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Biomedical subjects

M J Wells

Publications and source records attributed to M J Wells.

At least 37 records · Page 2Linked to original sources
PubMed1980

The effects of extracts from neurosecretory cells in the anterior vena cava and pharyngo-ophthalmic vein upon the hearts of intact free-moving octopuses.

Recordings of pressure and frequency were made from the hearts of free-moving Octopus vulgaris. The effects of extracts from neurosecretory endings in the anterior vena cava (AVC) and the pharyngo-ophthalmic vein (POV), injected through fine cannulae into a branchial heart, efferent branchial vessel or the dorsal aorta, were studied and compared with the effects of acetylcholine, 5-hydroxytryptamine, adrenaline, histamine and tyramine. AVC and POV extracts each produce a different spectrum of effects, unlike those of any of the drugs tested. AVC extract is effective at doses of less than 2% of the material extractable from a single vein per kg, increasing the force and amplitude of the heartbeats. With a natural release point just upstream of the branchial hearts the AVC material must be relevant to the normal performance of the hearts. POV extract is effective only at doses equivalent to several veins per kg, and is unlikely to have a role in cardiac regulation. Section of the visceral nerves did not affect the action of drugs or extracts, indicating that effects were not indirectly mediated via the CNA. Further experiments were made with hearts and the aorta in vitro with effects that did not always parallel those found in vivo. Reasons for these differences are discussed.

Acetylcholine↗
PubMed1980

Nervous control of the heartbeat in octopus.

The circulatory system of cephalopods is based on a trio of hearts, with two pairs of associated ganglia linked to the CNS by a pair of visceral nerves. The beat of the hearts was recorded from free-moving octopuses before and after surgical removal or disconnexion of elements of the nervous system. Severing the visceral nerves does not stop the hearts, which continue to beat in a powerful well co-ordinated manner in isolation from the CNS. The nerves seem to be concerned in raising the cardiac output in exercise, and with stopping the hearts when mantle movements cease, but they are not necessary for the initiation of maintenance of the normal rhythm. Removal of the fusiform ganglia severs all nervous connexions between the ywo gill hearts, and deprives the systemic heart of its nerve supply. The trio of hearts continues to beat as strongly as before. Removal or disconnexion of a cardiac ganglion disrupts the beat of the corresponding gill heart which now tends to contract in an ill-coordinated and rather feeble manner, though at much the same frequency as before; with both cardiacs gone the systemic heart, which contracts only when it is filled, tends to drop in frequency and the mean aortic pressure falls. The system remains rhythmic, however, and the beat may recover, to the point where aortic pressures and frequencies approach those found in intact animals at rest; even octopuses with both fusiform and both cardiac ganglia removed can survive for many hours. From the performance of the isolated branchial heart, the existence of a pulsating vesicle in each cardiac ganglion, the effects of cardiac ganglion removal and the remarkable steadiness of heartbeat frequency shown by intact animals under a variety of conditions, it is argued that the heartbeat rhythm is normally controlled by pacemakers in the branchial heart/ cardiac ganglion complexes, and perhaps, in intact animals, from within the cardiac ganglia themselves. The picture of the control of the heartbeat that emerges from the study of free moving essentially intact animals is quite different from that arising from in vitro and acute preparation studies. It suggests that the conventional wisdom about the control of the heartbeat in cephalopods (and perhaps by implication, in other molluscs) may need to be considerably revised.

Animals↗
PubMed1980

Distortion and adaptation in underwater sound localization.

Sounds should be localized at more medial positions under water than in air, because the values of the interaural temporal and intensity differences are reduced in water. Thirteen blindfolded divers were required to move a pointer towards the apparent location of a sound source under water, and they showed significant errors towards the median plane. In a second experiment, five divers were tested in air before and after underwater training at swimming towards a sound source. The search patterns of these divers showed systematic errors towards the median plane. A comparison of the first and second air tests showed some evidence of an aftereffect away from the median plane, discounting the most lateral angles (80 degrees left and right) where little effect would be expected. It is concluded that both a distortion of localization and some adaptation to the distortion occur under water.

Auditory Perception↗
PubMed1978

Reproduction versus somatic growth: hormonal control in Octopus vulgaris.

1. Octopus vulgaris can be forced into precocious maturity by removal of the subpedunculate lobe from the brain, an operation that releases the optic glands from inhibition, and allows them to secrete a gonadotropin. 2. 14C-leucine was injected into the bloodstream of immature animals and its subsequent incorporation into muscle protein followed by taking successive samples from the arms. The optic glands were then activated, and a further injection of 3H-leucine given and followed by means of further arm samples. 3. Optic gland secretion suppresses protein synthesis in the muscles. This is associated with an increase in the total amino acid pool in the muscles and with a considerable increase in the concentration of free amino acids circulating in the blood. 4. If an ovary is present these events are associated with a rapid growth of the ovary and its ducts, and a loss of weight elsewhere. In ovariectomized animals the ducts grow, but there is no yolk to absorb the large pool of free amino acids, and the animals gain weight by osmotic uptake of water into the muscles. 5. The developing ovary may produce a hormone that increases the release of amino acids from muscle, since the concentration circulating in the blood of intact animals remains at least as high as in ovariectomized octopuses, despite the demands of the developing ovary. 6. These matters are discussed in relation to other evidence for a gonadial hormone and in relation to the 'self-destruct' effect of the optic gland secretion in determining the post-reproductive death of octopuses.

Age Factors↗
PubMed1975

The subfrontal lobe and touch learning in the octopus.

Octopuses with the supraoesophageal lobes of the brain divided longitudinally can be taught to discriminate using the arms on either side. If there is no further lesion the two sides behave alike. Lesions limited to one side did not affect the performance of the contralateral, "control" side. Lesions made in the vertical (n=7) lobes led to a slight drop in the quality of performance in training to take a smooth sphere, in discrimination training (rough vs. smooth spheres) and in subsequent extinction and transfer tests. After removal of the median inferior frontal lobe (n = 10) there were somewhat greater effects in the same direction. Much larger effects followed interference with the subfrontal lobe (n = 20). Removal of parts from this always led to a marked loss of capacity for touch learning, broadly dependent on the amount of tissue removed. Removal of the whole of the subfrontal lobe (n = 6) produced animals that showed, at best, only very slight signs of learning. Such animals can adjust their overall level of response as a result of training but they seem incapable of adjusting response levels to two objects independently. These results are discussed in relation to the function of the subfrontal lobe as a memory store.

Animals↗
PubMed1975

An in vitro bioassay for a mulluscan gonadotropin.

1. Protein synthesis occurs at a high rate in the ovaries of maturing Octopus vulgaris and can be measured from the incorporation of [14C]leucine in vivo and in isolated groups of eggs in vitro. 2. Removal of the optic glands in vivo 1--3 days prior to testing markedly reduces amino acid incorporation in vivo or in vitro. After 5 days in vivo incorporation stops. 3. The rate of incorporation in vitro is increased by the addition of optic gland extract. 4. Analysis of the kinetics of leucine uptake and incorporation in vitro indicates that the hormone has an effect on the inward transport of leucine which is independent of its action on protein synthesis. 5. Electron-microscope studies of the follicle cells and ova show that the former are the site of protein synthesis. 6. Changes in either uptake or incorporation into protein by the follicle cells can be used as a qualitative biolobical assay for the optic gland hormone. Uptake is very easy to measure but incorporation is the more sensitive parameter. Either is potentially suitable as a quantitative assay for this and perhaps also for other molluscan gonadotropins.

Animals↗
PubMed1975

Optic gland implants and their effects on the gonads of Octopus.

1. Optic glands transplanted from one Octopus vulgaris into another cause enlargement of the gonads and ducts of the recipient. 2. Enlargement occurs whether or not the gland was secreting when implanted and regardless of the sex of the donor or recipient. 3. Glands derived from Eledone moschata or Octopus macropus implanted into O. vulgaris are as effective as glands derived from O. vulgaris. 4. Implants derived from Sepia officinalis or Loligo vulgaris appear to be ineffective.

Animals↗