Abstract
Stressful sensory input results in an immediate decrease in motor activity under certain conditions in rats. Although this acute response has long been recognized as "freezing behaviour", sympathetic response during this behaviour remains unknown. In the present study, we measured renal (RSNA) and lumbar (LSNA) sympathetic nerve activity simultaneously during loud noise exposure to study whether sympathetic outflows may be controlled differently during freezing behaviour in conscious rats. Wistar male rats were instrumented chronically with electrodes for the measurements of RSNA, LSNA, electroencephalogram, electrocardiogram and electromyogram, and catheters for the measurements of systemic arterial and central venous pressures. At least three days after the surgery, rats were exposed to white noise with 90 decibel (dB) over 10 min following 10 min control period. RSNA increased immediately after onset of the noise exposure and remained high level throughout the 10 min exposing period. By contrast to the RSNA response, LSNA did not change significantly throughout the experimental period. Heart rate decreased immediately after onset of the noise exposure, then it stated to recover gradually but did not reach the control level. Systemic arterial pressure showed a transient and small increase at the onset of the noise exposure but it returned to the control level thereafter. The present study demonstrated that RSNA and LSNA were differently regulated during freezing behaviour in rats. [J Physiol Sci. 2006;56 Suppl:S205]
