, 2007) but is reduced by entorhinal lesions that will mainly compromise excitation (Bragin et al., 1995). We show that EPSCs in GCs are coherent with the LFP in the theta frequency range but to a much smaller extent in the gamma frequency range. Conversely, IPSCs are more coherent in the gamma than in the theta frequency band. Thus, two spectrally and mechanistically distinct rhythmic

signals coexist in the dentate gyrus, with theta activity mainly relayed from the entorhinal cortex via excitation and gamma activity generated by local inhibition (Figure 1C). The classical model of generation of theta oscillation assumes that cholinergic input from the medial septum/diagonal band plays a critical role in theta generation (“atropine-sensitive theta”; Stewart and Fox, 1990). Additionally, disinhibition via local interneurons

may contribute to the theta rhythm (Freund GDC-0199 mouse and Antal, 1988). Finally, intrinsic oscillatory mechanisms may be involved (Goutagny et al., 2009). Our results demonstrate that GCs in vivo are exposed to massive functional glutamatergic input from the entorhinal cortex. EPSCs are theta coherent with the LFP, suggesting that they provide a major contribution to the rhythm. Direct cholinergic input on GCs plays only a minor role, since a main portion of excitatory activity is blocked by CNQX (Figure S3). Furthermore, disinhibition may not convey a major component of theta, since IPSCs are only weakly theta coherent (Figure 5). In contrast, our results suggest selleck kinase inhibitor that a major theta component is relayed from the entorhinal cortex (Figure 1C). Several lines of evidence suggest that GABAergic interneurons, especially fast-spiking,

parvalbumin-expressing subtypes, play a key role in the generation of gamma oscillations in various regions of the brain (Bartos et al., 2007, Buzsáki and Wang, 2012 and Varga et al., 2012). In the dentate gyrus, however, both the power and frequency of gamma oscillations are reduced by chronic lesions of the entorhinal cortex (Bragin et al., 1995). Our results show that EPSCs, although they have high-frequency components, are only weakly gamma coherent with the LFP. Thus, a scenario in which the gamma rhythm is relayed tuclazepam from the entorhinal cortex to the dentate gyrus in a 1:1 manner seems unlikely. In contrast, IPSCs show a high degree of gamma coherence. Thus, whereas the theta rhythm is mainly relayed from the entorhinal cortex via excitation, the gamma rhythm is primarily generated by inhibition, most likely locally by GABAergic interneurons (Bartos et al., 2007 and Buzsáki and Wang, 2012; Figure 1C). Although previous studies showed that perisomatic inhibition markedly contributes to gamma oscillations in vitro (Mann et al.