Reduction of spike generation frequency by cooling in brain slices from rats and from patients with epilepsy

Intraoperative evaluation using a multimodality probe of temperature-dependent neurovascular modulation during focal brain cooling

OBJECTIVE

This study aimed to assess the effects of focal brain cooling (FBC) on human brain tissue through use of multiple sensing techniques by monitoring cerebrovascular activity and brain temperature.

METHODS

Intraoperative brain activity monitoring using a multimodality probe capable of measuring brain temperature, electrocorticography (ECoG) and changes in cerebral hemoglobin concentration was performed in 13 patients with refractory epilepsy. Brain temperature and neurovascular activity were measured beneath and surrounding the FBC device. Data were categorized into three temperature ranges [low-temperature range (LTR, <18 °C), moderate-temperature range (MTR, 18 °C-28 °C), and high-temperature range (HTR, >28 °C)] for analysis.

RESULTS

Changes in oxyhemoglobin (ΔO2Hb) and deoxyhemoglobin (ΔHHb) across the temperature ranges showed a U-shape and inverted U-shape pattern, respectively. ΔO2Hb decreased and ΔHHb increased in the MTR, reflecting enhanced neuronal activity and increased oxygen consumption. Conversely, ΔO2Hb increased and ΔHHb decreased in the LTR, indicating suppressed neuronal activity and reduced oxygen consumption. These findings highlight the temperature-dependent modulation of neurovascular activity by FBC, driven by distinct non-linear patterns.

CONCLUSIONS

FBC selectively influenced brain electrical activity and hemoglobin concentration, highlighting its subtle effects on neurovascular dynamics.

SIGNIFICANCE

These findings provide critical insights into optimizing cooling strategies for neurological disorders using multimodality probes and FBC devices.

Focal brain cooling suppresses spreading depolarization and reduces endothelial nitric oxide synthase expression in rats

This study aimed to investigate the effects of focal brain cooling (FBC) on spreading depolarization (SD), which is associated with several neurological disorders. Although it has been studied from various aspects, no medication has been developed that can effectively control SD. As FBC can reduce neuronal damage and promote functional recovery in pathological conditions such as epilepsy, cerebral ischemia, and traumatic brain injury, it may also potentially suppress the onset and progression of SD. We created an experimental rat model of SD by administering 1 M potassium chloride (KCl) to the cortical surface. Changes in neuronal and vascular modalities were evaluated using multimodal recording, which simultaneously recorded brain temperature (BrT), wide range electrocorticogram, and two-dimensional cerebral blood flow. The rats were divided into two groups (cooling [CL] and non-cooling [NC]). Warm or cold saline was perfused on the surface of one hemisphere to maintain BrT at 37°C or 15°C in the NC and CL groups, respectively. Western blot analysis was performed to determine the effects of FBC on endothelial nitric oxide synthase (eNOS) expression. In the NC group, KCl administration triggered repetitive SDs (mean frequency = 11.57/h). In the CL group, FBC increased the duration of all KCl-induced events and gradually reduced their frequency. Additionally, eNOS expression decreased in the cooled brain regions compared to the non-cooled contralateral hemisphere. The results obtained by multimodal recording suggest that FBC suppresses SD and decreases eNOS expression. This study may contribute to developing new treatments for SD and related neurological disorders.

Unraveling brain diseases: The promise of brain-on-a-chip models

Brain disorders, encompassing a wide spectrum of neurological and psychiatric conditions, present a formidable challenge in modern medicine. Despite decades of research, the intricate complexity of the human brain still eludes comprehensive understanding, impeding the development of effective treatments. Recent advancements in microfluidics and tissue engineering have led to the development of innovative platforms known as "Brain-on-a-Chip" (BoC) i.e., advanced in vitro systems that aim to replicate the microenvironment of the brain with the highest possible fidelity. This technology offers a promising test-bed for studying brain disorders at the cellular and network levels, providing insights into disease mechanisms, drug screening, and, in perspective, the development of personalized therapeutic strategies. In this review, we provide an overview of the BoC models developed over the years to model and understand the onset and progression of some of the most severe neurological disorders in terms of incidence and debilitation (stroke, Parkinson's, Alzheimer's, and epilepsy). We also report some of the cutting-edge therapeutic approaches whose effects were evaluated by means of these technologies. Finally, we discuss potential challenges, and future perspectives of the BoC models.

Brain temperature in healthy and diseased conditions: A review on the special implications of MRS for monitoring brain temperature

Brain temperature determines not only an individual's cognitive functionality but also the prognosis and mortality rates of many brain diseases. More specifically, brain temperature not only changes in response to different physiological events like yawning and stretching, but also plays a significant pathophysiological role in a number of neurological and neuropsychiatric illnesses. Here, we have outlined the function of brain hyperthermia in both diseased and healthy states, focusing particularly on the amyloid beta aggregation in Alzheimer's disease.

Focal Cooling for Drug-Resistant Epilepsy: A Review

Importance

Epilepsy affects at least 1.2% of the population, with one-third of cases considered to be drug-resistant epilepsy (DRE). For these cases, focal cooling therapy may be a potential avenue for treatment, offering hope to people with DRE for freedom from seizure. The therapy leverages neuroscience and engineering principles to deliver a reversible treatment unhindered by pharmacology.

Observations

Analogous to (but safer than) the use of global cooling in postcardiac arrest and neonatal ischemic injury, extensive research supports the premise that focal cooling as a long-term treatment for epilepsy could be effective. The potential advantages of focal cooling are trifold: stopping epileptiform discharges, seizures, and status epilepticus safely across species (including humans).

Conclusions and Relevance

This Review presents the most current evidence supporting focal cooling in epilepsy. Cooling has been demonstrated as a potentially safe and effective treatment modality for DRE, although it is not yet ready for use in humans outside of randomized clinical trials. The Review will also offer a brief overview of the technical challenges related to focal cooling in humans, including the optimal device design and cooling parameters.

A daily temperature rhythm in the human brain predicts survival after brain injury

Patients undergo interventions to achieve a 'normal' brain temperature; a parameter that remains undefined for humans. The profound sensitivity of neuronal function to temperature implies the brain should be isothermal, but observations from patients and non-human primates suggest significant spatiotemporal variation. We aimed to determine the clinical relevance of brain temperature in patients by establishing how much it varies in healthy adults. We retrospectively screened data for all patients recruited to the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) High Resolution Intensive Care Unit Sub-Study. Only patients with direct brain temperature measurements and without targeted temperature management were included. To interpret patient analyses, we prospectively recruited 40 healthy adults (20 males, 20 females, 20-40 years) for brain thermometry using magnetic resonance spectroscopy. Participants were scanned in the morning, afternoon, and late evening of a single day. In patients (n = 114), brain temperature ranged from 32.6 to 42.3°C and mean brain temperature (38.5 ± 0.8°C) exceeded body temperature (37.5 ± 0.5°C, P < 0.0001). Of 100 patients eligible for brain temperature rhythm analysis, 25 displayed a daily rhythm, and the brain temperature range decreased in older patients (P = 0.018). In healthy participants, brain temperature ranged from 36.1 to 40.9°C; mean brain temperature (38.5 ± 0.4°C) exceeded oral temperature (36.0 ± 0.5°C) and was 0.36°C higher in luteal females relative to follicular females and males (P = 0.0006 and P < 0.0001, respectively). Temperature increased with age, most notably in deep brain regions (0.6°C over 20 years, P = 0.0002), and varied spatially by 2.41 ± 0.46°C with highest temperatures in the thalamus. Brain temperature varied by time of day, especially in deep regions (0.86°C, P = 0.0001), and was lowest at night. From the healthy data we built HEATWAVE-a 4D map of human brain temperature. Testing the clinical relevance of HEATWAVE in patients, we found that lack of a daily brain temperature rhythm increased the odds of death in intensive care 21-fold (P = 0.016), whilst absolute temperature maxima or minima did not predict outcome. A warmer mean brain temperature was associated with survival (P = 0.035), however, and ageing by 10 years increased the odds of death 11-fold (P = 0.0002). Human brain temperature is higher and varies more than previously assumed-by age, sex, menstrual cycle, brain region, and time of day. This has major implications for temperature monitoring and management, with daily brain temperature rhythmicity emerging as one of the strongest single predictors of survival after brain injury. We conclude that daily rhythmic brain temperature variation-not absolute brain temperature-is one way in which human brain physiology may be distinguished from pathophysiology.

Effects of Cooling Temperatures via Thermal K2P Channels on Regeneration of High-Frequency Action Potentials at Nodes of Ranvier of Rat Aβ-Afferent Nerves

Temperature-sensitive two-pore domain potassium channels (thermal K2P) are recently shown to cluster at nodes of Ranvier (NRs) and play a key role in action potential (AP) regeneration and conduction on Aβ-afferent nerves. Cooling temperatures affect AP regeneration and conduction on Aβ-afferent nerves but the underlying mechanisms are not completely understood. Here, we have performed patch-clamp recordings directly at the NR in an ex vivo trigeminal nerve preparation. We have characterized the effects of cooling temperatures on intrinsic electrophysiological properties and AP regeneration at the NR on rat Aβ-afferent nerves, and determined whether and how thermal K2P channels may be involved in the effects of cooling temperatures. We show that cooling temperatures from 35°C to 15°C decrease outward leak currents, increase input resistance, depolarize resting membrane potential (RMP), broaden AP width and increase latency of AP threshold at the NR. We further demonstrate that cooling temperatures impair regeneration of high-frequency AP trains at the NR. The effects of cooling temperatures on the intrinsic electrophysiological properties and regeneration of high-frequency AP trains at the NR can be partially reversed by BL-1249 (BL), arachidonic acid (AA), and intra-axonal protons, three thermal K2P activators, indicating the involvement of thermal K2P channels. Moreover, we show that at cooling temperatures there are interplays among thermal K2P channels, RMPs, and voltage-gated Na+ channels, which together limit regeneration of high-frequency AP trains at the NR. Our findings demonstrate a new role of thermal K2P channels in temperature-dependent conduction of high-frequency sensory signals.

A multimodal, implantable sensor array and measurement system to investigate the suppression of focal epileptic seizure using hypothermia

Objective.Local cooling of the brain as a therapeutic intervention is a promising alternative for patients with epilepsy who do not respond to medication.In vitroandin vivostudies have demonstrated the seizure-suppressing effect of local cooling in various animal models. In our work, focal brain cooling in a bicuculline induced epilepsy model in rats is demonstrated and evaluated using a multimodal micro-electrocorticography (microECoG) device.Approach.We designed and experimentally tested a novel polyimide-based sensor array capable of recording microECoG and temperature signals concurrently from the cortical surface of rats. The effect of cortical cooling after seizure onset was evaluated using 32 electrophysiological sites and eight temperature sensing elements covering the brain hemisphere, where injection of the epileptic drug was performed. The focal cooling of the cortex right above the injection site was accomplished using a miniaturized Peltier chip combined with a heat pipe to transfer heat. Control of cooling and collection of sensor data was provided by a custom designed Arduino based electronic board. We tested the experimental setup using an agar gel modelin vitro, and thenin vivoin Wistar rats.Main results.Spatial variation of temperature during the Peltier controlled cooling was evaluated through calibrated, on-chip platinum temperature sensors. We found that frequency of epileptic discharges was not substantially reduced by cooling the cortical surface to 30 °C, but was suppressed efficiently at temperature values around 20 °C. The multimodal array revealed that seizure-like ictal events far from the focus and not exposed to high drop in temperature can be also inhibited at an extent like the directly cooled area.Significance.Our results imply that not only the absolute drop in temperature determines the efficacy of seizure suppression, and distant cortical areas not directly cooled can be influenced.

A focal brain-cooling device as an alternative to electrical stimulation for language mapping during awake craniotomy: patient series

BACKGROUND

Functional mapping in awake craniotomy has the potential risk of electrical stimulation-related seizure. The authors have developed a novel mapping technique using a brain-cooling device. The cooling probe is cylindrical in shape with a thermoelectric cooling plate (10 × 10 mm) at the bottom. A proportional integration and differentiation-controlled system adjusts the temperature accurately (Japan patent no. P5688666). The authors used it in two patients with glioblastoma. Broca’s area was identified by electrical stimulation, and then the cooling probe set at 5°C was attempted on it.

OBSERVATIONS

Electrocorticogram was suppressed, and the temperature dropped to 8°C in 50 sec. A positive aphasic reaction was reproduced on Broca’s area at a latency of 7 sec. A negative reaction appeared on the adjacent cortices despite the temperature decrease. The sensitivity and specificity were 60% and 100%, respectively. No seizures or other adverse events related to the cooling were recognized, and no histological damage to the cooled cortex was observed.

LESSONS

The cooling probe suppressed topographical brain function selectively and reversibly. Awake functional mapping based on thermal neuromodulation technology could substitute or compensate for the conventional electrical mapping.

Suppressive Effects of Cooling Compounds Icilin on Penicillin G-Induced Epileptiform Discharges in Anesthetized Rats

More than 30% of patients with epilepsy are refractory and have inadequate seizure control. Focal cortical cooling (FCC) suppresses epileptiform discharges (EDs) in patients with refractory focal cortical epilepsy. However, little is known about the mechanism by which FCC inhibits seizures at 15°C, and FCC treatment is highly invasive. Therefore, new antiepileptic drugs are needed that produce the same effects as FCC but with different mechanisms of action. To address this need, we focused on transient receptor potential melastatin 8 (TRPM8), an ion channel that detects cold, which is activated at 15°C. We examined whether TRPM8 activation suppresses penicillin G (PG)-induced EDs in anesthetized rats. Icilin, a TRPM8 and TRP Ankyrin 1 agonist, was administered after PG injection, and a focal electrocorticogram (ECoG) and cortical temperature were recorded for 4 h. We measured spike amplitude, duration, firing rate, and power density in each band to evaluate the effects of icilin. PG-induced EDs and increased delta, theta, alpha, and beta power spectra were observed in the ECoG. Icilin suppressed EDs while maintaining cortical temperature. In particular, 3.0-mM icilin significantly suppressed PG-induced spike amplitude, duration, and firing rate and improved the increased power density of each band in the EDs to the level of basal activity in the ECoG. These suppressive effects of 3.0-mM icilin on EDs were antagonized by administering N-(3-aminopropyl)-2-[(3-methylphenyl) methoxy]-N-(2-thienylmethyl)-benzamide hydrochloride (AMTB), a selective TRPM8 inhibitor. Our results suggest that TRPM8 activation in epileptic brain regions may be a new therapeutic approach for patients with epilepsy.