BDNF regains function in hippocampal long-term potentiation deficits caused by diencephalic damage

Acute Ethanol Challenge Differentially Regulates Expression of Growth Factors and miRNA Expression Profile of Whole Tissue of the Dorsal Hippocampus

Acute ethanol exposure produces rapid alterations in neuroimmune gene expression that are both time- and cytokine-dependent. Interestingly, adolescent rats, who often consume binge-like quantities of alcohol, displayed reduced neuroimmune responses to acute ethanol challenge. However, it is not known whether growth factors, a related group of signaling factors, respond to ethanol similarly in adults and adolescents. Therefore, Experiment 1 aimed to assess the growth factor response to ethanol in both adolescents and adults. To test this, adolescent (P29-P34) and adult (P70-P80) Sprague Dawley rats of both sexes were injected with either ethanol (3.5 g/kg) or saline, and brains were harvested 3 h post-injection for assessment of growth factor, cytokine, or miRNA expression. As expected, acute ethanol challenge significantly increased IL-6 and IκBα expression in the hippocampus and amygdala, replicating our prior findings. Acute ethanol significantly decreased BDNF and increased FGF2 regardless of age condition. PDGF was unresponsive to ethanol, but showed heightened expression among adolescent males. Because recent work has focused on the PDE4 inhibitor ibudilast for treatment in alcohol use disorder, Experiment 2 tested whether ibudilast would alter ethanol-evoked gene expression changes in cytokines and growth factors in the CNS. Ibudilast (9.0 mg/kg s.c.) administration 1 h prior to ethanol had no effect on ethanol-induced changes in cytokine or growth factor changes in the hippocampus or amygdala. To further explore molecular alterations evoked by acute ethanol challenge in the adult rat hippocampus, Experiment 3 tested whether acute ethanol would change the miRNA expression profile of the dorsal hippocampus using RNASeq, which revealed a rapid suppression of 12 miRNA species 3 h after acute ethanol challenge. Of the miRNA affected by ethanol, the majority were related to inflammation or cell survival and proliferation factors, including FGF2, MAPK, NFκB, and VEGF. Overall, these findings suggest that ethanol-induced, rapid alterations in neuroimmune gene expression were (i) muted among adolescents; (ii) independent of PDE4 signaling; and (iii) accompanied by changes in several growth factors (increased FGF2, decreased BDNF). In addition, ethanol decreased expression of multiple miRNA species, suggesting a dynamic molecular profile of changes in the hippocampus within a few short hours after acute ethanol challenge. Together, these findings may provide important insight into the molecular consequences of heavy drinking in humans.

Adolescent Binge-Type Ethanol Exposure in Rats Mirrors Age-Related Cognitive Decline by Suppressing Cholinergic Tone and Hippocampal Neurogenesis

Heavy alcohol consumption followed by periods of abstinence (i.e., binge drinking) during adolescence is a concern for both acute and chronic health issues. Persistent brain damage after adolescent intermittent ethanol exposure in rodents, a model of binge drinking, includes reduced hippocampal neurogenesis and a loss of neurons in the basal forebrain that express the cholinergic phenotype. The circuit formed between those regions, the septohippocampal pathway, is critical for learning and memory. Furthermore, this circuit is also altered during the aging process. Thus, we examined whether pathology in septohippocampal circuit and impairments in spatial behaviors are amplified during aging following adolescent intermittent ethanol exposure. Female and male rats were exposed to intermittent intragastric gavage of water (control) or 20% ethanol (dose of 5 g/kg) for a 2 days on/off cycle from postnatal days 25-55. Either 2 (young adult) or 12-14 (middle-age) months post exposure, rats were tested on two spatial tasks: spontaneous alternation and novel object in place. Acetylcholine efflux was assessed in the hippocampus during both tasks. There was no adolescent ethanol-induced deficit on spontaneous alternation, but middle-aged male rats displayed lower alternation rates. Male rats exposed to ethanol during adolescence had blunted behavioral evoked acetylcholine during spontaneous alternation testing. All ethanol-exposed rats displayed suppression of the cholinergic neuronal phenotype. On the novel object in place task, regardless of sex, ethanol-exposed rats performed significantly worse than control-treated rats, and middle aged-rats, regardless of sex or ethanol exposure, were significantly impaired relative to young adult rats. These results indicate that male rats display earlier age-related cognitive impairment on a working memory task. Furthermore, male rats exposed to ethanol during adolescence have blunted behavior-evoked hippocampal acetylcholine efflux. In addition, middle-aged and ethanol-exposed rats, regardless of sex, are impaired at determining discrete spatial relationship between objects. This type of pattern separation impairment was associated with a loss of neurogenesis. Thus, binge-type adolescent ethanol exposure does affect the septohippocampal circuit, and can accelerate age-related cognitive impairment on select spatial tasks.

Sex differences in cholinergic circuits and behavioral disruptions following chronic ethanol exposure with and without thiamine deficiency

BACKGROUND

Few studies have investigated differences in the vulnerabilities of males and females to alcohol use disorder and alcohol-related brain damage (ARBD). According to epidemiological and clinical findings, females appear to be more sensitive to the effects of alcohol and thiamine deficiency and have a worse prognosis in recovery from neurocognitive deficits compared with males. This study aimed to characterize the effects of chronic ethanol (EtOH) toxicity and thiamine deficiency across the sexes using rodent models.

METHODS

Male and female Sprague Dawley rats were assigned to chronic forced EtOH treatment (CET), pyrithiamine-induced thiamine deficiency (PTD), combined CET-PTD, or pair-fed (PF) control treatment conditions. Following treatments, spatial working memory was assessed during a spontaneous alternation task while measuring acetylcholine (ACh) in the prefrontal cortex (PFC) and the hippocampus (HPC). The animals also underwent an operant-based attentional set-shifting task (ASST) for the analysis of behavioral flexibility.

RESULTS

Female and male rats did not differ in terms of EtOH consumption; however, the CET and CET-PTD-treated female rats had lower BECs than male rats. Compared with the PF group, the CET, PTD, and CET-PTD groups exhibited spatial working memory impairments with corresponding reductions in ACh efflux in the PFC and HPC. The ASST revealed that CET-PTD-treated males and females displayed impairments marked by increased latency to make decisions. Thalamic shrinkage was prominent only in the CET-PTD and PTD treatment conditions, but no sex-specific effects were observed.

CONCLUSIONS

Although the CET and CET-PTD-treated females had lower BECs than the males, they demonstrated similar cognitive impairments. These results provide evidence that female rats experience behavioral and neurochemical disruptions at lower levels of alcohol exposure than males and that chronic EtOH and thiamine deficiencies produce a unique behavioral profile.

Long-term potentiation in the hippocampal CA3 to CA1 synapses may be induced in vivo by activation of septal cholinergic inputs

PURPOSE/AIM

The role of cholinergic neurotransmission in the hippocampus remains controversial since different studies showed either no influence or its modulatory effect on glutamatergic hippocampal synapses. It remains unclear whether septal cholinergic input can modulate plasticity of synapses formed by CA3 pyramids on CA1 neurons. The aim of the study was to clarify the role of septal input in the development of LTP in this synapse.

MATERIALS AND METHODS

We recorded in vivo in rats under urethane anesthesia focal excitatory postsynaptic potential (fEPSP) characteristics in CA1 area after stimulation of the ventral hippocampal commissure (VHC), which contains both CA3 axons innervating CA1 neurons and cholinergic axons coming from the medial septum. We performed two series of experiments in which LTP was induced by tetanization of either VHC or medial septal area (MSA). Degeneration of cholinergic neurons in MSA was induced by intraseptal injection of 192IgG-saporin.

RESULTS

In both experimental series, tetanization induced an increase in fEPSP amplitude which lasted for at least 40 min after tetanic stimulation, although tetanization of VHC induced a larger increase in fEPSP amplitude compared to MSA tetanization. Elimination of septal cholinergic neurons by 192IgG-saporin abolished LTP development in both experimental series. This suppression of LTP in animals with cholinergic deficit was not due to loss of hippocampal neurons.

CONCLUSIONS

Our data suggest that activation of septal cholinergic fibers during tetanization is a critical factor of LTP induction in the hippocampal CA3 to CA1 synapses.

Cognitive Impact of Calorie Restriction: A Narrative Review

The impairment of cognitive function can cause substantial emotional and financial burdens. A recent global increasing trend in cognitive impairment and associated disorders has been observed, which will continue to grow as the population ages rapidly. As a nonpharmaceutical approach, calorie restriction (CR) has received extensive research interests due to its health benefits, including maintaining cognitive function. In this narrative review, we first briefly introduce the role of cognitive function in activities of daily living and CR as a part of healthy lifestyle behaviors to protect against cognitive decline. Second, we present results from human studies demonstrating that CR might be beneficial for improving age-related cognitive decline and cognitive impairment in the clinical population such as obesity and type 2 diabetes. Third, the potential mechanisms regarding the protective effects of CR on cognition are discussed. Fourth, specific suggestions are highlighted to be considered in future human studies. Overall, although there are few data available from human studies, CR appears to be beneficial for cognitive protection for both healthy and clinical populations. Further scientific investigations are needed before a firm conclusion can be made.

Piperine ameliorated memory impairment and myelin damage in lysolecethin induced hippocampal demyelination

AIMS

We still do not have effective treatment for hippocampal demyelination and memory deficit, the two common comorbidities in multiple sclerosis (MS). This study aimed to assess the therapeutic effect of Piperine (the main alkaloid of black pepper) in an experimental model of demyelination.

MAIN METHODS

Demyelination was induced in male Wistar rats by bilateral injection of lysolecithin (LPC) into the CA1 region of the hippocampus. Piperine (5, 10, 20 mg/kg) was daily injected intraperitoneally three days post LPC injection for ten days. The spatial memory was examined by the Morris water maze task. Demyelination and astrocyte activation were assessed by an immunohistological study. The gene expression analysis of TNF-α, IL1-β, NF-κB, IL-10, Foxp3, iNOS, Nrf2, HO1, MBP, and BDNF was done using qPCR. The total antioxidant capacity of hippocampal tissue was measured using FRAP assay.

KEY FINDINGS

Our results showed that piperine improved the memory performance and myelin repair in the hippocampal demyelination model. Piperine inhibited iNOS expression concomitant with enhanced expression levels of Nrf2, HO1 and the total antioxidant capacity in the hippocampal tissue. Piperine treatment significantly reduced the gene expression level of TNF-α, IL1-β, NF-κB, and glial activation in the injured area; however, the mRNA level of IL-10, Foxp3, BDNF and MBP were significantly increased.

SIGNIFICANCE

We found piperine to be an effective treatment for spatial memory impairment and myelin repair in the hippocampal demyelination model. However, further experimental evidence is needed to investigate the precise mechanisms underlying piperine as a promising therapeutic target in MS patients.

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

Nerve Growth Factor Is Responsible for Exercise-Induced Recovery of Septohippocampal Cholinergic Structure and Function

Exercise has been shown to improve or rescue cognitive functioning in both humans and rodents, and the augmented actions of neurotrophins within the hippocampus and associated regions play a significant role in the improved neural plasticity. The septohippocampal circuit is modified by exercise. Beyond an enhancement of spatial working memory and a rescue of hippocampal activity-dependent acetylcholine (ACh) efflux, the re-emergence of the cholinergic/nestin neuronal phenotype within the medial septum/diagonal band (MS/dB) is observed following exercise (Hall and Savage, 2016). To determine which neurotrophin, brain-derived neurotrophic factor (BDNF) or nerve growth factor (NGF), is critical for exercise-induced cholinergic improvements, control and amnestic rats had either NGF or BDNF sequestered by TrkA-IgG or TrkB-IgG coated microbeads placed within the dorsal hippocampus. Hippocampal ACh release within the hippocampus during spontaneous alternation was measured and MS/dB cholinergic neuronal phenotypes were assessed. Sequestering NGF, but not BDNF, abolished the exercise-induced recovery of spatial working memory and ACh efflux. Furthermore, the re-emergence of the cholinergic/nestin neuronal phenotype within the MS/dB following exercise was also selectively dependent on the actions of NGF. Thus, exercise-induced enhancement of NGF within the septohippocampal pathway represents a key avenue for aiding failing septo-hippocampal functioning and therefore has significant potential for the recovery of memory and cognition in several neurological disorders.

Treadmill exercise alters ecstasy- induced long- term potentiation disruption in the hippocampus of male rats

3, 4-methylenedioxymethamphetamine (MDMA) or ecstasy is a derivative of amphetamine that leads to long term potentiation (LTP) disruption in the hippocampal dentate gyrus (DG). Exercise has been accepted as a treatment for the improvement of neurodegenerative disease. Herein, the effects of exercise on the MDMA- induced neurotoxicity were assessed. Male Wistar rats received intraperitoneal injection of MDMA (10 mg/kg) and exercised for one month on a treadmill (Simultaneously or asynchronously with MDMA). LTP and expression of BDNF were assessed using electrophysiology and western blotting methods, respectively. MDMA attenuated the field excitatory post-synaptic potential (fEPSP) slope in comparison with the control group, whereas treadmill exercise increased this parameter when compared to MDMA group. Furthermore, BDNF expression significantly decreased in MDMA group and treadmill exercise could increase that. In conclusion, results of this study suggest that synchronous exercise is able to improve MDMA-induced LTP changes through increase of BDNF expression in the hippocampus of rats.