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Biomedical subjects

A D Pickering

Publications and source records attributed to A D Pickering.

At least 37 records · Page 2Linked to original sources
PubMed1991

Indirect measures of memory in a duration-judgement task are normal in amnesic patients.

Nine amnesic patients of mixed aetiology were studied in a duration-judgement task that allowed three measures of memory to be obtained. On each trial of the task, subjects attempted to read a briefly flashed word and to estimate the duration of the flash. Both word identification and duration estimation differed as a function of prior study. Words that were previously studied were identified more often and were estimated to have been flashed for a longer duration than were words not previously studied. These priming effects were found in young subjects in Experiment 1 and in amnesic patients and age-matched control subjects in Experiment 2. Priming effects were normal in the amnesic patients, whereas these patients were severely impaired at recognizing the same words. Previous results have also shown that amnesic patients can perform normally on certain memory tests, including priming of word identification. These results show that priming of duration judgements can also be included in the category of indirect measures of memory that are spared in amnesia.

Adult↗
PubMed1990

The effect of cortisol administration on hepatic and plasma estradiol-binding capacity in immature female rainbow trout (Oncorhynchus mykiss).

Implantation of a cortisol-containing pellet into the peritoneal cavity of immature female rainbow trout raised plasma cortisol levels within the range commonly observed in chronically stressed fish. In cortisol-implanted fish there was a significant decline in the concentration of hepatic estradiol-binding sites relative to sham-implanted controls. This consisted of a 35% drop in cytosolic binding sites and a 29% reduction in the number of nuclear estradiol-binding sites, by 4 weeks postimplantation. Plasma estradiol-binding capacity was also influenced by cortisol treatment. After 2 weeks there was a 33% increase in plasma estradiol-binding capacity of cortisol-implanted fish. Plasma estradiol levels were unaffected by cortisol implantation, suggesting that the effects of cortisol on estradiol-binding sites were not mediated by altering the rate of estradiol secretion. The results indicate a possible mechanism by which environmental stress may suppress vitellogenesis.

Animals↗
PubMed1989

The deleterious effects of cortisol implantation on reproductive function in two species of trout, Salmo trutta L. and Salmo gairdneri Richardson.

Implantation of a cortisol-releasing pellet (60 mg kg-1 fish) into the peritoneal cavity of brown trout, Salmo trutta L. (sexually maturing males and females), and rainbow trout, Salmo gairdneri Richardson (maturing males and immature fish of both sexes), significantly elevated their plasma cortisol level. At 18 days postimplantation, cortisol-implanted sexually maturing male brown trout had smaller gonads, a lower plasma testosterone level, and less gonadotropin in their pituitary gland than control fish. Plasma levels of 11-ketotestosterone and gonadotropin were not significantly affected. Cortisol-implanted sexually maturing female brown trout had smaller gonads, reduced plasma levels of 17 beta-oestradiol, testosterone, and vitellogenin, and a lower pituitary gland gonadotropin content than control fish. The plasma gonadotropin level was unaffected. At 36 days post-implantation, cortisol treatment of maturing male rainbow trout significantly suppressed plasma gonadotropin levels. Plasma levels of testosterone, 11-ketotestosterone, and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, pituitary gonadotropin content, and gonad size were not significantly affected. In sexually immature female rainbow trout, cortisol administration suppressed the level of vitellogenin in the plasma, compared to control-implanted fish. The 17 beta-oestradiol level was not affected. Cortisol implantation did not affect the plasma testosterone level in sexually immature male trout. These results suggest that prolonged elevation of plasma cortisol, to levels well within physiological range, can affect a wide range of reproductive parameters in both brown and rainbow trout. Further, some effects are manifest in immature as well as in mature fish. These findings are discussed in relation to the effects of cortisol treatment on the state of health of the treated fish.

Animals↗
PubMed1989

Amnesia and memory for modality information.

In this study, lists of words were used in a mixed-modality fashion (some read aloud by the subject, others read only by the experimenter). They were presented in this format to both Korsakoff amnesics and matched controls, with subjects only told to remember the words themselves. Controls and amnesics were matched on item-memory (forced-choice recognition) by using longer lists, tested at longer delays, for the controls. Despite this, however, the controls performed significantly better than the amnesics at modality-identification judgements about the items chosen during recognition. Whether the reported result reflects the memory deficit which causes amnesia, or whether it is more properly attributed to additional (frontal lobe) pathology present in only certain amnesics, is discussed.

Adult↗
PubMed1987

Sacciform cells in the epidermis of the brown trout, Salmo trutta, and the Arctic char, Salvelinus alpinus.

Sacciform cells containing an acidophilic, proteinaceous secretion, were identified in the epidermis of the brown trout and Arctic char. This cell type increased in number during the chronic stages of infestation by the ectoparasitic flagellate, Ichthyobodo sp., in immature brown trout, and decreased during sexual maturation in male brown trout and char. It is suggested that the salmonid sacciform cell produces a secretion which protects the fish against infestation or damage by skin parasites.

Animals↗
PubMed1987

The effects of acute and chronic stress on the levels of reproductive hormones in the plasma of mature male brown trout, Salmo trutta L.

Chronic confinement for 1 month caused a significant elevation of plasma cortisol but suppressed the levels of plasma testosterone and 11-ketotestosterone in sexually mature male brown trout. An acute handling stress for 1 hr elevated blood cortisol and ACTH levels and also suppressed circulating androgens. This androgen suppression in response to acute stress was accompanied by an elevation of plasma gonadotropin levels. These findings are discussed in relation to stress-induced suppression of reproductive function in mammals and the possible biological consequences of such a suppression in fish are outlined.

Adrenocorticotropic Hormone↗
PubMed1987

On the use of dexamethasone to block the pituitary-interrenal axis in the brown trout, Salmo trutta L.

Oral administration of dexamethasone in a single meal at a dose of 3 micrograms g-1 body wt was sufficient to block the secretion of ACTH and cortisol in brown trout subjected to a handling stress followed by 30 min confinement. This dose, however, also had a marked effect on several of the circulating blood cell types. Lymphocyte and neutrophil counts were reduced in dexamethasone-treated fish whereas erythrocyte counts increased. The value of dexamethasone as a tool for investigating the role of interrenal tissue during stress responses in teleost fish is limited by its cortisol-like effects on other steroid-sensitive tissues.

Adrenal Glands↗
PubMed1986

Independence of the pituitary-interrenal axis and melanotroph activity in the brown trout, Salmo trutta L., under conditions of environmental stress.

Adaptation of brown trout to a black or white background had no statistically significant influence on the activity of the pituitary-interrenal axis in unstressed fish, in fish under conditions of mild chronic stress, or in fish under conditions of severe, acute stress. This finding is in contrast to several other studies on salmonid fish in which background color adaptation has been shown to modulate the pituitary-interrenal response to environmental stress. It is argued that these differences in results may be related to the prior history of interrenal activation in the experimental fish and that in previously unstressed brown trout the activity of the pituitary-interrenal axis is independent of melanotroph activity in the pars intermedia when fish are exposed to subsequent stress.

Adaptation, Physiological↗
PubMed1985

Stress-induced elevation of plasma alpha-MSH and endorphin in brown trout, Salmo trutta L.

Handling and confinement caused a pronounced elevation in the plasma cortisol levels of brown trout. This response was more rapid, and the elevation greater, at 13.4 than at 5 degrees although basal cortisol levels were also higher at the warmer water temperature. The large increase in plasma cortisol caused by handling and confinement was not accompanied by any changes in the plasma levels of either alpha-MSH or endorphin. However, when handling and confinement was combined with a thermal shock, not only was there a rapid and pronounced elevation in plasma cortisol, but there were also concomitant and sustained rises in the plasma levels of both alpha-MSH and endorphin. The levels of a alpha-MSH and endorphin induced by the thermal shock were considerably higher than those recorded in long-term, black-adapted brown trout, the only other circumstance in fish known to cause an elevation of the plasma levels of these two peptides. These results indicate that handling and confinement only activated the corticotrophs of the pars distalis, not the melanotrophs of the neurointermediate lobe, whereas when combined with a thermal shock, both cell types were activated.

Acclimatization↗
PubMed1985

The effects of 11-ketotestosterone and testosterone on the skin structure of brown trout, Salmo trutta L.

11-Ketotestosterone and testosterone were administered by intraperitoneal implants to immature brown trout. Physiological levels of circulating androgens were maintained over a period of 4 months and this resulted in changes in skin structure which resembled those occurring in maturing male brown trout. 11-Ketotestosterone promoted both epidermal and dermal thickening, and markedly reduced the number of superficial goblet cells, whereas testosterone stimulated only epidermal thickening. The relative roles of these two androgens in the normal maturational processes of brown trout are discussed.

Androgens↗
PubMed1984

Cortisol-induced lymphocytopenia in brown trout, Salmo trutta L.

The administration of cortisol in the food of brown trout produced peak plasma cortisol titres of about 140 ng ml-1 at 12 hr and markedly reduced the number of circulating lymphocytes, which reached their lowest count at 36 hr. Cortisol did not affect the erythrocyte, thrombocyte, or neutrophil count. Sexual maturation of the male fish was associated with an increase in erythrocytes and a decrease in lymphocytes in the blood. These findings are discussed in relation to the increased susceptibility of the brown trout to a variety of infections during sexual maturation and under conditions of stress.

Animals↗
PubMed1983

Seasonal and diel changes in plasma cortisol levels of the brown trout, Salmo trutta L.

A marked diel variation in plasma cortisol concentration was demonstrated in the brown trout, Salmo trutta L. For most of the year this variation took the form of an elevation of cortisol levels during the hours of darkness. There was some evidence of a phase shift from a peak at 2400 hr during the spring and early summer to a peak at 0400 hr during the late summer and early autumn. During the winter months a nocturnal elevation of plasma cortisol was not evident. A shorter, episodic elevation of plasma cortisol was associated with feeding in the brown trout. These findings are discussed in relation to the effects of stress and intensive cultivation on teleost fish.

Animals↗
PubMed1980

Acidophilic granular cells in the epidermis of the brown trout, Salmo trutta L.

Acidophilic cells occur in the epidermis of several species of salmonid fish, although their abundance fluctuates considerable between individuals within the same population and at different times during the life cycle. The histology, histochemistry and ultrastructure of an acidophilic, granular cell-type in the epidermis of the brown trout, Salmo truuta L., is described. At the light microscope level this cell type is easily distinguished from the large, mucus-secreting, epidermal goblet cells by its acidophilic, proteinaceous secretion. At the ultrastructural level this secretion consists of membrane-bound granules formed by the very active Golgi region. It is argued that the acidophilic, granular cell is not a transformed blood cell but constitutes a normal epidermal component of the brown trout. Possible roles of this cell in the function(s) of the epidermis are discussed.

Animals↗
PubMed1977

Sexual dimorphism in the gills of the spawning river lamprey, Lampetra fluviatilis L.

Two types of mitochondria-rich cells were found in the interplatelet areas of the gills of sexually mature, male river lampreys. Type 1 cells (previolsy referred to as "male glandular cells") showed some ultrastructural characteristics in common with ion-transporting cells but were readily distinguished by large lipid structures with electron-lucent centres. Type 2 cells were found to be identical to the presumed ion-uptake cells during other stenohaline freshwater phases of the animal's life history. In the sexually mature female, only Type 2 cells were positively identified. This sexual dimorphism in gill structure is discussed in relation to the possible functions of the lamprey gill, with particular reference to ionic regulation.

Animals↗
PubMed1976

Changes in the ultrastructure of the gills of the river lamprey, Lampetra fluviatilis (L.), during the anadromous spawning migration.

Two types of mitochondria-rich cells were found in the interplatelet areas of the gills of the migrating river lamprey. Both cell types are thought to be responsible for ion-transport across the gills. In the fresh-run migrant the gills are dominated by large, flask-shaped cells which show some ultrastructural similarities with the teleost chloride cell and have been tentatively referred to as ion-excretory cells. During the spawning migration the ion-excretory cells are replaced by smaller, mitochondria-rich cells which are similar in structure to the presumed ion-transporting cells in the ammocoete gill. They lack the tubular, smooth-membraned endoplasmic reticulum so characteristic of the lamprey ion-excretory cell and the teleost chloride cell and have been referred to as ion-uptake cells. The ion-uptake cells are found during the stenohaline, freshwater phases of the lamprey's life history. Ion-excretory cells are present during the periods of the life cycle when the animal is euryhaline. The possibility that the ion-excretory cells are also responsible for ion-uptake in fresh water is discussed.

Animals↗
PubMed1976

Fine structure of the interplatelet area in the gills of the macrophthalmia stage of the river lamprey, Lampetra fluviatilis (L.).

The interplatelet epithelium of the gills of freshwater and seawater adapted macrophthalmia stages of the river lamprey, Lampetra fluviatilis, was studied by electron microscopy. Three main cell types: basal, ion-excretory and superficial cells were identified and described. Ion-excretory cells were exposed to the environment in sea water but covered by a layer of superficial cells in fresh water. Electron-dense secretory granules in the apex of the cell were more abundant in fresh water. In fresh water, a few of the superficial cells contained numerous mitochondria and were identified as ion-uptake cells. In view of the scarcity of ion-uptake cells, the possibility that the ion-excretory cells are also responsible for ion-uptake in fresh water is discussed. Phagocytic removal of degenerating ion-excretory cells may be an important mechanism for the conservation of materials in a starving animal.

Animals↗