Volume 125, Issue 3, Pages 786-794 (September 2003) Rectal intraganglionic laminar endings are transduction sites of extrinsic mechanoreceptors in the guinea pig rectum  Penny A Lynn, Catharina Olsson, Vladimir Zagorodnyuk, Marcello Costa, Simon J.H Brookes  Gastroenterology  Volume 125, Issue 3, Pages 786-794 (September 2003) DOI: 10.1016/S0016-5085(03)01050-3

Figure 1 Response of a rectal afferent to rapid circumferential stretch. (A ) Smooth muscle contraction and associated bursts of firing were evoked by stretch (1, 2, 3, 4 mm at 5 mm/s). After an initial contraction, associated with a burst of firing, muscle tension accommodated and firing adapted. Spontaneous contractions in the tissue also evoked bursts of firing (arrow). (B) Grouped data showing responses to imposed stretches lasting 10 seconds, averaged per second. Responses for 1-mm (♦), 2-mm (□), 3-mm (▴) and 4-mm (○) stretches are shown (n = 14, N = 10). Firing followed tension curves more closely than length curves, with a burst of firing during the contractile response and adaptation of firing during accommodation. Gastroenterology 2003 125, 786-794DOI: (10.1016/S0016-5085(03)01050-3)

Figure 2 Response of a rectal afferent to 4-mm stretch at different rates. (A ) In response to rapid stretch (4 mm, at 5 mm/s for 10 seconds), a burst of firing is evoked during the evoked contraction. (B) During slow stretch (20 μm/s), less tension is developed, and firing is correspondingly less. (C ) Symmetrical stretch over the same distance (at 100 μm/s) evoked afferent activity on the rising phase that stopped at the onset of the falling phase when the muscle showed accommodation. Gastroenterology 2003 125, 786-794DOI: (10.1016/S0016-5085(03)01050-3)

Figure 3 Identification of filled structures associated with rectal afferent hot spots. (A ) Low-magnification photomontage shows a biotinamide-filled rectal nerve trunk giving rise to branching varicose fibers in myenteric ganglia. Thirteen hot spots were marked with carbon and numbered. (B) The responses to a von Frey hair (0.4 mN; arrows) at hot spots 5, 8, and 10 are shown, with superimposed spikes below, showing that they all came from the same afferent fiber. Gastroenterology 2003 125, 786-794DOI: (10.1016/S0016-5085(03)01050-3)

Figure 4 Biotinamide fill of a recorded rectal nerve trunk. A-C show the correlation between hot spots (numbers as in Figure 3) and rectal intraganglionic laminar endings (rIGLEs). Bright field images of carbon marks were inverted and combined with fluorescence images. Ai: An rIGLE (∗) is located close to a hot spot. Aii: higher magnification of the same rIGLE . Bi: Two rIGLEs (∗,#) in the same myenteric ganglion emanate from the same axon, shown at higher magnification in Bii and Biii. Ci: One rIGLE (∗) coincides with the hot spot (Ci), and a second rIGLE (#, Cii) is seen in a neighboring ganglion. (D) Typical example of non-lamellar, varicose nerve fibers surrounding unlabeled myenteric nerve cell bodies. (E ) Biotinamide-labeled viscerofugal nerve cell body in a myenteric ganglion. ∗, # Show corresponding points on adjacent images. (Bars = 50 μm.) Gastroenterology 2003 125, 786-794DOI: (10.1016/S0016-5085(03)01050-3)

Figure 5 Rectal IGLEs in a preparation in which mechanical stimulation with von Frey hairs was minimized (0.08 mN stimulus). (A ) Montage shows a filled rectal nerve trunk giving rise to extensive branching of varicose axons in myenteric ganglia. Hot spots marked with carbon particles are visible. Two sites (hot spot 5 and 8) are shown at higher magnification, revealing the delicate lamellar structure of their endings. Gastroenterology 2003 125, 786-794DOI: (10.1016/S0016-5085(03)01050-3)

Figure 6 Responses of mechanosensitive afferents in distal colon. (A ) Brief phasic firing was evoked at the onset of circumferential stretch (4 mm at 5 mm/s, 10 seconds) and by a von Frey hair (0.09 mN). (B) Pooled data showed a smaller total number of spikes evoked by 1–4-mm stretches (5 mm/s, for 10 seconds) in colon (n = 6) compared with rectum (n = 14). Gastroenterology 2003 125, 786-794DOI: (10.1016/S0016-5085(03)01050-3)