Study On The Neurobiology Of Learning And Memory Of The Anterior Thalamic Nucleus Of Rats

Background and purpose:Learning and memory are indispensable function of survival to human and animals. Study is to obtain new information and new knowledge of neural processes. Memory is the access to information while encoding,consolidation, storage and reading out the neural process. The brain has multiple memory systems, such as declarative memory and non-declarative memory, etc. Different types of memories are stored in different brain regions, Hippocampus, thalamus, amygdala, prefrontal cortex and basal ganglia are all related to learning and memory. Recent studies have found that anterior thalamic nucleus(ATN) played an important role in spatial learning and memory.It was not until 1973 that long-term potentiation (LTP)of synaptic efficacy was originally described in the hippocampus of rabbits by Bliss and lomo. LTP is likely to be neurophysiological basis of learning and memory, the maintenance of LTP is related to an increased release of glutamate of presynaptic membrane.In our laboratory by immunogold electron microscopy techniques showed that the excitatory neurotransmitter is glutamate between learning and memory neural circuits of the ATN and limbic cortex. However, it is not clear if the ATN expresses NMDA receptors.A growing body of evidence has recently been accumulating that MAPK/ERK1/2 pathway activity is involved in LTP and the formation of memory. The present study found that ERK is activated in hippocampal CA1 after water maze training in rats, PD098059 inhibited p-ERK1/2 to affect the ERK1/2 pathway activity and impaired long-term spatial memory. It is not clear if ERK pathway is involved in the process of learning and memory of ATN.Immediate early genes (IEGs) are considered the nucleus of third messenger. After injecting c-fos antisense oligonucleotide into the hippocampus of rats, long-term memory consolidation in rats was impaired after Morris water maze training. During spatial learning and memory, it is not clear whether IEGs express in ATN.Synaptic plasticity consists of LTPand long-term depression(LTD). LTP and LTD are essential to a complete neural network of learning and memory, y-aminobutyric acid (GABA) is major inhibitory neurotransmitter, GABA is related to LTD. The expression of GABA and its receptor in the ATN are not clear.The aim of this study is to explore the expression of NMDA receptors and GABAA receptor expression in the ATN; And to explore that MAPK/ERK signal transduction and IEGs are related to spatial lerning and memory in the ATN.Methods:1.To observe the expression and distribution of NR1, NR2A and NR2BmRNA in the ATN of rats by in situ hybridization.2. The rats were divided into 3 groups:①PD group:Rats were injected intraventricularly with PD098059(3μg/5ul) after Place navigation training.②PD control group:intraventricular injection of 5ul DMSO solvent;③Normal group:no intraventricular injection. After 24 hours to do space exploration training. p-ERK was detected by means of immunohistochemistry.3. Adult male SD rats were divided into 3 groups:①Control group:without the Morris water maze training;②Training group:Morris water maze training;③Sham training group:removed platform, swim times and time with the same as training group. After training, half of the rats to detect the expression of c-Fos and c-Jun by means of immunohistochemistry. Another half to detect the expression of c-Fos and c-Jun by means of Westwen-Blot.4. GABAAR-alphal and GABAAR-beta2 receptor mRNA expression were determined through situ hybridization in the ATN. Results:1. The mRNA of NMDA receptor subunits NR1, NR2A and NR2B distributed in the intensively and homogeneously in the ATN. The mRNA of NMDA receptor subunits NR1, NR2A and NR2B were also visible in the hippocampus and retrosplenial granular cortex. Control sections were negative for the expression of mRNA of NMDA receptor subunits NR1, NR2A and NR2B.2. In the probe trial performance, the platform crossings in PD group were significantly reduced compared to the PD control group and normal control group (P<0.01). The percentage of time of PD group spent in the correct quadrant decreased significantly compared to the PD control group and the normal group (P<0.01).The platform crossings and the percentage of time of spent in the correct quadrant in PD control group showed no significantly different compared to normal control group (P> 0.05). p-ERK positive neurons were brown, round or oval. p-ERK expression in ATN of PD control group was significantly increased compared to PD group and the normal control group (P<0.01). p-ERK showed no significant difference between PD group and the normal control group. In the PD control group, p-ERK in the anterior dorsal nucleus (AD)was stronger than in anterior ventral nucleus(AV) (P<0.05).No expression of p-ERK-positive neurons was found in negative control sections.3. After Morris water maze training,The expression of c-Fos was distributed in the AD and AV. But AD was significantly enhanced compared to AV(P<0.05). The expression of c-Fos of the training group in the ATN was dramatically stronger compared to the normal control group and the sham training group (P<0.05). The expression of c-Jun was visible in the AD and AV. The expression of c-Jun protein in the AD was stained slightly stronger than in the AV. In the normal control group and sham training group. The expression of c-Jun protein was weak. The expression of c-Jun in the training group significantly increased compared to the control group and the sham training group(P<0.05).4. In situ hybridization:GABAAR-alpha1 and GABAAR-beta2 mRNA in situ hybridization-positive brown reaction products, mainly in the cytoplasm of neurons.In AD and AV, positive neurons were more intensive, more consistant morphology, the distribution in the AD and AV former slightly intensive. while such as the hippocampus and retrosplenial granular cortex the expressions of GABAAR-alphal and GABAAR-beta2 mRNA were also observed in the other parts of brain related to learning and memory.such as hippocampus and retrosplenial granular cortex.Conclusions1. The results suggest that the neurons of ATN are capable of producing NMDA receptors subunits of NR1,NR2A and NR2B.During signal transduction of learning and memory in the ATN, the cell membrane receptors are likely to be NR1-NR2A,NR1-NR2B,or NR1-NR2A-NR2B patterns.2. Post-training application ERK cascade inhibitors (PD098059) in rats, the spatial reference memory was impaired, and the expression of p-ERK was decreased. Suggesting a likely crucial role of MAPK/ERK signalling passway in spatial reference memory process of ATN. After Morris water maze training in the PD control group, the expression of p-ERK in the AD was significantly increased compared to AV.3. After Morris water maze training, the expression c-Fos and c-Jun in the ATN were increased dramatically, which indicates Fos form heterodimeric complexes with Jun to constitute the AP-1, which further regulates gene expression. After Morris water maze training, the expression of c-Fos in the AD was significantly increased compared to the AV, but the functions of AD and AV respectively in learning and memory are still further studied.4. GABAAR-alphal and GABAAR-beta2 mRNA were expressed in the ATN, suggesting that learning and memory process in the ATN was likely regulated by GABA.