Climate-driven variability of the Southern Ocean CO2 sink.

The Southern Ocean is a major sink of atmospheric CO2, but the nature and magnitude of its variability remains uncertain and debated. Estimates based on observations suggest substantial variability that is not reproduced by process-based ocean models, with increasingly divergent estimates over the past decade. We examine potential constraints on the nature and magnitude of climate-driven variability of the Southern Ocean CO2 sink from observation-based air-sea O2 fluxes. On interannual time scales, the variability in the air-sea fluxes of CO2 and O2 estimated from observations is consistent across the two species and positively correlated with the variability simulated by ocean models. Our analysis suggests that variations in ocean ventilation related to the Southern Annular Mode are responsible for this interannual variability. On decadal time scales, the existence of significant variability in the air-sea CO2 flux estimated from observations also tends to be supported by observation-based estimates of O2 flux variability. However, the large decadal variability in air-sea CO2 flux is absent from ocean models. Our analysis suggests that issues in representing the balance between the thermal and non-thermal components of the CO2 sink and/or insufficient variability in mode water formation might contribute to the lack of decadal variability in the current generation of ocean models. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Failure to induce stress reactions following vaccination against Marek's disease or Newcastle disease.

Chickens aged one or 21 days were given single injections of a vaccine against Marek's disease or Newcastle disease respectively, and monitored over a three week period for any signs of a stressor response. No consistent evidence of such a response was found. Some data on normal ontogenetic changes in various adrenal and plasma variables are also presented.

The response of the immature fowl to multiple injections of adrenaline.

Chicks were injected, from one to 21 days of age, with either L-adrenaline (500 mug/kg) or the solvent three times a week. Birds treated with adrenaline showed an imparied growth rate. Relative (mg/kg0.75), but not absolute (mg) adrenal weight was significantly increased. No changes in adrenal cholesterol content or concentration were noted.

Stressor effects of handling on the immature fowl.

Chicks were handled for 5 min twice daily for five consecutive days per week over a three-week period. The control birds were not handled once they had been allotted to their brooders. The growth rate of the treated birds was significantly decreased. There was no adrenal hypertrophy; the concentration, but not the content, of adrenal cholesterol was significantly increased. Plasma glucose, FFA and cholesterol concentrations were similar in the groups at the end of the experiment. The lipolytic response of the handled birds to a further stimulus of handling was significantly greater than that of unhandled birds experiencing novel handling stimulus. There was also a significant decrease in the concentration of corticosterone in the plasma of the handled birds but not in the unhandled group. There was thus no evidence of habituation.

Stressor effects of adrenaline on the immature fowl.

Chicks were injected with L-adrenaline (500 microgram/kg) thrice weekly from hatching for one, two or three weeks. The growth rate of treated chicks was depressed, particularly in the first week. When four-week-old chicks were given nine injections of adrenaline over a three-week period, growth rate was also depressed but less severely. The greater sensitivity of the younger chicks is thought to result from an immature blood-brain barrier. Relative adrenal mass (mg/kg) was generally increased but adrenal cholesterol depletion occurred only in three-week-old birds treated with adrenaline throughout. Plasma glucose and cholesterole concentrations were within the normal range after three weeks of treatment but there was a significant hypolipacidaemia in the younger birds treated for two or three weeks.

The effects of repeated injections of adrenaline on the response of the fowl to further alarm stimulation.

Chicks, aged two weeks, were injected with either adrenaline (300 microgram/kg) or saline daily for seven days. One day after the seventh injection it was found that the birds treated with adrenaline had become hypolipacidaemic and hypocholesteraemic and that there had been adrenal hypertrophy and an increase in the adrenal store of cholesterol. Plasma concentrations of glucose and corticosterone were within the normal range. The two groups (adrenaline- or saline-treated) were further subdivided each into two subgroups and were now injected with either adrenaline or saline, and their responses measured over a 120 min period. A significantly shorter period of hyperglycaemia was found in the birds pretreated with adrenaline and given a further injection of the hormone. These birds also showed an enhanced lipacidaemic response but the corticosterone response was not altered.

Stress of transportation for broilers.

Transporting birds for two to four hours over distances of up to 224 km (140 miles) induced hyperlipacidaemia and hypoglycaemia while the concentration of plasma cholesterol decreased and then increased significantly. These responses were the same in summer and winter. Body temperature was not affected by the experimental conditions. There was a consistent increase in plasma corticosterone which was greater in winter than in summer.

Re-establishment of the stress response in Gallus domesticus after hatching.

Cold caused a hypercorticosteronaemia and hypothermia in the 2-day-old chick. Heat did not affect plasma corticosterone concentrations, despite the birds becoming hyperthermic. The 2-day-old chick has a lower resting concentration of corticosterone than the 1-day-old. The minimum effective dose of corticotrophin in stimulating a hypercorticosteronaemia was 0.5 IU/kg in the former, 1.0 IU/kg in the latter. It is concluded that stress non-responsiveness persists for about 48 hr after hatching and that it is due to a temporary inhibition of hypothalamic function.

Failure of procaine penicillin and zinc bacitracin to modify the response of the fowl to stressors.

1. The effect of either procaine penicillin or zinc bacitracin (25 mg active base/kg food) on the response of young birds to three different stressors - withdrawal of food for 18 h, exposure to cold for 24 h or treatment with ACTH- has been examined. 2. Neither antibiotic had any consistent effect on the stress responses. 3. It is concluded that neither penicillin nor bacitracin has any stress-ameliorating activity at least under the conditions of the test.

The response of the immature fowl to multiple injections of adrenocorticotrophic hormone.

1. Treating chicks, from 1 d or 5 weeks of age with ACTH three times weekly for 3 weeks depresses growth and causes adrenal hypertrophy at dose rates of 30 IU/kg or more, and depletion of adrenal cholesterol (greater than 10 IU/kg). 2. Treating chicks five times weekly at a dose rate of 30 IU/kg was as effective as a dose of 120 IU/kg three times weekly. 3. Plasma glucose and FFA concentrations of chicks treated thrice weekly with 120 IU ACTH/kg for 3 weeks were within the normal range. 4. Rhode Island Reds were more sensitive to ACTH than Light Sussex. 5. Adrenal cholesterol stores in normal chicks show significant variations with season.

Short-term stressor effects of reserpine.

The effects of reserpine on plasma glucose, FFA and cholesterol and on adrenal cholesterol were determined in 1-and 21-d-old chicks over a 24-h period. 2. Irrespective of age, reserpinised chicks became hyperglycaemic and hypocholesteraemic, their stores of adrenal cholesterol were depleted and the mobilisation of the lipid was impaired. The response of the older bird was quantitatively larger than that of the younger bird. 3. Propranolol prevented the increase in plasma glucose concentration seen 1 h after reserpine but it did not affect subsequent changes. 4. It is concluded that reserpine acts as a stressor and it is shown that its effects have not been entirely overcome after 24 h.

Responses of the immature fowl to a single injection of adrenocorticotrophic hormone.

Chicks, aged 1 or 21 d, were injected with long-acting ACTH (6, 12, 30 or 60 IU/kg) and changes in plasma glucose and cholesterol and in adrenal weight and cholesterol measured. 2. No consistent response was observed in the 1-d-old chicks. 3. Hyperglycaemia and adrenal cholesterol depletion could be demonstrated in the 3-week-old bird at all doses. 4. The duration of the hyperglycaemic response was dose-dependent but there was only limited evidence that adrenal cholesterol depletion was similarly dependent. 5. Starving the 3-week-old bird overnight led to a significant hypercholesteraemia which was reduced after ACTH. In contrast no change in plasma cholesterol concentration was noted in fully fed birds.

An evaluation of adrenal mass and adrenal cholesterol as measures of adrenal activity.

1. The effects of twice daily injections of corticotrophin (1 IU/kg body weight) or restriction of food intake to 75% of normal on body mass, adrenal mass and adrenal cholesterol were determined on chicks from 1 to 21 d of age. 2. Only the birds subjected to restricted feeding showed a reduced growth rate. 3. There was no adrenal hypertrophy in birds receiving corticotrophin but in the restricted group there was transient hypertrophy at 2 weeks. 4. Depletion of adrenal cholesterol was noted only in the birds receiving corticotrophin. 5. It is concluded that neither depletion of cholesterol nor hypertrophy is an inevitable consequence of enhanced adrenal cortical activity.

Short-term stressor effects of propranolol.

1. The effects of propranolol (10 mg/kg) on plasma cholesterol, glucose, corticosterone and free fatty acids, on adrenal mass and cholesterol content and on body temperature were determined over a 24-h period in 3-week-old Light Sussex chicks. 2. Changes in plasma cholesterol were equivocal, though there was perhaps a trend towards hypercholesteraemia. 3. Birds became hypoglycaemic within an hour but were hyperglycaemic between 2 and 4 h. At 24 h they were normoglycaemic. 4. Plasma corticosterone was increased markedly at 1 h but was decreased compared with the control at 2 h ( P < 0.01). Thereafter the concentration was in the normal range. 5. There was an enhanced hyperlipacidaemia in the treated birds after 1 h. 6. Adrenal cholesterol stores were decreased by 10% at 4 h but were unaffected at all other times. 7. Colonic temperature decreased by 1x6 degrees C after 2 h but was normal by 4 h. 8. It is concluded that propranolol has mild stressor activity which is lost within 24 h.

Some responses of the immature fowl to the withdrawal of a stressor.

1. Light Sussex chicks were treated with corticotrophin (30 IU/kg) five times a week from hatching to 3 weeks of age. Their responses to the cessation of treatment were determined over the subsequent 2 weeks. 2. Growth rate was impaired by the treatment but had returned to normal after 7 d. 3. Adrenal mass was not affected by treatment but hypertrophy was evident after 14 d of recovery. Relative adrenal weight was greater in the treated group throughout the recovery period. 4. Adrenal cholesterol stores were depleted at the end of treatment, were repleted after 7 d but significantly depleted again at 14 d. 5. Plasma glucose concentration was not affected by treatment but birds were hyperglycaemic 7 and 14 d after treatment had ceased. 6. Plasma free fatty acid (FFA) concentrations were not affected at any time. 7. Plasma corticosterone concentration was not affected by the treatment but 7 d later it was greater in the treated birds. 8. Significant correlations between plasma glucose, FFA and corticosterone were found.

Dietary ascorbic acid or procaine penicillin and the response of the immature fowl to stressors.

1. The effectiveness of dietary ascorbic acid and procaine penicillin in ameliorating the response to the stressors glucagon, corticotrophin, withdrawal of food and water and extremes of environmental temperature, both short and long-term, has been assessed. 2. No consistent changes in the responses were found, but it is suggested that the rates of inclusion of the substances may be important.

Dietary aureomycin and the response of the fowl to stressors.

1. Conventional or gnotobiotic chicks, when injected from 1 d to 3 weeks of age with adrenocorticotrophic hormone (120IU/kg, three times weekly), showed a depressed growth rate, adrenal hypertrophy and depletion of cholesterol form the adrenal glands. 2. Feeding a diet supplemented with aureomycin (10 mg/kg) did not have any consistent ameliorating effect on the response of the stressed bird as judged by the above parameters. 3. It was found that treating germfree chicks with five daily injections of sterile milk on days 3 to 7 did not depress growth rate at any time, nor could differences in adrenal size or cholesterol stores be detected at the end of the 21-d experimental period. The responses were not modified by feeding an aureomycin-supplemented diet.

Genetic transformation of chickens using irradiated male gametes.

Results have been obtained which corroborate those of Pandey and Patchell (Molec. Gen. Genet., 186, 305, 1982) in demonstrating that genetic material from irradiated semen is incorporated into the embryo and expressed, albeit at rather a low rate, and is subsequently transmitted to progeny of the transfected birds. The method provides a technically straightforward means of transferring genetic material where rapid and reliable means of detecting the transferred gene exist. An advantage of the method is that regulatory regions are likely to be carried with the transferred gene but there is equally a disadvantage in the simultaneous transfer of unwanted material.

Genetic transformation of chickens using irradiated sperm: co-transfer of undesirable genes.

An attempt was made to utilise the recently demonstrated method of gene transfer using irradiated male gametes to transfer the B21 associated resistance to Marek's disease into a susceptible line of chickens. Although none of the 1486 progeny tested showed evidence of the transfer of the B21 haplotype a substantial proportion acquired a second marker, susceptibility to lymphoid leukosis virus. These results confirm and extend previous reports in suggesting that although gene transfer by this method occurs at a relatively high frequency, expression of the transferred genes is variable; whether this reflects properties of the DNA itself or of cellular mechanism of expression is not clear.