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Published on: December 22, 2016
Repetitive electroacupuncture causes prolonged increased met-enkephalin expression in the rVLM of conscious rats
Min Li1, Stephanie C Tjen-A-Looi, Zhi-Ling Guo
1Department of Medicine, School of Medicine, University of California, Irvine, 92697-4075, United States. mli4@uci.edu
Abstract:
Enkephalinergic neurons in the rostral ventrolateral medulla (rVLM), an important presympathetic region in the brainstem, are activated by 30 min of low frequency (2 Hz) electroacupuncture (EA) at acupoints P5-P6, which overlie the median nerves. To more closely model the clinical application of acupuncture, we administered EA for 30 min twice over a 72 h period to unsedated conscious rats to examine its prolonged action. We hypothesized that repetitive EA would increase preproenkephalin mRNA and met-enkephalin in the rVLM of unsedated conscious rats. Rats received either EA (1-4 mA, 0.5 ms, 2 Hz) or sham stimulation (needle placement without electrical stimulation) twice at P5-P6 acupoints bilaterally. Preproenkephalin mRNA and its peptide met-enkephalin in the rVLM were measured 24 or 48 h after the final EA or sham procedure. Relative ratios of preproenkephalin mRNA levels (normalized with the 18S housekeeping gene) were almost doubled at 24h compared to sham (6.1 ± 0.79 vs. 3.1 ± 0.47). Met-enkephalin measured in rVLM tissue pooled from several rats exposed to the same treatment was increased by repeated EA by 68% after 24h and 51% after 48h, relative to sham. These findings suggest that repeated application of EA in the conscious rats enhances transcription and translation of enkephalin in rVLM for days. Since opioids in the rVLM contribute importantly to the action of EA on sympathetic outflow, this mechanism may contribute to the prolonged action of acupuncture on elevated blood pressure in patients.
Insights
Repeated electroacupuncture (EA) in conscious rats significantly increased enkephalin levels in the brainstem
Area of Science:
- Neuroscience
- Integrative and Complementary Medicine
- Physiology
Background:
- Enkephalinergic neurons in the rostral ventrolateral medulla (rVLM) are crucial for sympathetic regulation.
- Electroacupuncture (EA) at P5-P6 acupoints activates these neurons.
- Previous studies show acute EA effects, but prolonged actions need further investigation.
Purpose of the Study:
- To investigate the prolonged effects of repeated electroacupuncture (EA) on enkephalin expression in the rVLM of conscious rats.
- To determine if repetitive EA enhances preproenkephalin mRNA and met-enkephalin levels in the rVLM.
- To model clinical acupuncture application more closely by using repeated, prolonged stimulation in unsedated animals.
Main Methods:
- Conscious rats received bilateral EA (2 Hz, 1-4 mA, 0.5 ms) or sham stimulation at P5-P6 acupoints twice over 72 hours.
- Preproenkephalin mRNA and met-enkephalin levels in the rVLM were quantified 24 or 48 hours after the final stimulation.
- mRNA levels were normalized to the 18S housekeeping gene.
Main Results:
- Repeated EA nearly doubled preproenkephalin mRNA levels in the rVLM at 24 hours post-stimulation compared to sham.
- Met-enkephalin peptide levels in the rVLM increased by 68% at 24 hours and 51% at 48 hours after repeated EA, relative to sham.
- These increases indicate enhanced enkephalin synthesis and release following repetitive EA.
Conclusions:
- Repeated electroacupuncture enhances both the transcription and translation of enkephalin in the rat rVLM for several days.
- This sustained increase in enkephalin, an endogenous opioid, in the rVLM may underlie the prolonged effects of acupuncture on sympathetic outflow and blood pressure.
- The findings support a neurobiological mechanism for the long-term benefits of acupuncture in managing hypertension.