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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 α 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 α 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 and (-30±4) vs (-40±1) mmHg]
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 α 2 adrenoceptors within the caudal ventrolateral medulla ( CVLM) in mediating the baroreceptor reflex in anesthetized rats. Underlying microinjection of idazoxan (2 nmol in 50 nl), a mixed antagonist of I1 imidazoline receptors and [alpha] 2 adrenoceptors, into the CVLM significantly (P <0.01) decreased blood pressure ), 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. More over, 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 neuron al 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 and (-30 ± 4) vs (-40 ± 1) mmHg]