Ginkgo biloba extract improves spatial memory in rats mainly but not exclusively via a histaminergic mechanism

[Effects of Histamine and Related Compounds on the Central Nervous System]

There has been little information about the role of histamine on the central nervous system (CNS), different from dopamine and serotonin. In the present study, therefore, the effects of histamine and related compounds on the CNS were studied using rats. Intracerebroventricular (i.c.v.) injection of histamine and 2-methylhistamine ameliorated memory deficit after long interrution of learning in active avoidance response. First generation H₁-antagonists inhibited active avoidance response, whereas newly develpoed H₁-antagonists showed little effect. α-Fluoromethylhistidine, an histidine decarboxylase inhibitor, also inhibited active avoidance response. In radial maze performance, almost the same findings were obtained. I.c.v. injection of histamine and H₁-agonists inhibited amygdaloid kindled seizures. First generation H₁-antagonists attenuated histamine-induced inhibition of amygdaloid kindled seizures. Both i.c.v. and intraperitoneal injections of H₃-antagonist, thioperamide, resulted in a dose-related inhibition of amygdaloid kindled seizures. The effect of thioperamide was inhibited by an H₃-agonists and H₁-antagonists. Similar to nitrazepam, diphenhydramine and chlorpheniramine caused a shortening of sleep latency. On the other hand, no significant effects were observed with second generation H₁-antagonists. These findings suggest that histamine plays an important role in learning and memory via H₁-receptors, an inhibition of amygdaloid kindled seizures induced by histamine occurred through not only H₁-receptors but also H₃-receptors, and that classic H₁-antagonists can be useful as a effective hypnotic for difficulty in falling asleep.

Relative prevalence of 10 types of pharmacodynamic interactions in psychiatric treatment

OBJECTIVE

To assess the relative prevalence and factors affecting the prescription of medication combinations with a theoretical efficacy limiting pharmacodynamic interaction, defined as two medications with opposing indications and side effects or antagonistic action at the primary receptor of mechanism of action.

METHOD

One hundred sixteen combinations were identified for 10 types of pharmacodynamic interactions. PubMed was searched for each combination to assess the quality of evidence either supporting clinical use or verifying reduced efficacy. Micromedex was searched to determine the presence of warnings to prescribers of reduced efficacy. The prevalence in clinical practice was determined by computer review of the Genoa Healthcare database for all prescribers at 10 participating community mental health centers. The expected prevalence was calculated as the product of the probability of each medication prescribed alone and was compared with the actual prevalence of the combination using the test of proportions.

RESULTS

The frequency of prescription of eight combinations met the Bonferroni corrected level of significance of p < 0.001. Four were combinations of amphetamine and D2 antagonists and each were prescribed less often than chance, p = 0.0001 consistent with epidemiological studies and multiple animal studies verifying an efficacy limiting interaction. Despite epidemiological studies indicating increased risk of accidents, alprazolam and amphetamine were prescribed more often than chance, p = 0.0001. Micromedex generated warnings for efficacy limiting interactions for five other combinations, but with no subsequent change in prescription frequency.

CONCLUSIONS

Neither presence of medical evidence nor warnings from Micromedex consistently affect the prescription of combinations with pharmacodynamic efficacy limiting interactions.

In vitro and ex-vivo cellular antioxidant protection and cognitive enhancing effects of an extract of Polygonum minus Huds (Lineminus™) demonstrated in a Barnes Maze animal model for memory and learning

Background

Polygonum minus Huds.is a culinary flavouring that is common in South East Asian cuisine and as a remedy for diverse maladies ranging from indigestion to poor eyesight. The leaves of this herb have been reported to be high in antioxidants. Flavonoids which have been associated with memory, cognition and protection against neurodegeneration were found in P. minus.

Method

This study examined a P. minus aqueous extract (Lineminus^™) for its antioxidant activity using the Oxygen Radical Absorbance Capacity (ORAC) assay, the ex vivo Cellular Antioxidant Protection of erythrocytes (CAP-e) assays and for potential anticholinesterase activity in vitro. Cognitive function and learning of Lineminus^™ was evaluated using scopolamine induced cognition deficits in a Barnes maze, rodent model of cognition.

Results

The extract displayed in vitro antioxidant activity with a total ORAC value of 16,964 μmole TE/gram. Cellular antioxidant protection from free radical damage using the CAP-e assay, with an IC50 of 0.58 g/L for inhibition of cellular oxidative damage, was observed. The extract inhibited cholinesterase activity with an IC50 of 0.04 mg/ml with a maximum inhibition of 68%. In a rodent model of cognition using scopolamine induced cognition deficits in the Barnes maze, the extract attenuated scopolamine induced disruptions in learning at the higher dose of 100 mg/kg.

Conclusion

These data shows that P. minus possesses antioxidant and anticholinesterase activity and demonstrated enhanced cognition in vivo. The data suggest neuroprotective properties of the extract.

Ginkgo biloba protects against intermittent hypoxia-induced memory deficits and hippocampal DNA damage in rats

The aim of the present study was to explore the potential protective effect of Ginkgo biloba extract (EGb 761) on intermittent hypoxia (IH)-induced memory deficits and oxidative stress in rats.

METHODS

The passive avoidance reflex (PAR) test was employed to assess the effect of concurrent EGb 761 treatment in different dose levels on the memory deficits that were induced by concurrent long-term exposure to IH (21 days). The levels of hippocampal malondialdehyde (MDA), nitric oxide (NO), and intracellular glutathione (GSH) and the activity of glutathione peroxidase (GSH-Px) were estimated. In addition, serum and hippocampal 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were assessed to study the effect of EGb 761 on hippocampal oxidative DNA damage induced by IH.

RESULTS

Exposure to long-term IH in rats induced marked memory impairment that was indicated by a significant decrease in the retention latency in the PAR test. This effect was accompanied by a significant increase in hippocampal oxidative stress and DNA damage. EGb 761 that was administered in either 50- or 100-mg/kg doses per day reversed IH-induced memory deficits, an effect that was accompanied by a significant decrease in hippocampal MDA and NO levels. The antioxidant defence (GSH and GSH-Px) that was depressed by IH was significantly reactivated by EGb 761. Furthermore, serum and hippocampal levels of 8-OHdG that were elevated by IH were significantly reduced.

CONCLUSIONS

EGb 761 can protect against IH-induced memory impairment, oxidative stress and neuronal DNA damage, possibly through multiple mechanisms involving its potential anti-oxidative effect.

The effects of rutin on the development of pentylenetetrazole kindling and memory retrieval in rats

Individuals with epilepsy often complain about memory deficits. Various synthetic derivatives of natural flavonoids are known to have neuroactive properties. Rutin is a flavonoid that is an important dietary constituent of foods and plant-based beverages. The aim of the present study was to investigate the effects of rutin on memory retrieval in pentylenetetrazole (PTZ)-kindled rats using a step-through passive avoidance task. We administered rutin and PTZ intraperitoneally every other day prior to the start of training. Two retention tests were subsequently performed to assess memory in these rats. The results suggest that pretreatment with rutin at 50 and 100mg/kg can attenuate seizure severity during the kindling procedure. Furthermore, rutin administration significantly increased the step-through latency in the passive avoidance paradigm. Taken together, these results indicate that rutin has a potential role in enhancing memory retrieval in kindled rats.

The effects of rutin on a passive avoidance test in rats

Various synthetic derivatives of natural flavonoids are known to have neuroactive properties. The aim of the present study was to investigate the effects of rutin (3, 3', 4', 5, 7-pentahydroxyflavone-3-rhamnoglucoside), a flavonoid that is an important dietary constituent of foods and plant-based beverages, on memory retrieval in rats. To this end, we assessed the effect of rutin on memory retrieval using a step-through passive avoidance task. Rutin (5, 10, and 100mg/kg) was administered intraperitoneally (i.p.) one week before the start of training. Three retention tests were performed to assess memory in rats. Rutin (10mg/kg) significantly increased the step-through latency of the passive avoidance response compared to the control in the three retention tests of the passive avoidance paradigm. These results indicate that rutin has a potential role in enhancing memory retrieval. Several mechanisms may contribute to the potential role of rutin in memory enhancement. This result supports the potential beneficial effects of rutin as a dietary supplement on memory retrieval in a passive avoidance task.

The impact of flavonoids on spatial memory in rodents: from behaviour to underlying hippocampal mechanisms

Emerging evidence suggests that a group of dietary-derived phytochemicals known as flavonoids are able to induce improvements in memory, learning and cognition. Flavonoids have been shown to modulate critical neuronal signalling pathways involved in processes of memory, and therefore are likely to affect synaptic plasticity and long-term potentiation mechanisms, widely considered to provide a basis for memory. Animal dietary supplementation studies have further shown that flavonoid-rich foods are able to reverse age-related spatial memory and spatial learning impairments. A more accurate understanding of how a particular spatial memory task works and of which aspects of memory and learning can be assessed in each case, are necessary for a correct interpretation of data relating to diet-cognition experiments. Further understanding of how specific behavioural tasks relate to the functioning of hippocampal circuitry during learning processes might be also elucidative of the specific observed memory improvements. The overall goal of this review is to give an overview of how the hippocampal circuitry operates as a memory system during behavioural tasks, which we believe will provide a new insight into the underlying mechanisms of the action of flavonoids on cognition.

Effect of Polygala tenuifolia root extract on scopolamine-induced impairment of rat spatial cognition in an eight-arm radial maze task

The effects of Polygala tenuifolia root fractions and the acyl groups of its constituents on the retrieval process of spatial cognition in rats were studied using an eight-arm radial maze task. Oral administration of a precipitate fraction (PTB) obtained by concentration of the n-BuOH-soluble portion from the extract of the roots significantly decreased the number of total errors (TEs) and that of working memory errors (WMEs) at doses of 100 mg/kg and 200 mg/kg. However, it caused no significant decrease in the number of reference memory errors (RMEs). In addition, the saponin-rich fraction (PTBM) obtained by purification of PTB also showed significant decreases in TEs and WMEs at a dose of 100 mg/kg. Among the cinnamic acid derivatives present as the acyl groups in the P. tenuifolia constituents, sinapic acid (SNPA) significantly decreased TEs and WMEs at doses of 10 to 100 mg/kg. These results indicated that P. tenuifolia extracts, PTB and PTBM, and SNPA had a beneficial effect on the memory impairment induced by dysfunction of the cholinergic system in the brain. The memory improvement in the scopolamine-induced memory impairment seen in the radial maze performance was due to improvement in the short-term memory. A contribution of some constituents other than SNPA to the memory improvement was also suggested.