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Biomedical subjects

M H Roberts

Publications and source records attributed to M H Roberts.

At least 109 records · Page 6Linked to original sources
PubMed1974

The modification of lumbar motoneurone excitability by stimulation of a putative 5-hydroxytryptamine pathway.

1 Changes in lumbar motoneurone excitability were monitored by recording spinal reflex activity from the ventral roots of rats anaesthetized with fluothane.2 Electrical stimulation of nucleus raphes medianus increased the amplitude of the monosynaptic reflex via a pathway having a slow conduction velocity. Stimulation elsewhere in the lower brain stem was less effective. This increase in motoneurone excitability was potentiated by the intravenous injection of L-tryptophan and reduced by intravenous injections of lysergic acid diethylamide (LSD), methysergide or Cinanserin.3 Extracellular field potential responses to stimulation of dorsal or ventral roots were recorded with six barrelled microiontophoresis electrodes. Stimulation of nucleus raphes medianus and iontophoretic application of 5-hydroxytryptamine (5-HT) both increased the excitability of lumbar motoneurones as reflected by an increase in field potential amplitude.4 Responses to both stimulation of raphe nuclei and iontophoretic application of 5-HT were reduced by iontophoretic application of Cinanserin and methysergide.5 The similarities of the responses of lumbar motoneurones to applied 5-HT and activity within the raphe-spinal pathway are discussed. It is suggested that activity within the raphe-spinal pathway can increase lumbar motoneurone excitability via the release of 5-HT in the ventral horn of the spinal cord.

Animals↗
PubMed1974

Effects of imipramine and desipramine on responses of single cortical neurones to noradrenaline and 5-hydroxytryptamine.

1 The technique of microelectrophoresis was used in order to study the effects of imipramine and desipramine on single neurones in the somatosensory cortex of the cat, anaesthetized with halothane.2 Imipramine and desipramine, when applied for a brief period, did not affect the firing rate of the vast majority of the neurones tested.3 Both potentiation and antagonism of excitatory responses to noradrenaline could be observed after a brief application of either of the antidepressants. Four drug-interaction patterns could be distinguished: potentiation of immediate onset; potentiation reaching its maximum after a delay; antagonism followed by potentiation; antagonism followed by recovery.4 When different doses of the same antidepressant were applied, it was found that the drug-interaction patterns were related to the dose of antidepressant applied, a lower dose causing potentiation, and a higher dose antagonism of the response.5 Both potentiation and antagonism of depressant responses to noradrenaline could be observed.6 Both excitatory and depressant responses to 5-hydroxytryptamine were modified by imipramine and desipramine: a smaller dose of the antidepressant potentiated, and a higher dose antagonized the responses.7 Excitatory responses to glutamate were not affected by imipramine and desipramine.

Action Potentials↗
PubMed1973

Kinetics of the release of noradrenaline from micropipettes: interaction between ejecting and retaining currents.

1. The role of ejecting and retaining currents in determining the kinetics of the release of [(14)C]-noradrenaline (NA) from micropipettes of the type used in microelectrophoresis experiments has been investigated by the liquid scintillation counting technique.2. In the absence of any electrophoretic current a constant rate of release of NA was established.3. All retaining currents examined gradually reduced the spontaneous release to zero. Higher retaining currents abolished spontaneous release more quickly.4. A linear relationship was identified between the rate of electrophoretic release of NA and the intensity of the ejecting current. The mean transport number of NA was found to be 0.17.5. All retaining currents studied reduced the amount of NA released during a subsequent application of an ejecting current. This was due to a prolongation of the time necessary to establish a steady-state rate of release. The magnitude of this effect was related to both the intensity and the duration of application of the retaining current.6. The results are discussed in terms of a theoretical model of ion movements within the tip of the micropipette.

Carbon Radioisotopes↗