The Journal of Neuroscience, December 1, 2001, 21(23):9315-9324
Regional Differences in Neurotrophin Availability Regulate
Selective Expression of VGF in the Developing Limbic Cortex
Kathie L.
Eagleson1,
Liane D.
Fairfull1,
Stephen
R. J.
Salton2, and
Pat
Levitt1
1 Department of Neurobiology, University of Pittsburgh
School of Medicine, Pittsburgh, Pennsylvania 15261, and
2 Fishberg Research Center for Neurobiology, Mount Sinai
School of Medicine, New York, New York 10029
Gene and protein expression patterns in the cerebral cortex are
complex and often change spatially and temporally through development.
The signals that regulate these patterns are primarily unknown. In the
present study, we focus on the regulation of VGF expression,
which is limited to limbic cortical areas early in development but
later expands into sensory and motor areas. We isolated neurons from
embryonic day 17 rat cortex and demonstrate that the profile of VGF
expression in perirhinal (expressing) and occipital (nonexpressing)
populations in vitro is similar to that in the perinatal
cortex in vivo. The addition of neutralizing neurotrophin antibodies indicates that endogenous brain-derived neurotrophic factor (BDNF) is necessary for the normal complement of
VGF-expressing neurons in the perirhinal cortex, although endogenous neurotrophin-3 (NT-3) regulates the expression of VGF in a
subpopulation of cells. ELISA analysis demonstrates that there is
significantly more BDNF present in the perirhinal cortex compared with
the occipital cortex in the perinatal period. However, the total amount
of NT-3 is similar between the two regions and, moreover, there is
considerably more NT-3 than BDNF in both areas, a finding seemingly in
conflict with regional VGF expression. Quantification of the
extracellular levels of neurotrophins in perirhinal and occipital
cultures using ELISA in situ analysis indicates that
perirhinal neurons release significantly more BDNF than the occipital
population. Furthermore, the amount of NT-3 released by the perirhinal
neurons is significantly less than the amount of BDNF. Local
injection of BDNF in vivo into a normally negative VGF
region results in robust ectopic expression of VGF. These
data suggest that the local availability of specific neurotrophins for
receptor occupation, rather than the total amount of neurotrophin, is a
critical parameter in determining the selective expression of
VGF in the developing limbic cortex.
Key words:
BDNF; NT-3; neurotrophins; VGF; cortical development; ELISA
Copyright © 2001 Society for Neuroscience 0270-6474/01/21239315-10$05.00/0