Colonic mechanoreceptor inputs to rat lumbo-sacral dorsal horn neurones: distribution, thresholds and chemosensory modulation

In order to better understand the central processing of visceral sensory in formation, we studied the responses of lumbo-sacral dorsal horn (L4-S1) neu rones to colonic stimuli in anaesthetized rats. Twenty-four neurones respon ded to distal colonic distension with a 2.5-cm balloon; six of these were t ested with proximal colonic distension, to which none responded. All neuron es tested responded to somatic non-noxious inputs (tail movement). Response s to colonic distension were excitatory (n=22) or inhibitory (n=2). Sixteen neurones responded at a threshold of 20 mmHg or less, five at 20-40 mmHg, and three at 40-80 mmHg, Three of 10 neurones tested showed increased respo nses to colonic distension after intraluminal perfusion with bile. Bile its elf did not evoke a response, We conclude that lumbo-sacral spinal neurones selectively receive mechanosensory inputs from the distal colon. Neurones respond at thresholds within and above the physiological range. Dorsal horn neurones receiving colonic mechanosensory inputs are not directly modulate d by chemosensory inputs, but their responsiveness to distension may be aug mented.