M. Taoka et al., INCREASED LEVEL OF NEUROKININ-1 TACHYKININ RECEPTOR GENE-EXPRESSION DURING EARLY POSTNATAL-DEVELOPMENT OF RAT-BRAIN, Neuroscience, 74(3), 1996, pp. 845-853
Substance P is known to elicit diverse actions via activating multiple
subtypes of tachykinin receptors, and these actions appear to be invo
lved not only in synaptic transmission but also in synaptic plasticity
during development of the mammalian cental nervous system. The availa
bility of sensitive quantitation of individual tachykinin receptor sub
types is crucial for elucidating the physiological function specifical
ly mediated by activation of a particular receptor subtype. We thus at
tempted to develop an assay to determine the level of messenger RNA mo
lecule encoding the neurokinin-l-type tachykinin receptor and apply it
for assessment of developmental changes in the neurokinin-l receptor
gene expression in the rat brain to explore the role of tachykinin rec
eptors during ontogeny. The assay was designed to use a competitive re
verse transcription-polymerase chain reaction co-amplifying endogenous
neurokinin-l receptor messenger RNA and internal standard, which enab
led specific quantification of the number of neurokinin-l receptor tra
nscripts, ranging from 3.1 x 10(3) to 1.3 x 10(5) molecules/mu g total
RNA. The levels of neurokinin-l receptor gene expression were examine
d in three different brain regions of the rat aged 0-56 days after bir
th. The order of neurokinin-l receptor messenger RNA expression was hi
ppocampus > cerebral cortex much greater than cerebellum at all ages e
xamined except postnatal day 0, where its expression was more abundant
in the cerebral cortex than in the hippocampus. From postnatal day 3
onward, the hippocampus contained 140-160% of the cortical levels. Alt
hough the tachykinin receptor expression in the cerebellum was too low
to be accurately assessed by conventional techniques, our assay enabl
ed us to determine the amount of cerebellar neurokinin-l receptor mess
enger RNA that changed in the range 7-23% of the cortical level during
postnatal development. A prominent feature revealed by this assay is
that the neurokinin-l receptor gene expression in the rat brain is dev
elopmentally regulated. The hippocampus displayed a transient peak of
neurokinin-l receptor messenger RNA at postnatal day 3 and a subsequen
t gradual decrease. In the cerebral cortex, the amount of the message
was highest at birth, and was followed by a moderate decrease during p
ostnatal development. At 56 days after birth, the expression levels in
both brain regions were down-regulated to approximately 50% of their
maximal levels. The transitory pattern of gene expression was also obs
erved in the cerebellum. The results of this study demonstrate that th
e reverse transcription-polymerase chain reaction-based assay is usefu
l to quantitate precisely the neurokinin-l tachykinin receptor message
in limited tissue samples derived from discrete brain regions. Togeth
er with previous findings, the increased level of neurokinin-l recepto
r messenger RNA expression in immature rat brain shown by the present
analysis suggests that the neurokinin-l-type tachykinin receptor may p
lay a role in the synaptic plasticity associated with morphological an
d functional development of the mammalian CNS. Copyright (C) 1996 IBRO
.