Biomedical subjects

A M Moudy

Publications and source records attributed to A M Moudy.

11 recordsLinked to original sources

PubMed1995

Abnormal calcium homeostasis and mitochondrial polarization in a human encephalomyopathy.

Patients with several inherited human encephalomyopathies exhibit systemic and neurological symptoms in association with specific mitochondrial mutations. The mechanisms by which these mitochondrial mutations result in cellular injury have not been elucidated. One potential cause of neuronal vulnerability is an inability to effectively buffer intracellular calcium. We report that fibroblasts from patients with one specific inherited encephalomyopathy, MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome, have elevated levels of ionized calcium and cannot normally sequester calcium influxes. Quantitative fluorescence imaging demonstrated that this abnormality was associated with a relative decrease in mitochondrial membrane potential compared to control fibroblasts. This documentation of pathological calcium homeostasis in a genetic neurological disease extends the calcium hypothesis of toxic cell injury to human mitochondrial encephalomyopathies.

Adenosine Triphosphate↗

PubMed1994

Rapid desensitization determines the pharmacology of glutamate neurotoxicity.

Glutamate (Glu), the major excitatory neurotransmitter in the nervous system, is toxic to neurons when it accumulates at high concentrations in the extracellular space. Even though Glu is a mixed agonist, capable of activating N-methyl-D-aspartate (NMDA) receptors and non-NMDA receptors, in many preparations Glu neurotoxicity is prevented by selective blockade of NMDA receptors. In cultures of hippocampal neurons, treatment with 500 microM Glu for 30 min killed more than 90% of the neurons. The simultaneous addition of the selective NMDA agonist methyl-10,11-dihydro-5-H-dibenzocyclo-hepten-5,10-imine (MK-801) reduced the cell loss to less than 30%. However, when Glu was combined with either diazoxide or cyclothiazide, two thiazides which dramatically diminish rapid Glu desensitization, MK-801 was no longer very protective and neuronal loss exceeded 80%. However, the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), in combination with MK-801, was able to prevent most Glu neurotoxicity in the presence of these thiazides. These experiments show that there are circumstances under which Glu neurotoxicity is produced by overactivation of non-NMDA receptors. Our observations offer a possible explanation for the recent finding that blockade of non-NMDA receptors is much more beneficial than NMDA receptor blockade in protecting the brain in some in vivo models of global ischemia.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1993

Development of dopamine-beta-hydroxylase-positive fiber innervation of the rat hippocampus.

Development of the noradrenergic fiber innervation of the rat hippocampus by the locus coeruleus was examined immunohistochemically in fixed tissue from animals aged 4 days through 55 days postnatal. The presence of tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) immunoreactive cells and fibers was evaluated in sections of hippocampus and locus coeruleus. Large, multipolar TH- and DBH-positive cells with long beaded fibers were visible within locus coeruleus at all ages; no immunopositive cell bodies were found in hippocampus. In hippocampal sections from mature animals (PN55), the highest density of DBH-stained fibers was found in stratum lucidum of CA3 and in the hilus and inner molecular layer of the dentate gyrus. Whereas similar patterns of fiber positivity were found at PN21 and PN10 (although with somewhat reduced density of immunopositive fibers), the pattern was quite different at PN4. Although fiber staining was relatively sparse at PN4, relative density of DBH fibers was highest in stratum radiatum of CA1 and subiculum. This change in staining pattern suggests that noradrenergic function in hippocampus may change as the rat matures. Double immunofluorescence techniques showed an overlap of DBH and TH positive fibers in all hippocampal regions at all ages. DBH immunostaining appeared to be somewhat more sensitive than the TH staining. These data made it impossible to confirm the presence of significant numbers of nonnoradrenergic, catecholamine-containing fibers in hippocampus.

Animals↗

PubMed1993

Development of dopamine-beta-hydroxylase-positive fiber innervation in co-cultured hippocampus-locus coeruleus organotypic slices.

Development of the noradrenergic innervation of the rat hippocampus by the nucleus locus coeruleus was examined immunohistochemically in the roller tube organotypic cultured slice preparation. Slices of rat hippocampus and locus coeruleus were co-cultured on glass coverslips for 2-6 weeks and evaluated for the presence of dopamine-beta-hydroxylase (DBH) and tyrosine hydroxylase (TH) immunoreactive cells and fibers. Large, multipolar DBH- and TH-positive cells were visible within the locus coeruleus; an occasional cell appeared near or just within co-cultured hippocampal tissue and in connecting fiber tracts. DBH-positive cells tended to concentrate near the edges of locus coeruleus tissue. Locus coeruleus slices cultured alone showed little indication of fiber outgrowth in any direction. In co-cultures, however, beaded DBH- and TH-positive fibers were directed toward the hippocampus. The majority of these fibers entered the hippocampus in the hilar/CA3 region and formed extensive collateral branches. Light microscopy suggests that DBH-positive fiber growth was densest at or near the pyramidal cell layer in CA3b and CA3c and in the infragranular region of the dentate hilus. This pattern of noradrenergic innervation of hippocampus by co-cultured locus coeruleus in vitro appears very similar to the pattern established in vivo (see Moudy et al., companion article, this issue).

Animals↗

PubMed1992

Pyramidal neurons in immature rat hippocampus are sensitive to beta-adrenergic agents.

The development of hippocampal neuronal sensitivities to the beta-noradrenergic agent, isoproterenol, was examined in tissue from immature rats. The in vitro hippocampal slice preparation was used to assess intracellularly recorded responses from hippocampal neurons to pressure-pulse and bath application of noradrenergic drugs. Effects of the drug on individual hippocampal CA3 pyramidal neurons were compared across several stages of development, ranging from postnatal day 4-5 (P4-5) to maturity. Isoproterenol, pressure-pulse applied to CA3c pyramidal cells, produced a depolarization of membrane potential and an increase in cell input resistance in tissue as young as P7. Spike frequency adaptation (in trains of action potentials triggered by depolarizing pulses) was reduced, as were the slow after-hyperpolarizations following the spike trains. All agonist effects were blocked by timolol, a beta-antagonist. Drug-induced changes in cell membrane and firing properties in immature tissue were qualitatively similar to beta-receptor-mediated noradrenergic effects in adult tissue. These results indicate that the beta-receptor-mediated component of the noradrenergic effect in rat hippocampus is physiologically functional by the seventh day of postnatal life; at earlier times (P4-5) these beta-receptor-mediated noradrenergic actions are, at best, equivocal.

Action Potentials↗

PubMed1989

A mu-specific opioid peptide agonist increases excitability of pyramidal neurons in untreated and receptor up-regulated hippocampus.

The rat hippocampus contains the major types of opioid receptors, delta, mu, and kappa, as determined by autoradiographic and membrane binding analyses. Chronic exposure to excessive amounts of opioid antagonists results in a doubling of the number of binding sites. However, the direct electrophysiological significance of this increased number of opioid receptors in the central nervous system remains uncharacterized. We examined the effects of an opioid peptide with high affinity and high specificity for mu receptors, DAMGO (D-ala2-mePhe4-gly-ol5 enkephalin), under normal conditions and after 1 or 2 weeks of continuous infusion of the opiate antagonist naltrexone. Chronic infusion of naltrexone administered to the whole animal resulted in significant up-regulation (71%) of mu opioid receptors in the rat hippocampus. Slices of the hippocampus were perfused with artificial cerebrospinal fluid while recording population spikes in stratum pyramidale, excitatory postsynaptic potentials in stratum radiatum and while stimulating afferents in the Schaffer collaterals. Superfusion of slices with DAMGO produced a concentration-dependent increase in the amplitude of population spikes. No significant change was observed in the simultaneously recorded excitatory postsynaptic potential slope. This selective increase in population spike amplitude led to a leftward shift (19%) in the derived input-output curve. In addition, DAMGO superfusion produced extra spiking at higher stimulus intensities. Naltrexone reversed the DAMGO-induced increase in excitability, as well as prevented additional spikes. DAMGO superfusion of slices taken from chronically treated rats produced a much greater shift (42%) in the input-output curve than it did in untreated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1987

Guanine nucleotide and cation regulation of mu, delta, and kappa opioid receptor binding: evidence for differential postnatal development in rat brain.

A study of the onset of cation and guanine nucleotide regulation of delta, mu, and kappa rat brain opioid receptors during postnatal development was undertaken. Site-specific binding assays were utilized for each receptor type and the effects of 0.5 mM MnCl2, 100 mM NaCl, and/or 50 microM guanosine-5'-(beta, gamma-imido) triphosphate [Gpp(NH)p] were assessed. The most pronounced changes of opioid binding were seen in the presence of Mn2+. In adults, agonist binding to delta sites was stimulated by Mn2+, whereas that to mu sites was not affected and kappa binding was inhibited. The postnatal development of Mn2+ regulation for the three receptor subtypes was distinctly different. The largest effects were seen on delta sites detected in the early neonatal period, Mn2+ eliciting a 68% stimulation of binding over controls at day 1. Significant inhibition of kappa site binding by Mn2+ was detected only after the third postnatal week. Mn2+ caused a significant reversal of Gpp(NH)p inhibition of delta binding in the early neonatal period, exceeding that in the absence of regulators. Inhibition of mu and delta receptor binding by Na+ was greater, and the Mn2+ reversal of this effect was smaller, in the first 2 postnatal weeks than in adults. Gpp(NH)p + Na+ regulation did not change appreciably during the postnatal period. However, Mn2+ reversal of the considerable inhibition elicited by the combination of Na+ and Gpp(HN)p was developmental time-dependent. The data are discussed in terms of multiple sites of interaction for guanine nucleotides and cations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Dorsal column stimulation does not inhibit segmental nociceptive reflexes of hind limbs.

Stimulation of the dorsal columns has been shown to inhibit many indices of nociception. We report here that dorsal column stimulation does not inhibit two such nociceptive reflexes in the decerebrate cat: the flexion and the crossed extension reflex. In fact, such stimulation typically facilitates these reflexes. These findings suggest that the use of segmental nociceptive reflexes as models of pain perception may not be wholly appropriate.

Animals↗

PubMed1986

Differences in nociception during voluntary flexion and extension.

The volar surface of the second toe on the right leg of 14 human subjects was stimulated with 10 msec electrical shocks at 1 Hz. Stimulus intensity was sufficient to evoke first and second pain and was kept constant throughout each trial. The right leg was held in a relaxed, flexed, or extended position for 10 shocks and was then moved to and held at another of the positions for another 10 shocks. Subjects were asked to report if the intensity of the stimulus remained constant, increased or decreased after moving to the second position in each trial. Several statistical analyses showed a significant (P = 0.04 to less than 0.001) trend for the perceived pain to be more intense when the leg was held in the flexed position than when in the extended position. The results support a hypothesis that populations of neurons may contribute simultaneously to sensory perception and segmental reflex responses evoked by noxious stimuli as well as to voluntary motor behavior.

Adult↗

PubMed1985

Differential up-regulation of microsomal and synaptic membrane mu opioid receptors.

Naltrexone was administered to rats for 7 days by osmotic minipump (5 mg/kg/day) and thereupon, forebrain mu opioid receptor levels in subcellular fractions were monitored by homologous displacement of [3H]D-ala2-mePhe4-gly-ol5 enkephalin binding. Microsomes displayed increases in mu receptor concentrations that were twofold greater than those associated with synaptic plasma membrane fractions (92 vs. 51%). Levels in crude membranes rose 77%. Binding affinities were unchanged.

Animals↗

PubMed1985

Changes in venous blood content from active and inactive hindlimb during isotonic exercise.

Venous blood samples were obtained from either exercising (n = 9) or nonexercising (n = 8) hindlimb during a progressive isotonic exercise in rabbits anesthetized with urethane and chloralose. Each experimental session consisted of 5-min nonexercise periods alternated with 6-min exercise periods, followed by a 10-min postexercise period. During each exercise period, stimulation of the distal stump of the right sciatic nerve at 1 Hz induced plantar flexions which lifted loads comparable to 2, 5, 8, 30, or 50% of an afterload at which only an isometric tension developed. Free-flowing venous blood samples were obtained before the first exercise period, during the last minute of each exercise period, and 10 min following the last exercise session. Increases in [Na+], [K+] and lactate concentration were obtained in blood from active limbs. Only lactate concentration increased in blood from nonexercising limbs, while [K+] decreased slightly. Inferences concerning the vascular volume response to this protocol would be quite different depending on the blood sampling site. Changes in blood from inactive tissue, further, may indicate only saturation of homeostatic mechanisms which normally compensate for vascular volume alterations initiated in active tissue.

Animals↗