Biomedical subjects

C R Gardner

Publications and source records attributed to C R Gardner.

At least 73 records · Page 4Linked to original sources

PubMed1988

(Imidazo[1,2-a]pyrimidin-2-yl)phenylmethanones and related compounds as potential nonsedative anxiolytics.

Several series of heterocyclic carboxylic esters were found to be active in the benzodiazepine receptor binding assay, a typical example being ethyl 7-ethyl-5-methoxyimidazo[1,2-a]quinoline-2-carboxylate (4b) with an IC50 of 150 nM. The corresponding phenylmethanone 5d was more potent with an IC50 of 14 nM and was orally active in animal models thought to predict anxiolytic effects. The synthesis of a large number of compounds resulted in the optimization of this activity in a series of (imidazo[1,2-a]pyrimidin-2-yl)phenylmethanones of which compounds 7e, 8b, 8h, 8j, and 8k were equipotent with chlordiazepoxide while exhibiting reduced anticonvulsant activity, little or no muscle relaxation, and negligible sedative effects.

Animals↗

PubMed1988

Controlled gastric emptying. 1. Effects of physical properties on gastric residence times of nondisintegrating geometric shapes in beagle dogs.

The importance of three physical parameters (size, shape, and flexibility) on gastric retention in fasting dogs was examined to assess the feasibility of designing a dosage form to achieve a consistent and predictable residence in the stomach. Test shapes were molded from Silastic elastomer or made from extruded polyethylene or polyethylene blends and included 15% barium sulfate for X-ray visualization. Beagle dogs were dosed with test shapes administered in gelatin capsules. Gastric retention was monitored by X ray over a 24-hr period. Six shapes (ring, tetrahedron, cloverleaf, disk, string, and pellet) were screened in vivo for their gastric retention potential. The tetrahedrons (each leg 2 cm in length) exhibited 91-100% retention at 24 hr. The rings (3.6-cm diameter) provided 100% retention at 24 hr. Rings and tetrahedrons of varying flexural moduli were prepared by blending low-density polyethylene and ethylene:vinyl acetate copolymer. A positive correlation existed between flexural modulus and gastric retention. The results indicate that it is feasible to design a platform for a dosage form that can be administered to beagle dogs in capsule form and be retained for 24 hr.

Animals↗

PubMed1987

Differential sensitivity of tumor targets to liver macrophage-mediated cytotoxicity.

Liver macrophages activated in vivo with bacterially derived lipopolysaccharide (LPS) display enhanced chemotaxis, phagocytosis, and oxidative metabolism. To determine if LPS also activates these mononuclear phagocytes for tumor cell killing, we compared the cytotoxic activity of macrophages from livers of rats treated with LPS (5 mg/kg, i.v.) with resident Kupffer cells. We found that both macrophage cell types displayed cytotoxicity towards rat N1S1 hepatoma and RBL-1 basophilic leukemia cells. Cytotoxicity of resident and LPS-activated liver macrophages towards these targets increased with cocultivation time, was dependent on the effector:target cell ratio, and appeared to involve extracellular lysis. No direct correlation between macrophage activation and cytotoxicity was observed towards these targets. While liver macrophages from LPS treated rats were more cytotoxic towards N1S1 cells, resident Kupffer cells were more cytotoxic towards RBL-1 cells. In further studies, resident Kupffer cells were also found to display extracellular cytolytic activity towards mouse P815 mastocytoma cells. In contrast, LPS-activated liver macrophage-mediated killing of these targets involved phagocytosis of intact tumor cells, as evidenced by light and electron microscopy and by uptake of 51Cr-labeled cells. These results suggest that cytotoxicity mediated by liver macrophages depends on the type of macrophage and the nature of the tumor cell target. In addition, cytotoxicity towards tumor targets appears to involve at least two different mechanisms including extracellular cytolysis and phagocytosis.

Animals↗

PubMed1987

Agonist and antagonist activities at benzodiazepine receptors of a novel series of quinoline derivatives.

Five members of a novel series of quinoline derivatives which all have similar activities on benzodiazepine receptor binding in vitro were compared in a food-motivated conflict and stress-induced ultrasounds models of anxiety and on suprahyoid muscle twitching in urethane-anaesthetised rats. RU 42382, RU 43028 and RU 39419 showed anxiolytic activity in both tests and RU 40410 was an antagonist. RU 40744 inhibited stress-induced ultrasounds but had little activity in the conflict test. Amphetamine-induced suprahyoid muscle twitching was only weakly inhibited by RU 42382 and RU 43028 in comparison with a classical benzodiazepine agonist. Ro15-1788 antagonised RU 42382 indicating that a major component of its action was agonism at benzodiazepine receptors. RU 39419 had no effect, RU 40744 tended to increase and RU 40410 evoked a small but statistically significant increase in twitching. The same rank order was observed in antagonism of a benzodiazepine in the muscle twitching model. RU 42382 was least effective as an antagonist and RU 40410 most effective. RU 39419 had no effect alone but antagonised the decrease of firing rate of cerebellar Purkinje cells induced by a benzodiazepine in urethane-anaesthetised rats. Comparison of in vivo occupancy of benzodiazepine receptors and efficacy in the conflict test in rats suggests a ranking of agonist intrinsic activity: RU 42382 greater than RU 43028 greater than RU 39419. A simple relationship between intrinsic activity at benzodiazepine receptors and structure of the compounds is proposed.

Action Potentials↗

PubMed1987

Effects of agents which interact with central benzodiazepine binding sites on stress-induced ultrasounds in rat pups.

Compounds of different chemical classes, with affinity for central benzodiazepine receptors, were investigated for effects on handling-induced ultrasonic cries in rat pups. Diazepam and clobazam inhibited ultrasounds and impaired motor performance at higher doses. Suriclone showed a similar profile to diazepam but premazepam clearly separated ultrasound inhibition from motor impairment. ZK 91296, CGS 9896, RU 39419 and RU 43028 inhibited ultrasounds with a lower maximal response but induced little or no motor incoordination. CL 218872 inconsistently inhibited sounds with no motor impairment and PK 8165 and PK 9084 had no consistent effects. Benzodiazepine antagonists weakly inhibited (RU 40410) or did not affect (Ro 15-1788 or CGS 8216) ultrasounds alone but fully (Ro 15-1788 or CGS 8216) or partially (RU 40410) antagonised the effects of benzodiazepines. Inverse agonists FG 7142, methyl-beta-carboline-3-carboxylate (BCM) and DMCM tended to increase ultrasounds alone, particularly when less stressful handling stimuli were used, and antagonised benzodiazepines. This procedure detects the differing behavioural effects of benzodiazepines receptor ligands and is proposed as a simple model of anxiety.

Animals↗

PubMed1987

Induction of chemotaxis in mouse peritoneal macrophages by activators of protein kinase C.

Two activators of calcium and phospholipid dependent protein kinase (protein kinase C), the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and the synthetic diacylglycerol, 1-oleoyl-2-acetylglycerol (OAG), were compared as chemotactic agents for mouse peritoneal macrophages. Both of these compounds were found to induce chemotaxis in the macrophages to a similar extent in a time and dose dependent manner. Induction of chemotaxis was observed in the concentration range of 10-100 nM for TPA and 25-250 microM for OAG. Two structurally related synthetic sn 1,2-diacylglycerols, 1,2-dioctanoylglycerol (diC8) and 1,2-didecanoylglycerol (diC10), were also found to be chemotactic for macrophages, while monoacylglycerol (2-monoolein) was inactive. Of the diacylglycerols, OAG was found to be the most active followed by diC8 and diC10. In contrast to TPA, the synthetic diacylglycerols had no effect on superoxide anion release by the cells, suggesting that the mechanism of superoxide anion release by TPA in macrophages is distinct from chemotaxis. Phorbol-12,13-diacetate, a biologically inactive phorbol ester analog that inhibits the binding of TPA to its cellular receptors, inhibited macrophage chemotaxis induced by TPA, the synthetic diacylglycerols, and the complement fragment, C5a. Taken together, our results suggest that chemotaxis in macrophages may be mediated by activation of protein kinase C.

Animals↗

PubMed1987

Activity of some benzodiazepine receptor ligands with reduced sedative and muscle relaxant properties on stress-induced electrocorticogram arousal in sleeping rats.

Arousal of the electrocorticogram induced by intermittent footshocks in sleeping rats was originally developed to detect hypnotic compounds. A modified shortened protocol is described in which a 2.5-hr nonstressed control period is followed by drug or vehicle administration and a further 5.5-hr recording of the electrocorticogram in the presence of intermittent footshock. The arousal induced by the footshock is reversed by the benzodiazepine chlordiazepoxide and by agents that displace brain benzodiazepine binding but that do not possess the muscle relaxant and sedative properties of benzodiazepines (CL218872, premazepam, ZK91296, RU 43028, and CGS9896). Nonstressed arousal during normal waking was reduced to only a small extent by chlordiazepoxide or any of the other agents tested, suggesting that the footshock-induced arousal is sensitive to the anxiolytic properties of such agents.

Animals↗

PubMed1987

Intestinal absorption of alpha-methyldopa: in vitro mechanistic studies in rat small intestinal segments.

The mechanism of intestinal uptake of alpha-methyldopa (Aldomet) was investigated using isolated segments of rat small intestine. Incubations were limited to 2 to 5 min as histological examination of the tissue showed significant loss of structural integrity after 10 to 20 min at 37 degrees C. alpha-Methyldopa in the tissue was extracted and assayed by high-pressure liquid chromatography. Corrections were applied for uptake into extracellular spaces using inulin (14C). Uptake was temperature- and concentration-dependent (Km congruent to 10 mM), was dependent on the location in the small intestine and was inhibited by ouabain (2 mM) or lack of sodium or glucose in the incubation medium. alpha-Methyldopa uptake also was inhibited by other neutral amino acids. The mucosal cell layer accounted for approximately 50% of the total drug accumulated in the tissue. Uptake was less when the serosal surface was exposed than when the tissue was everted. The similarity in uptake parameters between alpha-methyldopa and L-phenylalanine (parallel experiments) suggests that alpha-methyldopa is principally absorbed into rat small intestinal mucosal cells via an amino acid transport system.

Amino Acids↗

PubMed1986

Recent developments in 5HT-related pharmacology of animal models of anxiety.

The proposed anxioselective drug, buspirone, interacts with 5HT1 receptors. An analogue, MJ 13805, produces a 5HT behavioural syndrome blocked by central 5HT pathway lesion. Both compounds inhibit 5HT neurone firing. An association of any such action with models of anxiety is not yet possible. Several compounds selective for 5HT receptor sub-types have been tested in models of anxiety. Ritanserin, a selective 5HT2 antagonist, shows activity in an emergence test but not conflict models. Preliminary clinical reports indicate qualitatively different anxiolytic activity from that of benzodiazepines. TVXQ 7821 is selective for 5HT1 receptors and has shown activity in several models of anxiety. 8OHDPAT and RU 24969 are 5HT1 agonists, selective for 5HT1A and 5HT1B sites respectively. 8OHDPAT released punished drinking but reversed a similar effect of PCPA. Its mode of action remains unclear. RU 24969 has shown no marked anxiolytic-like activity in food or water-motivated conflicts. Further studies are necessary before associating modulation of central 5HT systems with anxiolytic activity, either in animal models or patients.

Animals↗

PubMed1986

Blockade of a putative GABA-mediated neurotransmission in the cerebellum by benzodiazepine receptor inverse agonists.

An exponential relationship was observed between the firing rate of cerebellar Purkinje cells in urethane-anaesthetized rats and the duration of inhibition evoked in these cells by electrical stimulation of the nearby cortical surface. Benzodiazepines, administered i.v., decreased cell firing and increased the duration of the inhibitory response but did not alter the relationship between the two parameters. These effects of one benzodiazepine, RU 32007, were reversed by the benzodiazepine antagonist Ro15-1788 which had little effect alone. The benzodiazepine inverse agonists methyl- or ethyl-beta-carboline-3-carboxylate increased cell firing with the expected reductions in duration of inhibitory response in some cases. However, in 50% of recordings the inhibitory response disappeared, independent of the firing rate. All the effects of the beta-carboline esters were reversed by Ro15-1788 or the benzodiazepine, RU 32007. This action of the benzodiazepine receptor inverse agonists represents an in vivo blockade of an endogenous synaptic inhibition which is thought to be mediated by release of GABA.

Action Potentials↗

PubMed1986

Effect of particle size and food on gastric residence time of non-disintegrating solids in beagle dogs.

The gastric residence times of various sizes of radio-opaque particles and tablets were measured in beagle dogs by X-ray, both in the fasted state and after a single meal. During the course of the studies, changes in intragastric pH were also monitored with a radiotelemetric pH sensor, the Heidelberg capsule. The gastric residence time increased with increasing particle size and with particles greater than or equal to 5 mm in diameter approached a plateau value both in the fasted state and after feeding. This value was about 7.5 h after feeding and about 1.5 h in the fasted state, and probably corresponded to the occurrence of the interdigestive migratory myoelectric complex (IMMC wave). The pH in the stomach was variable in the fasted state, but an abrupt pH increase (up to pH 6-7) was observed during the emptying of larger tablets. In some instances this high pH in the stomach was maintained until the next IMMC wave occurred. The gastric emptying of larger tablets administered with food was also associated with an abrupt pH increase.

Animals↗

PubMed1986

Acylcarnitines: drug absorption-enhancing agents in the gastrointestinal tract.

Acylcarnitines were tested as potential absorption-enhancing agents for drugs that are poorly absorbed from the gastrointestinal tract. Urethan-anesthetized Sprague-Dawley rats and conscious Beagle dogs were used. Palmitoyl-DL-carnitine was the most effective acylcarnitine tested, although significant increases in drug absorption were observed with acylcarnitines containing C12 through C18 fatty acid chains. Palmitoyl-DL-carnitine afforded significant increases in the absorption of cefoxitin, gentamicin, cytarabine, somatostatin analogue, and alpha-methyldopa. The response to palmitoyl-DL-carnitine was concentration dependent and reversible within 60-120 min. Histological examination of the intestinal tissue revealed no apparent change in mucosal structural integrity at doses of palmitoyl-DL-carnitine that resulted in increased drug absorption. The acylcarnitines were effective in increasing drug absorption from the small intestine and the rectal compartment of both rats and dogs. The data also demonstrated effectiveness with aqueous and solid dosage forms (Witepsol H-15 suppositories). The data suggest that acylcarnitines may be effective and safe absorption-enhancing agents for a variety of drugs.

Animals↗

PubMed1985

Actions and interactions of benzodiazepine agonists, antagonists and inverse agonists on suprahyoid muscle twitching.

Amphetamine-induced twitching of the suprahyoid muscle in nialamide-pretreated, urethane-anaesthetised rats was inhibited by the benzodiazepine agonists RU 32007, diazepam and chlordiazepoxide and the GABAA agonist muscimol. Ro15-1788 and CGS 8216 induced slight, or no reduction in twitching, respectively, but reversed the effect of RU 32007 and diazepam. Ro15-1788 did not reverse the effect of muscimol. Picrotoxin reversed both muscimol and RU 32007 effects at a dose which induced only a small increase in twitching alone. Higher doses of picrotoxin markedly increased amphetamine twitching and induced twitching in the absence of amphetamine. Ethyl-beta-carboline-3-carboxylate (BCE) weakly increased twitching and reversed the effect of RU 32007. CL 218872 weakly reduced twitching but also weakly antagonised RU 32007. In rats pretreated with a higher dose of nialamide methyl beta-carboline-3-carboxylate (BCM) and BCE induced twitching. BCE-induced twitching was antagonised by RU 32007, Ro15-1788, CGS 8216, muscimol and weakly by CL 218872. Thus, benzodiazepine agonists inhibit twitching and inverse agonists induce twitching, both being blocked by antagonists. Partial agonism (CL 218872) or partial inverse agonism (CGS 8216) may be detected by differential effects against different inducers of twitching.

Amphetamine↗

PubMed1985

Potential and limitations of drug targeting: an overview.

Potential and limitations of current efforts in drug targeting are discussed in terms of the criterion that targeting strategies must ultimately be gauged by their success in producing selectivity of pharmacological response thereby reducing or eliminating side effects which are not mechanism-related. A wide variety of approaches are considered, including: local drug administration, differential metabolism, carriers and vehicles, macromolecular recognition, site-specific activation and molecular specificity. Each approach is briefly assessed for its potential to be developed as a realistic candidate for human health care.

Administration, Topical↗

PubMed1985

Distress vocalization in rat pups. A simple screening method for anxiolytic drugs.

A method is described for reproducible measurement of ultrasonic vocalization induced by tail-holding stress in rat pups. The anxiolytic benzodiazepines, chlordiazepoxide, diazepam, and CL 218872, reduced the ultrasounds at doses inducing little CNS depressant activity. Gross behavioral disruption such as sedation (muscimol, prazosin, and chlorpromazine), tremors (yohimbine), myoclonus (MK 212), and immobility (morphine) resulted in reduction of ultrasounds. Non-behaviourally active doses of these compound or any doses tested of mephenesin, amphetamine, amitriptyline, haloperidol, and naloxone did not affect the ultrasounds. Metergoline inhibited ultrasounds at doses producing little change in overt behavior. This method is proposed as a convenient model of anxiety which may also be influenced by central 5-hydroxytryptamine transmission.

Animals↗

PubMed1985

Neuronal survival or death after dendrite transection close to the perikaryon: correlation with electrophysiologic, morphologic, and ultrastructural changes.

We investigated the probability of survival of mouse spinal neurons in monolayer cultures after transection lesions of dendrites made within 400 microns of the perikarya. Based on a total of 650 lesioned neurons, the following observations were made. First, neuronal survival is a function of lesion distance from the perikaryon and of process diameter at the lesion site. For an average lesion diameter of 3 microns, dendrite transections at 50 microns, 100 microns, and 150 microns were associated with survival probabilities of 30%, 53%, and 70%, respectively. Second, the fate of the injured cells was definitely established 24 hours after injury and very likely was determined as early as 2 hours. Third, early stages of deterioration leading to cell death were associated with cytoplasmic phase brightness on light microscopy, correlating with an appearance of numerous, small, electron-lucent vacuoles and swollen mitochondria on electron microscopy. The cytoplasm of these moribund cells stained darkly and contained no visible microtubules or neurofilaments. Fourth, the magnitude and time course of injury potentials recorded at the somata were a function of the lesion distance and did not return to prelesion levels within 30 minutes after transection. Fifth, at 24 hours after injury, the average membrane potential of lesioned neurons was 8% below that of control neurons. Sixth, at a lesion distance of approximately 300 microns both the injury potential and the probability of cell death approach zero. We conclude that, in the model system used, neuronal survival after dendrite amputation depends on physical parameters of the lesion that determine the magnitude of the injury current reaching the soma. Survival is not assured if the injury is inflicted within 250 microns of the cell body, and cell death is likely for lesions within 50 microns of the soma. The below-normal membrane potentials at 24 hours after injury suggest a possible greater vulnerability of recovering neurons to secondary insults. The characteristic mitochondrial disruption and loss of microtubules implies that the calcium component of the injury current contributes to cell death.

Animals↗

PubMed1985

Central effects of nicotinamide and inosine which are not mediated through benzodiazepine receptors.

The actions of nicotinamide and inosine were investigated on rat cerebellar Purkinje cells using ionophoretic and extracellular recording techniques. Ionophoretic application of nicotinamide or inosine showed that they were potent inhibitors of Purkinje cell firing. This inhibition differed from that induced by benzodiazepines in that it was not reversed by the GABA antagonists bicuculline methiodide and picrotoxin. RO 15-1788, the specific benzodiazepine antagonist, did not reverse the effects of nicotinamide. Chlordiazepoxide has been shown to increase significantly social interaction between pairs of male rats and this increase can be reversed by RO 15-1788, 20 mg kg-1 i.p. Nicotinamide also caused a small increase in social interaction but this effect was not reversed by the benzodiazepine antagonist. Inosine did not increase social interaction. [3H]-flunitrazepam binding studies showed that nicotinamide and inosine have only low affinities for the benzodiazepine binding site. These results suggest that while nicotinamide may exert some neuronal depressant and anxiolytic activity, its site of action appears not to be associated with the benzodiazepine receptor site. Similarly, inosine exerts a neuronal depressant effect dissimilar from that of benzodiazepines.

Action Potentials↗

PubMed1985

Pharmacological characterisation of a modified social interaction model of anxiety in the rat.

Social interaction (SI) between two unfamiliar male rats in a dimly lit, familiar environment has been investigated as a model of anxiety, where novelty of the partner remains as the principal anxiogenic stimulus. A range of centrally acting drugs have been tested in this situation. Chlordiazepoxide, nitrazepam, flunitrazepam, and flurazepam all increase SI, as does buspirone, CL 218872, suriclone, sodium valproate, and nicotinamide in the model described. Anxiogenic agents FG 7142 and yohimbine reduced SI without significant modification of motor activities. However, the stimulant amphetamine increased all behaviours in this condition. Amphetamine also increased all behaviours when rats were tested with their cagemates, when the desire for SI is largely satiated. CL 218872 also increased SI in this second situation, and it is suggested that this agent may have a non-specific component in its action in this test. Additionally, caffeine, theophylline, and piracetam may also have non-specific behavioural actions in this model.

Animals↗