Decreased electroconvulsive shock-induced diacylglycerols and free fatty acid accumulation in the rat brain by Ginkgo biloba extract (EGb 761): selective effect in hippocampus as compared with cerebral cortex

Anti-kindling effect of Ginkgo biloba leaf extract and L-carnitine in the pentylenetetrazol model of epilepsy

Epilepsy is one of the most common serious brain disorders, affecting about 1% of the population all over the world. Ginkgo biloba extract (GbE) and L-carnitine (LC) reportedly possess the antioxidative activity and neuroprotective potential. In this report, we investigated the possible protective and therapeutic effects of GbE and LC against pentylenetetrazol (PTZ)-induced epileptic seizures in rat hippocampus and hypothalamus. Adult male albino rats were equally divided into eight groups: control, GbE (100 mg/kg), LC (300 mg/kg), PTZ (40 mg/kg), protective groups (GbE + PTZ and LC + PTZ), and therapeutic groups (PTZ + GbE and PTZ + LC). The oxidative stress, antioxidant, and neurochemical parameters, viz., malondialdehyde (MDA), nitric oxide (NO), reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), acetylcholine esterase (AchE), dopamine (DA), norepinephrine (NE), and serotonin (5-HT), in the hippocampal and hypothalamic regions have been evaluated. PTZ injection leads to an increase in the seizure score, the levels of MDA and NO, and to a decrease in the activity of GSH, SOD, CAT, and GPx. Besides, monoamine neurotransmitters, DA, NE, and 5-HT, were depleted in PTZ-kindled rats. Furthermore, PTZ administration caused a significant elevation in the activity of AchE. Hippocampal and hypothalamic sections from PTZ-treated animals were characterized by severe histopathological alterations and, intensely, increased the ezrin immunolabeled astrocytes. Pre- and post-treatment of PTZ rats with GbE and LC suppressed the kindling acquisition process and remarkably alleviated all the aforementioned PTZ-induced effects. GbE and LC have potent protective and therapeutic effects against PTZ-induced kindling seizures via the amelioration of oxidative/antioxidative imbalance, neuromodulatory, and antiepileptic actions.

Ginkgo biloba: A Cognitive Enhancer?

Ginkgo biloba is an herb often used as an alternative treatment to improve cognitive functions. Like most herbal treatments, the use of ginkgo is poorly regulated by government agencies, on the basis of either its efficacy or its health risks. This article reviews the experimental evidence available regarding efficacy, neurobiological actions, and health risks. Findings obtained in studies of humans often include demonstrations of rather mild cognitive enhancement. Interpretation of these findings is complicated by somewhat inconsistent findings, by experimental designs that do not permit identification of cognitive functions susceptible to the influence of ginkgo, and by the paucity of direct comparisons with other treatments. The number of peer-reviewed reports of studies in nonhuman animals is surprisingly small. In this small set, the findings reveal mild behavioral effects that might be attributable to actions on cognitive functions. However, these experiments in rodents, like those in humans, do not involve the use of designs to assess ginkgo's effects on particular cognitive attributes, and generally do not include direct comparisons with other treatments. Interpretation of the findings is further complicated by evidence, obtained in studies of both humans and rats, showing that a single administration of the treatment enhances performance on cognitive measures.

If ginkgo has effects on cognition, there should be effects evident on biological processes as well. Neurobiological studies have largely examined the effects of chronic ginkgo administration, mirroring the most common design in behavioral studies. However, the addition of findings that single administration of ginkgo may influence behavior directs biological investigations to short-term actions of the treatment. Biological effects of ginkgo include vasodilation, protection of neurons from oxidative stress, and actions mediated by effects via neurotransmitters. Adverse reactions to ginkgo consumption have been observed but are relatively rare.

Collectively, the behavioral literature reviewed cannot be used conclusively to document or to refute the efficacy of ginkgo in improving cognitive functions. At best, the effects seem quite modest. In particular, it is questionable whether effects of ginkgo, if present, are equal to those obtained by administration of acetylcholinesterase inhibitors, hearing an arousing story, or ingesting glucose.

Effects of Gingko biloba Extract on Gap Junction Changes Induced by Reperfusion/Reoxygenation After Ischemia/Hypoxia in Rat Brain

Gap junction communication between astrocytes plays an important role in the brain. The purpose of this study was to investigate the effects of Gingko biloba extract (GBE) on the changes of connexin 43 (Cx43) mRNA and protein expression levels of rat cortex and hippocampus induced by ischemia-reperfusion and astrocyte gap junction intercellular communication (GJIC) induced by hypoxia-reoxygenation. After 2 hours of middle cerebral artery occlusion (MCAO) followed by 24 hours of reperfusion, there was obvious neurological deficit in rats. Cx43 mRNA and protein expression levels of rat cortex and hippocampus in the ischemia hemisphere were decreased significantly. When GBE at doses of 50 and 100 mg/kg body weight was administrated by p.o. daily for 7 days, the neurological deficit was improved, and lower Cx43 mRNA and protein expression levels induced by ischemia-reperfusion were recovered to normal. The i.p. injection of nimodipine (0.7 mg/kg weight body) also showed improvement on neurological deficit and Cx43 expression levels. Astrocyte GJIC was measured by the fluorescence recovery after photobleaching (FRAP). Hypoxia-reoxygenation induced a significant decrease in GJIC. Pretreatment with GBE (100 mg/l) and nimodipine (1.6 mg/l) significantly prevented the hypoxia-reoxygenation inhibition of GJIC. These results suggest that GBE could exert its neuroprotective effects by improvement of Cx43 expression and GJIC induced by hypoxia/ischemia-reoxygenation/ reperfusion injury.

The Ginkgo biloba extract (EGb 761) provides a neuroprotective effect on retinal ganglion cells in a rat model of chronic glaucoma

PURPOSE

To investigate the effect of Ginkgo biloba extract (EGb 761) against neurotoxicity of retinal ganglion cells of rats with chronic moderately elevated intraocular pressure (IOP).

METHODS

Unilateral chronic moderately elevated IOP was produced in rats by cautery of three episcleral vessels. Secondary degeneration was measured with and without EGb 761 for 5 months. At 5 months, retinal ganglion cells were labeled with a fast blue tracer applied to both superior colliculi. Densities of surviving retinal ganglion cells were estimated by counting fast blue labeled cells in whole mounted retinas.

RESULTS

When compared with their contralateral control eyes with normal IOP, in the peripheral retina, retinal ganglion cell loss in eyes with chronic, moderately elevated IOP was 29.8 +/- 1.5% (n=5) at 5 months in untreated animals and 4.6 +/- 4.5% (n=5) at 5 months in treated animals with EGb 761.

CONCLUSIONS

Pretreatment and early posttreatment with EGb 761 is an effective neuroprotectant in a rat model of chronic glaucoma.

Ginkgolide B, a constituent of Ginkgo biloba, facilitates glutamate exocytosis from rat hippocampal nerve terminals

Although previous studies have demonstrated that Ginkgo biloba extract has modest effects in the improvement of memory and cognitive function of the Alzheimer's disease patients, the mechanism(s) underlying its beneficial effects remain(s) unclear. In this study, the effect of ginkgolide B, one of the major constituents of Ginkgo biloba extract, on the release of endogenous glutamate from rat hippocampal nerve terminals (synaptosomes) was studied. Ginkgolide B facilitated the Ca2+-dependent release of glutamate evoked by 4-aminopyridine in a concentration-dependent manner. The facilitatory action of ginkgolide B was not due to it increasing synaptosomal excitability because ginkgolide B did not alter the 4-aminopyridine-evoked depolarization of the synaptosomal plasma membrane potential. Rather, examination of the effect of ginkgolide B on cytosolic free Ca2+ concentration revealed that the facilitation of glutamate release could be attributed to an enhancement of presynaptic voltage-dependent Ca2+ influx. Consistent with this, the ginkgolide B-mediated facilitation of glutamate release was significantly prevented in synaptosomes pretreated with a wide spectrum blocker of N-, P-, and Q-type Ca2+ channels, omega-conotoxin MVIIC. Moreover, the facilitation produced by ginkgolide B was completely abolished by the protein kinase A inhibitor, but not by the protein kinase C inhibitor. These results suggest that ginkgolide B effects a increase in protein kinase A activation, which subsequently enhances the Ca2+ entry through voltage-dependent N- and P/Q-type Ca2+ channels to cause a increase in evoked glutamate release from rat hippocampal nerve terminals. In addition, glutamate release elicited by Ca2+ ionophore (ionomycin) was also facilitated by ginkgolide B, which suggests that ginkgolide B may have a direct effect on the secretory apparatus downstream of Ca2+ entry. These actions of ginkgolide B may provide some information regarding the beneficial effects of Ginkgo biloba in the central nervous system.

Amyloid precursor protein metabolism is regulated toward alpha-secretase pathway by Ginkgo biloba extracts

Clinical trials report that Ginkgo biloba extracts (e.g., EGb761) reduce cognitive symptoms in age-associated memory impairment and dementia, including Alzheimer disease (AD). However, the mechanisms behind their neuroprotective ability remain to be fully established. In this study, the effect of EGb761 on the amyloid precursor protein (APP) metabolism has been investigated by both in vitro and in vivo models. To this aim, alpha-secretase, the enzyme regulating the non-amyloidogenic processing of APP and the release of alphaAPPs, the alpha-secretase metabolite, were studied in superfusates of hippocampal slices after EGb761 incubation, and in hippocampi and cortices of EGb761-treated rats. PKC translocation state was evaluated as well. EGb761 increases alphaAPPs release through a PKC-independent manner. This effect is not accompanied by a modification of either APP forms or alpha-secretase expression. Moreover, EGb761 influence on alphaAPPs release was strictly dependent on treatment dosage. Our findings suggest that the benefit of EGb761 reported by previous clinical studies is underscored by a specific biological mechanism of this compound on APP metabolism, directly affecting the release of the non-amyloidogenic metabolite. Additional research will be needed to clearly define the effective clinical relevance, thus considering EGb761 as a possible supplementary treatment in dementing diseases.

Chronic daily administration of selegiline and EGb 761 increases brain's resistance to ischemia in mice

Brief cerebral ischemia is reported to cause selective neuronal necrosis, apoptotic cell death, silent infarcts and, when recurrent, cognitive decline. Acute administration of selegiline and EGb 761 have been shown to have anti-apoptotic and neuroprotective effects in experimental ischemia. Their daily use is currently advised to slow down cognitive decline in patients with vascular dementia. Hence, unlike previous studies, we studied the neuroprotective action of chronic daily administration of these drugs in Swiss mice subjected to 30-min middle cerebral artery occlusion and 72 h of reperfusion since this model was reported to induce a slowly evolving infarct with profuse apoptotic cell death. Infarct area was evaluated by H&E staining on coronal brain sections and, apoptotic cells were identified by histological criteria, terminal transferase-mediated d-UTP nick-end labeling (TUNEL) and by immunohistochemical detection of caspase-cleaved actin fragments (fractin). Fifty-one mice received daily intraperitoneal injections of 10 mg/kg selegiline (n=18) or 50 mg/kg EGb 761 (n=17) or equal volume of saline (n=16) for 10-14 days before but not on the day of insult. The infarct volume, number of TUNEL- and fractin-positive cells were significantly reduced in treatment groups by 30, 42 and 51% (selegiline) and, 27, 27 and 29% (EGb 761), respectively. These data suggest that prophylactic use of selegiline and EGb 761 could increase the brain's resistance to mild ischemic injury.

A possible emerging role of phytochemicals in improving age-related neurological dysfunctions: a multiplicity of effects

It is rare to see a day pass in which we are not told through some popular medium that the population is becoming older. Along with this information comes the "new" revelation that as we enter the next millennium there will be increases in age-associated diseases (e.g., cancer, cardiovascular disease) including the most devastating of these, which involve the nervous system (e.g., Alzheimer's disease [AD] and Parkinson's disease [PD]). It is estimated that within the next 50 years approximately 30% of the population will be aged 65 years or older. Of those between 75 and 84 years of age, 6 million will exhibit some form of AD symptoms, and of those older than 85 years, over 12 million will have some form of dementia associated with AD. What appears more ominous is that many cognitive changes occur even in the absence of specific age-related neurodegenerative diseases. Common components thought to contribute to the manifestation of these disorders and normal age-related declines in brain performance are increased susceptibility to long-term effects of oxidative stress (OS) and inflammatory insults. Unless some means is found to reduce these age-related decrements in neuronal function, health care costs will continue to rise exponentially. Thus, it is extremely important to explore methods to retard or reverse age-related neuronal deficits as well as their subsequent, behavioral manifestations. Fortunately, the growth of knowledge in the biochemistry of cell viability has opened new avenues of research focused at identifying new therapeutic agents that could potentially disrupt the perpetual cycle of events involved in the decrements associated with these detrimental processes. In this regard, a new role in which certain dietary components may play important roles in alleviating certain disorders are beginning to receive increased attention, in particular those involving phytochemicals found in fruits and vegetables.

The Ginkgo biloba extract (EGb 761) protects hippocampal neurons against cell death induced by beta-amyloid

Substantial evidence suggests that the accumulation of beta-amyloid (Abeta)-derived peptides, and to a lesser extent free radicals, may contribute to the aetiology and/or progression of Alzheimer's disease (AD). Ginkgo biloba extract (EGb 761) is a well-defined plant extract containing two major groups of constituents, i.e. flavonoids and terpenoids. It is viewed as a polyvalent agent with a possible therapeutic use in the treatment of neurodegenerative diseases of multifactorial origin, e.g. AD. We have investigated here the potential effectiveness of EGb 761 against toxicity induced by (Abeta)-derived peptides (Abeta25-35, Abeta1-40 and Abeta1-42) on hippocampal primary cultured cells, this area being severely affected in AD. A co-treatment with EGb 761 concentration-dependently (10-100 microg/mL) protected hippocampal neurons against toxicity induced by Abeta fragments, with a maximal and complete protection at the highest concentration tested. Similar, albeit less potent protective effects were seen with the flavonoid fraction of the extract (CP 205), while the terpenes were ineffective. Most interestingly, EGb 761 (100 microg/mL) was even able to protect (up to 8 h) hippocampal cells from a pre-exposure to Abeta25-35 and Abeta1-40. EGb 761 was also able to both protect and rescue hippocampal cells from toxicity induced by H2O2 (50-150 microM), a major peroxide possibly involved in mediating Abeta toxicity. Moreover, EGb 761 (10-100 microg/mL), and to a lesser extent CP 205 (10-50 microg/mL), completely blocked Abeta-induced events, e.g. reactive oxygen species accumulation and apoptosis. These results suggest that the neuroprotective effects of EGb 761 are partly associated with its antioxidant properties and highlight its possible effectiveness in neurodegenerative diseases, e.g. AD via the inhibition of Abeta-induced toxicity and cell death.

The Ginkgo biloba extract (EGb 761) protects and rescues hippocampal cells against nitric oxide-induced toxicity: involvement of its flavonoid constituents and protein kinase C

An excess of the free radical nitric oxide (NO) is viewed as a deleterious factor involved in various CNS disorders. Numerous studies have shown that the Ginkgo biloba extract EGb 761 is a NO scavenger with neuroprotective properties. However, the mechanisms underlying its neuroprotective ability remain to be fully established. Thus, we investigated the effect of different constituents of EGb 761, i.e., flavonoids and terpenoids, against toxicity induced by NO generators on cells of the hippocampus, a brain area particularly susceptible to neurodegenerative damage. Exposure of rat primary mixed hippocampal cell cultures to either sodium nitroprusside (SNP; 100 microM) or 3-morpholinosydnonimine resulted in both a decrease in cell survival and an increase in free radical accumulation. These SNP-induced events were blocked by either EGb 761 (10-100 microg/ml) or its flavonoid fraction CP 205 (25 microg/ml), as well as by inhibitors of protein kinase C (PKC; chelerythrine) and L-type calcium channels (nitrendipine). In contrast, the terpenoid constituents of EGb 761, known as bilobalide and ginkgolide B, as well as inhibitors of phospholipases A [3-[(4-octadecyl)benzoyl]acrylic acid (OBAA)] and C (U-73122), failed to display any significant effects. Moreover, EGb 761 (50 microm) CP 205 (25 microg/ml), and chelerythrine were also able to rescue hippocampal cells preexposed to SNP (up to 1 mM). Finally, EGb 761 (100 microg/ml) was shown to block the activation of PKC induced by SNP (100 microM). These data suggest that the protective and rescuing abilities of EGb 761 are not only attributable to the antioxidant properties of its flavonoid constituents but also via their ability to inhibit NO-stimulated PKC activity.

Potential role for Ginkgo biloba extract in the treatment of glaucoma

Glaucoma is becoming recognized as a condition for which not only elevated intraocular pressure, but also non-pressure-dependent risk factors are responsible. New avenues of treatment into which investigations are being initiated include agents which could possibly improve blood flow to the eye and neuroprotective drugs. Only calcium channel blockers are presently available for such treatment in glaucoma, and these have not been widely adopted, in contrast to clinical trials involving a number of neuroprotectants in other neurologic disorders. Ginkgo biloba extract is freely available and has several biological actions which combine to make it a potentially important agent in the treatment of glaucoma: improvement of central and peripheral blood flow, reduction of vasospasm, reduction of serum viscosity, antioxidant activity, platelet activating factor inhibitory activity, inhibition of apoptosis, and inhibition of excitotoxicity. The effect of Ginkgo biloba extract as a potential antiglaucoma therapy deserves intensive scrutiny.

Dietary supplements and natural products as psychotherapeutic agents

Alternative therapies are widely used by consumers. A number of herbs and dietary supplements have demonstrable effects on mood, memory, and insomnia. There is a significant amount of evidence supporting the use of Hypericum perforatum (St. John's wort) for depression and Ginkgo biloba for dementia. Results of randomized, controlled trials also support the use of kava for anxiety and valerian for insomnia. Although evidence for the use of vitamins and amino acids as sole agents for psychiatric symptoms is not strong, there is intriguing preliminary evidence for the use of folate, tryptophan, and phenylalanine as adjuncts to enhance the effectiveness of conventional antidepressants. S-adenosylmethionine seems to have antidepressant effects, and omega-3 polyunsaturated fatty acids, particularly docosahexaenoic acid, may have mood-stabilizing effects. More research should be conducted on these and other natural products for the prevention and treatment of various psychiatric disorders.

Effects of EGb 761 on fatty acid reincorporation during reperfusion following ischemia in the brain of the awake gerbil

Transient cerebral ischemia (5 min) releases unesterified fatty acids from membrane phospholipids, increasing brain concentrations of fatty acids for up to 1 h following reperfusion. To understand the reported anti-ischemic effect of Ginkgo biloba extract (EGb 761), we monitored its effect on brain fatty acid reincorporation in a gerbil-stroke model. Both common carotid arteries in awake gerbils were occluded for 5 min, followed by 5 min of reperfusion. Animals were infused intravenously with labeled arachidonic (AA) or palmitic acid (Pam), and rates of incorporation of unlabeled fatty acid from the brian acyl-CoA pool were calculated by the model of Robinson et al. (1992), using quantitative autoradiography and biochemical analysis of brain acyl-CoA. Animals were treated for 14 d with 50 or 150 mg/kg/d EGb 761 or vehicle. Ischemia-reperfusion had no effect on the rate of unlabeled Pam incorporation into brain phospholipids from palmitoyl-CoA; this rate also was unaffected by EGb 761. In contrast, ischemia-reperfusion increased the rate of incorporation of unlabeled AA from brain arachidonoyl-CoA by a factor of 2.3-3.3 compared with the control rate; this factor was further augmented to 3.6-5.0 by pretreatment with EGb 761. There is selective reincorporation of AA compared with Pam into brain phospholipids following ischemia. EGb 761 further accelerates AA reincorporation, potentially reducing neurotoxic effects of prolonged exposure of brain to high concentrations of AA and its metabolites.

The neuroprotective properties of the Ginkgo biloba leaf: a review of the possible relationship to platelet-activating factor (PAF)

Ginkgo biloba (Ginkgoaceae) is an ancient Chinese tree which has been cultivated and held sacred for its health-promoting properties. There is substantial experimental evidence to support the view that Ginkgo biloba extracts have neuroprotective properties under conditions such as hypoxia/ischemia, seizure activity and peripheral nerve damage. Research on the biochemical effects of Ginkgo biloba extracts is still at a very early stage. One of the components of Ginkgo biloba, ginkgolide B, is a potent platelet-activating factor (PAF) antagonist. Although the terpene fraction of Ginkgo biloba, which contains the ginkgolides, may contribute to the neuroprotective properties of the Ginkgo biloba leaf, it is also likely that the flavonoid fraction, containing free radical scavengers, is important in this respect. Taken together, the evidence suggests that Ginkgo biloba extracts are worthy of further investigation as potential neuroprotectant agents.

Mediators of injury in neurotrauma: intracellular signal transduction and gene expression

Membrane lipid-derived second messengers are generated by phospholipase A2 (PLA2) during synaptic activity. Overstimulation of this enzyme during neurotrauma results in the accumulation of bioactive metabolites such as arachidonic acid, oxygenated derivatives of arachidonic acid, and platelet-activating factor (PAF). Several of these bioactive lipids participate in cell damage, cell death, or repair-regenerative neural plasticity. Neurotransmitters may activate PLA2 directly when linked to receptors coupled to G proteins and/or indirectly as calcium influx or mobilization from intracellular stores is stimulated. The release of arachidonic acid and its subsequent metabolism to prostaglandins are early responses linked to neuronal signal transduction. Free arachidonic acid may interact with membrane proteins, i.e., receptors, ion channels, and enzymes, modifying their activity. It can also be acted upon by prostaglandin synthase isoenzymes (the constitutive prostaglandin synthase PGS-1 or the inducible PGS-2) and by lipoxygenases, with the resulting formation of different prostaglandins and leukotrienes. Glutamatergic synaptic activity and activation of postsynaptic NMDA receptors are examples of neuronal activity, linked to memory and learning processes, which activate PLA2 with the consequent release of arachidonic acid and platelet-activating factor (PAF), another lipid mediator. Both mediators may exert presynaptic and postsynaptic effects contributing to long-lasting changes in glutamate synaptic efficacy or long-term potentiation (LTP), PAF, a potential retrograde messenger in LTP, stimulates glutamate release. The PAF antagonist BN 52021 competes for receptors in presynaptic membranes and blocks this effect. PAF may also be involved in plasticity responses because PAF leads to the expression of early response genes and subsequent gene cascades. The PAF antagonist BN 50730, selective for PAF intracellular binding, blocks PAF-mediated induction of gene expression. A consequence of neural injury induced by ischemia, trauma, or seizures is an increased release of neurotransmitters, that in turn generates an overproduction of second messengers. Glutamate, a key player in excitotoxic neuronal damage, triggers increased permeation of calcium mediated by NMDA receptors and activation of PLA2 in postsynaptic neurons. NMDA receptor antagonists reduce the accumulation of free fatty acids and elicit neuroprotection in ischemic damage. Increased production of free arachidonic acid and PAF converges to exacerbate glutamate-mediated neurotransmission. These neurotoxic actions may be brought about by arachidonic acid-induced potentiation of NMDA receptor activity and decreased glutamate reuptake. On the other hand, PAF stimulates the further release of glutamate at presynaptic endings. The neuroprotective effects of the PAF antagonist BN 52021 in ischemia-reperfusion are due, at least in part, to an inhibition of presynaptic glutamate release. PAF also induces expression of the inducible prostaglandin synthase gene, and PAF antagonists selective for the intracellular sites inhibit this effect. The PAF antagonist also inhibits the enhanced abundance, due to vasogenic cerebral edema and ischemia-reperfusion damage, of inducible prostaglandin synthase mRNA in vivo. Therefore, PAF, an injury-generated mediator, may favor the formation of other cell injury and inflammation mediators by turning on the expression of the gene that encodes prostaglandin synthase.

Stress-induced 5-HT1A receptor desensitization: protective effects of Ginkgo biloba extract (EGb 761)

The effects of sub-chronic cold stress on the functioning of hippocampal 5-HT1A receptors in old isolated rats and the possible protective effects of Ginkgo biloba extract (EGb 761) were investigated. Cold exposure during five days, produced a significant reduction of the inhibitory effect of 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) on forskolin-stimulated adenylyl cyclase activity. In contrast, neither the affinity nor the density of hippocampal [3H]8-OH-DPAT binding sites were affected indicating that the reduced sensitivity of 5-HT1A receptors induced by stress is probably due to a modification of their coupling mechanisms to adenylyl cyclase. The stress-induced desensitization of 5-HT1A receptors was prevented by the administration of EGb 761 (50 mg/kg per os/14 days). These results clearly indicate that 5-HT1A receptors are desensitized by stress and point out the reduced capacity of old rats to cope with the adverse effects of a chronic stressor. EGb 761 appears to restore the age-related decreased capacity to adapt to a chronic stressor.

Ginkgolide B accelerates vestibular compensation of spontaneous ocular nystagmus in guinea pig following unilateral labyrinthectomy

The aim of this study was to investigate the effects of ginkgolide B on the behavioral recovery process (vestibular compensation) which occurs following surgical removal of the vestibular receptor cells in one labyrinth (unilateral labyrinthectomy, UL). Guinea pigs received a single ip injection of ginkgolide B at the time of the UL (25, 50, or 100 mg/kg) and the effects on the compensation of the UL symptoms, spontaneous ocular nystagmus (SN), yaw head tilt (YHT), and roll head tilt (RHT), were evaluated. The effects of a single vehicle injection or a similar injection of ginkgolide A were used for comparison. Twenty-five mg/kg ginkgolide B significantly increased the rate of SN compensation compared to the vehicle control group (P < 0.02). However, 50 mg/kg ginkgolide B had no significant effect on either SN frequency or the rate of SN compensation. Ginkgolide B (100 mg/kg) significantly altered the rate of SN compensation (P < 0.02); however, SN frequency values were higher at most measurement times. YHT and RHT were not significantly affected by ginkgolide B at any of the doses used. Twenty-five mg/kg ginkgolide A had no significant effect on any of the UL symptoms. These results suggest that, at the optimal dose of 25 mg/kg, a single ip injection of ginkgolide B at the time of the UL can produce an acceleration of SN compensation.