Roles of the ventrolateral medulla in clonidine-induced cardiovascular effects of rats

Objective:To investigate the roles of the ventrolateral medulla (VLM) in mediating the cardiovascular response of clonidine.Methods: In urethane anesthetized SD rats,the responses of locally administrated clonidine within the caudal ventrolateral medulla (CVLM) and the rostral ventrolateral medulla (RVLM) to the cardiovascular activities were observed by methods of microinjection and extracellular recording.Results: Unilateral microinjection of clonidine (5 nmol/100 nl) into the CVLM not only produced significant ( P 0.01, n =10) increases in both arterial blood pressure (AP) and heart rate (HR),but also significantly increased the firing rate of the ipsilateral RVLM barosensitive neurons ( P 0.01, n =8).In addition,unilateral microinjection of clonidine (5 nmol/100 nl, n =9) into the RVLM significantly decreased in both AP and HR ( P 0.01).Conclusion: CVLM and RVLM might play different roles in the cardiovascular effects of clonidine.