Channelrhodopsin | EPFL Graph Search

Channelrhodopsins are a subfamily of retinylidene proteins (rhodopsins) that function as light-gated ion channels. They serve as sensory photoreceptors in unicellular green algae, controlling phototaxis: movement in response to light. Expressed in cells of other organisms, they enable light to control electrical excitability, intracellular acidity, calcium influx, and other cellular processes (see optogenetics). Channelrhodopsin-1 (ChR1) and Channelrhodopsin-2 (ChR2) from the model organism Chlamydomonas reinhardtii are the first discovered channelrhodopsins. Variants that are sensitive to different colors of light or selective for specific ions (ACRs, KCRs) have been cloned from other species of algae and protists. History Phototaxis and photoorientation of microalgae have been studied over more than hundred years in many laboratories worldwide. In 1980, Ken Foster developed the first consistent theory about the functionality of algal eyes. He also analyzed published action

The role of medial amygdala inhibitory neurons in regulating social behavior

Aiste Baleisyte

Aggression is an evolutionary conserved social behavior that is necessary for an animalÂŽs survival. The neural substrates coordinating aggression are known to exist in the amygdala and the hypothalamus. While the medial amygdala (MeA) and the ventrolateral subdivision of the ventromedial hypothalamus (VMHvl) have been implicated in aggression control and are known to be anatomically inter-connected, it has not yet been described at the circuit-level whether an interaction between these nuclei plays a role in aggression control.Posteriodorsal MeA (MeApd) is a majorly GABAergic nucleus (~70%), however the role of heterogeneous sub-populations of the MeA-GABA neurons in aggression is poorly understood. Since we were interested to identify the inhibitory cell types in the MeApd that control aggression, we first attempted to stimulate all the GABA neurons in the MeApd. Using a fast variant of channelrhodopsin-2E123T,H134R (ChETA) in VGATCre mice, we found that optogenetic stimulation of MeA-GABA neurons in the resident males interrupted intruder-directed aggression, contrary to the previous findings by Hong et al., where stimulation of MeApd-GABA neurons using channelrhodopsin-2H134R (ChR2) evoked aggression. An in-depth investigation of this discrepancy, using two AAV serotypes, revealed that optogenetic stimulation with ChETA suppressed aggression, whereas optogenetic stimulation with ChR2 increased aggression, irrespective of the AAV serotype. Recordings of the membrane potential changes reported larger plateau depolarizations, smaller action potential amplitudes, and larger local inhibition when using ChR2 as compared to ChETA. Thus, in the first part I showed that optogenetic stimulation of the brain areas with heterogenous population of interconnected GABA neurons such as the MeApd, can strongly depend on the properties of optogenetic tools.In the second part, we further explored how the MeApd-GABA neurons control aggression via long-range projections to their target nuclei in hypothalamus. Anterograde tracing revealed synapses from the MeApd-GABA neurons in the ventral premammillary (PMv) and the lateral ventromedial hypothalamic nuclei (VMHvl); both nuclei were previously identified in positive control of aggression (Lin et al., 2011; Stagkourakis et al., 2018). Ex-vivo optogenetic mapping of synaptic outputs from the MeApd-GABA projecting axons revealed evoked IPSCs in glutamatergic neurons in the VMHvl and the PMv, suggesting likely mechanism for inhibiting aggression. In-vivo optogenetic activation of the MeApd-GABA axonal terminals above the VMHvl or the PMv had no effect on aggression and instead led to an increased mounting, likely caused by optic fiber implantation in the hypothalamus. To avoid this artifact, we have combined retrograde AAV with Cre ON/Flip ON approach and specifically stimulated the VMHvl projecting MeApd-GABA neurons. This approach revealed that in aggressive mice, stimulation of this pathway tends to reduce aggression. Finally, we performed in-vivo Ca2+ imaging of the VMHvl projecting MeApd-GABA neurons during the RI test, which showed that these neurons are largely multimodal and get activated during different sub-types of social behaviours including aggression.This study shows that direct inhibitory path from the MeApd-GABA neurons to the VMHvl might suppress aggressive behaviour. Altogether, this work provides a step forward in our understanding of the neural substrates underlying aggression.

EPFL2021

Stimulation of medial amygdala GABA neurons with kinetically different channelrhodopsins yields opposite behavioral outcomes

Aiste Baleisyte, Olexiy Kochubey, Ralf Schneggenburger

The medial amygdala (MeA) receives pheromone information about conspecifics and has crucial functions in social behaviors. A previous study showed that activation of GABA neurons in the postero-dorsal MeA (MeApd) with channelrhodopsin-2(H)(134R) (ChR2) stimulates inter-male aggression. When performing these experiments using the faster channelrhodopsin(H134R)(,)(E123T) (ChETA), we find the opposite behavioral outcome. A systematic comparison between the two channelrhodopsin variants reveals that optogenetic activation of MeApd GABA neurons with ChETA suppresses aggression, whereas activation under ChR2 increases aggression. Although the mechanism for this paradoxical difference is not understood, we observe that activation of MeApd GABA neurons with ChR2 causes larger plateau depolarizations, smaller action potentials, and larger local inhibition than with ChETA. Thus, the channelrhodopsin variant used for in vivo optogenetic experiments can radically influence the behavioral outcome. Future work should continue to study the role of specific sub-populations of MeApd GABA neurons in aggression control.

CELL PRESS2022

Cortical afferents onto the nucleus Reticularis thalami promote plasticity of low-threshold excitability through GluN2C-NMDARs

Simone Astori, Gil Vantomme

Thalamus and cortex represent a highly integrated processing unit that elaborates sensory representations. Interposed between cortex and thalamus, the nucleus Reticularis thalami (nRt) receives strong cortical glutamatergic input and mediates top-down inhibitory feedback to thalamus. Despite growing appreciation that the nRt is integral for thalamocortical functions from sleep to attentional wakefulness, we still face considerable gaps in the synaptic bases for cortico-nRt communication and plastic regulation. Here, we examined modulation of nRt excitability by cortical synaptic drive in Ntsr1-Cre x ChR2(tg/+) mice expressing Channelrhodopsin2 in layer 6 corticothalamic cells. We found that cortico-nRt synapses express a major portion of NMDA receptors containing the GluN2C subunit (GluN2C-NMDARs). Upon repetitive photoactivation (10 Hz trains), GluN2C-NMDARs induced a long-term increase in nRt excitability involving a potentiated recruitment of T-type Ca2+ channels. In anaesthetized mice, analogous stimulation of cortical afferents onto nRt produced long-lasting changes in cortical local field potentials (LFPs), with delta oscillations being augmented at the expense of slow oscillations. This shift in LFP spectral composition was sensitive to NMDAR blockade in the nRt. Our data reveal a novel mechanism involving plastic modification of synaptically recruited T-type Ca2+ channels and nRt bursting and indicate a critical role for GluN2C-NMDARs in thalamocortical rhythmogenesis.

Nature Publishing Group2017

The role of medial amygdala inhibitory neurons in regulating social behavior

Aiste Baleisyte

EPFL2021