A Palm-Sized Cryoprobe System With a Built-In Thermocouple and Its Application in an Animal Model of Epilepsy.

OBJECTIVE: The purpose of this study is to propose a palm-sized cryoprobe system with a built-in thermocouple (TC) for highly accurate and sensitive temperature measurements, and to verify the effectiveness of the system. METHODS: Conventional cryoprobe systems based on the boiling effect of a refrigerant have triple coaxial tubes. In the proposed system, the outer and middle coaxial tubes are made of two different metals that are welded only at the probe tip, thereby forming a TC. The thermoelectric properties of the built-in TC and measurement accuracy were investigated in agar in a constant-temperature chamber. The system was also applied in a penicillin G-induced rat brain epilepsy model. RESULTS: We verified that the built-in TC has appropriate thermoelectric properties and that the system more accurately and sensitively measured transient temperature changes at the probe tip wall compared to conventional systems, showing the cooling performance of the system. In the rat model, epileptiform activities disappeared on freezing, and reliable cell necrosis was achieved at an end temperature of -45.2 ± 1.6 °C. CONCLUSIONS: The proposed system is suitable for reliable cryosurgery. SIGNIFICANCE: The system is probably to be valuable for clarifying the relationship between freezing temperature and cell necrosis in vivo.

Detailed spectral profile analysis of electrocorticograms during freezing against penicillin-induced epileptiform discharges in the anesthetized rat.

OBJECTIVES: Cryosurgery is an alternative technique for minimally invasive treatment of lesions. We have recently examined cryosurgery for epilepsy in animal models, and found that penicillin G (PG)-induced epileptiform discharges (EDs) mostly vanished after freezing. However, EDs were provoked again after insufficient freezing. Inadequate freezing is not visually detectable during and just after freezing and is not predictable beforehand. To manage this problem, we examined whether intraoperative monitoring of electrocorticograms (ECoGs) can predict recurrence of EDs after cryosurgery. METHODS: A palm-sized cryoprobe system was applied to focal seizures in a Wistar rat model in which EDs were induced in advance by intracerebral injection of PG. During stable induction of EDs, the cryoprobe was carefully inserted into the epileptic region and this region was immediately frozen. After the series of prefreezing, freezing, and postfreezing, rats in which PG-induced EDs relapsed within 3 h were defined as the ED-relapsed (EDR) group, and other rats were defined as the ED-vanished (EDV) group. Time-frequency analysis was conducted on the ECoGs in each group through each freezing series. RESULTS: Relapse of PG-induced EDs on ECoG after the freezing series was associated with the remaining power of the delta band in the freezing period more strongly in the EDR group than in the EDV group. CONCLUSIONS: Success or failure of the freezing procedure can be predicted by the specificity of the delta band of the ECoG obtained intraoperatively.

Epidural focal brain cooling abolishes neocortical seizures in cats and non-human primates.

Focal brain cooling (FBC) is under investigation in preclinical trials of intractable epilepsy (IE), including status epilepticus (SE). This method has been studied in rodents as a possible treatment for epileptic disorders, but more evidence from large animal studies is required. To provide evidence that FBC is a safe and effective therapy for IE, we investigated if FBC using a titanium cooling plate can reduce or terminate focal neocortical seizures without having a significant impact on brain tissue. Two cats and two macaque monkeys were chronically implanted with an epidural FBC device over the somatosensory and motor cortex. Penicillin G was delivered via the intracranial cannula for induction of local seizures. Repetitive FBC was performed using a cooling device implanted for a medium-term period (FBC for 30min at least twice every week; 3 months total) in three of the four animals. The animals exhibited seizures with repetitive epileptiform discharges (EDs) after administration of penicillin G, and these discharges decreased at less than 20°C cooling with no adverse histological effects. The results of this study suggest that epidural FBC is a safe and effective potential treatment for IE and SE.

The Palm-Sized Cryoprobe System Based on Refrigerant Expansion and Boiling and Its Application to an Animal Model of Epilepsy.

GOAL: The purpose of this study is to propose the palm-sized cryoprobe system based on a new concept and to suggest that the freezing technique could be used for treatment of epilepsy. METHODS: We propose herein a cryoprobe system based on the boiling effect that uses a specific refrigerants with a boiling point higher than that of liquid nitrogen yet low enough to result in cell necrosis. To evaluate and verify the effectiveness of the proposed system, cooling characteristics are investigated in agar. In addition, the system is applied to a Wistar rat brain-model, in which the epileptic activities are induced in advance by a potent epileptogenic substance. RESULTS: The design concept yielded the following benefits: 1) the selected refrigerant promotes sealing in the tank; 2) the tank can be made as compact as possible, limited only by the volume required for the refrigerant; 3) because the tank and probe units can be separated by a nonconducting, flexible, and high-pressure tube, the tank unit can be manipulated without disturbing the probe tip with mechanical vibrations and electrical noise. Although the agar experiments, we verified that the proposed system can uniquely and reproducibly create an ice ball. Moreover, in the rat experiments in vivo, it was confirmed that penicillin G-induced epileptic activities disappeared on freezing with the proposed system. CONCLUSIONS: The palm-sized system has desired characteristics and can apply for an animal model of epilepsy. SIGNIFICANCE: Results of in vivo experiments suggest that cryosurgery may be an effective treatment for epilepsy.

Inhibitory interference to abandonment of voluntary finger movement by single-pulse transcranial magnetic stimulation.

Brain function dynamics related to an inhibitory interference in voluntary motor abandonment was investigated with single-pulse transcranial magnetic stimulation (TMS) and electroencephalogram (EEG). As the voluntary motor movement, a point-to-point reaching movement of the right index-finger was conducted. The starting time of the movement was indicated with the clock making one revolution for 4 s. The time the clock hand passed the 9 o'clock position was defined as a go-signal. In the go trials, the subject was instructed to start the movement at the timing of the go signal. In some trials, called as pre-stop trials, a stop signal was presented with red LED illumination -100 ms from the timing of the go-signal. The go-trials and pre-stop trials were randomly performed in the series of the trials. In all trials, TMS or sham-TMS were conducted. TMS was delivered with a round coil on the subject's head at various timings. Sham-TMS trials were with a click sound of TMS produced by another coil located near the head without the brain stimulation. In the sham-TMS trials of the pre-stop trials, the subject was able to prevent the finger movement. However, the TMS conducted at -150, -100 or -50 ms from the go-signal induced the involuntary finger movement in the pre-stop trials. We also measured brain potentials in the sham-TMS and TMS trials. The potential at Fz electrode showed a large positive peak in the sham-TMS trials of the pre-stop trials, whereas the potentials at the same latency were attenuated in the TMS trials of the pre-stop trials. These results indicated that the single-pulse TMS applied around the stop-signal in the reaching finger movement could intervene in the brain function of the voluntary motor abandonment conducted at medial frontal cortex.

Penicillin-induced epileptiform activity elevates focal brain temperature in anesthetized rats.

To elucidate a relationship between changes in focal brain temperature and severity of abnormal brain activity, epileptiform discharges and behavioral seizures were induced by Penicillin G in anesthetized rats, and focal brain-temperature was measured. Penicillin G was injected into the right primary sensorimotor cortex (400IU/µl). After the injection, epileptiform discharges induced a temperature increase gradually by 0.65±0.24°C. Moreover, when behavioral seizures were induced by reducing the anesthesia level, the temperature was raised by 0.26±0.22°C. These results suggest that elevation of the focal brain temperature is associated with the severity of epileptic activity.

Neuroprotective effects of focal brain cooling on photochemically-induced cerebral infarction in rats: analysis from a neurophysiological perspective.

Although systemic hypothermia provides favorable outcomes in stroke patients, it has only been adopted in a limited number of patients because of fatal complications. To resolve these issues, focal brain cooling (FBC) has recently drawn attention as a less-invasive treatment for brain injuries. Therefore, we investigated whether FBC has a favorable effect on focal cerebral ischemia (FCI). Male-adult-Wistar rats were used. Under general anesthesia, a small burr hole was made and FCI was induced in the primary sensorimotor area (SI-MI) using photothrombosis. An additional craniotomy was made over the SI-MI and FBC was performed at a temperature of 15°C for 5h. Electrocorticograms (ECoG) were recorded on the border cortex of the ischemic focus. Thereafter, rats were sacrificed and the infarct area was measured. In another experiment, rats were allowed to recover for 5 days after cooling and neurobehavioral function was evaluated. FBC suppressed all ECoG frequency bands during and after cooling (p<0.05), except for the delta frequency band in the precooling versus rewarming periods. The injured areas in the cooling and non-cooling groups were 0.99±0.30 and 1.71±0.54 mm(2), respectively (p<0.03). The grip strength at 2 days after surgery was preserved in the cooling group (p<0.05). We report the novel finding that epileptiform discharges were suppressed in the ischemic border, the infarct area was reduced and neurobehaviour was preserved by FBC. These results indicate that FBC is neuroprotective in the ischemic brain and has demonstrated therapeutic potential for cerebral infarction.

Cooling of the epileptic focus suppresses seizures with minimal influence on neurologic functions.

PURPOSE: Focal brain cooling is effective for suppression of epileptic seizures, but it is unclear if seizures can be suppressed without a substantial influence on normal neurologic function. To address the issue, a thermoelectrically driven cooling system was developed and applied in free-moving rat models of focal seizure and epilepsy. METHODS: Focal seizures limited to the unilateral forelimb were induced by local application of a penicillin G solution or cobalt powder to the unilateral sensorimotor cortex. A proportional integration and differentiation (PID)-controlled, thermoelectrically driven cooling device (weight of 11 g) and bipolar electrodes were chronically implanted on the eloquent area (on the epileptic focus) and the effects of cooling (20, 15, and 10°C) on electrocorticography, seizure frequency, and neurologic changes were investigated. KEY FINDINGS: Cooling was associated with a distinct reduction of the epileptic discharges. In both models, cooling of epileptic foci significantly improved both seizure frequency and neurologic functions from 20°C down to 15°C. Cooling to 10°C also suppressed seizures, but with no further improvement in neurologic function. Subsequent investigation of sensorimotor function revealed significant deterioration in foot-fault tests and the receptive field size at 15°C. SIGNIFICANCE: Despite the beneficial effects in ictal rats, sensorimotor functions deteriorated at 15°C, thereby suggesting a lower limit for the therapeutic temperature. These results provide important evidence of a therapeutic effect of temperatures from 20 to 15°C using an implantable, hypothermal device for focal epilepsy.