The effects of trinitrobenzene sulfonic acid (TNBS)-induced inflammation on specialized, low-threshold, slowly adapting rectal mechanoreceptors were investigated in the guinea pig. Under isoflurane anesthesia, 300 microl saline or TNBS (15 mg/ml) in 30% ethanol was instilled 7 cm from the anal sphincter. Six or 30 days later, single unit extracellular recordings were made from rectal nerve trunks in flat-sheet in vitro preparations attached to a mechanical tissue stretcher. TNBS treatment caused macroscopic ulceration of the rectal mucosa at 6 days, which fully resolved by 30 days. Muscle contractility was unaffected by TNBS treatment. At 6 days posttreatment, responses of low-threshold rectal mechanoreceptors to circumferential stretch were increased, and the proportion of afferents responding with von Frey hair thresholds