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BEHAVIORAL PHARMACOLOGY
-Opioid Agonists: Differential Efficacy and Potency of SNC80, Its 3-OH (SNC86) and 3-Desoxy (SNC162) Derivatives in Sprague-Dawley Rats
Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan (E.M.J., E.B.E., J.R.T., J.H.W.); and Laboratory of Medicinal Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (J.E.F., K.C.R.)
Received October 8, 2003; accepted December 11, 2003.
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Abstract |
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 Top Abstract Materials and MethodsResultsDiscussionReferences |
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-opioid agonist SNC80 [(+)-4-[(
R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-methoxyphenyl)methyl]-N,N-diethylbenzamide] produces convulsions, antidepressant-like effects, and locomotor stimulation in rats. The present study compared the behavioral effects in Sprague-Dawley rats of SNC80 with its two derivatives, SNC86 [(+)-4-[(R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-hydroxyphenyl)methyl]-N,N-diethylbenzamide] and SNC162 [(+)-4-[(R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-phenyl)methyl]-N,N-diethylbenzamide], which differ by one functional group located in the 3-position of the benzylic ring. In behavioral measures, these three compounds demonstrated a rank order of potency and efficacy; SNC86 was the most potent and efficacious followed by SNC80 and then SNC162. In vitro, these compounds stimulated guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTP
S) binding in the caudate putamen of coronal brain slices from drug-naive rats as measured by in vitro autoradiography. In [35S]GTPS binding studies, SNC86 seemed to be a full agonist at the -opioid receptor; however, SNC162 demonstrated reduced stimulation compared with SNC86, consistent with partial agonist activity. Although SNC80 was not fully efficacious in [35S]GTPS autoradiography studies, it produced behavioral effects similar to those observed with SNC86, suggesting that the behavioral effects of SNC80 may be produced by its 3-hydroxy metabolite.
-opioid agonists produce a number of different behavioral effects. They produce convulsions in mice (Comer et al., 1993
; Hong et al., 1998), rats (Broom et al., 2002a,b), and monkeys (Dykstra et al., 1993; Negus et al., 1994; Pakarinen et al., 1995); stimulate locomotor activity in rats (Spina et al., 1998; Fraser et al., 2000; Broom et al., 2002a); produce antinociception in mice (Hong et al., 1998); and maintain discriminative control of behavior in rats (Stevenson et al., 2002) and monkeys (Dykstra et al., 1993; Negus et al., 1994; Pakarinen et al., 1995). In addition, recent studies reported that nonpeptidic, -opioid agonists demonstrated antidepressant-like effects in the forced swim test in rats (Broom et al., 2002a,b), and these compounds produced a greater magnitude of effect compared with known antidepressants such as desipramine and fluoxetine (Broom et al., 2002a). The antidepressant-like effects of the nonpeptidic -opioid agonists were mediated through the -opioid receptor, because these effects were blocked by the selective -opioid antagonist naltrindole.
Behavioral effects mediated by the -opioid receptor have been most thoroughly studied with the class of nonpeptidic -opioid receptor agonists known as the piperazinyl benzamides (SNC80 derivatives); however, few studies have compared the behavioral effects of these compounds within a given behavioral paradigm. Existing comparisons with SNC80 derivatives have only been made in drug discrimination paradigms in rats (Stevenson et al., 2002) and monkeys (Negus et al., 1998; Brandt et al., 1999). In addition to in vivo studies, these compounds have been compared in terms of binding affinities at the - and µ-opioid receptors and agonist activity in the mouse vas deferens and guinea pig ileum.
SNC80, SNC86, and SNC162 differ only at the 3-position of the benzylic ring (Fig. 1) and have demonstrated good binding affinity for cloned -opioid receptors (Knapp et al., 1996). SNC86, with a 3-hydroxyl substituent, was the least selective -opioid receptor agonist, but it had the highest affinity for the -opioid receptor. SNC162, with the 3-position unsubstituted, was the most selective with a µ/ ratio of 8770. SNC80 with a 3-methoxy group was less selective than SNC162 and had a lower affinity than SNC86.
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These findings were confirmed in studies in which SNC86 had high affinity for the -opioid receptor (IC50 = 1.49 nM) in rat brain membranes; but again, this compound was the least selective with a µ/ ratio for inhibition of radioligand ([3H][D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin and [3H][D-Ala2,D-Leu5]-enkephalin) binding of 6.5 (Calderon et al., 1997). These studies also demonstrated that SNC80 was less potent (IC50 = 2.88 nM) but was approximately 130-fold more selective for the -opioid receptor than SNC86. SNC162 (IC50 = 0.94 nM) was the most selective -opioid ligand with a µ/ ratio for inhibition of radioligand binding of greater than 2600. Similarly, in functional assays, SNC162 was approximately 4-fold less potent than SNC80 as determined by inhibition of contraction of electrically stimulated vas deferens of the mouse (Calderon et al., 1997).
As stated above, there are a limited number of studies that have compared the behavioral effects of SNC80 and its derivatives. In monkeys, SNC86 and SNC162 fully generalized in subjects trained to discriminate 0.32 mg/kg SNC80 (Brandt et al., 1999). In this study, SNC80 and SNC86 had similar ED50 values, but the ED50 value for SNC162 was 3-fold higher. Similarly, in rats trained to discriminate SNC80 from water, SNC162 produced SNC80-appropriate responding at a dose approximately 3-fold higher than the conditioning dose of SNC80; however, SNC162 only partially generalized for SNC80, suggesting partial agonist activity (Stevenson et al., 2002).
To further examine this suggestion, the present studies were designed to investigate efficacy and potency differences of piperazinyl benzamides in behavioral paradigms in Sprague-Dawley rats compared with ex vivo determinations of efficacy and potency. The study compared the behavioral effects of SNC80 and the two SNC80 derivatives (SNC86 and SNC162) that differ by one functional group located in the 3-position of the benzylic ring. SNC80, SNC86, and SNC162 were compared in [35S]GTPS binding assays in rat brain slices and in three different behavioral assays, measuring convulsions, antidepressant-like effects, and locomotor stimulation. These compounds were compared in observational studies to allow better evaluation of differences that may exist between these derivatives. The results demonstrated that SNC86 is the most potent and efficacious compound followed by SNC80 and then SNC162. In addition, these studies confirmed that the antidepressant-like effects of -opioid agonists are blocked by the selective -opioid antagonist naltrindole, but not by µ-selective doses of naltrexone or nonselective doses of naltrexone, indicating that the antidepressant-like effects are specific to the -opioid receptor system. Importantly, these studies demonstrated that efficacy differences between drugs can be evaluated in the forced swim test.
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Materials and Methods |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Procedures
Agonist-Stimulated [35S]GTPS Autoradiography. Agonist-stimulated [35S]GTPS autoradiography was performed as described previously (Sim et al., 1995). Naive rats were decapitated, and brains were removed and fresh frozen in 2-methylbutane (Sigma-Aldrich, St. Louis, MO) on dry ice. Coronal sections (20 µm) were cut in the striatum area of the brain on a cryostat maintained at -18°C, mounted on gelatin-subbed slides, and stored at -80°C for less than 4 weeks until use. Coronal striatal sections were rinsed in TME buffer (50 mM Tris-HCl, 3 mM MgCl2, 0.2 mM EGTA, 100 mM NaCl, and 0.1% bovine serum albumin, pH 7.4) at room temperature for 10 min. After this first incubation, slices were incubated in TME buffer containing 2 mM GDP and 9.5 mU/ml adenosine deaminase for 15 min at room temperature. Then, slices were incubated in TME buffer with GDP, adenosine deaminase, 0.04 nM [35S]GTPS, and varying concentrations of an agonist (either SNC80, SNC86, or SNC162) or no agonist or 10 µM cold GTPS (to determine nonspecific binding) for 2 h at room temperature. After the 2-h incubation, slices were rinsed twice for 2 min in cold 50 mM Tris buffer (pH 7.4) and once in distilled water for 1 min. Slides were air-dried for a few hours and exposed to film for 48 h in film cassettes together with 14C standards (Amersham Biosciences Inc., Piscataway, NJ). Images were digitized and densitometric analysis was conducted using NIH Image J software. All three compounds were tested on duplicate striatal slices from six rats.
Locomotor Activity Measurements. To measure changes in locomotor activity, singly housed rats were implanted with transmitters (model ER-4000 E-Mitter; Mini Mitter Co., Inc., Bend, OR). Under ketamine (100 mg/kg i.p.) and xylazine (10 mg/kg i.p.) anesthesia, a transmitter was implanted inside the peritoneum of a rat at least 6 days before conducting an experiment. The transmitter broadcasted changes in locomotor activity that were sent to a receiver (model ER-4000 receiver, Mini Mitter Co., Inc.) placed under the home cage of each rat. Data were collected and processed simultaneously by the Vital View data acquisition system (Mini Mitter Co., Inc.). Immediately after drug or vehicle injection, locomotor activity measurements were collected for each rat for approximately 5 h; however, locomotor activity counts from the first 4 h of data collection were displayed in graphs.
Forced Swim Test. To measure antidepressant-like activity, five to six rats per drug dose were subjected to a modified forced swim test as described previously (Broom et al., 2002a). Briefly, rats were placed in a clear cylindrical acrylic container (46 cm in height by 20 cm in diameter) filled with 30 cm of 25 ± 1°C water for a 1-day, 15-min swim session. Test compounds were administered as a single s.c. injection 60 min before the forced swim test or as a single i.v. injection infused over 20 s 30 min before the forced swim test. Cylinder water was changed after every rat. After each swim period, rats were removed from the water, towel-dried, and placed in a heated cage for 15 min.
Videotaped 15-min test swims were scored for immobility, swimming, and climbing behaviors (Detke et al., 1995). The individual scoring the videotapes was blinded to the drug treatments received by each rat. Every 5 s, the scorer rated the subject's behavior as one of the three behaviors: immobility, swimming, or climbing. The total counts of each behavior during the 15-min swim were averaged within treatment groups. These behaviors were defined as immobility, floating in the water without struggling and using only small movements to keep the head above water; swimming, moving limbs in an active manner (more than required to keep head above water) causing movement between quadrants of the cylinder; and climbing, making active movements with the forepaws in and out of the water, often directed at the wall of the swim tank.
Convulsion Observations. Immediately after s.c. or i.v. injection, rats were placed in an observation chamber for 20 min to observe for convulsions and cataleptic behaviors. Time to onset of convulsion, duration of convulsions, and duration of catalepsy were recorded. Catalepsy duration was defined as the time to remove forelimbs from a rod elevated approximately 5.08 cm (2 inches) off the ground. After the 20-min observation period, rats were returned to the home cage.
Intravenous Catheter Implantation. Catheters were constructed from approximately 15 cm of Micro-Renathane tubing (MRE-040; Braintree Scientific, Inc., Braintree, MA). Implantation of catheters was described previously (Baird et al., 2000). Briefly, rats were anesthetized with ketamine hydrochloride (100 mg/kg i.p.) and xylazine hydrochloride (10 mg/kg i.p.). The right jugular vein was isolated through a ventral incision in the neck. Approximately 3 cm of the catheter was inserted into the right jugular vein and the tubing was sutured to the vein and to the surrounding tissues at three or four points to secure the catheter placement. The remaining tubing was threaded subcutaneously to the dorsal incision point and secured in place by sutures to the musculature directly below the incision. Two to three centimeters of tubing remained exposed outside the rat's body. The catheter was plugged with a stainless steel pin (McMaster-Carr, Cleveland, OH). Immediately after and every day after the surgery, the catheters were flushed with approximately 0.5 ml of heparinized saline (50 U/ml). On average, rats were allowed 4 to 5 days of recovery from surgery before being used in an experiment.
Data Handling and Statistical Analysis
Data from the forced swim test were averaged within each treatment drug. Totals for each behavioral measure (immobility, swimming, or climbing) were analyzed by one-way analysis of variance, and Dunnett's post hoc tests were used to compare drug sessions to vehicle sessions (GraphPad Prism; GraphPad Software Inc., San Diego, CA). For antagonism studies, immobility scores were compared between pretreatment conditions for each drug by Student's t test.
Locomotor activity data were summed over 5-min intervals beginning at least 40 min before injection with drug and continuing for at least 5 h after an injection of a test compound. Means across rats for each treatment group were calculated as time after injection ±2 min. Data were also calculated as area under curve for each dose of the three drugs tested (GraphPad Prism).
For the [35S]GTPS autoradiography experiments, data were analyzed by nonlinear curve fitting of the data, and EC50 and maximum values were determined (GraphPad Prism).
Drugs
All test compounds were injected s.c. or i.v. in a volume of 1 ml/kg. SNC86 was dissolved in sterile water. SNC80 and SNC162 were dissolved in an 8% 1 M HCl solution. Ketamine hydrochloride (Vedco Inc., St. Joseph, MO) and xylazine hydrochloride (Fermenta Animal Health Co., Kansas City, MO) were all dissolved in sterile water.
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Results |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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S autography experiments, striatal slices from rat brain were used to determine dose-concentration curves. Some previous work has demonstrated that -opioid agonist-stimulated GTPS binding is greatest in the striatum (Hyytia et al., 1999). SNC86, SNC80, and SNC162 dose dependently stimulated [35S]GTPS binding in rat striatal slices with EC50 values (±S.E.M.) of 0.81 (0.11), 67 (2.7), and 33 nM (2.5), respectively (Fig. 2). In addition, SNC86 demonstrated higher maximal stimulation of [35S]GTPS binding [F(2,35) = 9.66; p = 0.0005], compared with SNC80 (p < 0.01) and SNC162 (p < 0.001).
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SNC80 and its derivatives (s.c.) increased locomotor activity, although the duration of the stimulation greatly differed (Fig. 3). Before injection at time 0, baseline locomotor activity was low for all rats, with values below approximately 30 counts (Fig. 3, a–c). SNC80 produced increases in locomotor activity counts that remained elevated for 2 to 3 h (Fig. 3a) with 3.2 and 32 mg/kg SNC80 elevating locomotor activity to similar levels. SNC86 produced dose-dependent increases in locomotor activity (Fig. 3b). Locomotor stimulation produced by 10 mg/kg SNC86 returned to baseline values after 3 h. In comparison with SNC80 and SNC86, SNC162 increased locomotor activity for a shorter duration (Fig. 3c). The highest tested dose (32 mg/kg SNC162) stimulated locomotor activity, but the effect dissipated after approximately 75 min. Figure 3d represents the data as the area under the curve, indicating the total amount of locomotor activity produced by each dose over time. Based on this representation, SNC86 clearly produced the most locomotor stimulation and was the most potent compound to increase activity (3-fold more potent than SNC80). SNC80 was approximately 10-fold more potent at increasing locomotor activity compared with SNC162. Also, SNC162 produced the lowest amounts of total locomotor activity compared with SNC86 and SNC80.
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SNC80 (s.c.) significantly decreased immobility [F(5,35) = 8.96; p < 0.0001] and increased swimming [F(5,35) = 2.98; p = 0.027] and climbing [F(5,35) = 3.65; p = 0.011] in the forced swim test in rats (Fig. 4a). SNC80 doses of 3.2 mg/kg and higher produced significant decreases in immobility (p < 0.001). SNC80, 10 mg/kg, significantly increased climbing (p < 0.05), and 32 mg/kg SNC80 significantly increased swimming (p < 0.05) and climbing (p < 0.01). SNC86 (s.c.) significantly decreased immobility [F(6,41) = 11.87; p < 0.0001] and increased swimming [F(6,41) = 8.71; p < 0.0001] and increased climbing [F(6,41) = 2.55; p = 0.04] (Fig. 4b). SNC86 at 3.2, 10, and 32 mg/kg decreased immobility (p < 0.01) and increased swimming (p < 0.01). There was a significant trend to increase climbing; however, no dose was significantly different from vehicle. SNC162 (s.c.) significantly decreased immobility [F(5,35) = 2.60; p = 0.046] only at the highest dose tested, but did not significantly alter swimming [F(5,35) = 2.49; p = 0.053] or climbing [F(5,35) = 1.68; p = 0.17] (Fig. 4c). The effect of SNC162 on swimming was nearly significant; however, there was no statistical difference between doses, and there was no identifiable trend to the swimming data.
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SNC80 and its derivatives also produced convulsions in rats when administered s.c. (Fig. 4d) (Broom et al., 2002a,b). -Opioid-induced convulsions in rats occurred within 6 to 15 min after an injection and lasted for approximately 5 to 25 s. The convulsion was manifested mainly in the head and forelimb areas. After a convulsion, rats were cataleptic, such that they failed a 15-s rod test, and they did not have a righting reflex. SNC80 produced a dose-dependent increase in the number of rats convulsing, with 100% of rats convulsing at the highest dose 100 mg/kg SNC80. SNC86 also produced dose-dependent increases in the number of rats convulsing, but it was more potent than SNC80. The highest dose of SNC86 tested (32 mg/kg) produced convulsions in 100% of rats. SNC162 produced convulsions in five of six rats at the highest of the tested doses (100 mg/kg).
Table 1 contains descriptive statistics of the convulsions and catalepsy produced by s.c. administration of SNC80, SNC86, and SNC162. With SNC80 and SNC86, higher doses increased the number of rats that convulsed and more than halved the time to onset of the convulsion. In contrast to SNC80 and SNC86, SNC162 produced a convulsion in only one rat with the lower dose of 32 mg/kg, 346 s after the injection. This convulsion occurred much faster than that observed with the same dose of SNC80. SNC162, 10 mg/kg, increased the number of rats convulsing, but it did not decrease the time to onset of convulsion. The convulsion duration and the duration of postconvulsive catalepsy did not differ greatly among doses or drugs.
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To confirm that the convulsive and antidepressant-like effects of high doses of SNC80 and its derivatives were mediated through the -opioid receptor, the selective -opioid receptor antagonist naltrindole was administered 30 min before each agonist (Fig. 5). With naltrindole vehicle pretreatments, 32 mg/kg SNC80 (p = 0.02), 10 mg/kg SNC86 (p = 0.002), and 100 mg/kg SNC162 (p = 0.02) significantly decreased immobility compared with the -opioid agonist vehicle control. Naltrindole (10 mg/kg) had no effect in the forced swim test (p = 0.69) (Fig. 5a); however, this dose blocked the convulsive (data not shown) and antidepressant-like effects of 32 mg/kg SNC80 (p = 0.003) (Fig. 5b), of 10 mg/kg SNC86 (p = 0.002) (Fig. 5c), and of 100 mg/kg SNC162 (p = 0.05) (Fig. 5d). In addition, a µ-opioid-selective dose of naltrexone was administered before 10 mg/kg SNC86 to determine whether there was a µ-component to the least selective -opioid agonist (Fig. 6). Naltrexone 0.032 mg/kg did not block the convulsive (data not shown) or antidepressant-like effects of SNC86 produced by s.c. (p = 0.07) or i.v. (p = 0.80) drug administration (Fig. 6, a and b, respectively).
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In general, SNC80 and its derivatives were more potent when administered intravenously. Intravenous administration of SNC80 significantly decreased immobility [F(4,29) = 12.98; p < 0.0001] and increased swimming [F(4,29) = 4.27; p = 0.009] and climbing [F(4,29) = 3.79; p = 0.02] counts in the forced swim test (Fig. 7a). SNC80, 3.2 mg/kg, decreased immobility (p < 0.01), increased swimming (p < 0.05), and increased climbing (p < 0.01). SNC86 (i.v.) significantly decreased immobility [F(3,23) = 15.12; p < 0.0001], increased climbing [F(3,23) = 4.26; p = 0.02], and nearly significantly increased swimming [F(3,23) = 2.76; p = 0.07] (Fig. 7b). SNC86 at a dose of 1.0 mg/kg decreased immobility only (p < 0.05). A higher dose of 3.2 mg/kg SNC86 decreased immobility (p < 0.01), increased swimming (p < 0.05), and increased climbing (p < 0.01). SNC162 (i.v.) significantly decreased immobility [F(2,16) = 3.69; p = 0.05], but it did not alter swimming [F(2,16) = 0.29; p = 0.75] or climbing [F(2,16) = 2.31; p = 0.14] (Fig. 7c). SNC162 (3.2 mg/kg) decreased immobility only (p < 0.05).
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SNC80 and its derivatives administered by i.v. route of administration also produced convulsions in rats (Fig. 7d). Convulsions produced by i.v. administration occurred during the 20-s i.v. infusion or within a few seconds of the end of the infusion. All compounds produced typical -opioid-mediated convulsions as described above. The first convulsive dose by i.v. administration of all compounds produced convulsions in some rats, with 1.0 mg/kg SNC80 producing convulsions in more rats than SNC86 and SNC162. The high dose of SNC80 and of SNC162 produced convulsions in all rats, whereas 3.2 mg/kg SNC86 produced convulsions in 66.7% of rats.
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Discussion |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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S binding in rat brain slices of the caudate putamen. These studies demonstrated that SNC86 was the most potent and efficacious compound. SNC80 and SNC162 produced similar levels of GTPS stimulation and had similar EC50 values (67 and 33 nM, respectively). However, in behavioral studies, these three compounds demonstrated a rank order of potency and efficacy with SNC86 as the most potent and efficacious compound, followed by SNC80 and then SNC162.
These studies contribute to the previous findings that compounds that activate -opioid receptors produce antidepressant-like effects in the forced swim test in rats (Broom et al., 2002a,b). Previously, it was demonstrated that the antidepressant-like effects remain intact after the locomotor-stimulating properties dissipated (Broom et al., 2002b). The present results also confirmed that locomotor stimulating properties might not be observed simultaneously with antidepressant-like effects. For example, 1.0 mg/kg SNC86 increased locomotor activity counts to similar levels observed with high doses of SNC80; however, 1.0 mg/kg SNC86 (s.c.) did not produce antidepressant-like effects in the forced swim test. These results demonstrate that the locomotor-stimulating properties and the antidepressant-like effects of -opioid agonists may coexist, but they are not dependent on each other.
In addition to separating the locomotor effects and antidepressant-like effects of -opioid agonists, the present data support the observation that convulsions are not required for the antidepressant-like effects of -opioid agonists (Broom et al., 2002b). For example, low doses of SNC80, 3.2 and 10 mg/kg, produced antidepressant-like effects in the forced swim test, but these doses did not induce convulsions in rats. Interestingly, SNC80 is the only -opioid agonist tested that produced antidepressant-like effects at doses that did not produce convulsions in any rats.
SNC80 and its derivatives produced large increases in locomotor activity; however, the duration of the effect differed among the compounds. High doses of SNC86 and SNC80 stimulated locomotor activity for 2 to 3 h, but SNC162-induced activity dissipated after 60 to 75 min. These data suggested that SNC162 might have different pharmacokinetics than SNC86 and SNC80, thus having short-lived effects on locomotor activity. When represented as area under curve to indicate the total amount of drug-induced locomotor activity over time, SNC86 was clearly the most potent and efficacious compound. SNC80 was approximately 3-fold less potent and was less efficacious than SNC86. SNC162 was the least potent, approximately 10-fold less potent than SNC80 and 32-fold less potent than SNC86; likewise, SNC162 was less efficacious than SNC86 and SNC80, such that at the highest dose tested, it produced a smaller magnitude increase in overall locomotor activity compared with either SNC86 or SNC80.
In the forced swim test after s.c. administration, SNC86 and SNC80 seemed equipotent; however, SNC86 had a slightly larger magnitude of effect (i.e., a larger decrease in immobility from control values). In forced swim test experiments, a statistically significant decrease in immobility from baseline typically demonstrates that the compound has antidepressant-like activity; however, the magnitude of change in immobility is rarely discussed or used to compare drugs. It is possible that the magnitude of maximal effect may be an indication of drug efficacy in a manner similar to that used in other paradigms. In addition, drugs tested in the forced swim test frequently produce dose-dependent decreases in immobility, demonstrating that the maximum effect is variable and graded effects can be observed. For example, in assays measuring antinociception, the effect is dose-dependent, and compounds with higher maximal effects can indicate higher efficacy compounds.
Comparing SNC80 and its derivatives at their peak effects, SNC86 produced the largest maximal reduction in immobility with a 38% decrease from vehicle at 10 mg/kg, whereas SNC80 produced a maximal decrease of 26% at 100 mg/kg, and SNC162 produced a maximal decrease of 15% at 100 mg/kg. Therefore, based on the previous discussion, SNC86 would be considered the most efficacious compound followed by SNC80 and then SNC162. Unlike SNC86 and SNC80, SNC162 only produced antidepressant-like effects at the highest dose of 100 mg/kg and was clearly the least potent and efficacious of the three compounds tested. These larger doses of -opioid agonists produced convulsive and antidepressant-like effects through the -opioid receptor, as demonstrated by antagonism of these effects by the -opioid antagonist naltrindole. Likewise, there was no µ-opioid component to these effects, because they could not be antagonized by µ-selective doses of naltrexone. This is further supported by the finding that agonist actions at µ-opioid receptors did not have antidepressant-like effects in the forced swim test in rats (Broom et al., 2002a).
Although SNC86, SNC80, and SNC162 produced different magnitudes of antidepressant-like effects, the agonist-induced convulsions and postconvulsive catalepsy measurements were relatively similar, independent of dose and of efficacy measures. The only difference existed in the time to onset of convulsion; however, so few rats convulsed with SNC86 and lower doses of SNC80 and SNC162, it is difficult to make useful comparisons among the compounds.
With i.v. administration, the dose-effect curves for the convulsive and antidepressant-like effects shifted to the left for SNC86 and SNC162 compared with those produced by s.c. administration; however, the doses of SNC80 (i.v.) that produce antidepressant-like effects remained unchanged compared with the effects observed with s.c. administration. SNC162 (i.v.) demonstrated the largest leftward shift in the antidepressant-like effects, approximately 30-fold. Although the potencies of the SNC80 derivatives changed after i.v. administration, the rank order of the compounds based on potency and efficacy did not change (SNC86 > SNC80 > SNC162). At a dose of 3.2 mg/kg i.v., SNC86 produced a 36% decrease in immobility compared with control, SNC80 produced a 25% decrease in immobility compared with control, and SNC162 produced a 13% decrease in immobility compared with control. Considering that the relative efficacy of SNC80 and its derivatives did not change with i.v. administration, these results suggested that the differential efficacies cannot be explained by differences in absorption and/or distribution after s.c. administration.
In the [35S]GTPS experiments, SNC86 was the most potent and efficacious compound tested and the other two derivatives, SNC80 and SNC162, demonstrated similar potencies and efficacies. Based on these ex vivo findings, it would be expected that SNC80 and SNC162 would have similar effects in behavioral assays; however, in the present experiments, SNC80 produced behavioral effects more equivalent to SNC86 than to SNC162. Previous studies demonstrated that, after intraperitoneal administration, SNC80 was metabolized to a "BW373U86-like" compound by O-demethylation of the methoxy group in the 3-position of the benzylic ring (Schetz et al., 1996). Because BW373U86 is the racemate of SNC86, SNC80 metabolism to SNC86 may contribute, in some portion, to the observed behavioral effects of SNC80. On the other hand, SNC162 lacks a functional group at the 3-position on the benzylic ring, and for that reason, it cannot be metabolized to the active 3-OH (SNC86) compound and thus seems a partial agonist in both ex vivo and in vivo assays.
In conclusion, the 3-hydroxy containing SNC86 was the most potent and efficacious compound of the SNC80 derivatives evaluated in behavioral measurements of convulsant activity, antidepressant-like effects, and locomotor stimulation. The 3-unsubstituted compound SNC162 was a partial agonist at -opioid receptor compared with SNC86. Although SNC80 produced similar effects to SNC162 in ex vivo studies, this compound was more efficacious in behavioral studies, potentially because it was metabolized to the more active SNC86 product. Consistent with previous in vitro studies (Knapp et al., 1996; Calderon et al., 1997), the present findings confirm that the 3-position of SNC80 alters efficacies and potencies in behavioral studies in Sprague-Dawley rats. In addition, these potency and efficacy differences were observed in the forced swim test, suggesting that this behavioral assay can be used to evaluate and to compare efficacy differences among drugs and possibly drug classes. These data may assist the design and development of safer, non-convulsive -opioid agonists as potential therapeutics to treat depression.
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Acknowledgements |
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Footnotes |
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS: [35S]GTPS, guanosine 5'-O-(3-[35S]thio)triphosphate; SNC80, (+)-4-[(R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-methoxyphenyl)methyl]-N,N-diethylbenzamide; SNC86, (+)-4-[(R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-hydroxyphenyl)methyl]-N,N-diethylbenzamide; SNC162, (+)-4-[(R)--[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-phenyl)methyl]-N,N-diethylbenzamide.
Address correspondence to: Dr. James H. Woods, 1301 MSRB 3, Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109-0632. E-mail: jhwoods{at}umich.edu
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Baird TJ, Deng S-X, Landry DW, Winger G, and Woods JH (2000) Natural and artificial enzymes against cocaine. I. Monoclonal antibody 15A10 and the reinforcing effects of cocaine in rats. J Pharmacol Exp Ther 295: 1127-1134.
Brandt MR, Negus SS, Mello NK, Furness MS, Zhang X, and Rice KC (1999) Discriminative stimulus effects of the nonpeptidic -opioid agonist SNC80 in rhesus monkeys. J Pharmacol Exp Ther 290: 1157-1164.
Broom DC, Jutkiewicz EM, Folk JE, Traynor JR, Rice KC, and Woods JH (2002a) Nonpeptidic delta-opioid receptor agonists reduce immobility in the forced swim assay in rats. Neuropsychopharmacology 26: 744-755.[CrossRef][Medline]
Broom DC, Jutkiewicz EM, Folk JE, Traynor JR, Rice KC, and Woods JH (2002b) Convulsant activity of a nonpeptidic delta-opioid receptor agonist is not required for antidepressant-like effects. Psychopharmacology 164: 42-48.[CrossRef][Medline]
Calderon SN, Rice KC, Rothman RB, Porreca F, Flippen-Anderson JL, Kayakiri H, Xu H, Becketts K, Smith LE, Bilsky EJ, et al. (1997) Probes for narcotic receptor mediated phenomena. 23. Synthesis, opioid receptor binding and bioassay of the highly selective agonist (+)-4-[(aR)-a-((2S,5R)-4-ally-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80) and related novel nonpeptide opioid receptor ligands. J Med Chem 40: 695-704.[CrossRef][Medline]
Comer SD, Hoenicke EM, Sable AI, McNutt RW, Chang K-J, De Costa BR, Mosberg HI, and Woods JH (1993) Convulsive effects of systemic administration of the delta opioid agonist BW373U86 in mice. J Pharmacol Exp Ther 267: 888-895.
Detke MJ, Rickels M, and Lucki I (1995) Active behaviors in the rat forced swimming test differentially produced by serotonergic and noradrenergic antidepressants. Psychopharmacology 121: 66-72.[CrossRef][Medline]
Dykstra LA, Schoenbaum GM, Yarbrough J, McNutt R, and Chang K-J (1993) A novel -opioid agonist, BW373U86, in squirrel monkeys responding under a schedule of shock titration. J Pharmacol Exp Ther 267: 875-882.
Fraser GL, Parenteau H, Tu T-M, Ducharme J, Perkins MN, and Clarke PBS (2000) The effects of agonists on locomotor activity in habituated and non-habituated rats. Life Sci 67: 913-922.[CrossRef][Medline]
Hong EJ, Rice KC, Calderon S, Woods JH, and Traynor JR (1998) Convulsive behavior of nonpeptide -opioid ligands: comparison of SNC80 and BW373U86 in mice. Analgesia 3: 269-276.
Hyytia P, Ingman K, Soini SL, Laitinen JT, and Korpi ER (1999) Effects of continuous opioid receptor blockade on alcohol intake and up-regulation of opioid receptor subtype signaling in a genetic model of high alcohol drinking. Naunyn-Schmiedeberg's Arch of Pharmacol 360: 391-401.
Knapp RJ, Santoro G, De Leon IA, Lee KB, Edsall SA, Waite S, Malatynska E, Varga E, Calderon SN, Rice KC, et al. (1996) Structure-activity relationships for SNC80 and related compounds at cloned human delta and mu opioid receptors. J Pharmacol Exp Ther 277: 1284-1291.
Negus SS, Butelman ER, Chang K-J, DeCosta B, Winger G, and Woods JH (1994) Behavioral effects of the systemically active delta opioid agonist BW373U86 in rhesus monkeys. J Pharmacol Exp Ther 270: 1025-1034.
Negus SS, Gatch MB, Mello NK, Zhang X, and Rice K (1998) Behavioral effects of the delta-selective opioid agonist SNC80 and related compounds in rhesus monkeys. J Pharmacol Exp Ther 286: 362-375.
Pakarinen ED, Woods JH, and Moerschbaecher JM (1995) Repeated acquisition of behavioral chains in squirrel monkeys: comparisons of a mu, kappa and delta opioid agonist. J Pharmacol Exp Ther 272: 552-559.
Schetz JA, Calderon SN, Bertha CM, Rice K, and Porreca F (1996) Rapid in vivo metabolism of methylether derivative of (±)-BW373U86: the metabolic fate of [3H]SNC121 in rats. J Pharmacol Exp Ther 279: 1069-1076.
Sim LJ, Selley DE, and Childers SR (1995) In vitro autoradiography of receptor-activated G-proteins in rat brain by agonist-stimulated guanylyl 5'-[-[35S]thiotriphosphate binding. Proc Natl Acad Sci USA 92: 7242-7246.
Spina L, Longoni R, Mulas A, Chang K-J, and Chiara G (1998) Dopamine-dependent behavioural stimulation by non-peptide delta opioids BW373U86 and SNC80: 1. Locomotion, rearing and stereotypies in intact rats. Behav Pharmacol 9: 1-8.[Medline]
Stevenson GW, Canadas F, Gomez-Serrano M, Ullrich T, Zhang X, Rice KC, and Riley AL (2002) Delta opioid discrimination learning in the rat: assessment with the selective delta agonist SNC80. Pharmacol Biochem Behav 71: 291-300.[CrossRef]
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), SNC80 (
), and SNC162 (
), respectively. Maximal stimulation values were 179.0, 157.2, and 154.5, respectively.
, p < 0.05 and 
