Long-term potentiation in hippocampal CA1: effects of afterdischarges, NMDA antagonists, and anticonvulsants.
Long-term potentiation (LTP) of the basal dendritic population excitatory postsynaptic potential (EPSP) in hippocampal CA1 was readily elicited in behaving rats, without afterdischarges (ADs), by theta-frequency-patterned primed bursts (PBs) delivered to the contralateral CA1. A long-lasting postictal potentiation (PIP) was also elicited by high-frequency trains (1 s at 200 Hz), following an AD and a 5- to 10-min depression. The N-methyl-D-aspartate (NMDA) antagonist 2-amino-phosphonovalerate was effective in blocking both LTP and PIP. The noncompetitive NMDA antagonist MK801 (0.5 mg/kg ip) attenuated the PB-induced LTP but enhanced PIP. The anticonvulsants phenytoin (40 mg/kg ip) and U54494A (25 or 50 mg/kg ip) had no effects on the LTP induced by a PB but they, like MK801, enhanced PIP to various degrees. The apparent enhancement of PIP by anticonvulsants may be a direct result of shortening the hippocampal AD duration and alleviation of the postictal EPSP depression. It is inferred that the typical hippocampal AD did not induce potentiation, but rather a postictal depression of the EPSP or a suppression of LTP. The mechanism of the postictal depression is likely different from the NMDA receptor-mediated LTP and PIP and it may depend on the AD duration (and perhaps excessive CA2+ influx) but not critically on NMDA receptors.
Leung
L S
LS
Department of Physiology, University of Western Ontario, London, Canada.
Shen
B
B
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004594:Electrophysiology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors*; D010672:Phenytoin / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time; D013569:Synapses / Q000502:physiology*
D000927:Anticonvulsants; D011759:Pyrrolidines; D010672:Phenytoin; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; C054216:U 54494A