Inflammation enhances reflex and spinal neuron responses to noxious visceral stimulation in rats

To improve understanding of sensory processes related to visceral inflammat ion, the effect of turpentine-induced inflammation on reflex (cardiovascula r/visceromotor) and extracellularly recorded lumbosacral dorsal horn neuron responses to colorectal distension (CRD) was investigated. A 25% solution of turpentine, applied to the colorectal mucosa, produced inflammation, dec reased compliance of the colonic wall, and enhanced reflex responses in una nesthetized rats within 2-6 h. At 24 h posttreatment, pressor responses to CRD (80 mmHg, 20 s) were 20% greater, and intraluminal pressures needed to evoke visceromotor reflexes were 30% lower than controls. Parallel electrop hysiological experiments in spinal cord-transected, decerebrate rats demons trated that two neuronal subgroups excited by CRD were differentially affec ted by turpentine administered 24 h before testing. During CRD, abrupt neur ons were 70% less active and sustained neurons were 25% more active than si milar neurons in controls. In summary, reflex and neuronal subgroup (sustai ned neurons) responses to CRD were both potentiated by chemical inflammatio n. This suggests that the neurophysiological basis for inflammation-induced increases in reflex responses to CRD is increased activity of this neurona l subgroup.