Generation of a CRF₁-Cre transgenic rat and the role of central amygdala CRF₁ cells in nociception and anxiety-like behavior

Corticotropin-releasing factor type-1 (CRF₁) receptors are critical to stress responses because they allow neurons to respond to CRF released in response to stress. Our understanding of the role of CRF₁-expressing neurons in CRF-mediated behaviors has been largely limited to mouse experiments due to the lack of genetic tools available to selectively visualize and manipulate CRF₁⁺ cells in rats. Here, we describe the generation and validation of a transgenic CRF₁-Cre-^tdTomato rat. We report that Crhr1 and Cre mRNA expression are highly colocalized in 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 ^tdTomato⁺ neurons are similar to those previously reported in GFP⁺ cells in CRFR1-GFP mice. We show that stimulatory DREADD receptors can be targeted to CeA CRF₁⁺ cells via virally delivered Cre-dependent transgenes, that transfected Cre/^tdTomato⁺ cells are activated by clozapine-n-oxide in vitro and in vivo, and that activation of these cells in vivo increases anxiety-like and nocifensive behaviors. Outside the amygdala, we show that Cre-^tdTomato is expressed in several brain areas across the brain, and that the expression pattern of Cre-^tdTomato cells is similar to the known expression pattern of CRF₁ cells. Given the accuracy of expression in the CRF₁-Cre rat, modern genetic techniques used to investigate the anatomy, physiology, and behavioral function of CRF₁⁺ neurons can now be performed in assays that require the use of rats as the model organism.