Seminários em Neurociências 2012.1

Seminários em Neurociências

Hora: 11h

Data: 18/04

Local: Auditório do ICe

Palestrante: Prof. Richardson Leão (ICe-UFRN)

Tema: CA1 OLM cells generate and modulate hippocampal theta oscillations

Richardson N. Leão, Sanja Mikulovic, Katarina Leão, Adriano Tort

Theta oscillations are regular and pronounced brain rhythms (4-12 Hz) involved in a multitude of cognitive processes, but the mechanisms behind their generation are still subject to intense debate. For decades, theta rhythmogenesis has been attributed to extra-hippocampal structures, especially to the medial septum/diagonal band of Brocca (MS/DBB) complex. In this work we show that theta oscillations can be generated in vivo by increasing the excitability of one single type of hippocampal interneuron, the oriens lacunosum-moleculare cells (OLM cells). In addition, optogenetic inhibition of OLM cells significantly decreases theta amplitude in animals anesthetised with urethane or performing exploratory behaviour. Our experiments further show that OLM cells can entrain the activity of pyramidal cell assemblies. We hypothesize that theta pacemaking activity in OLM neurons is produced by a combination of three factors, 1) intrinsic membrane properties, 2) the connectivity to pyramidal cells, and 3) the presence of gap junctions between OLM cells. Our results show a clear correlation between the activation of a well-defined interneuron population and the production of a network phenomenon ubiquitous to all mammals, i.e. theta oscillations. It furthermore demonstrates that the hippocampus is capable of generating theta oscillations independently of other structures, suggesting that an intrinsic hippocampal theta pacemaker could co-exist with extra-hippocampal rhythm generators.