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Biomedical subjects

R A Mueller

Publications and source records attributed to R A Mueller.

At least 91 records · Page 5Linked to original sources
PubMed1986

Developmental variations in CSF monoamine metabolites during childhood.

Cerebrospinal (CSF) fluid content of the stable metabolites homovanillic acid, 3-methoxy-4-hydroxyphenyl glycol and 5-hydroxyindoleacetic acid were measured in 19 children without neurological disease known to alter CSF monoamine metabolites. The CSF levels of all three metabolites were found to be up 6 times higher in early infancy compared to the values during adolescence. The levels decreased in a logarithmic fashion, and adult values (approx. 25-50 ng/ml) were reached at 3-5 years of age. Two different interpretations of the findings are discussed: (1) a higher release or turnover of central serotonin and catecholamine metabolites during early postnatal age, or (2) lower clearance of the stable acid metabolites from CSF during infancy due to relatively immature active transport mechanisms.

Adolescent↗
PubMed1986

Splanchnic insulin metabolism in obesity. Influence of body fat distribution.

The effects of obesity and body fat distribution on splanchnic insulin metabolism and the relationship to peripheral insulin sensitivity were assessed in 6 nonobese and 16 obese premenopausal women. When compared with the nonobese women, obese women had significantly greater prehepatic production and portal vein levels of insulin both basally and following glucose stimulation. This increase correlated with the degree of adiposity but not with waist-to-hip girth ratio (WHR). WHR, however, correlated inversely with the hepatic extraction fraction and directly with the posthepatic delivery of insulin. The latter correlated with the degree of peripheral insulinemia. The decline in hepatic insulin extraction with increasing WHR also correlated with the accompanying diminution in peripheral insulin sensitivity. Increasing adiposity is thus associated with insulin hypersecretion. The pronounced hyperinsulinemia of upper body fat localization, however, is due to an additional defect in hepatic insulin extraction. This defect is closely allied with the decline in peripheral insulin sensitivity.

Adipose Tissue↗
PubMed1986

Dopaminergic regulation of proenkephalin-A gene expression in the basal ganglia.

Dopaminergic denervation by 6-hydroxydopamine (6-OHDA) increased proenkephalin-A gene expression in the striatum as evidenced by increases in the levels of Met5-enkephalin (ME), precursor and preproenkephalin mRNA (PE-mRNA). This and other lines of evidence support the hypothesis that nigrostriatal dopamine input is inhibitory to striatal enkephalin neurons and that the removal of this inhibitory influence leads to an acceleration of ME biosynthesis. These findings suggest that the enkephalin system may be associated with the progression of adaptive changes subsequent to dopaminergic dysfunction in basal ganglia.

Animals↗
PubMed1986

Effects of antidepressant drugs injected into the amygdala on behavioral responses of rats in the forced swim test.

Experiments were conducted to determine if the actions of antidepressant drugs in a pharmacological screen would be localized to specific brain regions. Rats were infused in discrete brain regions with drugs of different pharmacological properties and processed in the forced swim test. Infusion of imipramine and pargyline into the amygdala produced behavioral responses similar to i.p. injections of the drugs. The regions of the amygdala from which positive responses could be elicited were highly selective. From cannula placements and diffusion studies with autoradiography it appears that a locus of action of imipramine and pargyline is confined to the central, basolateral and/or lateral nuclear regions of the amygdala. Behavioral responses of rats in which imipramine was infused into the anterior amygdala or caudate-putamen did not differ from saline controls. When infused into regions of the amygdala in which imipramine was active, iprindole, an "atypical" antidepressant, did not produce a behavioral response in the forced swim test. Two "false positives" in the forced swim test, atropine and amphetamine, were also not active when infused into the amygdala. These results indicate that the amygdala is a critical site of action for certain antidepressant drugs in the forced swim test, and that behavioral activation in the test induced by iprindole, amphetamine and atropine involve brain regions other than the amygdala.

Amygdala↗
PubMed1985

A centrally elicited respiratory stimulant effect by bombesin in the rat.

The effects of the tetradecapeptide bombesin on respiratory regulation in the rat were studied using a whole body plethysmographic model. Application of the peptide was made intracerebroventricularly (i.c.v.) as well as via microinjections into specific brainstem areas. I.c.v. injection (0.1-5 micrograms) resulted in a dose-dependent increase in tidal volume while respiratory frequency was decreased only at higher doses. The respiratory duty cycle remained unchanged while the respiratory drive was significantly increased. The respiratory effects were blunted by bilateral section of the tenth cranial nerve. Studies employing the occluded breath technique indicated a change in the threshold to afferent vagal signals while the time-setting for inspiration remained unchanged. Similar ventilation changes were elicited when the peptide was injected into the area of the nucleus ambiguous but not in several other areas of the brainstem. Such bombesin sensitive areas are consistent with a recent immunohistochemical study describing a dense pattern of immunoreactive somata in this area of the brainstem. The ventilatory stimulant effect seems to depend on an intact afferent vagal innervation.

Animals↗
PubMed1985

Bombesin-like immunoreactivity in the central nervous system of capsaicin-treated rats: a radioimmunoassay and immunohistochemical study.

The neuroanatomical distribution of bombesin-like immunoreactivity (BLI) in the rat central nervous system was investigated using radioimmunoassay and immunohistochemistry. Whereas cross-reactivity of the bombesin antiserum with substance P was problematic in the immunohistochemical experiments, no significant cross-reactivity with substance P was apparent in the radioimmunoassay. Results from the radioimmunoassay studies reveal particularly high concentrations of BLI in the hypothalamus, thalamus, medulla and spinal cord. Adult rats treated neonatally with capsaicin displayed significant depletions of somatostatin-like and substance P-like immunoreactivity and a small, statistically significant, reduction of BLI in the cervical spinal cord. Capsaicin treatment significantly reduced substance P-like immunoreactivity, but not somatostatin-like immunoreactivity, in the medulla and resulted in a small BLI depletion of borderline statistical significance in this brain region. Neonatally administered capsaicin treatment had no effect on the thalamic concentration of any of these three neuropeptides and neurotensin-like immunoreactivity was unchanged in all brain regions studied. These results suggest that the source of some of the BLI found in the spinal cord may be capsaicin-sensitive dorsal root ganglion cells.

Animals↗
PubMed1985

SCH-23390 antagonism of a D-2 dopamine agonist depends upon catecholaminergic neurons.

SCH-23390, a selective D-1 dopamine antagonist, was found to antagonize the locomotor stimulation induced by LY-171555, an action similar to that for haloperidol in control animals. However, this action of SCH-23390 was prevented in rats treated with 6-hydroxydopamine (6-OHDA) or with reserpine plus alpha-methyl-tyrosine pretreatment. These results indicate that the action of SCH-23390 to antagonize D-2 dopamine receptor actions is dependent upon functional catecholamine-containing neurons. In contrast to the lack of action of SCH-23390 to antagonize LY-171555 in 6-OHDA-treated rats, SCH-23390 blocked the locomotor stimulation induced by SKF-39393, a D-1 dopamine agonist, after this treatment. Thus, D-1 dopamine receptors are distinct from D-2 receptor sites and can exhibit a behavior similar to that observed when D-2 receptors are stimulated. These data suggest that D-1 receptor sites modulate D-2 dopamine receptor function through a mechanism dependent upon functionally intact catecholamine-containing neurons.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1985

Altered respiratory response to substance P in capsaicin-treated rats.

The present investigation sought to examine the importance of substance P in the altered respiratory activity after neonatal capsaicin administration. Halothane-anesthetized adult rats given capsaicin neonatally exhibit a decreased basal minute ventilation with PaCO2 equal to and PaO2 greater than vehicle injected controls. In addition, the minute ventilation-PaCO2 curve was displaced to the right. Acute bilateral cervical vagotomy severely blunted the minute ventilation response to PaCO2 and abolished the differences in ventilation between capsaicin treated and control rats. Neonatal capsaicin significantly reduced pons-medulla substance P content but not TRH, serotonin or 5-hydroxyindole acetic acid. Immunohistochemical studies revealed that substance P fibers of the trigeminal spinal nucleus were the most severely affected in the brain stem and that substance P fibers in the lung were totally absent. The intracerebroventricular administration of substance P increased minute ventilation similarly in both control and capsaicin treated rats, largely as a result of increases in tidal volume. The minute ventilation-PaCO2 curve was similar in both groups after substance P administration. Simultaneous administration of the peptidase inhibitor captopril with substance P increased the respiratory response to substance P in normal rats. Administration of captopril to capsaicin treated rats restored the ventilation-PaCO2 curve to the position observed in normal rats. The hypotensive response to intracerebroventricular captopril alone in control rats was less profound in rats given neonatal capsaicin. These results are consistent with the thesis that respiratory depression after capsaicin treatment is at least in part due to the loss of substance P primary afferent nerve terminals in the brain stem, suggesting that substance P fibers in the brain stem may participate in the normal modulation of respiratory activity.

Animals↗
PubMed1985

Effects of TRH, ethanol, and TRH-ethanol combination on activity in rats with altered monoamine content.

Investigations were undertaken with 5,7-dihydroxytryptamine and 6-hydroxydopamine treated rats to see whether activity changes induced by TRH, ethanol and the TRH-ethanol combination would be affected after reduced monoamine function. In keeping with earlier results, TRH increased activity, ethanol reduced activity and the TRH-ethanol combination produced activity counts greater than those for TRH alone. Neither the 5,7-dihydroxytryptamine-induced reduction of brain serotonin nor the 6-hydroxydopamine treatments which reduced brain catecholamines altered the hyperactivity induced by TRH or the TRH-ethanol combination. While reduction of brain serotonin did not affect the ethanol-induced changes in activity, preferential reduction of dopamine as well as reduction of both norepinephrine and dopamine significantly antagonized this measure of ethanol-induced depression. The reduction of dopamine alone produced the greatest effect on this action of ethanol. It can be concluded from the data that the increased locomotion induced by TRH and the TRH-ethanol combination does not depend upon endogenous monoamines, whereas the sedative effects of ethanol are apparently influenced by alterations in brain catecholamine function.

5,7-Dihydroxytryptamine↗
PubMed1985

Serotonin turnover and supersensitivity after neonatal 5,7-dihydroxytryptamine.

Adult awake rats which received neonatal pargyline and 5,7-dihydroxytryptamine to severely reduce CNS serotonin terminals and perikarya have a reduced rate of accumulation of brain stem 5-hydroxytryptophan after Ro-44602. The rate of accumulation in the cerebral cortex and spinal cord were near normal when adult, even though serotonin and 5-hydroxyindoleacetic acid were sharply reduced in these regions. The respiratory response to 5-methoxy N,N-dimethyl-tryptamine was much more pronounced in pargyline-5,7-dihydroxytryptamine treated rats than in controls. If supersensitivity in serotonin receptors only develops in areas with decreased transmitter turnover, the site of action of serotonin agonists to depress respiration would seem to reside in the brain stem region. The results also suggest that compensatory changes in turnover do not develop to a similar degree in all CNS areas with altered serotonin content.

5,7-Dihydroxytryptamine↗
PubMed1985

The role of vagal afferents and carbon dioxide in the respiratory response to thyrotropin-releasing hormone.

Rats treated neonatally with pargyline and 5,7-dihydroxytryptamine to decrease central serotonin-containing neurons have an accentuated respiratory response to i.c.v. thyrotropin-releasing hormone (TRH). Since these treated rats also evidence an elevated PaCO2, we sought to evaluate the importance of CO2 in determining the magnitude of the respiratory response to TRH. Neonatal treatment with capsaicin or acute vagotomy also produced adult animals whose basal PaCO2 was elevated and whose respiratory response to TRH was greater than that seen in control rats with lower PaCO2 values. In normal rats, however, administration of CO2 immediately before and after TRH administration does not alter the subsequent response to TRH. Thus, it appears that TRH facilitates the processing of CO2-dependent afferent impulses, and that CO2 does not alter disposition or pharmacokinetics of TRH.

5,7-Dihydroxytryptamine↗
PubMed1985

Characterization of adenosine-induced respiratory depression in the preterm rabbit.

The respiratory performance was studied after intraperitoneal administration of the adenosine agonists N6-phenyl-isopropyl-adenosine (PIA) and adenosine-5-ethylcarboxamide to preterm (gestational age 29-30 days) newborn halothane-anesthetized rabbits. Both agonists induced marked hypoventilation and irregular breathing by decreases in the breathing frequency as well as the tidal volume. Expiratory time was markedly prolonged, resulting in a decrease in the respiratory duty cycle (inspiratory time/total cycle duration). Analysis using the occluded-breath technique revealed that the adenosine analogues altered the time setting of the expiratory (inspiratory) neuronal circuits and lowered the inspiratory off-switch level, while inspiratory drive and the bulbopontine setting of the inspiratory phase were unaltered. The ventilatory response to CO2 was blunted after both adenosine analogues studied. Theophylline almost completely reversed the hypoventilation and irregular breathing seen after PIA injection. It is concluded that activation of central nervous adenosine receptors induced a marked respiratory depression in the preterm rabbit. Furthermore, our data imply that an overactivity of central adenosine mechanisms may have a pathophysiological significance for the irregular breathing or apnea of prematurity sometimes seen in the human neonate.

Adenosine↗
PubMed1985

Rapid down regulation of beta adrenergic receptors by combining antidepressant drugs with forced swim: a model of antidepressant-induced neural adaptation.

The hypothesis that behavioral responses to antidepressant drugs in the forced swim test are related to a rapid neural adaptation produced by the combination of drug treatment and swim stress was explored. As a measure of adaptation, brain beta adrenergic receptors were assayed using [3H]dihydroalprenolol [( 3H]DHA) binding to brain membranes from rats that were processed in the forced swim test. The combination of swim stress and imipramine treatment antagonized immobility induced by forced swimming and resulted in a reduction in [3H] DHA binding to membranes from forebrain preparations which did not include the corpus striatum. Administration of antidepressant drugs from other chemical classes, including pargyline, iprindole and nomifensine, also reduced immobility induced by the forced swim and produced a reduction in [3H]DHA binding to forebrain membranes. In homogenates of the corpus striatum, [3H]DHA binding was not altered by swim stress combined with antidepressant drug treatment. Chlordiazepoxide was without an effect on immobility or beta receptor binding when combined with forced swim. Even though atropine and amphetamine exhibited a positive activity in the forced swim test, they did not reduce [3H]DHA binding. Therefore, by combining behavioral and neurochemical analysis of animals processed in the forced swim test, it may be possible to differentiate, with greater confidence, potential antidepressant drugs from "false positives." The present studies support the hypothesis that antidepressant drug action in the forced swim test involves a rapid neural adaptation as reflected by the down regulation of beta adrenergic receptors. Thus, this behavioral paradigm may serve as a model of adaptive mechanisms induced by antidepressant drugs.

Adaptation, Physiological↗
PubMed1985

Dopamine agonist-induced locomotor activity in rats treated with 6-hydroxydopamine at differing ages: functional supersensitivity of D-1 dopamine receptors in neonatally lesioned rats.

Locomotor responses caused by dopamine receptor agonists with presumed specificity for D-1 or D-2 receptor subtypes were compared to apomorphine-induced locomotion in neonatally and adult 6-hydroxydopamine (6-OHDA)-treated rats. In adult 6-OHDA-treated rats, apomorphine and the D-2 agonist, LY-171555, produced a marked, dose-related increase in locomotor activity. Increases in locomotion observed in neonatally 6-OHDA-treated rats after apomorphine and LY-171555 administration were less than one-third of those seen in rats treated as adults with 6-OHDA. Neonatally 6-OHDA-treated rats, positive for L-dihydroxyphenylalanine-induced self-biting, exhibited a small increase in locomotion after a single exposure to SKF-38393, a D-1 dopamine agonist. Subsequent administration of SKF-38393 to these rats resulted in an additional elevation of the locomotor response which reached a maximum after four doses. Adult 6-OHDA-treated rats were less sensitive to the locomotor stimulant effects of SKF-38393 than were neonatally 6-OHDA-treated rats. SKF-38393 and LY-171555 produced several behaviors in neonatally 6-OHDA-treated rats that were similar. These results indicate that D-1 dopamine receptors contribute to modulation of central dopaminergic function. Haloperidol and cis-flupentixol antagonized apomorphine-induced locomotion comparably in control and adult 6-OHDA-treated rats. The D-1 dopamine receptor antagonist, SCH-23390, was a less effective blocker of apomorphine-induced locomotion in 6-OHDA-treated rats than in controls. Therefore, the ability of SCH-23390 to attenuate apomorphine in control rats is likely dependent upon intact catecholamine-containing neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1985

Evidence that D-1 dopamine receptors contribute to the supersensitive behavioral responses induced by L-dihydroxyphenylalanine in rats treated neonatally with 6-hydroxydopamine.

The present investigation supports the hypothesis that functionally supersensitive D-1 dopamine receptors are involved in the self-mutilation behavior (SMB) induced by L-dihydroxyphenylalanine (L-dopa) in rats treated neonatally with 6-hydroxydopamine (6-OHDA). This conclusion is based upon 1) the antagonism of this behavior by SCH-23390, a D-1 antagonist; 2) induction of SMB in neonatal-6-OHDA-treated rats by the D-1 agonist, SKF-38393; 3) the high correlation of the supersensitive locomotor responses to the D-1 agonist with the occurrence of L-dopa-induced SMB; and 4) the inability of the D-2 agonist, LY-171555, to induce SMB in rats treated neonatally with 6-OHDA. The specificity of SCH-23390 and SKF-38393 for the D-1 dopamine receptor was supported by the absence of action of SCH-23390 against locomotor activities induced by LY-171555 and its blockade of SKF-38393-induced locomotion in 6-OHDA-treated rats. Behavioral responses to D-1 and D-2 agonists did not show the same profile in adult and neonatally 6-OHDA-treated rats, providing further support for the view that the age at which dopaminergic neurons are destroyed has differing effects on motor output. Many of the behaviors observed when the D-2 dopamine receptor was activated by LY-171555 were apparent after SKF-38393 in neonatally 6-OHDA-treated rats. Similar behavioral responses to the D-1 and D-2 agonists were also observed in adult 6-OHDA-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1984

Early postnatal administration of 5,7-DHT: effects on serotonergic neurons and terminals.

Serotonergic neurons throughout the brain were destroyed by early postnatal treatment of rats with an intracisternal injection of 5,7-dihydroxytryptamine (5,7-DHT), as demonstrated with biochemical measurements of serotonin and immunocytochemical localization of serotonin-containing neurons. Using these methods, it was shown that approximately 75-98% of serotonergic neurons underwent cell death in rats which were treated on day 3. In contrast, intracisternal administration of 5,7-DHT in adult rats led to the loss of distal serotonergic terminals without apparent loss of the cell bodies. Desipramine pretreatment prevented significant effects of 5,7-DHT on noradrenergic neurons.

5,7-Dihydroxytryptamine↗
PubMed1984

Supersensitivity to the respiratory stimulatory effect of TRH in 5,7-dihydroxytryptamine-treated rats.

Rats treated neonatally with pargyline and 5,7-dihydroxytryptamine (5,7-DHT) have an elevated paCO2 and reduced minute ventilation when given 0.7% halothane in oxygen as adults. Serotonin content in the spinal cord of 5,7-DHT treated rats was undetectable and TRH content was reduced by 35%. The 5,7-DHT treated rats were supersensitive to the increase in minute ventilation and CO2 sensitivity produced by intraventricular TRH. It is possible that the supersensitivity to exogenous TRH after neonatal 5,7-DHT treatment may be secondary to decreased availability of TRH in the CNS.

5,7-Dihydroxytryptamine↗