Effects of standardized Ginkgo biloba extract on the acquisition, retrieval and extinction of conditioned suppression: Evidence that short-term memory and long-term memory are differentially modulated

Standardized extract of Ginkgo biloba treatment and novelty on the weak encoding of spatial recognition memory in rats

Long-term memory (LTM) formation is dependent on neurochemical changes that guarantee that a recently formed memory (short-term memory [STM]) remains in the specific neural circuitry via the consolidation process. The persistence of recognition memory has been evidenced by using behavioral tagging in young adult rats, but it has not been effective on aging. Here, we investigated the effects of treatment with a standardized extract of Ginkgo biloba (EGb) associated with novelty on the consolidation of object location memory (OLM) and its persistence after weak training of spatial object preference in young adult and aged rats. The object location task used in this study included two habituation sessions, training sessions associated or not associated with EGb treatment and contextual novelty, and short-term or long-term retention testing sessions. Altogether, our data showed that treatment with EGb associated with novelty close to the time of encoding resulted in STM that lasted for 1 h and persisted for 24 h for both young adult and aged rats. In aged rats, the cooperative mechanisms induced robust long-term OLM. Our findings support and extend our knowledge about recognition memory in aged rats and the modulating effects of EGb treatment and contextual novelty on the persistence of memory.

BDNF as a Putative Target for Standardized Extract of Ginkgo biloba-Induced Persistence of Object Recognition Memory

Despite considerable progress on the study of the effect of standardized extract of Gingko biloba (EGb) on memory processes, our understanding of its role in the persistence of long-term memory (LTM) and the molecular mechanism underlying its effect, particularly episodic-like memory, is limited. We here investigated the effects of EGb on the long-term retention of recognition memory and its persistence and BDNF expression levels in the dorsal hippocampal formation (DHF). Adult male Wistar rats (n = 10/group) were handled for 10 min/5 day. On day 6, the animals were treated with vehicle or 0.4 mg/kg diazepam (control groups) or with EGb (250, 500 or 100 mg/kg) 30 min before the training session (TR1), in which the animals were exposed to two sample objects. On day 7, all rats underwent a second training session (TR2) as described in the TR1 but without drug treatment. Object recognition memory (ORM) was evaluated on day 8 (retention test, T1) and day 9 (persistence test, T2). At the end of T1or T2, animals were decapitated, and DHF samples were frozen at -80 °C for analyses of the differential expression of BDNF by Western blotting. EGb-treated groups spent more time exploring the novel object in T2 and showed the highest recognition index (RI) values during the T1 and T2, which was associated with upregulation of BDNF expression in the DHF in a dose-and session-dependent manner. Our data reveal, for the first time, that EGb treatment before acquisition of ORM promotes persistence of LTM by BDNF differential expression.

Ginkgo biloba extract (GbE) attenuates obesity and anxious/depressive-like behaviours induced by ovariectomy

While several pieces of evidence link obesity and mood disorders in menopause, the mechanisms involved are not yet fully understood. We have previously demonstrated that Ginkgo biloba extract (GbE) both attenuated diet-induced obesity of male rats and restored serotonin-induced hypophagia in ovariectomized female rats. The present study aimed at exploring whether GbE treatment ameliorates ovariectomy-related obesity and anxious/depressive-like behaviours. Wistar female rats were either ovariectomized (OVX) or sham-operated (Sham). After 2 months, either 500 mg/kg of GbE or vehicle were administered daily by gavage for 14 days. Anxious/depressive-like behaviours were assessed by the Elevated Plus Maze and the Forced Swim Tests, respectively. Ovariectomy caused high visceral adiposity, hyperleptinemia, and hypercholesterolemia, and increased the anxiety index (p = 0.048 vs. Sham + GbE) while it decreased the latency to immobility (p = 0.004 vs. Sham). GbE treatment in OVX rats improved body composition, adiponectin levels and blood lipid profile. It also reduced the anxiety index (p = 0.004) and increased the latency to immobility (p = 0.003) of OVX rats. Linear regression analysis demonstrated that leptin (p = 0.047) and total cholesterol levels (p = 0.022) were associated with anxious-like behaviours while body adiposity (p = 0.00005) was strongly associated with depressive-like behaviours. The results showed that GbE therapy was effective in attenuating the deleterious effects of ovariectomy on body composition, lipid profile, and anxious/depressive-like behaviours. Further studies are warranted to better understand the therapeutic potential of GbE in menopause.

Hypobaric hypoxia induced fear and extinction memory impairment and effect of Ginkgo biloba in its amelioration: Behavioral, neurochemical and molecular correlates

Regulated fear and extinction memory is essential for balanced behavioral response. Limbic brain regions are susceptible to hypobaric hypoxia (HH) and are putative target for fear extinction deficit and dysregulation. The present study aimed to examine the effect of HH and Ginkgo biloba extract (GBE) on fear and extinction memory with the underlying mechanism. Adult male Sprague-Dawley rats were evaluated for fear extinction and anxious behavior following GBE administration during HH exposure. Blood and tissue (PFC, hippocampus and amygdala) samples were collected for biochemical, morphological and molecular studies. Results revealed deficit in contextual and cued fear extinction following 3 days of HH exposure. Increased corticosterone, glutamate with decreased GABA level was found with marked pyknosis, decrease in apical dendritic length and number of functional spines. Decline in mRNA expression level of synaptic plasticity genes and immunoreactivity of BDNF, synaptophysin, PSD95, spinophilin was observed following HH exposure. GBE administration during HH exposure improved fear and extinction memory along with decline in anxious behavior. It restored corticosterone, glutamate and GABA levels with an increase in apical dendritic length and number of functional spines with a reduction in pyknosis. It also improved mRNA expression level and immunoreactivity of neurotrophic and synaptic proteins. The present study is the first which demonstrates fear extinction deficit and anxious behavior following HH exposure. GBE administration ameliorated fear and extinction memory dysregulation by restoration of neurotransmitter levels, neuronal pyknosis and synaptic connections along with improved neurotrophic and synaptic protein expressions.

Ginkgo biloba treatments reverse the impairment of conditioned suppression acquisition induced by GluN2B-NMDA and 5-HT1A receptor blockade: Modulatory effects of the circuitry of the dorsal hippocampal formation

To improve our understanding of the effects of standardized extract of Ginkgo biloba (EGb) as a cognitive enhancer, we investigated the conditioned lick suppression-induced expression (mRNA and protein) of the GluN2B-containing N-methyl-D-aspartic acid receptor (GluN2B-NMDAR), serotonin (5-HT) 1A receptor (5-HT_1AR), gamma-aminobutyric acid type A receptor (GABA_AR) and glial fibrillary acidic protein (GFAP) in the dorsal hippocampal formation (dHF) of untreated and EGb-treated (0.25, 0.5 and 1.0 g.kg^-1) groups of rats. To substantiate our data, we analysed the molecular changes in dHF following treatment with vehicle, with agonists or antagonists of GABA_AR, GluN2B-NMDAR and 5-HT_1AR or with one of these antagonists prior to EGb and fear memory acquisition. Additionally, we performed a pharmacological analysis of the drug-receptor-receptor interactions and their supplemental role in fear memory by blocking individual receptors and analysed the possible changes in expression level with each of the other receptors in the study as well as astrocytes. Our data show for the first time that EGb treatment not only upregulated GluN2B, GABA_AR-α5, and GFAP compared with the control but also differentially upregulated GABA_AR-α1 in the dHF and 5HT_1AR in the CA3. We found that the activation of GABA_ARs (diazepam) and the inactivation of GluN2B-NMDARs (Ro25-6981) or 5-HT_1AR ((S)-WAY100135) resulted in memory impairment. Further, higher doses of EGb treatment reversed the effect of blocking GluN2B (P < 0.001) and 5-HT_1AR (P < 0.001). Here, treatment with Ro25-6981 + EGb or (S)-WAY100135 + EGb prevented the impairment of the acquisition of lick suppression in association with the upregulation or prevention of the downregulation of Grin2b expression as well as the expression of GluN2B-NMDA and/or α1 and α5 subunit-containing GABA_AR in the CA1 (P < 0.0001). Our data are in line with previous findings concerning the necessity of GluN2B for fear memory formation and add to the current knowledge of the role of the GABA_AR-α1 and -α5 subunits and of GluN2B as a target of cognitive enhancers. Furthermore, our data show that these receptors play a complementary role in controlling the neural circuitry in the dHF that seems to be essential to conditioned lick suppression and the modulatory effects of EGb.

Target Proteins in the Dorsal Hippocampal Formation Sustain the Memory-Enhancing and Neuroprotective Effects of Ginkgo biloba

We have previously shown that standardized extracts of Ginkgo biloba (EGb) modulate fear memory formation, which is associated with CREB-1 (mRNA and protein) upregulation in the dorsal hippocampal formation (dHF), in a dose-dependent manner. Here, we employed proteomic analysis to investigate EGb effects on different protein expression patterns in the dHF, which might be involved in the regulation of CREB activity and the synaptic plasticity required for long-term memory (LTM) formation. Adult male Wistar rats were randomly assigned to four groups (n = 6/group) and were submitted to conditioned lick suppression 30 min after vehicle (12% Tween 80) or EGb (0.25, 0.50, and 1.00 g⋅kg^-1) administration (p.o). All rats underwent a retention test session 48 h after conditioning. Twenty-four hours after the test session, the rats were euthanized via decapitation, and dHF samples were removed for proteome analysis using two-dimensional polyacrylamide gel electrophoresis, followed by peptide mass fingerprinting. In agreement with our previous data, no differences in the suppression ratios (SRs) were identified among the groups during first trial of CS (conditioned stimulus) presentation (P > 0.05). Acute treatment with 0.25 g⋅kg^-1 EGb significantly resulted in retention of original memory, without prevent acquisition of extinction within-session. In addition, our results showed, for the first time, that 32 proteins were affected in the dHF following treatment with 0.25, 0.50, and 1.00 g⋅kg^-1 doses of EGb, which upregulated seven, 19, and five proteins, respectively. Additionally, EGb downregulated two proteins at each dose. These proteins are correlated with remodeling of the cytoskeleton; the stability, size, and shape of dendritic spines; myelin sheath formation; and composition proteins of structures found in the membrane of the somatodendritic and axonal compartments. Our findings suggested that EGb modulates conditioned suppression LTM through differential protein expression profiles, which may be a target for cognitive enhancers and for the prevention or treatment of neurocognitive impairments.

Integration of botanicals in contemporary medicine: road blocks, checkpoints and go-ahead signals

The use of botanicals for maintaining good health and preventing diseases is undisputed. The claimed health benefits of natural health products and herbal medicines are based on traditional claims, positive results obtained in preclinical studies and early phase clinical trials that are not backed by safety and efficacy evidences approved by regulatory agencies. Although, the popularity of botanicals is growing, health care practitioners of modern medicine seldom recommend their use because of ill equipped database of their safety and potency. This review discusses problems that preclude botanicals from integrating into the mainstream contemporary therapeutics and cues that provide impetus for their realisation.