Antisense oligodeoxynucleotide to a delta-opioid receptor selectively blocks the spinal antinociception induced by delta-, but not mu- or kappa-opioid receptor agonists in the mouse

Direct Administration and Gene Modulation Using Antisense Oligonucleotides Within the CNS

Besides his vast contribution to the opioid receptor studies, Dr. G. W. Pasternak was among the early pioneers in the antisense oligonucleotide (ASO) field at the time when the crucial in vivo studies using ASO-mediated gene knockdown in the CNS were still impeded by the ASO's inability to cross the blood-brain barrier. This changed at the start of 1990s, when administration of oligonucleotides through intracerebroventricular or, later, intrathecal injection was undertaken at Cornell University Medical College and further developed in close collaboration with Pasternak lab. These early studies eventually led to the practical realization of the significant therapeutic potential of ASO-based drugs we see today.

Spinal ERK2 activation through δ2-opioid receptors contributes to nociceptive behavior induced by intrathecal injection of leucine-enkephalin

Intrathecal (i.t.) injection of leucine-enkephalin (Leu-ENK), co-administered with peptidase inhibitors, phosphoramidon (an endopeptidase 24.11 inhibitor), and bestatin (a general aminopeptidase inhibitor), produced behaviors consisting of the biting and/or licking of the hindpaw and the tail along with hindlimb scratching directed toward the flank, which peaked at 10-15 min after an injection. This characteristic behavior was not observed in mice treated with i.t. Leu-ENK alone. We also investigated the effect of the extracellular signal-regulated kinase (ERK) in spinal processing of nociception induced by i.t. co-administration of Leu-ENK with phospharamidon and bestatin. Western blot analysis of phospho-ERK (pERK) showed a significant increase of pERK2 in the lumbar spinal cord in response to i.t. Leu-ENK co-injected with peptidase inhibitors. The MAP kinase-ERK inhibitor, U0126 dose-dependently attenuated the nociceptive behavior and spinal ERK activation to i.t. Leu-ENK co-injected with peptidase inhibitors. Furthermore, the nociceptive behavior and spinal ERK activation evoked by i.t. Leu-ENK in combination with peptidase inhibitors were inhibited by co-administration of the non-selective δ-opioid receptor antagonist, naltrindole, the selective δ2-opioid receptor antagonist, naltriben, the non-competitive N-methyl-D-aspartate (NMDA) antagonist, MK-801 or the non-selective nitric oxide synthase inhibitor, L-NAME, the selective nNOS inhibitor, N(ω)-propyl-L-arginine or the selective iNOS inhibitor, W1400, but not by the selective δ1-receptor antagonist, BNTX (7-benzylidenenaltrexone). These results suggest that spontaneous nociceptive behaviors produced by i.t. co-administration of Leu-ENK with peptidase inhibitors may be induced by an activation of the glutamate-NO-ERK pathway through the δ2-opioid receptor in the dorsal spinal cord.

Mu opioids and their receptors: evolution of a concept

Opiates are among the oldest medications available to manage a number of medical problems. Although pain is the current focus, early use initially focused upon the treatment of dysentery. Opium contains high concentrations of both morphine and codeine, along with thebaine, which is used in the synthesis of a number of semisynthetic opioid analgesics. Thus, it is not surprising that new agents were initially based upon the morphine scaffold. The concept of multiple opioid receptors was first suggested almost 50 years ago (Martin, 1967), opening the possibility of new classes of drugs, but the morphine-like agents have remained the mainstay in the medical management of pain. Termed mu, our understanding of these morphine-like agents and their receptors has undergone an evolution in thinking over the past 35 years. Early pharmacological studies identified three major classes of receptors, helped by the discovery of endogenous opioid peptides and receptor subtypes-primarily through the synthesis of novel agents. These chemical biologic approaches were then eclipsed by the molecular biology revolution, which now reveals a complexity of the morphine-like agents and their receptors that had not been previously appreciated.

Differential noxious and motor tolerance of chronic delta opioid receptor agonists in rodents

In the present study, we asked whether multiple intrathecal injections of deltorphin II, a selective delta opioid receptor (DOPR) agonist, induced DOPR tolerance in three behavioral assays. Unilateral inflammation caused by complete Freund's adjuvant (CFA) injection into the rat or mouse hind paw (CFA model) induced thermal hyperalgesic response that was transiently and dose-dependently reduced by intrathecal administration of deltorphin II or morphine. In both rodent species, the effect of deltorphin II was not modified by a single prior administration of deltorphin II, suggesting an absence of acute tolerance in this paradigm. Repeated administration of intrathecal deltorphin II or s.c. SB-235863 (five consecutive injections over 60 h) also failed to impair the antihyperalgesic response to delta opioid receptor agonist, whereas repeated intrathecal or s.c. injections of morphine induced a significant decrease in the subsequent thermal antihyperalgesic response to morphine. In mice, deltorphin II also induced a rapid, transient motor incoordination/ataxia-like behavior as tested with the accelerating rotarod. In contrast to the antihyperalgesic responses, tolerance to the motoric effect of deltorphin II was evident in mice previously exposed to multiple intrathecal agonist injections, but not multiple saline administrations. Using the tail flick antinociceptive test, we found that DOPR-mediated analgesia was significantly reduced by repeated exposure to deltorphin II. Altogether, these observations suggest that repeated injections of DOPR agonists induce differential tolerance effects on antihyperalgesic, antinociceptive, and motor incoordination/ataxia-like behaviors related to DOPR activation by deltorphin II.

Spinal delivery of analgesics in experimental models of pain and analgesia

Systemic administration of analgesics can lead to serious adverse side effects compromising therapeutic benefit in some patients. Information coding pain transmits along an afferent neuronal network, the first synapses of which reside principally in the spinal cord. Delivery of compounds to spinal cord, the intended site of action for some analgesics, is potentially a more efficient and precise method for inhibiting the pain signal. Activation of specific proteins that reside in spinal neuronal membranes can result in hyperpolarization of secondary neurons, which can prevent transmission of the pain signal. This is one of the mechanisms by which opioids induce analgesia. The spinal cord is enriched in such molecular targets, the activation of which inhibit the transmission of the pain signal early in the afferent neuronal network. This review describes the pre-clinical models that enable new target discovery and development of novel analgesics for site-directed pain management.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.

Selective depression of nociceptive responses of dorsal horn neurones by SNC 80 in a perfused hindquarter preparation of adult mouse

Detailed electrophysiological characterisation of spinal opioid receptors in the mouse has been limited due to various technical difficulties. In this study, extracellular single unit recordings were made from dorsal horn neurones in a perfused spinal cord with attached trunk-hindquarter to investigate the role of delta-opioid receptor in mediating nociceptive and non-nociceptive transmission in mouse. Noxious electrical shock, pinch and heat stimuli evoked a mean response of 20.8+/-2.5 (n=10, P<0.005), 30.1+/-5.4 (n=58, P<0.005) and 40.9+/-6.3 (n=29, P<0.005) spikes per stimulus respectively. In 5 of 22 cells, repetitive noxious electrical stimuli applied to the hindpaw for 20 s produced a progressive increase in spike number, the phenomenon known as 'wind-up' and/or hyperactivity. When the selective delta-opioid receptor agonist (+)-4-[(alpha R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC 80) was perfused for 8-10 min, these evoked nociceptive responses were reversibly depressed. SNC 80 (2 microM) depressed the nociceptive responses evoked by electrical shock, pinch and heat by 74.0+/-13.7% (n=8, P<0.01), 66.5+/-16.6% (n=10, P<0.01) and 74.1+/-17.0% (n=10, P<0.01) respectively. The maximum depression by 5 microM SNC 80 was 92.6+/-6.8% (n=3). SNC 80 at 5 microM also completely abolished the wind-up and/or hypersensitivity (n=5). The depressant effects of SNC 80 on the nociceptive responses were completely blocked by 10 microM naloxone (n=5) and 3 microM 17-(cyclopropylmethyl)-6,7-dehydro-4,5 alpha-epoxy-14 beta-ethoxy-5 beta-methylindolo [2',3':6',7'] morphinan-3-ol hydrochloride (HS 378, n=8), a novel highly selective delta-opioid receptor antagonist. Interestingly, HS 378 (3 microM) itself potentiated the background activity and evoked responses to pinch and heat by 151.8+/-38.4% (P<0.05, n=8), 34.2+/-6.1% (P<0.01, n=7) and 45.5+/-11.8% (P<0.05, n=5) respectively. In contrast, the responses of non-nociceptive dorsal horn neurones were not inhibited by SNC 80 at a dose of up to 10 microM (n=5). These data demonstrate that delta-opioid receptor modulate nociceptive, but not non-nociceptive, transmission in spinal dorsal horn neurones of the adult mouse. The potentiation of neuronal activity by HS 378 may reflect an autoregulatory role of the endogenous delta-opioid in nociceptive transmission in mouse.

Spinal delta-opioid receptors mediate suppression of systemic SNC80 on excitability of the flexor reflex in normal and inflamed rat

Due to low central nervous system (CNS) bioavailability of delta-opioid peptides, little is known about the effect of systemic administration of delta-opioid receptor ligands. The present study examined the effect of non-peptidergic delta-opioid receptor agonists, (+)-4-[(alphaR)-alpha-((2R,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80) and (-)dibenzoyl-L-tartaric acid salt (SNC86), on the activity of alpha-motoneurons in decerebrate-spinal rats. The flexor reflex was facilitated by C-afferent conditioning inputs, shown by a decrease in mechanical threshold and increase in touch- and pinch-evoked responses. Systemic administration of SNC80 (10 micromol/kg) prevented and reversed the neuronal hyperactivity. We further examined the effect of this agonist on the hypersensitivity of the flexor reflex induced by intraplantar injection of Freund's adjuvant. SNC80 dose-dependently (1, 3, 5 and 10 micromol/kg) increased the mechanical threshold and decreased touch-, pinch- and Abeta-afferent inputs-evoked responses. Similar effects were seen with SNC86 (5 micromol/kg). Pretreatment with either naloxone (20 micromol/kg, i.p.) or (Cyclopropylmethyl)-6,7-dehydro-4,5alpha-epoxy-14beta-ethoxy-5beta-methylindolo [2',3':6',7']morphinan-3-ol hydrochloride (SH378; 5 micromol/kg, intraarterially (i.a.)), a novel selective delta-opioid receptor antagonist, completely abolished the anti-hypersensitivity effect of SNC80. The effect of SNC80 remained following intrathecal administration of mu-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP; 1.5 nmol). These results indicate that systemic injection of SNC80 exerted antihypersensitivity in models of both acute and tonic nociception and these effects are mediated mainly through a spinal delta-opioid mechanism.

Role of the phosphatidylinositol-specific phospholipase C pathway in delta-opioid receptor-mediated antinociception in the mouse spinal cord

Stimulation of delta-opioid receptors has been shown to activate phospholipase C via the activation of G-proteins in vitro. The present study was designed to determine, with the tail-flick method, whether the stimulatory effect of delta-opioid receptor agonists on phospholipase C and inositol lipid turnover participates in the mechanisms of the delta-opioid receptor-mediated antinociception in the mouse spinal cord. Intrathecal pretreatment with the phospholipase C inhibitors neomycin and U73122, which produced no changes in the basal tail-flick latencies when they were injected alone, significantly attenuated the antinociception induced by intrathecal administration of the selective delta-opioid receptor agonist [D-Ala(2)]deltorphin II in mice. The selective phosphatidylinositol-specific phospholipase C inhibitor ET-18-OCH(3) inhibited the antinociception induced by intrathecal administration of [D-Ala(2)]deltorphin II in a dose-dependent manner. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, the antinociception induced by intrathecal administration of [D-Ala(2)]deltorphin II was significantly reduced. Co-administration of D-myo-inositol-1,4,5-trisphosphate restored the [D-Ala(2)]deltorphin II-induced antinociception in LiCl-pretreated mice. On the other hand, intrathecal pretreatment with the selective protein kinase C inhibitor calphostin C, but not the protein kinase A inhibitor KT5720, resulted in a dose-dependent enhancement of the [D-Ala(2)]deltorphin II-induced antinociception. These results indicate a potential role for the phospholipase C-inositol-1,4, 5-trisphosphate pathway in the expression of delta-opioid receptor-mediated antinociception in the mouse spinal cord. Furthermore, activation of protein kinase C by the stimulation of delta-opioid receptors may constitute a significant pathway involved in negative modulation of spinal delta-opioid receptor-mediated antinociception.

Potent and nontoxic antisense oligonucleotides containing locked nucleic acids

Insufficient efficacy and/or specificity of antisense oligonucleotides limit their in vivo usefulness. We demonstrate here that a high-affinity DNA analog, locked nucleic acid (LNA), confers several desired properties to antisense agents. Unlike DNA, LNA/DNA copolymers were not degraded readily in blood serum and cell extracts. However, like DNA, the LNA/DNA copolymers were capable of activating RNase H, an important antisense mechanism of action. In contrast to phosphorothioate-containing oligonucleotides, isosequential LNA analogs did not cause detectable toxic reactions in rat brain. LNA/DNA copolymers exhibited potent antisense activity on assay systems as disparate as a G-protein-coupled receptor in living rat brain and an Escherichia coli reporter gene. LNA-containing oligonucleotides will likely be useful for many antisense applications.

delta-Opioid receptor agonists produce antinociception and [35S]GTPgammaS binding in mu receptor knockout mice

We examined the effects of [D-Pen(2),D-Pen(5)]enkephalin (DPDPE), [D-Ala(2),Glu(4)]deltorphin (DELT), and (+)-4-[(alphaR)-alpha((2S, 5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N, N-diethylbenzamide (SNC80) on [35S]GTPgammaS binding in brain membranes prepared from micro-opioid receptor knockout (-/-) mice. The potency and maximal response (E(max)) of these agonists were unchanged compared to control mice. In contrast, while the potency of [D-Pen(2),pCl-Phe(4),D-Pen(5)]enkephalin (pCl-DPDPE) was not significantly different, the E(max) was reduced as compared to controls. In the tail-flick test, intracerebroventricular (i.c.v.) or intrathecal (i.th.) DELT produced antinociceptive effects in -/- mice with potency that did not differ significantly from controls. In contrast, the antinociceptive potency of i.c.v. and i.th. DPDPE was displaced to the right by 4- and 9-fold in -/- compared to control mice, respectively. Reduced DPDPE antinociceptive potency in -/- mice, taken together with reduced DPDPE- and pCl-DPDPE- stimulated G protein activity in membranes prepared from -/- mice, demonstrate that these agonists require mu-opioid receptors for full activity. However, because DELT mediated G protein activation and antinociception were both comparable between -/- and wild type mice, we conclude that the mu-opioid receptor is not a critical component of delta-opioid receptor function.

Effects of antisense oligonucleotides on brain delta-opioid receptor density and on SNC80-induced locomotor stimulation and colonic transit inhibition in rats

1. To reduce the density of delta-opioid receptor protein, five antisense phosphorothioate oligodeoxynucleotides (aODN), targeting the three exons of rat delta-opioid receptor mRNA (DOR), were injected twice daily for 4 days or continuously infused for 7 days into brain lateral ventricles (i.c.v.) of Sprague-Dawley rats. Rats acting as controls were infused or injected with a mismatch sequence (mODN) of each aODN. The density of opioid receptors in rat brain membranes was measured by saturation binding experiments using selective ligands for delta, mu and kappa opioid receptors. 2. aODNs injected twice a day for 4 days left rat brain delta-opioid receptor density unchanged. The ODN targeting the DOR nucleotide sequence 280 - 299 (aODN280 - 299, exon 2), decreased brain delta-opioid receptor density significantly more than aODNs targeting exon 1 (aODN239 - 258), exon 2 (aODN361 - 380), or exon 3 (aODN741 - 760) (to 52% vs 79, 72, and 68%). None of the aODNs to the DOR changed the brain density of mu- or k-opioid receptors. 3. When in a novel environment (but not when kept in their home cages), the locomotor activity of aODN280 - 299 treated rats was significantly lower than that of saline or mODN treated rats. The delta-opioid agonist SNC80 (5 mg kg-1, s.c.) significantly and potently stimulated locomotion and delayed colonic propulsion in saline- and mODN-infused rats, but left motor behaviour and colonic transit of delta-knockdown rats unchanged. 4. The baseline nociceptive threshold and the antinociceptive response to morphine were unchanged in delta-knockdown rats.

In vivo modulation of G proteins and opioid receptor function by antisense oligodeoxynucleotides

The work in our laboratory has been designed to characterize the transducer mechanisms coupled to neurotransmitter receptors in the plasma membrane. Particular attention has been paid to the physiological/pharmacological effects mediated by the opioid system. Antisense oligodeoxynucleotides have proved useful in correlating opioid receptor clones with those defined pharmacologically. The involvement of the cloned opioid receptors mu, delta, and kappa in analgesia has been determined by means of in vivo injection of ODNs directed to the receptor mRNAs. Using this strategy the classes of G-transducer proteins regulated by each type/subtype of opioid receptor in the promotion of antinociception have also been characterized. After displaying different patterns of binding to their receptors, opioids trigger a variety of intracellular signals. The physiological implications and therapeutic potential of these findings merit consideration.

Use of selective antagonists and antisense oligonucleotides to evaluate the mechanisms of BUBU antinociception

Evidence suggests that the antinociceptive effects of selective delta-opioid receptor agonists may involve an activation of the mu-receptor in some experimental conditions. The aim of this study was to clarify the receptors involved in the antinociceptive responses of the selective and systemically active delta-opioid receptor agonist Tyr-D-Ser-(O-tert-butyl)-Gly-Phe-Leu-Thr-(O-tert-butyl) (BUBU). The antinociception induced by systemic (i.v.) or central (i.c.v.) administration of BUBU was measured in the hot plate (jumping and paw lick latencies) and tail immersion tests in mice. In both tests, the responses were more intense when BUBU was administered by central route. The pre-treatment with the mu-opioid receptor antagonist cyprodime blocked the effects induced by central BUBU in the hot plate and tail immersion tests. The delta-opioid receptor antagonist naltrindole had no effect on BUBU-induced antinociception in the hot plate but decreased BUBU responses in the tail immersion test. Further evidence for this dual receptor action of BUBU was demonstrated by using antisense oligodeoxynucleotides. Thus, a reduction in central BUBU-induced antinociception was observed in the tail immersion test after the administration of antisense probes that selectively blocked the expression of mu- or delta-opioid receptors. These findings clearly indicate using a dual pharmacological and molecular approach that BUBU mediates its antinociceptive effects via activation of both mu- and delta-opioid receptors.

delta opioid receptor modulation of several voltage-dependent Ca(2+) currents in rat sensory neurons

Endogenous enkephalins and delta opiates affect sensory function and pain sensation by inhibiting synaptic transmission in sensory circuits via delta opioid receptors (DORs). DORs have long been suspected of mediating these effects by modulating voltage-dependent Ca(2+) entry in primary sensory neurons. However, not only has this hypothesis never been validated in these cells, but in fact several previous studies have only turned up negative results. By using whole-cell current recordings, we show that the delta enkephalin analog [D-Ala(2), D-Leu(5)]-enkephalin (DADLE) inhibits, via DORs, L-, N-, P-, and Q-high voltage-activated Ca(2+) channel currents in cultured rat dorsal root ganglion (DRG) neurons. The percentage of responding cells was remarkably high (75%) within a novel subpopulation of substance P-containing neurons compared with the other cells (18-35%). DADLE (1 microM) inhibited 32% of the total barium current through calcium channels (I(Ba)). A delta (naltrindole, 1 microM), but not a mu (beta-funaltrexamine, 5 microM), antagonist prevented the DADLE response, whereas a DOR-2 subtype (deltorphin-II, 100 nM), but not a DOR-1 (DPDPE, 1 microM), agonist mimicked the response. L-, N-, P-, and Q-type currents contributed, on average, 18, 48, 14, and 16% to the total I(Ba) and 19, 50, 26, and 20% to the DADLE-sensitive current, respectively. The drug-insensitive R-type current component was not affected by the agonist. This work represents the first demonstration that DORs modulate Ca(2+) entry in sensory neurons and suggests that delta opioids could affect diverse Ca(2+)-dependent processes linked to Ca(2+) influx through different high-voltage-activated channel types.

Differential knockdown of delta-opioid receptor subtypes in the rat brain by antisense oligodeoxynucleotides targeting mRNA

Two antisense oligodeoxynucleotides (A-ODN), targeting delta-opioid receptor mRNA (DOR) and two mismatch ODN sequences (mODN) were continuously infused for 24 days into the lateral brain ventricles of Wistar rats. The density of delta-opioid receptors in rat brain homogenates was measured by saturation binding experiments using four selective ligands, two agonists ([D-Ala2, Glu4]-deltorphin and DPDPE) and two antagonists (Dmt-Tic-OH and naltrindole), and by immunoblotting SDS solubilized receptor protein. In brain membranes of mODN or saline-infused rats, the rank order of delta-opioid receptor density, calculated by Bmax values of the four delta-opioid receptor ligands, was: [D-Ala2, Glu4]deltorphin approximately Dmt-Tic-OH approximately naltrindole (86-118 fmo/mg protein) > DPDPE (73.6+/-6.3 fmol/mg protein). At the end of the 24 day infusion of A-ODN targeting DOR nucleotide sequence 280299 (A-ODN280-299), the Bmax of DPDPE (62.4+/-3.2 fmol/mg protein) was significantly higher than that of Dmt-Tic-OH (31.5+/-3.9 fmol/mg protein). Moreover, both the Kd value for DPDPE saturation binding and the Ki value for Dmt-Tic-OH displacement by DPDPE were halved. In contrast, an A-ODN treatment targeting exon 3 (A-ODN741-760) decreased the specific binding of [D-Ala2, Glu4]deltorphin and Dmt-Tic-OH significantly less (67%-81%) than the binding of DPDPE (53%), without changes in DPDPE Ki and KD values. No A-ODN treatment modified the specific binding of the micro-opioid agonist DAMGO and of the k-selective opioid receptor ligand U69593. On the Western blot of solubilized striatum proteins, A-ODN(280-299) and A-ODN(741-760) downregulated the levels of the DOR protein, whereas the corresponding mODN were inactive. The 24-day infusion of A-ODN(280-299) inhibited the rat locomotor response to [D-Ala2, Glu4]deltorphin but not to DPDPE. Intracerebroventricular (i.c.v.) infusion of A-ODN(741-760) reduced the locomotor responses to both delta-opioid receptor agonists, whereas mODN infusion never affected agonist potencies. In conclusion, these results demonstrate that 24-day continuous i.c.v. infusion of A-ODN targeting the nucleotide sequence 280-299 of DOR can differentially knockdown delta1 and delta2 binding sites in the rat brain.

Brain as a unique antisense environment

During the last few years, antisense oligodeoxyribonucleotides (asODN) have become a commonly used tool for blocking of gene expression in the mammalian central nervous system. Successful gene inhibition has been reported for such diverse targets as those encoding neurotransmitter receptors, neuropeptides, trophic factors, transcription factors, cytokines, transporters, ion channels, and others. This review presents a discussion of recent studies on ODN in the brain, with a focus on specific approaches taken by the researchers in this field and especially on peculiar features of this organ as a milieu for asODN action. It is concluded that from the presented literature survey no coherent view on how to rationally design ODN for brain studies has emerged.

What peptides these deltorphins be

The deltorphins are a class of highly selective delta-opioid heptapeptides from the skin of the Amazonian frogs Phyllomedusa sauvagei and P. bicolor. The first of these fascinating peptides came to light in 1987 by cloning of the cDNA of from frog skins, while the other members of this family were identified either by cDNA or isolation of the peptides. The distinctive feature of deltorphins is the presence of a naturally occurring D-enantiomer at the second position in their common N-terminal sequence, Tyr-D-Xaa-Phe, comparable to dermorphin, which is the prototype of a group of mu-selective opioids from the same source. The D-amino acid and the anionic residues, either Glu or Asp, as well as their unique amino acid compositions are responsible for the remarkable biostability, high delta-receptor affinity, bioactivity and peptide conformation. This review summarizes a decade of research from many laboratories that defined which residues and substituents in the deltorphins interact with the delta-receptor and characterized pharmacological and physiological activities in vitro and in vivo. It begins with a historical description of the topic and presents general schema for the synthesis of peptide analogues of deltorphins A, B and C as a means to document the methods employed in producing a myriad of analogues. Structure activity studies of the peptides and their pharmacological activities in vitro are detailed in abundantly tabulated data. A brief compendium of the current level of knowledge of the delta-receptor assists the reader to appreciate the rationale for the design of these analogues. Discussion of the conformation of these peptides addresses how structure leads to further hypotheses regarding ligand receptor interaction. The review ends with a broad discussion of the potential applications of these peptides in clinical and therapeutic settings.

Evidence for the existence of the beta-endorphin-sensitive "epsilon-opioid receptor" in the brain: the mechanisms of epsilon-mediated antinociception

Recently, mu-, delta- and kappa-opioid receptors have been cloned and relatively well-characterized. In addition to three major opioid receptor types, more extensive studies have suggested the possible existence of other opioid receptor types that can be classified as non-mu, non-delta and non-kappa. Based upon anatomical and binding studies in the brain, the sensitive site for an endogenous opioid peptide, beta-endorphin, has been postulated to account for the unique characteristics of the opioid receptor defined as a putative epsilon-opioid receptor. Many epsilon-opioid receptors are functionally coupled to G-proteins. The functional epsilon-opioid receptors in the brain are stimulated by bremazocine and etorphine as well as beta-endorphin, but not by selective mu-, delta- or kappa-opioid receptor agonists. Epsilon-opioid receptor agonists injected into the brain produce profound antinociception. The brain sites most sensitive to epsilon-agonist-induced antinociception are located in the caudal medial medulla such as the nucleus raphe obscures, nucleus raphe pallidus and the adjacent midline reticular formation. The stimulation of epsilon-opioid receptors in the brain facilitates the descending enkephalinergic pathway, which probably originates from the brainstem terminating at the spinal cord. The endogenous opioid Met-enkephalin, released in the spinal cord by activation of supraspinal epsilon-opioid receptors, stimulates spinal delta2-opioid receptors for the production of antinociception. It is noteworthy that the epsilon-opioid receptor-mediated pain control system is different from that of other opioid systems. Although there appears to be no epsilon-selective ligand currently available, these findings provide strong evidence for the existence of the putative epsilon-opioid receptor and its unique function in the brain.

G protein-coupled receptors: functional and mechanistic insights through altered gene expression

G protein-coupled receptors (GPCRs) comprise a large and diverse family of molecules that play essential roles in signal transduction. In addition to a constantly expanding pharmacological repertoire, recent advances in the ability to manipulate GPCR expression in vivo have provided another valuable approach in the study of GPCR function and mechanism of action. Current technologies now allow investigators to manipulate GPCR expression in a variety of ways. Graded reductions in GPCR expression can be achieved through antisense strategies or total gene ablation or replacement can be achieved through gene targeting strategies, and exogenous expression of wild-type or mutant GPCR isoforms can be accomplished with transgenic technologies. Both the techniques used to achieve these specific alterations and the consequences of altered expression patterns are reviewed here and discussed in the context of GPCR function and mechanism of action.

Antisense oligodeoxynucleotide to delta opioid receptors attenuates morphine dependence in mice

The effect of intracerebroventricular (i.c.v.) treatment with antisense oligodeoxynucleotide (A-oligo) to delta opioid receptor mRNA on the morphine-induced place preference and naloxone-precipitated jumping was examined in morphine-dependent mice. Morphine (5 mg/kg, s.c.) produced a significant place preference. I.c.v. pretreatment with A-oligo (0.01-1 microg/mouse) dose-dependently attenuated this morphine (5 mg/kg, s.c.)-induced place preference, while mismatched oligodeoxynucleotide (M-oligo; 1 microg/mouse, i.c.v.) was ineffective. Naloxone (3 mg/kg, s.c.) precipitated jumping in morphine-dependent mice. I.c.v. pretreatment with A-oligo (1 microg/mouse) attenuated this naloxone (3 mg/kg, s.c.)-precipitated jumping in morphine-dependent mice, while M-oligo (1 microg/mouse, i.c.v.) was ineffective. These data demonstrate that the selective reduction in supraspinal delta opioid receptor function caused by pretreatment with A-oligo attenuated the morphine-induced place preference and naloxone-precipitated jumping in morphine-dependent mice, suggesting that the rewarding effect of and physical dependence on morphine may be modulated by central delta opioid receptors.

Antisense strategies in neurobiology

The use of antisense oligodeoxynucleotides, targeted to the transcripts encoding biologically active proteins in the nervous system, provides a novel and highly selective means to further our understanding of the function of these proteins. Recent studies of these agents also suggest the possibility of their being used therapeutically for a variety of diseases involving neuronal tissue. In this paper we review studies showing the in vitro and in vivo effects of antisense oligodeoxynucleotides as they relate to neurobiological functions. Particular attention is paid to the behavioral and biochemical effects of antisense oligodeoxynucleotides directed to the various subtypes of receptors for the neurotransmitter dopamine. An example is also provided showing the effects of a plasmid vector expressing an antisense RNA targeted to the calmodulin mRNAs in the PC12 pheochromocytoma cell line. The advantages of antisense oligodeoxynucleotides over traditional pharmacological treatments are assessed, and the advantages of using vectors encoding antisense RNA over the use of antisense oligodeoxynucleotides are also considered. We also describe the criteria that should be used in designing antisense oligodeoxynucleotides and several controls that should be employed to assure their specificity of action.

Effect of supraspinal antisense oligodeoxynucleotide treatment on delta-opioid receptor mRNA levels in mice

Studies in vivo demonstrate that antisense oligodeoxynucleotide (ODN) treatment specifically reduces the functions mediated by numerous central nervous system (CNS) receptors, including opioid receptors. However, the effects of antisense ODN on the opioid receptor mRNA target, itself are rarely examined. In the present study, the effect of supraspinal antisense ODN administration on delta-opioid receptor (DOR) mRNA levels in selected CNS regions, was investigated in mice. ODN targeting a 20-nucleotide sequence of the DOR mRNA transcript was administered by intracerebroventricular (i.c.v.) injection twice daily for 3 days. First, to confirm that antisense ODN treatment decreases DOR function in this system, antinociception produced by DOR-selective agonist [D-Ala2]deltorphin II was assessed on day 4. A 2-fold reduction in [D-Ala2]deltorphin II potency was revealed in antisense ODN-treated mice compared to mice receiving control treatments. DOR mRNA levels in selected CNS regions which either mediate antinociception; medial thalamus (MThal), periaqueductal gray (PAG), frontal cortex (FCtx) and spinal cord (SpC) or exhibit relatively high levels of DOR mRNA; nucleus accumbens (Acb) and caudate-putamen (CPu) were then quantitated by solution hybridization. Levels of DOR mRNA in antisense ODN-treated mice were not different from levels in mice treated with saline vehicle, which ranged from 0.07 pg/microg total RNA in MThal and PAG to 0.26 pg/microg total RNA in CPu. These results are both consistent with previous reports that antisense oligodeoxynucleotide (ODN) treatment down-regulates DOR protein in vivo and indicate that this down-regulation is not associated with altered DOR mRNA levels.

Blockade of clomipramine and amitriptyline analgesia by an antisense oligonucleotide to mKv1.1, a mouse Shaker-like K+ channel

The effect of an antisense oligonucleotide to the K+ channel coding mKv1.1 mRNA on antinociception induced by the tricyclic antidepressants, clomipramine (20-35 mg kg(-1) s.c.) and amitriptyline (10-25 mg kg(-1) s.c.), was investigated in the mouse hot-plate test. Antisense oligonucleotide (0.5-1.0-2.0-3.0 nmol per i.c.v. injection) produced a dose-dependent inhibition of clomipramine and amitriptyline antinociception 72 h after the last i.c.v. injection. The sensitivity to both analgesic drugs returned 7 days after antisense oligonucleotide injection, indicating the absence of irreversible damage or toxicity. Treatment with a degenerated oligonucleotide did not modify the clomipramine- and amitriptyline-induced antinociception in comparison with that in naive (unpretreated controls), vector and saline i.c.v.-injected mice. A quantitative reverse transcription-polymerase chain reaction (RT-PCR) study demonstrated a reduction in mRNA levels only in the antisense oligonucleotide treated group. Antisense oligonucleotide, degenerated oligonucleotide or vector pretreatment, in the range of doses used, did not produce any behavioural impairment as revealed by the mouse rotarod and hole-board tests. The present results indicate that modulation of the mKv1.1 K+ channel plays an important role in the central analgesia induced by the tricyclic antidepressants, clomipramine and amitriptyline.

Antisense mapping DOR-1 in mice: further support for delta receptor subtypes

In contrast to the pharmacological studies implicating delta-opioid receptor subtypes, cloning studies have identified only a single cDNA encoding a delta receptor, DOR-1. Antisense studies have established the importance of DOR-1 in delta analgesia in mice. Antisense mapping extends this approach to include oligodeoxynucleotides which are targeted against each of the exons of the gene. Five different antisense oligodeoxynucleotides based upon the three DOR-1 exons all block both spinal and supraspinal analgesic actions of the delta2 ligand [D-Ala2,Glu4]deltorphin, consistent with the suggestion that DOR-1 encodes the delta2 receptor. At the spinal level, [D-Pen2,D-Pen5]enkephalin (DPDPE) acts also acts through delta2 receptors and all the antisense probes block spinal DPDPE analgesia. However, supraspinally only the two antisense probes targeting exon 3 block DPDPE analgesia. The remaining three antisense probes based upon exons 1 and 2 are inactive. Thus, the delta receptors responsible for spinal and supraspinal DPDPE analgesia can be discriminated at the molecular level by antisense mapping.

The effect of pretreatment with a delta 2-opioid receptor antisense oligodeoxynucleotide on the recovery from acute antinociceptive tolerance to delta 2-opioid receptor agonist in the mouse spinal cord

1. An intrathecal (i.t.) injection of a selective delta 2-opioid receptor agonist, [D-Ala2]deltorphin II, produced an acute antinociceptive tolerance to the antinociceptive effect of a subsequent i.t. challenge of [D-Ala2]deltorphin II. This acute tolerance lasted 3 to 9 h and completely subsided by 12 h. The experiments were designed to examine the effect of pretreatment with an antisense oligodeoxynucleotide to delta 2-opioid receptor mRNA (delta-AS oligo) on the recovery from tolerance to [D-Ala2]deltorphin II-induced antinociception in male ICR mice. 2. Pretreatment with delta-AS oligo (1.63 to 163 pmol, i.t.), but not mismatched oligo (MM oligo) (163 pmol), prevented the recovery from acute tolerance to [D-Ala2]deltorphin II-induced antinociception in a dose-dependent manner. However, treatment with delta-AS oligo (163 pmol) did not prevent the recovery from tolerance to either the mu-opioid receptor agonist [D-Ala2,NMePhe4,Gly(ol)5]enkephalin (DAMGO) or the kappa-opioid receptor agonist U50,488H, indicating subtype specificity in the mechanism by which delta-AS oligo inhibits recovery from delta 2-opioid tolerance. 3. Treatment with [D-Ala2]deltorphin II (i.t.) significantly reduced the binding of [tyrosyl-3,5-(3)H(N)]-Tyr-D-Ser-Gly-Phe-Leu-Thr ([3H]-DSLET), a delta 2-opioid receptor agonist ligand, in the spinal cord 3 h after treatment, but binding returned to control levels by 24 h after treatment. However, [3H]-DSLET binding in the spinal cord remained significantly reduced at 24 h if delta-AS oligo (163 pmol) was coadministered with [D-Ala2]deltorphin II (6.4 nmol). 4. Based on these findings, it is concluded that a single stimulation of spinal cord delta 2-opioid receptors by intrathecally-administered [D-Ala2]deltorphin II induces a long-lasting desensitization of delta 2-opioid receptors to [D-Ala2]deltorphin II. Recovery from delta 2-opioid receptor-mediated antinociceptive tolerance apparently depends on replenishment by newly synthesized delta 2-opioid receptor protein rather than immediate reversal of delta 2-opioid receptors.

The effect of mu-opioid receptor antisense on morphine potency and antagonist-induced supersensitivity and receptor upregulation

The present study examined the effect of in vivo antisense oligodeoxynucleotide treatment on naltrexone (NTX)-induced functional supersensitivity and mu-opioid receptor up-regulation in mice. On day 1 mice were implanted S.C. with a NTX or placebo pellet and injected I.T. and I.C.V. with dH2O or oligodeoxynucleotides. The oligodeoxynucleotides were designed so that they were either perfectly complementary to the first 18 bases of the coding region of mouse mu-opioid receptor mRNA, or had one (Mismatch-1) or four (Mismatch-4) mismatches. On days 3, 5, 7, and 9, mice were again injected I.T. and I.C.V. with dH2O or one of the oligodeoxynucleotides. After the final injections on day 9, placebo and NTX pellets were removed, and 24 h later mice were tested for morphine analgesia or sacrificed for saturation binding studies ([3H]DAMGO). Naltrexone increased the analgesic potency of morphine in dH2O treated mice by approximately 70%. In binding studies, NTX significantly increased density of brain (approximately 60%) and spinal cord (approximately 140%) mu-opioid receptors without affecting affinity. The mu-opioid antisense and the oligodeoxynucleotide with one mismatch (Mismatch-1) significantly reduced the potency of morphine by approximately twofold in placebo-treated mice. The oligodeoxynucleotide with four mismatches (Mismatch-4) did not significantly alter morphine potency. When placebo-treated mice were treated with either the antisense to the mouse mu-opioid receptor, Mismatch-4 or Mismatch-1 there were no significant changes in the density of mu-opioid receptors. Thus, mu-opioid antisense significantly reduced morphine potency without changing mu-opioid receptor density. When NTX and oligodeoxynucleotide treatments were combined, there was no change in NTX-induced supersensitivity and mu-opioid receptor upregulation. These data suggest that opioid antagonist-induced supersensitivity and upregulation of mu-opioid receptors does not involve changes in gene expression.

Antisense oligodeoxynucleotide to delta opioid receptors blocks cocaine-induced place preference in mice

The effect of intracerebroventricular (i.c.v.) treatment with antisense oligodeoxynucleotide (A-oligo) to delta opioid receptor mRNA on cocaine-induced place preference was examined in mice. Cocaine (10 mg/kg, s.c.) produced a significant place preference. I.c.v. treatment with A-oligo (0.001-1 microg/mouse) dose-dependently attenuated the cocaine (10 mg/kg, s.c.)-induced place preference, although mismatched oligodeoxynucleotide (1 microg/mouse, i.c.v.) was ineffective. In the present study, we found that the selective reduction in number and/or function of central delta opioid receptors by A-oligo suppresses the cocaine-induced place preference. These results suggest that the conditioned reward by cocaine may be partially mediated by central delta opioid receptors.

Antisense confirmation of mu- and kappa-opioid receptor mediation of morphine's effects on body temperature in rats

Previous studies showed that parenterally administered morphine at 4-16 mg/kg markedly increased body temperature in the rat, but higher doses of morphine (> or = 30 mg/kg, subcutaneously, sc) caused a profound decrease in body temperature. Based on the use of selective opioid agonists and antagonists, we postulated that these effects were due to morphine's actions on mu and kappa receptors, respectively. In the present study, we sought to determine whether an antisense (AS) oligodeoxynucleotide (oligo) against cloned mu or kappa opioid receptors could affect morphine-induced body temperature changes. AS oligos were directed against nucleotides 1-18 of the coding region of the mu receptor and 4-21 of the coding region of the kappa receptor. Male SD rats were surgically implanted with intracerebroventricular (icv) cannulae. Rats received icv injections of vehicle or oligo in the animal colony room on days 1, 3 and 5. Either AS oligo or missense (MS) oligo was infused in a volume of 5 microliters over 30 s to freely moving animals. On day 6, the rats were tested. The results showed that icv treatment with an AS oligo against mu opioid receptors, but not an MS oligo against the mu opioid receptor or an AS oligo against the kappa opioid receptor, significantly attenuated the hyperthermia normally produced by a relatively low dose of morphine administered sc. In addition, treatment with an AS oligo against kappa receptors, but not an MS oligo against kappa opioid receptor or an AS oligo against the mu opioid receptor, significantly blocked the hypothermia induced by a high dose of morphine. This study confirms our earlier postulate that morphine at 4 mg/kg, sc, induces an increase in body temperature primarily via mu opioid receptors in the brain and a high dose (30 mg/kg) of morphine administered sc produces a decrease primarily through kappa opioid receptors in the brain.

Antisense oligodeoxynucleotide to a delta-opioid receptor messenger RNA selectively blocks the antinociception induced by intracerebroventricularly administered delta-, but not mu-, epsilon- or kappa-opioid receptor agonists in the mouse

An antisense oligodeoxynucleotide to delta-opioid receptor messenger RNA was utilized to block the expression of mouse delta-opioid receptors for antinociception. The antinociception was measured by the tail-flick test in male ICR mice. Pretreatment with delta-antisense oligodeoxynucleotide (163 pmol) given intracerebroventricularly twice a day for one to four days produced a time-dependent inhibition of the tail-flick response induced by intracerebroventricularly administered (D-Ala2)deltorphin II (12.8 nmol). The (D-Ala2)deltorphin II-induced antinociception was significantly attenuated after three to four days of the delta-antisense oligodeoxynucleotide treatment, remained attenuated for two days and gradually recovered to the control level in four to 10 days after cessation of the pretreatment with delta-antisense oligodeoxynucleotide. Pretreatment with delta-antisense oligodeoxynucleotide (163 pmol) twice a day for four days markedly attenuated the antinociception induced by intracerebroventricularly administered (D-Ala2)deltorphin II and, to a lesser extent, by D-Pen2-D-Pen5-enkephalin and morphine, but not by (D-Ala2-MePhe4-Gly(ol)5)enkephalin, beta-endorphin or U50,488H. Mismatched oligodeoxynucleotide (163 pmol) was ineffective against the antinociception induced by these opioids. Our results provide the evidence that the cloned delta-opioid receptor is related to the pharmacologically classified delta 2-opioid receptor, and the antinociception induced by (D-Ala2)deltorphin II and, at least in part, by D-Pen2-D-Pen5-enkephalin and morphine given intracerebroventricularly is mediated by the stimulation of delta 2-opioid receptors. However, delta 2-opioid receptors are not involved in the antinociception induced by beta-endorphin, (D-Ala2-MePhe4-Gly(ol)5)enkephalin or U50,488H given intracerebroventricularly.

Use of a mu-antisense oligodeoxynucleotide as a mu opioid receptor noncompetitive antagonist in vivo

We examined whether mu-antisense (AS) oligodeoxynucleotide (oligo) treatment can be used in a manner similar to the mu-selective irreversible antagonist beta-funaltrexamine (beta-FNA) for in vivo pharmacology. Rats were injected intracerebroventricularly (icv) with a mu-AS or a missense (MS) oligo on days 1, 3, 5, 7, and 9 and were tested for the antinociceptive effect of sc injection of morphine on days 2, 4, 6, 8, and 10 in the cold water tail-flick (CWT) test. In another set of experiments, rats were also tested for the antinociceptive action of morphine twenty-four hours after icv injection of beta-FNA. Both beta-FNA and mu-AS produced rightward shifts in the dose-effect curves of morphine. In addition, pretreatment with 2.5 micrograms or more of beta-FNA or the mu-AS oligo for 5-9 days (but not for 1-3 days) reduced the maximal analgesic effect of morphine. The approximate fraction of functional receptor remaining for morphine was determined with the method of Furchgott to be 49.5% following 2.5 micrograms of beta-FNA; that after 5 days of the mu-AS oligo treatment was 50.8%. The results suggest that the mu-AS oligo can be used in the same manner as highly selective, irreversible mu opioid receptor ligands. Thus, properly designed AS oligos against receptors are of particular benefit when irreversible antagonists are not available. AS oligos represent a new class of selective and powerful pharmacological antagonists.

Delta-Opioid receptor modulation of the release of substance P-like immunoreactivity in the dorsal horn of the rat following mechanical or thermal noxious stimulation

The present study was undertaken to investigate the effects of the opioid peptide Met-enkephalin (met-enk) on the release of substance P-like immunoreactivity (SPLI) in the lumbar dorsal horn during the application of a noxious mechanical or thermal stimulus to the ipsilateral hind paw and lower limb of the rat. A push-pull cannula was introduced to the lumbar dorsal horn in non-anesthetized decerebrate/spinal transected rats. The dorsal horn was perfused with artificial CSF and the collected perfusates were assayed for SPLI using radioimmunoassay. A noxious mechanical or thermal stimulus was applied to different areas of the ipsilateral hind paw and lower limb. Met-enk (500 nM) applied to the dorsal horn through the perfusate reduced the basal release of SPLI by 29 +/- 9% and prevented the increase in the release of SPLI evoked by the noxious mechanical or thermal stimulus. The effect of met-enk was blocked by the selective delta-opioid receptor antagonist naltrindole (500 nM). Naltrindole (NTD) alone elicited a 75 +/- 30% increase in the basal release of SPLI. These data show that met-enk inhibits the thermally or mechanically evoked release of SPLI in the dorsal horn by activating the delta opioid receptors. These receptors are also involved in the tonic spinal regulation of the release of SPLI.

Role of protein kinase C in desensitization of spinal delta-opioid-mediated antinociception in the mouse

1. Receptor phosphorylation and down-regulation by protein kinases may be a key event initiating desensitization. The present studies were designed to investigate the effect of a potent protein kinase C (PKC) activator, phorbol 12,13-dibutyrate (PDBu), on antinociception induced by intrathecal (i.t.) administration of a selective delta-opioid receptor agonist [D-Ala2] deltorphin II in the male ICR mouse and on the specific binding of [3H]-[D-Ser2, Leu5]enkephalin-Thr6 (DSLET), a delta-opioid receptor ligand, in the crude synaptic membrane of the spinal cord. 2. Intrathecal (i.t.) pretreatment with PDBu at low doses, which injected alone did not affect the basal tail-flick latency, dose-dependently attenuated the antinociception induced by i.t. administration of [D-Ala2]deltorphin II. The attenuation of i.t.-administered [D-Ala2] deltorphin II-induced antinociception by PDBu was reversed in a dose-dependent manner by i.t. concomitant pretreatment with a specific PKC inhibitor, calphostin C. 3. In the binding experiment, incubation of the crude synaptic membrane of the spinal cord for 2 h at 25 degrees C with PDBu (0.03 to 10 microM) caused a dose-dependent inhibition of the [3H]-DSLET binding. Scatchard analysis of [3H]-DSLET binding revealed that PDBu at 10 microM displayed a 30.7% reduction in the number of [3H]-DSLET binding sites with no significant change in affinity, compared with the non-treatment control, indicating that the activation of membrane-bound PKC by PDBu causes a decrease in the number of specific delta-opioid agonist binding sites. 4. An i.t. injection of [D-Ala2]deltorphin II produced an acute antinociceptive tolerance to the antinociceptive effect of a subsequent i.t. challenge of [D-Ala2]deltorphin II. Concomitant pretreatment with calphostin C markedly prevented the development of acute tolerance to the i.t.-administered [D-Ala2]deltorphin II-induced antinociception. On the other hand, a highly selective protein kinase A (PKA) inhibitor, KT5720, did not have any effect on the development of acute tolerance to [D-Ala2]deltorphin II antinociception. 5. These findings suggest that a loss of specific delta-agonist binding by the activation of PKC by PDBu is involved in the PDBu-induced antinociceptive unresponsiveness to delta-opioid receptor agonist in the mouse spinal cord. Based on the acute tolerance studies, we propose that PKC, but not PKA, plays an important role in the process of homologous desensitization of the spinal delta-opioid receptor-mediated antinociception.

Treatment with an antisense oligodeoxynucleotide to the GABAA receptor gamma 2 subunit increases convulsive threshold for beta-CCM, a benzodiazepine "inverse agonist', in rats

The gamma 2 subunit of the gamma-aminobutyric acid type-A (GABAA) receptor is associated with the actions of benzodiazepines and related drugs. A phosphorothioate-modified antisense oligodeoxynucleotide directed against the gamma 2 subunit was given by i.c.v. injection (18 micrograms in 2 microliters saline) to male Sprague-Dawley rats every 12 h for 3 days. Controls received the corresponding sense oligodeoxynucleotide. 4-6 h after the last i.c.v. treatment, rats were given methyl-beta-carboline-3-carboxylate (beta-CCM), a benzodiazepine "inverse agonist', by slow i.v. infusion. Compared to naive rats, the beta-CCM threshold dose was not affected by the sense oligodeoxynucleotide, but was increased 87% in antisense oligodeoxynucleotide-treated rats. The treatment had no effect on the seizure threshold for picrotoxin. Both antisense and sense oligodeoxynucleotide treatments slightly increased the threshold for strychnine seizures. The results suggest that antisense oligodeoxynucleotide treatment altered GABAA receptor composition and interfered with the actions of a benzodiazepine receptor ligand in vivo, and may provide a tool for studying regulation of receptor structure and function.

Use of antisense oligodeoxynucleotide to determine delta-opioid receptor involvement in [D-Ala2]deltorphin II-induced locomotor hyperactivity

Intracerebroventricularly (i.c.v.)-administered [D-Ala2]deltorphin II (20 micrograms) produced a marked locomotor hyperactivity in male ICR mice. The locomotor hyperactivity induced in response to i.c.v. [D-Ala2]deltorphin II (20 micrograms) was suppressed by pretreatment with naltriben (NTB, 10 micrograms) but not 7-benzylidene naltrexone (BNTX, 1 microgram) and D-Phe-Cys-Tyr-D-Try-Orn-Thr-Phe-Thr-NH2 (CTOP, 100 ng). The influence of antisense oligodeoxynucleotide to delta-opioid receptor mRNA (delta-AS oligo) or a mismatch oligodeoxynucleotide (MM oligo) on the locomotor hyperactivity induced by [D-Ala2]deltorphin II was determined. Groups of mice pretreated i.c.v. with delta-AS oligo (1 microgram), MM oligo (1 microgram) or saline (4 microliters) once a day for 3 days, were injected i.c.v. [D-Ala2]deltorphin II (10 or 20 micrograms) and the locomotor response to [D-Ala2]deltorphin II was measured. The locomotor hyperactivity of i.c.v. [D-Ala2]deltorphin II (10 or 20 micrograms) were significantly suppressed by i.c.v. pretreatment with delta-AS oligo but not MM oligo. The present results indicate that pretreatment with delta-AS oligo suppresses mouse locomotor hyperactivity produced by stimulation of delta 2-opioid receptors in the brain.

Antisense oligodeoxynucleotides against the MOR-1 clone alter weight and ingestive responses in rats

MOR-1 encodes a mu receptor. In an effort to establish the relationship of this cloned opioid receptor with ingestive behavior and analgesia in rats, the present study examined the actions of four antisense oligodeoxynucleotides aimed at exons 1 (AS1), 2 (AS2), 3 (AS3) and 4 (AS4) of the MOR-1 clone, as well as a mismatch antisense sequence (MS1). Rats were administered intracerebroventricular injections (10 micrograms/2 microliters) of each of the oligodeoxynucleotides on days 1, 3 and 5. Body weight and spontaneous food and water intake were monitored daily. In addition, 2-deoxy-D-glucose (2DG)-induced hyperphagia, central Angiotensin II (ANG-II) induced hyperdipsia and central morphine analgesia were examined 24 h following the last antisense injection. AS1, AS2, AS3 and AS4 each significantly reduced body weight (7-17 g), food intake (8-13 g) and water intake (11-23 ml), while the vehicle or MS1 conditions significantly increased weight (9-20 g) and produced smaller reductions (2-4 g) in food intake. None of the AS probes altered the magnitude of either 2DG-induced hyperphagia or ANG-II-induced hyperdipsia. Central morphine analgesia was reduced by pretreatment with AS1 and AS4, but not AS2, AS3 or MS1. The sensitivity of general feeding to all four exons suggest that the receptor responsible for this action is encoded by the MOR-1 clone. The differences between feeding and morphine analgesia raise the possibility that these two actions are mediated through different mu receptor subtypes. Our results also demonstrate the viability of the in vivo antisense technique in modulating opioid-mediated ingestive responses.

Pretreatment with beta-endorphin facilitates the attenuation of delta-opioid receptor-mediated antinociception caused by delta-opioid receptor antisense oligodeoxynucleotide

Intracerebroventricular (i.c.v.) pretreatment of male ICR mice with beta-endorphin (0.6 nmol) or intrathecal (i.t.) pretreatment with antisense oligodeoxynucleotide to delta-opioid receptor mRNA (163 pmol) alone given 24 h earlier did not have any effect on i.t. administered delta-opioid receptor agonist [D-Ala2]deltorphin II (6.4 nmol)-induced antinociception. However, a concomitant i.c.v. pretreatments with beta-endorphin (0.08-0.6 nmol) and i.t. pretreatment with delta-opioid receptor antisense oligodeoxynucleotide (163 pmol) for 24 h dose-dependently attenuated i.t. challenged [D-Ala2]deltorphin II-induced antinociception. A concomitant i.c.v. pretreatment with mu-opioid receptor agonist [D-Ala2,N MePhe4,Gly(ol)5]enkephalin (DAMGO) or kappa-opioid receptor agonist U50,488H and i.t. pretreatment with delta-opioid receptor antisense oligodeoxynucleotide for 24 h did not affect i.t. challenged [D-Ala2]deltorphin II-induced antinociception. beta-Endorphin given supraspinally has been documented to release [Met5]enkephalin acting on delta-opioid receptors in the spinal cord. Our results indicate that supraspinal pretreatment with beta-endorphin selectively causes a loss of spinal delta-opioid receptor-mediated antinociception in mice receiving delta-opioid receptor antisense oligodeoxynucleotide.

Antisense oligodeoxynucleotide to a delta-opioid receptor blocks the antinociception induced by cold water swimming

The type of opioid receptors in the spinal cord involved in antinociception induced by cold water swimming (CWS) was studied in male ICR mice. Mice were submitted to CWS for 3 min and antinociception was measured 7 min after the CWS by the tail-flick test. Intrathecal (i.t.) injection of naltrindole (NTI, 5 micrograms) which blocked i.t. DPDPE ([D-Pen2,D-Pen5]en-kephalin, 5 micrograms)-induced antinociception, blocked the CWS-induced antinociception. On the other hand, i.t. injection of CTOP (D-Phe-Cys-Try-D-Try-Orn-Thr-Pen-Thr-NH2, 50 ng) and norbinaltorphimine (nor-BNI, 5 micrograms) which blocked i.t. DAMGO ([D-Ala2,NHPhe4,Gly-ol]enkephalin, 10 ng)- and U50,488H (trans(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)- cyclohexyl]benzeneacetamide, 75 micrograms)-induced antinociception, respectively, did not block CWS-induced antinociception. Intrathecal pretreatment with antisense oligodeoxynucleotide to delta-opioid receptor mRNA (delta-AS oligo, 163 pmol) once a day for 1 to 3 days caused a time-dependent attenuation of CWS-induced antinociception. delta-AS at doses from 1.6 to 163 pmol pretreated i.t. for 3 days caused a dose-dependent blockade of CWS-induced antinociception. However, i.t. pretreatment with mismatch oligodeoxynucleotide (MM oligo, 163 pmol) for 3 days did not affect the CWS-induced antinociception. The results indicate that CWS-induced antinociception is mediated by the stimulation of delta-opioid receptors in the spinal cord.

Stimulation of spinal delta-opioid receptors in mice selectively enhances the attenuation of delta-opioid receptor-mediated antinociception by antisense oligodeoxynucleotide

Intrathecal (i.t.) pretreatment of male ICR mice with antisense oligodeoxynucleotide to delta-opioid receptor mRNA once a day for 1-3 days caused a time-dependent attenuation of i.t. administered [D-Ala2]deltorphin II-induced antinociception as measured by the tail-flick test. The attenuation of the antinociception induced by i.t. administered [D-Ala2]deltorphin II, a delta-opioid receptor agonist, was enhanced by i.t. pretreatment for 1 day with [D-Ala2]deltorphin II, but not [D-Ala2,N MePhe4,Gly(ol)5]enkephalin (DAMGO), a mu-opioid receptor agonist, or U50,488H, a kappa-opioid receptor agonist, given together with antisense oligodeoxynucleotide to delta-opioid receptor mRNA. The present results indicate that stimulation of spinal delta-opioid receptors by i.t. injection of [D-Ala2]deltorphin II selectively causes a loss of delta-opioid receptor-mediated antinociception in mice pretreated with antisense oligodeoxynucleotide to delta-opioid receptor mRNA.

Antisense mapping the MOR-1 opioid receptor: evidence for alternative splicing and a novel morphine-6 beta-glucuronide receptor

Although MOR-1 encodes a mu opioid receptor, its relationship to the pharmacologically defined mu receptor subtypes has been unclear. Antisense mapping now suggests that these subtypes result from alternative splicing of MOR-1. Three oligodeoxynucleotide probes targeting exon 1 and another oligodeoxynucleotide directed against the coding region of exon 4 block supraspinal morphine analgesia, a mu1 action, while five of six oligodeoxynucleotides directed against exons 2 and 3 are inactive. Inhibition of gastrointestinal transit and spinal morphine analgesia, two mu2 actions, are blocked only by the probe against exon 4 and not by those directed against exon 1. In contrast, the analgesic actions of the extraordinarily potent mu drug morphine-6 beta-glucuronide are blocked by six different antisense oligodeoxynucleotides targeting exons 2 and 3, but not by those acting on exons 1 or 4. These results suggest that the mu1 and mu2 receptor subtypes originally defined in binding and pharmacological studies result from alternative splicing of MOR-1 while morphine-6 beta-glucuronide acts through a novel, previously unidentified receptor which is yet another MOR-1 splice variant.

Antisense oligodeoxynucleotides against mu- or kappa-opioid receptors block agonist-induced body temperature changes in rats

PL017 and dynorphin A1-17 were shown previously to cause a marked increase and a profound decrease in body temperature (Tb), respectively. In this study, we examined whether an antisense (AS) oligodeoxynucleotide (oligo) against cloned mu or kappa opioid receptors could block PL017- or dynorphin A-induced body temperature changes. Treatment with an AS oligo against mu receptors, but not sense (S) oligo, missense (MS) oligo or artificial cerebrospinal fluid (aCSF), abolished PL017-induced hyperthermia. In addition, treatment with an AS oligo against kappa receptors, but not S oligo, MS oligo or aCSF, greatly attenuated dynorphin A-induced hypothermia. This study further supports the notion that mu and kappa receptors mediate Tb regulation.

An antisense oligodeoxynucleotide to mu-opioid receptors inhibits mu-opioid receptor agonist-induced analgesia in rats

We examined effects of an antisense oligodeoxynucleotide against the mu-opioid receptor on mu-opioid receptor agonist-induced antinociception in the cold water (-3 degrees C) tail-flick test in rats. Rats were injected intracerebroventricularly (i.c.v.) with an antisense, sense or missense oligodeoxynucleotide or artificial cerebrospinal fluid on days 1, 3 and 5. On day 6, antinociceptive effects of opioid agonists were tested. Compared to the artificial cerebrospinal fluid treatment, the cumulative dose-effect curve for subcutaneous (s.c.) morphine was shifted to the right by the antisense oligodeoxynucleotide, but not by the missense oligodeoxynucleotide or the sense oligodeoxynucleotide treatment. Antisense oligodeoxynucleotide treatment reduced the analgesic effect of the mu-opioid receptor agonist PL017 ([N-MePhe3,D-Pro4]morphiceptin), but not the delta-opioid receptor agonist BW373U86 ((+/-)-4-((a-R*)-a-((2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazinyl)-3- hydroxybenzyl)-N,N-diethyl-benzamide) or the kappa-opioid receptor agonist spiradoline ((+/-)-(5a,7a,8b)-3,4-dichloro-N-methyl-N-[7-(1- pyrrolidinyl)-1-(oxaspiro-[4,5]dec-8-yl]benzeneacetamide monohydrochloride). The drugs were given by i.c.v. injection. These findings indicate that i.c.v. administration of a mu antisense oligodeoxynucleotide specifically blocks mu-, but not delta- or kappa-opioid receptor-mediated analgesia in the rat cold water tail-flick test.