Input processing by adult-born dentate granule cells

MA. BELEN PARDI; LUCAS MONGIAT; ALEJANDRO F. SCHINDER; ANTONIA MARIN BURGIN

New Orleans

Congreso; Society for Neuroscience Annual meeting 2012; 2012

Society for Neuroscience

The adult dentate gyrus generates new granule cells (GCs) that develop over several weeks and integrate into the preexisting network. Although adult hippocampal neurogenesis has been implicated in learning and memory, the specific role of new GCs remains unclear. We examined whether immature adult-born neurons contribute to information encoding. We worked on acute hippocampal slices obtained from adult C57Bl6/J mice injected with a retrovirus to express RFP in newborn GCs. Using electrophysiological recordings of postsynaptic responses evoked by activation of the perforant path, we observed that immature GCs required weaker stimuli than mature GCs to be activated,. Notably, immature GCs fired consistently in response to 10 Hz trains while mature GCs could fire at most only once. These properties suggest that while mature GCs are presumably more selective in their responses, immature GCs could be recruited by different inputs, allowing integrations to occur. To test this hypothesis, we monitored GC activity by loading them with the calcium-sensitive dye OGB-1 AM. Two electrodes were placed to stimulate different and independent medial perforant path inputs at various intensities. Under these conditions, the majority of mature GCs responded to only one of the two stimuli, but most immature GCs were recruited by both. Loose patch followed by whole cell recordings reveled that differences in the activation profile were a consequence of differences in the excitation/inhibition balance of afferent inputs. Particularly, immature GCs receive slower and weaker somatic inhibition than mature GCs. Our results suggest that immature GCs integrate different sources of information whereas mature neurons are recruited in a more specific manner. These functions could imply a differential role of both mature and immature GC populations in processing information arriving to the dentate gyrus.