The Expression Of 5-HT And 5-HTR_2A In The Laterodorsal Thalamic Nuclei Of Rat

The laterodorsal thalamic nucleus (LD) has been reported to be involved in spatial learning and memory. It consists of laterodorsal thalamic nucleus, dorsomedial part (LDDM) and laterodorsal thalamic nucleus, ventrolateral part (LDVL). 5-HT, as an important neurotransmitter, and 5-HTR_2A have been considered to play a very important role in the process of learning and memory.Objective: This study investigated the expression of 5-HT and 5-HTR_2A in the different regions of LD in the rat by using immunohistochemical techniques. Morphological information which could help us to further evaluate the relationship between them and learning or memory was provided .Methods: 8 Sprague-Dawley(SD) adult rats which were composed of male and female in equal, weight 200-250g. They were provided by the Experimental Animal Center of Dalian Medical University. The rats were received 4% chloral hydrate intraperitoneal anesthesia (1ml/100g body weight) and their hearts were rapidly exposed. The infusion needle inserted into the ascending aorta via the left ventricular and infused 200ml physiologic saline rapidly until effluent liquid from the right atrial appendage was colorless and transparent. 300ml 4% paraformaldehyde fixative solution (pH7.4) was reperfused. 100ml of solution was infused rapidly and 200ml was infused slowly. The whole process lasted about 2 hours. Then their brains were rapidly removed , the brain surface of the meninges were picked and placed in fixation at 4℃for overnight. Finally, consecutive 30μm coronal sections were cut on a vibration microtome. 3 sets sections obtained were used for 5-HT, 5-HTR_2A and control experiments separately. Floating immunohistochemical staining method was used to demonstrate the expression of 5-HT and 5-HTR_2A in different regions of LD in the rat. The sections were observed under light microscope. All experimental and control images were collected and analysed by identical image analysis system. Statistical significance was assessed by pared t-test using SPSS11.5 software. P values<0.5 were considered statistically significant.Results: 1. 5-HT immunohistochemical results showed that :under light microscope, there were a number of 5-HT positive nerve fiber terminals distributed throughout the LDDM and LDVL;Under high-power microscope, fiber terminals running distances longer, beaded. However there was no significant difference in the average optical density between LDDM and LDVL(p﹥0.05). No 5-HT-like immunoreactivities were detected in the LD in the rat in control group. 2. 5-HTR_2A immunohistochemistry results demonstrated that: under light microscope, there were a number of 5-HTR_2A positive neurons in LDDM and LDVL. The neurons were uniform distribution, medium-sized. The 5-HTR_2A-like immunoreactivities were found chiefly on the membrane, and were not detected in the cytoplasm and nucleus. There was no significant difference between LDDM and LDVL(p﹥0.05). No 5-HTR_2A-like immunoreactivities were detected in the LD in the rat in control group.Conclusions: 1.There were a number of 5-HT positive nerve fiber terminals distributed throughout the LD. 2. 5-HTR_2A were distributed in the LD.