Bowditch Lecture. Renal afferent inputs to ascending spinal pathways

Area of Science:

• Neuroscience
• Renal Physiology
• Pain Research

Background:

• Renal afferent fibers, including mechanoreceptors and chemoreceptors, play crucial roles in renorenal reflexes, cardiovascular control, and renal pain.
• While most renal afferent fibers enter the spinal cord, their functions are significantly influenced by supraspinal pathways.
• Recent research suggests a potential role for renal afferent fibers in regulating vasopressin secretion.

Purpose of the Study:

• To characterize spinal neurons that relay renal sensory information to the brain.
• To elucidate the pathways and mechanisms by which renal afferent signals are processed within the central nervous system.
• To investigate the coding of different renal receptor populations within the spinal cord.

Main Methods:

• Electrophysiological recordings in cats and monkeys.
• Stimulation of renal A delta and C fibers.
• Occlusion of the ureteropelvic junction and renal vein to activate mechanoreceptors.
• Recording neuronal responses to renal nerve stimulation and changes in renal vein pressure.

Main Results:

• Identified feline spinal neurons (L2-T11) projecting to the brainstem in response to renal A delta and C fiber input.
• Demonstrated that primate spinothalamic neurons (L3-T10) respond to renal nerve stimulation, with predominantly excitatory responses.
• Observed differential localization of spinal neurons responding to various renal occlusions, suggesting a coding mechanism for distinct receptor inputs.
• Found that distention of the renal pelvis strongly activates primate spinothalamic neurons, encoding noxious pressures relevant to renal pain.

Conclusions:

• Spinal neurons are critical relays for transmitting renal sensory information, including noxious stimuli, to supraspinal centers.
• The differential organization of spinal neurons suggests a sophisticated coding of diverse renal afferent signals.
• These findings contribute to understanding the neural basis of renorenal reflexes and renal pain mechanisms.