Download Participation of γ-Aminobutyric Acid Mechanism in the Nucleus

Participation of γ-Aminobutyric Acid Mechanism in the Nucleus Tractus Solitarius in
Electroacupuncture Reversal of Phenylbiguanide Induced Cardiopulmonary Depressor Effects
Megumi Sugimoto, Stephanie Chow
Mentors: Stephanie Tjen-a-looi, John Longhurst
In recent years, electroacupuncture (EA) has gained recognition as a safe and effective technique for treating
several cardiovascular complications, and studies have validated its ability in manipulating blood pressure and
heart rate. EA application at P5-6 acupoints stimulates the median nerves and reduces cardiopulmonary
depressor effect. It has been proven that parasympathetic cardiac neurons in the nucleus ambiguus (NAmb)
contribute to the EA reversal of bradycardia. It is also known that the γ-aminobutyric acid (GABA) system in
the NAmb is involved. NAmb is a nucleus that is subsequent to the nucleus tractus solitarius (NTS) and,
therefore, we hypothesized that GABAergic mechanism in the NTS also contributes to the reversal of
bradycardia and hypotension with EA. Phenylbiguanide (PBG) was intravenously injected into the right
atrium to establish hypotension and bradycardia in the feline model. Involvement of NTS in the PBGinduced cardiopulmonary depressor responses was also confirmed through the microinjection of kainic acid
(KA) into the NTS. Excitation of vagal afferents in anesthesized feline model was executed through repeated
injection of PBG with 10-minute intervals until consistent cardiovascular depressor response was observed.
EA applied at P5-6 acupoints for 30 minutes normalized the depressed blood pressure and heart rate.
GABAA receptors in the NTS were inhibited with an injection of gabazine. Blockade of the GABAergic
system in NTS eliminated the EA’s ability to normalize heart rate but did not affect blood pressure.
GABAergic mechanism in the NTS was proven to participate in the EA reversal of bradycardia but not
hypotension.