Abstract
Hippocampal function varies along its septotemporal axis, with the septal (dorsal) pole more frequently involved in spatial learning and memory and the temporal (ventral) pole playing a greater role in emotional behaviors. One feature that varies across these subregions is adult neurogenesis. New neurons are more numerous in the septal hippocampus but are more active in the temporal hippocampus during water maze training. However, many other aspects of adult neurogenesis remain unexplored in the context of septal versus temporal subregions. In addition, the dentate gyrus contains another functionally important anatomical division along the transverse axis, with the suprapyramidal blade showing greater experience-related activity than the infrapyramidal blade. Here we ask whether new neurons differ in their rates of survival and maturation along the septotemporal and transverse axes. We found that neurogenesis is initially higher in the infrapyramidal than suprapyramidal blade, but these cells are less likely to survive, resulting in similar densities of neurons in the two blades by four weeks. Across the septotemporal axis, neurogenesis was higher in septal than temporal pole, while the survival rate of new neurons did not differ. Maturation was assessed by immunostaining for the neuronal marker, NeuN, which increases in expression level with maturation, and for the immediate-early gene, Arc, which suggests a neuron is capable of undergoing activity-dependent synaptic plasticity. Maturation occurred approximately 1–2 weeks earlier in the septal pole than in the temporal pole. This suggests that septal neurons may contribute to function sooner; however, the prolonged maturation of new temporal neurons may endow them with a longer window of plasticity during which their functions could be distinct from those of the mature granule cell population. These data point to subregional differences in new neuron maturation and suggest that changes in neurogenesis could alter different hippocampus-dependent behaviors with different time courses.
Highlights
It is becoming increasingly clear that the hippocampus is not a homogeneous structure but instead has different properties and functions associated with its septal and temporal subregions [1,2]
There was a trend for lower BrdU+ cell density in the temporal dentate gyrus (DG) (Fig. 2a), consistent with previous findings showing reduced neurogenesis in the temporal DG as compared to the septal DG [21,22]
We found that the density of 1-week-old BrdU+ cells in the septal dentate gyrus was greater in the infrapyramidal blade than the suprapyramidal blade (Fig. 2c)
Summary
It is becoming increasingly clear that the hippocampus is not a homogeneous structure but instead has different properties and functions associated with its septal and temporal subregions [1,2]. There are no studies addressing functional differences between suprapyramidal and infrapyramidal granule cells at the behavioral level, there are well-described differences between granule cells in the two blades in the size of the dendritic tree, ratio of inhibitory interneurons, connectivity, and experience-induced activation [14,15,16,17,18,19,20]. Due to this heterogeneity, understanding the function of the hippocampus requires subregion-specific investigations
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
