Involvement of I(1)-imidazoline receptors in baroreceptor reflex in the caudal ventrolateral medulla of rats.
There is ample evidence to show the existence of center I(1)-imidazoline receptors that are involved in the regulation of cardiovascular activities. The purpose of this study was to examine the possible role of I(1)-imidazoline receptors and alpha(2)-adrenoceptors within the caudal ventrolateral medulla (CVLM) in mediating the baroreceptor reflex in anesthetized rats. Unilateral microinjection of idazoxan (2 nmol in 50 nl), a mixed antagonist of I(1)-imidazoline receptors and alpha(2)-adrenoceptors, into the CVLM significantly (P<0.01) decreased blood pressure (BP), heart rate (HR), and the firing rate of presympathetic neurons in the rostral ventrolateral medulla (RVLM) by 21+/-6 mmHg, 25+/-5 beats per min and 3.5+/-0.9 spikes/s, respectively. Moreover, unilateral injection of idazoxan into the CVLM significantly (P<0.01) reduced the inhibitory responses of the ipsilateral RVLM presympathetic neurons evoked by stimulation of aortic nerve and elevation of BP, and partially inhibited the neuronal cardiac cycle-related rhythm. Depressor responses evoked by aortic nerve stimulation were significantly (P<0.01) attenuated 10 and 20 min after bilateral microinjection of idazoxan (2 nmol in 50 nl for each side) into the CVLM (-20+/-4 and -30+/-4 vs. -40+/-1 mmHg). However, injection of yohimbine (500 pmol in 50 nl), a selective alpha(2)-adrenoceptor antagonist, into the CVLM did not affect the resting cardiovascular activities and baroreceptor reflex. It is concluded that the CVLM I(1)-imidazoline receptors are involved in maintenance of tonic cardiovascular activities and transmission of the baroreceptor reflex.
Wang
Wei-Zhong
WZ
Department of Physiology, Second Military Medical University, 800 Xiang-Yin Road, Shanghai 200433, China. wwz1968@hotmail.com
Yuan
Wen-Jun
WJ
Yang
Jun
J
Wang
Jian-Wen
JW
Tang
Chao-Shu
CS
Su
Ding-Feng
DF
D000200:Action Potentials / Q000187:drug effects; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects; D004558:Electric Stimulation; D004562:Electrocardiography / Q000187:drug effects; D004594:Electrophysiology; D018698:Glutamic Acid / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000502:physiology; D019329:Idazoxan / Q000494:pharmacology; D054755:Imidazoline Receptors; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D008845:Microinjections; D010275:Parasympathetic Nervous System / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology; D011955:Receptors, Drug / Q000037:antagonists & inhibitors / Q000502:physiology*; D013238:Stereotaxic Techniques; D009435:Synaptic Transmission / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D054755:Imidazoline Receptors; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug; D015016:Yohimbine; D018698:Glutamic Acid; D019329:Idazoxan