DISTRIBUTION OF CORTICOTROPIN-RELEASING FACTOR-RECEPTOR MESSENGER-RNAEXPRESSION IN THE RAT-BRAIN AND PITUITARY

Corticotropin-releasing factor (CRF) is a major hypophysiotropic pepti de regulating pituitary-adrenal response to stress, and it is also wid ely expressed in the central nervous system. The recent cloning of cDN As encoding the human ind rat CRF receptors has enabled us to map the distribution of cells expressing CRF receptor mRNA in rat brain and pi tuitary by in situ hybridization. Receptor expression in the forebrain is dominated by widespread signal throughout all areas of the neo-, o lfactory, and hippocampal cortices. Other prominent sites of CRF recep tor mRNA expression include subcortical limbic structures in the septa l region and amygdala. In the diencephalon, low levels of expression a re seen in a few discrete ventral thalamic and medial hypothalamic nuc lei. CRF receptor expression in hypothalamic neurosecretory structures , including the paraventricular nucleus and median eminence, is genera lly low. In the brainstem, certain relay nuclei associated with the so matic (including trigeminal), auditory, vestibular, and visceral senso ry systems, constituted prominent sites of CRF receptor mRNA expressio n. In addition, high levels of this transcript are present in the cere bellar cortex and deep nuclei, along with many precerebellar nuclei. I n the pituitary, moderate levels of CRF receptor mRNA expression were detected throughout the intermediate lobe and in a subset of cells in the anterior lobe identified as corticotropes by concurrent immunolabe ling. Overall, the central distribution of CRF receptor mRNA expressio n is similar to, though more expansive than, that of regions reported to bind CRF, and it shows limited overlap with loci expressing CRF-bin ding protein. Interestingly, CRF receptor mRNA is low or undetectable in several cell groups implicated as central sites of CRF action.