Rat: BrdU labeled cells per crypt in intestinal segments exposed to a capsaicin or a control solution.

<p>BrdU (50 mg/kg bwt) was given i.v. 2 h prior to removal of the intestinal segments. The number of labeled cells in 255 crypts in control (n = 5) and in 249 crypts in capsaicin segments (n = 5) were counted. Asterisk indicates statistical significance. Mean ± s.e.m. <b>Mouse: BrdU labeled cells per crypt in wild type or capsaicin receptor knock-out mice.</b> Five capsaicin receptor knock-out mice (−/−; 225 crypts) and in five wild type mice (WT; 215 crypts) were investigated. BrdU (100 mg/kg b.wt.) was administered i.p. 2 h before removal of the small intestine. Asterisk indicates statistical significance. Mean ± s.e.m.</p

The effect of neurotransmitter receptor antagonists on capsaicin evoked increase of thymidine kinase activity.

<p>The receptor antagonists tested were: Sendide (NK1 receptor antagonist); 8–37 α-GGRP (CGRP receptor antagonist); atropine (muscarinic receptor antagonist). Thymidine kinase activity is expressed in per cent of activity measured in control segments (no capsaicin). N = 6 for each antagonist experiments. Asterisks indicate statistical significance compared to control. Mean ± s.e.m.</p

BrdU labeling of the small intestine after i.v. administration.

<p>BrdU (50 mg/kg b.wt.), a thymidine analogue, was given 2 h prior to removing the intestine. The dark labeling by BrdU is exclusively located to the nuclei of intestinal crypt cells. Mayer's haematoxylin.</p

The localization of M5 muscarinic receptor immunoreactivity in intestinal crypts.

<p>The picture is photographed by confocal microscopy corresponding to a 4 µm thick section of the wall of the crypts. Hence, no crypt lumen is seen and the crypt cells are cross-sectioned. The left panel of the figure suggests that the M5 receptor is located to the plasma membrane of the crypt cells. Tissue sections exposed only to the secondary antibody did not exhibit any fluorescence (right panel).</p

Observations supporting the model of Figure 12.

<p>TS: this study.</p

Autoradiography of rat small intestine after giving tritiated thymidine i.v.

<p>The labeled compound (50 µCi ³H-methyl-thymidine) was administred 6 h prior to removing the intestine The left panel illustrates dark field microscopy of an autoradiogram showing radiolabeled cells (white spots) almost exclusively located in the epithelial layer of the crypts of Lieberkühn. To the right the same section is seen in light microscopy. Van Gieson.</p

The localization of M3 muscarinic receptor immunoreactivity on intestinal stem cells.

<p>The stem cells, indicated by arrows, are slender cells located between the Paneth cells (PC) at the very base of the crypts <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016295#pone.0016295-Barker1" target="_blank">[17]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016295#pone.0016295-Cheng1" target="_blank">[26]</a>. The left part of the figure indicates that the muscarinic receptor M3 is located to the plasma membrane of the presumed intestinal stem cells. The tissue section in the right panel was only exposed to the secondary antibody. Mayer's haematoxylin. CL  =  crypt lumen.</p

The effect of capsaicin on intestinal thymidine kinase activity after anesthetizing the mucosa with lidocaine.

<p>Thymidine kinase activity is expressed in per cent of activity measured in control segments (no capsaicin). Asterisks indicate statistical significance between the two groups of experiments (perfusion experiments, n = 8; non-perfusion experiments, n = 7). Mean ± s.e.m.</p

Model of axon reflex control of cell renewal in the small intestine.

<p>The model is in part based on the findings of the present study (<i>cf. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016295#pone-0016295-t001" target="_blank">Table 1</a>) and is consistent with known types of neurons in the intestinal wall. It implies that the direct control of the stem/progenitor cells is exerted by a cholinergic neuron, which, in turn, is under the influence of an axon reflex releasing CGRP/SP/acetylcholine. Ach: acetylcholine; CGRP: calcitonin gene related peptide; SP: substance P; CNS: central nervous system.</p

The effect on intestinal thymidine kinase activity of exposing the intestinal mucosa to capsaicin (0.16 or 1.6 mM).

<p>Thymidine kinase activity is expressed in per cent of activity measured in control segments (no capsaicin). The experiments were performed using two types of preparations. In most experiments only the proximal ends of the segments were cannulated with plastic tubing and the intestinal segment was perfused by means of a pump at a rate of 20 µL per min (“perfusion experiments”; n = 6). In other experiments the distal ends were also provided with plastic tubing closed by plugs (“non-perfusion experiments”; n = 7). Asterisks indicate statistical significance. Mean ± s.e.m.</p