The Effects Of Donepezil And Memantine On Neurodegenerative Symptoms In Presenilin-1/2Conditional Double Knockout Mice

Alzheimer’s disease (AD) is a progressive degenerative disease of the central nervous system. Currently, the number of AD patients is about36million people, and this number will turn out to be0.108billion by2050.With the intensification of global aging, the research of AD is very significant. The main pathology of AD includes neuronal apoptosis, synaptic loss, increase in senile plaques and neurofibrillary tangles, etc, but the pathogenesis of AD has not been revealed.The studies have shown that the majority of AD patients are sporadic, and a small number of AD patients have the feature of familial autosomal dominant inheritance (Familial Alzheimer’s disease, FAD).The gene mutation of presenilins is the major reason of early-onset FAD, and Presenilins include Presenilin-1and Presenilin-2types. The DKO mice, which are derived from PS1forebrain-specific knockout mice and PS2knockout mice, exhibits a series of AD-like symptoms, including hippocampus-dependent memory loss, tau protein hyperphosphorylation, neuronal apoptosis, cortical atrophy, enlarged lateral ventricles and the third ventricle, strong inflammatory response and cognitive dysfunction.At present, the FDA has approved drugs for the treatment of AD. Acetylcholinesterase inhibitors (donepezil,1996) and NMDA glutamate receptor antagonist (memantine hydrochloride,2003) are the primary drugs. Acetylcholine, which is an important chemical signal molecule in the brain cells, involves in memory, thinking, and judging capabilities. AD patients have lower levels of acetylcholine in the brain,which is mainly because of the degeneration of cholinergic neurons, leading to cognitive dysfunction. Acetylcholinesterase inhibitors (donepezil) can inhibit cholinesterase activity and hinder the decomposition of acetylcholine, thus,maintaining the level of acetylcholine. Finally,donepezil can improve the memory and cognitive function in AD.Glutamate, which is a major excitatory neurotransmitter in the central nervous system, involves in synaptic plasticity, learning and memory function. NMDA glutamate receptors mediate fast excitatory transmission. The levels of glutamate in AD increase, resulting in damage to synaptic plasticity, neuronal death, cell loss, and ultimately learning and memory disorders. NMDA glutamate receptor antagonist (memantine hydrochloride) can restrict the open of NMDA receptor channel when it is overexcited without affecting normal synaptic function, so that the neurons are protected from glutamate-mediated neurotoxicity, and eventually to improve cognitive function. To test the effects of donepezil and memantine on DKO mice,5-month old mice were administered donepezil and memantine hydrochloride for a month.Using behavioral experiments and molecular methods to test the effects of donepezil and memantine on neurodegenerative symptoms of DKO mice.1. The effects of donepezi on neurodegenerative symptoms of DKO mice5-month-old DKO mice and CON mice were intraperitoneally injected donepezil.Then the motor coordination, learning and memory, anxiety and apathy emotion were tested using behavioral experiments,using open field, novel object recognition, coat hanger, nest buiding, elevated plus maze, Barnes maze, fear conditioning paradigm, respectively. The results showed that donepezil could partially rescue the high spontaneous locomotion, non-spatial hippocampus-dependent learning and memory deficency of DKO mice.2. The molecular mechanisms of donepezil on neurodegenerative symptoms of DKO mice.After the end of behavioral experiments, we take samples from the experimental group of mice, using histological methods and microscopy techniques to observe the area of the third ventricle and lateral ventricles, the distribution of acetylcholinesterase; using microplate detection system to analyze acetylcholinesterase and choline acetyltransferase activity of hippocampus, cortex and cerebellum; using the Western Blot technique to detect the expression levels of caspase-3, Bcl-xl, BDNF from the hippocampus and cortex. Donepezil could partially rescue the artrophy of ventricle, and reduce the activity of acetylcholinesterase and the level of apoptosis of DKO mice, whereas could not affect the expression level of neurotrophins in DKO mice.3. The effects of memantine on neurodegenerative symptoms of DKO mice5-month-old DKO mice and CON mice were administered memantine with drinking water.Then the motor coordination, learning and memory, anxiety and apathy emotion were tested, using behavioral experiments,such as open field, novel object recognition, coat hanger, nest buiding, elevated plus maze, Barnes maze, fear conditioning. The results showed that memantine improve non-spatial hippocampus-dependent learning and memory abilities of DKO mice. NMDA receptor antagonists can partially improve the neurodegenerative symptoms of DKO mice.4. The molecular mechanisms of memantine on neurodegenerative symptoms of DKO mice.After the end of behavioral experiments, we take samples from the experimental group of mice, using Western Blot technique to detect the expression levels of caspase-3, Bcl-xl, BDNF protein from the hippocampus and cortex. The results showed that memantine did not influence the expression level of apoptosis and neurotrophins in DKO mice.In summary,donepezil can partially improve the neurodegenerative symptoms of DKO mice by inhibiting the activity of acetylcholinesterase.Memantine can also partially alleviate the neurodegenerative symptoms of DKO mice by the antagonism of NMDA receptor,but both drugs can’t entirely improve these symptoms,such as emotional behavior,neuronal apoptosis,motor coordination,spatial cognitive ability and fear memory capacity,etc.These results indicate that the central cholinergic neuronal loss and glutamate excitatory may not be the main cause of AD.Combining the results of studies in our laboratory,we propose,it is more effective to adopt multiple treatments for the AD treatment.