Reduced numbers of cortical GABA-immunoreactive neurons in the chronic D-galactose treatment model of brain aging

The Role of Glutamate Receptors in Epilepsy

Glutamate is an essential excitatory neurotransmitter in the central nervous system, playing an indispensable role in neuronal development and memory formation. The dysregulation of glutamate receptors and the glutamatergic system is involved in numerous neurological and psychiatric disorders, especially epilepsy. There are two main classes of glutamate receptor, namely ionotropic and metabotropic (mGluRs) receptors. The former stimulate fast excitatory neurotransmission, are N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), and kainate; while the latter are G-protein-coupled receptors that mediate glutamatergic activity via intracellular messenger systems. Glutamate, glutamate receptors, and regulation of astrocytes are significantly involved in the pathogenesis of acute seizure and chronic epilepsy. Some glutamate receptor antagonists have been shown to be effective for the treatment of epilepsy, and research and clinical trials are ongoing.

Boosting amygdaloid GABAergic and neurotrophic machinery via dapagliflozin-enhanced LKB1/AMPK signaling in anxious demented rats

Anxiety is a neuropsychiatric disturbance that is commonly manifested in various dementia forms involving Alzheimer's disease (AD). The mechanisms underlying AD-associated anxiety haven't clearly recognized the role of energy metabolism in anxiety represented by the amygdala's autophagic sensors; liver kinase B1 (LKB1)/adenosine monophosphate kinase (AMPK). Dapagliflozin (DAPA), a SGLT2 inhibitor, acts as an autophagic activator through LKB1 activation in several diseases including AD. Herein, the propitious yet undetected anxiolytic potential of DAPA as an autophagic enhancer was investigated in AD animal model with emphasis on amygdala's GABAergic neurotransmission and brain-derived neurotrophic factor (BDNF). Alzheimer's disease was induced by ovariectomy (OVX) along with seventy-days-D-galactose (D-Gal) administration (150 mg/kg/day, i.p). On the 43rd day of D-Gal injection, OVX/D-Gal-subjected rats received DAPA (1 mg/kg/day, p.o) alone or with dorsomorphin the AMPK inhibitor (DORSO, 25 μg/rat, i.v.). In the amygdala, LKB1/AMPK were activated by DAPA inducing GABA_B2 receptor stimulation; an effect that was abrogated by DORSO. Dapagliflozin also replenished the amygdala GABA, NE, and 5-HT levels along with glutamate suppression. Moreover, DAPA triggered BDNF production with consequent activation of its receptor, TrkB through activating GABA_B2-related downstream phospholipase C/diacylglycerol/protein kinase C (PLC/DAG/PKC) signaling. This may promote GABA_A expression, verifying the crosstalk between GABA_A and GABA_B2. The DAPA's anxiolytic effect was visualized by improved behavioral traits in elevated plus maze together with amendment of amygdala' histopathological abnormalities. Thus, the present study highlighted DAPA's anxiolytic effect which was attributed to GABA_B2 activation and its function to induce BDNF/TrkB and GABA_A expression through PLC/DAG/PKC pathway in AMPK-dependent manner.

Resveratrol and organic selenium-rich fermented milk reduces D-galactose-induced cognitive dysfunction in mice

Recently, dietary intervention has been considered as a prospective strategy in treating age-related cognitive dysfunction and brain plasticity degeneration. In this study, we developed a kind of functional fermented milk rich in resveratrol and organic selenium, and explored the effects on cognitive behavior, hippocampal neurogenesis and the neurotrophic signaling pathway in d-galactose model mice. Behavioral tests showed that the functional fermented milk significantly reversed spatial memory loss and showed a recognition behavior reduction in a novel object recognition task. Immunohistochemistry analysis demonstrated that the functional fermented milk significantly increased hippocampal neurogenesis. Moreover, walnut diets with dairy products reserved a d-galactose induced decrease of hippocampal p-ERK/ERK, p-CREB/CREB, and BDNF expression in the protein level. These findings confirmed that dietary treatment with the functional fermented milk could ameliorate cognitive dysfunction in d-galactose model mice, and yoghurt rich in resveratrol and organic selenium has the potential in treating age-related diseases.

Ionotropic Glutamate Receptors in Epilepsy: A Review Focusing on AMPA and NMDA Receptors

It is widely accepted that glutamate-mediated neuronal hyperexcitation plays a causative role in eliciting seizures. Among glutamate receptors, the roles of N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors in physiological and pathological conditions represent major clinical research targets. It is well known that agonists of NMDA or AMPA receptors can elicit seizures in animal or human subjects, while antagonists have been shown to inhibit seizures in animal models, suggesting a potential role for NMDA and AMPA receptor antagonists in anti-seizure drug development. Several such drugs have been evaluated in clinical studies; however, the majority, mainly NMDA-receptor antagonists, failed to demonstrate adequate efficacy and safety for therapeutic use, and only an AMPA-receptor antagonist, perampanel, has been approved for the treatment of some forms of epilepsy. These results suggest that a misunderstanding of the role of each glutamate receptor in the ictogenic process may underlie the failure of these drugs to demonstrate clinical efficacy and safety. Accumulating knowledge of both NMDA and AMPA receptors, including pathological gene mutations, roles in autoimmune epilepsy, and evidence from drug-discovery research and pharmacological studies, may provide valuable information enabling the roles of both receptors in ictogenesis to be reconsidered. This review aimed to integrate information from several studies in order to further elucidate the specific roles of NMDA and AMPA receptors in epilepsy.

Walnut diets up-regulate the decreased hippocampal neurogenesis and age-related cognitive dysfunction in d-galactose induced aged rats

Recently, dietary intervention has been considered as a prospective strategy in delaying age-related cognitive dysfunction and brain plasticity degeneration. This study explored the effect of walnut diets (6% and 9%, 8 weeks) on cognitive behavior, hippocampal neurogenesis and the neurotrophic signaling pathway in d-galactose (d-gal) model rats. Behavioral tests showed that walnut diets significantly reversed spatial memory loss in the Morris water test, locomotor activity deficiency in an open field test, and a recognition behavior reduction in a novel object recognition task. Immunohistochemistry analysis demonstrated walnut diets significantly increased the hippocampal neurogenesis in d-gal model rats. Moreover, western blot results indicated that walnut diets reserved a d-gal induced decrease of hippocampal pCREB (Ser133) and BDNF expression, two crucial intracellular molecules involved in hippocampal neurogenesis. These findings confirmed that chronic walnut-rich diets could ameliorate cognitive dysfunction in d-gal model rats, and the up-regulation of neurogenesis, as well as the expression of pCREB and BDNF in hippocampus, may be one of the molecular and cellular mechanisms underlying these effects.

The Effects of Light and Moderate Intensity Exercise on the Femoral Bone and Cerebellum of d-Galactose-Exposed Rats

Aging causes the degeneration of organs of the locomotor system, including the cerebellum and bones. Exercise may reverse this deterioration. d-galactose has been frequently used in rodents to accelerate aging. The present study aimed at investigating the effects of exercise on cerebellar and serum growth factors, motor activity, and the number of bone cells of the femoral head of d-galactose-treated rats. Twenty-four male Wistar rats were divided randomly into four groups, that is, three treated groups injected with 300 mg/(mL·kg) body weight (bw) d-galactose solution daily for 4 weeks, and a control group injected with normal saline. Following the 4-week administration of d-galactose solution, two of the treated groups performed light- (45% VO₂max) and moderate- (55% VO₂max) intensity exercise, by running on a treadmill 4 × a week for 4 weeks. Locomotor activity was examined in rotarod and open field tests. The cerebellar and serum Insulin-like Growth Factor 1 (IGF-1) and Brain-Derived Neurotrophic Factor (BDNF) levels were measured using enzyme-linked immunosorbent assay (ELISA). The number of osteoblasts and osteoclasts of femoral head was estimated using unbiased stereological methods. It was found that the number of osteoclasts was higher in the d-galactose-treated group than the normal control and moderate-intensity exercise groups. No significant difference between groups was found in the rotarod and open field test performance, IGF-1 and BDNF levels, as well as number of osteoblasts. In conclusion, a 4-week administration of high-dosed-galactose caused the increase of the number of osteoclasts. A subsequent 4-week moderate-intensity exercise reversed this increase to the normal level.

Changes in GABAergic markers accompany degradation of neuronal function in the primary visual cortex of senescent rats

Numerous studies have reported age-dependent degradation of neuronal function in the visual cortex and have attributed this functional decline to weakened intracortical inhibition, especially GABAergic inhibition. However, whether this type of functional decline is linked to compromised GABAergic inhibition has not been fully confirmed. Here, we compared the neuronal response properties and markers of GABAergic inhibition in the primary visual cortex (V1) of young adult and senescent rats. Compared with those of young adult rats, old rats’ V1 neurons exhibited significantly increased visually evoked responses and spontaneous activity, a decreased signal-to-noise ratio and reduced response selectivity for the stimulus orientation and motion direction. Additionally, the ratio of GABA-positive neurons to total cortical neurons in old rats was significantly decreased compared with that in young rats. Expression of the key GABA-synthesizing enzyme GAD67 was significantly lower in old rats than in young rats, although GAD65 expression showed a marginal difference between the two age groups. Further, expression of an important GABA_A receptor subunit, GABA_AR α₁, was significantly attenuated in old rats relative to young ones. These results demonstrate that ageing may result in decreased GABAergic inhibition in the visual cortex and that this decrease in GABAergic inhibition accompanies neuronal function degradation.

D-Galactose High-Dose Administration Failed to Induce Accelerated Aging Changes in Neurogenesis, Anxiety, and Spatial Memory on Young Male Wistar Rats

The model of accelerated senescence with the prolonged administration of d-galactose is used in anti-aging studies because it mimics several aging-associated alterations such as increase of oxidative stress and decline of cognition. However, there is no standardized protocol for this aging model, and recently some reports have questioned its effectiveness. To clarify this issue, we used a model of high-dose d-galactose on 1-month-old male Wistar rats and studied the hippocampus, one of the most affected brain regions. In one group (n = 10), d-galactose was daily administered intraperitoneally (300 mg/kg) during 8 weeks whereas age-matched controls (n = 10) were injected intraperitoneally with saline. A third group (n = 10) was treated with the same dose of d-galactose and with oral epigallocatechin-3-gallate (EGCG) (2 grams/L), a green tea catechin with anti-oxidant and neuroprotective properties. After treatments, animals were submitted to open-field, elevated plus-maze and Morris water maze tests, and neurogenesis in the dentate gyrus subgranular layer was quantified. There were no significant alterations when the three groups were compared in the number of doublecortin- and Ki-67-immunoreactive cells, and also on anxiety levels, spatial learning, and memory. Therefore, d-galactose was not effective in the induction of accelerated aging, and EGCG administered to d-galactose-treated animals did not improve behavior and had no effects on neurogenesis. We conclude that daily 300 mg/kg of d-galactose administered intraperitoneally may not be a suitable model for inducing age-related neurobehavioral alterations in young male Wistar rats. More studies are necessary to obtain a reliable and reproducible model of accelerated senescence in rodents using d-galactose.

Lactobacillus plantarum NDC 75017 alleviates the learning and memory ability in aging rats by reducing mitochondrial dysfunction

The aim of the present study was to investigate the protective effect of Lactobacillus plantarum NDC 75017 on D-galactose (D-gal)-induced mitochondrial dysfunction in the rat cerebral cortex. Fifty rats were randomly divided into five groups (n=10 in each group). The rats in the aging model group were subcutaneously injected with 100 mg/kg D-gal and those in the protective groups were additionally orally administered L. plantarum NDC 75017 at doses of 1×10⁸, 1×10⁹ or 1×10¹⁰ CFU/100 mg body weight/day, respectively. The control rats were administrated an equal volume of the vehicle. Following continuous treatment for seven weeks, the learning and memory abilities and mitochondrial ultrastructure, function and adenosine triphosphate (ATP) levels were examined. The results showed that the learning and memory abilities and mitochondrial levels of ATP were significantly decreased in the D-gal-induced aging model group compared with those in the control group (P<0.01). In addition, marked changes in the mitochondrial functions and ultrastructure were observed between the groups. Seven weeks of L. plantarum NDC 75017 and D-gal coadministration significantly improved the learning and memory abilities of the rats compared with the D-gal-induced aging model group. Furthermore, the combination regime significantly improved the mitochondrial ultrastructure and functions, including the mitochondrial respiratory chain, mitochondrial membrane potential and mitochondrial permeability transition. The results revealed that the L. plantarum NDC 75017 was able to alleviate learning and memory injuries in aging rats by reducing the mitochondrial dysfunction induced by D-gal.