title: Long-term in vivo imaging of dendritic spines in the hippocampus reveals structural plasticity.
abstract: Hippocampal function is important for learning and memory. During memory processing, hippocampal CA1 neurons play a crucial role by integrating excitatory synaptic input from CA3 and the entorhinal cortex. These neurons receive excitatory input almost exclusively on dendritic spines. The formation and elimination--structural plasticity--of dendritic spines reflect wiring changes within the hippocampal network. Despite the relevance of the hippocampus in learning and memory, most in vivo data on structural plasticity derive from cortical regions. We established a chronic hippocampal window approach using two-photon microscopy to visualize dendritic spines throughout all CA1 hippocampal layers and over a time course of weeks. Moreover, even granule cells in dentate gyrus could be reliably detected. We found that the spine density in stratum radiatum (∼1.1 per micrometer) remained stable over weeks. However, a small fraction (3.4%) of spines were formed and eliminated between imaging sessions, which demonstrated that spines of CA1 neurons exhibit structural plasticity in adult mice. In addition, we tested for possible inflammatory or behavioral side effects of hippocampal window implantation. Mice exhibited a transient increase in microgliosis and astrogliosis, which declined within a few weeks. We did not detect any difference in behavioral performance in an open-field and contextual fear-conditioning paradigm. In conclusion, hippocampal long-term two-photon imaging revealed structural plasticity of dendritic spines in CA1 pyramidal neurons. This approach may provide a powerful tool to analyze changes in neuronal network rewiring during hippocampal learning and memory processes in health and disease.
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Ligang
authors.initials: L
authors.lastname: Gu
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Kleiber
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Schmid
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Nebeling
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Chamoun
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Steffen
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Wagner
authors.affiliation: German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany martin.fuhrmann@dzne.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Fuhrmann
mesh_terms: D000818:Animals; D049229:Dendritic Spines / Q000502:physiology* / Q000648:ultrastructure*; D005260:Female; D006624:Hippocampus / Q000166:cytology* / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D009473:Neuronal Plasticity / Q000502:physiology*; D013997:Time Factors
keywords: behavior; dendritic spines; hippocampus; in vivo imaging; structural plasticity; two-photon imaging