Image-based “Neurosurveillance” Reveals How Seizures Disrupt the Brain’s Microcirculation

Although many neurological diseases (e.g. Alzheimer’s disease, brain cancers etc.) are characterized by disruptions in the brain’s microcirculation, it has been challenging to continuously track such microcirculatory changes over hours/days. This is largely due to the limitations of current imaging systems (e.g. MRI/PET) that require animals to be anesthetized during imaging, which also precludes continuous long-term imaging over the duration of the neuropathology being studied. To circumvent these limitations and image microcirculatory dysfunction during disease progression, we developed a novel, miniaturized microscope (or miniscope) that is capable of continuously imaging multiple aspects of the cerebral microcirculation over > 24 hours in freely behaving mice. We call this capability ‘neurosurveillance’. The miniscope acquires images at a resolution of 6 µm over a 3x3 mm 2 field of view, and relies on multiple contrast mechanisms. First, it uses the light absorption of erythrocyte-bound oxy- and deoxyhemoglobin to compute maps of cerebral blood volume (CBV) and intravascular oxygen saturation (S O2 ). Next it uses the orderly flow of erythrocytes inside microvessels detected via laser light to create maps of cerebral blood flow (CBF). It also detects the green fluorescence emitted by GCaMP-bound neuronal Ca 2+ to create maps of concurrent changes in neuronal activity (Neu ACT ). Equipped with the capability to conduct neurosurveillance, we interrogated changes in the brain’s microcirculation in a preclinical seizure model. Traditionally, seizures are considered to be aberrant electrical discharges within the brain. However, we hypothesized that if neurovascular coupling remains intact, the large neuronal activations triggered by a seizure would also result in large increases in CBV, CBF, and S O2 . To test this hypothesis, we induced seizures in a cohort of n=4 adult C57BL/6 mice (3F/1M), via an i.p. injection of pentylenetetrazol (PTZ), a GABA A antagonist. Maps of CBV, CBF, S O2 , and corresponding Neu ACT changes were acquired with the miniscope every 5 s over 24 hours through a surgically prepared cranial window over the murine sensorimotor cortex. Seizures were characterized by Neu ACT bursts lasting < 2 mins. Contrary to intact neurovascular coupling, we observed that seizure-induced neuronal hyperactivations were accompanied by brief periods of severe vasoconstriction (i.e. CBV reduction) and drops in CBF. These observations imply that seizures were accompanied by a compromised microcirculatory status for the duration of the seizure. Moreover, the recovery from this compromised status was short-lived, with the cerebrovasculature entering a second phase of severe vasoconstriction and CBF attenuation that was sustained for approximately an hour following seizure termination. Unlike during the seizure, this post-seizure CBV/CBF drop was accompanied by depressed Neu ACT levels and an almost complete lack of animal mobility. CBV/CBF drops did not translate into a consistent drop in S O2 , hinting at concomitant metabolic abnormalities. Finally, two out of four animals developed subsequent spontaneous seizures that were similarly characterized by vasoconstriction and hypoperfusion. Collectively, neurosurveillance enabled us to establish the central role of microcirculatory dysfunction during seizures, and constitutes a novel approach for characterizing the role of the cerebral circulation in health and disease. This work was supported by NIH/NCI grants: 2R01CA196701-06A1 and 5R01CA237597-04 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.