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R H Roth

Publications and source records attributed to R H Roth.

At least 343 records · Page 19Linked to original sources
PubMed1975

Tyrosine hydroxylase: allosteric activation induced by stimulation of central noradrenergic neurons.

Electrical stimulation of the rat locus coeruleus cases about a 300% increase in the activity of the tyrosine hydroxylase prepared from the hippocampus on the stimulated side and assayed in the presence of subsaturating concentrations of tyrosine and pteridine cofactor. Addition of calcium or cAMP to soluble preparations of tyrosine hydroxylase isolated from the hippocampus produces a similar activation of tyrosine hydroxylase. The activation of tyrosine hydroxylase produced by calcium is reversed by addition of the calcium chelator, EGTA, while the activation produced by cAMP addition or by electrical stimulation of the locus coeruleus is unaffected by addition of EGTA to the assay medium. The activation of tyrosine hydroxylase produced by electrical stimulation or by addition of calcium or cAMP to the assay medium appears to be mediated in part by alterations in the kinetic properties of the enzyme. All treatment causes the enzyme to have an increased affinity for substrate and pteridine cofactor and a decreased affinity for the endproduct inhibitor, norepinephrine. These results are suggestive that the activation of tyrosine hydroxylase which occurs during periods of increased impulse flow in noradrenergic neurons may be initiated by alterations in calcium fluxes or by changes in the steady state levels of cAMP which accompany neuronal depolarization.

Allosteric Regulation↗
PubMed1975

Sympathetic neurotransmitter metabolism in Hirschsprung's disease.

Tyrosine hydroxylase activity was measured in high speed supernatants obtained from full thickness segments of aganglionic and ganglionic colon of three children with Hirschsprung's disease. Tyrosine hydroxylase activity expressed as pmole DOPA/mg protein/min was 0.93 +/- 0.16 in ganglionic and 2.67 +/- 0.21 in aganglionic colon. Tyrosine hydroxylase activity in ganglionic colon rose to 2.29 +/- 0.11 following calcium stimulation (100 muM) but could not be further increased in aganglionic colon. Addition of norepinephrine (2 X 10(-4) M) to tissue homogenates inhibited tyrosine hydroxylase activity in ganglionic colon by 57 +/- 8% but only by 14 +/- 3% in aganglionic colon, suggesting that the enzyme present in aganglionic colon is insensitive to feedback inhibition by endogenous norepinephrine. The elevation of tyrosine hydroxylase activity in aganglionic colon and its insensitivity to calcium stimulation and norepinephrine inhibition is further evidence of sympathetic overactivity in the aganglionic colon and suggests a basic enzymatic abnormality in the pathogenesis of Hirschsprung's disease.

Calcium↗
PubMed1975

Activation by cyclic 3':5'-adenosine monophosphate of tyrosine hydroxylase in the rat brain.

Membrane-permeable derivatives of cyclic AMP (cAMP) produced concentration-dependent increases in activity of tyrosine hydroxylase (L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2) in membrane-limited nerve endings (synaptosomes) prepared from three regions of rat brain. Increased hydroxylation occurred even after preincubation and removal of dibutyryl cyclic AMP. In all brain regions, the hydroxylation of phenylalanine and tyrosine was increased, but dibutyryl cAMP had little effect on activity of tryptophan hydroxylase, no effect on aromatic amino-acid decarboxylase, on uptake of tyrosine or phenylalanine, uptake or efflux of dopamine, or distribution of hydroxylase between cytoplasmic and particulate components of the synaptosomes. Dibutyryl cAMP decreased inhibition of catecholamine synthesis in synaptosomes by dopamine and apomorphine. In a soluble preparation of striatal tyrosine hydroxylase, activity was increased by addition of lower concentrations of cAMP or dibutyryl cAMP than with unbroken nerve endings, when subsaturating concentrations of tyrosine and cofactor were employed, while butyrate, chloride, 5'-AMP, ADP, ATP, and cyclic GMP had no activating effect. Increased activity of soluble tyrosine hydroxylase was reflected in increased affinity (Km) for substrate and cofactor and decreased affinity (Ki) for inhibitory end-product (dopamine), suggesting a change in the physical-chemical state of the enzyme or an activator molecule. Cyclic AMP may activate tyrosine hydroxylase during periods of increased neuronal activity.

Animals↗
PubMed1975

Formation of dopamine and noradrenaline in rat vas deferens: comparison with guinea-pig vas deferens.

1 The formation of [14C]-3,4-dihydroxyphenylalanine (DOPA) from [14C]-tyrosine, in the presence of the amino acid decarboxylase inhibitor, brocresine (3-hydroxy-4-bromobenzyloxyamine dihydrogen phosphate), was greatly enhanced in rat vasa deferentia depolarized by a KCl-enriched Krebs-Henseleit solution (52 mM KCl) compared with tissues maintained in unmodified Krebs-Henseleit solution. 2 When the conversion of tyrosine was allowed to proceed as far as catecholamine (brocresine absent) no significant difference was observed between the accumulation of [14C]-catecholamines (CA) in depolarized rat vasa deferentia and the accumulation in control (non-depolarized) tissues. 3 Endogenous CA levels in the depolarized rat vasa deferentia fell to 67% of the controls after a 1 h incubation period and to 53% at the end of 2 hours. 4 Chromatographic separation on Amberlite CG-120 columns of the newly synthesized CA and catechol metabolites from the rat vas deferens revealed that a very high proportion was present as dopamine. The percentage distribution after 1 h incubation in control Krebs-Henseleit was: noradrenaline (NA): 30.6 +/- 5.2; dopamine 56.9 +/- 5.9; acid metabolites: 12.8 +/- 1.1; and in KCl-rich Krebs-Henseleit, NA: 32; dopamine: 44.7 and acid metabolites 23.3. In contrast to the newly synthesized (14C-labelled) CA, endogenous dopamine comprises only 10% of the endogenous CA stores in rat vas deferens. 5 The distribution of newly synthesized NA and dopamine in rat vas deferens is strikingly different from that of guinea-pig vas deferens where more than 80% of newly formed amine is present as NA. In the latter tissue depolarization with K+ causes a striking increase in CA biosynthesis.

Animals↗
PubMed1975

D & L amphetamine stereoisomers: comparative potencies in affecting the firing of central dopaminergic and noradrenergic neurons.

The effect of the d- and l-isomers of amphetamine on the activity of dopaminergic neurons in the substantia nigra zona compacta and noradrenergic neurons in the locus coeruleus was studied in anesthetized and gallamine paralyzed rats using single unit recording techniques. d- and l-Amphetamine administered intravenously were equally effective in depressing the activity of locus coeruleus cells. However, although d-amphetamine was a potent inhibitor of substantia nigra dopamine containing cells, l-amphetamine was ineffective in causing more than a 45% inhibition of over half of the DA cells studied, even when given in nearly lethal doses. In the remaining dopamine neurons l-amphetamine was only 0.2 to 0.05 times as potent as d-amphetamine in producing both 50 and 100% inhibition of firing rate. These findings, when combined with recent biochemical studies by other authors, suggest that l-amphetamine, at low doses, has a preferential effect on noradrenergic as compared to dopaminergic neurons. The consequences of these findings for the interpretation of studies in which d- and l-amphetamine have been used as pharmacological tools to determine the catecholamine system responsible for a particular behavior in man and animals is discussed.

Amphetamine↗
PubMed1975

Effects of molindone on central dopaminergic neuronal activity and metabolism: similarity to other neuroleptics.

The effect of molindone on the activity of dopaminergic (DA) neurons in the rat midbrain and on DA metabolism in the striatum and olfactory tubercles was studied using extracellular single unit recording and biochemical techniques respectively. Molindone in low intravenous doses (0.4-0.8 mg/kg) was found to reverse d-amphetamine and apomorphine induced depression of DA neurons and to block apomorphine induced depression of these cells. Molindone was also found to increase dopamine synthesis and dihydroxyphenylactic acid levels in the striatum and olfacotry tubercles. In all of these respects molindone behaves identically to most classical neuroleptics. However, unlike most antipsychotic drugs previously tested, molindone failed to increase the baseline firing rate of DA cells and blocked haloperidol induced increases in DA neuron activity. In this regard molindone most closely resembles thioridazine and clozapine. Possible mechanisms of action of molindone are discussed based on these findings.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1975

Piribedil and apomorphine: pre- and postsynaptic effects on dopamine synthesis and neuronal activity.

Piribedil and apomorphine can cause a complete but temporary inhibition in firing of the DA-containing neurons. The cells recover to approximately 30 to 40% of the original firing rate, and with subsequent administration of the drug become more and more resistant to further inhibition. At this point they are also resistant to inhibition by other direct- or indirect-acting DA agonists that are normally able to inhibit the firing of DA cells. This effect may be due to an interaction of the DA agonists with the postsynaptic DA receptors, but apomorphine at least is able to inhibit the firing of DA cells directly when iontophoresed onto the DA cell body (Aghajanian and Bunney, 1973). These drugs can block the increase in DA synthesis observed in the absence of impulse flow, indicating a presynaptic site of acttion. Taken together, these results suggest that in interpreting the effects of drugs interacting with the DA systems several points of interaction should be considered.

Animals↗
PubMed1974

Tyrosine hydroxylase: activation by nerve stimulation.

The synthesis of the sympathetic neurotransmitter, norepinephrine, is accelerated by electrical stimulation of the guinea pig vas deferens. The molecular mechanism responsible for this enhanced formation of transmitter is unknown but has been attributed to an increase in the activity of tyrosine hydroxylase (EC 1.14.16.2; tyrosine 3-monooxygenase) during nerve stimulation. In the present experiments, we found that crude preparations of tyrosine hydroxylase isolated from guinea pig vasa deferentia that were electrically stimulated or depolarized by potassium show an increase in activity compared with enzyme obtained from untreated paired control tissues. This increase in activity is partially antagonized by addition of the Ca(++) chelator, ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA), to the assay medium, and can be completely blocked if Ca(++) is removed from the potassium-rich medium used to depolarize the intact tissue, before preparation of the enzyme. A similar increase in enzyme activity occurs when Ca(++) ions are added directly to enzyme prepared from untreated vasa deferentia. In this instance, the activation is completely reversed by EGTA. The increase in activity produced by addition of Ca(++) to the isolated enzyme or by electrical stimulation or potassium depolarization of the tissue before isolation of the enzyme appears to be mediated by changes in the kinetic properties of tyrosine hydroxylase. All treatments appear to activate tyrosine hydroxylase by causing an increase in its affinity for substrate and pteridine cofactor and by decreasing its affinity for the end-product inhibitor, norepinephrine. These results provide direct evidence that the enhanced formation of norepinephrine seen during stimulation of sympathetically innervated tissues arises from an activation of tyrosine hydroxylase. The fact that the activation produced by nerve stimulation is mimicked by Ca(++) ions raises the intriguing possibility that the influx or mobilization of Ca(++) that accompanies nerve stimulation and that is intimately involved in release of transmitter may also participate in the activation of tyrosine hydroxylase.

Animals↗
PubMed1974

Variation in noradrenaline output with changes in stimulus frequency and train length: role of different noradrenaline pools.

1 During adrenergic nerve stimulation the output/pulse of noradrenaline from the rabbit vas deferens and portal vein is not constant but increases as the stimulus frequency or train length is increased. Depending upon the stimulus frequency and train length the fractional release of noradrenaline may vary from less than 10(-7) to greater than 10(-4).2 Endogenous tissue stores of noradrenaline were labelled by incubation with (-)-[(3)H]-noradrenaline and [(14)C]-tyrosine. The output/pulse of newly synthesized [(14)C]-noradrenaline remained constant as the train length was increased whilst the output/pulse of [(3)H]-noradrenaline increased under the same conditions. This phenomenon was independent of the stimulus frequency. Newly synthesized noradrenaline also appeared in the superfusate following nerve stimulation more rapidly than exogenously loaded noradrenaline.3 Both [(3)H]-noradrenaline and [(14)C]-tyrosine were found to label an easily releasable store of noradrenaline. Mobilization from this store was the same at low and high frequencies of nerve stimulation.4 It is concluded that at least two functional stores of noradrenaline exist within the adrenergic nerve ending. Newly synthesized noradrenaline is probably only a minor constituent of transmitter output under normal conditions of adrenergic nerve activity.5 At least two mechanisms control the amount of noradrenaline released per pulse during nerve stimulation. Facilitation of release with increasing train lengths appears to be due to the mobilization of transmitter from a secondary store. Facilitation of release with increasing stimulus frequency is not dependent on mobilization from any particular store and at present there is no satisfactory explanation for this phenomenon.

Animals↗