Methylene blue blocks cGMP production and disrupts directed migration of microglia to nerve lesions in the leech CNS.
Migration and accumulation of microglial cells at sites of injury are important for nerve repair. Recent studies on the leech central nervous system (CNS), in which synapse regeneration is successful, have shown that nitric oxide (NO) generated immediately after injury by endothelial nitric oxide synthase (eNOS) stops migrating microglia at the lesion. The present study obtained results indicating that NO may act earlier, on microglia migration, and aimed to determine mechanisms underlying NO's effects. Injury induced cGMP immunoreactivity at the lesion in a pattern similar to that of eNOS activity, immunoreactivity, and microglial cell accumulation, which were all focused there. The soluble guanylate cyclase (sGC) inhibitor methylene blue (MB) at 60 microM abolished cGMP immunoreactivity at lesions and blocked microglial cell migration and accumulation without interfering with axon conduction. Time-lapse video microscopy of microglia in living nerve cords showed MB did not reduce cell movement but reduced directed movement, with significantly more cells moving away from the lesion or reversing direction and fewer cells moving toward the lesion. The results indicate a new role for NO, directing the microglial cell migration as well as stopping it, and show that NO's action may be mediated by cGMP.
Duan
Yuanli
Y
Department of Physiology and Biophysics (R-430), University of Miami School of Medicine, 1600 NW 10th Avenue, Miami, Florida 33136, USA. yduan@newssun.med.miami.edu
Haugabook
Sharie J
SJ
Sahley
Christie L
CL
Muller
Kenneth J
KJ
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects* / Q000502:physiology; D002490:Central Nervous System / Q000293:injuries / Q000473:pathology / Q000503:physiopathology; D006152:Cyclic GMP / Q000096:biosynthesis*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007865:Leeches / Q000502:physiology*; D008751:Methylene Blue / Q000494:pharmacology*; D017628:Microglia / Q000187:drug effects* / Q000502:physiology; D009409:Nerve Crush; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000009:adverse effects; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D006152:Cyclic GMP; D008751:Methylene Blue