Effect Of Electrically Stimulating Saphenous Nerve On C-fos Gene Expression In Anterior Cingulate Gyrus Of Rats And Its Mechanism

Pain is one of the most common clinical symptoms, brings enormous agony to patients and has become a difficult problem of clinical treatment. Apparently, it has very important theoretical value and practical significance for study of algesia.For a long time, many scholars think that the anterior cingulate gyrus (ACG) plays an important role in reception of algesia, is an important center for nociceptive signal reception and modulation, and is involved in the emotional reactions of algesia. At present, great deals of data have been accumulated about ACG receiving and modulating somatic nociceptive information. Our laboratory has discovered that there are saphenous nerve (SN) representative area and somatic nociceptive neurons in ACG with intracellular recording method at the first time. But no studies have been done to examine which central neurotransmitter and gene take part in the process of ACG somatic nociception.Some reports show that c-fos proto-oncogene and the c-fos protein can be used as significant markers in study of nerve conduction pathway or brain function, and as pain markers of nerve center responsing to noxious stimulation. C-fos gene expression locations in central nervous system are usually the regions related to nociceptive information transfer, translation and integration. Study has discovered that during the neuron active procedure induced by periphery stimulation, c-fos gene is activated and express Fos protein. But no studies have been done to examine whether noxious electric stimulation to SN can cause signal transduction change in ACG neuron.Glutamic acid is the main excitatory neurotransmitter of brain and spinal cord, and displays postsynaptic effects through different receptors. Studies have discovered that noxious afferent signals cause increase in release of excitatory amino acids, especially glutamic acid of nerve centers and abnormal activation of their receptors. All types of glutamic acid receptors are involved in pain formation. But different glutamic acid receptors have different effects and mechanisms in formation of algesia. At present, whether somatic noxious stimulation can cause change of signal transduction in ACG neurons and the mechanism are not clear. It has very important theoretical value for exploitation of new pain-killer and analgesia, to elucidate whether somatic noxious stimulation can cause change of signal transduction in ACG neurons and the mechanism. Therefore, in the present study, immunohistochemistry methods were used to investigate effect of different time after electrically stimulating SN on c-fos gene expression in ACG neurons of rats, and the influence of morphine and glutamic acid receptor antagonist CNQX to c-fos gene expression in ACG neurons of rats induced by electrically stimulating SN, to examine whether somatic noxious stimulation can cause change of signal transduction in ACG neurons and the mechanism on the level of both neuron transmitter and gene, which could provide valuable data for the effect of ACG in algesia reception.60 male rats with weight from 230g to 270g were divided randomly into control groups and experimental groups in the present study. Experimental groups included 15 min, 30 min, 60 min, 120 min after electrically stimulating SN with 1.0mA; 10min after morphine subcutaneous injection followed by 30min after 1.0mA electric stimulations on SN; 10min after CNQX injection by caudal veins followed by 30min after 1.0mA electric stimulations on SN. Control groups included blank control group; experimental control group; 10min after normal saline subcutaneous injection followed by 30min after 1.0mA electric stimulations on SN;10min after normal saline injection by caudal veins followed by 30min after 1.0mA electric stimulations on SN. The Fos protein expression in ACG was examined by using Fos immunohistochemistry technique. Our study showed that compared with control groups, the ACG Fos protein expression of 15min after noxious electric stimulation on SN increased lightly, but there was no significant difference in integrated optical density (integrated OD) and percentage of positive cell area (P>0.05); there was significant difference in integrated OD and percentage of positive cell area in groups at 30min, 60min, 120min after nocuity electric stimulation on SN (P<0.05, P<0.01, P<0.05,respectively). At 30min after electric stimulation SN, Fos protein expression in ACG significantly increased, it reached its peak 60min after stimulating SN and started to decrease 120min after stimulating SN. So we presumed that nocuity electric stimulating SN could increase the expression of Fos protein in ACG. This expression was time-dependent, increased obviously at 30min after nocuity electric stimulation SN, more obviously at 60min and decreased at 120min after the stimulation. In addition,our study discovered that Fos protein expression in ACG increased lightly at 10min after morphine subcutaneous injection followed by 30min after 1.0mA stimulation on SN, but compared with control groups, there was no significant difference in integrated OD and percentage of positive cell area (P>0.05). Compared with control groups, there was significant difference in integrated OD and percentage of positive cell area (P<0.05), Fos protein expression in ACG increased obviously at 10min after normal saline subcutaneous injection followed by 30min after 1.0mA stimulation on SN. The result indicated that morphine inhibited the Fos protein expression in ACG caused by nocuity electric stimulation on SN. The study provided the first data and suggested that the contralateral ACG is one of the representative areas of the SN afferent pathway, and ACG can receive the nociceptive information afferent by SN with Fos immunohistochemistry technique.In the present study, although Fos protein expression in ACG increased lightly at 10min after CNQX (1mg/kg body weight) caudal vena injection followed by 30min after nocuity electric stimulation on SN, there was no significant difference in integrated OD and percentage of positive cell area compared with control groups (P>0.05). The expression of Fos protein in ACG increased obviously at 10min after normal saline caudal vena injection followed by 30min after nocuity electric stimulation on SN (P<0.05). There was significant difference in integrated OD and percentage of positive cell area compared with control groups. The obvious increase in expression of Fos protein in ACG induced by nocuity electric stimulation on SN was antagonized by CNQX, which suggested that AMPA/Kainate receptors take part in the course of increase in Fos protein expression in ACG induced by nocuity electric stimulation on SN.