No abstract

Hippocampus receives dense serotonergic input specifically from raphe nuclei. However, what information is carried by this input and its impact on behavior has not been fully elucidated. Here we used in vivo two-photon imaging of activity of hippocampal median raphe projection fibers in behaving male and female mice and identified two distinct populations: one linked to reward delivery and the other to locomotion. Local optogenetic manipulation of these fibers confirmed a functional role for these projections in the modulation of reward-induced behavior. The diverse function of serotonergic inputs suggests a key role in integrating locomotion and reward information into the hippocampal CA1.

We investigated the potential of antibody-vectorialized superparamagnetic iron oxide (SPIO) particles as cellular specific magnetic resonance contrast agents to image lymphocyte populations within the central nervous system (CNS), with the final goal of obtaining a reliable tool for noninvasively detecting and tracking specific cellular populations in vivo. We used superparamagnetic particles bound to a monoclonal antibody. The particle is the contrast agent, by means of its T₂* relaxation properties; the antibody is the targeting vector, responsible for homing the particle to target a surface antigen. To investigate the efficiency of particle vectorialization by these antibodies, we compared two types of antibody-vectorialized CD3-specific particles in vivo. We successfully employed vectorialized SPIO particles to image B220⁺ cells in a murine model of B-cell lymphoma. Likewise, we were able to identify CD3⁺ infiltrates in a murine model of multiple sclerosis. The specificity of the technique was confirmed by immunohistochemistry and electron microscopy of corresponding sections. Our findings suggest that indirect binding of the antibody to a streptavidinated particle allows for enhanced particle vectorialization compared to covalent binding of the antibody to the particle.

In the brain, spatial information is represented by neurons that fire when an animal is at specific locations, including place cells in hippocampus and grid cells in entorhinal cortex. But how this information is processed in downstream brain regions still remains elusive. Using chronic Ca2+ imaging, we examined the activity of neurons in anterior cingulate cortex (ACC), a brain region implicated in memory consolidation, and found neurons that fire in a manner consistent with the properties of place cells. While the ACC place cells showed stability, location and context specificity similar to the hippocampal counterparts, they also have unique properties. Unlike hippocampal place cells that immediately formed upon exposure to a novel environment, ACC place cells increased over days. Also, ACC place cells tend to have additional place fields whereas typical hippocampal place cells have only one. Hippocampal activity is required for the formation of ACC place cells, but once they are established, hippocampal inactivation did not have any impact on ACC place cell firing. We thus identified features of ACC place cells that carry spatial information in a unique fashion.