Biomedical subjects

G T Bolger

Publications and source records attributed to G T Bolger.

At least 37 records · Page 2Linked to original sources

PubMed1989

Modulation of solitarial deglutitive N-methyl-D-aspartate receptors by dihydropyridines.

The ability of the dihydropyridine calcium channel activators, (-)-S-BAY K 8644 and (+)-S-202-791 and the calcium channel inhibitor, (+)-R-BAY K 8644, to modify the differential deglutitive actions of glutamate and muscarine at premotor loci in the nucleus tractus solitarii was investigated in urethane-anaesthetised rats. At subnuclei ventralis and intermedialis loci, pneumophoretic application (20-100 pl) from multibarrelled glass micropipettes (tip diameter 2-5 microns) of glutamate (10-20 pmol) evoked aminophosphonovaleric acid (APV)-insensitive pharyngeal swallows; at sites in the subnucleus centralis of the nucleus tractus solitarii glutamate evoked an APV-sensitive single-wave oesophageal response, whereas muscarine (5-10 pmol) evoked rhythmic oesophageal contractions. Both (-)-S-BAY K 8644 and (+)-S-202-791, applied in prepulses of 10-20 fmol and 100-200 fmol, respectively, either had no effect or selectively and reversibly enhanced or inhibited the glutamate-evoked responses. Identical results were obtained by intravenous administration of (-)-S-BAY K 8644 (10-50 micrograms/kg). Micropneumophoretic (20-50 fmol) or intravenous (10-50 micrograms/kg) administration of (+)-R-BAY K 8644 suppressed the N-methyl-D-aspartate (NMDA)-mediated oesophageal responses in a reversible and selective manner. The dihydropyridine vehicle produced a transient depression of all types of deglutitive responses. It is concluded that, within the deglutitive subnuclei of the nucleus tractus solitarii, "L"-type voltage-operated calcium channels are associated with NMDA-receptor-mediated deglutitive mechanisms. The inhibition or a lack of effect produced by the dihydropyridine calcium channel activators is explained in part by their actions at other sites e.g. release of inhibitory transmitters.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Anticonvulsant activity of MK-801 and nimodipine alone and in combination against pentylenetetrazole and strychnine.

The effects of the N-methyl-D-aspartate receptor antagonist MK-801 and the dihydropyridine calcium channel antagonist nimodipine were assessed for their anticonvulsant activity alone and in combination against clonic convulsions to pentylenetetrazole (PTZ) and strychnine (STR) in mice. Nimodipine (2-20 mg/kg) and MK-801 (0.1 and 0.5 mg/kg) did not affect the number of mice displaying clonic convulsions to PTZ. However, nimodipine in a dose-dependent manner increased (100%) the latency to clonic convulsions and lethality (mortality from tonic extension convulsions and respiratory failure) following PTZ. In contrast, MK-801 did not increase the latency to PTZ convulsions, but prevented the lethal effects of PTZ. When combined, MK-801 and nimodipine produced a significant reduction in the number of animals (40-60%) displaying PTZ convulsions and a greater increase in the latency to PTZ convulsions than did nimodipine alone. In contrast, MK-801 decreased the onset time, and increased the severity of STR convulsions. A combination of MK-801 and nimodipine which afforded significant protection against PTZ convulsions did not affect STR convulsions. These findings suggest that MK-801 and nimodipine, while possessing significant anticonvulsant activity on their own, produce a potent anticonvulsant synergism against PTZ but not STR.

Animals↗

PubMed1989

Phencyclidine and MK-801: a behavioral and neurochemical comparison of their interactions with dihydropyridine calcium antagonists.

The impairment of rotarod ability and the convulsive activity of phencyclidine (PCP) and MK-801 were compared in male CD-1 mice. The putative interaction between nifedipine and PCP and MK-801 on these behavioral measurements was also quantitated and compared. MK-801 produced a dose dependent inhibition of rotarod ability with an ED50 of 0.5 mg/kg. Nifedipine potentiated the impairment of rotarod ability by MK-801. Both PCP and MK-801 produced convulsive behavior in mice which was characterized by jumping and wild running fits; the CD50 for MK-801 was 1.3 mg/kg. Nifedipine dose dependently inhibited the convulsions associated with MK-801 and PCP. PCP but not MK-801 increased [3H]nitrendipine binding to dihydropyridine (DHP) binding sites on mouse brain membranes. MK-801 blocked the effects of PCP on [3H]nitrendipine binding. These findings suggest that MK-801 is a potent PCP-like drug which interacts with nifedipine and neuronal DHP binding sites. Nifedipine's reduction of the hyperactivity and convulsions elicited by MK-801 may be of importance in the eventual development of MK-801 as an antiischaemic and anticonvulsant drug.

Animals↗

PubMed1989

Characterization of the effects of AHN 086, an irreversible ligand of "peripheral" benzodiazepine receptors, on contraction in guinea-pig atrial and ileal longitudinal smooth muscle.

The effects of AHN 086 and its reversibly acting structural analogue Ro 5-4864 were studied in the spontaneously beating guinea-pig atria and field-stimulated guinea-pig ileal longitudinal smooth muscle in the presence and absence of dihydropyridine calcium channel modulators. The treatment of guinea-pig atria with AHN 086 followed by extensive washing did not alter contraction. However, AHN 086 (0.5 microM) potentiated (88%) the positive inotropic responses by BAY K 8644, an effect that was not reversed by extensive washing of the tissue. Higher concentrations of AHN 086 (greater than 2 microM) irreversibly inhibited the intropic, but not the chronotropic responses to BAY K 8644, nifedipine, and isoproterenol. Ro 5-4864 (10 microM) produced a reversible enhancement of the inotropic responses and block of the chronotropic responses to BAY K 8644. In guinea-pig ileal longitudinal smooth muscle, both AHN 086 and Ro 5-4864 reversibly inhibited field-stimulated contractions. Neither Ro 5-4864 nor AHN 086 affected the ability of nifedipine to inhibit field-stimulated contractions of ileal longitudinal smooth muscle. Treatment of intact atrial with 5 microM AHN 086 followed by extensive washing resulted in a significant inhibition (30-50%) of [3H]Ro 5-4864 binding to peripheral benzodiazepine receptors and of [3H]nitrendipine binding to voltage-operated calcium channels, but did not affect [3H]dihydroalprenolol binding to beta-adrenergic receptors on atrial membranes. The same treatment applied to intact ileal longitudinal smooth muscle affected neither [3H] (-)-quinuclidinyl benzilate binding to muscarine receptors nor [3H]nitrendipine binding, but did result in a significant inhibition (30-50%) of [3H]Ro 5-4864 binding to ileal longitudinal smooth muscle membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Characterization of ion movements and their relationship to muscarinic receptor binding and excitation-contraction coupling in guinea pig ileal longitudinal smooth muscle.

The relationship between ion movements (sodium uptake and potassium release) and agonist-induced contractile responses or muscarinic receptor binding was investigated in the guinea pig ileal longitudinal muscle (GPLM). Sodium uptake and potassium release were agonist-dependent, concentration-dependent, and stereoselective, with the following rank order of maximum ion movement: muscarinic agonists greater than histamine greater than substance P = serotonin. Potassium depolarization did not initiate sodium uptake or potassium release. Sodium uptake was rapid and monophasic, preceding potassium release which was biphasic in nature. Full muscarinic agonists produced equal maximal increases in sodium uptake, while maximal potassium release varied for all muscarinic agonists and in addition differed from sodium uptake in the following ways: time course, stereoselectivity, sensitivity to calcium antagonists, modulation by the guanylyl nucleotide derivative, 5'-guanylylimidodiphosphate (Gpp(NH)p), and inhibition by muscarinic receptor blockade with benzilylcholine mustard. The calcium ionophores A23187 and ionomycin (SQ23377) did not produce any sodium uptake; A23187 but not ionomycin produced potassium release comparable to that evoked by muscarinic agonists. Ion movement in response to combinations of agonists were not additive. Muscarinic agonist binding as measured by competition for [3H]quinuclidinyl benzilate ([3H]QNB) binding, was best described by multiple sites and was regulated by Gpp(NH)p. Excellent correlations were observed between the dissociation constants for binding and sodium uptake, potassium release, and contraction. The best correlations were those between the pharmacologic responses and the high affinity binding site in the absence, and the low affinity site in the presence, of Gpp(NH)p, respectively. Furthermore, the potencies of muscarinic agonists to evoke ion movements and to inhibit [3H]QNB binding were similar, and from one to two orders of magnitude less than those for contraction. It is suggested that contraction and potassium release were mediated by the high affinity, and sodium uptake by the low and average affinity muscarinic agonist binding sites, respectively. These findings suggest an agonist-activated receptor-effector coupling model in GPLM that leads to the activation of sodium uptake, potassium release, and subsequently, contraction.

Animals↗

PubMed1989

Selective inhibition of [3H]nitrendipine binding to brain and cardiac membranes by bacitracin.

The effects of bacitracin were investigated on [3H]nitrendipine binding to rat brain and cardiac membranes in a low ionic strength (5 mM Tris-HCl) buffer. Bacitracin inhibited [3H]nitrendipine binding to rat brain and cardiac membranes with IC50 values of 400 +/- 100 and 4600 +/- 400 micrograms/mL, respectively. Scatchard analysis in brain membranes revealed that bacitracin inhibited [3H]nitrendipine binding primarily by reducing the Bmax but also by producing a small increase in the Kd. In brain membranes, Na+ (100 mM) and Ca2+ (2 mM) reduced the potency of bacitracin to inhibit [3H]nitrendipine binding by approximately sixfold with IC50 values of 2600 +/- 300 and 2100 +/- 400 micrograms/mL observed for bacitracin in the presence of 100 mM Na+ and 2 mM Ca2+, respectively. The EC50 values for the effects of Na+ and Ca2+ were 800 +/- 200 microM and 25 +/- 5 mM. K+, Mg2+, choline, and increasing the assay buffer of Tris-HCl to 50 mM also decreased the inhibition of [3H]nitrendipine binding by bacitracin. These results suggest that bacitracin specifically modulates [3H]nitrendipine binding in a cation-dependent manner and that brain and cardiac dihydropyridine binding sites are either biochemically different or exist in a different membrane environment.

Animals↗

PubMed1989

Electrophysiological actions of Ro5-4864 on cerebellar Purkinje neurons: evidence for "peripheral" benzodiazepine receptor-mediated depression.

The effects of Ro 5-4864 (4'-chlorodiazepam; the archetypic peripheral benzodiazepine receptor ligand) were examined on the electrophysiological responses of rat cerebellar Purkinje neurons maintained in vitro. Ro 5-4864 produced a biphasic response (consisting of an increase followed by a decrease in spontaneous firing) in approximately 50% of the neurons studied. The remaining neurons responded to Ro 5-4864 application with decreased spontaneous activity. The EC50 and IC50 values for the excitatory and depressant responses to Ro 5-4864 were 490 and 450 nM, respectively. Preincubation with PK 11195 [N-methyl-N-(methyl-1-propyl)chloro-2-phenyl-1-isoquinoline-3-carboxamid e; a peripheral benzodiazepine receptor antagonist] reduced the potency of Ro 5-4864 to inhibit cell firing in a competitive fashion, but did not alter Ro 5-4864-elicited excitations. A similar effect was observed with the monocarboxylic acid anion transport inhibitor UK 5099 [alpha-cyano-beta-(1-phenylindol-3-yl)acrylate]. In contrast, the increases in cell firing elicited by t-butylbicyclophosphorothionate (a GABA-gated chloride channel blocker) were enhanced 6-fold by coperfusion with both Ro 5-4864 and PK 11195. These findings suggest that the Ro 5-4864 induced depressions of Purkinje neuron spontaneous activity is mediated by peripheral benzodiazepine receptors, whereas the excitation may result from modulation of the gamma-aminobutyric acid-gated chloride ionophore.

Animals↗

PubMed1989

Radiation inactivation reveals discrete cation binding sites that modulate dihydropyridine binding sites.

In low ionic strength buffer (5 mM Tris.HCl), the binding of [3H] nitrendipine to dihydropyridine calcium antagonist binding sites of mouse forebrain membranes is increased by both Na+ and Ca2+. Radiation inactivation was used to determine the target size of [3H]nitrendipine binding sites in 5 mM Tris.HCl buffer, in the presence and absence of these cations. After irradiation, [3H] nitrendipine binding in buffer with or without Na+ was diminished, due to a loss of binding sites and also to an increase in Kd. After accounting for radiation effects on the dissociation constant, the target size for the nitrendipine binding site in buffer was 160-170 kDa and was 170-180 kDa in the presence of sodium. In the presence of calcium ions, [3H]nitrendipine binding showed no radiation effects on Kd and yielded a target size of 150-170 kDa. These findings suggest, as in the case of opioid receptors, the presence of high molecular weight membrane components that modulate cation-induced alterations in radioligand binding to dihydropyridine binding sites.

Animals↗

PubMed1988

Differential regulation of mu-opiate receptors in heroin- and morphine-dependent rats.

Rats made dependent on heroin and morphine exhibit both qualitative and quantitative differences in the characteristics of radioligand binding to mu-opioid receptors in the central nervous system. In brain membranes prepared from control animals, [3H]dihydromorphine (DHM) binding was best described by a two-site model, while in morphine-dependent rats, [3H]DHM binding was best described by a single-site model. In contrast, [3H]DHM binding to membranes from heroin-dependent animals was best described by a two-site model, with an increased density of the high-affinity, and no change in the low-affinity population compared to controls. Furthermore, both the number of binding sites for [3H]DAGO (a ligand that selectively labels a population of high-affinity mu-opiate receptors) and the sensitivity of [3H]DHM to sodium ions was increased in heroin; but not in morphine-dependent rats. These studies demonstrate that opiate receptors are differentially regulated in heroin- and morphine-dependent animals. Such neurochemical changes in mu-opiate receptors may underlie differences in the behavioral and pharmacological profiles of heroin and morphine reported in man.

Animals↗

PubMed1988

Purification and characterization of an endogenous protein modulator of radioligand binding to "peripheral-type" benzodiazepine receptors and dihydropyridine Ca2+-channel antagonist binding sites.

Acidified extracts of rat antral stomach chromatographed on octadecylsilane cartridges contained material that inhibited the binding of [3H]Ro 5-4864 (4'-chlorodiazepam) and [3H]nitrenidipine to "peripheral-type" benzodiazepine receptors and dihydropyridine Ca2+-channel antagonist binding sites respectively. This material reduced the apparent affinities of both radioligands without significantly affecting the maximum number of binding sites. In contrast, the binding of [3H]diazepam, [3H]Ro 15-1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5a][1,4] benzodiazepine-3-carboxylate), and [3H]3-carbomethoxy-beta-carboline to "brain-type" benzodiazepine receptors and [3H]dihydroalprenolol binding to beta-adrenergic receptors were unaffected by this material. Subsequent column chromatography on hydroxylapatite purified this material by greater than 2000-fold. This semi-purified substance was resolved by reverse phase HPLC as one u.v. adsorbing peak that inhibited both [3H]Ro 5-4864 and [3H]nitrendipine binding. The activity of this 16,000 dalton substance was destroyed completely by both heat treatment and pronase and partially reduced by trypsin. Furthermore, the inhibitory activity of this substance was enhanced by Ca2+ in a concentration-dependent fashion (0.1 to 10 mM). Comparison of TLC scans of 2-9,10[3H]dipalmitoyl-phosphatidylcholine incubated with either the HPLC purified material or authentic phospholipase A2(PLA2) (Naja naja) revealed that this substance has enzymatic properties indistinguishable from PLA2. These findings suggest that this endogenous protein may be a PLA2 isoenzyme which may modify both "peripheral-type" benzodiazepine receptors and dihydropyridine Ca2+-channel antagonist binding sites.

Animals↗

PubMed1988

Modulation of neurotransmitter metabolism by dihydropyridine calcium channel ligands in mouse brain.

The regional concentrations of dopamine, serotonin, dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindole acetic acid were measured in mouse brain following administration of the dihydropyridine calcium channel activator BAY K 8644, and antagonist, nifedipine. BAY K 8644 (1-8 mg/kg) produced dose- and time-dependent increases in dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindoleacetic acid concentrations in the caudate, without altering dopamine and serotonin levels. No changes in 5-hydroxyindoleacetic acid concentration were observed in the raphe nuclei, hypothalamus, hippocampus and frontal cortex. Nifedipine (4 mg/kg) blocked BAY K 8644- (2 mg/kg) elicited increases in dihydroxyphenylacetic acid in the caudate. Furthermore, a higher dose of nifedipine (8 mg/kg) decreased dihydroxyphenylacetic acid and homovanillic acid, but did not affect dopamine, serotonin or 5-hydroxyindoleacetic acid concentrations, while a lower dose of nifedipine (2 mg/kg) significantly increased serotonin, 5-hydroxyindoleacetic acid and homovanillic acid, but did not affect dopamine and dihydroxyphenylacetic acid concentrations. The findings that both BAY K 8644 and nifedipine affect neurotransmitter metabolism in vivo in a dose-, time- and brain region-dependent manner, suggest that high-affinity dihydropyridine calcium channel binding sites play an important role in regulating neurotransmitter turnover in the central nervous system.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1988

Enantiomer selectivity and the development of tolerance to the behavioral effects of the calcium channel activator BAY K 8644.

The putative behavioral effects of the enantiomers of BAY K 8644 and the behavioral responses to (+/-)-BAY K 8644 following chronic injection were assessed on motor function in mice. The interaction of the enantiomers of BAY K 8644 with mouse brain dihydropyridine binding sites was also evaluated. The calcium channel activating enantiomer (-)-S-BAY K 8644 impaired rotarod and motor activity with an ED50 value of 0.5 mg/kg. The calcium channel blocker enantiomer (+)-R-BAY K 8644 neither affected rotarod nor motor activity. (+)-R-BAY K 8644, and the structurally related dihydropyridine calcium channel blockers nifedipine and (-)-202-791 inhibited the impairment of rotarod activity by (-)-S-BAY K 8644 in a dose-dependent manner. (+/-)-BAY K 8644 produced convulsions in mice with a CD50 of 5 mg/kg. Chronic injection of (+/-)-BAY K 8644 (8 mg/kg IP once each day for four days) resulted in a significant tolerance to, and increase in recovery from, the motor deficits produced by (+/-)-BAY K 8644. Furthermore, chronic treatment with (+/-)-BAY K 8644 increased the onset time, but did not reduce the number of mice having convulsions to (+/-)-BAY K 8644. Chronic injection of nifedipine did not affect the motor deficit and convulsive activity of (+/-)-BAY K 8644. The behavioral effects of (+/-)-BAY K 8644 were observed at significant brain levels of drug. [3H]Nitrendipine binding to mouse brain dihydropyridine binding sites was unchanged in mice chronically injected with either (+/-)-BAY K 8644 or nifedipine.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1988

Chronic sweet intake lowers pain thresholds without changing brain mu- or delta-opiate receptors.

Sprague-Dawley rats drank sweetened (3% dextrose + 0.144% saccharin, w/v) or unflavored water for 18 days and subsequent pain reactivity was assessed using a hot plate. Compared to the rats that consumed unflavored water, the rats that consumed sweet water responded more quickly on the hot plate indicating that their threshold for pain was lowered. Another group of rats given identical exposure to the fluids had their brains prepared for measuring opiate receptor binding using the delta-receptor ligand [3H]D-Ala-D-Leu-enkephalin ([3H]DADLE) and the mu-receptor selective ligand [3H]Tyr-D-Ala-Gly-MePhe-Gly-ol ([ 3H]DAGO). Binding of these opiates to mu- and delta-receptors in the cerebral cortex, striatum, hippocampus, hypothalamus, brain stem, and remaining brain regions was the same for the rats that drank sweet fluids and those that drank unflavored water. These findings suggest that drinking sweet fluids lowers pain thresholds but does not alter mu- and delta-receptors.

Animals↗

PubMed1987

Regulation of dihydropyridine calcium antagonist binding sites in the rat hippocampus following neurochemical lesions.

The effects of catecholaminergic, cholinergic, serotonergic, and glutaminergic terminal destruction and neurotransmitter depletion on [3H]nitrendipine binding to rat brain membranes were determined using the neurotoxins 6-hydroxydopamine, 5,7-dihydroxytryptamine, and kainic acid and the neurotransmitter-depleting agent reserpine. Following intracisternal injection of 6-hydroxydopamine there were time-dependent increases (14-23%) in the density but not change in the affinity of hippocampal [3H]nitrendipine binding sites. 6-Hydroxydopamine significantly increased [3H]nitrendipine binding in the hippocampus 4 and 10 days following injection. However, no significant change in binding was observed at 16 and 26 days. [3H]Nitrendipine binding in the cerebral cortex, striatum, cerebellum, and brain stem was unaffected by 6-hydroxydopamine. Neither 5,7-dihydroxytryptamine nor kainic acid affected [3H]nitrendipine binding in the hippocampus and cerebral cortex. Acute and chronic reserpinization also did not affect [3H]nitrendipine binding in the hippocampus and cerebral cortex. These results indicate that dihydropyridine calcium antagonist bindings sites in rat brain are subject to brain region-specific regulation following neurochemical lesions and may be present in their largest densities on postsynaptic membranes.

Adrenergic Fibers↗

PubMed1987

Calcium antagonist binding in cat brain tolerant to electroconvulsive shock.

Cats subjected to daily (25-30 days) electroconvulsive shock (ECS) demonstrated an elevation of their electroconvulsive threshold or tolerance to ECS. [3H] Nitrendipine binding was measured to brain regions from non-tolerant (sham shocked) and ECS tolerant cats 24 hr following the last shock. ECS produced a significant increase (45%) in the density of [3H] nitrendipine binding sites in the cerebral cortex and a significant decrease (33%) in the apparent affinity of [3H] nitrendipine in the cerebellum. No changes in binding were observed in the hippocampus. The effects of ECS were also investigated in the rat, an animal not displaying tolerance to repeated ECS. [3H] Nitrendipine binding to rat brain was measured 10 min and 24 hr following one shock (acute) or ten shocks delivered transauricularly once daily (chronic). Twenty-four hours following chronic ECS, there was a significant increase (19%) and decrease (11%) in the density, but no change in the apparent affinity of [3H] nitrendipine binding sites in the cerebral cortex and hippocampus respectively. No significant change in [3H] nitrendipine binding was observed in rat cerebellum 24 hr following chronic ECS. There were no changes in [3H] nitrendipine binding in the cerebral cortex and hippocampus 10 min and 24 hr following acute ECS. These results indicate that ECS can alter [3H] nitrendipine binding to calcium channel linked dihydropyridine binding sites in the central nervous system. It is suggested that changes in [3H] nitrendipine binding in the cat cerebellum may be involved in the development of tolerance to ECS.

Animals↗

PubMed1987

The effects of chemically and electrically-induced convulsions on [3H]nitrendipine binding in mouse brain.

The effects of chemically and electrically-evoked seizures on [3H]nitrendipine binding to voltage-dependent calcium channels in mouse brain were determined 30 and 60 min following the initiation of convulsions. While maximal electroconvulsive shock, pentylenetetrazol and strychnine exhibited either no or marginal effects, Ro 5-4864 produced a decrease (14%) in the Bmax of [3H]nitrendipine at 30 min but not 60 min. The convulsant dihydropyridine calcium channel activator, BAY K 8644, produced a significant increase in the Kd (31%) of [3H]nitrendipine at 30 min, and a significant increase in both the Bmax (21%) and Kd (28%) of [3H]nitrendipine 60 min following the initiation of convulsions. While maximal electroconvulsive shock, pentylenetetrazol and strychnine exhibited either no or marginal effects, Ro 5-4864 produced a decrease (14%) in the Bmax of [3H]nitrendipine at 30 min but not 60 min following the initiation of convulsions. These findings indicate that modulation of voltage-dependent calcium channels by certain convulsants may be important in the genesis of seizures or in post-ictal compensatory processes.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1987

Enhancement of [3H]DAGO1 binding to rat brain by low concentrations of monovalent cations.

The effects of mono- and di-valent cations and the nonhydrolyzable guanyl nucleotide derivative 5'-guanylimidodiphosphate (Gpp(NH)p) on the binding of the selective, high affinity mu-opiate receptor agonist, [3H]DAGO ([3H]Tyr-D-Ala-Gly-Mephe-Gly-ol), to rat brain membranes were studied in a low ionic strength 5 mM Tris-HCl buffer. Na+ and Li+ (50 mM) maximally increased [3H]DAGO binding (EC50 values for Na+, 2.9 mM and Li+, 6.2 mM) by revealing a population of low affinity binding sites. The density of high affinity [3H]DAGO binding sites was unaffected by Na+ and Li+, but was maximally increased by 50 mM K+ and Rb+ (EC50 values for K+, 8.5 mM and Rb+, 12.9 mM). Divalent cations (Ca2+, Mg2+; 50 mM) inhibited [3H]DAGO binding. Gpp(NH)p decreased the affinity of [3H]DAGO binding, an effect that was enhanced by Na+ but not by K+. The binding of the mu-agonist [3H]dihydromorphine was unaffected by 50 mM Na+ in 5 mM Tris-HCl. In 50 mM Tris-HCl, Na+ (50 mM) inhibited [3H]DAGO binding by decreasing the density of high affinity binding sites and promoting low affinity binding. The effects of Na+ in 5 mM and 50 mM Tris-HCl were also investigated on the binding of other opiate receptor agonists and antagonists. [3H]D-Ala-D-Leu-enkephalin binding was increased and inhibited. [3H]etorphine binding increased and was unchanged, and both [3H]bremazocine and [3H]naloxone binding increased by 50 mM Na+ in 5 mM and 50 mM Tris-HCl, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Behavioral studies with anxiolytic drugs. IV. Serotonergic involvement in the effects of buspirone on punished behavior of pigeons.

Interactions of the nonbenzodiazepine anxiolytic, buspirone, with serotonin (5-HT) were studied using behavioral and neurochemical procedures. Punished responding was studied in pigeons as this behavior is a generally acknowledged preclinical predictor of anxiolytic activity and because buspirone increases punished responding of pigeons with greater potency and efficacy than in other species. Keypeck responses were maintained under either fixed-interval or fixed-ratio schedules of food presentation; every 30th response produced a brief electric shock and suppressed responding (punishment). Buspirone (0.1-5.6 mg/kg i.m.) produced dose-related increases in punished responding which reached a maximum at 1 mg/kg. A serotonin agonist, MK-212 (0.01 mg/kg), antagonized whereas the 5-HT antagonist, cyproheptadine (0.01 mg/kg), potentiated the effects of buspirone without having behavioral effects of their own. The characteristics of [3H]-5-HT binding in pigeon brain membranes were similar to results reported in mammalian brain. Neither buspirone, MJ-13805 (gepirone, a related analog), nor MJ-13653 (a buspirone metabolite), significantly affected [3H]-5-HT binding and none of the compounds appreciably inhibited uptake of [3H]-5-HT into pigeon cerebral synaptosomes. Hill coefficients significantly less than unity for all drugs except 5-HT suggested multiple serotonergic binding sites for buspirone and analogs. Buspirone and MJ-13805 (1 nM) inhibited [3H]ketanserin binding (a measure of 5-HT2 binding sites) in pigeon cerebrum with Ki values above 10(-6) M. The number of [3H]ketanserin binding sites was estimated to be 109 fmol/mg of protein in pigeon cerebrum compared to 400 fmol/mg of protein in rat cerebrum.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗