KOR-3, also known as ORL-1, is a member of the opioid receptor family, encoding the murine receptor for orphanin FQ/nociceptin. In the current studies we have identified five different splice variants of KOR-3 in mouse brain, three of which have not been previously reported. In addition to variants with a 15 bp deletion at the 3'-end of the first coding exon (KOR-3d) and an 81 bp insertion between the second and third coding exons (KOR-3e), three new variants with insertions of 34 (KOR-3a), 98 (KOR-3b), and 139 bp (KOR-3c) between the first and second coding exons have been obtained. The expression of the three variants in mouse brain varies markedly among brain regions with a distribution which is quite distinct from KOR-3 itself. Of greatest interest was the presence of high levels of KOR-3a in the striatum, a region with no demonstrable KOR-3, and in the cortex. KOR-3c was seen in the periaqueductal gray and hypothalamus, regions where KOR-3 predominated. The brainstem had similar levels of KOR-3, KOR-3a, and KOR-3d. In contrast, KOR-3d was most prominent in the cerebellum. KOR-3b levels were very low throughout.
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"et al., 1995). Nociceptin presents the highest homology to dynorphin, and NOP may be analogous to the kappa opioid receptor (Pan et al., 1998). In vivo experiments have demonstrated that nociceptin modulates a variety of biological functions such as nociception, food intake, memory process, locomotor activity, anxiety, etc. (Calo et al., 2000; Mogil and Pasternak, 2001; Chiou et al., 2007). "
[Show abstract][Hide abstract] ABSTRACT: The effects with pretreatment with nociceptin (0.03-30nmol, i.c.v.) were evaluated on the threshold for eliciting afterdischarge (ADT), generation and spread of seizure activity and postictal depression in rats with kindling stimulation. Nociceptin produced a decrease in ADT (32-45%) in rats with partial seizures (PS, stage II-III), and an increase (61-92%) in rats with generalized seizures (GS, kindled state). Nociceptin did not modify the behavioral changes, spike frequency and duration of afterdischarge elicited at ADT in both experimental groups. In rats with GS, nociceptin enhanced postictal depression (34-44%) evaluated with a recycling paradigm. Autoradiography experiments revealed enhanced nociceptin opioid receptor (NOP) binding in medial amygdala (22-26%), frontal (21-23%) and entorhinal (27-32%) cortices, and reduced binding in the substantia nigra pars compacta (28%) and medial central gray (29%) of rats with PS. The GS group displayed significant decreased NOP binding (40-70%) in most of the brain areas evaluated. These results suggest that nociceptin facilitates ictal activity in rats with PS, whereas in animals with GS, it induces inhibitory effects on ADT and enhances the postictal period. These effects correlate with significant changes in NOP binding.
Full-text · Article · Jan 2008 · Epilepsy Research
"Nociceptin/orphanin FQ (Noc) is an opiate-like peptide originally characterized as the endogenous ligand for the opiate receptor-like receptor (ORL-1) (Meunier et al., 1995; Reinscheid et al., 1995). Among opiate peptides, Noc exhibits the highest homology to dynorphin (Meunier et al., 1995), and ORL-1 may be analogous to the 3 receptor identified pharmacologically (Pan et al., 1998). Noc and ORL-1 are abundantly expressed throughout the hippocampus (Florin et al., 1997; Neal et al., 1999a; Letchworth et al., 2000), where Noc has postsynaptic augmenting actions on K ϩ currents of principal neurons in CA1, CA3, and the dentate (Ikeda et al., 1997; Yu and Xie, 1998; Madamba et al., 1999b; Amano et al., 2000). "
[Show abstract][Hide abstract] ABSTRACT: The opiate-like peptide nociceptin/orphanin FQ (Noc) and its receptor [opiate receptor-like receptor (ORL-1)] are highly expressed in the hippocampus. Noc has inhibitory postsynaptic actions in CA1, CA3, and the dentate and seems to lack the disinhibitory, excitatory actions demonstrated for some opiate peptides in the hippocampus. The CA3 hippocampal region is important in the generation of hippocampal seizures. Therefore, we tested the action of Noc on spontaneous epileptiform activity recorded extracellularly or intracellularly in CA3 and generated by removal of Mg(2+) from the bathing solution or by raising extracellular K(+) from 3.5 to 7.5 mm. Superfusion of Noc robustly depressed spontaneous bursting without desensitization. The ORL-1 antagonist [Phe(1)Psi(CH(2)-NH)Gly(2)]NC(1-13)NH(2) (1-2 microm) greatly attenuated the reduction of spontaneous bursting by Noc. To characterize the cellular mechanism of action of Noc, we recorded intracellularly from CA3 pyramidal neurons. Noc reduced EPSCs evoked by stimulating either mossy or associational/commissural fibers. Analysis of miniature EPSCs using whole-cell voltage-clamp recording suggests that Noc acts presynaptically to inhibit glutamate release. This is the first demonstration of a presynaptic effect for Noc in the hippocampus. Noc also increased K(+) currents in CA3 pyramidal neurons, including the voltage-sensitive M-current. Blocking the M-current with linopirdine increased the duration of individual CA3 bursts but did not attenuate Noc-mediated inhibition of bursting. Thus, Noc acts via multiple mechanisms to reduce excitation in CA3. However, Noc inhibition of epileptiform events is not dependent on augmentation of the M-current.
Full-text · Article · Oct 2001 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
"They do not, however, exclude the possibility that the effects of N/OFQ occur via receptor subtypes different from the " classical " N/OFQ receptor, which might originate from post-transcriptional modifications. The existence of different splice variants of the mouse N/OFQ receptor has indeed been demonstrated (Wang et al., 1994; Pan et al., 1998). There are, however, other possible explanations for differing potencies. "
[Show abstract][Hide abstract] ABSTRACT: Nociceptin/orphanin FQ (N/OFQ) and nocistatin (NST) are two neuropeptides derived from the same precursor protein that exhibit opposing effects on spinal neurotransmission and nociception. Here, we have used whole-cell, patch-clamp recordings from visually identified neurons in spinal cord dorsal horn slices of genetically modified mice to investigate the role of the N/OFQ receptor (N/OFQ-R) in the modulatory action of both peptides on excitatory glutamatergic and inhibitory glycinergic and gamma-aminobutyric acid (GABA)-ergic synaptic transmission. In wild-type mice, N/OFQ selectively suppressed excitatory transmission in a concentration-dependent manner but left inhibitory synaptic transmission unaffected. In contrast, NST reduced only inhibitory but not alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor-mediated excitatory synaptic transmission. N/OFQ-mediated inhibition of excitatory transmission was completely absent in N/OFQ-R receptor-deficient (N/OFQ-R(-/-)) mice and significantly reduced in heterozygous (N/OFQ-R(+/-)) mice, whereas the action of NST on inhibitory neurotransmission was completely retained. To test for the relevance of these results for spinal nociception, we investigated the effects of intrathecally injected N/OFQ in the mouse formalin test, an animal model of tonic pain. N/OFQ (3 nmol/mouse) induced significant antinociception in wild-type mice, but had no antinociceptive effects in N/OFQ-R(-/-) mice. These results indicate that the inhibitory action of N/OFQ on excitatory glutamatergic synaptic transmission and its spinal antinociceptive action are mediated via the N/OFQ receptor, whereas the action of NST is independent of this receptor.