Receptive properties of embryonic chick sensory neurons innervating skin
Martin Koltzenburg and Gary R. Lewin.
Department of Neurology, University of Wrzburg, D-97080 Wrzburg, Dept.of
Neurobiochemistry, Max-Planck-Institute for Psychiatry, D 82152, Planegg-
Martinsried, Germany.
APStracts 4:122N, 1997.
ABSTRACT
We describe a new in vitro skin-nerve preparation from chick embryos which
allows detailed study of the functional properties of developing sensory
neurons innervating skin. Functionally single sensory afferents were isolated
by recording from by their axons in microdissected filaments of the cutaneous
femoralis medialis nerve which innervates skin of the thigh. A total of 157
single neurons were characterized from embryos (E17-E21, n=115) and hatchlings
up to 3 weeks old (n=42). Neurons were initially classified on the basis of
their conduction velocity, those conducting below 1.0 m/s were being
classified as C-fibers and faster conducting fibers as A-fibers. The
proportions of A and C-fibers encountered in embryonic and hatchling
preparations was not very different indicating that myelination and axon
growth proceeds quite slowly over the period studied. Afferent fibers that
could subserve nociceptive and non-nociceptive functions were identified in
the time period studied. Subpopulations of low threshold myelinated afferent
units exhibited rapidly or slowly adapting discharges to constant force
stimuli and could have tactile functions. Many afferent fibers responded to
noxious heat and were excited and sensitized by exposure to inflammatory
mediators suggesting that they are nociceptors. The behavior of these units
changed in several respects over the period studied. The discharge of C-fibers
to noxious heat increased with age as did their mechanical thresholds. A
substantial population of heat responsive neurons (34% of the A-fibers)
present in embryos were not encountered in hatchling chicks. This indicates
that substantial changes in the physiological response properties of sensory
afferents occur after hatching. We conclude that this new preparation can be
used for quantitative assessment of the receptive properties of developing
sensory neurons and has considerable potential for the investigation of
factors, such as neurotrophins, that specify and influence the functional
phenotype of sensory neurons during embryonic development in vivo.
Received 2 July 1997; accepted in final form 2 July 1997.
APS Manuscript Number J942-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 24 July 1997