title: Specific thalamic nuclei function as novel 'nociceptive discriminators' in the endogenous control of nociception in rats.
abstract: Recently, we hypothesized that supraspinal structures may have important functions in discriminating between noxious mechanically and heat mediated nociception through distinct functions: facilitation and inhibition. In this study, conducted in conscious rats, we explored the role of different thalamic nuclei: the mediodorsal (MD) nucleus, the central medial (CM) nucleus, the submedius (SM) nucleus, the ventralmedial (VM) nucleus and the ventral posterolateral (VPL) nucleus, in the descending control of secondary and contralateral mechanical hyperalgesia and heat hypoalgesia occurring in intramuscularly hypertonic (HT, 5.8%) saline-induced muscle nociception. We found that the MD nuclei participated in the descending facilitation of mechanical hyperalgesia, and that the VM nuclei were specifically involved in the descending inhibition of heat hypoalgesia. Neither descending facilitation nor descending inhibition was affected after electrolytic lesion of the thalamic CM, SM, and VPL nuclei. This descending facilitatory and inhibitory modulation of nociception was strengthened by glutamate, and weakened by GABA, microinjected into the thalamic MD and VM nuclei. It is suggested that (1) thalamic MD nucleus and VM nucleus form two distinct endogenous systems in the control of noxious mechanically and heat evoked responses, and (2) the strengthening of descending inhibition and the weakening of descending facilitation by means of up regulation and down regulation of appropriate receptor expression in the VM and MD nuclei may provide a new strategic policy in treating pathological pain.
authors.affiliation: Center for Biomedical Research on Pain (CBRP), College of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China. Electronic address: yhj@mail.xjtu.edu.cn.
authors.forename: H-J
authors.initials: HJ
authors.lastname: You
authors.affiliation: Center for Biomedical Research on Pain (CBRP), College of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China.
authors.forename: J
authors.initials: J
authors.lastname: Lei
authors.affiliation: Center for Biomedical Research on Pain (CBRP), College of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China.
authors.forename: N
authors.initials: N
authors.lastname: Niu
authors.affiliation: Center for Biomedical Research on Pain (CBRP), College of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China.
authors.forename: L
authors.initials: L
authors.lastname: Yang
authors.affiliation: Department of Physiology, College of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China.
authors.forename: X-L
authors.initials: XL
authors.lastname: Fan
authors.affiliation: Department of Biomedicine, University of Bergen, N-5009 Bergen, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Tjølsen
authors.affiliation: Department of Physiology, College of Medicine, Xi'an Jiaotong University, Xi'an 710061, PR China.
authors.forename: Q
authors.initials: Q
authors.lastname: Li
mesh_terms: D000818:Animals; D018698:Glutamic Acid / Q000378:metabolism; D006358:Hot Temperature; D006930:Hyperalgesia / Q000503:physiopathology*; D008297:Male; D009043:Motor Activity / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology; D059225:Nociception / Q000502:physiology*; D017288:Pain Threshold / Q000502:physiology; D011897:Random Allocation; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic; D013787:Thalamic Nuclei / Q000503:physiopathology*; D014110:Touch; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D012462:Saline Solution, Hypertonic; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid