Nitric-oxide-directed synaptic remodeling in the adult mammal CNS.
In adult mammals, learning, memory, and restoration of sensorimotor lost functions imply synaptic reorganization that requires diffusible messengers-mediated communication between presynaptic and postsynaptic structures. A candidate molecule to accomplish this function is the gaseous intercellular messenger nitric oxide (NO), which is involved in synaptogenesis and projection refinement during development; however, the role of NO in synaptic reorganization processes in adulthood remains to be established. In this work, we tested the hypothesis that this free radical is a mediator in the adult mammal CNS synaptic remodeling processes using a model of hypoglossal axonal injury recently developed by us. Axonal injury-induced disconnection of motoneurons from myocytes produces withdrawal of synaptic inputs to motoneurons and concomitant upregulation of the neuronal isoform of NO synthase (NOS-I). After recovery of the neuromuscular function, synaptic coverage is reestablished and NOS-I is downregulated. We also report, by using functional and morphological approaches, that chronic inhibition of the NO/cGMP pathway prevents synaptic withdrawal evoked by axon injury, despite the persistent muscle disconnection. After successful withdrawal of synaptic boutons, inhibition of NO synthesis, but not of cGMP, accelerated the recovery of synaptic coverage, although neuromuscular disconnection was maintained. Furthermore, protein S-nitrosylation was upregulated after nerve injury, and this effect was reversed by NOS-I inhibition. Our results suggest that during synaptic remodeling in the adult CNS, NO acts as a signal for synaptic detachment and inhibits synapse formation by cGMP-dependent and probably S-nitrosylation-mediated mechanisms, respectively. We also suggest a feasible role of NO in neurological disorders coursing with NOS-I upregulation.
Sunico
Carmen R
CR
Area de Fisiología, Facultad de Medicina, Universidad de Cádiz, 11003 Cádiz, Spain.
Portillo
Federico
F
González-Forero
David
D
Moreno-López
Bernardo
B
D000818:Animals; D006152:Cyclic GMP / Q000502:physiology*; D004790:Enzyme Induction; D007002:Hypoglossal Nerve / Q000201:enzymology / Q000502:physiology*; D061228:Hypoglossal Nerve Injuries; D008297:Male; D009046:Motor Neurons / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009409:Nerve Crush; D009416:Nerve Regeneration / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D009569:Nitric Oxide / Q000096:biosynthesis / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013569:Synapses / Q000201:enzymology / Q000502:physiology*
D009419:Nerve Tissue Proteins; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester