Although it is recognized that im idazoline receptors play an im portant role in the central regulation of cardio- vascular activities,little is known about their role in the caudal ventrolateral m edulla.In m ale Spr...Although it is recognized that im idazoline receptors play an im portant role in the central regulation of cardio- vascular activities,little is known about their role in the caudal ventrolateral m edulla.In m ale Sprague- Dawley rats anes- thetized with urethane,we used antagonists of I1 - imidazoline receptor orα2 - adrenoceptor to assess the function of these recep- tors in the caudal ventrolateral m edulla in controlling the cardiovascular effects of clonidine.U nilateral microinjection of cloni- dine(6 nmol/ 5 0 nl) into the caudal ventrolateral m edulla significantly(P<0 .0 1 ) increased blood pressure and the discharge of the rostral ventrolateral medulla presym pathetic neurons,while heart rate remained unchanged.Microinjection of yohim - bine(a selectiveα2 - adrenoceptor antagonist,5 0 0 pm ol/ 5 0 nl) into the caudal ventrolateral medulla did notm odify blood pres- sure,heart rate,or the discharge of the rostral ventrolateral m edulla presym pathetic neurons,and failed to attenuate the local caudal ventrolateral m edulla clonidine- induced blood pressure elevation.However,unilateral microinjection of idazoxan (a mixed antagonist of imidazoline receptor andα2 - adrenoceptor,2 nmol/ 5 0 nl) into the caudal ventrolateral medulla signifi- cantly(P<0 .0 1 ) decreased m ean arterial pressure,heartrate,and the discharge of the rostral ventrolateral medulla presym - pathetic neurons,and completely abolished the pressor effect of clonidine.In addition,bilateral microinjection of idazoxan(4 nmol in1 0 0 nl for each side) into the caudal ventrolateral medulla effectively (P<0 .0 1 ) blocked the depressor effects of clonidine administered intravenously(5 and5 0 μg/ kg) .These results confirm that I1 - imidazoline receptors within the caudal ventrolateral medulla are involved inmaintaining the tonic cardiovascular activities and in the pressor effect of clonidine in the caudal ventrolateral medulla.In addition,itseem s that the caudal ventrolateral medulla plays an im portant role in the antihy- pertensive effects of systemically administered clonidine in展开更多
文摘Although it is recognized that im idazoline receptors play an im portant role in the central regulation of cardio- vascular activities,little is known about their role in the caudal ventrolateral m edulla.In m ale Sprague- Dawley rats anes- thetized with urethane,we used antagonists of I1 - imidazoline receptor orα2 - adrenoceptor to assess the function of these recep- tors in the caudal ventrolateral m edulla in controlling the cardiovascular effects of clonidine.U nilateral microinjection of cloni- dine(6 nmol/ 5 0 nl) into the caudal ventrolateral m edulla significantly(P<0 .0 1 ) increased blood pressure and the discharge of the rostral ventrolateral medulla presym pathetic neurons,while heart rate remained unchanged.Microinjection of yohim - bine(a selectiveα2 - adrenoceptor antagonist,5 0 0 pm ol/ 5 0 nl) into the caudal ventrolateral medulla did notm odify blood pres- sure,heart rate,or the discharge of the rostral ventrolateral m edulla presym pathetic neurons,and failed to attenuate the local caudal ventrolateral m edulla clonidine- induced blood pressure elevation.However,unilateral microinjection of idazoxan (a mixed antagonist of imidazoline receptor andα2 - adrenoceptor,2 nmol/ 5 0 nl) into the caudal ventrolateral medulla signifi- cantly(P<0 .0 1 ) decreased m ean arterial pressure,heartrate,and the discharge of the rostral ventrolateral medulla presym - pathetic neurons,and completely abolished the pressor effect of clonidine.In addition,bilateral microinjection of idazoxan(4 nmol in1 0 0 nl for each side) into the caudal ventrolateral medulla effectively (P<0 .0 1 ) blocked the depressor effects of clonidine administered intravenously(5 and5 0 μg/ kg) .These results confirm that I1 - imidazoline receptors within the caudal ventrolateral medulla are involved inmaintaining the tonic cardiovascular activities and in the pressor effect of clonidine in the caudal ventrolateral medulla.In addition,itseem s that the caudal ventrolateral medulla plays an im portant role in the antihy- pertensive effects of systemically administered clonidine in
