We found that a single and brief IR light pulse induced a TTX-independent membrane depolarization, whose amplitude depends on the pulse duration and total energy deposition. The depolarization facilitated action potential (AP) generation when the axon was near firing threshold. This depolarization was followed by a membrane hyperpolarization at higher energy levels, which reversed near potassium equilibrium potential and could inhibit AP firing. Pharmacological results indicated that barium-sensitive potassium channels contributed to the hyperpolarization, while further administration of TEA did not change the hyperpolarization. We show that individual and brief IR light pulses can evoke both excitatory and inhibitory effects.
Significance: Systematic studies of the physiological outputs induced by infrared (IR)-mediated inhibition of motor nerves can provide guidance for therapeutic applications and offer critical insights into IR light modulation of complex neural networks.
Aim: We explore the IR-mediated inhibition of action potentials (APs) that either propagate along single axons or are initiated locally and their downstream synaptic transmission responses.
Approach: APs were evoked locally by two-electrode current clamp or at a distance for propagating APs. The neuromuscular transmission was recorded with intracellular electrodes in muscle cells or macro-patch pipettes on terminal bouton clusters.
Results: IR light pulses completely and reversibly terminate the locally initiated APs firing at low frequencies, which leads to blocking of the synaptic transmission. However, IR light pulses only suppress but do not block the amplitude and duration of propagating APs nor locally initiated APs firing at high frequencies. Such suppressed APs do not influence the postsynaptic responses at a distance. While the suppression of AP amplitude and duration is similar for propagating and locally evoked APs, only the former exhibits a 7% to 21% increase in the maximum time derivative of the AP rising phase.
Conclusions: The suppressed APs of motor axons can resume their waveforms after passing the localized IR light illumination site, leaving the muscular and synaptic responses unchanged. IR-mediated modulation on propagating and locally evoked APs should be considered as two separate models for axonal and somatic modulations.
Pulsed infrared (IR) light in the 1.8 - 2 μm region can modulate neural activities with high spatial and temporal precision. However, the mechanisms underlying these photothermal interactions are not fully understood. Here we investigate the IR modulation of axon and muscle activities using the crayfish (Procambarus clarkii) opener neuromuscular preparation. A modulated fiber coupled laser diode (λ = 2 μm) is used to deliver pulsed light with durations between 10 – 500 ms. Twoelectrode current clamp (TECC) is performed to stimulate and monitor the neural activities. Laser-induced temperature changes are measured by an open patch pipette simultaneously with TECC. We find that IR pulses can reversibly inhibit or block axon (Na+ ) and muscle (Ca2+) spikes. In axons, single IR pulses can suppress the action potential (AP) amplitude and duration and increase the interspike interval. In addition, the rates of AP depolarization and repolarization are also modulated by IR pulses. Individual IR pulses can also block muscle fiber Ca2+ spikes. The IR-induced decrease in the input resistance (8.4%) can be a contributing factor for the inhibition phenomena reported here.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.