Palestra PPGNeuro/UFRN- IINN-ELS

Cellular mechanisms of assembly formation during sharp wave-ripple oscillations in vitro

Andreas Draguhn - Universidade de Heidelberg

Sharp waves and superimposed ripple oscillations (SPW-R) are well-delineated events in hippocampal networks which occur preferentially during slow-wave sleep or awake immobility. Unit recordings in behaving animals have shown that neuronal activity
during these events follows a strict spatio- temporal organization: i) firing of principal cells occurs sharply phase-coupled to the underlying field ripple oscillation; ii) place cells fire in a temporal order which reflects previous experience.  These observations suggest that hippocampal pyramidal cells are functionally divided into neurons which participate in SPW-R and those which remain silent. We have used an in vitro model of SPW-R to search for the underlying

Parallel cellular and field potential recordings from mouse hippocampal slices revealed that there is indeed a strict discrimination between participating and non-participating pyramidal cells during SPW-R. Participators increase their firing rate during SPW-R and discharge in strict phase synchrony, similar to previous observations in vivo. The action potentials, however, have a
non-canonical waveform, taking off from a  hyperpolarizing pre-potential rather than from a depolarization. Current injection in both directions showed that SPW-R-coupled spikes are largely insensitive to somatic potential. We conclude that these network-entrained action potentials are of ectopic axonal origin, i.e. they are antidromic spikes. GABAergic signaling plays a dual role: somato-dendritic inhibition suppresses activity of the non-participators during SPW-R, but activation of axonal GABA-A receptors facilitates generation of antidromic,  participating spikes.

Together, our data reveal three mechanisms defining SPW-R-coupled neuronal assemblies:

(1) somatodendritic inhibition suppresses "normal" orthodromic spike generation and thus enhances signal-to-background ratio; (2) phase-coupled action potentials of participating neurons are
generated in distal axonal compartments; (3) axonal GABA-A receptors facilitate the generation of participating spikes.

Quando: terça-feira, 24/08/2010, 17:00h
Onde: Auditório Centro de Pesquisas Natal

Rua Professor Francisco Luciano de Oliveira, 2460 – Candelária.

Notícia cadastrada em: 23/08/2010 11:15
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