High-ResolutionIn VivoImaging of Hippocampal Dendrites and Spines

Abstract

Structural changes in hippocampal dendrites and dendritic spines are thought to be a consequence of a wide range of experience-and activity-dependent manipulations. We explored the dynamics of hippocampal dendritic spines in vivo by developing a surgical preparation of the adult mouse brain that enabled two-photon imaging of fluorescently labeled CA1 pyramidal neurons. Dendritic trees and spines were repeatedly visualized over many hours in exquisite detail. We tested spine stability under both control conditions and during prolonged epileptic seizures. Remarkably, spines remained structurally stable after 30 min of experimental induction of epileptic seizures. Spines began to disappear only several hours after induction of epileptic activity. We thus demonstrate that this technique provides a methodology for direct in vivo optical studies of the intact mammalian hippocampus.

Adaptive optics two-photon endomicroscopy enables deep-brain imaging at synaptic resolution over large volumes

“…In addition, we also monitored the spine dynamics in mice with kainic acid-induced epileptic seizure. In contrast to the dynamic neuronal changes induced by laser microsurgery, our findings show that the changes in spine stability caused by kainic acid-induced epileptic seizure are insignificant, which is in agreement with another study of the hippocampus of mice experiencing pilocarpine-induced epileptic seizure (29). These results shed light on the neuronal mechanisms underlying neurodegenerative disorders.…”

Adaptive optics two-photon endomicroscopy enables deep-brain imaging at synaptic resolution over large volumes

“…In addition, we also monitored the spine dynamics in mice with kainic acid-induced epileptic seizure. In contrast to the dynamic neuronal changes induced by laser microsurgery, our findings show that the changes in spine stability caused by kainic acid-induced epileptic seizure are insignificant, which is in agreement with another study of the hippocampus of mice experiencing pilocarpine-induced epileptic seizure (29). These results shed light on the neuronal mechanisms underlying neurodegenerative disorders.…”

In vivo imaging of dendritic spines during electrographic seizures

“…However, a more recent study in acute hippocampal slices identified only transient spine swelling associated with long‐term potentiation, and that in only about 5% of spines 23. Our largely negative result is, therefore, quite compatible with these observations; furthermore, it is in agreement with another study that found minimal effects of epileptiform activity on dendritic spines in hippocampus in vivo over a short time scale 25…”

Hippocampal seizures cause depolymerization of filamentous actin in neurons independent of acute morphological changes

“…This reported variability in the effects of seizures on dendrites likely relates to a number of factors, such as the specific seizure model, time course, experimental approach, and concurrent modulatory conditions. In the present study, the lack of obvious structural changes in dendrites with seizures over a short time is consistent with previous studies using a similar 4-AP model (Yang and Rothman, 2001) and with other recent studies utilizing modern time-lapse imaging methods to directly assess spine changes during seizures in living tissue in vivo (Mizrahi et al, 2004;Rensing et al, 2005). Besides variability between different seizure models, this lack of acute seizure-induced effects on dendritic morphology in the present study may be attributed to a number of reasons and subject to some caveats.…”

Adaptive optics two-photon endomicroscopy enables deep-brain imaging at synaptic resolution over large volumes

“…In addition, we also monitored the spine dynamics in mice with kainic acid-induced epileptic seizure. In contrast to the dynamic neuronal changes induced by laser microsurgery, our findings show that the changes in spine stability caused by kainic acid-induced epileptic seizure are insignificant, which is in agreement with another study of the hippocampus of mice experiencing pilocarpine-induced epileptic seizure (29). These results shed light on the neuronal mechanisms underlying neurodegenerative disorders.…”

In vivo imaging of dendritic spines during electrographic seizures

“…However, a more recent study in acute hippocampal slices identified only transient spine swelling associated with long‐term potentiation, and that in only about 5% of spines 23. Our largely negative result is, therefore, quite compatible with these observations; furthermore, it is in agreement with another study that found minimal effects of epileptiform activity on dendritic spines in hippocampus in vivo over a short time scale 25…”

Hippocampal seizures cause depolymerization of filamentous actin in neurons independent of acute morphological changes

“…This reported variability in the effects of seizures on dendrites likely relates to a number of factors, such as the specific seizure model, time course, experimental approach, and concurrent modulatory conditions. In the present study, the lack of obvious structural changes in dendrites with seizures over a short time is consistent with previous studies using a similar 4-AP model (Yang and Rothman, 2001) and with other recent studies utilizing modern time-lapse imaging methods to directly assess spine changes during seizures in living tissue in vivo (Mizrahi et al, 2004;Rensing et al, 2005). Besides variability between different seizure models, this lack of acute seizure-induced effects on dendritic morphology in the present study may be attributed to a number of reasons and subject to some caveats.…”

Adaptive optics two-photon endomicroscopy enables deep-brain imaging at synaptic resolution over large volumes

“…In addition, we also monitored the spine dynamics in mice with kainic acid-induced epileptic seizure. In contrast to the dynamic neuronal changes induced by laser microsurgery, our findings show that the changes in spine stability caused by kainic acid-induced epileptic seizure are insignificant, which is in agreement with another study of the hippocampus of mice experiencing pilocarpine-induced epileptic seizure (29). These results shed light on the neuronal mechanisms underlying neurodegenerative disorders.…”

In vivo imaging of dendritic spines during electrographic seizures

“…However, a more recent study in acute hippocampal slices identified only transient spine swelling associated with long‐term potentiation, and that in only about 5% of spines 23. Our largely negative result is, therefore, quite compatible with these observations; furthermore, it is in agreement with another study that found minimal effects of epileptiform activity on dendritic spines in hippocampus in vivo over a short time scale 25…”

Hippocampal seizures cause depolymerization of filamentous actin in neurons independent of acute morphological changes

“…This reported variability in the effects of seizures on dendrites likely relates to a number of factors, such as the specific seizure model, time course, experimental approach, and concurrent modulatory conditions. In the present study, the lack of obvious structural changes in dendrites with seizures over a short time is consistent with previous studies using a similar 4-AP model (Yang and Rothman, 2001) and with other recent studies utilizing modern time-lapse imaging methods to directly assess spine changes during seizures in living tissue in vivo (Mizrahi et al, 2004;Rensing et al, 2005). Besides variability between different seizure models, this lack of acute seizure-induced effects on dendritic morphology in the present study may be attributed to a number of reasons and subject to some caveats.…”