Pme. Waite et Pj. Depermentier, EFFECT OF NEONATAL CAPSAICIN AND INFRAORBITAL NERVE-SECTION ON WHISKER-RELATED PATTERNS IN THE RAT TRIGEMINAL NUCLEUS, Journal of comparative neurology, 385(4), 1997, pp. 599-615
In the present study, we investigated the effect of neonatally adminis
tered capsaicin on whisker-related pattern formation in the rat trigem
inal complex. Both normal whisker-related patterns of barrelettes and
the modified patterns seen after neonatal section of the infraorbital
nerve were assessed. Capsaicin caused no change in the pattern or size
of cytochrome oxidase (GO) barrelettes in the principal trigeminal nu
cleus (Vp) or trigeminal nucleus interpolaris (Vi) or caudalis (Vc). I
njections of horseradish peroxidase (HRP) or wheatgerm agglutinin conj
ugated to HRP (WGA-HRP) into the posteroorbital (PO) whisker follicle
in vehicle-treated animals showed that WGA labelled a larger number of
trigeminal ganglion cells than HRP (203 +/- 23; cf. 158 +/- 19), With
an increased labelling of small-diameter neurons (HRP: 25.9 +/- 7.7 m
u m; WGA: 23.2 +/- 7.2 mu m). Capsaicin caused a loss of smaller diame
ter cells but had no effect on the location, cross-sectional area, or
rostrocaudal extent of the transganglionically labelled HRP terminatio
ns in Vp, Vi, Vc, and cervical dorsal horn. WGA-HRP labelling revealed
similar, but less dense, central terminal areas as HRP and an additio
nal area of superficial terminals in the caudal medulla; these were al
so unaffected by capsaicin treatment. After infraorbital nerve section
, CO patches and transganglionically labelled afferent terminations, c
orresponding to innervated nonmystacial whiskers, were approximately d
oubled in size. Capsaicin had no effect on the increased size of these
spared whisker patches or their afferent terminal areas. These result
s suggest that barrelette formation is not dependent on unmyelinated a
fferents and that the changes in response properties seen after capsai
cin, such as increased receptive fields, reflect functional changes ra
ther than anatomical expansion of afferent terminal areas. (C) 1997 Wi
ley-Liss, Inc.