The medial septum-diagonal band (MSDB) complex is considered as
a pacemaker for the hippocampal theta rhythm. Identification of
the different cell types, their electro-physiological properties
and their possible function in the generation of a synchronized
activity in the MSDB is a hot topic. A recent electro-
physiological study showed the presence of two antiphasically
firing populations of parvalbumin containing GABAergic neurons
in the MSDB. Other papers described a network of cluster-firing
glutamatergic neurons, which is able to generate synchronized
activity in the MSDB. We propose two different computer models
for the generation of synchronized population theta oscillation
in the MSDB and compare their properties. In the first model
GABAergic neurons are intrinsically theta periodic cluster-
firing cells; while in the second model GABAergic cells are
fast-firing cells and receive periodic input from local
glutamatergic neurons simulated as cluster-firing cells. Using
computer simulations we show that the GABAergic neurons in both
models are capable of generating antiphasic theta periodic
population oscillation relying on local, septal mechanisms. In
the first model antiphasic theta synchrony could emerge if
GABAergic neurons form two populations preferentially innervate
each other. In the second model in-phase synchronization of
glutamatergic neurons does not require specific network
structure, and the network of these cells are able to act as a
theta pacemaker for the local fast-firing GABAergic circuit. Our
simulations also suggest that neurons being non-cluster-firing
in vitro might exhibit clustering properties when connected into
a network in vivo.
