Neurotrophin-3 Promotes the Differentiation of Muscle Spindle Afferents in the Absence of Peripheral Targets

• Published in: The Journal of neuroscience Vol. 17; no. 11; pp. 4262 - 4274
• Main Authors: Oakley, Robert A, Lefcort, Frances B, Clary, Douglas O, Reichardt, Louis F, Prevette, David, Oppenheim, Ronald W, Frank, Eric
• Format: Journal Article
• Language: English
• Published: United States Soc Neuroscience 01.06.1997; Society for Neuroscience
• Subjects: Animals; Antibody Specificity; Cell Differentiation - drug effects; Cell Line - physiology; Cell Survival - drug effects; Chick Embryo; Ganglia, Spinal - cytology; Humans; Kidney - cytology; Limb Buds - surgery; Muscle Spindles - cytology; Muscle Spindles - drug effects; Muscle Spindles - physiology; Nerve Growth Factors - pharmacology; Neurons, Afferent - chemistry; Neurons, Afferent - cytology; Neurons, Afferent - drug effects; Neurotrophin 3; Proto-Oncogene Proteins - analysis; Proto-Oncogene Proteins - immunology; Receptor Protein-Tyrosine Kinases - analysis; Receptor Protein-Tyrosine Kinases - immunology; Receptor, Ciliary Neurotrophic Factor; Receptor, trkA; Receptor, trkC; Receptors, Nerve Growth Factor - analysis; Receptors, Nerve Growth Factor - immunology; Spinal Cord - cytology; Time Factors; Transfection
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/jneurosci.17-11-04262.1997

The neurons of the dorsal root ganglia (DRG) that supply muscle spindles require target-derived factors for survival. One necessary factor for these neurons is neurotrophin-3 (NT3). To determine whether NT3 can promote the survival of these neurons in the absence of other target-derived factors, we analyzed the effects of exogenous NT3 after early limb bud deletion in the chick. In control embryos, limb bud deletion eliminated approximately 90% of the trkC-positive (trkC+) neurons in lumbar DRG on the deleted side. In addition, the deletion led to a dramatic loss of collateral sensory projections to motoneurons. Exogenous NT3 restored a normal population of trkC+ neurons in lumbar DRG on the deleted side and increased the number of trkC+ neurons in DRG with normal targets (contralateral lumbar and thoracic). The effect was highly selective; NT3 increased the number of trkC+ neurons without significantly changing the number of either trkA+ or trkB+ neurons. The effect of NT3 was attributable to the rescue of DRG neurons from cell death, because exogenous NT3 reduced the number of pyknotic nuclei without significantly altering proliferation. Analysis of spinal projections showed further that many of the trkC+ neurons rescued by NT3 projected to the ventral spinal cord. These neurons thus had central projections characteristic of muscle spindle afferents. Together, our results indicate that NT3 signaling is both necessary and sufficient for the development of the proprioceptive phenotype, even in the absence of other signals from limb muscle.