Myenteric Neurons Do Not Replicate in Small Intestine Under Normal Physiological Conditions in Adult Mouse.

BACKGROUND & AIMS: The enteric nervous system (ENS) is the largest part of the peripheral nervous system; moreover, abnormal ENS development and function are associated with multiple human pathologies. Data from several groups suggest that under normal physiological conditions in adult animals, enteric nerve cells do not replicate. A study by Kulkarni et al in 2017 challenged this view and proposed that nearly 70% of enteric neurons in the myenteric ganglia are born in 1 week. The authors of this study suggested that differences in DNA labelling times and DNA denaturation conditions might explain discrepancies with previous reports. Previous studies were carried out using different conditions and labelling techniques in various regions of the gastrointestinal tract; thus, conclusions have remained elusive. METHODS: Here, we have eliminated those variables by analyzing the whole small intestine using the reagents and conditions that Kulkarni et al used. To exclude variables related to immunohistochemistry, we carried out parallel experiments with "click chemistry"-based detection of DNA replication. RESULTS: Although proliferation was readily detected in the epithelium, we found no evidence of neuronal replication in the myenteric ganglia. CONCLUSIONS: We conclude that within 1 week under normal physiological conditions, myenteric neurons in the small intestine do not replicate.

Gfra1 Underexpression Causes Hirschsprung's Disease and Associated Enterocolitis in Mice.

BACKGROUND & AIMS: RET, the receptor for the glial cell line-derived neurotrophic factor (GDNF) family ligands, is the most frequently mutated gene in congenital aganglionic megacolon or Hirschsprung's disease (HSCR). The leading cause of mortality in HSCR is HSCR-associated enterocolitis (HAEC), which is characterized by altered mucin composition, mucin retention, bacterial adhesion to enterocytes, and epithelial damage, although the order of these events is obscure. In mice, loss of GDNF signaling leads to a severely underdeveloped enteric nervous system and neonatally fatal kidney agenesis, thereby precluding the use of these mice for modeling postnatal HSCR and HAEC. Our aim was to generate a postnatally viable mouse model for HSCR/HAEC and analyze HAEC etiology. METHODS: GDNF family receptor alpha-1 (GFRa1) hypomorphic mice were generated by placing a selectable marker gene in the sixth intron of the Gfra1 locus using gene targeting in mouse embryonic stem cells. RESULTS: We report that 70%-80% reduction in GDNF co-receptor GFRa1 expression levels in mice results in HSCR and HAEC, leading to death within the first 25 postnatal days. These mice mirror the disease progression and histopathologic findings in children with untreated HSCR/HAEC. CONCLUSIONS: In GFRa1 hypomorphic mice, HAEC proceeds from goblet cell dysplasia, with abnormal mucin production and retention, to epithelial damage. Microbial enterocyte adherence and tissue invasion are late events and therefore unlikely to be the primary cause of HAEC. These results suggest that goblet cells may be a potential target for preventative treatment and that reduced expression of GFRa1 may contribute to HSCR susceptibility.

Dual-mode DFB laser diodes with apodized surface gratings.

Dual longitudinal mode distributed feedback lasers have been fabricated using surface gratings with and without apodization. Analytic formulas and simulations that have been used to derive design guidelines are presented. The fabricated device characteristics are in good agreement with the simulations. The grating apodization enables a lower threshold current density, a higher output power and a broader range of difference frequency tunability by bias, which can be extended beyond the measured 15-55 GHz by changing the device structure. The apodization and the complex coupling of the surface gratings reduce the effects of the uncontrollable phase of facet reflections, enabling the use of higher facet reflectivities, which leads to narrower intrinsic short time-scale linewidths.

Distributed feedback lasers with alternating laterally coupled ridge-waveguide surface gratings.

Distributed feedback lasers with laterally coupled ridge-waveguide surface gratings having the protrusions placed alternately on the lateral sides of the ridge are demonstrated. This configuration enables easier-to-fabricate wider trenches than in the gratings with protrusions placed symmetrically on both sides of the ridge. The design strategy and coupling coefficient calculations are discussed. The output characteristics of fabricated lasers show lower threshold currents and higher slope efficiencies for devices with first-order alternating gratings than for those with third-order symmetric gratings having comparable grating trench widths and similar coupling coefficients.