Selective enhancement of non-NMDA receptor-mediated responses following induction of long-term potentiation in entorhinal cortex.
The contribution of NMDA receptors to the expression of long-term potentiation (LTP) is controversial. In entorhinal cortex (EC) previous studies reported either that LTP was exclusively expressed through NMDA receptors or that both NMDA and non-NMDA receptors were involved in LTP expression. To reexamine this issue, horizontal entorhinal cortical slices were prepared from adult rats and electrical stimulation was delivered in layer II/III, while field potential recordings were made in layer III. In the standard condition (2.5 mM Mg(++)), LTP was reliably induced by theta burst stimulation, but was blocked by 100 microM D-AP5, an NMDA receptor antagonist. This corroborates previous reports that NMDA receptor activation is required for induction of EC LTP. The field potential response was not affected by D-AP5, but completely blocked by 10 microM CNQX, a non-NMDA receptor antagonist. This indicates that the expression of LTP is mediated by non-NMDA receptors in the standard condition. LTP of NMDA receptor-mediated responses was tested by comparing NMDA responses before and after applying theta burst stimulation in medium containing low magnesium (0.4-1 mM). Theta burst stimulation induced 43.2+/-9.7% increase of non-NMDA responses (i.e., AP5-insensitive fast component) but 5.6+/-9.0% decrease of the NMDA receptor component (AP5-sensitive slow component). These results indicate that activation of NMDA receptors is critical for induction of LTP, but LTP expression is mediated by non-NMDA receptors in EC under these experimental conditions.
Yun
S H
SH
Neuroscience Laboratory, Institute for Medical Sciences, Ajou University School of Medicine, Suwon 442-721, Korea.
Huh
K
K
Jung
M W
MW
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D018728:Entorhinal Cortex / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate