The Journal of Neuroscience, May 1, 2003, 23(9):3761
Long-Term Depression Is Not Induced by Low-Frequency Stimulation
in Rat Visual Cortex In Vivo: A Possible Preventing Role
of Endogenous Brain-Derived Neurotrophic Factor
Bin
Jiang1, 2,
Yukio
Akaneya1, 2,
Yoshio
Hata1, 2, and
Tadaharu
Tsumoto1, 2
1 Core Research for Evolutional Science and Technology,
Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012 Japan, and 2 Division of Neurophysiology, Osaka University
Graduate School of Medicine, 2-2 Yamadaoka, Suita 565-0871, Japan
Low-frequency stimulation (LFS) at 1 Hz for 15 min is an effective
protocol to induce homosynaptic long-term depression (LTD) in visual
cortical slices. It is reported that LFS becomes ineffective when
brain-derived neurotrophic factor (BDNF) is applied to slices. It is
not known, however, whether such a protocol induces LTD in visual
cortex in vivo, and whether endogenous BDNF has the same
or similar action. To address these questions, we recorded field
potentials of rat visual cortex evoked by stimulation of lateral
geniculate nucleus, white matter, or cortical layer IV. We found that
LFS did not induce LTD of cortical responses in vivo. To
test the possibility that spontaneous activity from retinas would interfere with the induction of LTD, both eyes were removed or
inactivated by tetrodotoxin. LTD was not induced in these conditions either. To test whether the difference in temperature between the two
preparations is a factor for the discrepancy, the temperature of slices
was increased from 31 to 37°C. LTD was induced in slices at either
temperature. Then, we hypothesized that endogenous BNDF and its
receptors, TrkB, prevent the induction of LTD. To test this, we infused
the cortex with an inhibitor of Trk receptor tyrosine kinases,
anti-TrkB IgG1, anti-BDNF, and anti-neurotrophin 4/5 antibodies.
LTD was induced when the BDNF-TrkB system was blocked. In slices, the
level of phosphorylation of Trks was found to decrease with time. These
results indicate that activation of TrkB signal pathway prevents LFS
from inducing synaptic depression in visual cortex in
vivo.
Key words:
long-term depression; LTD; low-frequency
stimulation; brain-derived neurotrophic factor; BDNF; visual cortex; in vivo; slices
Copyright © 2003 Society for Neuroscience 0270-6474/03/2393761-10$05.00/0