Differential role of tachykinin NK3 receptors on cholinergic excitatory neurotransmission in the mouse stomach and small intestine

Abstract

Background and purpose: Tachykinin NK(3) receptors are widely expressed in the mouse gastrointestinal tract but their functional role in enteric neuromuscular transmission remains unstudied in this species. We investigated the involvement of NK(3) receptors in cholinergic neurotransmission in the mouse stomach and small intestine.

Experimental approach: Muscle strips of the mouse gastric fundus and ileum were mounted in organ baths for tension recordings. Effects of NK(3) agonists and antagonists were studied on contractions to EFS of enteric nerves and to carbachol.

Key results: EFS induced frequency-dependent tetrodotoxin-sensitive contractions, which were abolished by atropine. The cholinergic contractions to EFS in the stomach were enhanced by the NK(3) antagonist SR142801, but not affected by the NK(3) agonist senktide or neurokinin B. The cholinergic contractions to EFS in the small intestine were not affected by SR142801, but dose-dependently inhibited by senktide and neurokinin B. This inhibitory effect was prevented by SR142801 but not by hexamethonium. SR142801, senktide or neurokinin B did not induce any response per se in the stomach and small intestine and did not affect contractions to carbachol.

Conclusions and implications: NK(3) receptors modulate cholinergic neurotransmission differently in the mouse stomach and small intestine. Blockade of NK(3) receptors enhanced cholinergic transmission in the stomach but not in the intestine. Activation of NK(3) receptors inhibited cholinergic transmission in the small intestine but not in the stomach. This indicates a physiological role for NK(3) receptors in mouse stomach contractility and a pathophysiological role in mouse intestinal contractility.

Figure 1

Typical experimental recordings of isolated muscle strips from the mouse gastric fundus (a–c) and ileum (d–f) showing cholinergic nerve-mediated contractions to electrical field stimulation (0.25–4 Hz) in control conditions (saline) and after incubation with 10 nM senktide (a and d), 100 nM neurokinin B (NKB; b and e) and 100 nM SR142801 (c and f). Horizontal bar represents scale of time (2 min) and vertical bar represents scale of force (5 mN). Stimulation trains for EFS were delivered at decreasing frequency as this results in more reproducible responses, especially at low-frequency stimulation (see Methods).

Figure 2

Frequency–response curves showing the cholinergic nerve-mediated contractions to electrical field stimulation (EFS) of muscle strips from the mouse gastric fundus. (a and b) show the effect of the NK₃ receptor agonist senktide (10 nM) and neurokinin B (NKB; 100 nM), respectively. (c) Shows the effect of the NK₃ receptor antagonist SR142801 (30–100 nM) on EFS-induced contractions. Results are expressed as mean±s.e.mean for six experiments. Student's t-test for paired observations did not show differences in the effect of senktide and NKB. ^*P⩽0.05, One-way ANOVA followed by Dunnett's post hoc test.

Figure 3

Frequency–response curves showing the cholinergic nerve-mediated contractions to electrical field stimulation (EFS) of muscle strips from the mouse ileum showing the effect of the NK₃ receptor agonist senktide (a) 0.1 nM, (b) 1 nM and (c) 10 nM, obtained in different muscle strips to avoid desensitization of NK₃ receptors. Results are expressed as mean±s.e.mean for six experiments. ^*P⩽0.05, Student's t-test for paired observations.

Figure 4

Frequency–response curves showing the cholinergic nerve-mediated contractions to electrical stimulation (EFS) of muscle strips from the mouse ileum showing the effect of neurokinin B (NKB; a) 1 nM, (b) 10 nM and (c) 100 nM, obtained in different muscle strips to avoid desensitization of NK₃ receptors. Results are expressed as mean±s.e.mean for five experiments. ^*P⩽0.05, Student's t-test for paired observations.

Figure 5

Frequency–response curves showing the cholinergic nerve-mediated contractions to electrical field stimulation (EFS) of muscle strips from the mouse ileum showing the effect of (a) SR142801 per se, (b) the effect of senktide in the presence of SR142801 and (c) the effect of neurokinin B (NKB) in the presence of SR142801. Results are expressed as mean±s.e.mean for five experiments. ^*P⩽0.05, Student's t-test for paired observations.

Figure 6

Frequency–response curves showing the cholinergic nerve-mediated contractions to electrical field stimulation (EFS) of muscle strips from the mouse ileum showing the effect of hexamethonium (hexa) and (a) hexamethonium plus senktide and (b) hexamethonium plus neurokinin B (NKB). Results are expressed as mean±s.e.mean for four to six experiments. One-way ANOVA followed by Bonferroni post hoc test, ^*P⩽0.05, significantly different from results obtained in control conditions; ^#P⩽0.05, significantly different from results obtained in the presence of hexamethonium.