The Effect Of Chronic Ethanol Exposure On Learning And Memory Ability And The Therapeutic Effect Of Valproate

Objective: Nowadays alcohol abuse has become a generally medical and social question. Chronic ethanol exposure can produce impairment of normal functions in central nervous system (CNS), which including the cognitive dysfunction in learning and memory, specially typified by Wernicke-Korsakoff syndrome. It is not exactly clear to understand the effect of alcoholism on CNS. It may regulate different normal conduction circuits and control the release of different neurotransmitters. Now a number of studies with regard to learning and memory focus on hippocampus. Hippocampus is a cerebral structure closely involved with memory, which takes part in the transformation from short-term memory to long-term memory, moreover it is one of susceptible target region to ethanol. Anatomical research of brains from human alcoholics has indicated that impairment of behavioral function was associated with the atrophy of hippocampal formation. Similarly, animal studies have also demonstrated that there are neuronal degeneration, atrophy and apoptosis in hippocampus of rats with chronic ethanol consummation. This atrophy could have the effect of disrupting normal synaptic interactions among neurons in hippocampus to produce mnemonic deficits. But chronic antioxidant consumption could restore the impaired neurons and recover the neural synaptic plasticity to produce the protective effects on brain of rats in learning and memory abilities. Brain-Derived Neurotrophic Factor (BDNF) has paid more attention to study the protective effects on brain.Decreased neurotrophic activity may be involved in ethanol-induced neurodegeneration in the adult brain and in the study of alcohol-related neurodevelopmental disorders. Many studies have demonstrated that BDNF protects neurons from ethanol-induced cell death in vitro. Polymorphisms in the genes coding for BDNF and its receptor TrkB are linked to affective, substance abuse and appetitive disorders and therefore may play a role in the development of alcoholism. Evidence has accumulated that implicates BDNF as a regulator of development, modulator of appetite, facilitator of synaptic plasticity, potential therapy for neurodegenerative disease and mediator of addiction.In recent studies, Valproate (VPA) has been found to have the neurotrophic effects. Chronic VPA treatment has known to increase the activated level of AMP response element binding protein (CREB) in rat hippocampus. As a transcription factor, CREB has been demonstrated to regulate the synthesis of a lot of proteins regarding with long-term memory.ρ-CREB, as an active form of CREB after it is phosphorylated by kinase, may modulate many cytokines in transcriptional level, including BDNF which plays an important role in adjustment of the neural synaptic plasticity. It is unknown whether VPA can improve the function of rats with chronic ethanol exposure in learning and memory, and whether BDNF is involved in.In the present study, we aim to know whether the change of BDNF level in rat hippocampus is associated with the impairment of learning and memory induced by chronic ethanol exposure, and whether VPA can improve the damages of learning and memory by increasing the BDNF level.Method: Part 1: There were no significant differences between the performances of Morris Water Maze (MWM) and Y Maze of all rats before experiment. Adult male Sprague-Dawley (SD) rats weighing 160g~180g (obtained from the Experimental Animal Center of Hebei Medical University) were randomly divided into a control group (n=14) and a chronic ethanol exposure group (n=14). Rats in the ethanol group were subjected to ethanol solution (10 ml/kg, ig) for 8 weeks at 9 o'clock a.m. Rats in the control group were established by lavage with normal saline. After withdraw 24 hours, 7 rats were randomly selected for body weight, withdrawal scores and behavioral tests (including Morris Water Maze and Y Maze), and the rest rats of each group were sacrificed for western blotting to detect the BDNF level in rats hippocampus. The rats were subjected to intragastric administration with solutions of ethanol and water for model of chronic alcoholism. Each rat was given 10 ml/kg per day. The first concentration of solutions was 5% (v/v) for one week, and the concentration of second week and third week respectively was 10% and 20% (v/v). The concentration of solutions kept 35% (v/v) from the fourth week to eighth week with the intake of ethanol for 3.5g/kg/d.Part 2: Adult male SD rats (selected in the same way as Part 1) were divided into 4 groups randomly:①E tOH+VPA;②EtOH+Vehicle;③NS+VPA;④NS+Vehicle, 14 rats in each group. Rats in four groups were treated respectively ethanol or saline (10 ml/kg, ig) once per day for a period of 8 weeks days. Each group was intraperitoneally injected VPA (200 mg/kg) or vehicle (1 ml/kg) respectively on the 5th week at 8:30 a.m. After withdraw 24 hours, 7 rats were randomly selected for body weight, withdrawal scores and behavioral tests (including Morris Water Maze and Y Maze), and the rest rats of each group were sacrificed for western blotting to detect the BDNF level in rats hippocampus.Results: In Part 1, there were no significant differences in weight of the rats between ethanol and control group (P>0.05). The withdrawal total scores in ethanol group were higher than those in control group (P<0.01). In Morris Water Maze, the escape latency of rats in ethanol group was longer than that of control group (P<0.05). During the 60 sec probe trial, the numbers of crossing the platform and the time percent spent in searching for the platform by rats in ethanol group in the platform quadrant was less than that in control group (P<0.05). In Y Maze, the error numbers of rats in ethanol group were higher than that in control group on first and second day (P<0.01). There were no marked differences in total response time between two groups (P>0.05). Compare to the performances of the first day, the error numbers of second day in control group were loss apparently (P<0.05). There were no evident differences in ethanol group between two days performances (P>0.05). In western blot, a reduction of the average optical density value ratio of BDNF was observed in ethanol group, as compared to control group (P<0.05).In Part 2, there were no significant differences in weight of rats in four groups (P>0.05). The withdrawal scores of rats in EtOH+VPA group were higher than that of EtOH+Vehicle group (P<0.01), but didn't differ from NS+VPA group and NS+Vehicle group (P>0.05). The performances of behavioral tests were improved remarkably in EtOH+VPA group compared with EtOH+Vehicle group. And relative value of BDNF also increased in EtOH+VPA group (P<0.01).Conclusion: 1 Chronic ethanol exposure can impair the learning and memory abilities, which may be associated with reduction of BDNF level in rat hippocampus.2 Valproate can reverse impairment of learning and memory caused by the chronic ethanol consumption through inducing the expression of BDNF in hippocampus.