Brain Research 885 2000 182–191 www.elsevier.com locate bres
Research report
Corticosterone inhibits generation of long-term potentiation in rat hippocampal slice: involvement of brain-derived neurotrophic factor
Jianzheng Zhou , Fang Zhang, Yongxiang Zhang
Laboratory of Neuropharmacology , Beijing Institute of Pharmacology and Toxicology, Beijing 100850, PR China
Accepted 29 August 2000
Abstract
In the present study, the effect of corticosterone CORT on the generation of long-term potentiation LTP and its underlying mechanism involving neurotrophin gene expression in CA1 synapses of rat hippocampal slice were examined. Our experimental results
showed incubation of hippocampal slice with CORT for 3 h had no effect on either the slope or amplitude of excitatory postsynaptic potentials EPSP evoked in hippocampal CA1 pyramidal dentrites, indicating no marked change in basal synaptic transmission. However,
when tetanic stimulation 100 pulses, 100 Hz was delivered to the Schaffer collateral pathway, CORT application significantly attenuated the tetanus-induced increases of both EPSP slope and amplitude, demonstrating an inhibitory effect of CORT on LTP generation. In
addition, CORT treatment significantly reduced both slope and amplitude ratios of the second evoked EPSP to the first one when paired-pulse facilitation PPF was established at different interpulse intervals from 20 to 40 ms, suggesting that a presynaptic mechanism
may be involved in CORT-induced hippocampal synaptic plasticity. Reverse-transcription polymerase chain reaction RT-PCR analysis showed that CORT-treated hippocampal CA1 cells underwent a significant decrease in the expression of mRNA for nerve growth factor-b
NGF-b and brain-derived neurotrophic factor BDNF, but not for neurotrophin-3 NT-3 compared with those in control. Moreover, BDNF co-applied with CORT significantly antagonized CORT-induced deficit in PPF. Taken together, the present results suggest that
CORT-induced inhibition of LTP may be, at least to some extent, mediated by a presynaptic mechanism and decrease in the BDNF expression in rat hippocampal CA1 cells induced by CORT may partially account for this presynaptic mechanism.
2000 Elsevier
Science B.V. All rights reserved.
Keywords : Corticosterone; Long-term potentiation; Paired-pulse facilitation; Synaptic plasticity; Synaptic transmission; Reverse-transcription-polymerase
chain reaction; Neurotrophin; Nerve growth factor NGF; Brain-derived neurotrophic factor BDNF; Neurotrophic factor-3 NT-3
1. Introduction glutamate, hypoxia, etc., to the hippocampal neurons
[1,2,5]. In addition, administration of CORT to rats in vivo Glucocorticoids are series of important steroid hormones
for 3 months led to significant impairment of learning and in regulating metabolism of glucose, fat and protein in
memory [37]. The underlying mechanisms were believed various peripheral tissues. Recent studies indicated that
to be closely related to accumulation of excitatory amino high concentration of glucocorticoids showed adverse
acids, energetic deficiency or cytosolic calcium overload effects on the central nervous system CNS, especially on
[17,29,36]. More recent studies show that glucocorticoids the hippocampus [12,37]. It was reported that application
may participate in regulating synaptic transmission and of corticosterone CORT in vitro not only impaired the
play an important role in maintaining the hippocampal primary cultured hippocampal neurons directly [45] but
synaptic strength [6,28]. Either adrenalectomy [34] or also exacerbated neurotoxicity of many insults, such as
exogenous CORT supplementation [46] inhibited LTP generation in the hippocampal dentate gyrus. Bodnoff et al.
reported that CORT application to middle-aged rats for 3 months led to impairment of learning and memory, great
neuron loss and inhibition of LTP formation in the
Corresponding author. Unit of Synaptic Development and Plasticity,
hippocampus [3]. These results implicated that the CORT-
Laboratory of Developmental Neurobiology, NICHD, NIH, Bldg. 49 Rm.
induced deficit in hippocampal synaptic efficacy might
6A67, Bethesda, MD 20892-4480, USA. E-mail address
: jzhoucodon.nih.gov J. Zhou.
result from the structural modification of the hippocampus.
0006-8993 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 2 9 3 4 - 6
J . Zhou et al. Brain Research 885 2000 182 –191
183
In our previous study [46], however, CORT applied 1 h tion. The hippocampus was carefully dissected in 95
before tetanus without causing any morphological modi- O 5 CO -saturated ice-cold artificial cerebrospinal fluid
2 2
fication also significantly inhibited both induction and ACSF. A transverse hippocampal slice with thickness of
maintenance phases of LTP in vivo, suggesting the inhib- 400–450 mm was prepared using a vibroslice World
itory effect may be mediated by a quick and direct Precision Instruments, USA and recovered in warmed,
mechanism. 95 O 5 CO -saturated ACSF for at least 1 h as
2 2
Neurotrophins are traditionally identified as a family of described previously [43]. The slices were then transferred
protein factors essential for neuronal survival and differen- in a submerged chamber perfused with warmed 348C
tiation. However, a series of recent studies suggested a ACSF pH 7.4 containing in mM NaCl 124, KCl 3.0,
novel role of neurotrophins in synaptic transmission and CaCl
2.5, MgCl 1.5, NaHCO
26, KH PO 1.25,
2 2
3 2
4
plasticity [4,22,24,39]. Long-term application of the BDNF glucose 10 and ascorbic acid 2. Field EPSP was evoked in
and NT-3 was found to enhance synaptic transmission at CA1 stratum radiatum by stimulating the Schaffer colla-
the developing
neuromuscular junction
in culture
teral pathway with twisted bipolar nichrome electrodes and [21,23,40]. The acute effects of neurotrophins on neuronal
recorded with ACSF-filled glass pipette ,5 MV using a activity and synaptic transmission were also observed in
microelectrode amplifier MEZ-8201, Nihon Kohden, cultured neurons and in slices by a number of laboratories
Japan. Test stimuli consisted of monophasic 100-ms [15,19,20]. Kang and Schuman [13] showed that acute
pulses of
constant current
delivered by
electronic application of BDNF and NT-3 enhanced basal excitatory
stimulator SEN-3201, Nihon Kohden. Basal synaptic synaptic transmission in CA1 synapse of adult hippocam-
transmission was examined by alternating, low-frequency pal slices. Tanaka [38] found BDNF did not affect basal
stimulation at 0.033 Hz one stimuli for every 30 s of two excitatory synaptic transmission but rapidly reduced IPSC
separate pathways
via two
stimulating electrodes
at CA1 synapses in hippocampal slices. Meanwhile, BDNF positioned on both sides of the recording electrode. Only
knock-out conferred deficit in generating LTP in mouse slices exhibiting EPSP of 2–3 mV in amplitude without
hippocampal CA1 synapses and this defect can be rescued superimposed population spikes were used. Stimulus in-
after prolonged incubation with BDNF-containing adeno- tensity was adjusted to produce an EPSP with |50 of
virus [16]. Application of exogenous BDNF promotes LTP maximum amplitude. Tetanic stimulation, which consisted
induction in neonatal hippocampal slices, where the endog- of 100 pulses at 100 Hz, was used to induce LTP. LTP was
enous BDNF levels are low [9]. In contrast, treatment with thought to be induced and expressed when both EPSP
TrkB-IgG, a fusion protein that scavenges endogenous amplitude and slope were potentiated more than 25
BDNF, reduces the magnitude of LTP in the adult hip- above the baseline for at least 30 min after tetanus. We also
pocampus [14], where the endogenous BDNF levels are employed PPF to examine the synaptic strength presynapti-
high. Moreover, BDNF perfused with mice hippocampal cally. A paired stimuli with interpulse intervals from 20 to
slice for 3 h enhanced PPF, suggesting that BDNF-induced 50 ms was given to the Schaffer collateral pathway and the
enhancement of synaptic efficacy may be somewhat in- evoked EPSPs were recorded. The ratios of evoked EPSP
volved in a presynaptic mechanism [10]. slope and amplitude in the second stimuli to those in the
In our present study, the effect of CORT on hippocam- first one were calculated to examine presynaptic facilita-
pal synaptic transmission and its underlying mechanism tion during PPF. Both slopes and amplitudes of EPSP were
involving the neurotrophin gene expression are explored. digitized 10 kHz, filtered at 1 kHz eight-pole Bessel
We found that CORT application significantly inhibited filter, stored on magnetic media using an acquisition
LTP, PPF as well as BDNF gene expression in rat system PClab 2.0 Beijing PClab Instruments, Beijing,
hippocampal CA1 synapses while perfusion with BDNF China and analyzed off-line. CORT was added directly
rescued the CORT-induced impairment of PPF, suggesting into the ACSF and perfused the rat hippocampal slice for 3
that the inhibitory effect of CORT on hippocampal synap- h before delivery of tetanus to the Schaffer collateral
tic plasticity may be closely related to BDNF gene pathway. PPF is believed to be established when both the
expression. Our experimental results provide further in- EPSP slope and amplitude in the second response is at
sight in understanding endangerment of glucocorticoids on least 15 above the first one.
the hippocampus. 2.2. Determination of the expression of mRNA for NGF-
2. Materials and methods b, BDNF and NT-3 by RT-PCR
