The Role of Nitric Oxide and NMDA Receptors in the Development of Motor Neuron Dendrites

Abstract

Nitric oxide (NO) has been implicated in the establishment of precise synaptic connectivity throughout the neuroaxis in several species. To determine the contribution of NO to NMDA receptor-dependent dendritic growth in motor neurons, we administered the NMDA antagonist MK-801 to wild-type mice and neuronal nitric oxide synthase (nNOS) knock-out mice between postnatal days 7 and 14. Compared to saline-treated wild-type animals the number of dendritic bifurcations was significantly reduced in nNOS knock-out animals and MK-801-treated wildtype animals. There was no significant difference in dendritic bifurcation between MK-801-treated wild-type, MK-801-treated nNOS knock-out, and saline-treated nNOS knock-out animals, suggesting that nNOS knock-out and NMDA receptor block had similar effects. The path of the longest dendrite and the number of primary dendrites was the same in all treatment groups, indicating an effect specific to bifurcation. Sholl analysis revealed that differences in bifurcation numbers occurred between 160 and 320 m from the cell body, the distance at which second, third, and fourth order dendrites are most prevalent. Dendrite order analyses confirmed a significant reduction in numbers, but not lengths, of third and fourth order dendrites in nNOS knock-out and drug-treatment groups. Finally, immunohistochemical examination of the developing spinal cord indicated that NMDA receptors and nNOS are colocalized within interneurons surrounding the motor neuron pool. These results support the view that at least part of NMDA receptordependent arborization of motor neuron dendrites is mediated by the local production of NO within the developing spinal cord.

Neuronal nitric-oxide synthase localization mediated by a ternary complex with synapsin and CAPON

“…NO has multiple functions within neurons, such as influencing release of neurotransmitters from synaptic vesicles (2,33,34), through a mechanism that most likely involves S-nitrosylation (35). Additionally, nNOS Ϫ/Ϫ mice display defects in dendritic arborization (5), which are similar to dendritic defects found in synapsin I knockout mice (26). It is intriguing to speculate that the deficits in dendritic morphology or neurotransmitter release in synapsin-deficient mice reflect decreased access of nNOS to synaptic sites.…”

Focal degeneration of astrocytes in amyotrophic lateral sclerosis

“…However, we also identified a degenerative process involving a subset of astrocytes strictly confined to the microenvironment of motor neuron cell bodies, that is within the area of influence of their dendritic trees. 22 The affected cells showed unusual spheroid morphology and most of them lacked the typical GFAP-positive processes. Noteworthy, all SGPCs were strongly immunopositive for ubiquitin.…”

Expression of Serum- and Glucocorticoid-Inducible Kinase Is Regulated in an Experience-Dependent Manner and Can Cause Dendrite Growth

“…At 5 d in vitro (5 DIV), the cells were fixed with 4% paraformaldehyde, immunostained for mitogen-activated protein-2/green fluorescent protein/serum-and glucocorticoid-inducible kinase (MAP-2/GFP/SGK), and visualized by using either fluorescence or the ␤-galactosidase reaction. ␤-Galactosidase-stained neurons were traced by using computer-assisted camera lucida software (Neurolucida; MicroBrightField, Williston, VT) as described previously (Inglis et al, 1998(Inglis et al, , 2000(Inglis et al, , 2002Gazula et al, 2004). Then, three to six neurons were traced per independent condition from any given in vitro preparation of neurons, and an average was derived.…”