Types Of Neurons Of The Prefrontal Cortex Involved In The Restraint Water-immersion Stress In Rats

Stress is a specific or non-specific reaction that is caused by a source of stress. It inducesdiscordant balance and threats to homeostasis. Restrain water-immersion stress (RWIS) is one ofthe main stress model which can cause gastric disfunction and acute gastric erosions. Theprefrontal cortex (PFC) is a sensitive area of the brain to harmful stress. The medial prefrontalcortex (mPFC), an important part of the PFC, can regulate many physiological reactions,especially the reactions to stress. But, what types of neurons (e.g. amono acidergic neurons,cholinergic neurons, or catecholaminergic neurons, etc.) involved in the RWIS reactions are littleknown up to now.The Fos protein is widely used for labeling of neurons activity in the brain caused by stress.Studies have shown that mPFC can express a lot of Fos protein under the RWIS. The mPFCincludes main two parts, prelimbic cortical area (PL) and infralimbic cortical area (IL). It wasreported that restraint stress can increase expression of c-fos mRNA in the PL and the IL. Ourresearch group explored the types of neurons in the neural circuits of the anterior hypothalamusbetween medulla oblongata gastrointestinal center involved in the RWIS responses in the rat.Some studies have shown that hypothalamic activity is not only modulated by the lower centralfeedback information, but also by the cerebral cortex, especially PFC. Our previous works foundthat in different periods of RWIS in rats, the mPFC c-Fos expression at RWIS1h is the mostintense. We suppose that the mPFC is a senior central involved in the RWIS responses. It is wellknown that GABA, the main inhibitory synaptic neurotransmitter, distributes widely in the brainregions. Some studies have shown that GABAergic neurons exist in mPFC. Then, do theGABAergic neurons participate in the RWIS reactions? The glutamate is a main neurotransmitterin the central nervous system. According to the reports that the glutamate increases by excitingneurons in the mPFC, we want to know are there glutamatergic (Glu-ergic) neurons in the mPFC?If there are, whether the Glu-ergic neurons participate in the RWIS reactions? In order to solvethese problems, we designed the following experiments.Male Wistar rats were divided into RWIS1h group (stress group) and control group(unstressed group). The processes of fasting, restrain water-immersion stress, heart perfusion andstripping out of the brain were in sequence dealt with in the rats. To evaluate the role ofglutamatergic neurons and GABAergic neurons in the mPFC during the RWIS, the singleimmunhistochemical method for collocations of the Fos, the glutamate decarboxylase (GAD) and the glutaminase (GLS) and the double immunohistochemical method for collocations of theFos with one of GAD and GLS were used. We separately counted the number of the Fos positiveneurons, GAD positive neurons (GABA positive neurons), GLS positive neurons (Glu positiveneurons), Fos+GAD positive neurons and Fos+GLS positive neurons in the PL and the IL of themPFC in rats.The results are as follows:1. In the RWIS1h group, the number of Fos positive neurons was significantly increased inboth sides of the PL and IL of mPFC. Fos positive neurons almost showed uniform distributionin the PL and IL. The enhancement of neuronal activity shows that the neurons in both sides ofthe PL and IL involved in RWIS and played a regulatory role.2. In both sides of PL, the number of GABAergic neurons in the RWIS group isrespectively1.08times and1.04times to that in control group, and the number of Fos+GADdouble-labeled neurons is respectively1.06times and1.27times.There are no significantdifferences between the two groups (P>0.05). These data suggest that GABAergic neurons inthe PL didn’t involve in the regulation of RWIS.3. In both sides of IL, the number of GABAergic neurons in the RWIS group is respectively1.33times and1.90times to that in control group, and the number of Fos+GAD double-labeledneurons is respectively1.33times and1.93times. The differences between the two groups arevery significant (P <0.05). These data suggest that GABAergic neurons in IL involved in theregulation of RWIS.4. In both sides of PL and IL, the number of glutamatergic neurons in RWIS group isrespectively1.06times (left PL),1.19times（right PL）,1.12times (left IL)and1.20times (rightIL)to that in control group, and the number of Fos+GLS neurons is respectively1.25times,1.12times,0.88times and1.00times. The differences between the two groups are not significant (P>0.25). These indicate that glutamatergic neurons in the PL and IL didn’t involve in theregulation of RWIS.