Abstract
Light-gated chloride channels are emerging as promising optogenetic tools for inhibition of neural activity. However, their effects depend on the transmembrane chloride electrochemical gradient and may be complex due to the heterogeneity of this gradient in different developmental stages, neuronal types, and subcellular compartments. Here we characterized a light-gated chloride channel, GtACR2, in mouse cortical neurons. We found that GtACR2 activation inhibited the soma, but unexpectedly depolarized the presynaptic terminals resulting in neurotransmitter release. Other light-gated chloride channels had similar effects. Reducing the chloride concentrations in the axon and presynaptic terminals diminished the GtACR2-induced neurotransmitter release, indicating an excitatory effect of chloride channels in these compartments. A novel hybrid somatodendritic targeting motif reduced the GtACR2-induced neurotransmitter release while enhancing the somatic photocurrents. Our results highlight the necessity of precisely determining the effects of light-gated chloride channels under specific experimental conditions and provide a much-improved light-gated chloride channel for optogenetic inhibition.
Highlights
Targeted manipulation of neural activity is a powerful approach in neuroscience that has provided fundamental insights into the roles of specific neurons in nervous system functions
The onsets of these inward currents followed the onset of the blue light by 3.19 ± 0.26 ms. These currents were abolished by the glutamatergic receptor antagonists, NBQX and CPP (Figure 1F), or the voltage-gated sodium channel blocker, tetrodotoxin (TTX; Figure 1G), indicating that they were monosynaptic excitatory postsynaptic current (EPSC) caused by the glutamate transmitter released from GtACR2+ neurons
Using acute brain slices from 3 to 6 week-old mice, we found that activation of GtACR2 in Pv neurons generated inhibitory postsynaptic currents (IPSCs) in all recorded GtACR2– layer 2/3 pyramidal neurons, and the IPSCs were abolished by Gabazine, a GABAA receptor antagonist, or TTX (Figure 1I–K)
Summary
Targeted manipulation of neural activity is a powerful approach in neuroscience that has provided fundamental insights into the roles of specific neurons in nervous system functions. The widely used light-driven inward chloride pumps and outward proton pumps, such as Natronomonas pharaonis halorhodopsin (NpHR) and Halorubrum sodomense archaerhodopsin (Arch), can hyperpolarize membrane potentials, independent of the electrochemical gradients, to inhibit action potentials with millisecond precision (Chow et al, 2010; Chuong et al, 2014; Han and Boyden, 2007; Han et al, 2011; Zhang et al, 2007) Their efficacies are limited because only one ion is transported per absorbed photon, and their activation does not decrease membrane resistance.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
