[CaMKIIα-positive excitatory hippocampal neurons mediate "Zusanli" (ST36) electroacupuncture induced increase of gastric function in mice].

OBJECTIVE: To observe the effect of electroacupuncture (EA) stimulation of "Zusanli"(ST36)on gastric function (food consumption and gastric emptying rate) and excitability of hippocampal glutamatergic neurons in mice, so as to explore its mechanism underlying enhancing gastrointestinal function. METHODS: The present study includes 2 parts. 1) C57BL/6 mice were randomly divided into normal and EA groups (n=12 in each group). EA (2 Hz/15 Hz, 1-3 mA) was applied to bilateral ST36 for 20 min, once daily for 7 days. In each group, 6 mice were used to measure the food consumption and gastric emptying rate, and the other 6 mice used to detect the hippocampal glutamate secretion content by using in vivo microdialysis and high performance liquid chromatography. 2) Thirty CaMKIIα-Cre mice received microinjection of a recombinant adeno-associated viral vector containing inhibitory designer receptor exclusively activated by a designer drug (DREADD, AAV-DIO-hM4Di-eYFP) into the hippocampus. Twenty-one days later, 3 mice were selected to observe the expression of eYFP-labeled hM4Di by immunohistochemistry, and 15 mice employed to observe the electrical activities of hM4Di-eYFP positive neurons exposed in chemogenetic activating drug Clozapine N-oxide (CNO) perfusion conditions (n=3) and without CNO in the recording chamber (n=6 in the control and EA groups) by using whole cell patch clamp. The rest 12 CaMKII-Cre mice were equally randomized into AAV-DIO-hM4Di-eYFP+CNO group and AAV-DIO-hM4Di-eYFP+CNO+EA group, and CNO was given by intraperitoneal injection for observing the effect of EA on gastric function. RESULTS: 1) In C57BL/6 mice, compared with the normal group, the food consumption, gastric emptying rate, and the glutamate content in the hippocampus were obviously increased in the EA group (P<0.01). 2) In CaMKIIα-Cre mice, the hM4Di-eYFP positive neurons distributing in the hippocampus showed an obvious increase of firing rates in the EA group relevant to the control group (P<0.01), and a hyperdepolarization potential after application of CNO. No significant changes were found between the AAV-DIO-hM4Di-eYFP+CNO and AAV-DIO-hM4Di-eYFP+CNO+EA groups in the food consumption and gastric emptying rate (P>0.05), suggesting an elimination of EA effect after acute DREADD-mediated activation of the CaMKIIα-positive hippocampal excitatory neurons. CONCLUSION: EA at ST36 can promote food intake and gastric emptying in normal mice but not in CaMKIIα-Cre mice with activated hippocampal hM4Di receptors，suggesting a contribution of the CaMKIIα-positive hippocampal excitatory neurons (glutamatergic neurons in particular) to the enhanced gastrointestinal function of EA at ST36.