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Biomedical subjects

L M Jordan

Publications and source records attributed to L M Jordan.

At least 73 records · Page 4Linked to original sources
PubMed1978

Differential projections of cat medullary raphe neurons demonstrated by retrograde labelling following spinal cord lesions.

Neurons of the medullary raphe nuclei in cats were retrogradely labelled following injection of horseradish peroxidase (HRP) into the L6 spinal cord segment. Brainstems were cut in sagittal section to facilitate examination of the rostral-caudal extent of raphe neurons projecting to the spinal cord. Large numbers of HRP-labelled neurons were found in nucleus raphe magnus, nucleus raphe pallidus, and nucleus raphe obscurus (as well as a few neurons in nucleus raphe pontis). Dorsal or ventral hemisections at the T12-L1 level restricted HRP retrograde transport to those pathways within the intact portion of spinal cord, allowing a determination of the part of the cord through which raphe neurons project to the lumbar enlargement. Neurons of nucleus raphe magnus were found to project primarily in dorsolateral fasciculus. A significant number of neurons of nucleus reticularis gigantocellularis also project in dorsolateral fasciculus. Nucleus raphe obscurus neurons were found to project primarily in ventral funiculus, while nucleus raphe pallidus neurons project in the ventrolateral fasciculi and ventral funiculus. The serotonergic (5HT) fibers described by Dahlström and Fuxe ('65) to terminate in the dorsal horn, intermediolateral cell column, and ventral horn are likely to coincide with the raphe-spinal projections documented in this work.

Animals↗
PubMed1978

Depression of primate spinothalamic tract neurons by iontophoretic application of 5-hydroxytryptamine.

The effects of iontophoretic applications of 5-hydroxytryptamine (5-HT) were tested upon primate spinothalamic tract neurons recorded extracellularly in the spinal cord of anesthetized monkeys. The activity of most high threshold and wide dynamic range spinothalamic tract cells was depressed. 5-HT also reduced the responses of the cells to glutamate pulses which by themselves had a powerful excitatory action. It is concluded that 5-HT has a depressant action upon the postsynaptic membranes of spinothalamic tract cells, although the action has a slow time course. The observations are consistent with, but by no means prove, the hypothesis that serotonergic pathways descending from the brain stem produce a postsynaptic inhibiton of spinothalamic tract neurons.

Animals↗
PubMed1976

Analysis of the effects of p-methoxy-phenylethylamine on spinal cord neurones.

1 Para-methoxyphenylethylamine (PMPEA) was applied microiontophoretically onto interneurones and motoneurones in the spinal cords of acute spinal cats anaesthetized with alpha-chloralose. Its effects were compared with those of noradrenaline (NA) and 5-hydroxytryptamine (5-HT). 2 PMPEA had effects on interneurones which were similar to those of NA and/or 5-HT; its action was predominantly depressant, and it rarely affected interneurones which could not be influenced by NA or 5-HT. 3 The actions of PMPEA on interneurones excited by electrical stimulation of leg nerves showed that the population of interneurones influenced by the drug coincides with the population affected by NA and 5-HT and by intravenously administered PMPEA. 4 Renshaw cells, which are depolarized by intravenous PMPEA, were hyperpolarized by micoiontophoretically applied PMPEA. 5 Alpha motoneurones, which are depolarized by intravenous PMPEA, were hyperpolarized by micoiontophoretically applied PMPEA. Antidromic firing of the cells could be blocked by PMPEA. 6 The differences between the effects of intravenous infusion and the iontophoretic application of PMPEA upon motoneurones is most easily explained by inhibition of interneurones and a concomitant disinhibition of motoneurones. A similar mechanism may also account for the different effects seen with intravenous and iontophoretic application of PMPEA on Renshaw cells.

Animals↗
PubMed1974

Failure to confirm cyclic AMP as second messenger for norepinephrine in rat cerebellum.

Microiontophoretic applications of adenosine 3',5'-monophosphate (cyclic AMP) to spontaneously active, electrophysiologically identified Purkinje cells of the rat cerebellum failed to mimic the strong depressant action of norepinephrine on the same cells. These findings, in combination with a reevaluation of other studies, cast doubt on the hypothesis that cyclic AMP mediates the depressant actions of norepinephrine in the cerebellum.

Action Potentials↗
PubMed1972

Acetylcholine inhibition in the intact and chronically isolated cerebral cortex.

1. Some spontaneously firing cells in the cerebral cortex of cats can be depressed by iontophoretically applied acetylcholine or acetyl-beta-methylcholine, and this depression is antagonized by atropine. Thirteen per cent of 101 spontaneously active neurones tested were depressed by cholinergic agents and 64% were excited.2. Single stimuli applied to the adjacent cortical surface excited 132 neurones orthodromically. Acetylcholine or acetyl-beta-methylcholine depressed this synaptic firing in 18% of the cells. The depression was blocked by atropine.3. The population of neurones in which cholinergic agents depressed spontaneous or synaptic firing was located within the superficial half of the cortex.4. Glutamate-induced firing was depressed by cholinergic agents in 41% of 211 cells tested; atropine and strychnine strongly antagonized this depressant action, while dihydro-beta-erythroidine was a weaker antagonist.5. Long duration inhibition of glutamate-induced firing evoked by repetitive stimulation of the cortical surface could be blocked by atropine or strychnine in both the intact and chronically isolated cortex. This provides strong evidence for a system of intracortical cholinergic neurones which make direct inhibitory contacts with neurones in the superficial layers of the cortex.

Acetylcholine↗