Sites of origin of corticotropin-releasing factor-like immunoreactive projection fibers to the paraventricular thalamic nucleus in the rat

Neurons containing the peptide corticotropin-releasing factor (CRF) are thought to play a pivotal role in orchestrating autonomic and behavioral responses to stress. CRF afferents to the thalamus are almost entirely concentrated in the midline nuclei, especially in the paraventricular thalamic nucleus. In chloral hydrate-anesthetized male Wistar rats, we sought to determine the sites of origin of the CRF projection fibers to the thalamus, employing a combination of retrograde neuronal tracing and immunocytochemistry for CRF. Prethalamic neurons showing CRF immunoreactivity were detected in the continuum formed by the central nucleus of amygdala and the bed nucleus of the stria terminalis. Additional sources of the CRF fibers to the thalamus were also detected in the parabrachial nuclei and ventrolateral medulla.