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J F Mitchell

Publications and source records attributed to J F Mitchell.

70 records · Page 4Linked to original sources
PubMed1969

The characteristics of acetylcholine release mechanisms in the auditory cortex.

1. The characteristics of the acetylcholine (ACh) release mechanism have been studied in the auditory cortex of rabbits on stimulation of the ipsilateral medial geniculate nucleus.2. On stimulation of the medial geniculate nucleus the mean release of ACh from the auditory receiving cortex was 6.1 times the spontaneous release; the mean release from other parts of the cortex was 2.2 times the spontaneous release.3. The frequency of stimulation most effective in evoking ACh release was found to be 10/sec.4. Both the spontaneous and evoked release of ACh were reduced by 40-65% in the absence of calcium from the solution bathing the auditory cortex, and increased by 15-25% when the calcium concentration in the bathing solution was doubled.5. The presence of low concentrations of magnesium in the fluid bathing the cortex was essential for the optimal release of ACh, but high magnesium concentrations lowered this release.6. The presence of triethylcholine (TEC) in the fluid bathing the auditory cortex reduced both the spontaneous and evoked release of ACh. This reduction was reversed in the presence of choline.7. The effects of calcium, magnesium and TEC on the ACh release mechanism in the cerebral cortex and at the neuromuscular junction are compared.

Acetylcholine↗
PubMed1967

The central release of acetylcholine during consciousness and after brain lesions.

1. Acetylcholine (ACh) has been collected from the visual cortex of anaesthetized rabbits during stimulation of the lateral geniculate body and after cutting central nervous pathways. ACh has also been collected from the visual cortex of conscious, free-moving rabbits.2. After a unilateral ;vertical' lesion separating the geniculate body from more centrally situated nuclei, ACh release evoked from the contralateral cortex by geniculate body stimulation was abolished but evoked release from the ipsilateral cortex was only reduced.3. After a bilateral, ;horizontal' lesion separating the thalamic nuclei from the reticular formation, unilateral geniculate stimulation gave an increased ACh release from the ipsilateral but not from the contralateral visual cortex.4. The ;vertical' and ;horizontal' lesions had no permanent effect on the spontaneous release of ACh from the visual cortex.5. Unilateral destruction of the geniculate body reduced the spontaneous release of ACh from the ipsilateral cortex but did not affect the contralateral release.6. The spontaneous and directly evoked ACh release from chronically undercut areas of cortex was found to be considerably lower than from intact areas of cortex.7. A high output of ACh was obtained from the visual cortex of conscious, free-moving rabbits. The rate of ACh release was closely related to the activity and state of arousal of the animals.8. These results support an earlier suggestion that two major ascending cholinergic systems exist in the rabbit brain. One pathway is the non-specific reticulo-cortical tract responsible for cortical arousal and the other is the more specific thalamo-cortical pathway associated with augmenting and repetitive after-discharge responses. The functional significance of these two cholinergic pathways and their role in the conscious animal are discussed.

Acetylcholine↗
PubMed1966

The central release of acetylcholine during stimulation of the visual pathway.

1. In rabbits anaesthetized with Dial ACh has been collected from the surface of the cerebral cortex during stimulation of the visual pathways.2. The spontaneous release of ACh from the visual and non-visual areas of the cortex was found to be similar.3. Stimulation of the retinae by diffuse light produced a large increase in ACh release from the primary visual receiving areas (4.3 times the spontaneous release) and a smaller increase (1.9 times the spontaneous release) from other parts of the cortex.4. Direct unilateral electrical stimulation of the lateral geniculate body evoked a large increase in ACh release (3.4 times the spontaneous release) from the ipsilateral visual cortex and a smaller increase (1.7 times the spontaneous release) from the contralateral visual area and other regions of the cerebral cortex. The evoked increase from the contralateral cortex was not mediated by transcallosal pathways.5. The increase in ACh release evoked from the visual cortex by stimulation of the ipsilateral lateral geniculate body was dependent on the frequency of stimulation. The evoked release was smallest at low stimulus frequencies and increased to a maximum at 20 stimuli/sec. The evoked ACh release from other areas of the cortex was independent of the frequency at which the lateral geniculate body was stimulated.6. The possible central nervous pathways associated with the spontaneous release of ACh and the release evoked by stimulation of the eyes by light and by direct stimulation of the lateral geniculate body are discussed.7. It is concluded that two ascending cholinergic systems may be involved; the non-specific reticulo-cortical pathways responsible for the e.e.g arousal response, and the more specific thalamo-cortical pathways associated with augmenting and repetitive after-discharge responses. The first system is thought to be concerned with the small but widespread increase in ACh release from the cortex following stimulation of the visual pathway while the second system could give rise to the larger increases evoked from the primary receiving areas of cortex. The spontaneous release of ACh from the surface of the brain may be the result of contributions from both systems.

Acetylcholine↗