Cellular, physiological, and behavioral validation of a CRFR1:Cre -tdTomato transgenic rat for use in basic neuroscience research

Corticotropin-releasing factor type-1 receptors (CRFR1) are important for mediating the endocrine stress response, modulating synaptic transmission in the central nervous system, and are involved in mediating behaviors that include stress reactivity, anxiety, fear, pain, motivation, and addiction. Understanding the precise role of specific CRFR1 neuronal populations and circuits/networks in CRFR1-relevant behavior is limited by a lack of genetic access to CRFR1-expressing cells in rats. Here, we describe the generation and validation of a transgenic CRFR1:Cre-tdTomato rat line on a Wistar background. Within the central amygdala (CeA) of male and female CRFR1:Cre-tdTomato rats, we show that Crfr1 and Cre mRNA expression are highly colocalized and that CRFR1:Cre-tdTomato cells are largely confined to the medial subdivision of the CeA, consistent with CRF expression patterns in outbred animals. Using tdTomato fluorescent protein as a reporter, we measured membrane properties, inhibitory synaptic transmission, and CRF sensitivity in CeA CRFR1-expressing cells and found that these properties were similar to those previously reported in CRFR1:Cre mice, and that CeA CRFR1 neurons were excited by exogenous CRF application. We also show that stimulatory Gq-coupled DREADD receptors can be targeted to CeA CRFR1 cells via Cre-dependent expression and that these cells can be activated by clozapine-n-oxide (CNO) in vitro and in vivo. Finally, we report that DREADD-mediated activation of CeA CRFR1 cells increases anxiety-like behavior and increases nocifensive responses. Our results demonstrate the utility of this novel CRFR1:Cre-tdTomato transgenic rat line for studying the anatomy, physiology, and behavioral function of select CRFR1-expressing cell populations and circuits under normal conditions and in rat models of human disease.