Stimulation of the nucleus locus coeruleus/subcoeruleus suppresses visceromotor responses to colorectal distention in the rat.
The aim of the present study was to examine whether the nucleus locus coeruleus/subcoeruleus (LC/SC) modulates visceromotor function. In the present study, an electromyogram (EMG) of the external abdominal oblique muscle evoked by colorectal distention was measured as a visceromotor reflex response, and inhibitory effects of LC/SC stimulation were estimated by the decrease of EMG activity. Under halothane anesthesia (1% in air), graded colorectal distentions (30, 60 or 80 mmHg) were produced by inflating a balloon inside the descending colon and rectum. A bipolar EMG electrode was inserted into the left external abdominal oblique muscle to record the EMG response to colorectal distention. Colorectal distention at a pressure of 30 mmHg did not evoke any EMG activity in the external abdominal oblique muscle in all rats tested. Electrical stimulation of the LC/SC (30, 50 and 70 microA, 100 Hz, 0.1 ms pulses) reduced EMG responses evoked by colorectal distention to 60 and 80 mmHg. LC/SC stimulation was effective both ipsilaterally and contralaterally indicating a bilateral effect. EMG responses decreased with an increase of LC/SC stimulation intensity. Following recordings of the inhibitory effects of LC/SC stimulation, lesions of the LC/SC ipsilateral to the EMG recording site were induced; 1 h after lesions the inhibitory effects of LC/SC stimulation were examined again. LC/SC stimulation did not reduce the EMG responses when LC/SC stimulation was applied to the ipsilateral LC/SC, whereas EMG responses were observed by stimulation of the intact LC/SC contralateral to the EMG recording site. From lesion experiments, it could be considered that suppression of the visceromotor response to colorectal distention is due to activation of the LC/SC. The results suggest that the visceromotor function is under the control of the centrifugal pathways from the LC/SC.
Tsuruoka
Masayoshi
M
Department of Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan. masa@dent.showa-u.ac.jp
Maeda
Masako
M
Inoue
Tomio
T
D000009:Abdominal Muscles / Q000294:innervation / Q000502:physiology*; D000818:Animals; D003106:Colon / Q000502:physiology*; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012007:Rectum / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D014781:Viscera / Q000502:physiology