Reversal of LTP in the hippocampal afferent fiber system to the prefrontal cortex in vivo with low-frequency patterns of stimulation that do not produce LTD.
We examined the efficacy of several patterns of low-frequency stimulation for producing long-term depression (LTD) or depotentiation in the hippocampal fiber pathway to the prefrontal cortex in the anesthetized rat. Field potentials elicited by stimulation of the CA1/subicular region of the ventral hippocampus were recorded in the prelimbic area of the prefrontal cortex. We found no evidence that low-frequency trains (0.5-1 Hz), consisting of either single pulses, paired pulses (35-ms interpulse interval), or two-pulse bursts (5-ms interval), produce LTD in the prefrontal cortex. In contrast, all three stimulus protocols were found to induce a small-amplitude, persistent potentiation of the amplitude of the negative wave of the field response recorded in the prefrontal cortex. We also examined the ability of patterns of low-frequency stimulation to produce depotentiation of previously established long-term potentiation (LTP). Although low-frequency stimulation with single pulses or paired pulses was ineffective, we found that the two-pulse burst protocol selectively produced a rapid reversal of LTP in the hippocampo-prefrontal cortex pathway. Depotentiation is reversible and can be induced >2 h after the induction of LTP. Repeated trains failed to decrease the prefrontal cortex response below the original, unpotentiated level. These findings demonstrate the existence of a depotentiation mechanism that is capable of exerting powerful control over ongoing or recently induced synaptic plasticity in hippocampocortical connections in vivo.
Burette
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F
Laboratoire de Neurobiologie de l'Apprentissage et de la Mémoire, Centre National de la Recherche Scientifique URA 1491, Université Paris Sud, Orsay, France.
Jay
T M
TM
Laroche
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S
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D015536:Down-Regulation; D004558:Electric Stimulation; D006624:Hippocampus / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley