhibited amnesia as reflected by impairment in learning ability as well as memory, when tested on both, water maze and elevated plus maze. Atorvastatin (5 mg kg(-1) orally) as well as Simvastatin (5 mg kg(-1) orally) significantly attenuated Alprazolam, Scopolamine and HFD induced amnesia. These results highlight the ameliorative role of statins in experimental amnesia with possible involvement of their cholesterol dependent as well as cholesterol independent actions.

The drug-induced helplessness test: an animal assay for assessing behavioral despair in response to neuroleptic treatment

RATIONALE

Neuroleptic dysphoria encompasses a range of unpleasant subjective responses and, as a result, is difficult to study in preclinical animal models.

OBJECTIVE

Based on the learned helplessness model of depression, increases in escape failures (EFs) in the drug-induced helplessness test (DH) are proposed to reflect drug-induced depressive-like state, a contributing factor to neuroleptic dysphoria in humans.

MATERIALS AND METHODS

Effects of the typical antipsychotic haloperidol and the atypical antipsychotics risperidone, olanzapine, aripiprazole, quetiapine, and clozapine were investigated in the DH test. We further characterized this test by examining compounds affecting motor function, cognition, anxiety, and those with antidepressant activity.

RESULTS

The antipsychotics haloperidol, risperidone, aripiprazole, and olanzapine, all increased EFs, while quetiapine had no effect, and clozapine reduced EFs. Amphetamine, diazepam, and ciproxifan, had no effect on EFs. Scopolamine significantly reduced EFs and MK-801 showed a trend toward reducing EFs at doses not significantly sti mulating locomotor activity. Subchronic, but not acute, imipramine and subchronic fluoxetine significantly reduced EFs at doses significantly suppressing locomotor activity. Dissociation appears to exist between performance in the DH test and compound effects on catalepsy or locomotor activity.

CONCLUSIONS

After discussing potential alternative interpretations of the drug-induced changes of EFs, we propose the DH test as a useful test for assessing a drug-induced, depressive-like state that may contribute to neuroleptic dysphoria.

Prenatal exposure to betamethasone decreases anxiety in developing rats: hippocampal neuropeptide y as a target molecule

Repeated antenatal administration of betamethasone is frequently used as a life-saving treatment in obstetrics. However, limited information is available about the outcome of this therapy in children. The initial prospective studies indicate that there are behavioral impairments in children exposed to repeated courses of prenatal betamethasone during the third trimester of pregnancy. In this study, pregnant rats received two betamethasone injections on day 15 of gestation. Using immunohistochemistry, the expression of a powerful anxiolytic molecule neuropeptide Y (NPY) was determined on postnatal day (PN) 20 in the hippocampus and basolateral amygdala (structures related to anxiety and fear) of the offspring. Prenatal betamethasone exposure induced significant increases in NPY expression in the hippocampus but not in the amygdala. Indeed, behavioral tests in the offspring, between PN20 and PN22 in the open field, on the horizontal bar, and in the elevated plus maze, indicated decreases in anxiety, without impairments in motor performance or total activity. Decreased body weight in betamethasone-exposed rats confirmed long-lasting effects of prenatal exposure. Thus, prenatal betamethasone treatment consistently increases hippocampal NPY, with decreases in anxiety-related behaviors and hippocampal role in anxiety in rats. Animal models may assist in differentiation between pathways of the desired main effect of the antenatal corticosteroid treatment and pathways of unwanted side effects. This differentiation can lead to specific therapeutic interventions directed against the side effects without eliminating the beneficial main effect of the corticosteroid treatment.

Holeboard discrimination learning in mice

We have adapted to mice a holeboard-learning task, which allows simultaneous assessment of spatial working and reference-memory performance. The holeboard apparatus consists of an open-field chamber with a 16-hole floor insert. Across trials, animals have to learn that the same four holes of 16 are always baited. Here, we show that C57BL/6 mice readily acquire this task within 4 days when submitted to six trials per day or within 8 days when submitted to only four trials per day. We also show that C57BL/6, Swiss-Webster, CD-1 and DBA/2 mice acquire this task similarly, despite the fact that some differences could be observed in measures of exploratory activity during habituation and training. Moreover, the muscarinic antagonist scopolamine disrupts learning at doses of 0.1 and 1.0 mg/kg, although the highest dose appeared to have side-effects. Lastly, we found that amyloid precursor protein transgenic mice have a selective disruption in their working-memory performance only during reversal training (i.e. after a change in the configuration of the baited holes). Overall, our data indicate that this spatial learning task is well adapted to mice and will be useful to characterize spatial memory in various genetic or pharmacological mouse models.

Effect of Withania somnifera root extract on reserpine-induced orofacial dyskinesia and cognitive dysfunction

Tardive dyskinesia is one of the major side effects of long-term neuroleptic treatment. The pathophysiology of this disabling and commonly irreversible movement disorder is still obscure. Vacuous chewing movements in rats are widely accepted as an animal model of tardive dyskinesia. Oxidative stress and products of lipid peroxidation are implicated in the pathophysiology of tardive dyskinesia. Repeated treatment with reserpine (1.0 mg/kg) on alternate days for a period of 5 days (days 1, 3 and 5) significantly induced vacuous chewing movements and tongue protrusions in rats. Chronic treatment with Withania somnifera root extract (Ws) for a period of 4 weeks to reserpine treated animals significantly and dose dependently (50 and 100 mg/kg) reduced the reserpine-induced vacuous chewing movements and tongue protrusions. Reserpine treated animals also showed poor retention of memory in the elevated plus maze task paradigm. Chronic Ws administration significantly reversed reserpine-induced retention deficits. Biochemical analysis revealed that chronic reserpine treatment significantly induced lipid peroxidation and decreased the glutathione (GSH) levels in the brains of rats. Chronic reserpine treated rats showed decreased levels of antioxidant defense enzymes, superoxide dismutase (SOD) and catalase. Chronic administration of Ws root extract dose dependently (50 and 100 mg/kg) and significantly reduced the lipid peroxidation and restored the decreased glutathione levels by chronic reserpine treatment. It also significantly reversed the reserpine-induced decrease in brain SOD and catalase levels in rats. The major findings of the present study indicate that oxidative stress might play an important role in the pathophysiology of reserpine-induced abnormal oral movements. In conclusion, Withania somnifera root extract could be a useful drug for the treatment of drug-induced dyskinesia.

NMDA receptor blockers prevents the facilitatory effects of post-training intra-dorsal hippocampal NMDA and physostigmine on memory retention of passive avoidance learning in rats

In the present study, the effects of post-training intra-dorsal hippocampal (intra-CA1) injection of an N-methyl-D-aspartate (NMDA) receptor agonist and competitive or noncompetitive antagonists, on memory retention of passive avoidance learning was measured in the presence and absence of physostigmine in rats. Intra-CA1 administration of lower doses of the NMDA receptor agonist NMDA (10(-5) and 10(-4) microg/rat) did not affect memory retention, although the higher doses of the drug (10(-3), 10(-2) and 10(-1) microg/rat) increased memory retention. The greatest response was obtained with 10(-1) microg/rat of the drug. The different doses of the competitive NMDA receptor antagonist DL-AP5 (1, 3.2 and 10 microg/rat) and noncompetitive NMDA receptor antagonist MK-801 (0.5, 1 and 2 microg/rat) decreased memory retention in rats dose dependently. Both competitive and noncompetitive NMDA receptor antagonists reduced the effect of NMDA (10(-2) microg/rat). In another series of experiments, intra-CA1 injection of physostigmine (2, 3 and 4 microg/rat) improved memory retention. Post-training co-administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) and physostigmine (1 microg/rat), doses which were ineffective when given alone, significantly improved the retention latency. The competitive and noncompetitive NMDA receptor antagonists, DL-AP5 and MK-801, decreased the effect of physostigmine (2 microg/rat). Atropine decreased memory retention by itself and potentiated the response to DL-AP5 and MK-801. In conclusion, it seems that both NMDA and cholinergic systems not only play a part in the modulation of memory in the dorsal hippocampus of rats but also have demonstrated a complex interaction as well.

Antagonistic effects of methanolic extract of Polygala telephioides on morphine responses in mice

The present study was undertaken to investigate the antagonistic effects of the methanolic extract of Polygala telephioides (PT) on morphine responses in mice. Single administration of PT tended to antagonize the morphine-induced analgesia in a hot-plate test. Moreover, PT (300 mg/kg, p.o.) improved the morphine-induced memory impairment in an elevated plus maze test. However, PT alone had no effect on behaviors in the open-field, hot-plate and elevated plus maze tests. We investigated the effects of PT on naloxone-induced jumping (as withdrawal sign) in morphine-dependent mice. To induce dependence, mice were twice daily treated with morphine (10-45 mg/kg, s.c.) for 5 days. Co-administrations of PT (10, 100 and 300 mg/kg, p.o.) during repeated morphine treatments significantly suppressed the naloxone (10 mg/kg, i.p.)-induced jumping. However, the naloxone-induced jumping was not affected by a single large administration of PT on the 5th day. The inhibitory effect of PT on the naloxone-induced jumping was due to the development of dependence rather than expression of withdrawal sign. Moreover, single administration of PT (30 mg/kg, p.o.) decreased the morphine levels in plasma. These results indicate that PT may be useful in facilitating narcotic detoxification.

NMDA receptor antagonists antagonize the facilitatory effects of post-training intra-basolateral amygdala NMDA and physostigmine on passive avoidance learning

In the present study, the effects of post-training intra-basolateral amygdala (BLA) injection of an N-methyl-d-aspartate (NMDA) receptor agonist and competitive or noncompetitive antagonists, on memory retention of passive avoidance learning was measured in the presence and absence of physostigmine in rats. Intra-BLA administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) did not affect memory retention, although higher doses of the drug (10(-3), 10(-2) and 10(-1) microg/rat) increased memory retention. The greatest response was obtained with 10(-1) microg/rat of the drug. The different doses of the competitive NMDA receptor antagonist DL-AP5 (1, 3.2 and 10 microg/rat) and noncompetitive NMDA receptor antagonist MK-801 (0.5, 1 and 2 microg/rat) decreased memory retention in rats dose dependently. Both competitive and noncompetitive NMDA receptor antagonists reduced the effect of NMDA (10(-2) microg/rat). In another series of experiments, intra-BLA injection of physostigmine (2, 3 and 4 microg/rat) improved memory retention. Post-training co-administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) and physostigmine (1 microg/rat), doses which were ineffective when given alone, significantly improved the retention latency. The competitive and noncompetitive NMDA receptor antagonists, DL-AP5 and MK-801, decreased the effect of physostigmine (2 microg/rat). Atropine decreased memory retention by itself and potentiated the response to DL-AP5 and MK-801. It may be concluded that amygdalar NMDA receptor mechanisms interact with cholinergic systems in the modulation of memory.

Reinstatement of morphine-conditioned reward is blocked by memantine

Protection of abstinent individuals from relapse is the main goal of drug dependence treatment. Relapse is frequently precipitated by exposure to small doses of the drug of abuse or exposure to the environment that was previously associated with the drug. Mice exposed to morphine (10 mg/kg) in a unique test-box environment display a conditioned place preference for this environment. Such preference can be extinguished by subsequent pairing of physiological saline administration with the same environment. Once extinguished, the original place preference can be reinstated after a priming dose (1-2.5 mg/kg) of morphine is given. However, mice treated with 7.5 (but not 3.75) mg/kg of memantine (the glutamate/NMDA receptor antagonist) during the extinction phase were insensitive to morphine's ability to reinstate the place preference 2 days after extinction conditionings. Effect of memantine was also observed when priming dose of morphine was given 21 days after extinction conditionings. In contrast, morphine's ability to reinstate conditioned response was not affected by treatment with 10 mg/kg of chlordiazepoxide, 0.5 mg/kg of LSD-25, or 1 mg/kg of morphine given during extinction conditionings. A separate experiment demonstrated that memantine (7.5 mg/kg) treatment did not affect learning. We show for the first time that memantine treatment during extinction conditionings may abolish the ability of drug-related cues to evoke reinstatement, suggesting that this NMDA receptor antagonist can be useful in preventing relapse in opioid dependent individuals.

A comparison of chlordiazepoxide, bretazenil, L838,417 and zolpidem in a validated mouse Vogel conflict test

RATIONALE

GABAA receptors containing an alpha2 subunit are proposed to mediate the anxiolytic effect of benzodiazepines (BZ) based on studies in transgenic mice using unconditioned models of anxiety. Conditioned models of anxiety were not assessed and are rarely encountered in phenotyping of genetically modified animals. The novel benzodiazepine site ligand L838,417 is a partial agonist at GABAA receptors containing an alpha2, alpha3 or alpha5 subunit and an antagonist at alpha1 receptors, giving an anxiolytic profile devoid of sedation. However, this compound has not previously been assessed in mice.

OBJECTIVES

(1) Establish the Vogel conflict test (VCT) in C57BL/6J mice and validate it with a range of pharmacological tools and (2) compare the full and partial GABAA receptor positive modulators chlordiazepoxide (CDP) and bretazenil (BRZ), respectively, with the subtype selective ligands zolpidem (ZOL; alpha1 selective) and L838,417.

RESULTS

(1) enhanced thirst (water deprivation or isoproterenol administration), analgesia (lamotrigine) or cognitive impairment (MK-801) did not generate false positives in the VCT; (2) CDP and BRZ engendered linear dose-related anti-conflict effects and also increased unpunished drinking; (3) L838,417 engendered a bell-shaped anti-conflict effect and did not increase unpunished drinking; (4) the anti-conflict effect of CDP and L838,417 were antagonised by flumazenil, whereas BRZ's effect was insensitive to this antagonist; and (5) ZOL induced motoric deficits and no anti-conflict effect.

CONCLUSION

We have established the VCT in C57BL/6J mice and validated this test behaviourally, physiologically and pharmacologically. The novel GABAA receptor ligand L838,417 was anxiolytic in this mouse model, and unlike the non-selective compounds, had no effect on unpunished drinking.

Modulation of spontaneous alternation performance of mice treated with thioperamide and tacrine in a cross maze task

A combination of sub-effective doses of thioperamide (7.5 mg/kg, i.p.) and tacrine (0.5 mg/kg, i.p.) enhanced performance in a spatial memory task in mice. This was shown by a significant increase in their spontaneous alternation scores in a cross maze test.

EFFECT OF NAPROXEN, A NON-SELECTIVE CYCLO-OXYGENASE INHIBITOR, ON PENTYLENETETRAZOL-INDUCED KINDLING IN MICE

1. Epilepsy is one of the major neurological disorders of the brain, affecting approximately 0.5-1.0% of the population worldwide. Various neurotransmitter abnormalities, especially of GABA and glutamate, have been reported to play a key role in the pathophysiology of epilepsy. 2. Cyclo-oxygenase (COX) is the rate-limiting enzyme in the production of prostaglandins and, as such, is a key target for many anti-inflammatory drugs. Cyclo-oxygenase has been reported to play a significant role in neurodegeneration. Recent studies have reported that COX plays a significant role in the pathophysiology of epilepsy. 3. The aim of the present study was to explore the possible role of COX and the effect of COX inhibitors in epilepsy. 4. Kindling is a chronic model of epilepsy. In the present study, kindling was induced in mice by chronic administration of a subconvulsive dose of pentylenetetrazole (PTZ; 40 mg/kg) on every other day for a period of 15 days. Naproxen was administered daily 45 min before PTZ or vehicle. The kindling score was recorded after PTZ administration. Seizure severity was measured according to a prevalidated scoring scale. Biochemical estimations were performed immediately after recording behavioural parameters on the 16th day of PTZ treatment. 5. Chronic treatment with PTZ significantly induced kindling in mice. Pretreatment with the non-selective COX inhibitor naproxen (7 and 14 mg/kg, i.p.) showed significant protection against PTZ-induced kindling in mice. Biochemical analysis revealed that chronic treatment with PTZ significantly increased lipid peroxidation and nitrite levels (NO levels), but decreased reduced glutathione (GSH) levels in brain homogenates. 6. In conclusion, the results of the present study strongly suggest that COX plays an important role in the pathophysiology of PTZ-induced kindling in mice and that COX inhibitors could be a useful neuroprotective strategy for the treatment of epilepsy.

Behavioral deficits in adult rats treated neonatally with glutamate

The present study evaluated long-term behavioral consequences of neonatal monosodium-l-glutamate (MSG) treatment in rats. The pups received MSG (3 mg/g sc) daily from postnatal day (PD) 5-12. Data from an automatic activity monitor showed that locomotion of MSG-treated females and males aged 56 and 84 days was significantly reduced. Beginning PD 120, three behavioral tests were performed. As compared to the controls, in the elevated plus maze test, modified to evaluate the adaptive form of spatial memory, MSG-treated animals of both sex had significantly prolonged start and transfer latencies. In the social recognition test, assessing olfactory working memory, MSG-treated males displayed a reduced interest in the juvenile conspecific as the stimulus partner during both the initial exposure and re-exposure performed 30 min later. In the open field test, a significant decrease in the habituation rate was found in MSG-treated animals. Sex-dependent differences in behavioral performance were suggested in the open field and elevated plus maze tests. Behavioral changes are discussed in light of the deficits in perception and processing of visual and olfactory stimuli.

The role of nitric oxide in the emotional learning of rats in the plus-maze

The present study evaluated the role of nitric oxide (NO) in the transfer latency (TL) paradigm in the elevated plus-maze. Male Wistar rats received i.p. injections of either 0.9% Saline, N(omega) Nitro-L-arginine-methyl-ester (L-NAME, an inhibitor of NO synthesis), d-NAME (inert isomer), scopolamine (SCO, antagonist of muscarinic receptors), or MK-801 (antagonist of NMDA receptors) and, after 30 min, were submitted to TL procedure. In an independent experiment, the ability of the same L-NAME treatments in changing the arterial pressure and blood glucose level (BGL) was evaluated in conscious rats. The treatment with SCO (1 mg kg(-1)), MK-801 (0.15 mg kg(-1)) and L-NAME (10 and 50 mg kg(-1)), but not with D-NAME, impaired the TL learning. The L-NAME-induced TL deficit was counteracted by L-ARG (100 and 200 mg kg(-1)), while the co-administration of sub-effective doses of L-NAME and MK-801 failed to impair the TL learning. The L-NAME (50 mg kg(-1)) treatment failed to alter the BGL. All treatments with L-NAME induced hypertension, but the rats treated with L-NAME (5 mg kg(-1)) were still able to learn the TL task. The data indicate that the TL deficit induced by L-NAME (10 and 50 mg kg(-1)) is not due to either hypertension or changes in the BGL. It is also possible to establish that NO production is important for emotional learning underlying the TL procedure in rats.

Role of learning of open arm avoidance in the phenomenon of one-trial tolerance to the anxiolytic effect of chlordiazepoxide in mice

A single exposure to the elevated plus-maze (EPM) test of anxiety reduces or abolishes the anxiolytic efficacy of benzodiazepines on a second trial. Some possible explanations to the occurrence of this phenomenon (one-trial tolerance-OTT) involve behavioral modifications thought to be consequence of some kind of learning in the first trial. In the present study, the influence of learning-impairing situations on the effects of the benzodiazepine chlordiazepoxide on mice re-tested in the EPM is investigated. The results showed that: (1) as expected, the administration of chlordiazepoxide to mice re-tested in the EPM- under the same conditions of the first trial- failed to induce anxiolysis; (2) a decreased percent time in the open arms was observed on the second trial of mice exposed to both trials under the same experimental conditions; (3) neither the increase in open arm avoidance by mice re-exposed to the EPM nor the OTT to chlordiazepoxide effect were modified by administration of the amnestic agent scopolamine; (4) the decrement of the duration of the first trial to 1 min or the change in light and noise conditions in both trials counteracted the increase in open arm avoidance on trial 2; (5) none of the later procedures modified the phenomenon of OTT. Although not discarding the modulation exerted by other memory processes in the OTT phenomenon, the results indicate that situations that impair the learned avoidance response to the open arms in the EPM do not modify the phenomenon of OTT.

Scopolamine given pre-Trial 1 prevents the one-trial tolerance phenomenon in the elevated plus-maze Trial 2

A learned avoidance response has been one of the hypotheses proposed to explain the 'one-trial tolerance' (OTT) phenomenon, which represents a drug's loss of anxiolytic-like effect in the elevated plus-maze (EPM) test in experienced rodents. Based on these facts, if some kind of learning occurs throughout Trial 1, then an impairment of its acquisition would maintain the drug's anxiolytic-like effect on Trial 2. Using male Wistar rats, the present study examined whether scopolamine (SCO; 0.5-1.5 mg/kg), a drug that impairs learning acquisition, given 30 min prior to Trial 1, actually prevents the OTT phenomenon to either the midazolam (MDZ; 0.5 mg/kg) or the memantine (MEM; 8.0 mg/kg) anxiolytic-like effect on the EPM Trial 2 (48 h later). According to the results, both MDZ and MEM increased open-arm exploration (indicating anxiolysis) on Trial 2 only in rats that had been treated previously with 1.5 mg/kg SCO. These results were observed in the absence of change in general exploratory activity. The present findings suggest that SCO impaired the acquisition of the behavioral strategy to cope with the subsequent EPM exposure that supposedly underlies the OTT phenomenon, thereby revealing the anxiolytic-like effects of MDZ and MEM on Trial 2.

Reversal of Reserpine-Induced Orofacial Dyskinesia and Cognitive Dysfunction by Quercetin

Tardive dyskinesia (TD) is a serious neurological syndrome associated with long-term administration of neuroleptics to humans and experimental animals. The pathophysiology of this disabling and commonly irreversible movement disorder is still obscure. It may be caused by a loss of dopaminergic cells or may be due to free radicals as a product of high synaptic dopamine levels. Quercetin is a bioflavonoid with strong antioxidant properties. Repeated treatment with reserpine (1.0 mg/kg) on each other day for a period of 5 days (days 1, 3 and 5) significantly induced vacuous chewing movements (VCMs) and tongue protrusions (TPs) in rats. Chronic treatment with quercetin for a period of 4 weeks to reserpine-treated animals significantly and dose dependently (50 and 100 mg/kg) reduced the reserpine-induced VCMs and TPs. Reserpine-treated animals also showed poor retention of memory in elevated plus-maze task paradigm. Chronic quercetin administration significantly reversed reserpine-induced retention deficits. Biochemical analysis revealed that chronic reserpine treatment significantly induced lipid peroxidation and decreased the glutathione (GSH) levels in the brains of rats. Chronic reserpine-treated rats showed decreased levels of antioxidant defense enzymes, superoxide dismutase (SOD) and catalase. Chronic administration of quercetin dose dependently (50-100 mg/kg) and significantly reduced the lipid peroxidation and restored the decreased GSH levels by chronic reserpine treatment. It also significantly reversed the reserpine-induced decrease in brain SOD and catalase levels in rats. The results of the present study clearly indicated that quercetin has a protective role against reserpine-induced orofacial dyskinesia and memory impairment. Consequently, the use of quercetin as a therapeutic agent for the treatment of TD should be considered.

Impaired memory following predatory stress in mice is improved by fluoxetine

The first purpose of the present study was to investigate possible effects of predatory stress (i.e., 5-min cat exposure) on short-term learning abilities in Swiss mice using the object recognition test (ORT). The second aim was to evaluate the effects of anxiolytics (i.e., diazepam and fluoxetine) on learning/memory abilities in the ORT following predatory stress. Results showed that predatory exposure impaired learning and produced amnesia of acquired information or impairment to retrieve learned information (48 and 96 h poststressor). The learning impairment in the ORT in stressed mice was restored by acute fluoxetine treatment, but not by diazepam that instead affected learning in nonstressed animals. Taken together, these findings indicate that this animal model of exposure of mice to unavoidable predatory stimuli produces early cognitive changes analogous to those seen in patients with acute stress disorder (ASD).

Effect of kami-untan-to on the impairment of learning and memory induced by thiamine-deficient feeding in mice

We have recently reported that thiamine deficient (TD) mice show an impairment of learning and memory on the 20th day after start of TD feeding. Interestingly, it has been reported that the kampo medicine, "kami-untan-to" (KUT) may be useful as a potential therapeutic agent in diseases associated with cholinergic deficit such as Alzheimer's disease. In the present study, we investigated the effects of KUT on the impairment of memory-related behavior concomitant with psychoneuronal symptoms after TD feeding in mice. Oral administration of KUT had no effect on the food intake, body weight or locomotor activity in TD mice, but the mortality rate in the KUT-treated TD group was significantly lower compared with that in the non-treated TD group. Daily administration of KUT from the 1st day of TD feeding protected against the impairment of memory-related behavior induced by TD. The intensity of the choline acetyltransferase fluorescence decreased in the field of CA1 and dentate gyrus in the hippocampus in TD mice compared with pair-fed mice as the control group, and KUT treatment inhibited this decrease. These results suggest that the effect of KUT on the impairment of memory-related behavior induced by TD feeding may be closely related to the activation of cholinergic neurons in the hippocampus.

Anxiolytic-like effects of NMDA/glycine-B receptor ligands are abolished during the elevated plus-maze trial 2 in rats

RATIONALE

Drugs enhancing the GABA(A) and/or reducing the NMDA/glycine-B receptor activity produce an anxiolytic effect. Regarding the former drugs (e.g. benzodiazepines), prior elevated plus-maze (EPM) test experience abolishes the trial 2 anxiolytic activity, a phenomenon referred to as "one-trial tolerance" (OTT).

OBJECTIVES

The present study examined whether the OTT phenomenon occurs with drugs that reduce the NMDA/glycine-B receptor activity.

METHODS

Maze-naive and maze-experienced (prior EPM exposure) rats were treated with (+/-)-HA-966 (2.0 or 4.0 mg/kg), (+)-MK-801 (0.03 or 0.06 mg/kg) or memantine (4.0 or 8.0 mg/kg) and submitted to the EPM. To investigate whether the loss of drug responsiveness was due to pharmacological tolerance, rats received memantine (8.0 mg/kg) both 48 h and 30 min before the first EPM exposure.

RESULTS

All drugs increased open arms exploration, indicating an anxiolytic effect, in maze-naive but not in maze-experienced rats, in which increased open arms avoidance was observed. An anxiolytic effect was also observed after repeated memantine administration in maze-naive/drug-experienced rats. These effects were observed in the absence of changes in enclosed arms entries, an EPM general exploratory activity index.

CONCLUSIONS

The present findings extend the OTT phenomenon to drugs that reduce the NMDA/glycine-B-receptor activity, and emphasize the repeated test exposure rather than repeated drug administration as a critical determinant for the drug anxiolytic activity. Considering the mechanisms by which the EPM experience alters the drug effects, the present findings favor the hypothesis in which the OTT phenomenon emerge as a consequence of the development and adoption of an anxiolytic-insensitive behavioral strategy.

Morphine tolerance and reward but not expression of morphine dependence are inhibited by the selective glutamate carboxypeptidase II (GCP II, NAALADase) inhibitor, 2-PMPA

Inhibition of glutamate carboxypeptidase II (GCP II; NAALADase) produces a variety of effects on glutamatergic neurotransmission. The aim of this study was to investigate effects of GCP II inhibition with the selective inhibitor, 2-PMPA, on: (a) development of tolerance to the antinociceptive effects, (b) withdrawal, and (c) conditioned reward produced by morphine in C57/Bl mice. The degree of tolerance was assessed using the tail-flick test before and after 6 days of twice daily (b.i.d.) administration of 2-PMPA and 10 mg/kg of morphine. Opioid withdrawal was measured 3 days after twice daily morphine (30 or 10 mg/kg) administration, followed by naloxone challenge. Conditioned morphine reward was investigated using conditioned place preference with a single morphine dose (10 mg/kg). High doses of 2-PMPA inhibited the development of morphine tolerance (resembling the effect of 7.5 mg/kg of the NMDA receptor antagonist, memantine) while not affecting the severity of withdrawal. A high dose of 2-PMPA (100 mg/kg) also significantly potentiated morphine withdrawal, but inhibited both acquisition and expression of morphine-induced conditioned place preference. Memantine inhibited the intensity of morphine withdrawal as well as acquisition and expression of morphine-induced conditioned place preference. In addition, 2-PMPA did not affect learning or memory retrieval in a simple two-trial test, nor did it produce withdrawal symptoms in morphine-dependent, placebo-challenged mice. Results suggest involvement of GCP II (NAALADase) in phenomena related to opioid addiction.

Modulatory role of cyclooxygenase inhibitors in aging- and scopolamine or lipopolysaccharide-induced cognitive dysfunction in mice

Inflammation processes may play a critical role in the pathogenesis of the degenerative changes and cognitive impairments associated with Alzheimer's disease (AD). Non-steroidal anti-inflammatory drugs are reported to be effective in reducing the risk of developing AD or cognitive impairments. Present experiments were performed to study the possible effect of various NSAIDs on cognitive performance of young, aged and scopolamine or lipopolysaccharide (LPS) treated mice (an animal model of AD) using one trial step through type of passive avoidance and in elevated plus maze task. Chronic administration of NSAIDs at the ED(50) doses (nimesulide, rofecoxib and naproxen for 15 days) significantly reversed the age or scopolamine-induced retention deficits in both test paradigms. However, in both the memory paradigms chronic administration of NSAIDs failed to modulate the retention performance of young mice. Acute administration of LPS (50 mcg/mouse, i.p.) significantly exhibited retention deficits after 24 h and seventh day of its administration in both test paradigms. Chronic administration (7 days) of rofecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor (1.92 mg/kg, p.o.) significantly reversed the LPS-induced retention deficits in both tests. The results of this study showed chronic treatment of NSAIDs reverses the cognitive deficits in age and scopolamine or LPS treated mice. These findings establish a link between the central nervous system expression of various pro-inflammatory cytokines and learning impairment in mice.

Oxiracetam prevented the scopolamine but not the diazepam induced memory deficits in mice

In mice, the elevated plus-maze paradigm was used to investigate the effect of scopolamine hydrobromide and diazepam and their interaction with oxiracetam on the retrieval of spatial memory trace. This paradigm measures (using the transfer latency) an animal's capacity to escape from the open arm to the enclosed one. The retention session followed 24 h after the acquisition one. Experiment 1: Scopolamine (0.25 and 0.5 mg/kg) and diazepam (0.5 and 1.0 mg/kg) given 30 min before the retention session significantly prolonged the transfer latency as compared with the saline treated mice and those given the lowest dose of scopolamine (0.125 mg/kg) and diazepam (0.25 mg/kg). Experiment 2: Oxiracetam administered at doses of 3, 10 and 30 mg/kg immediately after the acquisition session prevented the scopolamine induced prolongation of the transfer latency. Thus, oxiracetam forestalled the impairment of retrieval of memory trace: the animals were able to remember the spatial configuration of the plus-maze. On the contrary, oxiracetam was not effective in the diazepam treated mice. We suggest that beneficial effect of oxiracetam might be confounded or blocked by the anxiolytic effect of diazepam.

MK-801 induced amnesia for the elevated plus-maze in mice

MK-801, a non-competitive NMDA receptor antagonist, has been shown to have amnesic properties in animal models. The purpose of the present study was to examine potential amnesic effects of MK-801 in mice using the modified elevated plus-maze paradigm. An animal was placed on the distal end of an open arm, and the transfer latency, i.e. the time in which it moves to the enclosed arm, was measured. Four different experimental schedules (i.e. the combination of the treatment and the testing) were used: MK-801 (0.075, 0.15, 0.25 and 0.4 mg/kg or saline) were given (a) 30 min before the acquisition session, (b) immediately after the acquisition session, (c) 60 min after the acquisition session, and (d) 30 min before the retention session. The retention session always followed 24 h after the acquisition session. Analysis of data showed a significant shortening of the transfer latency in saline-treated animals during the retention session. Further, MK-801 (at the dose range of 0.15--0.4 mg/kg) administered before and immediately after the acquisition session as well as before the retention session prolonged the transfer latency during the retention session. In fact, transfer latencies in MK-801 treated mice did not differ from those measured during the acquisition session. Thus, prolongation of the transfer latency in MK-801-treated mice indicates deficits in 'memorization' processes. On the contrary, MK-801 given 60 min after the acquisition session failed to increase the transfer latency, which suggests that the memory trace was sufficiently consolidated at this time. Based on the present results, the glutamatergic NMDA receptor mechanisms play an important role in a spatial orientation of mice placed on the elevated plus-maze.

Elevated T-maze as an animal model of memory: effects of scopolamine

The elevated T-maze (ETM) is a putative model for the assessment of anxiety and memory in rodents. This study was designed to further evaluate the utility of the ETM in the study of memory processes. We compared the performance of rats in the ETM, the water maze (WM) and the two-way avoidance task (TWA), after pretreatment with scopolamine (SCO; 0.3 or 1.2 mg/kg i.p.). In the ETM, rats were first trained to meet the criterion of remaining inside the enclosed arm for 300 seconds. Seventy-two hours after training, a retrieval test session was performed. At the lower dose, SCO impaired performance in the retrieval session on all three tasks, whereas in the training session an effect was noted only on the WM task. At the higher dose, SCO impaired the performance of rats in the training sessions for ETM and WM, but not TWA. In a fourth experiment using the elevated plus-maze, SCO showed anxiolytic-like effects at the higher dose only. In conclusion, the effects of SCO in rats submitted to the ETM were dose dependent, with the lower dose exerting a selective effect detected only on retrieval, whereas the higher dose induced motor effects that disrupted inhibitory avoidance acquisition, resulting in impaired retrieval. The results are discussed in terms of the utility of the ETM in the study of drug effects and the neurobiological mechanisms underlying anxiety, learning and memory.

Nootropic-like effect of ashwagandha (Withania somnifera L.) in mice

Ashwagandha (Withania somnifera L.) root extract (50, 100 and 200 mg/kg; orally) improved retention of a passive avoidance task in a step-down paradigm in mice. Ashwagandha (50, 100 and 200 mg/kg; orally) also reversed the scopolamine (0.3 mg/kg)-induced disruption of acquisition and retention and attenuated the amnesia produced by acute treatment with electroconvulsive shock (ECS), immediately after training. Chronic treatment with ECS, for 6 successive days at 24 h intervals, disrupted memory consolidation on day 7. Daily administration of ashwagandha for 6 days significantly improved memory consolidation in mice receiving chronic ECS treatment. Ashwagandha, administered on day 7, also attenuated the disruption of memory consolidation produced by chronic treatment with ECS. On the elevated plus-maze, ashwagandha reversed the scopolamine (0.3 mg/kg)-induced delay in transfer latency on day 1. On the basis of these findings, it is suggested that ashwagandha exhibits a nootropic-like effect in naive and amnesic mice.

Hypericum perforatum as a nootropic drug: enhancement of retrieval memory of a passive avoidance conditioning paradigm in mice

Depression, among other non-cognitive symptoms, is common in patients with dementia. The effect of Hypericum perforatum (St. John's Wort) extract, with well-documented antidepressant activity, was tested on memory retrieval 24 h after training on a one-trial passive avoidance task in mice. Acute administration of Hypericum extract (4.0, 8.0, 12.0, and 25.0 mg/kg i.p.) before retrieval testing increased the step-down latency during the test session. The same doses of Hypericum extract, on the other hand, failed to reverse scopolamine-induced amnesia of a two-trial passive avoidance task. The involvement of serotonergic, adrenergic, and dopaminergic mechanisms in the facilitatory effect of Hypericum extract on retrieval memory was investigated. Pretreatment of the animals with serotonergic 5-HT1A receptor antagonist (-)-pindolol (0.3, 1.0, and 3.0 mg/kg), serotonergic 5-HT2A receptor blocker spiperone (0.01, 0.03, and 0.1 mg/kg), alpha adrenoceptor antagonist phentolamine (1, 5, and 10 mg/kg), beta receptor antagonist propranolol (5, 7.5, and 10 mg/kg), dopaminergic D1 receptor antagonist SCH 23390 (0.01, 0.05, and 0.1 mg/kg), and dopaminergic D2 receptor antagonist sulpiride (5, 7.5, and 10 mg/kg) revealed the involvement of adrenergic and serotonergic 5-HT1A receptors in the facilitatory effect of Hypericum extract on retrieval memory. It is concluded that Hypericum extract may be a better alternative for treatment of depression commonly associated with dementia than other antidepressants known to have anticholinergic side effects causing delirium, sedation and even exacerbating already existing impaired cognition. In dementias of old age, Hypericum perforatum would, therefore, serve as one medication targeting both depression and amnesia with lower potential side effects.

Possible antioxidant mechanism in melatonin reversal of aging and chronic ethanol-induced amnesia in plus-maze and passive avoidance memory tasks

Cognitive dysfunction is one of the most striking age-related impairments seen in human beings and animals. This impairment probably is due to the vulnerability of the brain cells to increased oxidative stress during aging process. Pineal hormone melatonin is reported to be an endogenous antioxidant, whose peak plasma level declines during aging and in Alzheimer's disease (AD). Present experiments were performed to study the possible effect of exogenously administered melatonin on cognitive performance of young, aged, or ethanol-intoxicated mice (an animal model for AD) using one trial step-down type of passive avoidance and elevated plus-maze task. Aged or chronic ethanol-treated mice showed poor retention of memory in step-down passive avoidance and in elevated plus-maze task. Chronic administration of melatonin (0.1-10 mg/kg, sc) for 30 d or its coadministration with ethanol (15% W/V, 2 g/kg perorally) for 24 d significantly reversed the age-induced or chronic ethanol-induced retention deficits in both the test paradigms. However, in both the memory paradigms chronic administration of melatonin failed to modulate the retention performance of young mice. Chronic administration of melatonin (0.1-10 mg/kg) for 30 d also reversed age-associated decline in forebrain total glutathione (tGSH) level. Chronic ethanol administration to young mice produced decline in forebrain tGSH level and enhanced brain lipid peroxidation, which was significantly reversed by coadministration of melatonin (10 mg/kg). The results of this study showed chronic melatonin treatment reverses cognitive deficits in aged and ethanol-intoxicated mice, which is associated with its antioxidant property.

Selective and long-term learning impairment following neonatal hypoxic-ischemic brain insult in rats

We examined four different learning and memory tasks in rats which had been subjected to left carotid artery ligation followed by 2 h hypoxia (8% oxygen) when they were 7 days old. The examination began on the 4th week after insult and continued to 18 weeks post-insult. Compared with the control group, the hypoxic-ischemic group showed significant learning impairments in choice reaction time tasks relating to the attention process, and in plus-maze tasks and water maze tasks which examine long-term reference memory. In eight-arm radial maze tasks representing both short-term working memory and long-term reference memory, inferiority of the hypoxic-ischemic group was transient. Results of the sensorimotor test were normal in the hypoxic-ischemic group although slight flexion and twisting in the right forelimb was observed in 30% of the hypoxic-ischemic group when suspended by the tail. These abnormalities did not affect the results of learning tests. Findings of the study indicate that left-side brain damage produced by hypoxia-ischemia at 7 days of age resulted in selective and long-lasting learning and memory impairment.