title: Involvement of neuropeptide Y in the acute, chronic and withdrawal responses of morphine in nociception in neuropathic rats: behavioral and neuroanatomical correlates.
abstract: Although morphine is a potent antinociceptive agent, its chronic use developed tolerance in neuropathic pain (NP). Furthermore, opioid antagonist naloxone attenuated the antinociceptive effect of neuropeptide Y (NPY). The present study investigated the role of NPY and NPY Y1/Y5 receptors in acute and chronic actions of morphine in neuropathic rats using thermal paw withdrawal test and immunocytochemistry. In acute study, intracerebroventricular (icv) administration of morphine, NPY or NPY Y1/Y5 receptors agonist [Leu(31),Pro(34)]-NPY produced antinociception, whereas selective NPY Y1 receptors antagonist BIBP3226 caused hyperalgesia. While NPY or [Leu(31),Pro(34)]-NPY potentiated, BIBP3226 attenuated morphine induced antinociception. Chronic icv infusion of morphine via osmotic minipumps developed tolerance to its antinociceptive effect, and produced hyperalgesia following withdrawal. However, co-administration of NPY or [Leu(31),Pro(34)]-NPY prevented the development of tolerance and withdrawal hyperalgesia. Sciatic nerve ligation resulted in significant increase in the NPY-immunoreactive (NPY-ir) fibers in ventrolateral periaqueductal gray (VLPAG) and locus coeruleus (LC); fibers in the dorsal part of dorsal raphe nucleus (DRD) did not respond. While chronic morphine treatment significantly reduced NPY-ir fibers in VLPAG and DRD, morphine withdrawal triggered significant augmentation in NPY-immunoreactivity in the VLPAG. NPY-immunoreactivity profile of LC remained unchanged in all the morphine treatment conditions. Furthermore, removal of sciatic nerve ligation reversed the effects of NP, increased pain threshold and restored NPY-ir fiber population in VLPAG. NPY, perhaps acting via Y1/Y5 receptors, might profoundly influence the processing of NP information and interact with the endogenous opioid system primarily within the framework of the VLPAG.
authors: Department of Pharmaceutical Sciences, Rashtrasant Tukadoji Maharaj Nagpur University Campus, Nagpur 440 033, India.
authors: Manoj A
authors: MA
authors: Upadhya
authors: Manoj P
authors: MP
authors: Dandekar
authors: Dadasaheb M
authors: DM
authors: Kokare
authors: Praful S
authors: PS
authors: Singru
authors: Nishikant K
authors: NK
authors: Subhedar
mesh_terms: D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000378:metabolism; D001522:Behavior, Animal / Q000502:physiology*; D004361:Drug Tolerance; D006930:Hyperalgesia / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D009020:Morphine / Q000627:therapeutic use*; D009478:Neuropeptide Y / Q000737:chemistry / Q000378:metabolism*; D010147:Pain Measurement; D010523:Peripheral Nervous System Diseases / Q000473:pathology / Q000503:physiopathology; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D017476:Receptors, Neuropeptide Y / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012584:Sciatic Nerve / Q000473:pathology / Q000503:physiopathology; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*
chemical_list: D000701:Analgesics, Opioid; C092926:BIBP 3226; D009478:Neuropeptide Y; D017476:Receptors, Neuropeptide Y; D009020:Morphine; D001120:Arginine