CRF₂ mediates the increased noradrenergic activity in the hypothalamic paraventricular nucleus and the negative state of morphine withdrawal in rats.
OBJECTIVE
Recent evidence suggests that corticotropin-releasing factor (CRF) receptor signalling is involved in modulating the negative symptoms of opiate withdrawal. In this study, a series of experiments were performed to further characterize the role of CRF-type 2 receptor (CRF₂) signalling in opiate withdrawal-induced physical signs of dependence, hypothalamus-pituitary-adrenal (HPA) axis activation, enhanced noradrenaline (NA) turnover in the hypothalamic paraventricular nucleus (PVN) and tyrosine hydroxylase (TH) phosphorylation (activation), as well as CRF₂ expression in the nucleus of the solitary tract-A₂ noradrenergic cell group (NTS-A₂).


METHODS
The contribution of CRF₂ signalling in opiate withdrawal was assessed by i.c.v. infusion of the selective CRF₂ antagonist, antisauvagine-30 (AS-30). Rats were implanted with two morphine (or placebo) pellets. Six days later, rats were pretreated with AS-30 or saline 10 min before naloxone and the physical signs of abstinence, the HPA axis activity, NA turnover, TH activation and CRF₂ expression were measured using immunoblotting, RIA, HPLC and immunohistochemistry.


RESULTS
Rats pretreated with AS-30 showed decreased levels of somatic signs of naloxone-induced opiate withdrawal, but the corticosterone response was not modified. AS-30 attenuated the increased production of the NA metabolite, 3-methoxy-4-hydroxyphenylglycol, as well as the enhanced NA turnover observed in morphine-withdrawn rats. Finally, AS-30 antagonized the TH phosphorylation at Serine40 induced by morphine withdrawal.


CONCLUSIONS
These results suggest that physical signs of opiate withdrawal, TH activation and stimulation of noradrenergic pathways innervating the PVN are modulated by CRF₂ signalling. Furthermore, they indicate a marginal role for the HPA axis in CRF₂-mediation of opiate withdrawal.
Group of Cellular and Molecular Pharmacology, University School of Medicine, Murcia, Spain.
Javier
J
Navarro-Zaragoza
Cristina
C
Núñez
Jessica
J
Ruiz-Medina
M Luisa
ML
Laorden
Olga
O
Valverde
M Victoria
MV
Milanés
D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000378:metabolism; D058990:Molecular Targeted Therapy; D009021:Morphine Dependence / Q000188:drug therapy / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology / Q000627:therapeutic use; D010766:Phosphorylation / Q000187:drug effects; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D018019:Receptors, Corticotropin-Releasing Hormone / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism; D013375:Substance Withdrawal Syndrome / Q000378:metabolism* / Q000517:prevention & control; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
C101531:CRF receptor type 2; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D018019:Receptors, Corticotropin-Releasing Hormone; C116607:antisauvagine 30; D008734:Methoxyhydroxyphenylglycol; D014446:Tyrosine 3-Monooxygenase; D009638:Norepinephrine