Theta generators in combined transected hippocampal formation slices

Rhythmic slow activity (RSA, theta) is commonly associated with the hippocampal formation (HPC). It is generally agreed that HPC theta rhythm is dependent on an intact septal area that act as a pacemaker for the RSA. However, hippocampal neurons cannot be considered as passive followers of rhythmic septal inputs. The local hippocampal networks may also contribute to the RSA – application of the cholinergic agonist, carbachol produce theta rhythm in HPC slices in vitro. The evaluation of theta amplitude and phase profi le indicates the existence of two theta generators located in CA1 and DG areas. Moreover, model of slice preparation demonstrated that in the CA3c HPC region the third RSA generator is localized. In our previous experiments we hypothesized that completely isolated DG area is not capable of theta rhythm generation. In the present study we attempted to verify this hypothesis, using model of combined transected HPC slices. We analyzed theta activity in two different transected slices: DG slices containing CA1 area and DG slices containing CA3c region. We demonstrated that both CA1 and CA3c regions are capable of independent generation high amplitude RSA, whereas theta recorded in DG was characterized by signifi cantly lower theta amplitude. Our in vitro obtained fi ndings are consistent with earlier reports suggesting that HPC theta generators are localized in CA1 and CA3c but not in DG region. Supported by grant MNiSzW NN 303 091 834.