Journal of Neuroscience, Vol 12, 1135-1143, Copyright © 1992 by Society for Neuroscience
Visceral targets specify calcitonin gene-related peptide and substance P enrichment in trigeminal afferent projections
K Horgan and D van der Kooy
Department of Anatomy, University of Toronto, Ontario, Canada.
Rat trigeminal ganglion projections to a visceral target (intracranial
blood vessels) are enriched in calcitonin gene-related peptide (CGRP) and
substance P (Sub P) compared to trigeminal ganglion projections to a
cutaneous target (the forehead skin). We asked if transplants of a novel
visceral target (fetal stomach antrum tissue) into the path of the neonatal
rat trigeminal frontal nerve projection to forehead skin would induce
neuronal CGRP and Sub P enrichment. By postnatal day (P) 25, the percentage
of nerves containing CGRP increased from 14-15% in the control trigeminal
projection to forehead skin to 20-31% (in different experiments) in the
trigeminal projection to transplanted stomach antrum. The percentage of Sub
P-containing neurons increased from 10% in the control forehead skin
projection to 22% in the trigeminal projection to stomach transplants over
the same time period. The number of neurons in the trigeminal frontal nerve
projection to stomach antrum transplants was not significantly different
from the number of frontal neurons projecting to control forehead skin. We
suggest that respecification of trigeminal neurons to the CGRP and Sub P
phenotype, not selective survival of CGRP- and Sub P-positive afferents, is
the mechanism by which stomach antrum induces enrichment of CGRP and Sub P.
A subpopulation of rat trigeminal neurons with cutaneous forehead skin
projections also sends a transient axon collateral projection to a visceral
target (the cerebral arteries) during early postnatal development.
Postnatal maintenance of an axonal projection to a cutaneous target
(forehead skin) may be incompatible with a neuron also maintaining a
visceral collateral to the cerebral arteries.(ABSTRACT TRUNCATED AT 250
WORDS)