Intracellular injection of a Ca 2+ chelator prevents generation of anoxic
LTP.
Crepel, V. and Y. Ben-Ari.
Universite Ren[acute]e Descartes and INSERM U 29, 123 Boulevard de Port-Royal,
75674 Paris cedex 14 France.
APStracts 2:0300N, 1995.
SUMMARY AND CONCLUSIONS
1. The effects of intracellular injection of Ca 2+ chelator 1,2-bis (2-
aminophenoxy) ethane N,N,N_,N_-tetra-acetic acid (BAPTA; 50 mM) on anoxia-
aglycemia-induced long-term potentiation were investigated in the CA1 region
of hippocampal slices using extra- and intra-cellular recording techniques.
Experiments were performed in artificial cerebrospinal fluid (ACSF) containing
10 _M bicuculline and 10 _M 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to
pharmacologically isolate N-methyl-D-aspartate (NMDA) receptor-mediated
responses. NMDA receptor-mediated EPSPs and field potentials were evoked by
stimulation of the Schaffer collateral/commissural pathway in presence of 0.3
mM MgCl 2 and 10 _M glycine to promote NMDA receptor-mediated responses. Under
these conditions, application of 50 _M D-2-amino-phosphonovalerate (D-APV)
abolished EPSPs and field potentials. 2. Anoxic-aglycemic (AA) episodes (2-2.5
min duration) potentiated the initial slope (measured within 3 ms from the
onset of the synaptic responses) of EPSPs by 108 +/- 14.3 % (mean +/- S.E., p
= 0.0012, n = 7). We refered to this long-term potentiation (LTP) of NMDA
receptor-mediated synaptic responses as anoxic LTP. 3. Intracellular injection
of the Ca 2+ chelator BAPTA (with the intracellular recording electrode filled
with 50 mM BAPTA in 3M KCl) prevented anoxic LTP. Thirty to fourty minutes
after the AA episode, in BAPTA loaded cells, the initial slope of the EPSPs
was not significantly changed (+ 7.12 +/- 5 %, p = 0.35, n = 5). In contrast,
the initial slope of the field potentials, measured at the same time in the
same slices, were persistently increased (+ 49 +/- 2.8 %, p = 0.0022, n = 5).
4. High frequency tetanic stimulation (100 Hz for 500 ms, 2 times and 30 s
apart) of the Schaffer collateral/commissural pathway, applied more than half
an hour after the AA episode, induced an additional significant and persistent
increase in the initial slope of the field potential (tetanic LTP, + 35.4 +/-
9.8%, p = 0.012, n = 5). In BAPTA loaded cells, there was no further change in
the initial slope of the EPSP (+ 3.9 +/- 3.4 %, p = 0.205, n = 5) after the
tetanic stimulation. 5. We also report that AA episodes or tetanic stimulation
induced a persistent increase in a late synaptic component which was blocked
by 50 _M D-APV. This late component was mediated polysynaptically, since its
time to peak decreased with increasing stimulation intensities and it was
strongly reduced by high divalent cation superfusate (ACSF containing 7 mM Ca
2+ ). This component, which had a delay of around 8-30 ms, contaminated mainly
the peak amplitude and the decay of the monosynaptic response without
affecting its initial slope. Thus, the measure of the initial slope takes into
account only the early phase of the monosynaptic response. 6. We conclude that
(i) a rise in intracellular Ca 2+ is necessary to generate anoxic LTP of NMDA
receptor-mediated responses, as is the case for tetanic LTP. (ii) In presence
of bicuculline and low extracellular Mg 2+ , AA episodes and tetanic
stimulations induced a long-lasting enhancement of a polysynaptic component
mediated or controlled by NMDA receptors.
Received 18 April 1995; accepted in final form 28 August 1995.
APS Manuscript Number J264-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95