The Role Of Opioid Receptor In Stress - Induced Spatial Reference Learning And Memory Impairment

Memory is a fundamental mental process, and without memory we are capable of nothing but simple reflexes and stereotyped behaviors. We define memory as a behavioral change caused by an experience, and define learning as a process for acquiring memory.A variety of endogenous systems are considered to be involved in learning and memory. These include the opioid system, which has been demonstrated in various cognitive tasks to play an important role in the memory processes and memory storage. The neuroanatomical distribution of theu-opioid receptor in the CNS reflects their potential endogenous role in many major biological processes. μ-opioid receptor gene are abundant in the areas, such as neocortex, caudate nucleus, nucleus accumbens(Nac), amygdale, periaqueductal gray (PAG), thalamus. It is closely linked to the gene that μ-opioid receptor are expressed primarily in the amygdale. μ-opioid receptor are distributed throughout the human, rodent central nervous systems (CNS), which reflects its potential role in many major physiological processes, such as cognitive, pain, emotion. Previous study suggests that spatial memory examined by Morris water maze was impaired in μ-opioid receptor knockout mice; Injections of β-FNA into the CA3region, but not into intracerebroventricular, caused a significant impairment in the spatial learning. On the contrary, pre-training morphine impair spatial memory acquisition.In comparison with previous year, the amount of studies investigating the mechanism of the physiological function of stress in learning and memory has dramatically increased. The initial studies have shown that many stressors interact with some neurotransmitter, such as ACH、DA、Glu. Moreover, the precise role of opioid peptides and opioid receptors in the response to stimuli has been observed. Studies on how different stress strength and the stress-related μ opioid receptor affect learning and memory have yielded inconsistent findings. The impacts of the stress-related μ opioid receptor on different memory components have not been clearly addressed. So, the aim of present study was to evaluate the effect of the stress-induced μ opioid receptor changes on memory acquisition, retrieval in mice.In the morris water task,Kun-ming mice received μ opioid receptor agonist DAMGO or antagonist CTAP before the first trial on each training day. Pre-training DAMGO administration (i.c.v.) impaired the spatial reference memory, whereas pre-training CTAP is no effect on the spatial reference memory(Exp.l).The study has suggested that elevated platform stress could affect the spatial reference memory,which can be reversed by CTAP pretreatment (Exp.2). But Kun-ming mice received μ opioid receptor antagonist CTAP in pre-probe is fail to reverse(Exp.3).In the conclusion, This experiments support theories that endogenous μ opioid system is essential both in the normal learning and memory and the stress-introduced damage of learning and memory.