Developmental emergence of hippocampal fast-field "ripple" oscillations in the behaving rat pups.
Sharp wave and associated fast oscillatory ripples (140-200 Hz) in the cornu ammonis 1 region are the most synchronous hippocampal patterns in the adult rat. Spike sequences associated with sharp waves are believed to play a critical role in transferring transient memories from the hippocampus to the neocortex and the emergence of superfast ripples is pathognostic in temporal lobe epilepsy. Sharp waves in cornu ammonis 1 stratum radiatum are induced by a strong depolarization by the cornu ammonis 3 Schaffer collaterals, due to the synchronous discharge of cornu ammonis 3 pyramidal cells. Although during the first postnatal week, sharp-wave events are associated with hippocampal unit bursts in the pyramidal layer, ripple oscillations are absent. We investigated the emergence of fast-field oscillations in rat pups ranging from postnatal day 12-20 by recording with wire tetrodes in freely behaving pups and with 16-site linear silicon probes in head fixed animals. Cornu ammonis 1 pyramidal cell layer was determined by the presence of multiple unit activity and a reversal of the field potential in the deeper electrode sites. On-line verification of the recording sites was determined via an evoked response to commissural stimulation, showing a clear reversal in the field potential. Sharp wave-associated fast-field oscillations did not begin to emerge until the end of the second postnatal week and showed a gradual increase until day 18. Once ripples emerged, the intra-ripple frequency assumed adult values. The developmental time course of the ripple parallels the switch in the GABA(A) receptor-mediated signaling from excitation to inhibition. The time course may also reflect hitherto unidentified emergence of neuronal gap junctions.
Buhl
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DL
Center for Molecular and Behavioral Neuroscience, Rutgers, The State University of New Jersey, Newark, 07102, USA.
Buzsáki
G
G
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal / Q000502:physiology*; D001683:Biological Clocks; D004558:Electric Stimulation; D004569:Electroencephalography; D006624:Hippocampus / Q000254:growth & development* / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley