Effects of adult-generated granule cells on coordinated network activity in the dentate gyrus

• Published in: Hippocampus 2012-01, Vol.22 (1), p.106-116
• Main Authors: Lacefield, Clay O., Itskov, Vladimir, Reardon, Thomas, Hen, René, Gordon, Joshua A.
• Format: Article
• Language: English
• Subjects: adult neurogenesis; Animals; Cytoplasmic Granules - physiology; Cytoplasmic Granules - radiation effects; dentate gyrus; Dentate Gyrus - cytology; Dentate Gyrus - physiology; Dentate Gyrus - radiation effects; gamma oscillations; in vivo multielectrode recording; input-output curves; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Nerve Net - cytology; Nerve Net - physiology; Nerve Net - radiation effects; Neural Pathways - cytology; Neural Pathways - physiology; Neural Pathways - radiation effects; Neurogenesis - physiology; Neurogenesis - radiation effects; Neuronal Plasticity - physiology; Neuronal Plasticity - radiation effects; Neurons - cytology; Neurons - physiology; Neurons - radiation effects
• ISSN: 1050-9631; 1098-1063
• DOI: 10.1002/hipo.20860

Throughout the adult life of most mammals, new neurons are continuously generated in the dentate gyrus of the hippocampal formation. Recent work has documented specific cognitive deficits after elimination of adult hippocampal neurogenesis in rodents, suggesting that these neurons may contribute to information processing in hippocampal circuits. Young adult‐born neurons exhibit enhanced excitability and have altered capacity for synaptic plasticity in hippocampal slice preparations in vitro. Still, little is known about the effect of adult‐born granule cells on hippocampal activity in vivo. To assess the impact of these new neurons on neural circuits in the dentate, we recorded perforant‐path evoked responses and spontaneous network activity from the dentate gyrus of urethane‐anesthetized mice whose hippocampus had been focally X‐irradiated to eliminate the population of young adult‐born granule cells. After X‐irradiation, perforant‐path responses were reduced in magnitude. In contrast, there was a marked increase in the amplitude of spontaneous γ‐frequency bursts in the dentate gyrus and hilus, as well as increased synchronization of dentate neuron firing to these bursts. A similar increase in gamma burst amplitude was also found in animals in which adult neurogenesis was eliminated using the GFAP:TK pharmacogenetic ablation technique. These data suggest that young neurons may inhibit or destabilize recurrent network activity in the dentate and hilus. This unexpected result yields a new perspective on how a modest number of young adult‐generated granule cells may modulate activity in the larger population of mature granule cells, rather than acting solely as independent encoding units. © 2010 Wiley Periodicals, Inc., Inc.