Properties of renobulbar afferent fibers in rats

Myelinated renobulbar sensory fibers project directly from the kidney to the dorsomedial medulla. They can be activated by punctate stimulation of the kidney. In these experiments we studied the physiological modality and the intrarenal locations of the receptors for renobulbar fibers. Renobulbar fibers were identified in recordings from the renal nerves of anesthetized rats. Although nonmyelinated renal afferent fibers were activated by increased intrarenal pressure and by chemical stimuli, no renobulbar fiber activated by punctate mechanical stimulation was activated by these other stimuli. Occasionally single fibers could be activated by punctate stimulation of two or more sites on the surface of the kidney, and responses from each site could be selectively blocked with a local anesthetic. Renobulbar fibers could be activated by electrical stimulation of discrete regions deep within the renal parenchyma. Increased intrarenal pressure increased the sensitivity of receptors to punctate stimulation but not to electrical stimulation of the kidney. We conclude that myelinated renal afferent fibers in the rat respond to external mechanical stimuli, lie deep within the renal parenchyma, and occasionally have more than one receptor.