Decreased smooth muscle function, peristaltic activity, and gastrointestinal transit in dystrophic (mdx) mice.

BACKGROUND: Duchenne muscular dystrophy (DMD) is characterized by the lack of dystrophin in skeletal, cardiac, and smooth muscle. Slow colonic transit and constipation are common in DMD patients and animal models of DMD. However, the cause of this hypocontractility and the expression of contractile proteins in smooth muscle are unknown. The aim of the study was to investigate the expression of contractile proteins in the colonic smooth muscle and the function of the colon in control and mdx mice. METHODS: Muscle contraction was measured in muscle strips and isolated muscle cells. Peristaltic activity was measured in ex vivo preparations by spatiotemporal mapping, and gastrointestinal (GI) transit in vivo was measured by the distribution of fluorescent marker along the intestine and colon. mRNA expression of contractile proteins smoothelin, caldesmon, calponin, and tropomyosin was measured by qRT-PCR. RESULTS: Expression of mRNA for contractile proteins was decreased in colonic smooth muscle of mdx mice compared with control. Contraction in response to acetylcholine and KCl was decreased in colonic muscle strips and in isolated muscle cells of mdx mice. Distension of ex vivo colons with Krebs buffer induced peristalsis in both control and mdx mice; however, significantly fewer full peristaltic waves were recorded in the colons of mdx mice. GI transit was also inhibited in mdx mice. CONCLUSION AND INFERENCES: The data indicate that the lack of dystrophin causes decrease in colonic smooth muscle contractility, peristalsis, and GI transit and provides the basis for analysis of mechanisms involved in smooth muscle dysfunction in DMD.

Expression and function of umami receptors T1R1/T1R3 in gastric smooth muscle.

BACKGROUND: l-amino acids, such as monosodium glutamate (MSG), activate the umami receptor T1R1/T1R3. We previously showed increased peristalsis in response to activation of T1R1/T1R3 by MSG in mouse colon. However, the expression and function of these receptors in the different regions of the stomach are not clear. METHODS: Mouse gastric smooth muscle cells (SMCs) were isolated and cultured in Dulbecco's Modified Eagle Medium. Expression of T1R1 and T1R3 was measured by RT-PCR and Western blot. The effect of MSG with and without inosine monophosphate (IMP, an allosteric activator of T1R1/T1R3) on acetylcholine (ACh)-induced contraction was measured in muscle strips and isolated SMCs by scanning micrometry. The effect of MSG with or without IMP on activation of G proteins and ACh-induced Ca2+ release was measured in SMCs. KEY RESULTS: Monosodium glutamate inhibited ACh-induced contractions in muscle strips from both antrum and fundus and the effect of MSG was augmented by IMP; the effects were concentration-dependent and not affected by the nitric oxide synthase inhibitor, L-NNA, or tetrodotoxin suggesting a direct effect on SMCs. In isolated gastric SMCs, T1R1 and T1R3 transcripts and protein were identified. Addition of MSG with or without IMP inhibited ACh-induced Ca2+ release and muscle contraction; the effect on contraction was blocked by pertussis toxin suggesting activation of Gαi proteins. MSG in the presence of IMP selectively activated Gαi2 . CONCLUSIONS AND INFERENCES: Umami receptors (T1R1/T1R3) are present on SMCs of the stomach, and activation of these receptors induces muscle relaxation by decreasing [Ca2+ ]i via Gαi2 .

Reduction of dorsolateral prefrontal cortex gray matter in late-life depression.

Postmortem studies have documented abnormalities in the dorsolateral prefrontal cortex (dlPFC) in depressed subjects. In this study we used magnetic resonance imaging to test for dlPFC volume differences between older depressed and non-depressed individuals. Eighty-eight subjects meeting DSM IV criteria for major depressive disorder and thirty-five control subjects completed clinical evaluations and cranial 3T magnetic resonance imaging. After tissue types were identified using an automated segmentation process, the dlPFC was measured in both hemispheres using manual delineation based on anatomical landmarks. Depressed subjects had significantly lower gray matter in the left and right dorsolateral prefrontal cortex (standardized to cerebral parenchyma) after controlling for age and sex. Our study confirmed the reduction of dorsolateral prefrontal cortex in elderly depressed subjects, especially in the gray matter. These regional abnormalities may be associated with psychopathological changes in late-life depression.