Targeting corticotropin-releasing factor (CRF) projections from the oval nucleus of the BNST using cell-type specific neuronal tracing studies in mouse and rat brain

Abstract

The bed nucleus of the stria terminalis (BNST) is known to play a critical role in mediating the behavioral and autonomic responses to stressors. The oval nucleus of the BNST (BNSTov) contains cell bodies that synthesize the stress hormone, corticotropin releasing factor (CRF). Although afferent fibers originating from the BNSTov have been shown to innervate several key structures of the neuroendocrine and central autonomic system, the question remains as to whether, some of these fibers are CRF-positive. To directly address this question, we injected a "floxed" anterograde tracer (rAAV5/EF1a-DIO-mCherry) into the BNSTov of CRFp3.0Cre^GFP transgenic mice, which express a green fluorescent protein (GFP) under the control of the CRF promoter. Serial sections were then analyzed for the presence of double-labeled fibers in potential projection sites. To determine whether CRF neurons in the rat BNSTov send comparable projections, we infused rat BNSTov with an AAV in which the human synapsin promoter drives enhanced GFP expression. We then used CRF immunoreactivity to examine double-labeled fluorescent fibers and axon terminals in projection sites from brain sections of the AAV-infused rats. We have observed several terminal fields in the mouse and rat brain with double-labeled fibers in the Dorsal raphe nucleus (DRD), the Paraventricular nucleus of the hypothalamus, and to a lesser extent in the Ventral tegmental area. We found double-labeled terminal boutons in the nucleus accumbens shell, prelimbic cortex, and posterior basolateral nucleus of the amygdala. The most intense double-labeling was found in midbrain, including substantia nigra pars compacta, red nucleus, periaqueductal gray, pontine nuclei, as well as DRD. The results of our study indicate that CRF neurons are the output neurons of the BNSTov and they send projections to the centers of neuroendocrine and autonomic regulation, but also regions modulating reward and motivation, vigilance, motor function, as well as affective behavior.

This article is protected by copyright. All rights reserved.

http://ift.tt/2fbeQmU