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Biomedical subjects

M Fillenz

Publications and source records attributed to M Fillenz.

At least 37 records · Page 2Linked to original sources
PubMed1986

The effect of presynaptic receptor stimulation on adenosine 3',5'-cyclic monophosphate concentrations in rat cortical synaptosomes.

Changes in adenosine 3',5'-cyclic monophosphate (cAMP) concentration were measured in cortical synaptosomes. Preincubation with adenosine deaminase reduced cAMP concentration by 45%. Oxotremorine, clonidine, gamma-aminobutyric acid (GABA) and baclofen produced no change in basal concentration. 2-Chloroadenosine and noradrenaline (NA), acting at beta-adrenoceptors, both caused a dose-dependent increase in cAMP; the NA-stimulated increase was depressed by GABA and by baclofen.

2-Chloroadenosine↗
PubMed1986

Microcomputer-controlled voltammetry in the analysis of transmitter release in rat brain.

Microcomputer-based linear sweep voltammetry with carbon-paste electrodes has the following features: Subtraction of the background current produces a voltammogram with three well-resolved peaks: an ascorbate signal reflecting excitatory amino acid release; a uric acid signal that may be related to purine metabolism; and an HVA signal that is an index of dopamine release under certain conditions. Voltammograms from up to eight electrodes (for example, four electrodes in two rats or two electrodes in four rats) can be recorded simultaneously together with motor activity for each rat over extended periods. Electrodes remain stable over periods of many weeks as measured by the constancy of the mean peak height in a 24-hr period. Microcomputers in voltammetry provide flexibility of all recording parameters and a wide variety of methods of analysis. The combination of stable electrodes and the ability to monitor over extended periods means that interactions between transmitters in different brain regions and their relation to physiological processes can be studied.

Amino Acids↗
PubMed1986

Effects of light reversal on the circadian pattern of motor activity and voltammetric signals recorded in rat forebrain.

To investigate the functional relationships between the circadian changes in rat motor activity and changes in the extracellular concentration of ascorbic acid and homovanillic acid (HVA) monitored in the striatum and nucleus accumbens, reversal of the light/dark cycle was used to disturb the pattern of motor activity. Microcomputer-controlled linear sweep voltammetry with carbon-paste electrodes was used to continuously monitor circadian changes in the ascorbate signal and the HVA signal simultaneously in nucleus accumbens and striatum over a 13 day period in unrestrained rats; total motor activity for each animal was also recorded. Regression analyses were carried out on each day's data to investigate the relationships between motor activity and the two voltammetric signals. During days 1-5, the lighting was on normal 12/12 light/dark cycle and high correlations were observed. Reversal of the light/dark cycle on day 6 caused an immediate change in the pattern of motor activity and electrochemical signals; by days 7-8 after light reversal the relationships between lighting, ascorbate, HVA and motor activity were reestablished under the new lighting conditions. During the intervening period, however, there was a complete breakdown in some of the correlations. The findings are discussed in the light of the hypothesis that changes in brain extracellular ascorbate reflect changes in the release of excitatory amino acids, and in terms of a recent model of the role, in the control of motor activity, for cortical and mesencephalic inputs to forebrain subcortical regions.

Animals↗
PubMed1985

Stimulation of noradrenaline synthesis by the calcium ionophore A23187 and its modulation by presynaptic receptors.

Noradrenaline (NA) synthesis in rat hippocampal synaptosomes is increased by calcium ionophore, A23187, in the presence of calcium. Activation of presynaptic muscarinic, gamma-aminobutyric acidB (GABAB) and alpha 2-adrenergic receptors causes inhibition of the ionophore-stimulated synthesis. The results suggest that different mechanisms mediate the depression by presynaptic receptors of NA release and NA synthesis.

Adenosine Deaminase↗
PubMed1985

Low-frequency septal stimulation increases tyrosine hydroxylase activity in the hippocampus.

Rats were chronically implanted with recording electrodes in the dorsomedial subiculum and stimulating electrodes in the septal area. Low-frequency septal stimulation (regular inter-pulse interval = 130 msec) was used over a period of 10 days to drive the hippocampal theta rhythm at 7.7 Hz (a régime shown previously to proactively facilitate acquisition of barpressing and retard its extinction), and high frequency (77 Hz) stimulation was used to block theta rhythm (a régime shown previously to proactively retard acquisition of barpressing and facilitate its extinction). The activity of soluble tyrosine hydroxylase from hippocampus increased in animals killed 15-33 days after the end of the period of 7.7 Hz septal stimulation but not after high-frequency stimulation. Irregular low-frequency stimulation with a mean inter-pulse of 130 msec produced the same effect on tyrosine hydroxylase activity as regular 7.7 Hz theta-driving. The possible relations between the effects of low-frequency septal stimulation on hippocampal tyrosine hydroxylase and on behavior are discussed.

Animals↗
PubMed1985

Effects of guanyl nucleotides on [3H]flunitrazepam binding to rat hippocampal synaptic membranes: equilibrium binding and dissociation kinetics.

The effects of guanyl nucleotides on the binding of [3H]flunitrazepam to rat hippocampal synaptic membranes were studied. In equilibrium binding studies, gamma-amino-n-butyric acid (GABA) increased and GTP decreased the binding affinity of [3H]flunitrazepam; GTP also caused a decrease in binding capacity. The effect, however, is variable. In studies of the dissociation kinetics of [3H]flunitrazepam using diazepam and the antagonist Ro 15-1788 as the displacers, there was evidence of two dissociation rate constants. GTP increased both the fast- and slow-dissociation rate constants and increased the ratio of the slow-dissociation binding state. The effect of GTP was mimicked by its nonhydrolyzable analogue 5'-guanylylimidodiphosphate but not by ATP and occurred when diazepam, but not when Ro 15-1788, was used as the displacer. GABA antagonized the effect of GTP on the dissociation of [3H]flunitrazepam. The nature of the benzodiazepine receptor, its actions, and the possible role of cyclic AMP as a second messenger are discussed.

Adenosine Triphosphate↗
PubMed1979

Effect of runway training on rat brain tyrosine hydroxylase: differential effect of continuous and partial reinforcement schedules.

Previous experiments have implicated ascending noradrenergic systems in the development of the behavioural responses to different patterns of reward. In this report food deprived male Sprague--Dawley rats were trained to run a straight alley for good reward on a continuous reinforcement (CRF) or a partial reinforcement (PRF) schedule. Tyrosine hydroxylase measured in a partially solubilized preparation from hippocampus and hypothalamus at the end of acquisition was not different from controls, indicating that enzyme induction does not occur during either training schedules. However, hippocampal synaptosomal tyrosine hydroxylation rates from the CRF group was significantly higher than from either the PRF group or the handled controls. This indicates that at the end of the acquisition schedule the noradrenergic projection to hippocampus was more active in the CRF group than with the PRF group or the handled control.

Animals↗
PubMed1979

Noradrenaline release in rats during prolonged cold-stress and repeated swim-stress.

1 Plasma noradrenaline concentration in rats was measured during prolonged cold-stress and repeated swim-stress. 2 Cold exposure for 6 h caused a rise in plasma noradrenaline which reached a peak at 4 h. 3 Administration of desmethylimipramine and normetanephrine to block neuronal and extra-neuronal uptake of noradrenaline raised plasma noradrenaline concentration without changing the pattern of the response to cold exposure. 4 Repeated cold exposure on subsequent days produced no change in the pattern of plasma noradrenaline concentration. 5 Five successive 1-min swims at 30-min intervals caused a rise in plasma noradrenaline concentration which was maximal after the third swim. 6 It is suggested that prolonged and repeated activation of sympathetic nerve terminals leads to a decline in noradrenaline release.

Animals↗
PubMed1978

Changes in plasma noradrenaline concentration as a measure of release rate.

1 A method is described for repeated sampling of plasma noradrenaline (NA) in freely moving rats. Na concentration does not change during the day or after adrenalectomy. 2 Exogenous NA has a half-life of 1.5 min; drugs which block neuronal and extra-neuronal uptake lengthen this to 6.3 min. 3 Swim-stress leads to a steep rise followed by a rapid decline in plasma NA concentration. 4 This method of plasma NA sampling can serve as a measure of both steady and rapid changes in release rate over long periods of time.

Adrenalectomy↗