Development of fusimotor innervation correlates with group Ia afferents but is independent of neurotrophin-3.
Fusimotor neurons, group Ia afferents and muscle spindles are absent in mutant mice lacking the gene for neurotrophin-3 (NT3). To partition the effect of Ia afferent or spindle absence from that of NT3 deprivation on fusimotor neuron development, we examined the fusimotor system in a mutant mouse (NesPIXpNT3) that lacks Ia afferents and spindles, but has normal or elevated tissue levels of NT3 during embryogenesis. Fusimotor fibers were absent in lumbar ventral spinal roots, and limb muscles were devoid of Ia afferents and spindles in adult NesPIXpNT3 mice. In contrast, no deficiency in motoneuron numbers was observed in the trigeminal nucleus which contains cell bodies of motor axons innervating muscles of mastication. Spindles and Ia afferents were also present in the masticatory muscles. Thus, the development and/or survival of fusimotor neurons correlates with the presence of Ia afferents and/or spindles, and not with the amount of NT3 in the spinal cord or muscle.
Ringstedt
T
T
Laboratory of Molecular Neurobiology, Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
Copray
S
S
Walro
J
J
Kucera
J
J
D000818:Animals; D001259:Ataxia / Q000503:physiopathology; D007568:Jaw / Q000294:innervation; D008409:Mastication / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000502:physiology / Q000648:ultrastructure; D009470:Muscle Spindles / Q000473:pathology / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000473:pathology; D009413:Nerve Fibers, Myelinated / Q000473:pathology / Q000502:physiology; D009414:Nerve Growth Factors / Q000235:genetics*; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D020933:Neurotrophin 3; D011434:Proprioception / Q000502:physiology
D009414:Nerve Growth Factors; D020933:Neurotrophin 3