Role of brain-derived neurotrophic factor in the plasticity of enteric nervous-smooth muscle and its effects on gastrointestinal motility in mice

Abstract

Objective To observe the role of brain-derived neurotrophic factor (BDNF) in the plasticity of enteric nervous-smooth muscle system, and to investigate the effects of BDNF induced plasticity on gastrointestinal motility in mice. Methods Male hybrid BDNF knockout (BDNF+ /-) mice and wild type (BDNF+ /+ ) mice were selected, eight in each group. Gastrointestinal motility of BDNF+ /+ mice and BDNF+ /- mice were tested and compared. Longitudinal muscle strips of mice colon smooth muscle were prepared.The effects of carbachol (1×10-5 mol/L) and BDNF (1×10-7 mol/L) on contractile function of muscle strips were observed. And the effects of tetrodotoxin (TTX, 1×10-6 mol/L) on BDNF induced contractile function of muscle strips were also studied. The changes of the density of mice intestinal myenteric plexus and the expression of smooth muscle α-actin (α-SMA) in colon smooth muscle were detected by immunohistochemical techniqne. The ultrastructural alterations of myenteric plexus, neuromuscular junction (NMJ) and smooth muscle cells were detected by transmission electron microscope (TEM). T-test or Rank sum test was performed for comparison between groups. Results Number of feces particles and water content in feces of BDNF+ /- mice ((3.80±0.75) and (39.60±1.47)%) were both lower than those of BDNF+ /+ mice ((6.30±1.03) and (51.00±1.61)%), and the differences were statistically significant (t=4.792, 12.827; both P<0.05). Carbachol (1×10-5 mol/L) could significantly increase contraction activity of smooth muscle of BDNF+ /+ mice (R=3.26±0.43) and BDNF+ /- mice (R=2.15±0.36), and the difference was statistically significant (t=15.754, 9.632; both P<0.05). The effects on contraction exciting of smooth muscle strips of BDNF+ /+ mice were more significant than BDNF+ /- mice, and the difference was statistically significant (t=5.972, P<0.05). BDNF could significantly increase contraction of muscle strips of BDNF+ /+ mice and R value increased from 1 to 1.41±0.09, and the differences were statistically significant (t=13.674, P<0.05). TTX could obviously inhibit the excitatory effects of BDNF, R value decreased from 1.41±0.09 to 1.03±0.04 (t=11.692, P<0.05). The density of myenteric plexus of BDNF+ /- mice (median 5.8%, interquartile range 4.2%-7.0%) was significantly lower than that of BDNF+ /+ mice (median 9.0%, interquartile range 7.1%-10.8%), and the difference was statistically significant (Z=3.730, P<0.05). The expression of α-SMA of BDNF+ /- mice (median 33.4%, interquartile range 28.8%-38.5%) was significantly lower than that of BDNF+ /+ mice (median 44.6%, interquartile range 39.2%-48.8%), and the difference was statistically significant (Z=4.565, P<0.05). The results of TEM indicated ultrastructural alterations of myenteric plexus, NMJ and smooth muscle in BDNF+ /- mice. Conclusionss BDNF could induce the plasticity of morphology and function in enteric nervous-smooth muscle system, which may play an important role in mice gastrointestinal motility. Key words: Brain-derived neurotrophic factor; Enteric nervous system; Plasticity of smooth muscle; Gastrointestinal motility; Mice