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The Journal of Neuroscience, April 4, 2007, 27(14):3686-3694; doi:10.1523/JNEUROSCI.0197-07.2007

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Development/Plasticity/Repair
Prenatal Exposure to Elevated NT3 Disrupts Synaptic Selectivity in the Spinal Cord

Zhi Wang,¹ Ling Ying Li,¹ Michael D. Taylor,² Douglas E. Wright,² and Eric Frank¹

¹Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111, and ²Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas 66160

Correspondence should be addressed to Dr. Eric Frank, Department of Physiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111. Email: eric.frank{at}tufts.edu

Monosynaptic connections between muscle spindle (Ia) afferents and motoneurons (MNs), the central portion of the stretch reflex circuit, are highly specific, but the mechanisms underlying this specificity are primarily unknown. In this study, we report that embryonic overexpression of neurotrophin-3 (NT3) in muscles disrupts the development of these specific Ia–MN connections, using transgenic (mlc/NT3) mice that express elevated levels of NT3 in muscles during development. In mlc/NT3 mice, there is a substantial increase in the amplitudes of monosynaptic EPSPs evoked by Ia afferents in MNs as measured with extracellular recordings from ventral roots. Despite this increased functional projection of Ia afferents, there is no obvious change in the anatomical density of Ia projections into the ventral horn of the spinal cord. Intracellular recordings from MNs revealed a major disruption in the pattern of Ia–MN connections. In addition to the normal connections between Ia afferents and MNs supplying the same muscle, there were also strong monosynaptic inputs from Ia afferents supplying unrelated muscles, which explains the increase seen in extracellular recordings. There was also a large variability in the strength of Ia input to individual MNs, both from correct and incorrect Ia afferents. Postnatal muscular administration of NT3 did not cause these changes in connectivity. These results indicate that prenatal exposure to elevated levels of NT3 disrupts the normal mechanisms responsible for synaptic selectivity in the stretch reflex circuit.

Key words: synaptic specificity; stretch reflex; neurotrophin-3; Ia fibers; spinal cord; EPSP

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Received Jan. 17, 2007; revised Feb. 13, 2007; accepted March 5, 2007.

Correspondence should be addressed to Dr. Eric Frank, Department of Physiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111. Email: eric.frank{at}tufts.edu

This article has been cited by other articles:

				Z. Wang, L. Li, M. Goulding, and E. Frank Early Postnatal Development of Reciprocal Ia Inhibition in the Murine Spinal Cord J Neurophysiol, July 1, 2008; 100(1): 185 - 196. [Abstract] [Full Text] [PDF]

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