, 1998). This is consistent with the strong activation of bistratified cells by simultaneous inputs from CA1 and CA3. The firing of bistratified cells (Klausberger et al., 2004) coupled to SWRs rarely dropped below 80 Hz, providing entrainment of the innervated small pyramidal cell dendrites in cooperation with PV+ basket cells that innervate the soma

and proximal dendrites (Lapray et al., 2012 and Varga et al., 2012). However, all O-LM cells were silent during at least some SWRs, and on average also decreased their firing, which indicates that some inhibitory KRX-0401 input, activated during SWRs, contributes to their silencing. The O-LM cells are known to be innervated by vasoactive intestinal polypeptide-expressing, GABAergic

interneuron-specific IS-III cells (Acsády et al., 1996 and Chamberland et al., 2010) and also receive septal GABAergic innervation (Gulyás et al., 1990), which participate Tyrosine Kinase Inhibitor Library mw in their inhibition (Chamberland et al., 2010). Unfortunately, the activity patterns of neither of these GABAergic inputs are known in vivo. In any case, the withdrawal of GABA and SOM released by O-LM cells from the most distal dendrites in CA1 may enable the return input from the entorhinal cortex and a reverberation between CA1 and the entorhinal cortex during closely timed repeated ripples (Davidson et al., 2009). In the mouse, O-LM cells fired at higher rates in vitro during SWR-like bursts

in CA1 (Pangalos et al., 2013) and CA3 (Hájos et al., 2013) or during awake immobility in vivo (Varga et al., 2012). The difference between these reports and our results could be due to species differences, loss of some of the inhibitory circuits in vitro, and higher firing rates during SWRs in awake compared to sleep states. The O-LM cells reported here fired significantly more during awake-SWRs than during SWRs in sleep. During theta oscillations, the pyramidal cell input to O-LM and bistratified cells may account for the firing of both cell types maximally around the theta trough, when pyramidal cells fire at highest probability in CA1. This was also see more predicted from tetrode recordings of pyramidal layer interneurons (Czurkó et al., 2011). However, the two cell types differ in that bistratified, but not O-LM, cells (Kim et al., 2012) receive input from CA3. Moreover, septal cholinergic input selectively activates O-LM cells via nicotinic acetylcholine receptors in arousal (Leão et al., 2012 and Lovett-Barron et al., 2014). Both cell types are also likely to receive septal GABAergic innervation (Gulyás et al., 1990), which may include a population of PV-expressing medial septal neurons that discharge at the peak of theta in anesthetized rats (Borhegyi et al., 2004) and temporally lead hippocampal theta (Hangya et al., 2009).