Polysynaptic potentiation in the lateral septum following stimulation of the fimbria in anesthetized rats.
In anesthetized rats, electrical stimulation of fimbria fibers evoked, in the ipsilateral lateral septum (LS), a field potential consisting of two negative components: an initial negativity (N2-3 complex wave) of high amplitude at 6.7 ms (+/- 0.8 ms; peak latency) and a slow negative wave (N4 wave) of small amplitude at 14.4 ms (+/- 2.4 ms). The N2-3 complex wave represents the monosynaptic activation of LS neurons while the N4 wave corresponds to polysynaptic activation of neurons in the mediolateral part of the LS. In this study, we investigated the effects of high-frequency stimulation of fimbria fibers on LS field potentials and compared them with those observed in the CA3 area. Tetanic stimulation of the fimbria did not change the characteristics of the N2-3 wave but induced a long-lasting increase in amplitude and slope of the N4 wave. A positive correlation was found between the magnitude of CA3 LTP and lateral septal polysynaptic potentiation of the N4 component. These results indicate that patterns of stimulation delivered to the same input fibers (fimbria fibers) produce similar changes in a polysynaptic input to the LS and in a monosynaptic input to the CA3 and emphasize the complexity of signal processing in serial networks.
Garcia
R
R
Laboratoire de Neurosciences Comportementales et Cognitives, CNRS URA 339, Université de Bordeaux I, Talence, France. garcia@neurocog.u-bordeaux.fr
Tocco
G
G
Baudry
M
M
Thompson
R
R
D000758:Anesthesia; D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology; D006624:Hippocampus / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012686:Septal Nuclei / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*