Pro-nociceptin/orphanin FQ and NOP receptor mRNA levels in the forebrain of food deprived rats.
Forebrain injections of nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the NOP opioid receptor, previously referred to as ORL1 or OP4 receptor, stimulate feeding in freely feeding rats, while the NOP receptor antagonist [Nphe(1)]N/OFQ(1-13)NH(2) inhibits food deprivation-induced feeding. To further evaluate whether the N/OFQ-NOP receptor system plays a physiological role in feeding control, the present study evaluated forebrain mRNA levels for the N/OFQ precursor (pro-N/OFQ), as well as for the NOP receptor in food deprived rats. The results obtained show that food deprived rats have lower mRNA levels for the NOP receptor in several forebrain regions; a significant reduction was found in the paraventricular and lateral hypothalamic nuclei and in the central nucleus of the amygdala. Food deprived rats also exhibited lower pro-N/OFQ mRNA levels in the central amygdala. These results suggest that the N/OFQ-NOP receptor system may have a physiological role in feeding control. The observation that food deprivation reduces gene expression of the N/OFQ-NOP receptor system is apparently not consistent with a direct hyperphagic action for N/OFQ. Taking into account that N/OFQ exerts inhibitory actions at cellular level, the present results may be in keeping with the hypothesis that N/OFQ stimulates feeding by inhibiting neurons inhibitory for food intake; under conditions of food deprivation, these neurons may be silent and the N/OFQ-NOP receptor system, which controls them, may also be regulated at a lower level. Consistently, in the present study N/OFQ stimulated food intake in freely feeding rats, but did not further increase feeding in food deprived rats.
Rodi
Donata
D
Department of Clinical and Experimental Medicine, Section of Pharmacology, and Neuroscience Center, University of Ferrara, Ferrara, Italy.
Polidori
Carlo
C
Bregola
Gianni
G
Zucchini
Silvia
S
Simonato
Michele
M
Massi
Maurizio
M
D000679:Amygdala / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001069:Appetite Regulation / Q000187:drug effects / Q000235:genetics*; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D005508:Food Deprivation / Q000502:physiology*; D007026:Hypothalamic Area, Lateral / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000235:genetics; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018847:Opioid Peptides / Q000235:genetics* / Q000494:pharmacology; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016548:Prosencephalon / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000235:genetics*; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D018847:Opioid Peptides; D012333:RNA, Messenger; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C000722285:Oprl1 protein, rat