Optogenetic strategies to investigate neural circuitry engaged by stress

Abstract

Optogenetic techniques have given researchers unprecedented access to the function of discrete neural circuit elements and have been instrumental in the identification of novel brain pathways that become dysregulated in neuropsychiatric diseases. For example, stress is integrally linked to the manifestation and pathophysiology of neuropsychiatric illness, including anxiety, addiction and depression. Due to the heterogeneous populations of genetically and neurochemically distinct neurons in areas such as the bed nucleus of the stria terminalis (BNST), as well as their substantial number of projections, our understanding of how neural circuits become disturbed after stress has been limited. Using optogenetic tools, we are now able to selectively isolate distinct neural circuits that contribute to these disorders and perturb these circuits in vivo, which in turn may lead to the normalization of maladaptive behavior. This review will focus on current optogenetic strategies to identify, manipulate, and record from discrete neural circuit elements in vivo as well as highlight recent optogenetic studies that have been utilized to parcel out BNST function.

Keywords: AAV; AGRP; ARC; Arch; BLA; BNST; CRF; CaMKIIα; CeA; ChR2; Circuit mapping; DAT; GABA; HSV; LDT; LED; LH; LHb; MeA; NAc; NPY; NpHR; Optogenetics; PAG; PBN; POMC; PRV; PTSD; PVH; RG; RMTg; SNr; Stress; TH; TTX; TVA; Vgat; Vglut; W; adeno-associated virus; agouti-related peptide; archaerhodopsin; arcuate nucleus of the hypothalamus; avian retroviral receptor; basolateral amygdala; bed nucleus of the stria terminalis; calcium–calmodulin dependent protein kinase IIα; central nucleus of the amygdala; channelrhodopsin-2; corticotropin releasing factor; dopamine transporter; halorhodopsin; herpes simplex virus; lateral habenula; lateral hypothalamus; laterodorsal tegmentum; light emitting diode; medial nucleus of the amygdala; neuropeptide Y; nucleus accumbens; parabrachial nucleus; paraventricular nucleus of the hypothalamus; periaqueductal gray; post traumatic stress disorder; pro-opiomelanocortin; pseudorabies virus; rabies virus envelop glycoprotein; rostromedial tegmental nucleus; substantia nigra reticulata; tetrodotoxin; tyrosine hydroxylase; vesicular GABA transporter; vesicular glutamate transporters; watts; γ-Aminobutyric acid.

Figure 1. Optogenetic strategies for circuit mapping

a. Schematic detailing how to employ ChR2 assisted circuit mapping in slice electrophysiology. Presynaptic neurons are transduced with ChR2-eYFP. Optical stimulation (473 nm light to optimally activate ChR2) of transduced presynaptic terminals results in the detection of ChR2 mediated currents in the patch clamped postsynaptic neuron. Additionally, the recording pipette can be filled with dye to identify its neurochemical makeup. b. Schematic detailing how to employ a rabies viral delivery strategy in order to manipulate VTA neurons terminating in the NAc. Pseudorabies (PRV) that express a functional cre protein is injected into the NAc. PRV-cre is taken up by presynaptic terminals in the NAc. Infusion of a cre-inducible ChR2 into the VTA. Only neurons that express cre will express ChR2. An optical fiber is implanted above the VTA in order to manipulate VTA neurons that project to the NAc.

Figure 2. Potential BNST stress neural circuits

The BNST sends projections to the VTA, PAG, CeA, PBN, and LH. These potential stress neural circuits can be analyzed using optogenetic strategies detailed above.