Cortical spreading depolarization (CSD) is a propagating wave of tissue depolarization characterized by a large increase of extracellular potassium concentration and prolonged subsequent electrical silencing of neurons. Waves of CSD arise spontaneously in various acute neurological settings, including migraine aura and ischemic stroke. Recently, we have reported that pan-inhibition of adrenergic receptors (AdRs) facilitates the normalization of extracellular potassium after acute photothrombotic stroke in mice. Here, we have extended that mechanistic study to ask whether AdR antagonists also modify the dynamics of KCl-induced CSD and post-CSD recovery in vivo. Spontaneous neural activity and KCl-induced CSD were visualized by cortex-wide transcranial Ca2+ imaging in G-CaMP7 transgenic mice. AdR antagonism decreased the recurrence of CSD waves and accelerated the post-CSD recovery of neural activity. Two-photon imaging revealed that astrocytes exhibited aberrant Ca2+ signaling after passage of the CSD wave. This astrocytic Ca2+ activity was diminished by the AdR antagonists. Furthermore, AdR pan-antagonism facilitated the normalization of the extracellular potassium level after CSD, which paralleled the recovery of neural activity. These observations add support to the proposal that neuroprotective effects of AdR pan-antagonism arise from accelerated normalization of extracellular K+ levels in the setting of acute brain injury.
The pathophysiology of depression remains elusive, and its early diagnostic method has not been established. Accumulated evidence demonstrate that environmental stress affects the hippocampus, functioning in cognition and sociality, and causes various depressive symptoms. In addition, recent findings showed that environmental stress influenced the hippocampal activity correlated with neuroinflammation, and impaired the hippocampal sharp wave ripples (SWRs), pattens of spike sequences, and the theta rhythms, a strong oscillation observed in the hippocampus.
Neurons in the cerebral cortex and hippocampus discharge synchronously in a brain state-dependent manner to transfer information. Published studies have highlighted the temporal coordination of neuronal activities between the hippocampus and a cortical area, however, how the spatial extent of cortex activity relates to hippocampal activity remains largely unknown. We imaged macroscopic cortical activity while recording hippocampal local field potentials in unanesthetized GCaMP-expressing transgenic mice. We found that cortical activity elevates before and after hippocampal sharp wave ripples (SWR). SWR-associated cortical activities occurred predominantly in vision-related regions including visual, retrosplenial and prefrontal cortex. While pre-SWR cortical activities were frequently observed in awake and sleep states, post-SWR cortical activity decreased significantly in sleep. During hippocampal theta oscillation states, phase-locked oscillations of calcium activity was observed throughout the entire cortex state. Environmental effects on cortico-hippocampal dynamics were also assessed by comparing mice reared in an enriched environment (ENR) or under isolated conditions (ISO). In both SWR and theta oscillations, mice reared in an isolated condition exhibited clearer brain state-dependent dynamics than those reared in an enriched environment. Our data demonstrate that the cortex and hippocampus exhibit heterogeneous activity patterns that characterize brain states, and postnatal experience plays a significant role in modulating these patterns.Significant StatementThe hippocampus is a center for memory formation. However, the memory formed in the hippocampus is not stored forever, but gradually transferred into the cerebral cortex. As an underlying mechanism, phase-locked synchronized activities between the cortex and hippocampus has been hypothesized. However, spatio-temporal dynamics between hippocampus and whole cortical areas remained mostly unknown. We measured cortical calcium activities with hippocampal electroencephalogram (EEG) simultaneously, and found that the activities of widespread cortical areas are temporally associated with hippocampal EEG. The cortico-hippocampal dynamics is primarily regulated by animal awake/sleep state. Even if similar EEG patters were observed, temporal dynamics between the cortex and hippocampus exhibit distinct patterns between awake and sleep period. In addition, animals’ postnatal experience modulates the dynamics.
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