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The Journal of Neuroscience, February 27, 2008, 28(9):2006-2014; doi:10.1523/JNEUROSCI.5609-07.2008

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Behavioral/Systems/Cognitive
Myelinated Skin Sensory Neurons Project Extensively throughout Adult Mouse Substantia Gelatinosa

M. Danilo Boada and C. Jeffery Woodbury

Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071

Correspondence should be addressed to C. Jeffery Woodbury, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071. Email: woodbury{at}uwyo.edu

The substantia gelatinosa (SG) of the dorsal horn of the spinal cord is a recipient zone for unmyelinated sensory neurons in adults. Recent studies of the central anatomy of physiologically identified skin sensory neurons in neonatal mice have shown that this region also receives substantial inputs from a variety of myelinated afferents. The present experiments were performed to determine whether these neonatal inputs represent a transient phenotype that retracts from the SG. Studies were conducted in an in vivo spinal cord preparation from adult mice; thoracic levels were targeted to facilitate comparisons with previous in vitro findings. We show that the SG continues to receive substantial projections from myelinated skin sensory neurons throughout life. A large population of myelinated nociceptors conducting in the upper A and low Aβ range maintained extensive projections throughout all areas of the SG well into adulthood; the latter gave rise to dorsally recurving "flame"-shaped arbors extending into the marginal layer that were identical to afferents described in neonates and after nerve injury in adult rats. Furthermore, exquisitely sensitive down hair follicle afferents projected throughout the inner half of the SG (i.e., lamina IIi) and sent dense clusters of terminals well into the outer SG (IIo), where they intermingled with those of unmyelinated nociceptors. Arguments are presented that the SG likely plays a predominant role in tactile processing under normal conditions, but that this role switches rapidly to nociceptive-only during environmental exigencies imposed by temperature extremes.

Key words: mouse; skin; sensory neurons; nociceptors; superficial dorsal horn; tactile

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Received Oct. 6, 2007; revised Jan. 13, 2008; accepted Jan. 13, 2008.

Correspondence should be addressed to C. Jeffery Woodbury, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071. Email: woodbury{at}uwyo.edu

This article has been cited by other articles:

				C. A. Daniele and A. B. MacDermott Low-Threshold Primary Afferent Drive onto GABAergic Interneurons in the Superficial Dorsal Horn of the Mouse J. Neurosci., January 21, 2009; 29(3): 686 - 695. [Abstract] [Full Text] [PDF]

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