Manipulation of different cortical neuron subtypes with optogenetics

Abstract

Optogenetics is widely used to investigate the function of neural systems via manipulation of activities in specific neuronal subtypes. Our long-term goal is to manipulate the plasticity of excitatory-inhibitory balance in the neocortical circuitry responsible for spatial processing and relevant behaviors. To achieve this, we have to express functional channelrhodopsin- 2 (ChR-2) and halorhodopsin (NpHR) in excitatory and inhibitory neurons of the neural circuits. To target excitatory neurons, we took the advantage of calcuim kinase II (CamK II) protmoter that is known to drive gene product that is characteristic for these neurons. After the injection of viral-based vector for ChR-2 or NpHR in the neocortex of rats for 3 weeks, we showed that blue light triggered an inward current in ChR-2-positive neurons whereas green light induced an outward current in NpHR-positive neurons. On the other hand, inhibitory neurons, as visualized by YFP expression in vesicular GABA transporter (VGAT)-Venus transgenic mice, rarely expressed ChR-2 protein, indicating high selectivity of this optogenetic virus for excitatory neurons. Instead, we used parvalbumin (PV) promoter to drive specific expression of light-sensitive channels in PV neurons, a subtype of GABAergic neurons, of Cre-PV-transgenic mice. Blue light exerted an excitatory action on ChR-2-expressing neurons whereas green light triggered an inhibitory current in NpHR-positive neurons. That these light-gated channels were predominantly expressed in PV neurons suggests high selectivity of the virus for PV neurons. Overall, we have established a platform in expressing functional ChR-2 and NpHR in target neuron phenotypes, paving the way for future studies in animal behavior.