Optogenetic tools enable examination of how specific cell types contribute to brain circuit functions. A long-standing question is whether it is possible to independently activate two distinct neural populations in mammalian brain tissue. Such a capability would enable the study of how different synapses or pathways interact to encode information in the brain. Here we describe two channelrhodopsins, Chronos and Chrimson, discovered through sequencing and physiological characterization of opsins from over 100 species of alga. Chrimson's excitation spectrum is red shifted by 45 nm relative to previous channelrhodopsins and can enable experiments in which red light is preferred. We show minimal visual system-mediated behavioral interference when using Chrimson in neurobehavioral studies in Drosophila melanogaster. Chronos has faster kinetics than previous channelrhodopsins yet is effectively more light sensitive. Together these two reagents enable two-color activation of neural spiking and downstream synaptic transmission in independent neural populations without detectable cross-talk in mouse brain slice.

/pdf/independent-optical-excitation-of-distinct-neural-1xsoogmey8.pdf

Independent optical excitation of distinct neural populations

Inwardly rectifying K+ (Kir) channels allow K+ to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are ...

Inwardly Rectifying Potassium Channels: Their Structure, Function, and Physiological Roles

▪ Abstract GTPase-activating proteins (GAPs) regulate heterotrimeric G proteins by increasing the rates at which their α subunits hydrolyze bound GTP and thus return to the inactive state. G protein GAPs act allosterically on Gα subunits, in contrast to GAPs for the Ras-like monomeric GTP-binding proteins. Although they do not contribute directly to the chemistry of GTP hydrolysis, G protein GAPs can accelerate hydrolysis >2000-fold. G protein GAPs include both effector proteins (phospholipase C-β, p115RhoGEF) and a growing family of regulators of G protein signaling (RGS proteins) that are found throughout the animal and fungal kingdoms. GAP activity can sharpen the termination of a signal upon removal of stimulus, attenuate a signal either as a feedback inhibitor or in response to a second input, promote regulatory association of other proteins, or redirect signaling within a G protein signaling network. GAPs are regulated by various controls of their cellular concentrations, by complex interactions wit...

GTPase-Activating Proteins for Heterotrimeric G Proteins: Regulators of G Protein Signaling (RGS) and RGS-Like Proteins

The ability to group stimuli into meaningful categories is a fundamental cognitive process. To explore its neural basis, we trained monkeys to categorize computer-generated stimuli as "cats" and "dogs." A morphing system was used to systematically vary stimulus shape and precisely define the category boundary. Neural activity in the lateral prefrontal cortex reflected the category of visual stimuli, even when a monkey was retrained with the stimuli assigned to new categories.

/pdf/categorical-representation-of-visual-stimuli-in-the-primate-47gjsj71i7.pdf

Categorical Representation of Visual Stimuli in the Primate Prefrontal Cortex

Little is known about the identity of endoplasmic reticulum (ER) export signals and how they are used to regulate the number of proteins on the cell surface. Here, we describe two ER export signals that profoundly altered the steady-state distribution of potassium channels and were required for channel localization to the plasma membrane. When transferred to other potassium channels or a G protein-coupled receptor, these ER export signals increased the number of functional proteins on the cell surface. Thus, ER export of membrane proteins is not necessarily limited by folding or assembly, but may be under the control of specific export signals.

https://science.sciencemag.org/content/sci/291/5502/316.full.pdf

Role of ER export signals in controlling surface potassium channel numbers.

Ion selectivity is critical for the biological functions of voltage-dependent cation channels and is achieved by specific ion binding to a pore region called the selectivity filter. In voltage-gated K+, Na+ and Ca2+ channels, the selectivity filter is formed by a short polypeptide loop (called the H5 or P region) between the fifth and sixth transmembrane segments, donated by each of the four subunits or internal homologous domains forming the channel. While mutagenesis studies on voltage-gated K+ channels have begun to shed light on the structural organization of this pore region, little is known about the physical and chemical interactions that maintain the structural stability of the selectivity filter. Here we show that in an inwardly rectifying K+ (IRK) channel, IRK1, short range interactions of an ion pair in the H5 pore loop are crucial for pore structure and ion permeation. The two residues, a glutamate and an arginine, appear to form exposed salt bridges in the tetrameric channel. Alteration or disruption of such ion pair interactions dramatically alters ion selectivity and permeation. Since this ion pair is conserved in all IRK channels, it may constitute a general mechanism for maintaining the stability of the pore structure in this channel superfamily.

https://www.jstor.org/stable/pdfplus/41372.pdf

Stabilization of ion selectivity filter by pore loop ion pairs in an inwardly rectifying potassium channel

The G-protein gated inward rectifier K+ channel (GIRK) is activated in vivo by the Gβγ subunits liberated upon Gi-coupled receptor activation. We have recapitulated the acute desensitization of receptor-activated GIRK currents in heterologous systems and shown that it is a membrane-delimited process. Its kinetics depends on the guanine nucleotide species available and could be accounted for by the nucleotide exchange and hydrolysis cycle of G proteins. Indeed, acute desensitization is abolished by nonhydrolyzable GTP analogues. Whereas regulators of G-protein signaling (RGS) proteins by their GTPase-activating protein activities are regarded as negative regulators, a positive regulatory function of RGS4 is uncovered in our study; the opposing effects allow RGS4 to potentiate acute desensitization without compromising GIRK activation.

https://www.pnas.org/content/pnas/95/20/11727.full.pdf

Evidence that the nucleotide exchange and hydrolysis cycle of G proteins causes acute desensitization of G-protein gated inward rectifier K+ channels

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Papers

Role of ER export signals in controlling surface potassium channel numbers.

Stabilization of ion selectivity filter by pore loop ion pairs in an inwardly rectifying potassium channel

Evidence that the nucleotide exchange and hydrolysis cycle of G proteins causes acute desensitization of G-protein gated inward rectifier K+ channels