Rapid disruption of cortical activity and loss of cerebral blood flow in a mouse model of mild traumatic brain injury

• Main Author: Witkowski, Ellen
• Other Authors: Davison, Ian
• Language: en_US
• Published: 2019
• Subjects: Neurosciences; Activity; Blood; Cortex; Traumatic brain injury
• Online Access: https://hdl.handle.net/2144/36638

Every year 2.8 million Americans suffer a traumatic brain injury (TBI). Despite the prevalence and debilitating consequences of TBI, effective treatment options are scarce due to the limited understanding of the neurobiological effects of injury, especially in acute phases when the cellular processes leading to neuropathology are first initiated. To identify changes in neural function and cerebral blood flow (CBF) that might account for TBI-induced cognitive and sensory deficits, we took a multidisciplinary approach, examining synaptic function, cortical activity patterns, and microvascular hemodynamics. we used a weight drop model in mice to induce mild TBI, the most common form in humans, and focused on responses within the first hours of injury where existing data are particularly limited. For synaptic function, we measured excitatory and inhibitory input onto pyramidal cells in the piriform cortex with whole-cell recordings in acute brain slices. Increased excitation appeared at one hour but excitatory-inhibitory balance was reestablished by 48 hours, highlighting the importance of studying rapid-onset injury responses. We also compared neural activity before and after TBI using in vivo two-photon calcium imaging of pyramidal cells in visual cortex. While neural activity substantially decreased in most cells one hour after injury, a minority of cells showed hyperactivation or prolonged increases in intracellular calcium, again indicating major physiological disturbances during immediate post-injury phases. Finally, we measured in vivo changes in CBF throughout the cortical microvasculature with laser speckle contrast imaging and optical coherence tomography, tracking injury effects up to three weeks after TBI. CBF and capillary flow were dramatically reduced within minutes and remained suppressed for over one hour. As neurons’ high energetic needs require a constant supply of glucose and oxygen from local vasculature, decreased CBF likely contributes to altered neural activity and loss of ion homeostasis and thus potentially cognitive and sensory deficits after TBI. Our results reveal that even mild injury creates rapid, pronounced, and heterogeneous alterations in neural activity and capillary flow. The transient nature of these effects suggests that the first two hours after injury may be a key window for delivering interventions, and that restoring CBF may reduce damage due to metabolic stress.