Monitoring cerebral oxygenation and local field potential with a variation of isoflurane concentration in a rat model

The effect of burst suppression on cerebral blood flow and autoregulation: a scoping review of the human and animal literature

Background: Burst suppression (BS) is an electroencephalography (EEG) pattern in which there are isoelectric periods interspersed with bursts of cortical activity. Targeting BS through anaesthetic administration is used as a tool in the neuro-intensive care unit but its relationship with cerebral blood flow (CBF) and cerebral autoregulation (CA) is unclear. We performed a systematic scoping review investigating the effect of BS on CBF and CA in animals and humans. Methods: We searched MEDLINE, BIOSIS, EMBASE, SCOPUS and Cochrane library from inception to August 2022. The data that were collected included study population, methods to induce and measure BS, and the effect on CBF and CA. Results: Overall, there were 66 studies that were included in the final results, 41 of which examined animals, 24 of which examined humans, and 1 of which examined both. In almost all the studies, BS was induced using an anaesthetic. In most of the animal and human studies, BS was associated with a decrease in CBF and cerebral metabolism, even if the mean arterial pressure remained constant. The effect on CA during periods of stress (hypercapnia, hypothermia, etc.) was variable. Discussion: BS is associated with a reduction in cerebral metabolic demand and CBF, which may explain its usefulness in patients with brain injury. More evidence is needed to elucidate the connection between BS and CA.

How general anesthetics work: from the perspective of reorganized connections within the brain

General anesthesia is critical for various procedures and surgeries. Despite the widespread use of anesthetics, their precise mechanisms remain poorly understood. Anesthetics inevitably act on the brain, primarily through the modulation of target receptors. Even if the action is specific to an individual neuron, however, long-range effects can occur due to the tremendous interconnectedness of neuronal activity. The strength of this connectivity can be understood using mathematical models that allow for the study of neuronal connectivity dynamics. These models also allow researchers to develop hypotheses on the candidate mechanisms of action of different types of anesthesia. This review highlights the theoretical background associated with the study of the mechanisms of action of anesthetics. We propose a candidate framework that describes how anesthetics act on the brain and consciousness in general.

Changes of Apomorphine-Induced Vaginal Hemodynamics in an Ovariectomized Rat Model Using Near-Infrared Spectroscopic Probe

INTRODUCTION

Female sexual arousal disorder (FSAD) can be caused by the change in vaginal structure due to the decline of estrogen and one of the main symptoms is vaginal dryness. FSAD is a prevalent problem afflicting women all over the world and thus the interest is growing on the matter, but related studies of monitoring FSAD using a non-invasive optical method barely have been carried out.

AIM

This study aims to investigate the longitudinal changes in female sexual arousal response induced by apomorphine (APO) administration in the ovariectomized rat using near-infrared spectroscopy (NIRS) probe.

METHODS

To elicit sexual arousal, APO was administered subcutaneously to animals (n = 6) before and after ovariectomy, and the changes in oxyhemoglobin (OHb), deoxyhemoglobin (RHb), total hemoglobin (THb) concentration, and temperature on the vaginal wall after APO administration were monitored bi-weekly for 8 weeks. Furthermore, estradiol hormone, vaginal secretion, and body weight have been measured for comparison with the results from vaginal hemodynamics.

RESULTS

APO administration caused the increase of vaginal OHb and RHb concentration but a decrease in temperature. The amplitude of OHb, RHb, and THb increase induced by APO gradually decreased over 8 weeks after ovariectomy while the decrease in vaginal temperature became profound. The level of estradiol and vaginal secretions also decreased over 8 weeks after ovariectomy, but bodyweight showed an increasing trend.

CONCLUSIONS

A comparison between the parameters measured from the NIRS probe and the others (estradiol level, amount of vaginal secretion, and body weight) proved that the NIRS has the potential as a monitoring tool to evaluate female sexual arousal response. Jeong H, Lee HS, Seong M, et al. Changes of Apomorphine-Induced Vaginal Hemodynamics in an Ovariectomized Rat Model Using Near-Infrared Spectroscopic Probe. J Sex Med 2021;18:1328-1336.

Wearable Transcranial Ultrasound System for Remote Stimulation of Freely Moving Animal

OBJECTIVE

Transcranial focused ultrasound (tFUS) has drawn considerable attention in the neuroscience field as a noninvasive approach to modulate brain circuits. However, the conventional approach requires the use of anesthetized or immobilized animal models, which places considerable restrictions on behavior and affects treatment. Thus, this work presents a wireless, wearable system to achieve ultrasound brain stimulation in freely behaving animals.

METHODS

The wearable tFUS system was developed based on a microcontroller and amplifier circuit. Brain activity induced by tFUS was monitored through cerebral hemodynamic changes using near-infrared spectroscopy. The system was also applied to stroke rehabilitation after temporal middle cerebral artery occlusion (tMCAO) in rats. Temperature calculations and histological results showed the safety of the application even with prolonged 40 min sonication.

RESULTS

The output ultrasonic wave produced from a custom PZT transducer had a central frequency of 457 kHz and peak to peak pressure of 426 kPa. The device weight was 20 g, allowing a full range of motion. The stimulation was found to induce hemodynamic changes in the sonicated area, while open-field tests showed that ultrasound applied to the ipsilateral hemisphere for 5 consecutive days after the stroke facilitated recovery.

CONCLUSION

The wearable tFUS system has been designed and implemented on moving rats. The results showed the ability of device to cause both short- and long lasting effects.

SIGNIFICANCE

The proposed device provides a more natural environment to investigate the effects of tFUS for behavioral and long-term studies.

Design of an Optical Probe to Monitor Vaginal Hemodynamics during Sexual Arousal

An optical probe was developed to measure the change of oxy-hemoglobin (OHb), deoxy- hemoglobin (RHb), and total hemoglobin (THb) along with temperature from the vaginal wall of female rats. Apomorphine (APO, 80 μg/kg) was administered to elicit sexual arousal in female Sprague Dawley rats (SD, 180–200 g). The behavior changes caused by APO administration were checked before monitoring vaginal responses. The changes of oxy-, deoxy-, and total hemoglobin concentration and the temperature from the vaginal wall were monitored before, during, and after APO administration. Animals were under anesthesia during the measurement. After APO administration, the concentration of OHb (55 ± 29 μM/DPF), RHb (33 ± 25 μM/DPF), and THb (83 ± 59 μM/DPF) in the vaginal wall increased in a few min, while saline administration did not cause any significant change. In case of the vaginal temperature change, APO decreased the temperature slightly in the vaginal wall while saline administration did not show any temperature change in the vaginal wall. As the outcomes demonstrated, the developed probe can detect hemodynamic and temperature variation in the vaginal wall. The hemodynamic information acquired by the probe can be utilized to establish an objective and accurate standard of female sexual disorders.

Non-invasive measurement of hemodynamic change during 8 MHz transcranial focused ultrasound stimulation using near-infrared spectroscopy

BACKGROUND

Transcranial focused ultrasound (tFUS) attracts wide attention in neuroscience as an effective noninvasive approach to modulate brain circuits. In spite of this, the effects of tFUS on the brain is still unclear, and further investigation is needed. The present study proposes to use near-infrared spectroscopy (NIRS) to observe cerebral hemodynamic change caused by tFUS in a noninvasive manner.

RESULTS

The results show a transient increase of oxyhemoglobin and decrease of deoxyhemoglobin concentration in the mouse model induced by ultrasound stimulation of the somatosensory cortex with a frequency of 8 MHz but not in sham. In addition, the amplitude of hemodynamics change can be related to the peak intensity of the acoustic wave.

CONCLUSION

High frequency 8 MHz ultrasound was shown to induce hemodynamic changes measured using NIRS through the intact mouse head. The implementation of NIRS offers the possibility of investigating brain response noninvasively for different tFUS parameters through cerebral hemodynamic change.

The changes of cerebral hemodynamics during ketamine induced anesthesia in a rat model

Current electroencephalogram (EEG) based-consciousness monitoring technique is vulnerable to specific clinical conditions (eg, epilepsy and dementia). However, hemodynamics is the most fundamental and well-preserved parameter to evaluate, even under severe clinical situations. In this study, we applied near-infrared spectroscopy (NIRS) system to monitor hemodynamic change during ketamine-induced anesthesia to find its correlation with the level of consciousness. Oxy-hemoglobin (OHb) and deoxy-hemoglobin concentration levels were continuously acquired throughout the experiment, and the reflectance ratio between 730 and 850 nm was calculated to quantify the hemodynamic changes. The results showed double peaks of OHb concentration change during ketamine anesthesia, which seems to be closely related to the consciousness state of the rat. This finding suggests the possibility of NIRS based-hemodynamic monitoring as a supplementary parameter for consciousness monitoring, compensating drawbacks of EEG signal based monitoring.