A hippocampal circuit linking dorsal CA2 to ventral CA1 critical for social memory dynamics

Recent results suggest that social memory requires the dorsal hippocampal CA2 region as well as a subset of ventral CA1 neurons. However, it is unclear whether dorsal CA2 and ventral CA1 represent parallel or sequential circuits. Moreover, because evidence implicating CA2 in social memory comes largely from long-term inactivation experiments, the dynamic role of CA2 in social memory remains unclear. Here, we use pharmacogenetics and optogenetics in mice to acutely and reversibly silence dorsal CA2 and its projections to ventral hippocampus. We show that dorsal CA2 activity is critical for encoding, consolidation, and recall phases of social memory. Moreover, dorsal CA2 contributes to social memory by providing strong excitatory input to the same subregion of ventral CA1 that contains the subset of neurons implicated in social memory. Thus, our studies provide new insights into a dorsal CA2 to ventral CA1 circuit whose dynamic activity is necessary for social memory.We thank David H. Brann and the other members of the Siegelbaum laboratory for helpful discussions and João Cerqueira for critical input. This work was supported by R01 MH104602 and R01 MH106629 from the NIH (S.A.S.), by PD/BD/113700/2015 from the Portuguese Foundation for Science and Technology (T.M.) and by the European Molecular Biology Organization (A.O.)

The lateral septum mediates kinship behavior in the rat

Kinship behavior in rodents has been documented in the laboratory setting but the neural mechanisms that mediate kinship behavior are not known. Here, the authors show that the lateral septum has a key role in organizing mammalian kinship behavior

μSR studies of magnetic order in La_2-xSr_xNiO₄

We report muon-spin-relaxation measurements on a series of compounds with composition La2-xSrxNiO4+δ where the net hole concentration x+2δ is greater than 0.4. A magnetic transition is found in all the samples studied which occurs at a composition-dependent temperature TM. Below TM clear precession signals are observed in zero applied magnetic field, indicating the existence of at least short-range magnetic order on a time scale greater than 10-8 s. Above TM the correlation times decrease by several orders of magnitude. The measurements of TM as a function of the net hole concentration extend the determination of Néel temperatures by previous neutron diffraction measurements to higher doping levels

Probing magnetic order in heavily doped La_{2-x}Sr_{x}NiO_{4+delta}

We report mu SR measurements on a series of compounds with composition La2-xSrxNiO4+delta where the net hole concentration x + 2 delta is greater than 0.4. A magnetic transition is found in all the samples studied which occurs at a composition-dependent temperature T-M. Below T-M, clear precession signals are observed in zero applied magnetic field. The possible muon sites are discussed within the context of dipole-field calculations