Antagonist Naloxone Research Articles

Tail chasing in a Bull Terrier

A Bull Terrier that was continuously chasing its tail was examined clinically, electroencephalographically, and by computed tomography of the head. The dog was also given test treatments with an anticonvulsant (diazepam) and a pure opioid antagonist (naloxone). The dog appeared to be hysterical and dissociated from its surroundings. Electroencephalography revealed a seizure pattern that was most marked over the temporal lobe, and computed tomography revealed mild hydrocephalus. Diazepam effectively controlled tail chasing, whereas naloxone did not. The dog was discharged on anticonvulsant therapy but subsequently had to be euthanatized when aggression developed. Results of examination and treatment have led the investigators to propose a hereditary mechanism for tail chasing, perhaps related to zinc malabsorption.

Opioid Effects on Contractility, Ca2+-transients and Intracellular pH in Cultured Cardiac Myocytes

Morphine, the opioid-agonist, and the antagonist naloxone and levallorphan exerted direct effects on spontaneously-contracting cultures of cardiac myocytes from neonatal rats. Naloxone and levallorphan induced an increase in the amplitude of systolic cell motion (ASM) and in the size of [Ca2+],-transients, measured as indo-1 fluorescence ratio (IFR), whereas morphine caused an increase in IFR with no change in ASM. Both morphine and naloxone caused a transient increase in 45Ca2+ influx into the cardiomyocytes. Analysis of the relationship between changes in ASM and IFR indicated dual action of the drug: (a) An increase in [Ca2+]-transients elicited by morphine and the antagonists, apparently resulting from a transient increase of Ca2+ influx. (b) Altered myofibril responsiveness to Ca2+; the agonists decreased it, and the antagonists increased it. Intracellular pHi measurements in cardiomyocytes loaded with the fluorescent indicator BCECF revealed that morphine caused acidosis and the antagonists caused alkalosis. These pH changes were inhibited by pertussis-toxin, protein kinase inhibitor K323a, phorbol-ester and ethylisopropyl-amiloride, indicating pathways mediated by GTP-binding proteins and altered activities of protein kinase C and Na+/H+ exchanger. Preincubation with pertussis toxin prior to the addition of morphine prevented the decrease in the myofibril responsiveness to Ca2+ as well as the decrease in pHi but did not affect the increase in [Ca2+]-transients and the increase in the rate of Ca2+ influx. As a result, addition of morphine after preincubation with pertussis toxin caused a positive inotropic effect. Our results indicate that morphine acts by two different pathways distinguishable by their sensitivity to pertussis toxin (1), increases Ca2+ influx leading to increased Ca2+-transients and (2) decreased intracellular pH leading to reduced myofibril responsiveness to Ca2+.

The highly selective δ agonist BUBU induces an analgesic effect in normal and arthritic rat and this action is not affected by repeated administration of low doses of morphine

The effect of various doses of the selective δ agonist BUBU (Tyr- d-Ser( O-t-butyl)-Gly-Phe-Leu-Thr( O-t-butyl) on the vocalization threshold to paw pressure were compared in normal and arthritic rats, a suitable clinical model of chronic pain. In both group of rats, the intravenous administration of BUBU (6, 9, 12 mg/kg in normal and 1.5, 3, 6, mg/kg in arthritic rats) led to significant antinociceptive effects. The same dose of BUBU (6 mg/kg i.v.) produced a much more potent antinociceptive effect in arthritic than in normal rats, and a dose as low as 1.5 mg/kg produced a significant analgesic effect in the arthritic animal, whereas at 3 mg/kg BUBU was ineffective in normal rats. The analgesic effects of BUBU (9 mg/kg in normal and 3 mg/kg in arthritic rats) were completely prevented by the selective δ antagonist naltrindole (1 mg/kg i.v. a dose devoid of analgesic potency per se), while they were not affected by the selective μ antagonist naloxone (0.05 mg/kg i.v.). In addition, 3 mg/kg i.v. of BUBU remained effective in morphine tolerant arthritic rats. These results suggest that δ opioid receptor activation can modulate the transmission of cutaneous mechanical nociceptive information in rats, especially in inflammatory pain conditions.

Opioid receptor-mediated inhibition of evoked catecholamine release from cultured neurons of rat ventral mesencephalon and locus coeruleus

The effects of selective opioid agonists on the evoked release of [ 3H]dopamine and [ 3H]noradrenaline were studied in cultured dopaminergic neurons of the ventral mesencephalon (containing the substantia nigra and ventral tegmental area) and in cultured neurons of the noradrenergic locus coeruleus, respectively. The cultures were prepared from embroyonic day 15 rat brains. After 9 days in culture, the calcium-dependent release of [ 3H]dopamine from dopaminergic substantia nigra/ventral tegmental aera neurons induced by 23 mM k + appeared to be inhibited exclusively by activation of κ-opioid receptors, as [ 3H]dopamine release was inhibited selectively by the κ- agonists U69,593 and dynorphin-(1–13) (EC 50 8 and 5 nM, respectively), and this inhibitory effect was antagonized by the κ-selective antagonist nor-binaltorphine (K i 0.07 nM). In contrast, cultured noradrenergic locus coeruleus neurons appeared to contain release-inhibitory μ-opioid receptors only, as evoked [ 3H]noradrenaline release was inhibited selectively by the μ agonist [D-Ala 2, MePhe 4, Gly-ol 5]enkephalin (EC 50 45 nM), a response that was antagonized by the preferential μ antagonist naloxone (K i = 0.7 nM). The δ-opioid receptor agonist [D-Ser 2(O-butyl), Leu 5]enkephaly-Thr 6 did not affect catecholamine release. Dopamine release from cultured ventral mesencephalic neurons, induced by 100 μM N-Methyl-D-Aspartate (NMDA), also appeared to be subject to κ receptor-mediated inhibition, whereas NMDA-induced noradrenaline release from cultured locus coeruleus neurons was under the inhibitor control of μ receptors. It is therefore concluded that in rat brain neurotransmitter release from dopaminergic and noradrenergic neurons, originating from the substantia nigra/vental tegmental area and the locus coeruleus, is liable to inhibition by homogenous populations of κ- and μ-opioid receptors, respectively, independent of the input of non-opioid neurons from distict nuclei.

Effect of dalargin, a synthetic leu-enkephalin analogue on synaptic transmission in the Lorenzini ampullae of rays

Effects of dalargin, a synthetic leu-enkephalin analogue and its antagonist naloxone on synaptic transmission in afferent synapses of ray electroreceptors were investigated using an isolated preparation of Lorenzini ampullae from Black sea rays. It was shown that dalargin (10−6–10−10 mole liter) both decreased background activity and evoked activity of an afferent fiber in a dose-dependent manner. Naloxone (10−5 mole/liter) also inhibited afferent impulsation and completely blocked responses of the Lorenzini ampullae to dalargin application. L-glutamate-induced excitatory responses were reduced in the presence of dalargin. It is suggested that the modulatory action of dalargin on glutamatergic synaptic transmission in the Lorenzini ampullae is exerted via specific opiate receptors.

Influence of pertussis toxin on thermic responses to morphine and neurotensin in rats

The influence of pertussis toxin (PTX) on thermic responses elicited by morphine and neurotensin was evaluated in unrestrained rats kept at 22°C. High doses of morphine (9–36 μg/rat i.c.v.) lowered body temperature and low doses (1.25. 2.5 μg/rat i.c.v.) produced hyperthermia. The hyperthermic effect was more resistant than the hypothermie effect to naloxone antagonism. Neurotensin (50, KM)μg/rat i.c.v.) induced marked hypothermia followed by hyperthermia. I.c.v. injection of PTX (1 μg), six days before morphine (18 μg/rat i.c.v.). replaced the opiate hypothermia by consistent hyperthermia and reduced by 60% the hyperlhermia elicited by morphine (2.5 μg/rat i.c.v.). The toxin also affected the thermic responses induced by neurotensin (50 μg/rat i.c.v.) administered six days after PTX (1 μg/rat i.c.v.). The initial hypothermia was enhanced by 173% and the late hypcrthermia was fully antagonized. It thus appears that PTX-scnsitivc G-protcins play different roles in the molecular events underlying the thcrmoregulatory responses to morphine and neurotensin.

Intravenous cocaine challenges during naltrexone maintenance: A preliminary study

In 1976 Byck hypothesized that opioid antagonists would block the euphoric effect of cocaine, and recent clinical observations have suggested lower rates of cocaine abuse by people receiving naltrexone (NTX) than by those receiving methadone (Kosten et al 1989). Although early workers found that both rodents and primates maintained on antagonists showed no attenuation of cocaine self-administration (Killian et al 1978; Carroll et al 1986), more recent studies have found attenuation with NTX administration (Mello et al 1990; DeVry et al 1989; Ramsey and van Ree 1991). Furthermom, Bain and Kornetsky (1987), using rewarding brain stimulation in rodents, showed that the antagonist naloxone can reverse cocaine's potentiation of this stimulation. An early human study using cocaine administration found a potentiation rather than a reduction of cocaine effect after acute high-dose naloxcne (20 mg i.e.; Byck et al 1982), but this situation is clearly different from maintenance blocking with lower doses of NTX. We therefore undertook the current cocaine challenge study during chronic NTX.

Estrogen suppresses mu-opioid- and GABAB-mediated hyperpolarization of hypothalamic arcuate neurons

The effects of estrogen on the response of hypothalamic arcuate neurons to mu-opioid and GABAB agonists were investigated. Intracellular recordings were made from arcuate neurons in slices prepared from ovariectomized guinea pigs that were pretreated with estrogen or vehicle. Estrogen shifted the dose-response curve to the mu-opioid agonist DAMGO (Tyr-D-Ala-Gly-MePhe-Gly-ol) by 3.4-fold; the EC50 for DAMGO was 240 +/- 25 nM in estrogen-treated females versus 70 +/- 12 nM in the controls. The maximal hyperpolarization induced by DAMGO was equivalent in neurons from both groups. The Ke for the naloxone antagonism of the DAMGO response was similar in both groups, which would indicate that the affinity of the mu-receptor was unchanged. To explore where in the receptor/G-protein/K+ channel cascade estrogen may be acting to attenuate the mu-opioid-mediated hyperpolarization, the response to the GABAB agonist baclofen was also tested. Estrogen treatment also shifted the dose-response curve for the baclofen-induced hyperpolarization by 3.3-fold without altering the maximum hyperpolarization; the EC50 shifted from 11.0 +/- 4.0 microM to 36.0 +/- 5.0 microM. All of the neurons were identified after linking the intracellular biocytin with streptavidin-FITC, and a subpopulation of cells in both groups were immunoreactive for beta-endorphin. We conclude that estrogen decreases the functional coupling of the mu-opioid and GABAB receptors to the inwardly rectifying K+ channel possibly through an action on the G-protein.

Characterization of intestinal smooth muscle responses and binding sites for endothelin.

The contractile activity of and binding sites for endothelin-1 (ET-1) were investigated in isolated guinea-pig ileal longitudinal smooth muscle (GPILM). ET-1 produced concentration-dependent contractions of GPILM that either slowly subsided in the continued presence of ET-1 or rapidly subsided following washing of the tissue. The ED50 value for ET-1 contractions was 4.2 +/- 1.3 x 10(-9) M. The removal of extracellular calcium or pretreatment with nifedipine produced a complete inhibition of the contractions to ET-1. The IC50 value of nifedipine for inhibition of ET-1 mediated contractions was 3.0 +/- 0.8 x 10(-8) M. ET-1 produced a marked prolonged homologous desensitization of its contractile response but did not affect the responses mediated by carbachol, histamine, serotonin, substance P, and PLA2. High-affinity binding sites for 125I-labelled ET-1 were identified on microsomal membranes prepared from GPILM with Kd and Bmax values obtained by Scatchard analysis of 3.5 +/- 0.6 x 10(-10) M and 2138 +/- 159 fmol/mg protein, respectively. The binding of 125I-labelled ET-1 to GPILM microsomes was characterized by a rapid association (kob value of 0.077 min-1 at a radioligand concentration of 0.45 nM and an extremely slow dissociation (k1 value of 0.011 min-1; t1/2 value of 793 min). The binding was unaffected by the calcium channel antagonists nifedipine, verapamil, and diltiazem (10(-6) M); the receptor antagonists phenoxybenzamine, atropine, and naloxone (10(-6) M) and propranolol; and the peripheral benzodiazepine receptor antagonists Ro 5-4864 and PK 11195 and psychotomimetic drug phencyclidine (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen Uptake during Recovery Following Naloxone Relationship with Intraoperative Heat Loss

The increased metabolic and respiratory demand during naloxone recovery from opioid-based anesthesia could be related to the return of thermoregulation in hypothermic patients and thus be avoided by preventing intraoperative hypothermia. In this study, we measured O2 uptake (VO2) during naloxone-induced recovery in two groups of patients to determine the effect of intraoperative heat loss on postoperative VO2 changes. In seven patients, intraoperative hypothermia was prevented (normothermic group), whereas hypothermia was allowed to develop in seven other patients (hypothermic group). Core and skin temperatures were measured throughout the study to calculate changes in body heat content. Before naloxone antagonism of fentanyl-supplemented anesthesia, core temperature (mean +/- SEM) was 36.8 +/- 0.1 degrees C in the normothermic group and 34.2 +/- 0.2 degrees C in the hypothermic group (P less than 0.001). After titrated administration of naloxone during recovery, VO2 and minute ventilation (VE) increased in the hypothermic group, by 114 +/- 37% and 97 +/- 52% respectively (P less than 0.05), with a three-fold increase in four patients. In the normothermic group, VO2 increased significantly less (25 +/- 5%), without any significant change in VE. The change in VO2 and VE was significantly greater in patients who were hypothermic. VO2 was integrated throughout the recovery period to calculate recovery energy expenditure. Recovery energy expenditure and intraoperative heat loss were highly correlated (r = 0.88; P less than 0.01). This study demonstrates that the metabolic and respiratory stresses associated with naloxone-induced recovery from opioid-based anesthesia depend on the intraoperative heat loss and can therefore be reduced by preventing intraoperative hypothermia.

Naloxone blocks conditioned place preference induced by substance P and [pGlu 6]-SP(6–11)

The effect of prior treatment with the opioid receptor (opioceptor) antagonist naloxone on conditioned place preference produced by the neurotachykinin substance P (SP) and its C-terminal hexapeptide analog [pGlu 6]-SP(6–11) (SPC) was investigated in rats. Place conditioning was assessed using a circular open field partitioned into four quadrants that were equally preferred by the rats prior to drug treatment. On three successive days, rats received an intraperitoneal (i.p.) injection of naloxone-HCl (1 mg/kg) or vehicle 15 min before an i.p. injection of either 37 nmol/kg SP, equimolar dosed SPC or corresponding diluent vehicle. After injection the rats were placed into their assigned treatment corral for 15 min. During the test for conditioned corral preference (CCP), when provided a choice between the four quadrants, rats injected with SP or SPC spent more time in the treatment corral compared to vehicle controls, indicative of a positive reinforcing action of these peptides. The pre-treatment with naloxone blocked the positive reinforcing effects of both SP and SPC; when injected alone, naloxone did not influence the preference behavior. Gross locomotor activity was affected by neither treatment. Thus, the positive reinforcing effects of SP and SPC may be mediated via interactions with the endogenous opioid system(s).

Nociceptive quality of the orbicularis oculi reflexes as evaluated by distinct opiate- and benzodiazepine-induced changes in man

The corneal reflex and the three components of the blink reflex (R1, R2, and R3) were recorded electromyographically in volunteers. The area of these responses was measured before and after administration of the narcotic-analgesic fentanyl (1.5 mg i.m.) and its antagonist naloxone, and after administration of the benzodiazepine diazepam (10 mg i.v.) and its antagonist flumazenil. Saline was given as a control placebo. The corneal reflex was 71% reduced by fentanyl, 43% by diazepam. R1 was 35% reduced and R2 was 60% reduced by diazepam. R3 was abolished by both drugs. Whereas the fentanyl-induced changes were completely reversed by naloxone, the diazepam-induced changes were only partly reversed by flumazenil. The corneal reflex appears to be a ‘nociceptive’ reflex under all points of view. Recording of the orbicularis oculi reflexes in man may be valuable in the evaluation of central-acting neurotropic drugs.

Salmon calcitonin-induced modulation of free intracellular calcium

Salmon calcitonin (sCT), a hormone shown to modulate calcium in the periphery modulated free, intracellular calcium, ([Ca ++]i), in mouse brain synaptosomes as measured by changes in fura-2-mediated fluorescence. A 5-min incubation of synaptosomes with sCT produced an increase in the basal levels of [Ca ++]i and an increase in KCl-stimulated levels of [Ca ++]i. A 5-min pretreatment of mice with intraventricularly administered sCT antagonized morphine-induced antinociception in the tail-flick test, and facilitated naloxone antagonism of morphine. Conversely, pretreatment of synaptosomes for 1 h with salmon CT produced a decrease in depolarization-stimulated levels of [Ca ++]i. The sCT-induced decrease in the stimulated rise in [Ca ++]i at 1 h correlated temporally to sCT-induced antinociception in vivo. The effects of sCT in the electrically stimulated guinea pig ileum bioassay appeared to correlate to sCT effects in vivo. The data indicate that calcitonin may function as a neuromodulator via modulation of Ca ++ within the central nervous system.

Opioid control of the release of Met-enkephalin-like material from the rat spinal cord

The possible control by opioids of the release of Met-enkephalin-like material (MELM) from the rat spinal cord was investigated in vitro and in vivo. Superfusion of slices of the dorsal zone of the lumbar enlargement with the μ selective agonists DAGO or PL 017 or the ∂ selective agonist DTLET produced a significant reduction in the K +-evoked MELM release from these tissues. These effects persisted in the presence ot tetrodotoxin, as expected from their mediation through presynaptically located opioid autoreceptors. Furthermore, the inhibitory effect of DAGO and PL 017, but not that of DTLET, was prevented by the preferential μ antagonist naloxone. Conversely, the effect of DTLET was prevented by the ∂ antagonist naltrindole but not by naloxone. In vivo experiments performed in halothane-anaesthetized rats have shown that the intrathecal perfusion of DAGO and DTLET significantly depressed the spontaneous MELM outflow from the whole spinal cord. In contrast to these μ and ∂ agonists, the κ selective agonist U 50488 H did not affect the in vivo- and only slightly reduced (at a very high concentration: 50 μM) the in vitro-release of MELM from the rat spinal cord. These data indicate that both μ and ∂ opioid autoreceptors are involved in a local presynaptic autoinhibitory control of MELM release in the rat dorsal horn.

Naloxone augments muscle sympathetic nerve activity during isometric exercise in humans

The influence of an endogenous opioid peptide (EOP) antagonist (naloxone, 1.2 mg iv bolus) on muscle sympathetic nerve activity (MSNA, microneurography) was studied on 19 young male and female volunteers. Isometric handgrip, cold pressor test, and acute baroreceptor unloading with sodium nitroprusside (autonomic stresses) were carried out under two conditions, one group (n = 11) before (control responses) and after naloxone and another group (n = 8) before and after placebo saline. Monitored cardiovascular variables included heart rate, central venous pressure (jugular vein catheter), arterial blood pressure (radial artery catheter), circulating catecholamines, and forearm blood flow. At rest, cardiovascular variables and MSNA were not affected by either naloxone or saline. MSNA (total activity = burst frequency x burst amplitude/100 cardiac cycles) increased during isometric handgrip to a greater extent (30 +/- 6 vs. 16 +/- 5 arbitrary units) after naloxone compared with control trials (P less than 0.05). After naloxone, arterial systolic and diastolic blood pressures were higher during handgrip exercise. These augmented arterial pressures and MSNA responses were not evident during either the cold pressor test or the sodium nitroprusside stress. These data suggest that isometric muscle contraction elicits a sympathetic neural response that may be modified by EOP. This interaction is not evident during two other stresses, when sympathetic responses are equal to or greater than those provoked by isometric handgrip exercise.

Comparison of the stimulus effects of ethylketocyclazocine in fischer and Sprague‐Dawley rats

AbstractThe discriminative stimulus effects of ethylketocyclazocine (EKC) were characterized in Fischer and Sprague‐Dawley rats trained to discriminate 0.3 mg/kg of EKC (s. c.) from saline in a two‐choice, discrete‐trial avoidance paradigm. The putative mu‐opioid receptor agonists morphine and fentanyl, as well as the putative kappa‐opioid receptor agonists EKC and U50,488H generalized completely with the EKC cue in both strains of rats. Only small quantitative differences between strains were observed in the generalization of these agonists with EKC. However, Sprague‐Dawley rats were notably more sensitive than Fischer rats to the depressant effects of fentanyl. Only small quantitative differences between strains were also observed in the dose of naloxone necessary for complete antagonism of the EKC‐like stimulus effects of the mu‐ and kappa‐opioid agonists. The mu‐opioid agonists were approximately 2–6 times more sensitive to naloxone antagonism than the kappa‐opioid agonists in both Fischer and Sprague‐Dawley rats. However, due to inter‐animal variability, this difference was not statistically significant. The results of this study suggest that one or more opioid receptor subtype(s) may be involved in the production of the EKC cue in both strains of rats.

Opioid peptide regulation of neurons in the bed nucleus of the stria terminalis: a microiontophoretic study

Single unit activity was recorded from neurons in the bed nucleus of the stria terminalis (BNST) in response to single or combined microiontophoretic ejection of d-Ala 2-Met 5-enkephalinamide (DAME) and naloxone. BNST neurons showed predominantly excitatory responses following small iontophoretic applications of DAME, and these responses were antagonized by naloxone. In contrast, inhibitory responses that were elicited by DAME required larger ejection currents and usually failed to show naloxone antagonism. The results indicate that activation of enkephalin-sensitive BNST neurons by DAME is primarily, but not exclusively, excitatory, which suggests that these responses may reflect differences in receptor sensitivity to the applied agonist.

Opioid receptor ligands in the neonatal rat spinal cord: binding and in vitro depression of the nociceptive responses

1. Opioid receptors in the neonatal rat spinal cord have been characterized by measurements of ligand binding to crude membrane fractions and by functional tests on the nociceptive spinal response in a spinal cord-tail preparation in vitro. 2. There were high affinity binding sites for [3H]-[D-Ala2, MePhe4, Gly(ol)5]enkephalin (DAGOL), [3H]-U69593, and [3H]-ethylketocyclazocine (EKC) on spinal cord membranes from neonatal rats. Hill slopes for binding of [3H]-DAGOL and [3H]-U69593 were close to unity. The Hill slope for binding of [3H]-EKC was less than unity, even after its interactions at mu-receptors had been blocked with 100 nM unlabelled DAGOL. Binding sites for [3H]-[D-Pen2, D-Pen5]enkephalin (DPDPE) could not be detected. 3. In competition assays U50488 was as potent as PD117302 and U69593 in competition for either [3H]-U69593 or [3H]-EKC binding sites. Hill slopes for a range of competing ligands at [3H]-DAGOL or [3H]-U69593 sites were close to unity. Hill slopes for competition at [3H]-EKC sites were less than one. 4. In the spinal cord-tail preparation from neonatal rats, opioid receptor agonists depressed spinal nociceptive responses evoked by application of capsaicin or heat to the tail. The order of potency was DAGOL greater than U69593 = PD117302 greater than morphine greater than U50488 = [D-Pen2, L-Pen5]enkephalin (DPLPE). 5. The antagonist naloxone was about equally potent against DAGOL, morphine and DPLPE, and about ten times less potent against U69593 and PD117302. The effects of U50488 were much less sensitive to blockade by naloxone than the effects of PD11703 or U69593. The Kappa antagonist, nor-binaltorphimine was equipotent against all three Kappa agonists. 6. The absence of delta-binding sites, and the low potency and relatively high sensitivity to naloxone suggest that DPLPE could be working at mu-receptors in the neonatal rat spinal cord. 7. The binding assays show that U50488 has the same affinity as PD1 17302 and U69593 for Kappa-receptors, yet it was less effective in the depression of nociceptive responses. This may be because U50488 has a relatively low efficacy at Kappa-receptors. It is possible that at high concentrations U50488 activates receptors not affected by other Kappa-ligands. These additional receptors may be non-opioid receptors (hence the insensitivity to naloxone), or they could be a subtype of Kappa-opioid receptor.

Agonist‐Selective Protection of the Opioid Receptor‐Coupled G Proteins from Inactivation by 5′‐p‐fluorosulphonylbenzoyl Guanosine

The guanine nucleotide analogue, 5'-p-fluorosulphonylbenzoyl guanosine (FSBG), can react covalently with GTP-binding proteins (G proteins). In rat brain membranes, FSBG causes a time-dependent loss of beta,gamma-imido[8-3H]guanosine 5'-triphosphate binding sites. Using 1 mM FSBG, the guanyl nucleotide modulation of opioid agonist binding is abolished, whereas the guanyl nucleotide sensitivity of neurotensin binding is retained. The action of FSBG can be prevented by the presence of opioid agonists, but not the antagonist naloxone. Iodoacetamide treatment of membranes in the presence of agonist, but not antagonist, can attenuate the action of FSBG in blocking guanyl nucleotide modulation of opioid agonist binding. These results suggest that FSBG covalently modifies essential thiol groups, whose exposure to the reagent is modified by agonist occupancy of the receptor, on a species of G protein linked to opioid receptors, but not on a species of G protein linked to neurotensin receptors. Thus, FSBG may have selectivity for the forms of Gi or Go, proteins associated with opioid receptors.

Rostral and caudal ventricular infusion of antibodies to dynorphin A(1–17) and dynorphin A(1–8): effects on electrically-elicited feeding in the rat

Lateral ventricular injection of antibodies to dynorphin A(1–13) was previously shown to elevate lateral hypothalamic stimulation frequency threshold for eliciting feeding behavior. The antibodies utilized in that study cross-react completely with dynorphin A(1–17) and, to a lesser extent, dynorphin A(1–8). In the present study, highly specific antibodies to dynorphin A(1–17) and dynorphin A(1–8) were infused into the lateral ventricle and mesopontine aqueduct to determine which biologically active dynorphin A fragment mediates feeding and at what level of the CNS this activity is likely to occur. Both antibodies were found to elevate the feeding threshold. Dynorphin A(1–8) antibodies were effective at both injection sites while dynorphin A(1–17) antibodies were only effective at the lateral ventricular site. These findings suggest that feeding-related dynorphin A(1–17) activity may occur predominantly within the forebrain, while dynorphin A(1–8) activity occurs within the brainstem. Only the dynorphin A(1–8) antibodies, infused into the aqueduct, produced a naloxone-like pattern of progressive elevation in serially determined thresholds; this pattern was previously interpreted to reflect a reduction in consummatory reward. Dynorphin A(1–8) activity within some brainstem structure(s) may therefore contribute prominently to the opioid mechanism whose mediation of the hedonic response to food was previously inferred from naloxone antagonism.