Journal of Neuroscience, Vol 10, 2485-2492, Copyright © 1990 by Society for Neuroscience
Prenatal specification and target induction underlie the enrichment of calcitonin gene-related peptide in the trigeminal ganglion neurons projecting to the cerebral vasculature
K Horgan, TP O'Connor and D van der Kooy
Department of Anatomy, University of Toronto, Ontario, Canada.
The neurotransmitter calcitonin gene-related peptide (CGRP) is enriched in
the adult rat trigeminal visceral projection to the cerebral arteries
compared both to other neurotransmitters in this projection and to the
percentage of CGRP-positive trigeminal cells projecting to cutaneous
targets. In colchicine-treated ganglia approximately 30% of adult
trigeminal ganglion cells projecting to the middle cerebral artery contain
CGRP. Several possible developmental mechanisms underlying this enrichment
were investigated. Some of this enrichment is accounted for by a prenatal
selection of CGRP cells in the cerebrovascular projection. The remainder of
the enrichment can be explained by a late (postnatal days 55-90)
target-induced expression of CGRP in some trigeminal neurons innervating
cerebral arteries. Most surprisingly, the massive postnatal regression in
the trigeminal projection to the cerebral arteries (between postnatal days
5 and 55, cell death and axon retraction delete 3/4 of the neurons that
innervate the middle cerebral artery neonatally) has no role in the CGRP
enrichment in the cells remaining at maturity in this projection. These
regressive events appear to affect equally the CGRP-positive and CGRP-
negative populations. However, axon retraction is involved in the postnatal
loss of CGRP enrichment seen in 1 small subpopulation of the trigeminal
projection. Each trigeminal cell in this population sends axon collaterals
to both the cerebral artery and the forehead skin neonatally, and then
later most of these dually projecting neurons retract only their artery
collaterals but do not die. A low percentage of CGRP-containing neurons
does not appear to predate artery collateral retraction.(ABSTRACT TRUNCATED
AT 250 WORDS)