Generation and validation of a CRF ₁ :Cre transgenic rat: The role of central amygdala CRF ₁ in nociception and anxiety-like behavior

Corticotropin-releasing factor type-1 (CRF ₁ ) receptors are critical to stress responses because they allow neurons to respond to CRF released in response to stress. Our understanding of the precise role of CRF ₁ -expressing neuronal populations in CRF-mediated behaviors has been largely limited to mouse experiments due to the lack of genetic tools available to selectively visualize and manipulate CRF ₁ ⁺ cells in rats. Here, we describe the generation and validation of a transgenic CRF ₁ :Cre- ^td Tomato rat, which expresses a bicistronic iCre-2A- ^td Tomato transgene directed by 200kb of promoter and enhacer sequence surrounding the Crhr1 cDNA present within a BAC clone, that has been transgenically inserted into the rat genome. We report that Crhr1 and Cre mRNA expression are highly colocalized in CRF ₁ :Cre- ^td Tomato rats within both the central amygdala (CeA), composed of mostly GABAergic neurons, and in the basolateral amygdala (BLA), composed of mostly glutamatergic neurons. In the CeA, membrane properties, inhibitory synaptic transmission, and responses to CRF bath application in ^td Tomato ⁺ neurons are similar to those previously reported in GFP ⁺ cells in CRFR1-GFP mice. We show that stimulatory DREADD receptors can be selectively targeted to CeA CRF ₁ ⁺ cells via virally delivered Cre-dependent transgenes, that transfected Cre/ ^td Tomato ⁺ cells are activated by clozapine-n-oxide in vitro and in vivo , and that activation of these cells in vivo increases anxiety-like behavior and nocifensive responses. Given the accuracy of expression in the CRF ₁ :Cre rat, modern genetic techniques used to investigate the anatomy, physiology, and behavioral function of CRF ₁ ⁺ neurons and circuits can now be performed in assays that require the use of rats as the model organism.