Abstract
.Near-infrared radiation (NIR) has been described as one of the highest-resolution tools for neuromodulation. However, the poor tissue penetration depth of NIR has limited its further application on some of the deeper layer neurons in vivo. A 980-nm short-wavelength NIR (SW-NIR) with high penetration depth was employed, and its inhibitory effect on neurons was investigated in vivo. In experiments, SW-NIR was implemented on the rat’s cochlear nucleus (CN), the auditory pathway was activated by pure-tones through the rat’s external auditory canal, and the neural responses were recorded in the inferior colliculus by a multichannel electrode array. Neural firing rate (FR) and the first spike latency (FSL) were analyzed to evaluate the optically induced neural inhibition. Meanwhile, a two-layered finite element, consisting of a fluid layer and a gray matter layer, was established to model the optically induced temperature changes in CN; different stimulation paradigms were used to compare the inhibitory efficiency of SW-NIR. Results showed that SW-NIR could reversibly inhibit acoustically induced CN neural activities: with the increase of laser radiant exposures energy, neural FR decreased significantly and FSL lengthened steadily. Significant inhibition occurred when the optical pulse stimulated prior to the acoustic stimulus. Results indicated that the inhibition relies on the establishment time of the temperature field. Moreover, our preliminary results suggest that short-wavelength infrared could regulate the activities of neurons beyond the neural tissues laser irradiated through neural networks and conduction in vivo. These findings may provide a method for accurate neuromodulation in vivo.
Highlights
IntroductionNeuromodulation is an efficient technique to study how neural activities operate brain functions, and it requires effective neural stimulation and high precision.[1,2,3,4] Among all neuromodulation techniques, pulsed near-infrared (NIR) radiation (wavelength between 1850 and 2120 nm) is considered a strong candidate for precise control of neural activity, due to its high stimulating spatial resolution and contact-free advantages.[5,6,7,8,9,10] NIR has been widely used to modulate the functionality of the peripheral[5,6,7,11,12] and the central nervous system.[8,9,10,13,14] Most previous studies have focused on NIR-induced neural activation;[6,7,8,9,15] neural suppression is indispensable in neuroscience, especially for brain disorder treatment.[16,17,18]Recently, evidence has gradually appeared showing that NIR could reversibly inhibit unwanted neural activity[16,19,20] or block neural signal propagation with high precision.[21,22] current NIR-based neural inhibition experiments have mostly been carried out on peripheral nerves,[21,23] neurons cultured in vitro,[19,20,24] and superficial cortex;[10] research investigating the inhibitory effect of NIR on neurons in deeper layers in vivo has been limited
We mainly focused on high-frequency neurons in inferior colliculus (IC) (CF more than 16 kHz) since the neurons with high characteristic frequency (CF) were mostly located in dorsal cochlear nucleus (DCN), which corresponded to the site of laser irradiation
The present study demonstrated that short-wavelength NIR (SW-NIR) with a wavelength of 980 nm could reversibly inhibit the CN neural activities induced by acoustical stimuli, and block the transmission of neural signals to the higher level of the central nervous system
Summary
Neuromodulation is an efficient technique to study how neural activities operate brain functions, and it requires effective neural stimulation and high precision.[1,2,3,4] Among all neuromodulation techniques, pulsed near-infrared (NIR) radiation (wavelength between 1850 and 2120 nm) is considered a strong candidate for precise control of neural activity, due to its high stimulating spatial resolution and contact-free advantages.[5,6,7,8,9,10] NIR has been widely used to modulate the functionality of the peripheral[5,6,7,11,12] and the central nervous system.[8,9,10,13,14] Most previous studies have focused on NIR-induced neural activation;[6,7,8,9,15] neural suppression is indispensable in neuroscience, especially for brain disorder treatment.[16,17,18]Recently, evidence has gradually appeared showing that NIR could reversibly inhibit unwanted neural activity[16,19,20] or block neural signal propagation with high precision.[21,22] current NIR-based neural inhibition experiments have mostly been carried out on peripheral nerves,[21,23] neurons cultured in vitro,[19,20,24] and superficial cortex;[10] research investigating the inhibitory effect of NIR on neurons in deeper layers in vivo has been limited. Neuromodulation is an efficient technique to study how neural activities operate brain functions, and it requires effective neural stimulation and high precision.[1,2,3,4] Among all neuromodulation techniques, pulsed near-infrared (NIR) radiation (wavelength between 1850 and 2120 nm) is considered a strong candidate for precise control of neural activity, due to its high stimulating spatial resolution and contact-free advantages.[5,6,7,8,9,10] NIR has been widely used to modulate the functionality of the peripheral[5,6,7,11,12] and the central nervous system.[8,9,10,13,14] Most previous studies have focused on NIR-induced neural activation;[6,7,8,9,15] neural suppression is indispensable in neuroscience, especially for brain disorder treatment.[16,17,18]. The main reason for this, in addition to the complexity of the central nervous system and complex neural
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