Corticotropin-releasing factor-containing afferents to the inferior colliculus of the rat brain

Using a modified cobalt-glucose oxidase-diaminobenzidine (Co-GOD) method in a combination of horseradish peroxidase (HRP) retrograde tracing and immunohistochemistry, a widespread localization of corticotropin releasing factor-like immunoreactive (CRFI) structures in the rat inferior colliculus (IC), and a CRFI-containing pathway from the subthalamus and the hypothalamus to the IC have been observed. By means of the modified Co-GOD method, CRFI cells were detected in almost all the subdivisions of the IC, including the dorsomedial part of the central nucleus, the ventrolateral part of the central nucleus, the pericentral nucleus and the external nucleus. Neural processes with CRFI were observed in all of the above areas. Following HRP injection into the IC, double-labeled cells which contained a homogeneous brown immunoreaction product of CRF and a granular black reaction product of retrogradely transported HRP were identified in the lateral hypothalamic area (LH), zona incerta (ZI) and perifornical hypothalamic area (PeF). These double-labeled cells provide direct evidence for CRFI projections from the LH, ZI and PeF to the IC. Thus, the present study supports the view that CRF may act as a neurotransmitter or neuromodulator in the brain.