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Biomedical subjects

G C Wagner

Publications and source records attributed to G C Wagner.

At least 73 records · Page 4Linked to original sources

Mandatory continuing medical education in risk management training: the University of Florida's experience.

The University of Florida has been able to provide the physicians of Florida with a continuing medical education opportunity to meet their immediate needs. It offers quality education at a modest cost to the individual with considerable savings in time and cost to the individual physician. By using self-study tapes, we have developed a method of teaching physicians that provides positive reinforcement while presenting an overview of the malpractice crisis and detailing its causes. We believe we have made a significant contribution toward improving risk management techniques for the Florida physician.

Education, Medical, Continuing↗

The effects of repeated administration of fluprazine on target biting and intruder-evoked attacks.

The effects of repeated administration of fluprazine, an "aggression"-reducing drug, were evaluated in mice using the target biting and resident-intruder paradigms. Under baseline conditions there was a high target biting rate immediately after the delivery of a 2.0 mA tail shock, an intermediate target biting rate during a 2-min intershock interval, and a low target biting rate during a 15-s tone stimulus which signaled the shock. During the 10-min resident intruder test sessions, resident males attacked bulbectomized intruders an average of six times with an average latency to the first attack of 258 s. In the prechronic dose-response curve determination, fluprazine caused a dose-dependent decrease in postshock and intershock interval target biting behavior, increased the latency to the first attack, and decreased the number of attacks in the intruder-evoked aggression paradigm. During the chronic administration of the ED50 dose of fluprazine, intershock interval target biting gradually increased to a level equal to those subjects receiving chronic saline. Moreover, a shift (to the right) in the during-chronic fluprazine dose-response curve for postshock and intershock interval target biting, was observed. Likewise, during the chronic administration of the ED50 dose of fluprazine, resident number of attacks gradually increased to a level equal to those subjects receiving chronic saline. However, no shift in the during-chronic dose-response curve was observed in subjects tested in this paradigm.

Aggression↗

Attenuation of MPTP-induced dopaminergic neurotoxicity by a serotonin uptake blocker.

Monoamine oxidase-B (MAO-B) has been determined to be the enzyme responsible for the conversion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into its toxic metabolite 1-methyl-4-phenylpyridine ion (MPP+). Since this enzyme has been localized primarily in astrocytes and serotonergic neurons, it would appear that MPP+ is being produced outside the dopaminergic neurons. To investigate this possibility, the administration of MPTP was preceded by systemically administered fluoxetine. In keeping with its demonstrated ability to inhibit uptake into serotonergic neurons and serotonin uptake into astrocytes, fluoxetine pretreatment resulted in a significant attenuation of MPTP-induced depletions of striatal dopamine and serotonin concentration. These results support the extra-dopaminergic production of MPP+.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

Changes in macronutrient selection as a function of dietary tryptophan.

It has been hypothesized that the serotonergic system is involved in the regulation of carbohydrate and/or protein intake. Tests of this hypothesis using added dietary tryptophan and diets varying in the ratio of carbohydrate/protein resulted in depressed intakes of high carbohydrate/low protein diets, elevated intakes of low carbohydrate/high protein diets, and a reduction of total caloric intake. The present studies gave rats increased options for adjusting to added tryptophan by providing them with separate sources of protein, carbohydrate, and fat. The results showed the expected decrease in carbohydrate intake, but also increases in fat intake and, to a lesser extent, protein intake. Total caloric intake was conserved. Hypothalamic concentrations of serotonin and 5-hydroxyindole acetic acid indicated increased activity of the serotonergic system. These results lend support to serotonin's involvement in nutrient selection, in that carbohydrate consumption decreased in response to tryptophan loading, but indicate that other nutrients may also be affected. Given the option of altering fat intake, the animals maintained a constant caloric intake despite the reduction of carbohydrate consumption.

Animals↗

Dietary pyridoxine interaction with tryptophan or histidine on brain serotonin and histamine metabolism.

We studied the metabolic effects of high dietary intakes of pyridoxine and of the substrate-cofactor interaction between dietary histidine or tryptophan and pyridoxine in rat brain. In the substrate-cofactor interaction study, histamine and serotonin levels were determined in rats fed elevated or requirement levels of substrate (histidine: 0.3% and 0.8%, tryptophan: 0.15% and 0.6%) and excess or requirement levels of pyridoxine HCl (7 mg vs. 3,000 mg/kg). Excess pyridoxine intake caused a differential effect on brain histamine concentration--inhibitory with the requirement level of histidine (-29%), and stimulatory (+21%) with the elevated level of histidine. When dietary tryptophan was fed at the requirement level, excess pyridoxine caused essentially no changes in hypothalamic serotonin and 5HIAA (-2%, -2%). With elevated tryptophan intake, excess pyridoxine significantly increased serotonin and 5HIAA (+32%, +20%) in the hypothalamus. These results indicate a clear interaction between substrate and coenzyme precursor which influences brain metabolism of histamine and serotonin.

Animals↗

Fenfluramine-induced behavior changes in rats prefed serotonin-altering amounts of tryptophan and pyridoxine.

It has been well established that elevated dietary tryptophan (TRP) levels can increase brain serotonin concentrations, thereby influencing serotonergic transmission. We previously examined interaction between dietary substrate (TRP: 0.15 and 0.6%) and the cofactor precursor (pyridoxine HCl: 3 and 3,000 mg/kg) on brain serotonin metabolism, observing significant increases in serotonin concentrations from such dietary interaction. The present experiments were designed to explore possible behavioral consequences of the substrate-cofactor interaction. After the IP injection of fenfluramine (FA: at 5, 10, 15, and 20 mg/kg), serotonin-mediated behavior traits and the appearance of flushing were observed in rats fed experimental diets as stated above. With a 5 mg/kg dose of FA, a differential dietary effect was most visible. However, at higher FA levels (15 and 20 mg/kg), such dietary effects were no longer discernible. The appearance of flushing was also dependent on dietary TRP intake and the dosage of FA. These results indicate a clear substrate-cofactor interaction on certain serotonin-mediated behavior traits in the rat.

Animals↗

The effects of L-tryptophan on haloperidol-induced movement disorder in the rat.

An animal model of haloperidol-induced tardive dyskinesia was studied in relation to the dietary manipulation of tryptophan and its effect on the movement disorder. This study showed a significant negative behavioral response to the neuroleptic drug, haloperidol. Increased dietary tryptophan (1.0 vs. 0.3%) significantly reduced the frequency of drug-induced head movements. Brain serotonin levels were elevated by the drug treatment. Brain serotonin levels correlated significantly with the behavioral response. Contrary to expectation, brain dopamine levels did not correlate with the behavioral response. These findings suggest a possible serotonergic involvement in neuroleptic-induced tardive dyskinesia and an amelioration of the disorder through tryptophan supplementation.

3,4-Dihydroxyphenylacetic Acid↗

Increased sensitivity of mice to tremorogenic agents following MPP+.

The behavioral effects following intrastriatal MPP+, the neurotoxic metabolite of MPTP, were evaluated in mice. Bilateral injections of 10 micrograms MPP+ to mice previously trained in the shuttle box paradigm produced a 66% decrease in striatal dopamine and significant deficits in all measures of conditioned avoidance responding. In addition, although these mice showed no deficits in baseline rotorod performance, challenge with the cholinergic agonist oxotremorine revealed that MPP+-treated mice exhibited an increased sensitivity to the disruptive effects of the drug at each dose and time point. Finally, MPP+-treated mice also exhibited an increase in tremor induced by 0.1 and 0.15 mg/kg oxotremorine. These observations are discussed in reference to idiopathic parkinsonism.

1-Methyl-4-phenylpyridinium↗

Effects of single or multiple choice trials per session on drug discrimination performance.

Drug discrimination procedures typically provide for multiple choice opportunities per training session. This practice allows non-drug cues (presence or absence of reinforcement) to mediate choice behavior during that portion of the session following the initial choice. In this experiment, rats were trained to discriminate 1.0 mg/kg cyclazocine from saline using a novel procedure that employed a single-choice trial per training session. Drug discrimination acquisition and generalization were compared to those of rats given discrimination training with 30 choice trials per session. The one-trial procedure yielded stable and reliable acquisition but more slowly than did the multiple trials procedure. The one-trial procedure produced longer first trial choice latencies and enhanced the tendency for subjects to respond on both choice levers during the first trial. The cyclazocine generalization functions were comparable, but the one-trial subjects more often responded on both choice levers, particularly when administered intermediate test doses of cyclazocine. Control of choice behavior by the reinforcer cue was evaluated on a mid-session cue reversal test. Multiple-trial subjects persisted in responding on the saline level following a mid-session injection of cyclazocine, whereas one-trial subjects shifted to the cyclazocine-appropriate lever.

Animals↗

Effects of fluprazine (DU27716) and ethanol on target biting behavior and intruder-evoked attacks.

The effects of an "aggression"-reducing drug, fluprazine, and an "aggression"-enhancing drug, ethanol, were evaluated in mice using the target biting and resident-intruder paradigms. Under baseline conditions there was a high target biting rate immediately after the delivery of a 2.0 mA tail shock, an intermediate target biting rate during a 2-min intershock interval, and a low target biting rate during a 15-s tone stimulus which signaled the shock. During the 10-min resident intruder test sessions, resident males attacked bulbectomized intruders an average of 11.3 times with an average latency to the first attack of 68.3 s. Fluprazine caused a dose-dependent decrease in postshock and intershock interval target biting behavior, increased the latency to the first attack, and decreased the number of attacks in the intruder-evoked aggression paradigm. Ethanol exerted a biphasic effect in both paradigms. A dose of 0.5 g/kg increased and 4.0 g/kg decreased intershock interval target biting behavior. Likewise, ethanol at a dose of 1.0 g/kg increased the number of intruder-evoked attacks and 0.5 g/kg reduced the latency to the first attack whereas 2.0 g/kg ethanol reduced the number of intruder-evoked attacks. These observations are discussed in reference to the specificity with which different drugs and paradigms are able to dissociate offensive versus defensive aggression.

Aggression↗

L-dopa reverses the effects of MPP+ toxicity.

The behavioral and neurochemical consequences of the intrastriatal administration of 1-methyl-4-phenylpyridinium ion (MPP+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), were evaluated using the shuttlebox avoidance paradigm. MPP+ caused a significant depletion of striatal dopamine and significant disruption of shuttlebox performance. L-Dopa administration reversed both the dopamine depletion and the behavioral deficits. These observations are discussed in reference to the rodent-MPTP model of Parkinson's disease.

1-Methyl-4-phenylpyridinium↗

Ascorbic acid reduces the dopamine depletion induced by methamphetamine and the 1-methyl-4-phenyl pyridinium ion.

The neurotoxic actions of methamphetamine and the 1-methyl-4-phenyl pyridinium ion (MPP+) have been ascribed, at least in part, to the generation of free radicals. This hypothesis was evaluated by attempting to reduce the toxic actions of these compounds by pretreatment with an antioxidant, ascorbic acid. The intrastriatal administration of methamphetamine caused a 37% depletion of dopamine. Treatment with 100 or 1000 mg/kg of ascorbic acid significantly reduced the methamphetamine-induced dopamine depletion (by 21 and 27%, respectively). The intrastriatal administration of MPP+ caused an 88% depletion of dopamine. Treatment with 100 or 1000 mg/kg of ascorbic acid significantly reduced the MPP+-induced dopamine depletion (by 22 and 45%, respectively). Thus, free radicals may mediate the toxic actions of these compounds.

1-Methyl-4-phenylpyridinium↗

The effects of prenatal morphine on the responsiveness to morphine and amphetamine.

The effects of morphine administered to pregnant Sprague-Dawley rats on the schedule-controlled behavior of the offspring were examined. It was observed that both male and female adult rats exposed prenatally to morphine were tolerant to the disruptive effects of morphine on fixed-interval responding compared to age-matched controls. These morphine-treated rats, however, were neither tolerant nor supersensitive to the disruptive effects of the catecholaminergic agonist, amphetamine, and did not exhibit any alteration in their steady state levels of central monoamines. These observations are discussed in relation to the effects of prenatal morphine exposure on unconditioned behaviors.

Amphetamine↗

Pargyline and naltrexone fail to antagonize the gustatory avoidance response induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

The administration of the dopaminergic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to rats following the consumption of a novel saccharin solution induced a gustatory avoidance response evidenced by a significant decrease in saccharin intake following its representation. Pretreatment with pargyline, an agent which prevents the metabolism of MPTP to the 1-methyl-4-phenylpyridinium ion (MPP+), did not potentiate or antagonize the magnitude of this aversion. Likewise, pretreatment with naltrexone, an opiate antagonist, failed to alter the gustatory avoidance response induced by MPTP. These observations indicate that MPTP is capable of inducing a gustatory avoidance response and that the mechanism mediating this response is not dependent upon the conversion of MPTP to MPP+ and does not involve the opiate receptor.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

The 2.6-A crystal structure of Pseudomonas putida cytochrome P-450.

The crystal structure of Pseudomonas putida cytochrome P-450cam in the ferric, camphor bound form has been determined and partially refined to R = 0.23 at 2.6 A. The single 414 amino acid polypeptide chain (Mr = 45,000) approximates a triangular prism with a maximum dimension of approximately 60 A and a minimum of approximately 30 A. Twelve helical segments (A through L) account for approximately 40% of the structure while antiparallel beta pairs account for only approximately 10%. The unexposed iron protoporphyrin IX is sandwiched between two parallel helices designated the proximal and distal helices. The heme iron atom is pentacoordinate with the axial sulfur ligand provided by Cys 357 which extends from the N-terminal end of the proximal (L) helix. A substrate molecule, 2-bornanone (camphor), is buried in an internal pocket just above the heme distal surface adjacent to the oxygen binding site. The substrate molecule is held in place by a hydrogen bond between the side chain hydroxyl group of Tyr 96 and the camphor carbonyl oxygen atom in addition to complementary hydrophobic contacts between the camphor molecule and neighboring aliphatic and aromatic residues. The camphor is oriented such that the exo-surface of C5 would contact an iron bound, "activated" oxygen atom for stereoselective hydroxylation.

Amino Acid Sequence↗

Long-term effects of repeated methylamphetamine administration on monoamine neurons in the rhesus monkey brain.

Previous studies indicate that the repeated administration of D-methylamphetamine (MA) produces a long-lasting depletion of dopamine (DA), norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) in various brain regions of a number of species. The objectives of the present study were: (1) to establish a short, subcutaneous injection regimen which would reliably produce the neuronal alterations; (2) to evaluate MA-induced NE depletions produced by this new regimen; and (3) to determine whether central MA-induced neuronal changes are reflected in changes in cerebrospinal fluid monoamine metabolite concentrations. It was observed that high doses of MA administered (s.c.) over a 2-week period to rhesus monkeys produced decreases in DA and 5-HT, but not NE levels, in various brain regions. The decrease in caudate DA levels was accompanied by a decrease in the number of DA uptake sites, a decrease in the level of homovanillic acid (HVA) and an increase in DA turnover. This decrease in brain DA was also accompanied by a decrease in the cerebrospinal fluid concentration of HVA.

Animals↗

Neurochemical and functional consequences following 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) and methamphetamine.

The neurochemical and functional consequences following MPTP administration to the rat were evaluated and compared to similar effects following methamphetamine administration. It was observed that MPTP induced long lasting depletions of striatal dopamine concentrations and this neurotoxic effect could be prevented by pargyline pretreatment. The MPTP-induced neuronal damage produced a tolerance to the disruptive effects of amphetamine and a supersensitivity to the disruptive effects of apomorphine in rats responding in a schedule controlled paradigm. Methamphetamine, like MPTP, produced depletions of striatal dopamine but these actions were potentiated by pargyline pretreatment. These observations are discussed in reference to possible deleterious effects following the administration of pargyline to patients with Parkinson's Disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

Drug discrimination training with a single choice trial per session.

All drug discrimination procedures share in common the practice of providing for multiple choice opportunities per training session. This practice allows nondrug cues (presence or absence of reinforcement) to mediate choice behavior during that portion of the session following the initial choice. Investigators who have acknowledged this problem typically use only first-trial choice performance to evaluate discriminative control by the drug cue, and consider additional choice training following the delivery or nondelivery of the first reinforcer to be facilitatory in establishing drug-mediated discriminative control. In this experiment, rats were trained to discriminate 4.0 mg/kg morphine from saline in a novel procedure that employed a single choice trial per training session. Choice performance was characterized during discrimination acquisition and in subsequent stimulus generalization testing. The results indicated that when all reinforcers are made contingent on correct performance during a single choice trial, rapid and stable control of drug-mediated choice behavior, is observed. In addition, the results demonstrated that additional choice training following the delivery or nondelivery of the first reinforcer is not a necessary antecedent toward establishing drug-mediated discriminative control.

Animals↗