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1 Medicine, University of California Irvine, Irvine, California, United States
2 Medicine, University of California, Irvine, Irvine, California, United States
3 Department of Medicine, University of California, Irvine, Irvine, California, United States
4 Departments of Medicine, Physiology and Biophysics, University of California, Irvine, Irvine, California, United States
* To whom correspondence should be addressed. E-mail: wzhou2{at}uci.edu.
Visceral sympathoexcitatory reflexes induced by stimulation of the gallbladder with bradykinin (BK) are attenuated by electroacupuncture (EA) at Neiguan-Jianshi (P 5-6) acupoints located over the median nerve. Previous studies have shown that neurons in the rostral ventral lateral medulla (rVLM) receive convergent input from visceral organs and somatic nerves (activated by EA). Glutamate (Glu) is an important excitatory neurotransmitter in the rVLM in processing visceral sympathoexcitatory cardiovascular reflexes. In the present study, we determined the relationship between EA-mediated opioidergic-modulation of visceral cardiovascular responses and glutamate. Reflex cardiovascular responses were evoked by application of BK on the gallbladder before and after EA in anesthetized cats. Glutamate concentrations [Glu] were measured by HPLC from samples collected by microdialysis probe(s) inserted unilaterally or bilaterally into the rVLM. BK-induced reflex responses and [Glu] were attenuated by 45% and 70%, respectively following 30 min of EA (n=6). EA alone did not change [Glu] in the rVLM (n=6, P > 0.05). However, microdialysis of naloxone (100 mM) into the rVLM reversed acupuncture-related inhibition of blood pressure and [Glu] (n=5). Immunohistochemical visualization showed that 
-opioid receptors co-localized and were in close apposition to perikarya and processes of rVLM neurons double-labeled with vesicular glutamate transporter 3 and c-Fos following gallbladder stimulation with BK. These data suggest that EA attenuates BK-induced visceral sympathoexcitatory reflexes through opioid-mediated inhibition of glutamate's action in the rVLM.
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