Low and high frequency electroacupuncture at Hoku elicits a distinct mechanism to activate sympathetic nervous system in anesthetized rats

To address the effect of electroacupuncture (Ea) on autonomic nerve activity, the responses of rhythmic micturition contraction (RMC), urine excretion (UE), blood pressure (BP), renal sympathetic nerve activity (RNA) and pelvic parasympathetic nerve activity (PNA) to Ea were investigated in urethane-anesthetized rats. The acupoint Hoku (Li-4) was tested with two different stimulation frequencies (2 Hz and 20 Hz). Elongation of the RMC cycle and an increase in UE associated with the elevation of BP and RNA was elicited during Ea at Hoku. However, the pressor response induced by low frequency Ea (LFEa) was different from that by high frequency Ea (HFEa), i.e. a tonic effect was elicited by LFEa, while a phasic one was induced by HFEa. These results imply that: (1) Ea at Hoku may selectively activate the sympathetic, but not the parasympathetic nervous system, (2) Ea at Hoku with a different stimulation frequency may elicit a distinct mechanism to activate the sympathetic nervous system and (3) Ea at Hoku may ameliorate the hyperactive bladder in clinical therapy.