Intraganglionic laminar endings are mechano-transduction sites of vagal tension receptors in the guinea-pig stomach

1. Distension-sensitive vagal afferent fibres from the cardiac region of th e guinea-pig stomach were recorded extracellularly, then filled with biotin amide, using an anterograde tracing technique. 2. Most of the stretch-sensitive units of the guinea-pig stomach (41 out of 47; number of animals N = 26) had low thresholds (less than 1 mm) to circu mferential stretch and showed slow adaptation. Twenty of these units fired spontaneously under resting conditions (mean: 1.9 +/- 0.3 Hz, n = 20, N = 1 4). 3. Adaptation of firing during slow or maintained stretch correlated closel y with accommodation of intramural tension, but tension-independent adaptat ion was also present. 4. Nicardipine (3 muM) with hyoscine (3 muM) reduced stretch-evoked firing of gastric vagal afferents, by inhibiting smooth muscle contraction. Gadoli nium (1 mM) blocked distension-evoked firing. 5. Focal stimulation of the stomach muscle wall with a von Frey hair (0.4 m N) identified one to six punctate receptive fields in each low threshold va gal distension-sensitive afferent. These were marked on the serosal surface of the stomach wall. 6. Anterograde filling of recorded nerve trunks revealed intraganglionic la minar endings (IGLEs) within 142 +/- 34 mum (n = 38; N = 10) of marked rece ptive fields. The mean distance from randomly generated sites to the neares t IGLE was significantly greater (1500 +/- 48 mum, n = 380, N = 10, P < 0.0 001). Viscerofugal nerve cell bodies, intramuscular arrays and varicose axo ns were not associated with receptive fields. The results indicate that IGL Es are the mechanotransduction sites of low threshold, slowly adapting vaga l tension receptors in the guinea-pig upper stomach.