In vitro recordings of afferent fibres with receptive fields in the serosa, muscle and mucosa of rat colon

1. Colonic afferent fibres were recorded using a novel in vitro preparation . Fibres with endings in the colonic mucosa are described, along with those in muscle and serosa, and their responses to a range of mechanical and che mical luminal stimuli. 2. Mechanical stimuli were applied to the tissue, which included stretch, b lunt probing of the mucosa and stroking of the mucosa with von Frey hairs ( 10-1000 mg). Chemical stimuli were applied into a ring that was placed over the mechanoreceptive field of the fibre; these were distilled water, 154 a nd 308 mM NaCl, 100 mu M capsaicin, 50 mM HCl, and undiluted and 50 % ferre t bile. 3. Recordings were made from 52 fibres, 12 of which showed characteristics of having endings in the mucosa. Mucosal afferents were sensitive to a 10 m g von Frey hair and were generally chemosensitive to greater than or equal to 1 chemical stimulus. 4. Ten fibres showed characteristics of having receptive fields in the musc ular layer. These fibres responded readily to circumferential stretch, as w ell as to blunt probing. 5. Twenty-seven fibres showed characteristics of having endings in the sero sal layer. They adapted rapidly to circumferential stretch and responded to blunt probing of the serosa. Fifteen of 19 serosal fibres tested also resp onded to luminal chemicals. 6. Three fibres were unresponsive to all mechanical stimuli but were recrui ted by chemical stimuli. 7. This is the first characterization of colonic afferent fibres using an i n vitro method and the first documentation of afferent fibres with their en dings in the mucosa of the colon. These fibres are likely to be important i n aspects of colonic sensation and reflex control.