Alice.nc.huji.ac.il
2001 Nature Publishing Group http://neurosci.nature.com
brief communications
L-type Ca2+ channel-
In sharp contrast to the lack of effect on single IPSCs, blockade
of L-type Ca2+ channels eliminated PTP and turned it into a depres-
mediated short-term
sion lasting for about 80 s (
Fig. 2b–
d). In nifedipine, the post-
tetanus eIPSC1 was reduced to 85.3 ± 11% of control, versus
plasticity of GABAergic
129 ± 12% of control before nifedipine was perfused (
p < 0.05,
n= 4, paired
t-test). In diltiazem, the post-tetanus eIPSC1 was 76.3
synapses
± 7.1% of control (
Fig. 3b), versus 122 ± 6.4% of control before
diltiazem (
p < 0.05,
n = 4). These findings are consistent with a crit-
ical role of L-type Ca2+ channels in the induction of post-tetanic
potentiation of GABAergic IPSCs. In the presence of nifedipine,
the post-tetanic IPSCs showed paired-pulse facilitation, so that the
Department of Neurology, RNRC 3-131, University of California, Los Angeles
eIPSC2:eIPSC1 ratio increased from 0.69 ± 0.06 to 1.07 ± 0.15 (
Fig.
School of Medicine, 710 Westwood Plaza, Los Angeles, California 90095, USA
3c,
p < 0.05, paired
t-test). In diltiazem, the tetanus increased the
Correspondence should be addressed to I.M. (mody@ucla.edu)
eIPSC2:eIPSC1 ratio from 0.86 ± 0.07 to 1.27 ± 0.25 (
p < 0.05). The
osci.nature
L-type channel antagonists had no effect on the progressive tetan-
Published online: 10 September 2001, DOI: 10.1038/nn722
ic depression of the eIPSCs occurring during the 80-pulse stimu-lation at 40 Hz (
p > 0.05). Nifedipine and diltiazem also failed to
In the cerebral cortex, the major inhibitory neurotransmitter GABA
block the post-tetanus increase in spontaneous IPSCs. (See the sup-
(γ-aminobutyric acid) is released by GABAergic neurons1 onto
plementary information page of
Nature Neuroscience online.)
GABAA and GABAB receptors, and regulates neuronal excitability,
Here we confirm that L-type Ca2+ channels are not involved in
oup http://neur
postsynaptic action potential firing, and dendritic and synaptic inte-
low-frequency synaptic transmission at GABAergic synapses8. How-
gration2. Various interneurons use either N- or P/Q-type Ca2+ chan-
ever, the contribution of L-type channels to synaptic transmission
nels for the Ca2+ influx into their terminals3, whereas L-type Ca2+
became evident when GABAergic synapses were driven by high-
channels are not normally associated with GABA release. In dual
frequency firing in the gamma-frequency range4, which led to PTP.
lishing Gr
recordings from hippocampal basket cells and granule cells, we now
The rapid onset of PTP suggests that the presynaptic L-type Ca2+
report that short-term plasticity of GABA release is controlled by
channels are located near the GABAergic terminals. This is sur-
L-type Ca2+ channels at presynaptic firing rates in the gamma-fre-
prising because L-type channels have yet to be anatomically detect-
quency (40 Hz) range4; at these GABAergic synapses, L-type Ca2+
ed at these sights. Given that L-type Ca2+ channel antagonists block
channel antagonists converted post-tetanic potentiation into depres-
PTP but not the ‘late release’ (above and ref. 8), whereas EGTA-AM
sion, identifying L-type Ca2+ channels as important modulators of
blocks ‘late release’ but not PTP7,9, we propose that the L-type Ca2+
channels are coupled to second messenger cascades regulating the
2001 Nature Pub
Fast-spiking basket cells (
Fig. 1a) were identified on the border
availability of transmitter vesicle pools. L-type Ca2+ channel activ-
between the granule cell layer and the hilus in the rat dentate gyrus
ity could activate calmodulin-mediated processes10,11, which in
in brain slices. In dual recordings from basket cells and granule cellsin 3 mM kynurenic acid, stimulation of the basket cell to fire sin-gle action potentials (APs) evoked a GABAA receptor-mediated
IPSC (eIPSC) in the granule cell (
Fig. 1b). Baseline responses were
obtained by presynaptic paired-pulse stimulation (50 ms interval)
evoking two eIPSCs (eIPSC1 and eIPSC2) every 5 s. The amplitude
of eIPSC1 was 139 ± 32 pA (33°C,
n = 9) and showed quantal-like
variations, including failures (11.1 ± 5.4%). Perfusion of the L-type
Ca2+ channel antagonist nifedipine (10 µM) did not affect thepresynaptic AP (half-width, 0.53 ± 0.06 ms in control versus 0.60 ± 0.08 ms with nifedipine,
p > 0.05,
n = 4). Nifedipine alsohad no effect on the eIPSC1 amplitude (96 ± 15% of control,
p > 0.05,
n = 4) or its variance, latency, 10–90% rise time or decaykinetics. Another L-type Ca2+ channel blocker, diltiazem (25 µM),also failed to affect eIPSC1 (amplitude, 105 ± 16% of control,
p > 0.05,
n = 4) or the presynaptic AP. Miniature IPSCs recordedin granule cells in the presence of CdCl
We then examined the short-term plasticity of IPSCs evoked by
high-frequency APs in the range of the normal firing behavior ofbasket cells5. We induced post-tetanic potentiation (PTP) of eIP-SCs by stimulating the basket cells in the gamma-frequency range(40 Hz, 2 s). PTP is a reversible enhancement of transmitter release
Fig 1. Nifedipine did not affect GABAergic IPSCs evoked by low-fre-
that lasts for minutes, and has been observed at many synapses6,7. In
quency basket cell firing. (
a) Basket cell firing in the dentate gyrus in rat
brain slices. (
b) Dual whole-cell recording from a basket cell and a gran-
5–45 s post-tetanus,
p < 0.05, paired
t-test) and lasted about 120 s
ule cell (bottom) in 3 mM kynurenic acid. Stimulation of the basket cell
(
Fig. 2a and
d,
n = 12). During this enhancement, paired-pulse
to fire single action potentials evoked short-latency eIPSCs in the gran-
depression of the eIPSCs also increased, consistent with PTP being
ule cell. Consecutive eIPSCs were evoked every 5 s and superimposed.
The L-type Ca2+ channel antagonist nifedipine (10 µM) did not affect the
a presynaptic phenomenon. Hence, the eIPSC2:eIPSC1 ratio
eIPSCs. (
c) The presynaptic action potential and the eIPSCs shown on
decreased from 0.95 ± 0.06 to 0.84 ± 0.07 (
p < 0.05, paired
t-test).
an expanded time scale. Their time course was unaffected by nifedipine.
nature neuroscience • volume 4 no 10 • october 2001
2001 Nature Publishing Group http://neurosci.nature.com
brief communications
osci.nature
Fig. 3. The post-tetanic eIPSC amplitude and paired-pulse modulation.
(
a) PTP in a single cell pair. Data were analyzed as indicated by brackets.
Pre-tetanic, average of 12 eIPSCs before the tetanus; post-tetanic, aver-
age of 9 eIPSC after the tetanus; recovery, average of 12 eIPSCs when
the responses had recovered. (
b) Post-tetanic eIPSC1 in control (white
oup http://neur
bars,
n = 12), in nifedipine (
n = 4) and in diltiazem (
n = 4). The normal-
ized eIPSC1 amplitudes showed PTP in control, and depression in
nifedipine and diltiazem (
p < 0.05). (
c) The eIPSC2:eIPSC1 ratios illus-
trating the paired-pulse behavior of the IPSCs. In control, post-tetanic
lishing Gr
IPSCs showed a small increase in paired-pulse depression (white bars,
p< 0.05). In the presence of the L-type Ca2+ channel blockers, post-tetanic eIPSCs displayed paired-pulse facilitation (
p < 0.05), indicatingthat the release probability had been lowered.
channel-mediated potentiation of GABA release, which may be crit-
2001 Nature Pub
ical for frequency shifts15 in the cerebral cortex. Therefore, L-type
Ca2+ channels could be important in controlling the populationactivity in highly interconnected hippocampal neurons.
Fig. 2. Post-tetanic potentiation of IPSCs was blocked by L-type Ca2+
channel antagonists. (
a) Paired-pulse stimulation of the basket cell to
Note: Supplementary methods are available on the Nature Neuroscience web site
fire APs evoked two IPSCs (eIPSC1 and eIPSC2) every 5 s in the granulecell. After tetanic stimulation of the basket cell (40 Hz, 2 s), eIPSC
(http://neuroscience.nature.com/web_specials.)
played post-tetanic potentiation by 75% and the paired-pulse depres-
sion of eIPSC2 increased. (
b) Following perfusion of nifedipine, the
ACKNOWLEDGEMENTS
pre-tetanic eIPSC1 was unaffected, whereas the post-tetanic eIPSC1 was
This work was supported by NIH grant NS 30549 and the Coelho Endowment to
depressed to 63% of control and eIPSC2 showed paired-pulse facilita-
I.M. K.J. is a Glaxo/Wellcome scholar.
tion. (
c) The L-type channel antagonist diltiazem (25 µM) also caused
post-tetanic depression. (
d) Post-tetanic potentiation of eIPSC1 in con-
RECEIVED 2 JULY; ACCEPTED 18 AUGUST 2001
trol (
n = 12) compared with post-tetanic depression in nifedipine (
n = 4)or diltiazem (
n = 4). Tetanic stimulation of the basket cell was deliveredat 0 s. For each trial, eIPSC
1. Freund, T. F. & Buzsaki, G.
Hippocampus 6, 347–470 (1996).
2. Miles, R., Toth, K., Gulyas, A. I., Hajos, N. & Freund, T. F.
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tetanic baseline (100%), plotted and averaged across cells. The plot was
smoothed by a running average of six responses. The standard error for
3. Poncer, J. C., McKinney, R. A., Gahwiler, B. H. & Thompson, S. M.
Neuron 18,
each group (also smoothed) is shown below.
4. Tamas, G., Buhl, E. H., Lorincz, A. & Somogyi, P.
Nat. Neurosci. 3, 366–371
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(MLCK), controlling vesicle recycling and the mobilization of a
6. Kamiya, H. & Zucker, R. S.
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vesicle reserve pool12. Ca2+ entry through L-type Ca2+ channels
7. Jensen, K., Jensen, M. S. & Lambert, J. D.
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8. Jensen, K., Jensen, M. S. & Lambert, J. D.
J. Neurophysiol. 81, 1225–1230
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observed a transient post-tetanic depression when L-type channels
9. Atluri, P. P. & Regehr, W. G.
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10. Holt, E. H., Broadus, A. E. & Brines, M. L.
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synaptic depression induced by extensive presynaptic trains13. With
11. Zuhlke, R. D., Pitt, G. S., Deisseroth, K., Tsien, R. W. & Reuter, H.
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the potentiating L-type Ca2+ channel-dependent mechanism
12. Ryan, T. A.
J. Neurosci. 19, 1317–1323 (1999).
engaged, the terminals would be protected against synaptic depres-
13. Kraushaar, U. & Jonas, P.
J. Neurosci. 20, 5594–5607 (2000).
sion by the increase of the releasable pool.
In vivo, GABAergic bas-
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ket cells14 fire at frequencies in the 40 Hz (gamma) range5. Thus,
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Int.
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nature neuroscience • volume 4 no 10 • october 2001
Source: http://alice.nc.huji.ac.il/~netazach/synapse/jensen%202001.pdf
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