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Biomedical subjects

D L Murphy

Publications and source records attributed to D L Murphy.

At least 127 records · Page 7Linked to original sources
PubMed1996

Differential inhibition of neuronal and extraneuronal monoamine oxidase.

This study examined whether the neuronal and extraneuronal sites of action of two monoamine oxidase (MAO) inhibitors, l-deprenyl and debrisoquin, could be distinguished by their effects on plasma concentrations of catecholamine metabolites. Plasma concentrations of the intraneuronal deaminated metabolite of norepinephrine, dihydroxyphenylglycol (DHPG), were decreased by 77% after debrisoquin and by 64% after l-deprenyl administration. Plasma concentrations of the extraneuronal O-methylated metabolite of norepinephrine, normetanephrine, were increased substantially more during treatment with l-deprenyl than with debrisoquin (255% compared to a 27% increase). The comparable decreases in plasma concentrations of DHPG indicate a similar inhibition of intraneuronal MAO by both drugs. Much larger increases in normetanephrine after l-deprenyl than after debrisoquin are consistent with a site of action of the latter drug directed at the neuronal rather than the extraneuronal compartment. Thus, differential changes in deaminated and O-methylated amine metabolites allows identification of neuronal and extraneuronal sites of action of MAO inhibitors.

Adult↗
PubMed1996

Long-term antidepressant treatment restores clonidine's effect on growth hormone secretion in a genetic animal model of depression.

We have recently demonstrated that various doses of clonidine failed to increase growth hormone (GH) in Fawn-hooded (FH) rats (a rat strain suggested to represent a genetic model of depression). In the present study, we investigated whether long-term antidepressant treatment might normalize clonidine's effect on GH secretion in male FH rats. Long-term (16 days) treatment with the tricyclic antidepressant, imipramine (5 mg/kg/day), the 5-HT uptake inhibiting antidepressant, fluoxetine (2.5 mg/kg/day), and the noradrenergic uptake inhibiting antidepressant, desipramine (5 mg/kg/day), accentuated clonidine's effect on GH levels. On the other hand, long-term treatment with the monoamine oxidase type-A inhibiting antidepressant, clorgyline (1 mg/kg/day) and the alpha 2-noradrenergic antagonists, yohimbine and 1-phenylpiperazine (1 mg/kg/day, each) did not modify clonidine's effect. These findings suggest enhancement of 5-HT2c receptor-mediated function following long-term treatment with uptake inhibiting antidepressants in a genetic animal model of depression.

Adrenergic alpha-2 Receptor Agonists↗
PubMed1996

Repeated administration of meta-chlorophenylpiperazine or 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane produces tolerance to its stimulatory effect on adrenocorticotropin hormone but not prolactin or corticosterone secretion in rats.

In an attempt to clarify whether m-chlorophenylpiperazine-(m-CPP) and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane-(DOI) induced increases in plasma adrenocorticotropin hormone, corticosterone and prolactin secretion are mediated by the same or different mechanisms, we studied the time course of development of tolerance to the neuroendocrine effects of m-CPP (2.5 mg/kg/day) and DOI (2.5 mg/kg/day) in rats and, furthermore, also evaluated possible cross-tolerance in responses to m-CPP and DOI. We observed the development of tolerance in adrenocorticotropin hormone responses after a single i.p. injection of m-CPP. However, there was no cross-tolerance to DOI when chronic (13 days) m-CPP-treated animals were challenged with DOI (2.5 mg/kg). Injections of DOI (2.5 mg/kg) for six days were required before tolerance developed to the effect of DOI on adrenocorticotropin hormone. Furthermore, cross-tolerance was observed when DOI-treated animals (2.5 mg/kg/day x 6) were challenged with m-CPP (2.5 mg/kg) on day 7. In contrast, daily administration of m-CPP and DOI for 13 days did not produce tolerance to their stimulating effects on corticosterone and prolactin secretion. Hypothalamic levels of 5-hydroxyindoleacetic acid but not 5-HT were significantly reduced after acute or subchronic administration of both m-CPP and DOI. Furthermore, no change in the approximate 50% reduction in 5-hydroxyindoleacetic acid after m-CPP was observed after subchronic administration of this drug. These findings suggest that separate mechanisms mediate m-CPP and DOI-induced adrenocorticotropin hormone secretion in rats.

Adrenocorticotropic Hormone↗
PubMed1996

Transgenic mice with high levels of superoxide dismutase activity are protected from the neurotoxic effects of 2'-NH2-MPTP on serotonergic and noradrenergic nerve terminals.

Administration of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) analog 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP; 4 x 15 mg/kg) to CD-1 mice was found to cause substantial decreases in cortical and hippocampal 5-hydroxytryptamine (5-HT) and norepinephrine (NE) to 20-30% of control 3 weeks after treatment. The magnitude of these depletions was similar to those reported previously in Swiss Webster and C57BL/6 mice given 4 x 20 mg/kg 2'-NH2-MPTP, and in keeping with these prior studies, striatal dopamine levels were unchanged by 2'-NH2-MPTP treatment in CD-1 mice. Subsequently, transgenic CD-1 mice producing high levels of human cytosolic Cu-Zn superoxide dismutase (SOD) were studied to assess the role of oxygen radicals in the mechanism of action of 2'-NH2-MPTP. In contrast to the results described above, 5-HT and NE levels were almost completely unaffected by 2'-NH2-MPTP treatment in homozygous SOD mice bearing 5-fold increases in brain SOD activity. In 2'-NH2-MPTP-treated heterozygous SOD mice, which showed an average 3-fold increase in brain SOD activity, only moderate depletions in cortical and hippocampal 5-HT (50-60% of control) and NE (30-40% of control) were observed. Additionally, the density of [125I]RTI-55-labeled 5-HT uptake sites was studied to further assess possible 5-HT terminal loss. In various cortical and hippocampal subregions of nontransgenic mice, 5-HT uptake sites were reduced to 20-35% of control after 2'-NH2-MPTP treatment, in comparison with homozygous SOD mice, which were affected only minimally by 2'-NH2-MPTP administration, and heterozygous SOD mice, which showed intermediate reductions in 5-HT uptake site density on the order of 55-80% of control. Together, these data indicate that mice genetically endowed with increased SOD activity are protected from 2'-NH2-MPTP-induced toxicity, thereby implicating superoxide radicals in the mechanism of action of a neurotoxin that selectively depletes 5-HT and NE without affecting dopamine.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1995

Long-term antidepressant treatments alter 5-HT2A and 5-HT2C receptor-mediated hyperthermia in Fawn-Hooded rats.

We have recently demonstrated that hyperthermia induced by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and m-chlorophenylpiperazine (m-CPP) are separately mediated by selective stimulation of 5-HT2A and 5-HT2C receptors, respectively in Wistar rats. Furthermore, hyperthermia induced by either DOI or m-CPP was found to be significantly less in Fawn-Hooded rats (a rat strain suggested to represent a genetic model of depression) relative to Wistar rats. In the present study, we studied the effects of long-term antidepressant treatments on DOI (2.5 mg/kg)-induced and m-CPP (2.5 mg/kg)-induced hyperthermia in male Fawn-Hooded rats. Long-term (21 days) treatment with the tricyclic antidepressants, imipramine or clomipramine (each 5 mg/kg/day), attenuated DOI-induced hyperthermia, while m-CPP-induced hyperthermia was accentuated. On the other hand, long-term (21 days) treatment with the monoamine oxidase type-A inhibiting antidepressant, clorgyline (1 mg/kg/day), did not modify m-CPP-induced hyperthermia, but significantly attenuated DOI-induced hyperthermia. These findings demonstrate that long-term antidepressant treatments alter 5-HT2A and 5-HT2C receptor-mediated hyperthermia in a genetic animal model of depression.

Adaptation, Physiological↗
PubMed1995

Hormonal responses to the administration of m-chlorophenylpiperazine in patients with seasonal affective disorder and controls.

We report on the plasma cortisol and prolactin responses to the serotonergic agonist m-CPP (0.1 mg/kg) in 10 patients with winter seasonal affective disorder (SAD) and 10 controls during the winter, in both untreated and bright light-treated conditions; and on 8 other SAD patients and 8 other controls during the summer. Following m-CPP infusion, untreated patients had exaggerated prolactin (p < .05) and cortisol (p < .05) responses compared to controls. Light treatment significantly reduced responses of both hormones to m-CPP (prolactin: p < .01; cortisol: p < .01). When untreated winter subjects and summer subjects were compared, cortisol, but not prolactin responses to m-CPP were found to be higher in patients than in controls during the winter, and lower in patients than in controls during the summer (diagnosis by season: p < .05). These results are consistent with those of our previous report on the behavioral responses to m-CPP in the same patients and suggest an abnormality in serotonergic function in untreated SAD patients in winter, which is normalized following treatment with light therapy and naturally during the summer.

Adult↗
PubMed1995

Primary structure of the serotonin transporter in unipolar depression and bipolar disorder.

Genetic factors have been implicated in the etiology of affective disorders but due to the complex inheritance patterns of these disorders, identification of the responsible gene(s) has so far been unsuccessful. Decreased platelet serotonin (5-HT) transport and reduced binding of imipramine or paroxetine to brain and platelet 5-HT uptake sites/transporters in patients with depression and suicide victims define the 5-HT transporter (5-HTT) as a candidate gene. The primary structure of the 5-HTT was analyzed in 17 patients meeting DSM-III-R diagnostic criteria for major depressive or bipolar disorder and in 4 healthy controls using polymerase chain reaction (PCR-) amplification and sequencing of complementary deoxyribose nucleic acid (cDNA) synthesized from platelet 5-HTT messenger ribose nucleic acid (mRNA). Direct PCR sequencing of the protein coding region failed to reveal changes in the deduced amino acid sequence of the platelet/brain 5-HTT (40,000 base pairs sequence screened), although a conservative single-base substitution representing a silent polymorphism was found. The results provide preliminary evidence that alterations in the primary structure of 5-HTT are not generally involved in the pathogenesis of unipolar depression and manic-depressive illness.

Adult↗
PubMed1995

Neuronal protective and rescue effects of deprenyl against MPP+ dopaminergic toxicity.

Intranigral infusion of 1-Methyl-4-phenylpyridinium ion (MPP+, 2.1-16.8 nmol) dose-dependently injured nigral neurons as reflected by reduced dopamine levels in the ipsilateral striatum four days after the infusion of this toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Coadministration of deprenyl (4.2 nmol) with MPP+ into the substantia nigra protected against MPP(+)-induced moderate (20-50%) but not severe (over 70%) nigral injury as reflected in striatal dopamine reductions. However, supplementary treatment with deprenyl (0.25 mg/kg, s.c., twice daily for 4 days) after intranigral infusion of MPP+ significantly rescued nigral neurons from more severe damage caused by a higher MPP+ does (8.4 nmol) manifested by a lesser striatal dopamine decrease (-31%) compared to the non-deprenyl treated group (-70%). Thus, in addition to the blockade of bioactivation of MPTP, deprenyl can protect and/or rescue nigral neurons from MPP(+)-induced dopaminergic neurotoxicity. These in vivo data add further evidence to suggest that deprenyl, a putative and clinically unproven neuroprotective agent, may be of value in slowing the progressive nigral degeneration in "early" Parkinson's disease, but may prove to be less so in its terminal stages.

1-Methyl-4-phenylpyridinium↗
PubMed1995

Evidence that 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced hyperthermia in rats is mediated by stimulation of 5-HT2A receptors.

The effects of various 5-HT receptor subtype-selective antagonists were studied on phenylisopropylamine hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced hyperthermia in Wistar rats, in an attempt to characterize the 5-HT receptor subtype mediating DOI-induced hyperthermia. Intraperitoneal administration of DOI to rats produced hyperthermia with a peak effect at 60 min. Pretreatment with propranolol (beta-adrenoceptor antagonist that also has binding affinity for 5-HT1A, 5-HT1B and 5-HT2C sites), MDL-72222 or ondansetron (5-HT3 antagonists) did not attenuate DOI-induced hyperthermia. In contrast, pretreatment with metergoline (5-HT1/5-HT2 antagonist), ketanserin, LY53857, mesulergine, mianserin and ritanserin (5-HT2C/5-HT2A antagonists), as well as spiperone (5-HT1A/5-HT2A/D2 antagonist), significantly attenuated DOI-induced hyperthermia. Furthermore, daily administration of DOI (2.5 mg/kg per day) for 17 days did not produce either tolerance to its hyperthermic effect or modify m-CPP-induced hyperthermia in rats. These findings suggest that DOI-induced hyperthermia in rats is mediated by stimulation of 5-HT2A receptors.

Amphetamines↗
PubMed1995

Temperature, food intake, and locomotor activity effects of a 5-HT3 receptor agonist and two 5-HT3 receptor antagonists in rats.

This study investigated three physiologic functions known to be modulated by serotonin-temperature, food intake and locomotor activity - using the 5-HT3 receptor agonist, m-chlorophenylbiguanide (m-CPBG), and two 5-HT3 antagonists, MDL-72222 and ondansetron. m-CPBG produced dose-dependent elevations in rectal temperature. MDL-72222, which had no effects on temperature when given alone, significantly attenuated m-CPBG-induced hyperthermia. Food intake in food-deprived rats was reduced during the first hour by the highest dose of m-CPBG. Food intake was also dose-dependently reduced by MDL-72222; m-CPBG plus MDL-72222 led to greater reductions in food intake. Food intake in freely fed rats was unaffected by m-CPBG or MDL-72222. Locomotor activity was unaffected by m-CPBG, but was dose-dependently reduced by MDL-72222, an effect which may have contributed to its hypophagic effects. Ondansetron, used in ten-fold lower doses than MDL-72222, was inactive in all of these paradigms. These data: (1) provide some evidence for 5-HT3 receptor-mediated changes in temperature; (2) are in agreement with two prior studies which reported locomotor activity reductions following 5-HT3 antagonists; but (3) do not support an important role for 5-HT3 receptors in the regulation of food intake in rats.

Animals↗
PubMed1995

Serotonergic modulation of anticholinergic effects on cognition and behavior in elderly humans.

Cholinergic neurotransmission is thought to be modulated by serotonin as documented in animal and human studies. We examined the effects of the muscarinic antagonist scopolamine (0.4 mg IV) given alone or together with the serotonin mixed agonist/antagonist m-chlorophenylpiperazine (m-CPP, 0.08 mg/kg IV), and the selective 5-HT3 receptor antagonist ondansetron (0.15 mg/kg IV). Ten normal elderly volunteers each received five separate pharmacologic challenges (placebo, ondansetron, scopolamine, scopolamine+ondansetron, and scopolamine+m-CPP). Cognitive, behavioral, and physiologic variables were analyzed using repeated measures analysis of variance. The acute effects of scopolamine in certain cognitive, behavioral, and physiological measures were significantly exaggerated by the addition of m-CPP. Scopolamine's cognitive effects were unaffected by ondansetron at the dose tested, nor did ondansetron given alone affect basal cognitive performance. This pilot study suggests that the serotonin mixed agonist/antagonist m-CPP may influence cholinergic neurotransmission. The changes associated with the combination of scopolamine and m-CPP do not appear to be secondary to simple pharmacokinetic alterations and suggest a complex interaction between the cholinergic and serotonergic systems centrally.

Aged↗
PubMed1995

The NMDA receptor complex modulates clonidine-induced increases in growth hormone levels in rats.

Intraperitoneal administration of clonidine (50 micrograms/kg) produced increases in growth hormone levels in male Wistar rats. Pretreatment with NMDA receptor antagonists including (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP/NMDA site), ifenprodril (polyamine site), and dizocilpine maleate (MK-801) or phencyclidine (PCP) (channel blockers) did not have any significant effect on clonidine-induced increases in growth hormone levels. In contrast, pretreatment with 5,7-dichlorokynurenic acid and 6,7-dinitroquinoxaline-2,3-dione (DNQX) (NMDA receptor-associated glycine site antagonists) significantly attenuated clonidine-induced increases in growth hormone levels. Attenuation of clonidine's effect on growth hormone levels by NMDA receptor-associated glycine site antagonists appears most likely due to an interaction between their effects on the NMDA receptor complex with growth hormone releasing factor.

Animals↗
PubMed1995

Lack of cross-tolerance for hypophagia induced by DOI versus m-CPP suggests separate mediation by 5-HT2A and 5-HT2C receptors, respectively.

Intraperitoneal administration of 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) produced significant decreases in the first-hour food intake on day 1 and on day 2 relative to saline-treated animals. Complete tolerance developed to DOI-induced hypophagia by day 3. However, there was no cross-tolerance to m-chlorophenyl-piperazine (m-CPP)-induced hypophagia. Similarly, complete tolerance developed to m-CPP-induced hypophagia by day 3, but again there was no cross-tolerance to DOI-induced hypophagia. These findings suggest that DOI and m-CPP-induced hypophagia are mediated by different mechanisms, most likely by selective stimulation of 5-HT2A receptors by DOI and 5-HT2C receptors by m-CPP. The functional sensitivity changes did not parallel changes in hypothalamic [3H]-mesulergine-labeled 5-HT2C receptors or [3H]-ketanserin-labeled 5-HT2A receptors following chronic m-CPP or DOI treatment, although both treatments significantly reduced 5-HT2A and 5-HT2C receptors in cortex. Thus, future studies investigating the effects of daily m-CPP and DOI administration on phosphoinositide hydrolysis or mRNA for 5-HT2C and 5-HT2A receptors in the hypothalamus might help explain the functional sensitivity changes observed in the present study.

Amphetamines↗
PubMed1995

Serotonin and thermoregulation. Physiologic and pharmacologic aspects of control revealed by intravenous m-CPP in normal human subjects.

Meta-chlorophenylpiperazine (m-CPP), a probe of central serotonergic function, elevates core temperature in rodents, nonhuman primates, and humans via serotonin receptor-mediated mechanisms. To further characterize the thermoregulatory aspects of this response, we studied 16 healthy volunteers using multiple core and skin temperature recording sites. Compared to placebo, intravenous m-CPP (0.08 mg/kg) produced statistically significant biphasic changes in rectal temperature, characterized by initial hypothermia (-0.04 degrees C at 12 minutes) followed by progressive hyperthermia (+0.17 degrees C at 90 minutes). m-CPP also produced significant increases in plasma norepinephrine concentrations. Analysis of the skin temperature recordings suggests that the effector mechanism primarily responsible for m-CPP-induced core hyperthermia is increased metabolic thermogenesis. Individual differences in the magnitude of the hyperthermia were independent of m-CPP plasma concentrations but were found to be linearly correlated with the level of the previous night's core rectal temperature minimum and mean. It appears that m-CPP activates a mode of metabolic thermogenesis governed by a nocturnally sensitive proportional control mechanism. The operation of such a proportional controller is characterized by a set point and a gain, and has been implicated in the general economy of mammalian energy balance.

Adult↗
PubMed1995

Plasma metadrenalines: do they provide useful information about sympatho-adrenal function and catecholamine metabolism?

1. The clinical utility of plasma metadrenalines for examination of sympatho-adrenal function and catecholamine metabolism was assessed from plasma measurements of these metabolites in a number of clinical conditions (hypertension, cardiac failure, bilateral adrenalectomy and X-chromosomal deletions of the gene for monoamine oxidase), and before and during activation of sympathetic outflow or infusions of noradrenaline and adrenaline. 2. Plasma concentrations of normetadrenaline were less than 25% of those of noradrenaline, concentrations of metadrenaline and adrenaline were similar and those of sulphate-conjugated metadrenalines were 20- to 30-fold higher than free metadrenalines. Hypertensive patients had elevated plasma concentrations of adrenaline, noradrenaline and conjugated but not free metadrenalines. Cardiac failure patients had 2- to 4-fold increases in plasma noradrenaline and free and conjugated normetadrenaline. Adrenalectomy resulted in undetectable plasma concentrations of adrenaline, 91-97% decreases in free and conjugated metadrenaline and a 40% decrease in normetadrenaline relative to noradrenaline. Patients with X-chromosomal deletions of the gene for monoamine oxidase had 6- and 16-fold increases in plasma free and conjugated normetadrenaline and 2- and 4-fold increases in free and conjugated metadrenaline. 3. Infusion of catecholamines increased plasma concentrations of free metadrenalines by less than 6% of increases in precursor amines, indicating that most plasma normetadrenaline (84%) and metadrenaline (90%) is derived from metabolism of catecholamines before their entry into the circulation. Considerable O-methylation of catecholamines within the adrenals explains why sympatho-adrenal activation resulted in smaller proportional increases in plasma metadrenalines than catecholamines. 4. Plasma metadrenalines provide supplementary information about sympatho-adrenal activity to that provided by catecholamines, but are more useful for examination of the extraneuronal inactivation of catecholamines, particularly detection of neurochemical phenotypes in genetic disorders of catecholamine metabolism. Significant formation of metadrenalines within chromaffin tissue explains why measurements of plasma metadrenalines provide an extraordinarily sensitive method for diagnosis of phaeochromocytoma.

Adrenal Glands↗
PubMed1995

Working memory as assessed by subject-ordered tasks in patients with obsessive-compulsive disorder.

We tested patients with obsessive-compulsive disorder (OCD) and normal subjects (n = 18 per group) on a self-paced, working memory task that, based on studies of patients with focal brain lesions and functional brain imaging studies of normals, is largely mediated by prefrontal cortex. The OCD patients had normal working memory spans and normal recognition memory for all types of material tested (abstract words, common objects, and novel nonsense objects). The patients, however, were slow (p < .005), and the time they took to complete the tasks was significantly correlated with ratings of OCD symptoms (r = .539, p < .05) and depression (r = .643, p < .01), but not anxiety. Slowed performance on this self-paced task was discussed in relation to normal response times by OCD patients under typical laboratory conditions. It was suggested that this discrepancy may be related to a broader dissociation between real-world and laboratory performance as seen in some patients with prefrontal lobe dysfunction.

Adult↗