Intrahypothalamic neuroendocrine actions of corticotropin-releasing factor

The corticotropin-releasing factor receptor-1 pathway mediates the negative affective states of opiate withdrawal

The negative affective symptoms of opiate withdrawal powerfully motivate drug-seeking behavior and may trigger relapse to heroin abuse. To date, no medications exist that effectively relieve the negative affective symptoms of opiate withdrawal. The corticotropin-releasing factor (CRF) system has been hypothesized to mediate the motivational effects of drug dependence. The CRF signal is transmitted by two distinct receptors named CRF receptor-1 (CRF1) and CRF2. Here we report that genetic disruption of CRF1 receptor pathways in mice eliminates the negative affective states of opiate withdrawal. In particular, neither CRF1 receptor heterozygous (CRF1+/-) nor homozygous (CRF1-/-) null mutant mice avoided environmental cues repeatedly paired with the early phase of opiate withdrawal. These results were not due to altered associative learning processes because CRF1+/- and CRF1-/- mice displayed reliable, conditioned place aversions to environmental cues paired with the kappa-opioid receptor agonist U-50,488H. We also examined the impact of CRF1 receptor-deficiency upon opiate withdrawal-induced dynorphin activity in the nucleus accumbens, a brain molecular mechanism thought to underlie the negative affective states of drug withdrawal. Consistent with the behavioral indices, we found that, during the early phase of opiate withdrawal, neither CRF1+/- nor CRF1-/- showed increased dynorphin mRNA levels in the nucleus accumbens. This study reveals a cardinal role for CRF/CRF1 receptor pathways in the negative affective states of opiate withdrawal and suggests therapeutic strategies for the treatment of opiate addiction.

Lactation as a model for naturally reversible hypercorticalism plasticity in the mechanisms governing hypothalamo-pituitary- adrenocortical activity in rats

Steady state levels of hypothalamic expression of the genes encoding corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), arginine vasopressin (AVP), and oxytocin (OT) were studied in rats to investigate the mechanisms underlying the transitions between hypercorticalism during lactation and normocorticalism upon weaning. During lactation, CRH mRNA levels and blood titers of adrenocorticotropin (ACTH) were found to be significantly reduced, although POMC mRNA levels in the anterior pituitary were not significantly different from those found in cycling virgin (control) rats; during all phases of lactation, an inverse relationship was observed between the blood levels of ACTH and corticosterone (CORT). Plasma prolactin (PRL) concentrations were elevated approximately 30-fold during lactation. Whereas steady state levels of OT mRNA were markedly increased throughout lactation, those of AVP mRNA were only transiently (initially) elevated, and the blood levels of these hormones were not significantly altered in lactating as compared with cycling virgin and postlactating rats. CRH and POMC gene expression and blood levels of ACTH, CORT, and PRL were normalized within 1-3 d of removal of suckling pups. The temporal relationships between the biosynthetic profiles of the various peptide hormones and the patterns of ACTH and CORT secretion during the two physiological states suggest that lactation-associated hypercorticalism does not merely result from increased ACTH secretion; although still not well substantiated at this time, the evidence points to contributory roles of PRL, OT, and AVP in the hypercorticalismic state found during lactation.

Cloning and characterization of a functionally distinct corticotropin-releasing factor receptor subtype from rat brain

The present study reports the isolation of a cDNA clone that encodes a second member of the corticotropin-releasing factor (CRF) receptor family, designated as the CRF2 receptor. The cDNA was identified using oligonucleotides of degenerate sequence in a PCR paradigm. A PCR fragment obtained from rat brain was utilized to isolate a full-length cDNA from a rat hypothalamus cDNA library that encoded a 411-amino acid protein with approximately 70% identity to the known CRF1 receptor over the entire coding region. When expressed in mouse Ltk- cells, this receptor stimulates cAMP production in response to CRF and known CRF-like agonists. CRF and the nonmammalian CRF-related peptides sauvagine and urotensin I stimulate adenylate cyclase activity in a dose-dependent manner with a rank order of potency different from that of the CRF1 receptor: sauvagine > urotensin > or = rat/human CRF > ovine CRF. Tissue distribution analysis of the mRNAs by reverse transcriptase-PCR shows CRF2 receptor mRNA is present in rat brain and detectable in lung and heart. In situ hybridization studies indicate specific expression within the brain in the ventromedial nuclei of the hypothalamus, the lateral septum, the amygdala, and entorhinal cortex, but there is unremarkable expression in the pituitary. An additional splice variant of the CRF2 receptor with a different N-terminal domain has been identified by PCR, encoding a putative protein of 431 amino acids. Thus, the data demonstrate the presence of another functional CRF receptor, with significant differences in the pharmacological profile and tissue distribution from the CRF1 receptor, which would predict important functional differences between the two receptors.