Single-unit and multiunit analyses of renorenal reflexes elicited by stimulation of renal chemoreceptors in the rat.

Stimulation of renal chemoreceptors, induced by backflow of concentrated urine into the renal pelvis, elicited a reflex increase in the rate of multiunit efferent renal nerve activity in rats. Ipsilateral stimulation increased the rate by 17.1 +/- 4.5%; contralateral stimulation increased the rate by 20.8 +/- 4.5%. Efferent activity returned toward control levels within the first minute following removal of the stimulus. The reflex responses were quantitatively similar in rats anesthetized with sodium pentobarbital or alpha-chloralose, but increased following complete transection of the spinal cord at C3. Studies of single efferent units indicated that responses to the stimuli were nonuniform. The majority of single units exhibited an increase in firing frequency during the stimulus; other units showed no change or, less frequently, a reduction in activity during the stimulus. Some postganglionic neurons projecting to the kidney were activated by stimuli applied to either kidney. It was concluded that stimulation of intrarenal chemoreceptors provokes bilateral excitatory renorenal reflexes in the rat. The observation of nonuniform responses among single units suggests that renal nerves contain a mixture of efferent fibers which may contact different targets in the kidney.