Regulation of serine (Ser)-31 and Ser40 tyrosine hydroxylase phosphorylation during morphine withdrawal in the hypothalamic paraventricular nucleus and nucleus tractus solitarius-A2 cell group: role of ERK1/2.
Our previous studies have shown that naloxone-induced morphine withdrawal increases the hypothalamic-pituitary-adrenocortical (HPA) axis activity, which is dependent on a hyperactivity of noradrenergic pathways [nucleus tractus solitarius (NTS) A(2)] innervating the hypothalamic paraventricular nucleus (PVN). Short-term regulation of catecholamine biosynthesis occurs through phosphorylation of tyrosine hydroxylase (TH), which enhances enzymatic activity. In the present study, the effect of morphine withdrawal on site-specific TH phosphorylation in the PVN and NTS-A(2) was determined by quantitative blot immunolabeling and immunohistochemistry using phosphorylation state-specific antibodies. We show that naloxone-induced morphine withdrawal phosphorylates TH at Serine (Ser)-31 but not Ser40 in PVN and NTS-A(2), which is associated with both an increase in total TH immunoreactivity in NTS-A(2) and an enhanced TH activity in the PVN. In addition, we demonstrated that TH neurons phosphorylated at Ser31 coexpress c-Fos in NTS-A(2). We then tested whether pharmacological inhibition of ERK activation by ERK kinase contributes to morphine withdrawal-induced phosphorylation of TH at Ser31. We show that the ability of morphine withdrawal to stimulate phosphorylation at this seryl residue is reduced by SL327, an inhibitor of ERK(1/2) activation. These results suggest that morphine withdrawal increases noradrenaline turnover in the PVN, at least in part, via ERK(1/2)-dependent phosphorylation of TH at Ser31.
Núñez
Cristina
C
Department of Pharmacology, University School of Medicine, Campus de Espinardo, Murcia, Spain.
Laorden
M Luisa
ML
Milanés
M Victoria
MV
D000818:Animals; D015153:Blotting, Western; D015870:Gene Expression / Q000187:drug effects; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology*; D009020:Morphine / Q000494:pharmacology*; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*