Disease relevance of Oprk1

• 2DG-induced hyperphagia was significantly reduced by AS ODNs directed against exon 2 (44-51%), but not exons 1 or 3 of the KOR-1 clone across a 4 h time course [1].
• To this end, we examined three different KOR agonists and their effects upon infarct size and arrhythmia development [2].
• However, KOR agonists also produce emesis and dysphoria, making it difficult to determine if their effects on self-administration are due to an action on reward mechanisms or are secondary to the drug's direct aversive effects [3].
• Kappa-opioid receptors (KOR) have been implicated in neuroprotection from ischemic neuronal injury, but less work has been performed with transient focal cerebral ischemia to determine the role of KOR during reperfusion [4].
• We tested the effects of a selective and specific KOR agonist, BRL 52537 hydrochloride [(+/-)-1-(3,4-dichlorophenyl)acetyl-2-(1-pyrrolidinyl) methylpiperidine], on infarct volume and nitric oxide production after transient focal ischemia in the rat [5].

High impact information on Oprk1

• In contrast, the ability of EMD 61,753 to dose-dependently attenuate responses of pelvic nerve afferent fibers to noxious colonic distension was unaffected in the same rats in which the antisense ODN effectively knocked-down the KOR as assessed in the formalin test [6].
• Additionally, Western blot analysis demonstrated a significant downregulation of KOR protein in the L4-S1 dorsal root ganglia of antisense, but not mismatch ODN-treated rats [6].
• Efficacy of the KOR antisense ODN treatment was behaviorally evaluated by assessing the antinociceptive effects of peripherally administered kappa- (EMD 61, 753 and U 69,593), mu- (DAMGO) and delta- (deltorphin) ORAs in the formalin test [6].
• We examined the cellular and subcellular distribution of the cloned kappa opioid receptor (KOR1) and its trafficking to the presynaptic plasma membrane in vasopressin magnocellular neurosecretory neurons [7].
• We used immunohistochemistry to show that KOR1 immunoreactivity (IR) colocalized with vasopressin-containing cell bodies, axons, and axon terminals within the posterior pituitary [7].

Biological context of Oprk1

• The potential open reading frame that starts further upstream in KORx may lead to the translation of a variant KOR protein having a novel peptide sequence at its amino terminus [8].
• By using two different approaches (reverse transcription/polymerase chain reaction and in situ hybridization), we have detected, for the first time, expression of the kappa opioid receptor (KOR) gene in the cerebellar cortex of the rat [9].
• Quantitative light microscopic densitometry of the superficial dorsal horn revealed that there were no significant differences in KOR densities among spinal segments C1--C2, T2, T13--L1, and L6--S1 in either the estrus or diestrus phases [10].
• Quantitative light microscopic densitometry of the superficial dorsal horn revealed that rats in diestrus had significantly lower KOR densities than those in proestrus or estrus [11].
• This suggests that female reproductive hormones regulate spinal KOR levels, which may contribute to variations in analgesic effectiveness of KOR agonists across the estrous cycle [11].

Anatomical context of Oprk1

• In chronic treatment, both Oprk1 and Oprm1 expression levels, that encoded kappa and mu-opioid receptor respectively, showed significant decreases in the periaqueductal gray and striatum [12].
• The aim of the present study was therefore to identify and localize the mu (MOR), delta (DOR) and kappa (KOR) opioid receptor subtypes within the rat cochlea [13].
• In addition, MOR- and KOR-containing nerve fibers were observed in the limbus [13].
• DOR and KOR immunoreactivity was found in inner and outer hair cells, bipolar cells of the spiral ganglion and interdental cells of the limbus [13].
• Amplification of RNAs from rat cerebral cortex (positive control) and rat cochlea with MOR, DOR and KOR primers resulted in products of the predicted lengths, 564, 356 and 276 bp, respectively [13].

Associations of Oprk1 with chemical compounds

• Coronal sections through rat brain were double-stained using antibodies against the alpha 1 subunit of GABA(A) receptor that were combined with antibodies either against the cloned mu-opioid receptor (MOR1) or the cloned kappa-opioid receptor (KOR1) [14].
• All three KOR agonists studied, U50,488, ICI 204,448, and BRL 52537 significantly reduced infarct size to levels comparable to that of BW373U86 [2].
• In the present study using whole-cell patch-clamp recordings, we demonstrate that a selective KOR agonist (U69593, 1 microm) directly inhibits a subset of principal and tertiary but not secondary neurons in the VTA [15].
• Significantly, regardless of cell class, KOR-mediated inhibition was found only in tyrosine hydroxylase-immunoreactive and thus dopaminergic neurons [15].
• In contrast, U50,488 treatment of AtT-20 cells expressing KOR having alanine substituted for serine-369 (KSA) did not increase phospho-p38 [16].

Regulatory relationships of Oprk1

• KOR mRNA was expressed at a relatively high level at P0 and P4 followed by a decrease while MOR mRNA was expressed at a low level at P0 and P4 followed by an increase by P8 and P16 [17].

Other interactions of Oprk1

• Our results point to an involvement of KOR and nNOS in the same intracellular network that controls the development of morphine tolerance and dependence [18].
• These converging antagonist and AS ODN data firmly implicate the kappa(1)-opioid receptor and the KOR-1 and KOR-3/ORL-1 opioid receptor genes in the mediation of dynorphin-induced feeding [19].
• alpha-Neoendorphin (alpha-NEO) is a proenkephalin B-derived opioid peptide and kappa type opioid receptor agonist [20].

Analytical, diagnostic and therapeutic context of Oprk1

• A semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to detect changes in the expression of delta- (DOR) kappa- (KOR) and mu- (MOR) opioid receptor mRNAs in rat cochleae at P0, P4, P8 and P16 [17].
• While it is generally accepted that activation of the delta-opioid receptor (DOR) is cardioprotective, and may indeed be an important mediator of ischemic preconditioning, the role of the kappa-opioid receptor (KOR) is less well understood [2].
• Microinjection of kappa opioid receptor (KOR) agonists into the rostral ventromedial medulla (RVM) attenuates mu-opioid receptor mediated antinociception and stress-induced analgesia, yet is also reported to have an analgesic effect [21].
• We investigated possible anatomical correlates of this modulation by using dual labeling electron microscopy to examine the cellular distributions of antibodies raised against KOR and the R1 subunit of the NMDA receptor (NR1) [22].

References