Dependence of sympathetic vasomotor tone on bilateral inputs from the rostral ventrolateral medulla in the rabbit: role of baroreceptor reflexes.
A unilateral microinjection of muscimol into the pressor region in the rostral ventrolateral medulla (RVLM) of anaesthetised baroreceptor-denervated rabbits resulted in large and sustained decreases in mean arterial pressure, renal sympathetic nerve activity and heart rate (maximal decreases of 41 +/- 4 mmHg, 64 +/- 3%, and 59 +/- 8 beats/min, respectively). Subsequently, muscimol microinjection into the contralateral RVLM pressor region resulted in further but much smaller decreases in these variables. In contrast, it is well established that in baro-intact animals unilateral inactivation of the RVLM pressor region has little effect on resting sympathetic activity or arterial pressure - bilateral inactivation is required to produce large and sustained decreases. The results of the present study indicate that the baroreceptor reflex plays a crucial role in maintaining resting sympathetic vasomotor activity under circumstances in which the activity of RVLM presympathetic neurons is partially impaired.
Horiuchi
J
J
Department of Physiology and Institute for Biomedical Research, University of Sydney, New South Wales, Australia. joujiho@physiol.usyd.edu.au
Dampney
R A
RA
D000818:Animals; D001158:Arteries / Q000294:innervation; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D006224:Cricetinae; D003714:Denervation; D005260:Female; D006321:Heart / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D007668:Kidney / Q000187:drug effects / Q000294:innervation; D008168:Lung / Q000294:innervation; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D009118:Muscimol / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology*; D011817:Rabbits; D012018:Reflex / Q000187:drug effects / Q000502:physiology*
D009118:Muscimol