Optical recording of brain functions based on voltage-sensitive dyes

To better understand the spatial distribution of brain functions,we need to monitor and analyze neuronal activities.Electrophysiological technique has provided an important method for the exploration of some neural circuits.However,this method cannot simultaneously detect the activities of nerve cell groups.Therefore,methods that can monitor the spatial distribution of neuronal population activity are demanded to explore brain functions.Voltage-sensitive dyes(VSDs)shift their absorption or emission optical signals in response to different membrane potentials,allowing assessing the global electrical state of neurons.Optical recording technique coupled with VSDs is a promising method to monitor the brain functions by detecting optical signal changes.This review focuses on the fast and slow responses of VSDs to membrane potential changes and optical recordings utilized in the central nervous system.In this review,we attempt to show how VSDs and optical recordings can be used to obtain brain functional monitoring at high spatial and temporal resolution.Understanding of brain functions will not only greatly improve the cognition of information transmission of complex neural network,but also provide new methods of treating brain diseases such as Parkinson’s and Alzheimer’s diseases.

Neurolemma-Injected Xenopus Oocytes: An Innovative Ex Vivo Approach to Study the Effects of Pyrethroids on Ion Channels in Their Native State

Microtransplantation of rat brain neurolemma into the plasma membrane of Xenopus laevis oocytes is an ex vivo method used to study channels and receptors in their native state using standard electrophysiological approaches.In this review,we show that oocytes injected with adult rat brain neurolemma elicited tetrodotoxin-sensitive inward ion currents upon membrane depolarization,which were increased in a concentration-dependent manner by treatment with the pyrethroid insecticides permethrin and deltamethrin.Under our initial protocols,oocyte health was reduced over time and neurolemma incorporation varied between batches of oocytes from different frogs,limiting the usefulness of the assay for regulatory issues.A collection of changes to the assay procedure,data acceptance criteria,and analysis method yield substantially improved precision and,hence,assay performance.These changes established this ex vivo approach as a toxicologically relevant assay to study the toxicodynamic action of pyrethroids on ion channels in their native state using neurolemma fragments prepared from juvenile and adult rat brains.

Optical recordings reveal the differential distribution of glutamatergic transmission in the cochlear and vestibular nuclei in the newborn mouse brainstem

Objective Using optical imaging in brainstem slices, we studied evoked responses in the mouse cochlear (CN) and vestibular (VN) nuclei. Methods The use of optical imaging allowed us to visualize the spatiotemporal patterns of excitatory propagation in the CN and VN. Optical recordings can differentiate excitatory propagation in the ventral CN(VCN) from that in the dorsal CN(DCN). Furthermore, we assessed the relative distribution of NMDA and non-NMDA receptors in these regions using the glutamate antagonists APV (NMDA receptor antagonist) and CNQX (non-NMDA receptor antagonist) in mouse brainstem slices during postnatal days 1 to 3. Results The average sensitivity to APV was 99.1% in the VCN, 76.0% in the DCN and 64.9% in the VN. The average sensitivity to CNQX was 0.9% in the VCN, 24.0% in the DCN and 35.1% in the VN. These results indicate that the effect of APV dominated in the VCN, while both APV and CNQX were effective antagonists in the DCN and VN. In the VN, the distribution of APV-and CNQX-sensitive cells was almost completely uniform. However, in the DCN the distribution of APV-and CNQX-sensitive cells was highly complex. The area that was more sensitive to CNQX was located in the superficial layer of the DCN while the area with a higher sensitivity to APV was located progressively in the deep layer. Conclusion This optical recording data suggests that there is a differential distribution of NMDA and non-NMDA receptor mediated neurotransmission in the VCN, DCN and VN.

Development of Functional Interlaminar Pathways in the Mouse Superior Colliculus Revealed by Optical Imaging with Axonal Labeling

The superior colliculus (SC) is a laminated midbrain structure responsible for visual orientation behaviors. In the mature SC, neurons in the stratum griseum superficiale (SGS) receive visual inputs that contribute to exciting premotor neurons in the stratum griseum intermediale (SGI) through a dorsoventral pathway. SGI activation generates feedback signals to the SGS through a ventrodorsal pathway. However, the developmental changes in signal transmission within the SC around the time of eye opening are not yet well understood. We compared the functional connections between the SGS and SGI before and after eye opening by imaging the neuronal population responses using a voltage-sensitive absorption dye in mouse SC slices. Electrophoresis of a fluorescent dye from the stimulating electrodes was used to fill the cells in the stimulated site. We here show that the dorsoventral transmission is present both before and after eye opening. This is in contrast to our previous finding that the ventrodorsal transmission develops after eye opening. Functions of intrinsic inhibitory systems mediated by gamma-aminobutyric acid were also investigated with the antagonist. The processes stained by electrophoresis from stimulating electrodes before eye opening were confined within the respective stimulated layers. Whereas, after eye opening, the processes were widely extended especially dorsoventrally and ventrodorsally invading the SGI and SGS, respectively. These corresponded well to the early component of voltage responses that is known to reflect the activation of presynaptic elements, presumably the axonal arborizations and varicosities. Thus, the optically-revealed functional connections between the SGS and SGI were correlated to the morphology.