Transient expression of NOS-II during development of the murine enteric nervous system

Abstract

In the enteric nervous system, nitric oxide (NO) is regarded as an important messenger for the non-adrenergic and non-cholinergic neurotransmission. Synthesized mainly by the constitutive nitric oxide synthase (NOS) isoforms NOS I and NOS III, this molecule exerts prejunctional inhibitory effects in the submucosal plexus as well as relaxation of enteric smooth muscles. In order to elucidate the role for NO during enteric development, we looked for the expression of all three NOS-isoforms in the enteric nervous system during mouse development from E8 to E20 using immunohistochemistry. Starting around midgestation, a transient expression of the NOS-II isoform during the very early development of enteric neurones was detected in parallel to that of HNK-1 exclusively in the myenteric plexus. Similar to findings for other neuronal systems, NOS-I and NOS III isoforms could be traced starting significantly later to increase toward the end of embryonic development when NOS II immunoreactivity faded and a strong expression of the vasointestinal peptide could be detected. In contrast to the NOSII expression, the constitutive isoforms can also be detected in the submucosal plexus. Altogether, these findings suggest NOS-II to be exclusively involved during early steps of enteric nervous system development. Absence of downstream signalling elements, such as sGC and cGMP both in neurons and in enteric muscle until the end of the second third of gestation, may indicate different effects executed by NO during development, expressed by Ca(2+) -dependent and Ca(2+) -independent NOS isoforms.

The developmental stage and cell type dependent phosphorylation of eNOS in murine enteric mucosa and myenteric plexus

“…These staining intensities of eNOS, phospho-eNOS at Ser 116 increased from E18.5 to P3 developmental stage. In the murine enteric mucosa of E11 and E12, localization for iNOS in cells of the myenteric plexus was revealed (Arnhold et al 2004). In these results, the higher levels of iNOS in E11 and E12 were decreased from E11/E12 to the E16 developmental stage.…”

“…This anti-apoptotic role for NO in epithelial cells is mediated by cGMP. The localization of cGMP in cells of the enteric mucosa epithelium and in cells of the myenteric plexus (Arnhold et al 2004) may support an anti-apoptotic role for eNOS and phosphorylation of eNOS in epithelial cells of the enteric mucosa and in neurons of the myenteric plexus.…”

“…NO produced by eNOS was identified in neurons of the myenteric plexus of the enteric mucosa during enteric nervous development (Arnhold et al 2004). In the present results, from E14.5 up to P3, phosphorylation sites of eNOS at Ser 1177 and at Ser 116 were detected with enhanced staining intensities in the enteric Fig.…”

“…The lipopolysacharide (LPS) induced iNOS expression in the rat intestine was found at P4 and at P15 (Morin et al 2001). A localization of eNOS was identified in neurons of the myenteric plexus of the enteric mucosa during enteric nervous development (Arnhold et al 2004). …”

Stimulation of voltage-dependent Ca2+channels by NO at rat myenteric neurons

“…In the small intestine of the same species, NO has been reported to act as a retrograde transmitter released from interneurons affecting synaptic transmission between these interneurons and sensory neurons (38). Further evidence for potential neuronal effects of NO comes from immunohistochemical studies which show that the expression pattern of NOS isoforms in the murine myenteric plexus changes during development with an early but transient expression of NOS-2 during embryogenesis, followed by the expression of NOS-1 and NOS-3, suggesting a role for NO in the development of the enteric nervous system (1).…”