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

Utility of an elevated plus-maze for the evaluation of memory in mice: effects of nootropics, scopolamine and electroconvulsive shock

An elevated plus-maze consisting of two open and two enclosed arms was employed for an evaluation of memory in mice. Mice in the plus-maze escaped from the open arm to the enclosed arm because mice apparently dislike open and high spaces. The time it took for the mice to move from the open arm to the enclosed arm (transfer latency) was recorded. The transfer latency after the 2nd day was significantly shorter than that on the 1st day when it was recorded at a rate of one trial a day for 5 days. The transfer latency on the 2nd day was significantly prolonged in the mice administered electroconvulsive shock (300 V, 1 s) or scopolamine (20 micrograms, ICV) immediately after the first trial compared to the transfer latency in the control group. The prolongation of transfer latency in the mice administered an electroconvulsive shock was reversed by pretreatment with aniracetam (20 mg/kg, PO), but not tacrine and physostigmine. The prolongation of transfer latency in the mice administered scopolamine was reversed by pretreatment with aniracetam (10 and 20 mg/kg, PO) tacrine (1 and 3 mg/kg, PO), or physostigmine (0.025-0.2 mg/kg, IP). These results suggest that transfer latency may be one of the parameters of learning and memory.

Pharmacology of nootropics and metabolically active compounds in relation to their use in dementia

The development of effective drugs for the treatment of dementia is an important therapeutic target. Drugs which stop the progression of dementia have not been developed; however, nootropics and metabolically active compounds such as the vinca alkaloids and the ergot alkaloids as well as alkylxanthines are widely used to alleviate the symptoms. This review summarises animal studies investigating the mechanism of action of these compounds and highlights gaps in our knowledge of their pharmacology. Nootropics, such as piracetam, facilitate learning and retrieval of information and protect the brain from physical and chemical intoxication. Nootropics may produce these effects via an enhancement of acetylcholine or dopamine release; however, this postulate requires further evaluation. The pharmacology of vinca alkaloids is reviewed with particular reference to vinpocetine. This compound attenuates cognitive deficits, reduces ischaemia-induced hippocampal cell loss and increases cerebral blood flow and glucose utilisation. These effects may be induced by modulation of cyclic nucleotide levels and adenosine re-uptake inhibition. An extensively examined ergot alkaloid is co-dergocrine; this compound increases both the oxygen tension and the electrical activity of the ischaemic cerebral cortex. Alkylxanthines have a wide range of pharmacological activities, and in this review the pharmacology of pentoxifylline, propentofylline and denbufylline is contrasted with that of theophylline and caffeine. In particular, the pharmacology of propentofylline and the selective low Km cyclic AMP phosphodiesterase inhibitor denbufylline is summarised. Although more carefully controlled clinical trials in well defined patient collectives are required, present evidence suggests some therapeutic efficacy for nootropics and metabolically active compounds. Further studies to more closely evaluate their mechanism of action may lead to the development of more effective agents for the therapy of dementia.

The safety and lack of efficacy of vinpocetine in Alzheimer's disease

Fifteen Alzheimer patients were treated with increasing doses of vinpocetine (30, 45, and 60 mg per day) in an open-label pilot trial during a one-year period. Patients were assessed seven times both on and off drug with: the Buschke Selective Reminding Task, a letter fluency test, a category fluency test, the Boston Naming Test, a cognitive capacity screening examination, and a clinical global impression. Vinpocetine failed to improve cognition on psychometric testing or overall functioning, as measured by the clinical global impression, at any dose tested. Patients showed significant decline in most measures during the course of the study, at the same rate as a matched control group, consistent with progressive dementia. There were no significant side effects from drug therapy. We conclude that vinpocetine is ineffective in improving cognitive deficits and does not slow the rate of decline in individuals with Alzheimer's disease.

Idebenone and vinpocetine augment long-term potentiation in hippocampal slices in the guinea pig

The effects of idebenone and vinpocetine which reportedly prevent impairment of learning and memory were studied in vitro, on the long-term potentiation of the population spike in the pyramidal layer of CA3 region of slices of hippocampus in the guinea pig. Idebenone (10(-9) M-10(-6) M) or vinpocetine (10(-7) M-10(-6) M) significantly augmented long-term potentiation in the mossy fibre-CA3 pyramidal cell system, without any significant changes in population spikes in the absence of tetanic stimulation. These results suggest that both drugs have direct actions on the hippocampal neurones to augment long-term potentiation at fairly small concentrations. Further, when the two drugs were applied together, the augmenting effects were additive.

Manipulation of serotonin protects against an hypoxia-induced deficit of a passive avoidance response in rats

The 5-HT antagonists ketanserin, mianserin, methysergide, and cyproheptadine and the 5-HT uptake inhibitors fluoxetine and zimeldine were evaluated for their ability to protect against an hypoxia-induced performance deficit in a passive avoidance (PA) task. The ability to retain a PA response was found to decrease as the oxygen concentration decreased with the largest retention deficit occurring at 6.5% O2. The 5-HT2 selective antagonists ketanserin (0.01-10.0 mg/kg SC) and mianserin (0.05-10.0 mg/kg SC) administered one minute after PA training produced dose-dependent increases in retention latencies following exposure to a 6.5% oxygen environment. Peak effective doses (PED) for ketanserin and mianserin were 3.0 mg/kg SC and 0.05 mg/kg SC, respectively. In contrast, methysergide (0.05-30.0 mg/kg SC) and cyproheptadine (0.05-7.0 mg/kg SC), antagonists that show less affinity for the 5-HT2 receptor subtype, were not effective in preventing the hypoxia-induced amnesia. Inhibition of 5-HT reuptake by fluoxetine (0.01-1.0 mg/kg SC) produced dose-dependent increases in retention latencies with a PED of 0.05 mg/kg SC while zimeldine (0.1-10.0 mg/kg SC), another 5-HT reuptake inhibitor, had no effect on the amnesia. The results of this study suggest that modification of 5-HT after exposure to hypoxia can ameliorate a performance deficit in an animal model of learning and memory.

Pre-clinical evaluation of cognition enhancing drugs

1. The need of the treatment of cognitive impairment due to aging or dementia has led to the search for potential cognition enhancing drugs. The various compounds presently under development represent an alternative to the cholinomimetic therapy and include new chemical entities as well as piracetam and its newer analogs. 2. Recent results from pre-clinical evaluation of the effects on learning on memory are summarized. Emphasis is put on learning and memory experiments under normal and pathological conditions. Most of the nootropics attenuate experimental amnesias induced by scopolamine, cycloheximide, ECS, hemicholinium-3 or forebrain ischemia. These findings suggest that the nootropics may be influencing a common mechanism underlying the amnesias. 3. Biochemical data suggest a potential cholinergic neuronal activity of some of the piracetam analogs. They increase high-affinity choline uptake, and antagonize scopolamine- and ECS-induced decreases in acetylcholine concentrations in the hippocampus. The mode of action of these and all other nootropic compounds, however, is still not known. 4. Despite the interesting results from learning and memory studies and from biochemical investigations, the clinical relevance of these results for amelioration of the cognitive impairment in humans remains to be proven for most of the compounds.

Attenuation of forgetting by pharmacological stimulation of aminergic neurotransmitter systems

Mice were trained in one-way active avoidance to a criterion of 3/4 avoidances and tested under extinction conditions one week later when substantial forgetting had occurred. Thirty min prior to testing animals were injected with either saline or different doses of drugs which activate the noradrenergic (phenylephrine, salbutamol, clonidine) dopaminergic (L-dopa(Sinemet) transdihydrolisuride, apomorphine) and serotonergic (fluoxetine, 5-methoxy DMT) neurotransmitter systems. Results showed that all agents alleviated forgetting in a dose dependent fashion. Untrained mice treated with the most effective dose of representative drugs from each class did not exhibit avoidance behavior at testing indicating that the improved performance of trained animals was probably not the result of increased activity or other non-memorial effects of the drugs. It was concluded that pharmacological agents which stimulate monoamine systems may improve memory retrieval by activating a non-specific neural system which controls arousal, attention and motor readiness.

Animal models of Alzheimer's disease: experimental cholinergic denervation

Several animal models of AD have been developed, based upon the consistent finding of a presynaptic cholinergic deficit in AD. Significant cell loss in the NBM, the primary cortical cholinergic afferent, has been reported in AD. Lesions of the corresponding nuclei in the rodent and primate produce a persistent cholinergic deficit, but no consistent change in other neurotransmitter systems. Significant mnestic and cerebral metabolic deficits are observed acutely after lesion, which are responsive to pharmacological reversal and recover over time. Administration of AF64A produces similar mnestic and cholinergic deficits as NBM lesion, but these effects may be less responsive to pharmacological reversal. Administration of scopolamine, a muscarinic receptor antagonist, produces transient receptor blockade, mnestic deficits and deficits in cerebral metabolism, which can be reversed with a variety of pharmacological agents. The primary dissociations between these models and the deficits in AD are the lack of pharmacological response and recovery of function in AD patients and the presence of non-cholinergic neurochemical and cytoskeletal abnormalities. Future research should focus upon the systematic production and analysis of non-cholinergic neurotransmitter and cytoskeletal abnormalities to determine the contribution of these factors to the pathology seen in AD and the production of deficit in aged animals, which may more closely approximate the deficits in AD. The analysis of factors involved in recovery of function and pharmacological response in animal models may provide insight into potential treatment approaches to AD.

Vinpocetine enhances retrieval of a step-through passive avoidance response in rats

Vinpocetine, vincamine, apovincaminic acid, vinconate, aniracetam, Hydergine, and pemoline were evaluated for their ability to enhance retrieval of a step-through passive avoidance response in rats. The percentage of rats performing the avoidance response was found to decrease as a function of the number of days between training and retention testing (Day 1, 100%; Day 2, 65%; Day 3, 23%; Days 4 and 5, 0%). Vinpocetine administered 60 minutes prior to testing for retention significantly increased the number of rats performing the passive avoidance response. Retrieval enhancement was dose-related in an inverted U-shaped function with the effective doses at 18 and 30 mg/kg PO. In contrast, apovincaminic acid (1-400 mg/kg PO), vincamine (1-200 mg/kg PO), vinconate (1-200 mg/kg PO), aniracetam (1-300 mg/kg PO), Hydergine (0.1-10 mg/kg PO), and pemoline (1-30 mg/kg PO) were not effective. These data support the view that vinpocetine has cognition-activating abilities as defined in an animal model of memory retrieval.