Search PubMed⌕ Search

Biomedical subjects

B C Yoburn

Publications and source records attributed to B C Yoburn.

At least 37 records · Page 2Linked to original sources
PubMed1994

Spinal and supraspinal effects of pertussis toxin on opioid analgesia.

The effects of in vivo pertussis toxin (PTX) treatment on the functional effects of opioid agonists were examined in the mouse. Mice were injected intracerebroventricularly (ICV), or intrathecally (IT), or IT and ICV with PTX, and dose-response studies of the antinociceptive action of systemic (SC) morphine, fentanyl, and etorphine were conducted 10 days later. IT PTX decreased the potency (approximately 4.5-fold) of morphine more than ICV administration (approximately 1.5-fold), whereas the combination of IT and ICV administration produced an additive effect. When PTX was administered spinally and supraspinally, the potency of morphine, fentanyl, and etorphine was reduced similarly (approximately 5-7-fold), indicating that the effect of PTX does does not vary considerably among agonists of different intrinsic efficacies. These studies indicate that in vivo PTX can reduce the potency of opioid agonists with different intrinsic efficacies, and that spinal mechanisms appear to be more sensitive to PTX treatment.

Analgesics↗
PubMed1994

A simple procedure for assaying cAMP.

A step-by-step protocol for assaying cAMP is presented. This method is based on the standard binding protein assay that is available commercially. However, using the present procedure, the per tube cost is dramatically reduced. In the current protocol, four different binding proteins are compared for their ability to bind cAMP. The source of all reagents is noted as well as necessary precautions for insuring reliable assays. A simple tissue preparation method is outlined for assaying cAMP in brain. The utility of the assay is illustrated by demonstrating the effect of forskolin on cAMP in mouse striatal tissue.

Animals↗
PubMed1994

Opioid antagonist-induced receptor upregulation: effects of concurrent agonist administration.

The present study examined whether opioid antagonist-induced receptor upregulation could be antagonized by simultaneous treatment with opioid agonists. Mice were treated concurrently with opioid agonists (morphine, fentanyl, etorphine) and antagonists (naloxone, naltrexone) over a period of 7-8 days. Concurrent morphine (1 or 4, 75 mg SC implanted pellets), fentanyl (5.0 mg/kg/day, infusion) or etorphine (0.25 mg/kg/day, infusion) administration were unable to inhibit upregulation of mu opioid (DAMGO) receptors by either naloxone (1 mg/kg/day, infusion) or naltrexone (15 mg or 2 mg SC implanted pellet). Only a very high infusion dose of etorphine (10 mg/kg/day) inhibited upregulation by naltrexone (2mg SC implanted pellet). These results indicate that antagonist-induced upregulation is a robust, receptor-mediated phenomenon.

Animals↗
PubMed1993

Opioid receptor regulation in mice.

The effect of chronic treatment with opioid agonists and antagonists on mu opioid receptor density and opioid potency was examined in mice. Mice were implanted s.c. with osmotic mini-pumps that infused etorphine (50-500 micrograms/kg/day), fentanyl (0.03-5.0 mg/kg/day) or naloxone (0.1-10.0 mg/kg/day) for 7 to 8 days. Other mice were implanted s.c. with a morphine pellet (75 mg) for 3 or 7 days or were injected s.c. once daily for 7 days with fentanyl (0.3 mg/kg). At the end of treatment, saturation binding studies were conducted ([3H]DAMGO) or antinociceptive tolerance was evaluated using the tail-flick assay. Etorphine produced dose-dependent tolerance as well as down-regulation of mu receptor density. Fentanyl infusions produced upregulation of opioid receptors at lower (0.03 and 1.00 mg/kg/day) doses and down-regulation at the highest dose (5.00 mg/kg/day). The lowest fentanyl infusion dose also produced tolerance. Daily s.c. administration of fentanyl (0.30 mg/kg) increased receptor density and produced tolerance to fentanyl. Morphine pellets increased (3 day) and then had no effect (7 day) on receptor density, although tolerance to morphine was observed at 7 days. Naloxone dose-dependently increased mu opioid receptor density. Receptor affinity was not systematically altered by the drug treatments. Control binding studies indicated that acute etorphine interfered with binding at mu receptors 15 min after administration, but that all drug was eliminated by 16 hr. Thus, binding and tolerance studies using etorphine were conducted 16 hr after the end of infusion, when all drug had been eliminated.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesics↗
PubMed1992

Chronic d-amphetamine inhibits opioid receptor antagonist-induced supersensitivity.

Chronic treatment with an opioid antagonist, such as naltrexone, increases opioid receptor density and opioid agonist potency. Since stimulants such as d-amphetamine can increase opioid potency and opioid abusers may administer stimulants during naltrexone treatment, the effect of chronic d-amphetamine on naltrexone-induced opioid receptor upregulation and supersensitivity was examined in mice. Mice were implanted s.c. with a 15 mg naltrexone or placebo pellet for 8 days. Mice were injected daily with saline or d-amphetamine (7.5 or 5.0 mg/kg per day s.c.) for 7 days beginning 24 h following implantation. Naltrexone and placebo pellets were removed on the 8th day, and 24 h later mice were tested for morphine analgesia (tail-flick) or whole brain was removed and opioid receptor binding studies were conducted. Chronic naltrexone significantly enhanced the analgesic potency of morphine in saline-treated mice. However, naltrexone treatment did not increase morphine potency in mice treated with d-amphetamine. In binding studies, naltrexone increased [3H][D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAGO) Bmax (+60-70%) without altering KD in both saline- and d-amphetamine-treated mice. Results from studies with 2 nM [3H][D-Pen2,D-Pen5]enkephalin (DPDPE) were similar. These studies indicate that daily d-amphetamine can limit naltrexone-induced supersensitivity but not receptor upregulation. Thus, upregulation can be dissociated from functional supersensitivity.

Animals↗
PubMed1992

Potentiation of opioid analgesia by cocaine: the role of spinal and supraspinal receptors.

These studies examined the effect of cocaine on the analgesia produced by systemically and centrally administered opioid agonists. Cocaine (50 mg/kg, s.c.) increased the analgesic potency of systemic, ICV and IT morphine; and the ICV and IT analgesic effects of the delta selective peptide, [D-Pen2,D-Pen5]enkephalin (DPDPE). Cocaine also increased the analgesic potency of the mu selective ligand [D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAGO) administered ICV. However, cocaine did not alter the ED50 for IT DAGO. GC-MS studies indicated that brain cocaine concentration was approximately 3.0 micrograms/g wet weight 45 min following s.c. administration. These results suggest that cocaine-induced increases in opioid analgesic potency are mediated at brain mu and delta receptors and spinal mu receptors. Furthermore, there might be functional differences between spinal and supraspinal sites at which DAGO produces analgesia.

Analgesics, Opioid↗
PubMed1992

Effect of adrenal and sex hormones on opioid analgesia and opioid receptor regulation.

The role of endocrine factors on opioid analgesia (antinociception) and opioid receptors was studied in male and female Swiss-Webster mice. Morphine was more potent in male than in female mice, although this difference appears to be due to greater availability of morphine to the brain in males. Saturation binding studies indicated that the density and affinity of brain mu- and delta-opioid binding sites were equivalent in males and females. Males and females were implanted SC with naltrexone (NTX) or placebo pellets for 8 days, and then the pellets were removed. This treatment increased the density of mu and delta binding sites in brain and increased the potency of morphine for both sexes, although the increase in antinociceptive effects for males was greater than for females. Adrenalectomy (ADX) in male mice increased the potency of morphine and methadone but did not alter the brain levels of either drug. ADX did not alter brain opioid binding of either mu or delta ligands. When male ADX and control mice were treated with NTX, the potency of morphine and brain opioid binding sites were increased equivalently in both groups. Gonadectomy (GDX) in male mice tended to decrease morphine potency, although this was not found to be a very reliable effect. When male GDX and control mice were implanted with NTX, brain opioid binding was increased similarly in both groups, although morphine potency was increased less in GDX mice. Overall, these studies show that sex differences and hormones of the adrenals and gonads in male mice do not alter brain opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex Hormones↗
PubMed1991

Evaluation of receptor mechanism mediating fentanyl analgesia and toxicity.

In the present study the antagonism of fentanyl pharmacodynamics was studied in the mouse and the receptor populations mediating the analgesic and lethal effects of fentanyl were examined. Both 1 and 8 days following implantation (s.c.) of a 15 mg naltrexone pellet there was a significant shift to the right of the fentanyl dose-response curves for analgesia and lethality. The analgesia dose-response curves were shifted significantly more (80- to 264-fold) than the lethality curves (13- to 16-fold) in the presence of naltrexone. In addition, acute naloxone (0.1 mg/kg s.c.), antagonized fentanyl analgesia more than lethality. Consequently, the relative safety ratio of fentanyl (LD50/ED50) was decreased in the presence of opioid antagonists. Pretreatment with naloxonazine (35 mg/kg s.c.) 24 h prior to testing effectively inhibited fentanyl-induced analgesia, but not fentanyl-induced lethality. However, pretreatment with beta-funaltrexamine (beta-FNA) (20 mg/kg, s.c.) 24 h prior to testing inhibited both fentanyl-induced analgesia and lethality. Implantation (s.c.) of a 75 mg morphine pellet for 72 h resulted in cross-tolerance to both fentanyl analgesia and lethality. However, the degree of the cross-tolerance was 1.8-fold for analgesia and 4.5-fold for lethality. Displacement studies of [3H]naltrexone by fentanyl in mouse brain homogenate indicated two populations of binding sites. Taken together, the pharmacodynamic studies and the binding studies suggest that fentanyl exerts its analgesic and lethal effects through different receptor populations.

Analgesics↗
PubMed1991

Modification of morphine-induced analgesia and toxicity by pertussis toxin.

The present study evaluates the effect of pertussis toxin (PTX) on morphine-induced analgesia and lethality. Mice were injected with 0.2 microgram PTX intracerebroventricularly (i.c.v.) and 0.2 micrograms PTX intrathecally (i.t.) or saline. Mice were tested for morphine-induced analgesia (tail flick) and lethality 16 days later; mice were also examined for pentobarbital-induced mortality. Morphine analgesic potency was decreased by approximately 4-fold in PTX-treated mice compared to controls. Conversely, the lethal potency of morphine was increased by 10-fold in PTX-treated mice compared to controls. PTX treatment did not alter the lethal potency of pentobarbital. Morphine-induced analgesia and lethality were dose-dependently antagonized by naloxone in both PTX and saline-treated groups. The results of this study suggest that morphine analgesia is mediated through PTX-sensitive G proteins. On the other hand, morphine-induced lethality appears to be limited by PTX-sensitive factor(s) since PTX treatment enhanced morphine's lethal potency. The increase in lethal potency of morphine may be due to unmasking of an excitatory opioid receptor mediated effect by PTX.

Analgesia↗
PubMed1991

Species differences in mu- and delta-opioid receptors.

The mu opioid receptor ligand [D-Ala2, NMePhe4, Gly-ol5]enkephalin (DAGO) and delta opioid receptor ligand [D-Pen2,D-Pen5]enkephalin (DPDPE) show similar specificity in competition binding studies in whole brain homogenate in rat and mouse. However, in saturation studies, the density and affinity of DPDPE binding sites were substantially greater in the mouse. There was no difference between the mouse and rat in the density and affinity of DAGO sites. Results from dose-response studies for analgesia using the same ligands administered i.c.v. in both species paralleled the binding studies. DAGO was approximately 2 times more potent in the mouse compared to the rat; while DPDPE was more than 15 times more potent in the mouse. Thus, binding capacity and affinity differences appear to be related to the functional potency of the mu and delta ligands in the two species. These results suggest that the difference in potency of DPDPE between rat and mouse is related to the differences in brain delta opioid receptors.

Analgesics↗
PubMed1991

Dissociation of opioid receptor upregulation and functional supersensitivity.

Alterations in brain opioid binding and opioid pharmacodynamics following chronic (8-day) naltrexone (NTX) treatment were determined in pertussis toxin (PTX)-treated mice. Intrathecal (IT) and intracerebroventricular (ICV) PTX produced a time-dependent, long-lasting inhibition of morphine (SC) analgesia without modifying basal nociception. Inhibition was maximal 16 days following PTX treatment, and was still observed at 40 days. Relative to placebo controls, NTX treatment produced supersensitivity to morphine analgesia in all control mice and in mice pretreated with PTX 1 day before NTX. Supersensitivity was not observed in 7-day PTX-pretreated mice. [3H][D-Ala2-D-Leu5]enkephalin ([3H]DADLE) and [3H][D-Ala2-MePhe4-Gly(ol)5]enkephalin ([3H]DAMGO) binding sites were increased by NTX treatment in saline- and PTX-pretreated groups. KDs were unchanged. These results indicate that PTX does not alter opioid antagonist-induced receptor upregulation. However, PTX treatment can diminish morphine potency in upregulated and control mice. Therefore, opioid analgesia in control and upregulated mice appears to be mediated by receptors linked to a common PTX-sensitive G-protein. Furthermore, in 7-day PTX-pretreated mice, NTX increased binding sites without altering morphine potency, which suggests that new binding sites can appear without being functionally coupled.

Analgesia↗
PubMed1991

Preproenkephalin mRNA and enkephalin in normal and denervated adrenals in the Syrian hamster: comparison with central nervous system tissues.

The distribution and characteristics of preproenkephalin (PPenk) mRNA and enkephalin-containing (EC) peptides are compared in CNS and adrenal tissues from Syrian hamsters and Sprague-Dawley rats. Total cellular RNA extracts from both rat and hamster tissues produce a single hybridization band of PPenk mRNA of approximately 1500 bases when analyzed by Northern blot hybridization. Quantitation by solution hybridization reveals that in the hamster the highest levels of PPenk mRNA are found in adrenal (16.3 +/- 1.4 pg equivalents/micrograms RNA (mean +/- S.E.M.)) and striatum (13.3 +/- 0.7), followed by hypothalamus (0.8 +/- 0.2), and hippocampus (0.4 +/- 0.2). In the rat the highest levels of PPenk mRNA are in the striatum (35 +/- 2 pg/micrograms RNA) followed by the hypothalamus (3.0 +/- 0.5), hippocampus (0.3 +/- 0.1) and adrenal (0.18 +/- 0.04). Thus, the rank order of abundance of PPenk mRNA is similar in these CNS tissues for rat and hamster. The hamster adrenal levels are more than 90-fold greater than those of the rat. The abundance of EC peptides in both hamster and rat tissues mirror the rank order found with PPenk mRNA. Hamster adrenal contains the highest level of EC peptides (441 +/- 37 pmol/mg protein (mean +/- S.E.M.)) which is more than 400-fold greater than that of the rat adrenal and 8- to 12-fold greater than that found in rat and hamster striatum or hypothalamus. Both size exclusion chromatography and Western blot analysis indicate that EC peptides in hamster adrenal are predominantly large proenkephalin-like peptides with approximately 6 copies of Met- and 1 copy of Leu-enkephalin and that included in their number is a prominent EC peptide with a molecular weight of 34 kDa. Unilateral denervation of the hamster adrenal results in a time-dependent ipsilateral decrease in EC peptide and PPenk mRNA levels. Thus, by day 8 postsurgery, PPenk mRNA levels have declined by an average of 80% while EC peptides are reduced by 68% when compared to the innervated contralateral adrenal. These results demonstrate the great abundance of PPenk mRNA and EC peptides in the hamster adrenal. They also demonstrate the apparent need for transsynaptic impulse activity to maintain the high steady-state levels of PPenk and EC peptides. These characteristics of the hamster adrenal system provide opportunities for physiological and pharmacological investigations of the regulation of proenkephalin gene expression.

Adrenal Glands↗
PubMed1991

Transsynaptic activity regulates proenkephalin and tyrosine hydroxylase gene expression and the response to reserpine in the hamster adrenal.

Transsynaptic neurogenic activity and reserpine are two signals that cause the proenkephalin (Penk) gene to alter the levels of preproenkephalin (PPenk) mRNA and enkephalin-containing (EC) peptides. In the Syrian hamster adrenal, but not in rat adrenal, both of these signals appear to be positive activators of Penk gene expression. The separate and combined effects of reserpine and denervation on EC peptides and catecholamine systems were investigated in the adrenal of the hamster, a species with relatively high medullary PPenk mRNA and EC peptide levels. Unilateral adrenal denervation resulted in a rapid decrease in PPenk mRNA levels of 54% after 2 days, and by 11 days 90% of Penk mRNA had disappeared. After 4 days both EC peptide and PPenk mRNA levels fell in parallel, whereas total RNA and soluble protein levels were unchanged. Denervation had no effect on TH mRNA levels until 8 days after surgery, and after 11 days both TH mRNA and catecholamine levels had decreased by 35-45%. Reserpine produced a dose- and time-dependent depletion of EC peptides and catecholamines. One day after 5 mg/kg reserpine (given subcutaneously on each of 2 consecutive days), EC peptides were reduced by 80%, norepinephrine by 79%, and epinphrine by greater than 95%. By 4 days after treatment, EC peptides and catecholamines slightly exceeded or had returned to control (concurrent vehicle treatment) values. PPenk mRNA levels, as measured by solution hybridization, were doubled (206 +/- 17%, mean +/- standard error) by day 4. Tyrosine hydroxylase (TH) mRNA levels were increased nearly 7-fold (686 +/- 71%) 24 hr after the first reserpine dose and declined thereafter. Northern blot analysis demonstrated that reserpine did not alter the size of either PPenk or TH mRNAs. Size exclusion chromatography showed a small (20%) reserpine-induced increase in processing of high molecular weight Penk-like peptides. The effects of reserpine, which increases PPenk mRNA, EC peptides, and TH mRNA, were completely blocked by unilateral denervation, whereas the contralateral innervated gland showed the expected responses. The co-localized EC peptide and catecholamine systems, as reflected in their mRNAs, respond differently in both time sequence and magnitude to reserpine and to denervation. Our results support a critical role, in vivo, for transsynaptic mechanisms in the maintenance of the high levels of Penk gene expression in this species and for the positive activation (mediated by reflex neurogenic stimulation) of reserpine on Penk and TH gene expression.

Adrenal Glands↗
PubMed1991

The role of opioid receptor density in morphine tolerance.

The effect of chronic opioid antagonist-induced functional supersensitivity and receptor upregulation on morphine tolerance was examined in Swiss Webster mice obtained from Taconic Farms and Charles River Laboratories. Mice were implanted s.c. with either naltrexone (NTX) or placebo pellets for 8 days. After 8 days, the pellets were removed, and 24 h later mice were either injected with morphine (50 or 100 mg/kg) or saline (acute tolerance protocol) or implanted with a 75-mg morphine or placebo pellet for 72 h (chronic tolerance protocol). Mice were tested for morphine analgesia 24 h after injections or 72 h after pellet implantations. Mice from Taconic Farms were more sensitive to morphine analgesia than Charles River mice, although the degree of tolerance in both strains was similar. Acute morphine produced a 1.7- and 1.9-fold increase in the ED50 for morphine analgesia in NTX and placebo pretreated mice, respectively. the chronic tolerance protocol produced the same shift (2.4-fold) in the ED50 in both NTX and placebo pretreated mice. In both tolerance protocols, NTX-pretreated mice were significantly more sensitive to the analgesic effects of morphine than placebo pretreated controls. Binding studies ([3H][D-Ala,2NMePhe4,Gly-ol5]enkephalin) indicated an approximately 40% increase in opioid receptor density with no significant alteration in affinity after chronic NTX treatment. These results indicate that acute and chronic tolerance to morphine develops comparably in control and upregulated, supersensitive mice. These findings suggest that new binding sites in upregulated mice mediate tolerance similarly to existing binding sites and that the degree of tolerance is unrelated to the density of opioid receptors.

Animals↗
PubMed1990

Simultaneous development of opioid tolerance and opioid antagonist-induced receptor upregulation.

Mice treated chronically with opioid antagonists have increased receptor density in brain and are supersensitive to the pharmacodynamic action of morphine. In the present study mice were implanted subcutaneously with naltrexone or placebo pellets for 8 days. During implantation mice received daily injections of morphine (100 or 250 mg/kg) or saline. Morphine analgesia was completely blocked in mice that were implanted with naltrexone at the low dose of morphine; while some analgesic action was observed at the higher dose. Mice implanted with placebo were analgesic following the daily morphine treatment. At the end of 8 days the pellets were removed and 24 h later some mice were tested for morphine analgesia while others were examined in binding studies. Naltrexone treatment increased [3H]naloxone, 3H[D-Ala2-D-Leu5]enkephalin (DADLE) and 3H[D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAGO) binding compared to controls and increased the analgesic potency of morphine. Daily treatment with morphine did not alter brain opioid binding or naltrexone-induced receptor upregulation. Mice injected daily with morphine were significantly less sensitive to morphine (tolerant) than their respective saline control group for both the placebo and the naltrexone-treated groups. However, naltrexone-treated mice were more sensitive to morphine than placebo controls regardless of whether they were injected daily with morphine or not. These results indicate that if naltrexone-induced opioid receptor upregulation occurs in the presence of repeated agonist administration, the new binding sites mediate tolerance via desensitization to morphine.

Analgesia↗
PubMed1990

Tolerance develops to spinal morphine analgesia but not morphine-induced convulsions.

Administration of morphine into the spinal intrathecal (i.t.) space produced dose-dependent analgesia in the mouse. At higher doses i.t. morphine induced seizures of the hindlimbs. Mice treated chronically with morphine (75 mg pellet, s.c.) for 72 h were tolerant to the analgesic effects of i.t. morphine, but not to the proconvulsant action. Spinal morphine analgesia was attenuated by naloxone, whereas i.t. morphine-induced seizures were not. These results indicate that spinal opioid receptors mediate analgesia but not seizures following i.t. morphine treatment in the mouse.

Analgesia↗
PubMed1990

Differentiation of spinal and supraspinal opioid receptors by morphine tolerance.

Mice treated for 72 hrs with morphine (subcutaneously implanted pellets) were tested with a variety of opioid receptor agonists to examine the development of tolerance and cross-tolerance to their analgesic action. The development of spinal and supraspinal tolerance following morphine treatment was evaluated by administering compounds systemically (sc), intrathecally (IT) and intracerebroventricularly (ICV). Following morphine treatment, tolerance to morphine analgesia was observed following IT, ICV and sc administration. Chronic morphine treatment also produced cross-tolerance to the analgesic effects of the selective delta opioid receptor agonist [D-Pen2, D-Pen5]enkephalin (DPDPE) following IT and ICV administration. However, morphine treatment selectively produced cross-tolerance to ICV [D-Ala2, NMePhe4, Gly-ol5]enkephalin (DAGO) (mu receptor agonist) analgesia, without altering IT DAGO analgesia. These results suggest that brain and spinal cord receptors mediating the effects of DAGO differ in terms of the development of cross-tolerance to morphine; and suggest that tolerance to systemic morphine may be due to changes in spinal delta and brain mu and delta receptor mechanisms.

Animals↗