Vinpocetine: nootropic effects on scopolamine-induced and hypoxia-induced retrieval deficits of a step-through passive avoidance response in rats

Neuroprotective Effect of Chlorogenic Acid in an Animal Model of Sporadic Alzheimer's Disease Induced by Streptozotocin

Alzheimer's Disease is a degenerative neurological condition which leads to a decline in memory and cognitive function. Chlorogenic Acid (CGA) presents properties including neuroprotective, antioxidant and anti-inflammatory. The aim of this study was to examine the impact of CGA on cognitive impairments, neuroinflammation and neuronal damage in mice submitted to an experimental model of Sporadic Alzheimer Disease (SAD) induced by intracerebroventricular administration of streptozotocin (ICV-STZ). Male Swiss mice received bilateral ICV-STZ injections (3 mg/Kg) on days 1 and 3. The treatment with CGA (5 mg/Kg, orally) or vehicle (water, orally), was initiated and continued for 26 days, starting 2 h after the second induction procedure. At first, there was no change in serum glucose levels after SAD induction. ICV-STZ induces impairments in aversive, recognition, and spatial memory, while CGA treatment significantly alleviated these memory deficits. Furthermore, locomotor activity, working memory, and anxiety-related activities remained unaffected by the treatments. CGA treatment protects against ICV-STZ-induced increase in the nitrite/nitrate and TBARS levels. ICV-STZ induced a reduction in viable cells, depletion of BDNF, and triggered astrogliosis and microgliosis in the cortex and hippocampus. Treatment with CGA preserves viable cell count in the prefrontal cortex, CA1, and CA3 regions of the hippocampus. Additionally, it prevented BDNF depletion in the prefrontal cortex and hippocampus (CA1, CA3, and DG regions), and mitigated astrogliosis and microgliosis in the prefrontal cortex and hippocampus (CA1, CA3, and DG regions). These findings indicate the neuroprotective effects of CGA, underscoring their potential as therapeutic agents or adjuncts in the treatment of SAD.

Effects of 3R, 16S-2-hydroxyethyl apovincaminate (HEAPO), donepezil and galantamine on learning and memory retention in naïve Wistar rats

The effects of 3R,16S-2-hydroxyethyl apovincaminate (HEAPO, RGH-10885) compared with those of two cholinesterase inhibitors, donepezil and galantamine, were examined in naïve Wistar rats using standard active and passive avoidance tests. The active avoidance test (shuttle box) and two passive avoidance tests (step-through and step-down) were performed according to the experimental design. There were 10 groups of rats (n = 8) and the substances studied were applied orally before each testing session. In the active avoidance test, the number of conditioned stimuli (avoidances), unconditioned stimuli (escapes) and intertrial crossings were observed. In step-down and step-through passive avoidance tests, the latencies of reactions were observed. All the studied compounds showed positive effects in the learning and memory tests, compared to the controls. It was concluded that HEAPO, donepezil and galantamine had a memory-enhancing effect in active and passive avoidance tests.

Vinpocetine, cognition, and epilepsy

OBJECTIVE

Vinpocetine has been shown to enhance memory in animal models, with possible cognitive benefit in humans. The present study sought to demonstrate if vinpocetine can enhance cognition in healthy volunteers or patients with epilepsy. In addition, we compare blood levels of vinpocetine and its active metabolite (apovincaminic acid; AVA) in humans and animals to further characterize factors related to possible therapeutic benefit.

METHODS

The cognitive effects of vinpocetine were assessed in healthy adult volunteers (n = 8) using a double-blind, randomized, crossover design at single doses (placebo, 10, 20, and 60 mg oral). Cognitive effects of vinpocetine in patients with focal epilepsy (n = 8) were tested using a double-blind, randomized, crossover design at single doses (placebo, 20 mg oral) followed by one-month open label at 20 mg oral three times a day. The neuropsychological battery included both computerized and non-computerized tests. Levels of vinpocetine and AVA in the human studies were compared to levels in 45 mice across time dosed at 5-20 mg/kg intraperitoneal of vinpocetine.

RESULTS

No significant cognitive benefits were seen in healthy volunteers or patients with epilepsy. No appreciable side effects occurred. Vinpocetine and AVA levels were lower in humans than animals.

CONCLUSIONS

Vinpocetine was well tolerated, but was not associated with positive cognitive effects. However, blood levels obtained in humans were substantially less than levels in animals obtained from dosages known to be effective in one model. This suggests that higher dosages are needed in humans to assess vinpocetine's cognitive efficacy.

Therapeutic potential of phosphodiesterase inhibitors in the treatment of osteoporosis: Scopes for therapeutic repurposing and discovery of new oral osteoanabolic drugs

Cyclic nucleotide phosphodiesterases (PDEs) are ubiquitously expressed enzymes that hydrolyze phosphodiester bond in the second messenger molecules including cAMP and cGMP. A wide range of drugs blocks one or more PDEs thereby preventing the inactivation of cAMP/cGMP. PDEs are differentially expressed in bone cells including osteoblasts, osteoclasts and chondrocytes. Intracellular increases in cAMP/cGMP levels in osteoblasts result in osteogenic response. Acting via the type 1 PTH receptor, teriparatide and abaloparatide increase intracellular cAMP and induce osteoanabolic effect, and many PDE inhibitors mimic this effect in preclinical studies. Since all osteoanabolic drugs are injectable and that oral drugs are considered to improve the treatment adherence and persistence, osteogenic PDE inhibitors could be a promising alternative to the currently available osteogenic therapies and directly assessed clinically in drug repurposing mode. Similar to teriparatide/abaloparatide, PDE inhibitors while stimulating osteoblast function also promote osteoclast function through stimulation of receptor activator of nuclear factor kappa-B ligand production from osteoblasts. In this review, we critically discussed the effects of PDE inhibitors in bone cells from cellular signalling to a variety of preclinical models that evaluated the bone formation mechanisms. We identified pentoxifylline (a non-selective PDE inhibitor) and rolipram (a PDE4 selective inhibitor) being the most studied inhibitors with osteogenic effect in preclinical models of bone loss at ≤ human equivalent doses, which suggest their potential for post-menopausal osteoporosis treatment through therapeutic repurposing. Subsequently, we treated pentoxifylline and rolipram as prototypical osteogenic PDEs to predict new chemotypes via the computer-aided design strategies for new drugs, based on the structural biology of PDEs.

The protective and therapeutic effects of vinpocetine, a PDE1 inhibitor, on oxidative stress and learning and memory impairment induced by an intracerebroventricular (ICV) injection of amyloid beta (aβ) peptide

Alzheimer's disease (AD) is a neurodegenerative disease leading to cognitive and memory impairment. This study aimed at investigating the therapeutic and preserving effects of vinpocetine on amyloid beta (Aβ)-induced rat model of AD. Sixty male adult Wistar rats were randomly divided into 6 groups (n = 10 per group) as follows: 1; control, 2; sham, 3; Aβ, 4; pre-treatment (vinpocetine + Aβ): oral gavage administration of vinpocetine at 4 mg/kg for 30 days followed by intracerebroventricular (ICV) injection of Aβ, 5; treatment (Aβ + vinpocetine): Aβ ICV injection followed by vinpocetine administration for 30 days, 6; pre-treatment + treatment (vinpocetine + Aβ + vinpocetine): vinpocetine administration for 30 days before and 30 days after AD induction. Following treatments, the animals' learning and memory were investigated using passive avoidance learning (PAL) task, Morris water maze (MWM), and novel object recognition (NOR) tests. The results demonstrated that Aβ significantly enhanced escape latency and the distance traveled in the MWM, decreased step-through latency, and increased time spent in the dark compartment in PAL. Vinpocetine ameliorated the Aβ-infused memory deficits in both MWM and PAL tests. Administration of vinpocetine in the Aβ rats increased the discrimination index of the NOR test. It also significantly diminished the nitric oxide and malondialdehyde levels and restored the reduced glutathione (GSH) levels. Vinpocetine can improve memory and learning impairment following Aβ infusion due to its different properties, including antioxidant effects, which indicates that vinpocetine administration can lead to the amelioration of cognitive dysfunction in AD.

Vinpocetine in the treatment of poststroke cognitive dysfunction: A protocol for systematic review and meta-analysis

BACKGROUND

Previous clinical trials have reported that vinpocetine can be used for the treatment of cognitive dysfunction. However, its efficacy is still inconclusive. In this systematic review study, we aim to assess its efficacy and safety for the treatment of poststroke cognitive dysfunction (PSCD).

METHODS

We will search the following electronic databases from the inception to the present to evaluate the efficacy and safety of vinpocetine for patients with PSCD. These databases include CENTRAL, EMBASE, MEDILINE, CINAHL, AMED, and four Chinese databases. All randomized controlled trials (RCTs) of vinpocetine for PSCD will be considered for inclusion without the language restrictions. The methodological quality of all included RCTs will be evaluated by the Cochrane risk of bias tool. The 95% confidence intervals will be utilized to calculate the continuous data, the mean difference or standard mean difference, and dichotomous data with risk ratio.

DISSEMINATION AND ETHICS

The results of this review will be disseminated through peer-reviewed journals. Its results may provide important evidence for the clinical practice, as well as the future studies. It does not require ethical approval, because this systematic review will not involve the individual data.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42018115224.

A PDE1 inhibitor reduces adipogenesis in mice via regulation of lipolysis and adipogenic cell signaling

Vinpocetine, a phosphodiesterase (PDE) type-1 inhibitor, increases cAMP and cGMP levels and is currently used for the management of cerebrovascular disorders, such as stroke, cerebral hemorrhage, and cognitive dysfunctions. In this study, we first determined that vinpocetine effectively suppressed adipogenesis and lipid accumulation. However, we questioned which molecular mechanism is involved because the role of PDE in adipogenesis is still controversial. Vinpocetine decreased adipogenic cell signaling, including the phosphorylation of ERK, AKT, JAK2, and STAT3, and adipokine secretion, including IL-6, IL-10, and IFN-α. Interestingly, vinpocetine increased the phosphorylation of HSL, suggesting the induction of the lipolysis pathway. Moreover, vinpocetine increased UCP1 expression via increasing cAMP and PKA phosphorylation. The administration of vinpocetine with a normal-chow diet (NFD) or a high-fat diet (HFD) in mice attenuated body weight gain in mice fed both the NFD and HFD. These effects were larger in the HFD-fed mice, without a difference in food intake. Vinpocetine drastically decreased fat weight and adipocyte cell sizes in gonadal and inguinal white adipose tissues and in the liver in both diet groups. Serum triacylglycerol levels and fasting blood glucose levels were reduced by vinpocetine treatment. This study suggested that vinpocetine prevents adipocyte differentiation through the inhibition of adipogenesis-associated cell signaling in the early stages of adipogenesis. Moreover, upregulating cAMP levels leads to an increase in lipolysis and UCP1 expression and then inhibits lipid accumulation. Therefore, we suggest that vinpocetine could be an effective agent for treating obesity, as well as improving cognition and cardiovascular function in older individuals.

A compound extracted from the periwinkle plant can limit the over-production of fat cells and may be a useful agent for treating obesity. Being overweight is the result of changes in the size and number of fat cells, or adipocytes, in the body. Scientists are searching for molecules that can limit the growth and replication of adipocytes, but many anti-obesity agents found to date have unpleasant side-effects. Kyung-Hee Chun at Yonsei University in Seoul, South Korea and co-workers examined the effects of 502 naturally occuring compounds on adipocyte differentiation in cell culture. One compound called vincamine, which is safely used to treat vascular diseases in the brain, decreased cell signaling pathways involved in adipocyte generation in mice and also lowered fasting blood glucose levels.

Protective effect of vinpocetine against neurotoxicity of manganese in adult male rats

Manganese (Mn) is required for many essential biological processes as well as in the development and functioning of the brain. Extensive accumulation of Mn in the brain may cause central nervous system dysfunction known as manganism, a motor disorder associated with cognitive and neuropsychiatric deficits similar to parkinsonism. Vinpocetine, a synthetic derivative of the alkaloid vincamine, is used to improve the cognitive function in cerebrovascular diseases. It possesses antioxidant and antiinflammatory properties. The present work was designed to explore the potential neuroprotective mechanisms exerted by vinpocetine in the Mn-induced neurotoxicity in rats. Rats were allocated into four groups. First group was given saline. The other three groups were given MnCl₂; two of them were treated with either L-dopa, the gold standard antiparkinsonian drug, or vinpocetine. Rats receiving MnCl₂ exhibited lengthened catalepsy duration in the grid and bar tests, motor impairment in the open-field test and short-term memory deficit in the Y-maze test. Additionally, histological examination revealed structural alterations and degeneration in different brain regions. Besides, striatal monoamines and mitochondrial complex I contents were declined, apoptotic biomarker caspase-3 expression and acetylcholinesterase activity were elevated. Moreover, oxidative stress and inflammation were detected in the striata. L-dopa or vinpocetine exerted protective effects against MnCl₂-induced neurotoxicity. It could be hypothesized that modulation of monoamines, upregulation of mitochondrial complex I, antioxidant, antiinflammatory, and antiapoptotic activities are significant mechanisms underlying the neuroprotective effect of vinpocetine in the Mn-induced neurotoxicity model in rats.

Neuroinflammatory response to experimental stroke is inhibited by boldine

Inflammation plays a pivotal role in the development of ischemic brain damage. Astrocyte activation promotes the production of several proinflammatory mediators, such as TNF-α and iNOS. Eventually, neuronal death occurs, leading to the development of motor and memory deficits in patients. Boldine is the main alkaloid in the leaves and bark of the Peumus boldus Molina, and has anti-inflammatory and antioxidant properties. The aim of this work was to investigate the neuroprotective effect of boldine on neuroinflammation and memory deficits induced by permanent middle cerebral artery occlusion (pMCAO) in mice. Thirty minutes before pMCAO and during the next 5 days, animals received vehicle (0.025 µmol/l HCl) or boldine (8, 16 and 25 mg/kg, intraperitoneally). The extension of the infarct area, neurological scores, and myeloperoxidase activity were evaluated 24 h after pMCAO. Locomotor activity, working, and aversive memory were evaluated 72 h after pMCAO, object recognition memory was tested 96 h after pMCAO, and spatial memory was tested 120 h after pMCAO. Cresyl violet, Fluoro-Jade C staining, and immunohistochemical for GFAP, TNF-α, and iNOS were also carried out. The treatment with boldine significantly decreased the infarct area, improved the neurological scores, and increased cell viability. The vertical exploratory activity and aversive, spatial, object recognition, and working memory deficits induced by pMCAO were prevented by boldine. Moreover, myeloperoxidase activity and GFAP, TNF-α, and iNOS immunoreactivity were decreased significantly by boldine. Although various mechanisms such as its antioxidant activity should be considered, these results suggest that the neuroprotective effect of boldine might be related in part to its anti-inflammatory properties.

Caffeic acid protects mice from memory deficits induced by focal cerebral ischemia

Brain ischemia pathophysiology involves a complex cascade of events such as inflammation and oxidative stress that lead to neuronal loss and cognitive deficits. Caffeic acid (CA) is a natural phenolic compound with antioxidant and anti-inflammatory properties. To evaluate the neuroprotective efficacy of this compound in mice subjected to a permanent middle cerebral artery occlusion, animals were pretreated and post-treated with CA, 2, 20, and 60 mg/kg/day, intraperitoneally, at 24, 48, 72, 96, or 120 h after ischemia. Animals were evaluated at 24 h after the permanent middle cerebral artery occlusion for brain infarction and neurological deficit score. At 72 h after the occlusion, animals were evaluated for locomotor activity, working memory, and short-term aversive memory; long-term aversive memory was evaluated 24 h after the evaluation of short-term aversive memory. Finally, at 120 h after the event, spatial memory and the expression levels of synaptophysin (SYP), SNAP-25, and caspase 3 were evaluated. The treatment with CA reduced the infarcted area and improved neurological deficit scores. There was no difference in locomotor activity between groups. The working, spatial, and long-term aversive memory deficits improved with CA. Furthermore, western blotting data showed that the expression of SYP, which correlates with synaptic formation and function, decreased after ischemic insult, and CA inhibited the reduction of SYP expression. Ischemia also increased, and CA treatment decreased, caspase 3 expression. These results suggest that CA exerts neuroprotective and antidementia effects, at least in part, by preventing the loss of neural cells and synapses in ischemic brain injury.

Scopolamine provocation-based pharmacological MRI model for testing procognitive agents

There is a huge unmet need to understand and treat pathological cognitive impairment. The development of disease modifying cognitive enhancers is hindered by the lack of correct pathomechanism and suitable animal models. Most animal models to study cognition and pathology do not fulfil either the predictive validity, face validity or construct validity criteria, and also outcome measures greatly differ from those of human trials. Fortunately, some pharmacological agents such as scopolamine evoke similar effects on cognition and cerebral circulation in rodents and humans and functional MRI enables us to compare cognitive agents directly in different species. In this paper we report the validation of a scopolamine based rodent pharmacological MRI provocation model. The effects of deemed procognitive agents (donepezil, vinpocetine, piracetam, alpha 7 selective cholinergic compounds EVP-6124, PNU-120596) were compared on the blood-oxygen-level dependent responses and also linked to rodent cognitive models. These drugs revealed significant effect on scopolamine induced blood-oxygen-level dependent change except for piracetam. In the water labyrinth test only PNU-120596 did not show a significant effect. This provocational model is suitable for testing procognitive compounds. These functional MR imaging experiments can be paralleled with human studies, which may help reduce the number of false cognitive clinical trials.

Differential effects of paradoxical sleep deprivation on memory and oxidative stress

Sleep has important functions for every organ in the body and sleep deprivation (SD) leads to disorders that cause irreparable damage. The aim of this study was to investigate behavioral and brain structural alterations in mice deprived of paradoxical sleep for 48 and 72 h. Working memory, aversive memory as well as levels of nitric oxide (NO) and thiobarbituric acid reactive substances (TBARS) in the hippocampus, body striatum, and prefrontal cortex were evaluated. Working memory was affected in the 48- and 72-h SD groups while aversive memory was altered only in the 48-h SD group (p ≤ 0.05). Our findings showed that SD reduces NO levels in most brain areas (p < 0.05): NO levels were unaltered in the striatum of animals sleep-deprived for 48 h. Higher levels of TBARS were observed in all areas of the SD groups (p ≤ 0.05). Thus, we confirmed that SD has duration-dependent effects on behavior as well as on NO and TBARS levels in the brain. Preserved striatum NO levels suggest that this structure is less vulnerable to oxidative stress and is only affected by SD of longer duration. Increased TBARS and reduced NO levels in the hippocampus and prefrontal cortex confirm a central role for both these structures in working memory and aversive memory. Contextual fear conditioning was not affected by longer periods of SD. Thus, our findings suggest that shorter SD time may be more beneficial to avoid aversive memory where this may have implications for the management of posttraumatic stress.

Catechin attenuates behavioral neurotoxicity induced by 6-OHDA in rats

This study was designed to investigate the beneficial effect of catechin in a model of Parkinson's disease. Unilateral, intrastriatal 6-hydroxydopamine (6-OHDA)-lesioned rats were pretreated with catechin (10 and 30 mg/kg) by intraperitoneal (i.p.) injection 2h before surgery and for 14 days afterwards. After treatments, apomorphine-induced rotations, locomotor activity, working memory and early and late aversive memories were evaluated. The mesencephalon was used to determine the levels of monoamines and measurement of glutathione (GSH). Immunohistochemical staining was also used to evaluate the expression of tyrosine hydroxylase (TH) in mesencephalic and striatal tissues. Catechin administration attenuated the increase in rotational behavior and the decrease in locomotor activity observed in lesioned rats. Although catechin did not rescue the impairment of late aversive memory, it protected the animals against 6-OHDA-induced working memory deficits. Furthermore, catechin treatment restored GSH levels, and significantly increased dopamine and DOPAC content, and TH-immunoreactivity in 6-OHDA-lesioned rats. Catechin protected 6-OHDA-lesioned rats due to its antioxidant action, indicating that it could be useful as an adjunctive therapy for the treatment of Parkinson's disease.

Amelioration of intracerebroventricular streptozotocin induced cognitive dysfunction and oxidative stress by vinpocetine -- a PDE1 inhibitor

Enhancing cyclic nucleotides signaling by inhibition of phosphodiesterases (PDEs) is known to be beneficial in disorders associated with cognitive decline. The present study was designed to investigate the effect of vinpocetine (PDE1 inhibitor) on intracerebroventricular (i.c.v.) streptozotocin induced experimental sporadic dementia of Alzheimer's type. Infusion of streptozotocin impaired learning and memory, increased oxidative-nitritive stress and induced cholinergic hypofunction in rats. Chronic treatment with vinpocetine (5, 10 and 20 mg/kg i.p.) for 21 days following first i.c.v. streptozotocin infusion significantly improved learning and memory in Morris water maze and passive avoidance paradigms. Further, vinpocetine significantly reduced the oxidative-nitritive stress, as evidenced by decrease in malondialdehyde (MDA) and nitrite levels, and restored the reduced glutathione (GSH) levels. Significant increase in acetylcholinesterase activity and lactate dehydrogenase levels was observed in the present model indicating cholinergic hypofunction and increase in neuronal cell damage. Chronic treatment with vinpocetine also reduced significantly the increase in acetylcholinesterase activity and lactate dehydrogenase levels indicating restorative capacity of vinpocetine with respect to cholinergic functions and preventing the neuronal damage. The observed beneficial effects of vinpocetine on spatial memory may be due to its ability to favorably modulate cholinergic functions, prevent neuronal cell damage and possibly through its antioxidant mechanism also.

Increased particulate phosphodiesterase 4 in the prefrontal cortex supports 5-HT4 receptor-induced improvement of object recognition memory in the rat

RATIONALE

Serotonin receptors (5-HT4Rs) are critical to both short-term and long-term memory processes. These receptors mainly trigger the cyclic adenosine monophosphate (cAMP)/protein kinase A signaling pathway, which is regulated by cAMP phosphodiesterases (PDEs).

OBJECTIVES

We investigated the mechanisms underlying the effect of the selective activation of 5-HT4R on information acquisition in an object recognition memory task and the putative regulation of PDE.

MATERIALS AND METHODS

The effect of RS 67333 (1 mg/kg, intraperitoneally [i.p.], injected 30 min before the sample phase) was examined at different delay intervals in an object recognition task in Sprague-Dawley rats. After the testing trial, PDE activity of brain regions implicated in this task was assayed.

RESULTS

RS 67333-treated rats spent more time exploring the novel object after a 15-min (P < 0.001) or 4-h delay (P < 0.01) but not after a 24-h delay, whereas control animals showed no preference for the novel object for delays greater than 15 min. We characterized the specific patterns and kinetic properties of PDE in the prefrontal and perirhinal cortices as well as in the hippocampus. We demonstrated that particulate PDE activities increase in both the prefrontal cortex and hippocampus following 5-HT4R stimulation. In the prefrontal cortex, PDE4 activities support the RS 67333-induced modification of PDE activities, whereas in the hippocampus, all cAMP-PDE activities varied. In contrast, particulate PDE variation in the hippocampus was not found to support improvement of recognition memory after a 4-h delay.

CONCLUSIONS

We provide evidence that the increase in particulate PDE4 activity in the prefrontal cortex supports the 5-HT4R-induced increase in information acquisition.

Vinpocetine prevents 4-aminopyridine-induced changes in the EEG, the auditory brainstem responses and hearing

OBJECTIVE

The purpose of the present study was to investigate if the sodium channel blocker and memory enhancer, vinpocetine, was capable to overcome the epileptic cortical activity, the abnormalities in the later waves of the auditory brainstem responses (ABRs) and the hearing loss induced by 4-AP at a convulsing dose in the guinea pig in vivo.

METHODS

EEG and ABR recordings before and at specific times within 2h after the injection of 4-AP (2 mg/kg, i.p.) were taken in animals pre-injected i.p. with vehicle or with vinpocetine (2 mg/kg) 1 h before 4-AP. The amplitude and latency of the ABR waves induced by a monoaural stimulus of high intensity (100 dB nHL) at 4 and 8 kHz pure tone frequencies and the ABR threshold were determined in the animals exposed to the different experimental conditions.

RESULTS

Vinpocetine inhibited the EEG changes induced by 4-AP for the ictal and post-ictal periods as well as the alterations in amplitude and latency of P3 and P4 and the increase in the ABR threshold induced by 4-AP.

CONCLUSIONS

Vinpocetine prevents the retro-cochlear alterations and the hearing decline that accompany the epileptic cortical activity.

SIGNIFICANCE

Vinpocetine could be a promising alternative for the treatment of epilepsy.

The effect of venlafaxine on behaviour, body weight and striatal monoamine levels on sleep-deprived female rats

Partial sleep deprivation is clinically associated with fatigue, depressive symptoms and reduced memory. Previously, it has been demonstrated that venlafaxine, an atypical antidepressant, increases the levels of noradrenaline and serotonin in rat hippocampus. The aim of this study was to evaluate the effects of venlafaxine on depression, anxiety, locomotor activity and memory in a model of REM sleep (REMs) deprivation in rats. We have also studied the influence of venlafaxine on monoamine levels in the striatum. Six groups of animals (N=20 each) were treated with saline or venlafaxine (1 or 10 mg/kg) during 10 days, submitted or not to REMs deprivation and studied with the forced swimming test of Porsolt (STP), plus-maze, passive avoidance and open-field tests right after sleep deprivation. Animals were also studied for passive avoidance 24 h later (rebound period). Brain samples for monoamine measurements were collected either immediately after REMs deprivation or after 24 h. Both REMs deprivation and venlafaxine showed an antidepressant effect. An anxiolytic effect was also observed after REMs deprivation. Previous treatment with venlafaxine blocked the antidepressant and anxiolytic effects of REMs deprivation. REMs deprivation alone and treatment with venlafaxine 10 mg/kg increased locomotor activity, and this effect was inhibited by venlafaxine in REMs deprived rats. Both venlafaxine treatment and REMs deprivation induced weight loss. Venlafaxine treatment, but not REMs deprivation, induced an increase in striatal dopamine (DA) levels. The combination of REMs deprivation and venlafaxine treatment was associated with an increase in serotonin turnover 24 h after rebound sleep. In this study, venlafaxine treatment hindered most behavioral effects of REMs deprivation and was associated with an interference on dopamine and serotonin systems in the striatum.

Vinpocetine for cognitive impairment and dementia

BACKGROUND

Vinpocetine is a synthetic ethyl ester of apovincamine, a vinca alkaloid obtained from the leaves of the Lesser Periwinkle (Vinca minor) and discovered in the late 1960s. Although used in human treatment for over twenty years, it has not been approved by any regulatory body for the treatment of cognitive impairment. Basic sciences studies have been used to claim a variety of potentially important effects in the brain. However, despite these many proposed mechanisms and targets, the relevance of this basic science to clinical studies is unclear.

OBJECTIVES

To assess the efficacy and safety of vinpocetine in the treatment of patients with cognitive impairment due to vascular disease, Alzheimer's disease, mixed (vascular and Alzheimer's disease) and other dementias.

SEARCH STRATEGY

The Cochrane Dementia & Cognitive Improvement Group's Specialized Register was searched using the terms vinpocetin*, cavinton, kavinton, Rgh-4405, Tcv-3B, "ethyl apovincaminate", vinRx, periwinkle, "myrtle vincapervinc" and cezayirmeneksesi. The manufacturers of vinpocetine were asked for information on trials of vinpocetine for dementia. In addition we tried to collect articles not listed in MEDLINE or other sources on the Internet (e.g. articles in Hungarian and Romanian).

SELECTION CRITERIA

All human, unconfounded, double-blind, randomized trials in which treatment with vinpocetine was administered for more than a day and compared to control in patients with vascular dementia, Alzheimer's dementia or mixed Alzheimer's and vascular dementia and other dementias. Non-randomized trials were excluded.

DATA COLLECTION AND ANALYSIS

Data were independently extracted by the two reviewers (SzSz and PW) and cross-checked. Data from "washout" periods were not used for the analysis. For continuous or ordinal variables, such as cognitive test results, the main outcomes of interest were the change in score from baseline. The categorical outcome of global impression was transformed to binary data (improved or not improved) as was the occurrence of adverse effects; here the endpoint itself was of interest the Peto method of the "typical odds ratio" was used. A test for heterogeneity of treatment effects between the trials was made if appropriate. Data synthesis and analysis were performed using the Cochrane Review Manager software (RevMan version 4.1).

MAIN RESULTS

All identified studies were performed before the 1990s and used various terms and criteria for cognitive decline and dementia. The three studies included in the review involved a total of 583 people with dementia treated with vinpocetine or placebo. The reports of these studies did not make possible any differentiation of effects for degenerative or vascular dementia. The results show benefit associated with treatment with vinpocetine 30mg/day and 60 mg/day compared with placebo, but the number of patients treated for 6 months or more was small. Only one study extended treatment to one year. Adverse effects were inconsistently reported and without regard for relationship to dose. The available data do not demonstrate many problems of adverse effects but intention-to-treat data were not available for any of the trials.

REVIEWER'S CONCLUSIONS

Although the basic science is interesting, the evidence for beneficial effect of vinpocetine on patients with dementia is inconclusive and does not support clinical use. The drug seems to have few adverse effects at the doses used in the studies. Large studies evaluating the use of vinpocetine for people suffering from well defined types of cognitive impairment are needed to explore possible efficacy of this treatment.

Aniracetam attenuates apoptosis of astrocytes subjected to simulated ischemia in vitro

The aim of the present study was to establish whether aniracetam is capable of protecting cultured rat astrocytes against ischemic injury. Treatment of the cultures with aniracetam (1, 10 and 100 mM) during 24 h ischemia simulated in vitro significantly decreased the number of apoptotic cells. The antiapoptotic effects of the drug were confirmed by the increase of intracellular ATP and phosphocreatine (PCr) levels and the inhibition of the caspase-3 activity. Aniracetam also attenuated cellular oxidative stress by decreased production of reactive oxygen species (ROS). These effects were associated with the decrease in levels of c-fos and c-jun mRNA in primary astrocyte cultures exposed to 24 h ischemia. When cultured astrocytes were incubated during 24 h simulated ischemia with wortmannin, a phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor or PD98059, a mitogen-activated protein (MAP)/extracellular signal regulated kinase (ERK) (MEK) inhibitor the cell apoptosis was accelerated. This effect was antagonized by adding 100 mM aniracetam to the culture medium. These findings suggest that the protective effect of aniracetam is mediated by PI 3-kinase and MEK pathways in the downstream mechanisms.

Effects of a phosphodiesterase IV inhibitor rolipram on microsphere embolism-induced defects in memory function and cerebral cyclic AMP signal transduction system in rats

The effects of treatment with rolipram, a specific phosphodiesterase IV inhibitor, on learning and memory function and on the cyclic AMP/PKA/CREB signal transduction system were examined in rats with microsphere embolism (ME)-induced cerebral ischaemia. Sustained cerebral ischaemia was induced by the injection of 900 microspheres (48 microm in diameter) into the right hemisphere of the rat brain. The animals were treated once daily with 3 mg kg(-1) rolipram i.p. from 6 h after the onset of the operation for consecutive 10 days. Microsphere-embolized rats showed prolongation of the escape latency in the water maze task starting from day 7 after the operation and lasting for 3 consecutive days. Treatment with rolipram reduced the escape latency. ME decreased the cyclic AMP content, cytosolic PKA Cbeta level, and nuclear PKA Calpha and Cbeta levels, as well as reduced the pCREB level and the DNA-binding activity of CREB in the cerebral cortex and hippocampus on day 10 after the operation. These alterations were attenuated by treatment with rolipram. These results suggest that ME-induced failure in learning and memory function may be mediated by dysfunction of the cyclic AMP/PKA/CREB signal transduction system, that rolipram may ameliorate ME-induced impairment of learning and memory function, and that the drug effect may be partly attributed to activation of the cyclic AMP/PKA/CREB signal transduction system.

Evidence for the involvement of the muscarinic cholinergic system in the central actions of pentoxifylline

This study shows that pentoxifylline (ptx), a xanthine derivative, significantly attenuates scopolamine-induced memory impairment in rats, as demonstrated in a passive avoidance task (50 mg/kg intraperitoneally [i.p.]) and in an elevated T-maze (10 and 50 mg/kg i.p.). Ptx (25, 50 and 100 mg/kg i.p.) also potentiates oxotremorine-induced tremors in mice, in a dose-dependent manner, and this effect was completely prevented by atropine. In addition, ptx (50 and 100 mg/kg i.p.) increased the number of animals developing pilocarpine-induced seizures, and potentiated the latency to the first pilocarpine-induced convulsion. Hippocampus homogenates from rats treated with ptx (100 mg/kg) for 1 week and sacrificed 15 min after the last injection showed a significant decrease in the muscarinic receptor numbers, indicative of a downregulation phenomenon. Similar effects were observed when assays were performed 24 h after the last ptx injection (10 and 50 mg/kg i.p.), but not after 72 h. Additionally, in vitro assays showed that ptx inhibits acetylcholinesterase activity in a dose-dependent manner when incubated with homogenates from rat hippocampus. Our data suggest that the muscarinic agonist effect of ptx could possibly depend on factors such as endogenous cholinergic activity.

Cerebroprotective drugs shorten the hypoxia-induced onset of electrical silence in unanesthetized rats

Pharmacological agents that delay the hypoxic arrest of neuronal electrical activity, as indicated by the suppression of electroencephalogram (EEG), have previously been thought to increase brain resistance to oxygen insufficiency. On the other hand, acceleration of the EEG suppression may offer some protection against severe hypoxia by reducing neuronal energy spending on electrogenesis. In unanesthetized rats we examined the effects of several antihypoxic drugs on the time of appearance of isoelectric EEG (tiEEG), caused by normobaric hypoxia. In addition, alterations in cerebral blood flow induced by hypoxia and by some drugs were monitored using polarographic techniques to determine if cerebrocirculatory changes play a significant role in the drug effects on tiEEG. We also assessed drug effects on behavioral recovery after hypoxia by measuring the latency of restoration of the head-withdrawal reflex upon vibrissae stimulation. Pentobarbital (30 and 60 mgkg(-1)i.p.), chloralhydrate (400 mgkg(-1)i.p.) flunarizine (50-100 mgkg(-1)p.o.), hydergine (3-50 mgkg(-1)p.o.), nicergoline (50 mgkg(-1)and 85 mgkg(-1)p.o.), sabeluzole (3 and 7.5 mgkg(-1)i.p.) and vincamine (80 mgkg(-1)p.o.) reduced tiEEG (mean 27.1 +/- 3.3 min prior to drugs). In contrast, idebenone (29-85 mgkg(-1)p.o.) and vinpocetine (29-85 mgkg(-1)p.o.) had no significant effects on tiEEG. The divergent effects on cerebral blood flow suggest an insignificant role for cerebrocirculatory changes in the drug-induced reduction of tiEEG during severe hypoxia. The drug effects on recovery of the head-withdrawal reflex (mean 4.2 +/- 1.3 min prior to drugs) varied from a delay (sabeluzole) to acceleration (flunarizine) with no correlation to the effects on tiEEG, suggesting that EEG criteria alone may not predict the course of functional recovery.

Pentoxifylline improves learning and memory in glutamate-lesioned rats

The present work shows the effects of pentoxifylline (ptx), on learning and memory in rats with hippocampal lesions induced by glutamate (glu). Immediately after stereotaxic procedures and in the absence or presence of glu lesions, animals were treated with ptx (50, 100, or 200 mg/kg, IP) for 6 days. Twenty-four hours after the last injection, behavior and memory tests were performed, animals were sacrificed, and hippocampi dissected for cAMP determination or histopathological studies. Results from the T-maze task showed a less learning ability in the glu-lesioned group compared to other ones. Ptx alone or associated with glu significantly improved memory acquisition, but not memory consolidation compared to glu-lesioned rats. Except for the increased locomotor activity observed in the ptx100+glu-treated group compared to saline, no other difference was detected in the open-field test. A significant impairment in avoidance performance was observed in glu-lesioned group as compared to saline or to other groups in the short as well as in the late phase of memory. All groups showed an improved water-maze performance over time with similar performances on the final day of acquisition. The impairment in memory retention observed in glu-lesioned rats was reversed by the pretreatment with ptx200. Glu induced hippocampal lesion and reduced cAMP levels. Both effects were blocked by ptx, suggesting that its action may be the result of increased cAMP levels and/or inhibition of adenosine A1 receptors.

Ameliorating effects of rolipram on experimentally induced impairments of learning and memory in rodents

The effects of rolipram, a cAMP-specific phosphodiesterase (phosphodiesterase 4) inhibitor, on experimentally-induced amnesia were examined using a 3-panel runway paradigm in rats and a passive avoidance task in mice. Scopolamine, cerebral ischemia induced by four-vessel occlusion and electric convulsive shock impaired working memory in the 3-panel runway task. Rolipram at 0.1 mg/kg reduced the increase in errors induced by scopolamine or cerebral ischemia. Rolipram at 0.32 mg/kg also reduced the increase in errors induced by electric convulsive shock. Dibutyryl cAMP also had similar effects in 3-panel runway experiments. In the passive avoidance task, rolipram reversed the impairments of the avoidance response induced by scopolamine, cycloheximide and electric convulsive shock at 10, 10 and 3 mg/kg, respectively. These results indicate that rolipram ameliorates impairments of learning and memory in rats and mice, and suggest that rolipram might ameliorate the impairments of learning and memory by elevating cAMP levels.

Cognitive enhancers and hippocampal long-term potentiation in vitro

We review our works on the pharmacological modulation of long-term potentiation (LTP) at guinea pig hippocampal mossy fiber-CA3 synapses in vitro. The magnitude of tetanus-induced LTP at the mossy fiber synapse was augmented by perfusion of slices with several cognitive enhancers, such as bifemelane (1 microM). The mossy fiber LTP was enhanced by somatostatin (0.32 microM) and inhibited in somatostatin-depleted slices from cysteamine-treated guinea pigs. An involvement of the 5-HT3 receptor also showed that granisetron (0.1 microM) enhanced the mossy fiber LTP. The above-mentioned enhancements by perfused agents were commonly reversed, at least in part, by muscarinic antagonists. However, the magnitude of mossy fiber LTP was bidirectionally modulated by muscarinic stimulations of slices with physostigmine or carbachol at different concentrations. The enhancing effects of high-concentration carbachol was antagonized by pirenzepine, and in contrast, the inhibition by low-concentration carbachol was antagonized in the presence of AF-DX116. When guinea pigs were preinjected with the cholinotoxin AF64A, the magnitude of LTP was decreased in the slices prepared from AF64A-treated animals. These results suggest that endogenous acetylcholine dominantly plays facilitatory roles through muscarinic M1 receptors in the induction of mossy fiber LTP. The pharmacological characterization of mossy fiber LTP may be of help to the evaluation of cognitive enhancers at a neuronal circuit level.

The influence of nimodipine and MK-801 on the brain free arachidonic acid level and the learning ability in hypoxia-exposed rats

1. The influence of voltage dependent calcium channel blocker (VDCC), nimodipine and N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 on the brain free arachidonic acid (FAA) level and on the learning ability in hypoxia-exposed rats was examined. 2. Some animals were decapitated after cerebral hypoxia had been obtained and the brain FAA level was determined by gas chromatography. The other animals were trained in a passive avoidance procedure and were exposed to hypoxic conditions immediately after the learning trial response had been acquired. A passive avoidance retention test was performed 24 hours later. 3. Various doses of nimodipine (0.03; 0.1; 0.3 and 1.0 mg/kg) and MK-801 (0.03; 0.1 and 0.3 mg/kg) had been injected 30 minutes before biochemical or behavioral procedures started. 4. It was found that hypoxia strongly increased the brain FAA level and impaired the retention of the passive avoidance response. 5. Pretreatment with 0.3 mg/kg and 1.0 mg/kg of nimodipine prevented the brain FAA accumulation. It has also been shown that all tested doses of nimodipine significantly improved the retention deficit in the animals exposed to hypoxia. 6. Neither the one of tested doses of MK-801 influenced significantly the increase of the brain FAA level and/or passive avoidance behavior in hypoxic animals. 7. These results confirm the hypothesis that the brain FAA accumulation and cognitive impairment, caused by hypoxia, are maybe associated with disturbances in calcium homeostasis and that nimodipine may be useful in ameliorating the hypoxia-induced brain tissue damage. Blocade of NMDA receptor-channel complex by MK-801 was not sufficient to prevent hypoxia-induced neuronal damage.

Effects of D-cycloserine and aniracetam on spatial learning in rats with entorhinal cortex lesions

A great body of behavioural and neurophysiological evidence suggests that excitatory amino acids are involved in mechanisms of learning and memory. Moreover, degeneration of glutamatergic pathways may underlie the cognitive deficits seen in various disorders such as Alzheimer's dementia. As direct stimulation of glutamatergic receptors with agonists may increase the risk of toxicity and accelerate neuropathological changes, a more valid approach seems to be positive modulation of glutamatergic receptors that may reverse the symptoms with a lower risk of excitotoxic effects. Such a possibility offered by partial agonists of the strychnine-insensitive glycine site of the NMDA receptor (Gly-B site) or positive modulators of AMPA receptors, such as aniracetam. In the present study, the effects of d-cycloserine and aniracetam were tested in two animal models of cognitive deficits (entorhinal cortex lesion-induced deficits evaluated in the radial maze and scopolamine-induced amnesia evaluated in passive avoidance test). D-cycloserine (6 mg/kg, for 10 days) had no effect on spatial working memory deficit induced by entorhinal cortex lesions. It did, however, reverse scopolamine-induced deficits in the passive avoidance test when given acutely at the same dose. In contrast, aniracetam (50 mg/kg, for 10 days) produced beneficial effects in the radial maze test in rats with entorhinal cortex lesions, but given at the same dose acutely did not influence scopolamine-induced amnesia. The positive effect of d-cycloserine against scopolamine-induced amnesia may be probably related to the cholinergic-glutamatergic interaction in the hippocampus. The negative data obtained with d-cycloserine in the model of entorhinal cortex lesions-induced cognitive deficits could be taken as a hint that it is probably not suitable for the symptomatological therapy of Alzheimer's disease. The mechanism of positive action of aniracetam cannot be explained on the basis of AMPA receptor modulation, as the dose used (50 mg/kg) is well below that required for the effect at AMPA receptors. Other actions such as peripheral effects or modulation of metabotropic receptors seem more likely.

Piracetam and other structurally related nootropics

Nearly three decades have now passed since the discovery of the piracetam-like nootropics, compounds which exhibit cognition-enhancing properties, but for which no commonly accepted mechanism of action has been established. This review covers clinical, pharmacokinetic, biochemical and behavioural results presented in the literature from 1965 through 1992 (407 references) of piracetam, oxiracetam, pramiracetam, etiracetam, nefiracetam, aniracetam and rolziracetam and their structural analogues. The piracetam-like nootropics are capable of achieving reversal of amnesia induced by, e.g., scopolamine, electroconvulsive shock and hypoxia. Protection against barbiturate intoxication is observed and some benefit in clinical studies with patients suffering from mild to moderate degrees of dementia has been demonstrated. No affinity for the alpha 1-, alpha 2-, beta-, muscarinic, 5-hydroxytryptamine-, dopamine, adenosine-A1-, mu-opiate, gamma-aminobutyric acid (GABA) (except for nefiracetam (GABAA)), benzodiazepine and glutamate receptors has been found. The racetams possess a very low toxicity and lack serious side effects. Increased turnover of different neurotransmitters has been observed as well as other biochemical findings, e.g., inhibition of enzymes such as prolylendopeptidase. So far, no generally accepted mechanism of action has, however, emerged. We believe that the effect of the racetams is due to a potentiation of already present neurotransmission and that much evidence points in the direction of a modulated ion flux by, e.g., potentiated calcium influx through non-L-type voltage-dependent calcium channels, potentiated sodium influx through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor gated channels or voltage-dependent channels or decreases in potassium efflux. Effects on carrier mediated ion transport are also possible.

MKC-231, a choline uptake enhancer, ameliorates working memory deficits and decreased hippocampal acetylcholine induced by ethylcholine aziridinium ion in mice

The effects of acute and chronic administration of MKC-231, a new choline uptake enhancer, and two other nootropic agents, linopiridine (Dup 996) and tetrahydroaminoacridine (THA) on working memory deficits and decreased hippocampal acetylcholine (ACh) content were studied in a delayed non-matching to sample task, using a T-maze, in ethylcholine aziridinium ion (AF64A)-treated mice. Treatment with AF64A (3.5 nmol, i.c.v.) produced memory deficits and decreased hippocampal ACh content. In acute behavioral experiments, MKC-231 and THA had no significant effect on AF64A-induced memory deficits at any doses tested (0.3, 1.0 and 3.0 mg/kg), whereas Dup 996, at a dose of 1.0 mg/kg, significantly improved memory deficits. In chronic experiments, MKC-231 improved memory deficit at all doses tested (0.3, 1.0, or 3.0 mg/kg p.o., once daily for 11 days) and Dup 996 did so only at a dose of 3.0 mg/kg, whereas THA did not improve memory deficit at any doses tested. In acute neurochemical experiments, MKC-231 and THA did not reverse the AF64A-induced hippocampal ACh depletion. Dup 996, however, further decreased hippocampal ACh content compared to that in the AF64A-treated group. In chronic experiments, MKC-231 significantly reversed hippocampal ACh depletion at doses of 0.3 and 1.0 mg/kg, whereas neither Dup 996 nor THA reversed hippocampal ACh depletion at any doses tested. These results indicate that MKC-231 improved the AF64A-induced working memory deficit and hippocampal ACh depletion, probably by recovering reduced high-affinity choline uptake and ACh release.

Hypoxia produces cell death in the rat hippocampus in the presence of an A1 adenosine receptor antagonist: an anatomical and behavioral study

Endogenous adenosine depresses synaptic transmission in rat hippocampal slices during periods of hypoxia, a potentially neuroprotective cellular response that is attenuated by the adenosine antagonist 8-cyclopentyltheophylline. In this study, rats were exposed to moderate hypoxic conditions (5% O2- 95% N2, 40 min x three days) in the presence or absence of 8-cyclopentyltheophylline, and the effects of reducing adenosinergic inhibition during hypoxia were assessed histologically and behaviorally. Half the rats exposed to low levels of oxygen in the presence of 8-cyclopentyltheophylline (10 mg/kg) suffered unilateral or bilateral hippocampal damage largely limited to the CA1 subfield. Animals which had suffered hippocampal damage were also impaired in their performance of a working memory version of the Morris Water Maze, but not a passive avoidance task (step-through). Hypoxia alone did not result in neuronal damage or behavioral impairment. These results provide further evidence that endogenous adenosine provides an important level of neuronal protection during even prolonged periods of hypoxia.

Behavioral screening for cognition enhancers: from indiscriminate to valid testing: Part I

Preclinical efforts to detect and characterize potential cognition enhancers appear to have been dominated by a strategy of demonstrating a wide variety of apparently beneficial behavioral effects with little attention given to the specific psychological mechanisms underlying behavioral enhancement. In particular, the question of whether or not behavioral facilitation is based on relevant mnemonic mechanisms and is independent of the stimulus properties and/or the motivational and attentional components of a task is not often considered. As a result, an overwhelming number of compounds have failed to produce the clinical effects predicted for them on the basis of preclinical research. The available data suggest that a more successful approach requires deductive research strategies rather than the indiscriminate accumulation of apparently beneficial effects in a variety of behavioral tasks and animal models. The first step towards such an approach is a systematic and rigorous evaluation of the different aspects of validity for the models most frequently used in preclinical research. It is concluded that a combination of good construct validity and good face validity represents a necessary condition for screening tests with predictive validity, and that the most popular paradigms fail to fulfil these criteria. Future screening programs for cognition enhancers will probably be characterized by a depreciation of "fast and dirty tests" in favor of approaches focussing on the validity of the effects of potential cognition enhancers.

Non-peptide angiotensin II receptor antagonist and angiotensin-converting enzyme inhibitor: effect on a renin-induced deficit of a passive avoidance response in rats

Non-peptide receptor ligands with differential affinity for the angiotensin II-1 (AII-1) receptor (EXP3312, EXP3880) or the AII-2 receptor (PD123177) and an angiotensin converting enzyme (ACE) inhibitor captopril were evaluated for the ability to protect against a renin-induced performance deficit in a passive avoidance (PA) task in rats. The ability to retain a PA response was shown to decrease as the dose of intracerebroventricularly (i.c.v.) administered renin increased with maximal retention deficits occurring at 1.0 micrograms/5 microliters i.c.v. EXP3312 (1-100 micrograms/5 microliters i.c.v.) and EXP3880 (1-100 micrograms/5 microliters i.c.v.) produced dose-dependent increases in retention latencies when co-administered with renin. The peak effect dose (PED) for EXP3312 and EXP3880 was 3 and 30 micrograms i.c.v., respectively. In contrast, PD123177 was not effective in preventing the renin-induced decrease in retention across a broad range of doses (0.1-100 micrograms/5 microliters i.c.v.). Captopril (1-100 micrograms/5 microliters i.c.v.) also prevented the renin-induced performance deficit with a PED of 30 micrograms/5 microliters i.c.v. These results suggest that renin given i.c.v. produces a deficit in performance of a PA response in rats and that this effect can be attenuated by an ACE inhibitor, AII-1 receptor ligands, but not AII-2 receptor blocker.

Enhanced resistance effect of piracetam upon hypoxia-induced impaired retention of fixed-interval responding in rats

Rats were trained on a fixed-interval schedule of 60 s (FI 60). After stabilization of performance, rats were chronically submitted to hypoxic treatment (3.5% O2, 10 min) once a day, immediately after the daily FI 60 session. Hypoxia disturbed the retention of FI responding. It was mainly characterized by a decrease in response rate and in pause duration, and by changes in the temporal distribution of responses. Animals receiving piracetam (100 mg/kg, IP) 30 min before each FI session followed by hypoxia were significantly less affected than saline-treated animals. Results are discussed with reference to the effects of hypoxia and piracetam on nonspecific factors and on memory function. It is suggested that the effects of piracetam are due to alleviation of hypoxia-induced memory retrieval deficit rather than to a protection against hypoxic brain cell injury.

Visual recognition memory in squirrel monkeys: effects of serotonin antagonists on baseline and hypoxia-induced performance deficits

Cognitive deficits resulting from neuropathological brain changes such as Alzheimer's Disease or normal aging are most likely due to alterations in multiple neurotransmitter systems. While the majority of preclinical studies have focused on the effects of acetylcholine (ACh), it has been shown that activation of the serotonergic (5-HT) pathways in the central nervous system interferes with passive avoidance retention in rats. In contrast, decreased 5-HT activity has been shown to improve learning and memory in rats using similar procedures. In the present experiment, 5-HT antagonists were evaluated for their effects on performance in a delayed match to sample task (DMTS) in two groups of squirrel monkeys: one in which the baseline level of performance was low (less than 65% correct, N = 5; group 1) and another in which DMTS performance was high (greater than 80% correct, N = 3; group 2) but impaired by exposure to hypoxia. Initial parametric tests exposing group 2 to various levels of oxygen deprivation were conducted to determine optimal conditions for performance deficits. Each monkey in both normoxia (group 1) and hypoxia (group 2) served as his own control and received an individualized range of doses for each test compound. For both groups, ketanserin and mianserin, the 5-HT2-selective antagonists, produced dose-dependent increases in DMTS performance at 0.3-1.5 mg/kg PO and 0.05-1.5 mg/kg PO, respectively. Pirenperone, another 5-HT2-selective antagonist, was active in improving performance in group 1 at 0.001 to 0.2 mg/kg PO but was not effective against hypoxia-induced performance deficits.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of several cerebroprotective drugs on NMDA channel function: evaluation using Xenopus oocytes and [3H]MK-801 binding

The effects of several cerebroprotective and nootropic drugs on the function of excitatory amino acid (EAA) receptor subtypes expressed in Xenopus oocytes after injection of rodent brain poly(A)+ mRNA were investigated. The oocyte response to N-methyl-D-aspartate (NMDA) in the presence of glycine (Gly) was inhibited dose-dependently by bifemelane, indeloxazine, vinpocetine and vincamine while no effect was observed by idebenone, Ca hopantenate, aniracetam or piracetam. Bifemelane, indeloxazine and vinpocetine suppressed the maximum response of NMDA and Gly without affecting their EC50 values. Unlike Mg2+, they did not affect the current-voltage relationship of the NMDA response below 0 mV. On the non-NMDA-type responses of the injected oocytes to kainate (KA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and quisqualate (QA), no significant effects were observed by these drugs at 100 microM. On the binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) to brain membranes, the estimated IC50 values were 88 microM for bifemelane, 102 microM for indeloxazine, and 115 microM for vinpocetine. The dissociation rate of [3H]MK-801 was significantly slowed by Zn2+ and vinpocetine, but not affected by bifemelane or indeloxazine. The Kd value for [3H]MK-801 binding was increased by bifemelane and indeloxazine while Bmax was unchanged. These results suggest that the inhibition of NMDA channels by vinpocetine shows a similarity to the action of Zn2+ which closes the gate of the NMDA channel. In contrast, bifemelane and indeloxazine may affect the phencyclidine (PCP)-site in the open channels and inhibit NMDA function.

Reversal effect of DM-9384 on scopolamine-induced acetylcholine depletion in certain regions of the mouse brain

The effect of a new cognition enhancer, DM-9384, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, on regional acetylcholine (ACh) levels and against scopolamine-induced ACh depletion was examined in mouse brain. In addition, the effects of DM-9384 were compared with those of oxiracetam, physostigmine and tacrine. Independent administration of DM-9384 (1, 3, 10 or 30 mg/kg, PO) or oxiracetam (10 or 50 mg/kg, PO) to mice had no effect on the ACh level in the hippocampus, frontal cortex, amygdala and striatum. Nevertheless, in all brain regions, pretreatment with DM-9384 significantly reduced the depletion of ACh induced by scopolamine (0.5 mg/kg, IP) in a nondose-related bell-shaped manner. By contrast, oxiracetam attenuated the effect of scopolamine in the hippocampus, frontal cortex and striatum but not in the amygdala. Physostigmine (0.2 mg/kg, SC) significantly increased ACh levels and reversed the scopolamine-induced ACh depletion in all brain regions. Unlike physostigmine, tacrine (10 mg/kg, PO) increased ACh levels in the striatum but not in the other regions. Tacrine reversed the effect of scopolamine in the hippocampus, amygdala and striatum, but not in the frontal cortex. In the present study, DM-9384 more effectively inhibited scopolamine-induced depletion of ACh levels than the other agents tested. The results obtained indicate that the protective action of DM-9384 against scopolamine-induced amnesia is due to its ability to reverse the ACh depletion.

Effects of vinburnine on experimental models of learning and memory impairments

Retrograde amnesia can be induced experimentally in mice by injecting them with scopolamine (3 mg/kg, IP) or by inducing seizures with pentylenetetrazol (50 mg/kg, IP), and in rats by subjecting them to hypobaric hypoxia (at a barometric pressure of 300 mmHg for 3 min). We have studied the effects of vinburnine (VNB) in these amnesic states compared to vincamine (VNC) and nicergoline (NCG), in order to assess its activity on drug-induced learning and memory impairments. Vinburnine reduced the disrupting effect of both scopolamine and pentylenetetrazol-induced seizures on the retention of a step-through passive avoidance behavior in mice and on the acquisition of shuttle-box active avoidance behavior in rats. This effect was dose-related up to 20 mg/kg, the peak effect dose after IP administration, and more pronounced than that of VNC and NCG in some tests. These results indicate that VNB influences learning and memory processes disrupted by a pharmacological manipulation. In particular, as scopolamine acts as anticholinergic drug, it is possible that VNB mechanism of action includes also a stimulation of acetylcholine neurotransmission.

Comparison of DuP 996, with physostigmine, THA and 3,4-DAP on hypoxia-induced amnesia in rats

DuP 996, 3,3-bis(4-pyrindinylmethyl)-1-phenylindolin-2-one, physostigmine (PH), tetrahydroaminoacridine (THA) and 3,4-diaminopyridine (3,4-DAP) were compared for their ability to protect against hypoxia-induced performance deficits in a passive avoidance (PA) task. The ability to retain PA response was found to decrease as the oxygen concentration decreased with the largest retention deficit occurring at 6.5% oxygen. DuP 996 (0.01-0.1 mg/kg SC), 3,4-DAP (0.1-10.0 mg/kg SC), THA (0.3-5.0 mg/kg SC) and PH (0.001-0.1 mg/kg SC) administered one minute after PA training produced dose-dependent increases in retention latencies following exposure to 6.5% oxygen. In comparing each compound for side effects, DuP 996 induced tremor and mortality at 10 and 40 mg/kg SC, respectively, and PH at 0.3 and 0.8 mg/kg SC, respectively. With PH the 0.3 mg/kg SC dose also produced hypersalivation and a decrease in lift strength. THA produced tremor and mortality at 6.0 and 40 mg/kg SC, respectively, and 3,4-DAP at 50 and 200 mg/kg SC, respectively. 3,4-DAP also produced chromodacryorrhea and hypersalivation at 50 mg/kg SC. Dividing the dose necessary to produce mortality by the highest effective dose active in the hypoxia test yielded a safety ratio for DuP 996 of 400, for 3,4-DAP 20, for PH 8, and for THA 8, showing a greater safety margin for DuP 996 than the other cholinergic agents. These results suggest that DuP 996 may be of use in the treatment of diseases associated with cognitive impairment and may have a greater safety margin than other cholinergic agents.

The use of Xenopus oocytes to evaluate drugs affecting brain Ca2+ channels: effects of bifemelane and several nootropic agents

Effects of nootropic or cerebroprotective drugs on voltage-sensitive Ca2+ channels (VSCC) in the mammalian brain were evaluated comparatively by depolarization-evoked Ca2+ channel currents in Xenopus oocytes injected with brain mRNA and by a high K(+)-stimulated 45Ca uptake into synaptosomes. It was found that several anti-amnesic agents (bifemelane, idebenone and vinpocetine) inhibited these VSCC-related responses with stronger potency than phenytoin and flurazepam. On the inhibiting potency of various compounds, there was a significant but weak correlation between the results from synaptosomes and those from the injected oocytes, since nifedipine, verapamil and diltiazem at 100 microM did not reduce 45Ca influx in synaptosomes but partly inhibited VSCCs in the oocytes. The blockade of neuronal L- and N-type VSCCs may participate in the anti-ischemic/hypoxic actions of nootropic drugs.

A novel dibenzoxazepine derivative (BY-1949) increases regional cerebral blood flow

The effects of BY-1949, a novel dibenzoxazepine derivative, on the regional cerebral blood flow were investigated in conscious cats. Oral administration of BY-1949 (10-50 mg/kg) significantly increased in a dose-related manner the regional cerebral blood flow in all brain regions examined. Vinpocetine (20 mg/kg p.p.) had similar effects that were shorter-lasted than those of BY-1949. From these results, it seems likely that amelioration by BY-1949 of cognitive impairment following cerebral ischemia/hypoxia or that occurs on ageing is at least partly explainable in terms of its effects on the cerebral circulation.