Sleep Disturbances as a Potential Mechanism of Post-Traumatic Epileptogenesis

Principal Investigator: ULYANOVA, ALEXANDRA V

Proposal Number: EP210075

Award Number: W81XWH-22-1-0287

Period of Performance: 5/1/2022 - 4/30/2025

PUBLIC ABSTRACT

Disrupted sleep is common and persistent symptom after traumatic brain injury (TBI), which can significantly complicate recovery for civilian population and for military personnel with deployment TBI history. In epilepsy, some types of seizure occur primarily during sleep and can be exacerbated by sleep deprivation. However, the relationship between sleep disturbances following brain trauma and development of post-traumatic epilepsy (PTE) remains poorly understood. To improve quality of life in Service Members and Veterans with PTE, an understanding of the varied mechanisms triggered by TBI is required to prevent or optimally manage development of epileptogenesis. Therefore, our long-term goal in this proposal is to uncover fundamental principles of sleep disturbances during development of post-traumatic epileptogenesis.

Rationale: (1) Characterization of the circuits involved in PTE: While sleep disturbances such as difficulty falling and staying asleep are often caused by a disruption of the circadian rhythm, they can be misdiagnosed due to symptomatic overlap with insomnia. Interestingly, the circadian rhythm center, the suprachiasmatic nucleus of the hypothalamus (SCN), is composed exclusively of the inhibitory GABA-ergic interneurons, a type of neurons preferentially affected by trauma. However, the mechanisms underlying the extent of circadian-related sleep disruption following TBI remain poorly understood, as are the potential effects of brain trauma on the circadian rhythms circuitry.

(2) Development of new models or better characterization of existing etiologically relevant models for PTE: While the majority of work using animal models of PTE have utilized rats and mice, rodent models of TBI are not capable to accurately represent the biomechanics of brain injury in a gyrencephalic brain, or the effects of white matter injury observed in human TBI. Therefore, brains of large animals such as pigs, with their gyrencephalic structure and appropriate white-to-grey matter ratios, are more closely resemble human architecture and, hence, are important for an accurate biomechanical modeling of all aspects of human TBI.

(3) Innovative Research: Currently, there is a lack of studies utilizing continuous electrophysiological monitoring to detect disrupted sleep and circadian rhythms in subcortical regions and deep brain structures starting at “time zero” and chronically over time post-TBI. The use of continuous electroencephalogram (EEG) instead of sporadic EEG recordings immediately and over time post-TBI will significantly advance our understanding of TBI-induced sleep disturbances.

Using continuous EEG monitoring in a large animal model (swine) of controlled-cortical impact (CCI) injury, we demonstrated sleep disturbances starting at the time zero and up to 5 months post-injury. Moreover, using behavioral video monitoring, we demonstrated that marked alterations in sleep states are potentially caused by a disruption of the circadian rhythms. Over time, CCI-injured but not control animals developed seizures predominantly during sleep and detected in the injured cortex. These preliminary results together with histopathological changes observed in the SCN have led to our central hypothesis that network changes in the circadian rhythm center lead to disrupted sleep states over time post-injury and potentially contribute to the development of PTE. Our objectives in this proposal are to identify the extent of interneuron-related pathologies in the SCN that lead to the development of sleep disturbances observed over time post-CCI injury.

Our proposal “Sleep disturbances as a potential mechanism of post-traumatic epileptogenesis” directly addresses several the Focus Areas requested in the Fiscal Year 2021 Epilepsy Research Program ERP Idea Development Award program announcement. The objectives of this proposal will address the “Innovative Research” Focus Area, specifically falling under the following areas: “Development of new models or better characterization of existing etiologically relevant models for PTE” and “Characterization of the circuits involved in PTE.” Examination of the circuit level changes in a clinically relevant large animal model, in parallel with neuropathological outcome, provides a powerful translational approach to understanding disturbances in normal sleep and circadian rhythms following brain trauma. Determining whether observed interneuronal loss in the CCI-injured cortex and, potentially, in the SCN correlate with early and late EEG and histopathological findings in these animals.

TECHNICAL ABSTRACT

Background: Disrupted sleep is common and persistent symptom after traumatic brain injury (TBI), which can significantly complicate recovery for civilian population and for military personnel with deployment TBI history. In epilepsy, some types of seizure occur primarily during sleep and can be exacerbated by sleep deprivation. While sleep disturbances such as difficulty falling and staying asleep are often caused by a disruption of the circadian rhythm, they can be misdiagnosed due to symptomatic overlap with insomnia. Interestingly, the circadian rhythm center, the suprachiasmatic nucleus of the hypothalamus (SCN), is composed exclusively of the inhibitory GABAergic interneurons, a type of neurons preferentially affected by trauma. However, the exact mechanisms underlying the extent of circadian-related sleep disruption following TBI remain poorly understood, as are the potential effects of trauma on the SCN.

Hypothesis: To improve quality of life in Service Members and Veterans with post-traumatic epilepsy (PTE), an understanding of the varied mechanisms triggered by TBI is required to prevent or optimally manage development of epileptogenesis. Therefore, our long-term goal in this proposal is to uncover fundamental principles of sleep disturbances during development of PTE. Using in vivo electrophysiology in a large animal model (swine) of controlled-cortical impact (CCI) injury, we have demonstrated sleep disturbances immediately and up to 5 months following TBI. Moreover, using behavioral monitoring, we demonstrated that marked alterations in sleep states following CCI injury are potentially caused by a disruption of the circadian rhythms. These preliminary results, together with histopathological changes observed in the SCN, led to our central hypothesis that network oscillatory disruptions in the circadian rhythm center lead to disrupted sleep states over time post-injury. Our objectives in this proposal are to identify the extent of interneuron-related dysfunction and pathology in the SCN that may lead to the development of sleep-wake disturbances observed over time post-CCI injury. Our interdisciplinary team of electrophysiologists, a trauma neuropathologist, and a neurosurgeon is uniquely poised to address this fundamental question by combining our broad background in swine in vivo electrophysiology, behavior, and histopathology. In this way, we will use our unique, large animal model of PTE (swine), along with in vivo electrophysiology, continuous home cage video monitoring, and histopathology, to identify the extent to which pathological changes in the SCN interneurons disrupt normal sleep during post-traumatic epileptogenesis.

Aim 1: To measure neuronal activity in the SCN at acute and sub-acute time point post-injury. In Sub-Aim1A, we will use multichannel in vivo electrophysiology to record neural signals in the SCN. We will identify the features of neuronal action potentials (firing rate, amplitude, width, and burstiness) recorded simultaneously from multiple SCN neurons located in the ventral (core) and dorsal (shell) regions of the SCN at 5 days (n=8) and 4 weeks (n=8) post-CCI. We will use cross-correlation in the timing of spikes between neurons to understand the SCN circuitry. In Sub-Aim1B, we will stimulate light-sensitive neurons located in the ventral SCN by delivering electrical pulses via stimulation electrode placed in the retinohypothalamic tract (RHT) to simulate activation by light. We will use cross-correlation in the timing of spikes between neurons to determine the extent to which electrical stimulation affects neuronal properties and network synchronization in the SCN post-TBI. We will compare results from Sub-Aims 1A and1B between the sham (n=6) and the CCI (n=10) groups of animals.

Aim 2: To measure neuronal activity in the SCN continuously up to 5 months post-injury. In Sub-Aim2A, we will use awake multichannel in vivo electrophysiology to record neural signals in the SCN as well as sleep detected on electrocorticography (ECoG) skull screws continuously up to 5 months post-injury. We will identify the features of neuronal action potentials (firing rate, amplitude, width, and burstiness) recorded simultaneously from multiple SCN neurons and use cross-correlation in the timing of spikes between neurons to understand changes the SCN circuitry over time post-injury. In Sub-Aim2B, we will use home cage video EEG monitoring to measure changes in locomotor activity (phase). We will measure sleep disruptions as changes in slow wave sleep detected on ECoG skull screws over time. We will compare results from Sub-Aims 2A and 2B between the sham (n=3) and the CCI (n=5) groups. At the end point of the study, we will confirm placement of electrodes within ventral and dorsal regions of the SCN histopathologically. We will identify the neurons of the core (express vasoactive intestinal polypeptide, VIP) and the shell (express arginine vasopressin, AVP) regions of the SCN and asses potential neuronal loss in these regions at acute and subacute time points.

Innovation and Impact: Examination of the circuit level changes in a clinically relevant large animal model of PTE, in parallel with neuropathological outcome, provides a powerful translational approach to understanding disturbances in normal sleep and circadian rhythms during development of PTE. In particular, determining whether a decrease in sleep duration and an increase in daytime sleepiness are driven by the pathologies in the SCN may reveal novel targets for intervention.