title: Inactivation of the periaqueductal gray attenuates antinociception elicited by stimulation of the rat medial preoptic area.
abstract: The medial preoptic area (MPOA) is a sexually dimorphic structure that plays key roles in gonado-steroidal regulation and thermoregulation. The MPOA may be involved in sex-based differences in nociceptive processing and steroid hormones effect on pain thresholds. Consistent with this, there is evidence that MPOA can produce antinociception or hyperalgesia. MPOA stimulation inhibits spinal cord or trigeminal neuronal responses to noxious stimuli or produces analgesia, yet most of these studies utilized electrical stimulation which antidromically activates periaqueductal gray (PAG) and rostroventromedial medulla (RVM) neurons involved in descending modulation of nociception. Effects of selective activation of MPOA neurons on behavioral indices of antinociception and the site-specificity of such responses are unknown. To address these questions, we examined the influence of MPOA microinjections of d,l homocysteate (DLH) on hindlimb and tail nocifensive reflexes in lightly anesthetized rats. DLH, but not saline, microinjections into several MPOA subregions markedly increased withdrawal response latencies to noxious thermal stimuli. Antinociceptive effects of MPOA activation were abolished by microinjection of lidocaine into PAG. These results suggest that activation of MPOA neurons produces antinociception that is at least partly mediated by projections to PAG.
authors.affiliation: Department of Anatomy and Neurobiology, Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN 38163, USA. yzhang32@utmem.edu
authors.forename: Yi-Hong
authors.initials: YH
authors.lastname: Zhang
authors.forename: Matthew
authors.initials: M
authors.lastname: Ennis
mesh_terms: D000698:Analgesia / Q000379:methods; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D006710:Homocysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D006930:Hyperalgesia / Q000188:drug therapy / Q000503:physiopathology; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000033:anatomy & histology / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000188:drug therapy / Q000503:physiopathology*; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D011301:Preoptic Area / Q000033:anatomy & histology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D012018:Reflex / Q000187:drug effects / Q000502:physiology
chemical_list: D000779:Anesthetics, Local; D006710:Homocysteine; C007956:homocysteic acid; D008012:Lidocaine