Tonic and baroreflex effects on arterial pressure and ventilation of pentobarbital and nicotine on the rat ventral medullary surface

Unilateral aortic depressor nerve stimulation caused depression of arterial pressure (baropressure reflex) and ventilation (baro-ventilatory reflex) in urethane-anesthetized, spontaneously breathing Sprague-Dawley rats. Application of sodium pentobarbital to the ventral medullary surface (VMS) depressed baseline arterial pressure and ventilation, and attenuated the baro-pressure reflex, but not the baro-ventilatory reflex. Application of nicotine on the VMS decreased baseline arterial pressure and increased ventilation, but left both baro-pressure and baro-ventilatory reflexes unaltered. The results suggest that some of the structures that affect vasomotor tone may not be involved in the baroreflex inhibition of arterial pressure. Additionally, neither the neural structures near the VMS which modulate CO 2 control of ventilation, nor those that affect tonic control of vasomotor tone are likely to be significantly involved in the baro-ventilatory reflex.