No abstract

The retinas of many vertebrates have cone photoreceptors that express multiple visual pigments. In many of these animals, including humans, the original cones to appear in the retina (which express UV or blue opsin) may change opsin types, giving rise to new spectral phenotypes. Here we used microspectrophotometry and in situ hybridization with cDNA probes to study the distribution of UV and blue cones in the retinas of four species of Pacific salmon (coho, chum, chinook, and pink salmon), in the Atlantic salmon, and in the rainbow/steelhead trout. In Pacific salmon and in the trout, all single cones express a UV opsin at hatching (lambda(max) of the visual pigment approximately 365 nm), and these cones later transform into blue cones by opsin changeover (lambda(max) of the blue visual pigment approximately 434 nm). Cones undergoing UV opsin downregulation exhibit either of two spectral absorbance profiles. The first is characterized by UV and blue absorbance peaks, with blue absorbance dominating the base of the outer segment. The second shows UV absorbance diminishing from the outer segment tip to the base, with no sign of blue absorbance. The first absorbance profile indicates a transformation from UV to blue phenotype by opsin changeover, while the second type suggests that the cone is undergoing apoptosis. These two events (transformation and loss of corner cones) are closely associated in time and progress from ventral to dorsal retina. Each double cone member contains green (lambda(max) approximately 510 nm) or red (lambda(max) approximately 565 nm) visual pigment (double cones are green/red pairs), and, like the rods (lambda(max) approximately 508 nm), do not exhibit opsin changeover. Unlike Pacific salmonids, the Atlantic salmon shows a mixture of UV and blue cones and a partial loss of corner cones at hatching. This study establishes the UV-to-blue cone transformation as a general feature of retinal growth in Pacific salmonids (genus Oncorhynchus).

. Seasonal dynamics of flight muscle fatty acid binding protein and catabolic enzymes in a migratory shorebird. Am J Physiol Regulatory Integrative Comp Physiol 282: R1405-R1413, 2002; 10.1152/ ajpregu.00267.2001.-We developed an ELISA to measure heart-type fatty acid binding protein (H-FABP) in muscles of the western sandpiper (Calidris mauri), a long-distance migrant shorebird. H-FABP accounted for almost 11% of cytosolic protein in the heart. Pectoralis H-FABP levels were highest during migration (10%) and declined to 6% in tropically wintering female sandpipers. Premigratory birds increased body fat, but not pectoralis H-FABP, indicating that endurance flight training may be required to stimulate H-FABP expression. Juveniles making their first migration had lower pectoralis H-FABP than adults, further supporting a role for flight training. Aerobic capacity, measured by citrate synthase activity, and fatty acid oxidation capacity, measured by 3-hydroxyacylCoA-dehydrogenase and carnitine palmitoyl transferase activities, did not change during premigration but increased during migration by 6, 12, and 13%, respectively. The greater relative induction of H-FABP (ϩ70%) with migration than of catabolic enzymes suggests that elevated H-FABP is related to the enhancement of uptake of fatty acids from the circulation. Citrate synthase, 3-hydroxyacyl-CoA-dehydrogenase, and carnitine palmitoyl transferase were positively correlated within individuals, suggesting coexpression, but enzyme activities were unrelated to H-FABP levels. endurance exercise; fuel selection; lipid transport; metabolism THE INSTANTANEOUS COST OF flight is high relative to other forms of locomotion; flying birds expend energy at 10 to 15 times basal metabolic rate (BMR), and the minimum cost of flight may be twice the aerobic limit (V O 2 max ) of similarly sized running mammals (4, 38). In the special case of migratory flight, during which this intensity of exercise is maintained for as long as 50 or even 100 h, energy metabolism is almost completely dominated (85-95%) by the oxidation of exogenous fatty acids (FA) delivered to flight muscles from extramuscular adipose tissue (21,23,44). The use of stored fat as a metabolic fuel makes migratory flight possible, yet there currently exists no general mechanistic understanding of how birds achieve the high rates of exogenous FA transport and oxidation required to support such high-intensity endurance exercise.The most complete information on fuel selection during exercise comes from studies of running mammals (including humans). Generally, the relative contribution of FA oxidation to total fuel demand declines as exercise intensity increases, with the balance of energy derived mainly from carbohydrate oxidation (36). Exogenous FA contribute only a small fraction of the energy needed for exercise of even moderate intensity, and near V O 2 max exogenous FA oxidation contributes ϳ10% of energy demand (43, 45). The rate of utilization of exogenous FA appears to be most limited by transport across the sa...

No abstract

No abstract