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Biomedical subjects

J W Villiger

Publications and source records attributed to J W Villiger.

31 records · Page 2Linked to original sources
PubMed1984

Binding of buprenorphine to opiate receptors. Regulation by guanyl nucleotides and metal ions.

The effects of guanosine-5'-triphosphate (GTP), sodium chloride and manganese chloride on the binding of buprenorphine to opiate receptors present in rat brain has been studied. Manganese chloride significantly decreased the affinity of binding of both [3H] buprenorphine and unlabelled buprenorphine to morphine and enkephalin receptors. Guanosine-5'-triphosphate increased the affinity of buprenorphine for morphine sites, but had no effect on binding of buprenorphine to enkephalin or benzomorphan sites, or binding of [3H]buprenorphine. Sodium chloride had no effect on binding of buprenorphine. Control studies indicated similar apparent affinities of buprenorphine for morphine (Ki = 0.30 nM) and enkephalin (Ki = 0.31 nM) sites, and lower affinity for benzomorphan sites (Ki = 4.16 nM). No evidence could be obtained for a differential effect of ions or guanosine-5'-triphosphate on binding of buprenorphine to opiate receptor subtypes.

Animals↗
PubMed1984

Morphiceptin: biphasic inhibition of mu-opiate receptor ligands.

The interaction between morphiceptin and the morphine (mu) opiate receptor present in rat brain membranes has been examined. Detailed competitive displacement curves of morphiceptin against the mu receptor ligands [3H]fentanyl and [3H]naloxone were biphasic, with Hill coefficients of 0.78 and 0.60 respectively. Hoftsee plots of these displacement curves suggested that 30-35% of the morphiceptin binding was to a high affinity site and the residual binding was to a site with lower affinity. These results indicate that morphiceptin binding to the mu opiate receptor does not obey the law of mass action, and raises the possibility that morphiceptin distinguishes subclasses of mu binding site.

Analgesics↗
PubMed1984

CL 218,872 binding to benzodiazepine receptors in rat spinal cord: modulation by gamma-aminobutyric acid and evidence for receptor heterogeneity.

The binding of the triazolopyridazine CL 218,872 to central benzodiazepine receptors identified with [3H]Ro 15-1788 was studied in extensively washed homogenates of rat spinal cord and cerebral cortex. CL 218,872 displacement curves were shallow in both spinal cord (nH = 0.67) and cortex (nH = 0.54), suggesting the presence of type 1 and type 2 benzodiazepine receptors in both tissues. CL 218,872 had lower affinity in spinal cord (IC50 = 825 nM) than cortex (IC50 = 152 nM), possibly reflecting the presence of fewer type 1 sites in the cord. Activating gamma-aminobutyric acid (GABA) receptors with 10 microM muscimol resulted in a two- to threefold increase in CL 218,872 affinity in both tissues without changes in the displacement curve slope. This indicates that GABA enhances CL 218,872 affinity for both type 1 and type 2 sites in both spinal cord and cerebral cortex.

Animals↗
PubMed1983

Characteristics of [3H]fentanyl binding to the opiate receptor.

The present study characterises the binding of the highly lipophilic opiate agonist [3H]fentanyl to homogenates of the rat central nervous system. At 25 degrees C, association of [3H]fentanyl with its binding site was rapid (t1/2 = 2.5 min). Dissociation from the binding site was biphasic (t1/2's = 4.0 and 100 min) suggesting the existence of high and low affinity binding sites. Scatchard plots of saturation isotherms were curvilinear, confirming the presence of high (KD = 0.46 nM) and low KD = 4.26 nM) affinity binding sites. Increasing temperature and the concentration of sodium ion decreased the [3H]fentanyl binding. Opiate agonists, antagonists and mixed agonist-antagonists were all potent (IC50's less than 20 nM) in displacing [3H]fentanyl and displacement by levorphanol and dextrorphan indicated that [3H]fentanyl binding was stereospecific. The mu and delta selective peptides, morphiceptin and [D-Ala2,D-Leu5]enkephalin, had IC50 values of 87 and 9.2 nM respectively. The regional distribution of [3H]fentanyl binding was in the rank order striatum approximately equal to midbrain greater than hypothalamus greater than cortex greater than hippocampus greater than brainstem greater than spinal cord greater than cerebellum. Comparison of [3H]fentanyl, [3H]naloxone and [3H-D-Ala2,D-Leu5]enkephalin binding in the hypothalamus-thalamus (mu-enriched) compared with the frontal cortex-striatum (delta-enriched) indicated that the pattern of [3H]fentanyl labelling was similar to that obtained with [3H]naloxone, but differed from that obtained with [3H-D-Ala2,D-Leu5]enkephalin. These characteristics suggest that [3H]fentanyl binds to the mu-opiate receptor. These findings are discussed in relation to the high lipid solubility of fentanyl as compared with morphine.

Animals↗
PubMed1982

Characteristics of type 1 and type 2 benzodiazepine receptors in the ovine brain.

Analysis of the displacement of 3H-diazepam binding to membranes prepared from the ovine frontal cortex by the triazolopyradiazine CL218,872 yielded a Hill coefficient significantly below unity. By analogy with similar studies of this drug in rat brain this suggested the existence of Types 1 and 2 benzodiazepine receptors. The degree of displacement of 3H-diazepam by CL218,872 (200 nM, Type 1; 800 nM, Type 2) in homogenates of brain regions differed, the rank order being cerebellum greater than parietal cortex greater than frontal cortex congruent to temporal cortex congruent to hippocampus greater than striatum. Displacement of 3H-diazepam by CL218,872 was enhanced by 10(-5) M GABA in the striatum (at 200 nM and 800 nM CL218,872) and cerebellum (at 200 nM CL218,872). Benzodiazepine receptors in the ovine frontal cortex were least sensitive to CL218,872 (200 nM) in young fetuses (54-68 days gestation) and achieved adult levels of sensitivity by late gestation. Finally, the potency of CL218,872 to displace 3H-diazepam was not effected by the 3H-ligand concentration (0.5 nM or 5.0 nM), suggesting that Types 1 and 2 benzodiazepine receptors are not identical to the high and low affinity 3H-diazepam binding sites we have previously identified in the ovine brain.

Animals↗
PubMed1982

Buprenorphine: high-affinity binding to dorsal spinal cord.

The binding of the mixed opiate agonist-antagonist [3H]buprenorphine was compared with [3H]naloxone and [3H]dihydromorphine binding in membranes prepared from rat whole brain and dorsal spinal cord. Scatchard analysis of binding to whole brain yielded KD values close to 1.0 nM for all three 3H-ligands studied, although [3H]buprenorphine labelled five times as many binding sites. [3H]Naloxone and [3H]dihydromorphine bound to dorsal spinal cord with approximately the same affinity as to whole brain, although both 3H-ligands labelled fewer sites in the spinal cord. In contrast, Scatchard analysis of [3H]buprenorphine binding to spinal cord yielded curvilinear Scatchard plots, suggesting the presence of a very high-affinity (KD = 0.12 nM) binding site in addition to the high-affinity site (KD = 1.0 nM) present in the brain. Studies on the displacement of [3H]buprenorphine by opiates and D-Ala2,Met5-enkephalinamide supported the presence of two binding sites for this ligand in the spinal cord.

Animals↗
PubMed1982

Ontogenesis of opiate receptors in regions of the ovine brain.

We have studied the ontogenesis of opiate receptors in homogenates prepared from different regions of the ovine brain using 3H-naloxone and 3H-D-Ala2, Met5-enkephalinamide. At the concentration employed (0.5 nM) these 3H-opiates labeled both high (KD less than 0.5 nM) and low (KD greater than 1.3 nM) affinity binding sites. When midgestation fetus (68-77 day), late gestation fetus (83-134 day), and neonate (147-173 day) brain regions were compared the majority of regions showed a steady increase in 3H-opiate binding with development. However, marked variation was noted in postnatal development when neonate and adult (greater than 730 days) brains were compared. In some brain regions binding plateaued or increased slightly (thalamus, hippocampus, temporal cortex, and occipital cortex), while opiate receptor binding decreased significantly from neonate to adult in other regions (hypothalamus, striatum, and midbrain). In the pons/medulla, binding was highest in fetal tissues and declined during postnatal life. A comparison of 3H-naloxone binding in adult ovine and rat brains indicated similar regional distribution and concentrations of opiate receptors between these species, although the ovine midbrain and hippocampus contained only 25-30% of the binding sites present in comparable rat brain regions.

Age Factors↗
PubMed1982

Multiple benzodiazepine receptors in the ovine brain: ontogenesis, properties, and distribution of 3H-diazepam binding.

Benzodiazepine receptors in the ovine frontal cortex were present at 56 days gestation and developed slowly until 96 days when the number increased rapidly, reaching adult levels by 120 days gestation. Scatchard analysis of 3H-diazepam specifically bound to cortical membranes suggested high (KD approximately equal to 2.0 nM) and low (KD approximately equal to 20.0 nM) affinity benzodiazepine receptors at all stages of development. Whereas the affinity of these receptors for 3H-diazepam did not alter during development, the number of both high and low affinity receptors increased significantly between 56 and 120 days gestation. The number of low affinity receptors were higher in late gestation and early neonatal life than in adulthood. The functional state of these receptors as determined by sensitivity to GABA did not alter during development. However, in the adult, nitrazepam, flunitrazepam, midazolam, and 1-methylisoguanosine were more potent in displacing 3H-diazepam at the low affinity than the high affinity receptor, whereas chlordiazepoxide and diazepam had greater potency at the high affinity binding site. Development of the benzodiazepine receptor in the majority of other brain regions studied occurred primarily after 68 days gestation, as was the case in frontal cortex. In contrast, hindbrain and midbrain benzodiazepine receptors had reached adult levels by 68 days gestation.

Animals↗
PubMed1981

Testing cyclic AMP mediation of memory: reversal of alpha-methyl-p-tyrosine-induced amnesia.

Treatments that increased intracellular cyclic 3',5' adenosine monophosphate (cAMP) levels following catecholamine depletion caused by alpha-methyl-p-tyrosine (AMPT) provided a prophylactic effect against AMPT-induced amnesia. This effect gives evidence that cAMP mediated the formation of memory. In Experiment I, the phosphodiesterase inhibitor papaverine (50 mg/kg), immediately after a one-trial acquisition task, functionally increased cAMP levels and prevented amnesia 3 h after treatment with AMPT (200 mg/kg) for New Zealand A strain (NZ/A) mice tested in a step-through passive avoidance apparatus. Retention test latencies 72 h later were significantly higher for animals that received only saline and for animals that received AMPT and papaverine than for animals that received AMPT and saline (the amnesic group). In a similar task (Experiment II), mice that received an intracerebroventricular injection of either 5 or 10 microgram dibutyryl cAMP immediately after acquisition and 3 h after AMPT administration showed significantly higher retention test latencies than animals that received AMPT and saline. The AMP plus 10 microgram dibutyryl cAMP group showed facilitated performance even compared to the saline plus saline group.

Amnesia↗