Nitric Oxide Influences Injury-Induced Microglial Migration and Accumulation in the Leech CNS

Abstract

Damage to the leech or mammalian CNS increases nitric oxide (NO) production and causes accumulation of phagocytic microglial cells at the injury site. The aim of this study was to determine whether NO plays a role in microglial migration and accumulation at lesions in which NO is generated by a rapidly appearing endothelial nitric oxide synthase (eNOS) in leeches. Immunohistochemistry and cytochemistry demonstrated active eNOS before and throughout the period of microglial accumulation at the lesion. Decreasing NO synthesis by application of the NOS inhibitor N(w)-nitro-L-arginine methyl ester (1 mM) significantly reduced microglial accumulation, whereas its inactive enantiomer N(w)-nitro-D-arginine methyl ester (1 mM) resulted in microglial accumulation similar to that in crushed controls. Increasing NO with the donor spermine NONOate (SPNO) (1 mM) also inhibited accumulation, but not in the presence of the NO scavenger 2-(4-carboxyphenyl)-4,4,5, 5-teramethylimidazoline-oxyl-3-oxide (50 microM). The effect of SPNO was reversed by washout. SPNO application reduced average microglial migratory speeds and even reversibly arrested cell movement, as measured in living nerve cords. These results suggest that NO produced at a lesion may be a stop signal for microglia to accumulate there and that it can act on microglia early in their migration. Thus, NO may assume a larger role in nerve repair and recovery from injury by modulating accumulation of microglia, which appear to be important for axonal regeneration.

Stromal Cell-Derived Factor 1α-Induced Chemotaxis in T Cells Is Mediated by Nitric Oxide Signaling Pathways

“…NO has been shown to have opposing and complex effects on chemotactic responses exerted by various stimuli. For example, it has been shown that NO enhances chemotactic responses in some cell types (45,46,(61)(62)(63) upon certain stimuli, while inhibiting cell migration in others (47,64). Furthermore, NO has been shown to modulate T cell chemotaxis in Peyer's patches and in the nonlymphoid region of the intestine (65).…”

Physiology of Microglia

“…When the leech nerve cord is injured, microglia migrate towards the lesion and accumulate at the damage site (145,482,556,970). In response to injury, leech connective glia and some microglia express endothelial nitric oxide synthase (eNOS) as revealed by immunolabeling.…”

“…The NO could mediate the accumulation of microglia at the lesion site in the leech: a NOS inhibitor significantly reduced microglial accumulation. The nitric oxide (NO) donor spermine NONOate also inhibited accumulation, reduced average microglial migratory speed, and even reversibly arrested cell movement, indicating that NO is a stop signal for microglia and results in accumulation (145). NO's action on the migratory behavior of leech microglia may be mediated by cGMP (228).…”

Netrin-1 signaling mediates NO-induced glial precursor migration and accumulation

“…Previous studies reported that both the gaseous messenger molecule nitric oxide (NO) [2][3][4] and widely studied axon guidance/migration cues such as Netrins [5,6] regulated the migratory behavior of cells in the nervous system. However, little is known about whether there is any crosstalk between NO and guidance/migration cues during neural cell migration and accumulation.…”