Application of N-methyl-d-aspartate induces long-term potentiation in the medial perforant path and long-term depression in the lateral perforant path of the rat dentate gyrus in vitro

Wang, Yue, Jianqun Wu, Michael J. Rowan, and Roger Anwyl. Conditions for the induction of long-term potentiation and long-term depression by conjunctive pairing in the dentate gyrus in vitro. J. Neurophysiol. 78: 2569–2573, 1997. The conditions under which long-term potentiation (LTP) and long-term depression (LTD) of excitatory postsynaptic currents were induced by the conjunctive pairing-type protocol of afferent stimulation and postsynaptic depolarization were studied in the medial perforant pathway-granule cell synapse of the dentate gyrus in vitro. The conjunctive pairing of 1-Hz afferent stimulation and steady state postsynaptic depolarization to 0 mV did not induce LTP or LTD. Inhibition of LTD induction with a phosphatase inhibitor or ruthenium red resulted in induction of LTP after the conjunctive pairing. Such LTP induction was N-methyl-d-aspartate dependent. Conversely, inhibition of LTP induction with a kinase inhibitor resulted in LTD induction after the conjunctive pairing. Thus the failure to induce LTP or LTD with the pairing protocol involving depolarization to 0 mV membrane potential was due to simultaneous activation of intracellular processes that generate the induction of LTP and LTD. Increasing the frequency of afferent stimulation to 200 Hz, even for just eight stimuli, resulted in LTP induction. The studies show that two factors govern the induction of LTP/LTD, membrane potential and frequency of afferent stimulation, with either increased depolarization or increased afferent stimulation favoring LTP induction.

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In Vivo Recordings of Long-Term Potentiation and Long-Term Depression in the Dentate Gyrus of the Neonatal Rat

Journal of Neurophysiology ◽

10.1152/jn.00307.2003 ◽

2004 ◽

Vol 91 (2) ◽

pp. 613-622 ◽

Cited By ~ 4

Author(s):

Michael P. O'Boyle ◽

Viet Do ◽

Brian E. Derrick ◽

Brenda J. Claiborne

Keyword(s):

Dentate Gyrus ◽

Granule Cells ◽

Long Term Potentiation ◽

Neonatal Rat ◽

Perforant Path ◽

Long Term Depression ◽

Term Potentiation ◽

Old Rats

Previous in vitro studies demonstrated that long-term potentiation (LTP) could be elicited at medial perforant path (MPP) synapses onto hippocampal granule cells in slices from 7-day-old rats. In contrast, in vivo studies suggested that LTP at perforant path synapses could not be induced until at least days 9 or 10 and then in only a small percentage of animals. Because several characteristics of the oldest granule cells are adult-like on day 7, we re-examined the possibility of eliciting LTP in 7-day-old rats in vivo. We also recorded from 8- and 9-day-old rats to further elucidate the occurrence and magnitude of LTP in neonates. With halothane anesthesia, all animals in each age group exhibited synaptic plasticity of the excitatory postsynaptic potential following high-frequency stimulation of the MPP. In 7-day-old rats, LTP was elicited in 40% of the animals and had an average magnitude of 143%. Long-term depression (LTD) alone (magnitude of 84%) was induced in 40% of the animals, while short-term potentiation (STP) alone (magnitude of 123%) was induced in 10%. STP followed by LTD was elicited in the remaining 10%. Data were similar for all ages combined. In addition, the N-methyl-d-aspartate (NMDA) antagonist ( R,S)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked the occurrence of LTP at each age and doubled the percentage of animals expressing LTD alone for all ages combined. These results demonstrate that tetanic stimulation can elicit LTP or LTD at MPP synapses in 7-day-old rats, supporting our premise that at least a portion of the dentate gyrus is functional at this early age.

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