MULTIDIRECTIONAL PROPAGATION OF SPW-R COMPLEXES IN THE RAT HIPPOCAMPUS, IN VITRO
Ágnes Kandrács1, 2, Csilla Szabó1, 2, Hédi Maczelka2, 3, Veronika Kardos1, 2, Piroska Teleki1, 2, István Ulbert1, 2, 4, Lucia Wittner1, 2, 4
Sharp wave-ripple (SPW-R) complexes are observed in the mammalian hippocampus on EEG during slow-wave sleep and immobility. These synchronous population discharges are considered to play an essential role in memory consolidation and the replay of wakefulness-acquired memory. An in vitro SPW-R model was investigated on rat hippocampal slices using a 24-channel linear electrode. Instead of assuming a classical trisynaptic circle of information flow from the DG to the CA3 (Type I), our studies showed that SPW-Rs could also be propagated in the opposite direction (Type II), or generated simultaneously in both areas (Type III). Based on these results, it can be stated that bidirectional information flow occurs between the DG and the CA3 region of the rat hippocampus. At the initiation site of the SPW-R complexes, more cells were activated than at other regions. Pyramidal cells of the CA3 fired more and showed denser connectivity than granule cells of the DG. A metabotropic glutamate receptor agonist, DCG-IV was used to investigate the role of the mossy fibres in the generation of SPW-Rs. In DCG-IV bath, the recurrence frequency of Type I SPW-Rs increased, while that of Type II SPW-Rs showed a slight drop. The propagation of SPW-Rs decelerated, while the LFPg deflections and the superimposed multiunit activities were reduced. The role of reverse information flow might be to intensify the information packages transmitted by the SPW-R complexes by adding another network to the trisynaptic circle for more efficient memory consolidation. Although the clarification of underlying mechanisms needs further experiments.