A 5-HT(4)-receptor activation-induced neural plasticity enhances in vivo reconstructs of enteric nerve circuit insult

BACKGROUND

It was recently reported that some 5-HT(4)-receptor agonists increased neuronal numbers and length of neurites in enteric neurons developing in vitro from immunoselected neural crest-derived precursors. We aimed to explore a novel approach in vivo to reconstruct the enteric neural circuitry that mediates a fundamental distal gut reflex.

METHODS

The neural circuit insult was performed in guinea pigs by rectal transection and subsequent end-to-end one layer anastomosis. A 5-HT(4)-receptor agonist, mosapride citrate (10-100 micromol L(-1)) (applied for a patent) was applied locally at the anastomotic site.

KEY RESULTS

Mosapride promoted the regeneration of the neural circuit in the impaired myenteric plexus and the recovery of the defecation reflex in the distal gut. Furthermore, mosapride generated neurofilament (NF)-, 5-HT(4)-receptor- and 5-bromo-2'-deoxyuridine (BrdU)-positive cells and surprisingly formed neural network in the newly formed granulation tissue at the anastomotic site 2 weeks after enteric nerve circuit insult. Possible neural stem cell markers, anti-distal less homeobox 2 (DLX2)- and p75-positive and NF-positive cells increased during the same time period. All actions by mosapride were inhibited by the specific 5-HT(4)-receptor antagonist, GR113808 (10 micromol L(-1)).

CONCLUSIONS & INFERENCES

These results indicate that activation of enteric neural 5-HT(4)-receptors promotes reconstruction of an enteric neural circuit leading to the recovery of the defecation reflex in the distal gut, and that this reconstruction involves possibly neural stem cells. These findings indicate that treatment with 5-HT(4) agonists could be a novel therapy for generating new enteric neurons to rescue aganglionic gut disorders.

A novel role for Fyn: Change in sphere formation ability in murine embryonic stem cells

Fyn, a member of the Src-family protein tyrosine kinase (PTK), is an essential factor in myelination in the CNS and is involved in murine embryonic stem (ES) cell growth and differentiation. Although dysfunctions of Fyn have been comparatively studied, the gain of function by ectopic expression, especially using ES cells, has seldom been investigated. In this article, we give the first report of the involvement of Fyn alteration in the sphere formation ability of murine ES cells. First, transient transfection of Fyn hardly affected multiplication and specialization. Then, we investigated Fyn overexpression using ES cells, which stably express Fyn. As a result, altered sphere formation capability was observed in all clones stably expressing Fyn. These results may provide important information for reproduction medical treatment using ES cells.

L3/Lhx8 is involved in the determination of cholinergic or GABAergic cell fate

The LIM homeobox family of transcription factors is involved in many processes during the development of the mammalian central nerves system. L3, also called Lhx8 (L3/Lhx8), is a recently identified member of the LIM homeobox gene family and is selectively expressed in the medial ganglionic eminence (MGE). Our previous study demonstrated that L3/Lhx8-null mice specifically lacked cholinergic neurons in the basal forebrain. In this study, we reduced L3/Lhx8 function in the murine neuroblastoma cell line, Neuro2a (N2a), using L3/Lhx8-targeted small interfering RNA (siRNA) produced by H1.2 promoter-driven vector. The levels of cholinergic markers per cell were diminished without a reduction in the number of marker-positive cells. Intriguingly, GABAergic marker expression and the number of GABAergic cells were dramatically increased in the differentiating L3/Lhx8-knockdown N2a. These results suggest the possibility that L3/Lhx8 is involved in the determination of transmitter phenotypes (GABAergic or cholinergic cell fate) in a population of neurons during basal forebrain development.