Effects of focal brain cooling on extracellular concentrations of neurotransmitters in patients with epilepsy

Effects of focal cortical cooling on somatosensory evoked potentials in rats

Although the focal brain cooling technique is widely used to examine brain function, the effects of cortical temperature at various levels on sensory information processing and neural mechanisms remain underexplored. To elucidate the mechanisms of temperature modulation in somatosensory processing, this study aimed to examine how P1 and N1 deflections of somatosensory evoked potentials (SEPs) depend on cortical temperature and how excitatory and inhibitory inputs contribute to this temperature dependency. SEPs were generated through electrical stimulation of the contralateral forepaw in anesthetized rats. The SEPs were recorded while cortical temperatures were altered between 17-38 °C either without any antagonists, with a gamma-aminobutyric acid type A (GABAA) receptor antagonist (gabazine), with an aminomethylphosphonic acid (AMPA) receptor antagonist (NBQX), or with an N-Methyl-D-aspartic acid (NMDA) receptor antagonist ([R]-CPP). The effects of different gabazine concentrations (0, 1, and 10 µM) were examined in the 35-38 °C range. The P1/N1 amplitudes and their peak-to-peak differences plotted against cortical temperature showed an inverted U relationship with a maximum at approximately 27.5 °C when no antagonists were administered. The negative correlation between these amplitudes and temperatures of ≥ 27.5 °C plateaued after gabazine administration, which occurred progressively as the gabazine concentration increased. In contrast, the correlation remained negative after the administration of NBQX and (R)-CPP. These results suggest that GABAergic inhibitory inputs contribute to the negative correlation between SEP amplitude and cortical temperature around the physiological cortical temperature.

Suppressive Effects of Transient Receptor Potential Melastatin 8 Agonist on Epileptiform Discharges and Epileptic Seizures

Epilepsy is a relatively common condition, but more than 30% of patients have refractory epilepsy that is inadequately controlled by or is resistant to multiple drug treatments. Thus, new antiepileptic drugs based on newly identified mechanisms are required. A previous report revealed the suppressive effects of transient receptor potential melastatin 8 (TRPM8) activation on penicillin G-induced epileptiform discharges (EDs). However, it is unclear whether TRPM8 agonists suppress epileptic seizures or affect EDs or epileptic seizures in TRPM8 knockout (TRPM8KO) mice. We investigated the effects of TRPM8 agonist and lack of TRPM8 channels on EDs and epileptic seizures. Mice were injected with TRPM8 agonist 90 min after or 30 min before epilepsy-inducer injection, and electrocorticograms (ECoGs) were recorded under anesthesia, while behavior was monitored when awake. TRPM8 agonist suppressed EDs and epileptic seizures in wildtype (WT) mice, but not in TRPM8KO mice. In addition, TRPM8KO mice had a shorter firing latency of EDs, and EDs and epileptic seizures were deteriorated by the epilepsy inducer compared with those in WT mice, with the EDs being more easily propagated to the contralateral side. These findings suggest that TRPM8 activation in epileptic regions has anti-epileptic effects.

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.

Substantia nigra pars reticulata-mediated sleep and motor activity regulation

STUDY OBJECTIVES

The substantia nigra pars reticulata (SNR) is a major output nucleus of the basal ganglia. Animal studies have shown that lesions of the SNR cause hyposomnia and motor hyperactivity, indicating that the SNR may play a role in the control of sleep and motor activity.

METHODS

Eight 8- to 10-week-old adult male Sprague-Dawley rats were used. After 3 days of baseline polysomnographic recording, dialysates were collected from the lateral SNR across natural sleep-wake states. Muscimol and bicuculline were microinfused into the lateral SNR.

RESULTS

We found that GABA release in the lateral SNR is negatively correlated with slow wave sleep (SWS; R = -0.266, p < 0.01, n = 240) and positively correlated with waking (R = 0.265, p < 0.01, n = 240) in rats. Microinfusion of muscimol into the lateral SNR decreased sleep time and sleep quality, as well as eliciting motor hyperactivity in wake and increased periodic leg movement in SWS, while bicuculline infused into the lateral SNR increased sleep and decreased motor activity in SWS in rats. Muscimol infusion skewed the distribution of inter-movement intervals, with most between 10 and 20 s, while a flat distribution of intervals between 10 and 90 s was seen in baseline conditions.

CONCLUSIONS

Activation of the lateral SNR is important for inducing sleep and inhibiting motor activity prior to and during sleep, and thus to the maintenance of sleep. Abnormal function of the lateral SNR may cause hyposomnia and motor hyperactivity in quiet wake and in sleep.

Research Progress of the Application of Hypothermia in the Eye

Hypothermia is widely used in the medical field to protect organs or tissues from damage. Different research fields have different explanations of the protection mechanism of hypothermia. Hypothermia is also widely used in the field of ophthalmology, for example, in the eye bank, the preservation of corneal tissue and the preservation of the eyeball. Low temperature can also be applied to some ophthalmic diseases, such as allergic conjunctivitis, retinal ischemia, and retinal hypoxia. It is used to relieve eye symptoms or reduce tissue damage. Hypothermic techniques have important applications in ophthalmic surgery, such as corneal refractive surgery, vitrectomy surgery, and ciliary body cryotherapy for end-stage glaucoma. Hypothermia can reduce the inflammation of the cornea and protect the retinal tissue. The eyeball is a complex organ, including collagen tissue of the eyeball wall and retinal nerve tissue and retinal blood vessels. The mechanism of low temperature protecting eye tissue is complicated. It is important to understand the mechanism of hypothermia and its applications in ophthalmology. This review introduces the mechanism of hypothermia and its application in the eye banks, eye diseases (allergic conjunctivitis, retinal ischemia, and hypoxia), and eye surgeries (corneal transplant surgery, corneal refractive surgery, and vitrectomy).

Focal Cortical Surface Cooling is a Novel and Safe Method for Intraoperative Functional Brain Mapping

OBJECTIVE

Electric cortical stimulation (ECS) has been the gold standard for intraoperative functional mapping in neurosurgery, yet it carries the risk of induced seizures. We assess the safety of focal cortical cooling (CC) as a potential alternative to ECS.

METHODS

We reviewed 40 patients (13 with tumor and 27 with mesial temporal lobe epilepsy) who underwent intraoperative CC at the University of Iowa Hospital and Clinics (CC group), of whom 38 underwent ECS preceding CC. Intraoperative and postoperative seizure incidence, postoperative neurologic deficits, and new postoperative radiographic findings were collected to assess CC safety. Fifty-five patients who underwent ECS mapping without CC (ECS-alone group) were reviewed as a control cohort. Another 25 patients who underwent anterior temporal lobectomy (ATL) without CC or ECS (no ECS/no CC-ATL group) were also reviewed to evaluate long-term effects of CC.

RESULTS

Seventy-nine brain sites in the CC group were cooled, comprising inferior frontal gyrus (44%), precentral gyrus (39%), postcentral gyrus (6%), subcentral gyrus (4%), and superior temporal gyrus (6%). The incidence of intraoperative seizure(s) was 0% (CC group) and 3.6% (ECS-alone group). The incidence of seizure(s) within the first postoperative week did not significantly differ among CC (7.9%), ECS-alone (9.0%), and no ECS/no CC-ATL groups (12%). There was no significant difference in the incidence of postoperative radiographic change between CC (7.5%) and ECS-alone groups (5.5%). Long-term seizure outcome (Engel I+II) for mesial temporal epilepsy did not differ among CC (80%), ECS-alone (83.3%), and no ECS/no CC-ATL groups (83.3%).

CONCLUSIONS

CC when used as an intraoperative mapping technique is safe and may complement ECS.

Recent antiepileptic and neuroprotective applications of brain cooling

Hypothermia is a widely used clinical practice for neuroprotection and is a well-established method to mitigate the adverse effects of some clinical conditions such as reperfusion injury after cardiac arrest and hypoxic ischemic encephalopathy in newborns. The discovery, that lowering the core temperature has a therapeutic potential dates back to the early 20th century, but the underlying mechanisms are actively researched, even today. Especially, in the area of neural disorders such as epilepsy and traumatic brain injury, cooling has promising prospects. It is well documented in animal models, that the application of focal brain cooling can effectively terminate epileptic discharges. There is, however, limited data regarding human clinical trials. In this review article, we will discuss the main aspects of therapeutic hypothermia focusing on its use in treating epilepsy. The various experimental approaches and device concepts for focal brain cooling are presented and their potential for controlling and suppressing seizure activity are compared.

[Gender differences in the pool of free amino acid neurotransmitters in Krushinsky-Molodkina rats]

The study of the role of neurotransmitter systems in the pathogenesis of epilepsy is one of the priorities of epileptology. New data on the functions of free neurotransmitter-like amino acid in the central nervous system are of the greatest importance and determine the prospects for the development of novel effective anticonvulsants. It is widely believed in clinical medicine that epilepsy has distinct gender characteristics. The aim of this study was to investigate the gender peculiarities in the content of neurotransmitter amino acids in the brain of Krushinsky-Molodkina (KM) rats, which were used as model organisms for the study of genetically induced audiogenic epilepsy. The content of Asp, Glu, GABA, Gly, and Tau of the medulla oblongata, hippocampus and cerebral cortex were determined using high-performance liquid chromatography (HPLC) in intact KM rats, KM rats exposed to a series of epileptiform seizures, and Wistar rats (control group). Both the Wistar and KM rats had gender distinctions in the distribution of free amino acids among the investigated brain parts. The audiogenic epilepsy was characterized by smoothing gender differences as well as differences between the concentrations of free amino acids in the cortex and medulla oblongata, specific for Wistar rats. The changes observed in male rats after the set of seizures included the increase in GABA concentration and a decrease in the Gly level in all investigated brain parts, as well as the decrease of the Tau content in the cortex and hippocampus. At the same time, the Glu content in cortex increased, while the Asp level decreased. After 6 days of audiogenic stimulations the female KM rats demonstrated the increase in the Glu level in all investigated brain parts, the increase in Gly and Asp levels in hippocampus, and no changes in the GABA content. Thus, after the set of epileptiform seizures the KM rats achieved a new steady state of the studied amino acids pool, which differed in males and females. In this case, gender differences significantly changed after the seizures.

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

This study aimed to understand the mechanism by which brain cooling terminates epileptic discharge. Cortical slices were prepared from rat brains (n = 19) and samples from patients with intractable epilepsy that had undergone temporal lobectomy (n = 7). We performed whole cell current clamp recordings at approximately physiological brain temperature (35℃) and at cooler temperatures (25℃ and 15℃). The firing threshold in human neurons was lower at 25℃ (-32.6 mV) than at 35℃ (-27.0 mV). The resting potential and spike frequency were similar at 25℃ and 35℃. Cooling from 25℃ to 15℃ did not change the firing threshold, but the resting potential increased from -65.5 to -54.0 mV and the waveform broadened from 1.85 to 6.55 ms, due to delayed repolarization. These changes enhanced the initial spike appearance and reduced spike frequency; moreover, spike frequency was insensitive to increased levels of current injections. Similar results were obtained in rat brain studies. We concluded that the reduction in spike frequency at 15℃, due to delayed repolarization, might be a key mechanism by which brain cooling terminates epileptic discharge. On the other hand, spike frequency was not influenced by the reduced firing threshold or the elevated resting potential caused by cooling.

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.

Limitations of Local Brain Cooling on Generalized Motor Seizures from Unknown Foci in Awake Rats

Local brain cooling of an epileptic focus at 15°C reduces the number of spikes on an electrocorticogram (ECoG), terminates seizures, and maintains neurological functions. In this study, we attempted to suppress generalized motor seizures (GMSs) by cooling a unilateral sensorimotor area. GMSs were induced in rats by intraperitoneal injection of bicuculline methiodide, an antagonist of gamma-aminobutyric acid. While monitoring the ECoG and behavior, the right sensorimotor cortex was cooled for 10 min using an implanted device. The number of spikes recorded from the cooled cortex significantly decreased to 71.2% and 62.5% compared with the control group at temperatures of 15 and 5°C (both P <0.01), respectively. The number of spikes recorded from the contralateral mirror cortex reduced to 61.7% and 62.7% (both P <0.05), respectively. The ECoG power also declined to 85% and 50% in the cooled cortex, and to 94% and 49% in the mirror cortex by the cooling at 15 and 5°C, respectively. The spikes regained in the middle of the cooling period at 15°C and in the late period at 5°C. Seizure-free durations during the 10-min periods of cooling at 15 and 5°C lasted for 4.1 ± 2.2 and 5.9 ± 1.1 min, respectively. Although temperature-dependent seizure alleviation was observed, the effect of local cortical cooling on GMSs was limited compared with the effect of local cooling of the epileptic focus on GSMs.

Metal-organic frameworks as affinity agents to enhance the microdialysis sampling efficiency of fatty acids

Microdialysis (MD) has been extensively used for in vivo sampling of hydrophilic analytes such as neurotransmitters and drug metabolites. In contrast, there have been few reports on sampling of lipophilic analytes by MD. Lipophilic analytes are easily adsorbed on the surfaces of the dialysis membrane and the inner wall of tubing, which leads to a very low relative recovery (RR). In this work, a strategy to develop an enhanced MD sampling of fatty acids (FAs) by using metal-organic frameworks (MOFs) as affinity agents in the perfusion fluid was investigated. Two MOFs, MIL-101 and ZIF-8, were synthesized and tested for the first time. A 2 times higher RR, about 70% RR, was obtained. The FT-IR experiment showed that the unsaturated metal sites in MOFs could coordinate with FAs, therefore the FAs were encapsulated into MOFs, avoiding FAs to be absorbed on the surfaces of the dialysis membrane and the inner wall of tubing. Moreover, incorporation of FAs into MOFs led to a decrease of free concentration of FAs inside the MD membrane and an increase of concentration gradient, allowing more FAs to diffuse across the membrane. Consequentially, an enhanced RR was obtained. The approach was successfully used to monitor the time profile of targeted FAs in cell culture media after lipopolysaccharide (LPS)-induced inflammation.

Epileptic Seizure Suppression by Focal Brain Cooling With Recirculating Coolant Cooling System: Modeling and Simulation

A focal brain cooling system for treatment of refractory epilepsy that is implantable and wearable may permit patients with this condition to lead normal daily lives. We have developed such a system for cooling of the epileptic focus by delivery of cold saline to a cooling device that is implanted cranially. The outflow is pumped for circulation and cooled by a Peltier device. Here, we describe the design of the system and evaluate its feasibility by simulation. Mathematical models were constructed based on equations of fluid dynamics and data from a cat model. Computational fluid dynamics simulations gave the following results: 1) a cooling device with a complex channel structure gives a more uniform temperature in the brain; 2) a cooling period of <10 min is required to reach an average temperature of 25.0°Cat 2 mm below the brain surface, which is the target temperature for seizure suppression. This time is short enough for cooling of the brain before seizure onset after seizure prediction by an intracranial electroencephalogram-based algorithm; and 3) battery charging would be required once every several days for most patients. These results suggest that the focal brain cooling system may be clinically applicable.

Differential temperature sensitivity of synaptic and firing processes in a neural mass model of epileptic discharges explains heterogeneous response of experimental epilepsy to focal brain cooling

Experiments with drug-induced epilepsy in rat brains and epileptic human brain region reveal that focal cooling can suppress epileptic discharges without affecting the brain's normal neurological function. Findings suggest a viable treatment for intractable epilepsy cases via an implantable cooling device. However, precise mechanisms by which cooling suppresses epileptic discharges are still not clearly understood. Cooling experiments in vitro presented evidence of reduction in neurotransmitter release from presynaptic terminals and loss of dendritic spines at post-synaptic terminals offering a possible synaptic mechanism. We show that termination of epileptic discharges is possible by introducing a homogeneous temperature factor in a neural mass model which attenuates the post-synaptic impulse responses of the neuronal populations. This result however may be expected since such attenuation leads to reduced post-synaptic potential and when the effect on inhibitory interneurons is less than on excitatory interneurons, frequency of firing of pyramidal cells is consequently reduced. While this is observed in cooling experiments in vitro, experiments in vivo exhibit persistent discharges during cooling but suppressed in magnitude. This leads us to conjecture that reduction in the frequency of discharges may be compensated through intrinsic excitability mechanisms. Such compensatory mechanism is modelled using a reciprocal temperature factor in the firing response function in the neural mass model. We demonstrate that the complete model can reproduce attenuation of both magnitude and frequency of epileptic discharges during cooling. The compensatory mechanism suggests that cooling lowers the average and the variance of the distribution of threshold potential of firing across the population. Bifurcation study with respect to the temperature parameters of the model reveals how heterogeneous response of epileptic discharges to cooling (termination or suppression only) is exhibited. Possibility of differential temperature effects on post-synaptic potential generation of different populations is also explored.