Optogenetic analysis of synaptic function

Abstract

We introduce optogenetic investigation of neurotransmission (OptIoN) for time-resolved and quantitative assessment of synaptic function via behavioral and electrophysiological analyses. We photo-triggered release of acetylcholine or gamma-aminobutyric acid at Caenorhabditis elegans neuromuscular junctions using targeted expression of Chlamydomonas reinhardtii Channelrhodopsin-2. In intact Channelrhodopsin-2 transgenic worms, photostimulation instantly induced body elongation (for gamma-aminobutyric acid) or contraction (for acetylcholine), which we analyzed acutely, or during sustained activation with automated image analysis, to assess synaptic efficacy. In dissected worms, photostimulation evoked neurotransmitter-specific postsynaptic currents that could be triggered repeatedly and at various frequencies. Light-evoked behaviors and postsynaptic currents were significantly (P <or= 0.05) altered in mutants with pre- or postsynaptic defects, although the behavioral phenotypes did not unambiguously report on synaptic function in all cases tested. OptIoN facilitates the analysis of neurotransmission with high temporal precision, in a neurotransmitter-selective manner, possibly allowing future investigation of synaptic plasticity in C. elegans.

Graded synaptic transmission at the Caenorhabditis elegans neuromuscular junction

“…As an alternative to field stimulation, motor neurons can be selectively activated using the light-activated ion channel channelrhodopsin-2 (hereafter referred to as channelrhodopsin) (14). Channelrhodopsin is a 7-pass trans-membrane protein from the green algae Chlamydomonas reinhardtii (15), and forms a cation channel activated by blue light.…”

Optogenetic analyses of neuronal network function and synaptic transmission in Caenorhabditis elegans

“…Mechanisms of synaptic transmission can also be analyzed in C. elegans using optogenetic methods (optogenetic investigation of neurotransmission, OptIoN; Liewald et al [25]). Since C. elegans neurons usually generate graded potentials and no action potentials, the strength of the light-induced depolarization largely correlates in a linear manner with the amount of neurotransmitter released [26,37,38].…”

“…Since C. elegans neurons usually generate graded potentials and no action potentials, the strength of the light-induced depolarization largely correlates in a linear manner with the amount of neurotransmitter released [26,37,38]. Postsynaptic effects can be quantified on the basis of the triggered behavior (e.g., depolarization of cholinergic neurons leads to a strong contraction of the entire animal), or on the basis of electrophysiological recordings of the induced postsynaptic currents [25]. Thus, the effects of mutations in the synaptic machinery can be quantified via their effects on the release or the recycling of neurotransmitter (vesicles).…”

Laser-evoked synaptic transmission in cultured hippocampal neurons expressing channelrhodopsin-2 delivered by adeno-associated virus

“…ChR2 has been used to identify presynaptic partners of an electrophysiologically recorded postsynaptic neuron (Arenkiel et al, 2007;Petreanu et al, 2007;Wang et al, 2007). Other applications include mapping neuronal circuits, probing synaptic function in genetically defined populations of neurons, and inducing plasticity at single synapses (Atasoy et al, 2008;Liewald et al, 2008;Wang et al, 2007;Zhang et al, 2008;Zhang and Oertner, 2007). In principle, ChR2 could also be used to study the responses of networks to complex spatiotemporal patterns of stimulation.…”

“…ChR2 has also been targeted to genetically defined populations of neurons through cell-type specific promoters and Cre-dependent constructs to examine neural circuits based on cell types (Atasoy et al, 2008;Liewald et al, 2008). Availability of different AAV serotypes provides additional means to selectively target different neuron types (Burger et al, 2004;Shevtsova et al, 2005;Tenenbaum et al, 2004).…”