Immunocytochemical localization of corticotropin releasing factor (CRF)-like immunoreactivity in the thalamus of the rat

The distribution of corticotropin releasing factor (CRF)-immunoreactive structures in the rat thalamus was studied after treatment with high doses of colchicine (100 μg/100 g b.wt.) with peroxidase-antiperoxidase (PAP) immunocytochemistry in vibratome sections. CRF-immunopositive perikarya were found in the 'posteromedial complex' of the thalamus, including the ventromedial, paracentral, mediodorsal, rhomboid, parafascicular nuclei, centrum medianum and ventromedial portion of the posterolateral nucleus. In addition, CRF-containing perikarya were observed in the pretectal and subthalamic nuclei. CRF-immunoreactive processes were seen in most of the medial nuclei of the thalamus. The presence of CRF-immunopositive structures in the thalamus suggests that CRF not only functions as a hypophysiotropic hormone regulating the release of ACTH and β-endorphin from the pituitary, but also as a neurotransmitter or neuromodulator, playing an important role in nociception and analgesia.