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Biomedical subjects

G A Cottrell

Publications and source records attributed to G A Cottrell.

At least 91 records · Page 5Linked to original sources
PubMed1981

An unusual synaptic response mediated by a serotonin neurone.

Impulse activity in an identified serotonin-containing neurone produces a delayed slow excitatory response in another identified neurone. An axon of the serotonin neurone passes very close to the follower neurone perikaryon. The synaptic response is frequently accompanied by oscillations of the membrane potential. Constant-current pulsing experiments suggest that it could result from a reduction in membrane conductance. The response is markedly voltage-sensitive, being greatly reduced at potentials in excess of about -55 mV. Serotonin, locally applied, produces a very similar effect. The response to serotonin does not involve a change in conductance to either Na+ or Cl-, but Ca2+ appears to be involved, either by virtue of its influence on K+ conductance, or directly in its transfer of charge across the membrane.

Animals↗
PubMed1980

Morphology and ultrastructure of an identified histamine-containing neuron in the central nervous system of the pond snail, Lymnaea stagnalis L.

An identifiable histamine-containing neuron is located on the anterior dorsal surface of the visceral ganglion of Lymnaea stagnalis L. After [3H]histamine was injected into the perikaryon of this neuron, labelled axonal ramifications were seen in the neuropils of all ganglia except the pedals and right cerebral, and labelled axons occurred in seven nerve trunks. Electron microscopical examination of the perikaryon of the histamine neuron revealed the presence of large aggregations of granulated vesicles (80-200 microns diameter), elaborate endoplasmic reticulum, and numerous mitochondria, Golgi complexes and lysosome-like organelles.

Animals↗
PubMed1979

Ionic basis of different synaptic potentials mediated by an identified dopamine-containing neuron in Planorbis.

A specified dopamine neuron in Planorbis corneus produces dopamine-mediated e.p.s.ps, i.p.s.ps or biphasic, depolarizing-hyperpolarizing p.s.ps in different follower neurons. The excitatory potentials were of three types. Some follower neurons exhibited slow e.p.s.ps (ca 1 s), and a long-lasting, slowly desensitizing, depolarizing response to iontophoresed dopamine. Others showed rapid (ca. 150 ms) e.p.s.ps, often of variable amplitude, and a rapid, quickly desensitizing, response to iontophoresed dopamine. The rapid e.p.s.ps were sometimes followed by the inhibitory response (biphasic potential). The e.p.s.ps were potentiated by hyperpolarization and reduced by depolarization, though they could not be inverted. The slow e.p.s.p. was shown to be associated with an increase in membrane conductance, but it has proved difficult to elucidate the ions involved. A third type of e.p.s.p. was produced by electrical transmission. The inhibitory potentials were generally reduced in amplitude by artificial hyperpolarization but could rarely be inverted. This is probably due in part to the presence of of electrotonic coupling between these follower neurons. The i.p.s.ps were associated with an increase in conductance which appeared small when measured in the cell body. However, the i.p.s.ps produced considerable shunting of electrotonic transmission between coupled followers indicating a large increase in conductance at the synapse. I.p.s.ps were unaffected by Cl-free solution but they were greatly reduced, though rarely inverted, by increasing the external K concentration. They were blocked by intracellular tetraethylammonium, or cooling. The effects on corresponding responses to iontophoresed dopamine were in each case the same as on the i.p.s.ps. It is concluded that the i.p.s.ps mediated by the dopamine neuron are produced by an increase in permeability to K+. On a few occasions i.p.s.ps mediated by the dopamine neuron were potentiated by hyperpolarization. This appeared to be caused by a sharp increase in membrane resistance with hyperpolarization of these particular neurons. However, mediation by a mechanism of conductance decrease could not be completely excluded.

Animals↗
PubMed1978

Cellular accumulation of amines and amino acids in the central ganglia of a gastropod mollusc, Planorbis corneus: an autoradiographic study.

The distribution of radioactivity was examined autoradiographically in ganglia exposed to 10 different tritium-labelled compounds, some putative transmitters and the others transmitter precursors. The autoradiographic pattern was found to vary greatly for different substances, suggesting the presence of several different accumulating systems in the ganglia. Identified amine-containing neurons take up their own transmitter substance specifically. However, whereas uptake by dopamine-containing, and presumed histamine-containing neurons occurs over both perikarya and processes, in 5-HT-containing neurons it appears restricted to axon processes. The transmitter precursors L-DOPA and 5-hydroxytryptophan were taken up by the perikarya of both dopamine- and 5-HT-containing neurons, possibly by the same uptake system. In high concentrations, tyramine was selectively accumulated by cells containing dopamine and by non-dopamine (possibly octopamine- or tyramine-containing) neurons, but in low concentrations it labelled only the latter. GABA labelled a separate population of neurons and was particularly concentrated in their processes. Some, if not all, of the neurons specifically labelled after exposure to glutamic acid are neurosecretory cells. Tyrosine and glycine appeared to be accumulated in a non-specific manner and many of the substances were also accumulated by glial cells or by parts of the connective tissue capsule.

5-Hydroxytryptophan↗
PubMed1977

Effect of corticosteroids in the hippocampus on passive avoidance behavior in the rat.

The site of action of corticosteroids in avoidance learning was investigated in 110 rats. Injection of cycloheximide, 30 min before one-trial training on a passive avoidance task suppressed corticosteroid secretion in response to footshock, and produced an avoidance deficit in a test 6 days later. However, an additional injection of hydrocortisone, either subcutaneously or intra-hippocampally within 5 min of training, restored the avoidance response in the test. Septal and hypothalamic injections of the hormone were ineffective in reversing the cycloheximide effect, whereas the effect of hormone injection into the amygdala was equivocal because of an increased level of activity. Corticosteroids secreted following an aversive experience appear to act upon the steroid-sensitive neurons in the hippocampus to influence the animal's later performance of passive avoidance response.

Adrenal Cortex Hormones↗
PubMed1975

Excitatory, inhibitory and biphasic synaptic potentials mediated by an identified dopamine-containing neurone.

1. A giant dopamine-containing cell, situated in the left pedal ganglion of the water snail Planorbis corneus, was identified in isolated living preparations of the central nervous system. Spectrophotofluorimetric analysis confirms that the cell contains dopamine, whereas noradrenaline appears to be absent. The cell is unique in being a repeatedly identifiable dopamine-containing neurone. 2. Stimulation of the giant dopamine-containing cell resulted in excitatory, inhibitory or biphasic (depolarizing-hyperpolarizing) synaptic potentials in a number of follower neurones. The duration of the e.p.s.p.s and i.p.s.p.s was 0-3-5 sec; they ranged from barely detectable responses to ones 7 mV in amplitude in different cells. The depolarizing phase of a biphasic synaptic potential (b.p.s.p.) was usually less than 1 mV in amplitude (max. 3mV) and lasted 40-400 msec. The latency of i.p.s.p.s was long (70-120 msec) compared with that of e.p.s.p.s and b.p.s.p.s (20 msec). Abolition of the depolarizing phase of b.p.s.ps. by tubocurarine left a long-latency (70-120 msec) i.p.s.p. All responses showed summation and marked facilitation. 3. Evidence is presented that the post-synaptic potentials are produced by direct connections from the giant cell and result from a release of dopamine. Of eight putative transmitter substances tested on these different groups of neurones, only dopamine produced a potential change which in each case was of the same polarity as the post-synaptic potential when this was monophasic. However, generally applied dopamine produced only a hyperpolarization in follower cells showing b.p.s.p.s. This result is probably partly due to rapid desensitization of the receptors mediating the depolarization and also to a masking of the depolarization by the more effective hyperpolarizing response. 4. Erogometrine and 6-hydroxydopamine specifically antagonized the i.p.s.p.s and dopamine receptors mediating inhibition. Neither the e.p.s.p.s nor the excitatory dopamine response were blocked by high concentrations of hexamethonium. Hexamethonium was also ineffective in blocking the depolarizing phase of a b.p.s.p., which was, however, selectively eliminated by tubocurarine. 5. It is suggested that dopamine is the transmitter released from the giant cell and that it can mediate excitatory, inhibitory or biphasic responses in different follower neurones.

Acetylcholine↗