V. Fouces

COMPARATIVE SKELETAL MUSCLE FIBRE MORPHOMETRY AMONG WILD BIRDS WITH DIFFERENT LOCOMOTOR BEHAVIOUR

Six muscles of the mallard duck (Anas platyrhynchos), the common coot (Fulica atra) and the yellow‐legged gull (Larus cachinnans) were analysed morphometrically, with special emphasis on their functional implications and physiological needs. Oxidative fibres always had significantly smaller size than anaerobic fibres, although no differences in the number of capillaries per fibre were found. This resulted in greater capillary counts per unit of fibre area and perimeter in oxidative than anaerobic fibres, which indicates that the greater demand for oxygen supply may be achieved by decreasing the size of the muscle fibre rather than by increasing the number of associated capillaries. Fast oxidative fibres of the pectoralis and the triceps of the gull had greater sizes than the fast oxidative fibres of the mallard and the coot, which correlates with the difference in energetic demands between flapping and gliding flight. Greater fibre cross‐sectional areas and perimeters seem suited to afford the long‐lasting activity with low metabolic demands required during gliding. By contrast, mallards and coots attain a high oxidative metabolism, during sustained flapping flight, by reducing fibre size at the expense of a diminished ability for force generation. Between‐species comparisons of the hindlimb muscles only yielded differences for the anaerobic fibres of the gastrocnemius, as an important adaptive response to force generation during burst locomotion. The need to manage sustained swimming abilities effectively may result in similar FOG fibre morphometry of the hindlimb muscles studied, indicating that a compromise between the oxygen flux to the muscle cell and the development of power is highly optimised in oxidative fibres of the bird species studied.

Capillarity and fibre types in locomotory muscles of wild mallard ducks (Anas platyrhynchos)

Six locomotory muscles from wild mallard ducks (Anas platyrhynchos) were analysed by histochemical methods. Special care was taken in sample procedure in order to describe the heterogeneity found throughout each muscle. Capillarity and fibre-type distributions were correlated to the functional implications and physiological needs of each muscle. Comparisons between our results and similar previous reports on dabbling and diving ducks are also discussed. Muscles from the leg presented the most heterogeneous fibre-type distributions, which are correlated to the wide range of terrestrial and aquatic locomotory performances shown by these animals. More specialized muscles such as pectoralis, used almost exclusively for flapping flight, had more homogeneous fibretype distributions, whereas muscles from the wing presented a high proportion of glycolytic fibres probably recruited during non-steady flapping flight. Deep muscle pectoralis zones and parts of the gastrocnemius which are closer to the bone are remarkable for their high capillarity indices and oxidative capacities, which suggests that these parts are recruited during sustained flapping flight and swimming. However, two different strategies for achieving these high oxygen needs are evident, indicating that the fibre cross-sectional area plays an important role in the modulation of the oxygen supply to the muscle cells.

A histochemical ATPase method for the demonstration of the muscle capillary network.

A histochemical method for demonstration of the capillaries in skeletal muscle of birds is proposed. The present method, which is a modification of a previously reported myosin ATPase technique used for simultaneous staining of capillaries and fiber types, provides an accurate count of capillaries associated with different fiber types in avian skeletal muscles. We have applied the original and the modified method to serial adjacent sections of certain skeletal muscles and our results show that after the application of the original technique: (a) in muscles having dark Type II fibers, these fibers produce a masking effect on their adjacent capillaries; (b) a consistent and significant undercounting in capillary densities can be seen even in muscles having no dark Type II fibers; and (c) the staining quality and capillary count are substantially improved with the use of the modified method. We attribute the better results obtained with our modification to differences in thermosensitivity of ATPase activity from the capillary endothelium and of the myofibers. A mathematical treatment is therefore proposed to correct the values of capillary count obtained with the original method.

Skeletal muscle capillarization and fiber types in urban and homing pigeons (Columba livia)

1. Fiber types, capillary supply and other morphometrical parameters were analysed in pectoral, gastrocnemius and pronator muscles of homing and urban pigeons. 2. The two kinds of birds were analysed before and after a restrainment period of at least 5 months. 3. Only slight differences in fiber type frequencies were noted between urban and homing pigeons in control conditions. 4. The effect of restrainment on the different parameters studied was unclear in gastrocnemius and pronator muscles and negligible in M. pectoralis. 5. Mean diffusion distances for oxygen from capillaries were smaller in oxidative fibers; also, vascularization indexes were higher for these fiber types. 6. The contribution of each fiber type to total sectional ara of muscle remains stable in spite of fiber type frequencies heterogeneity.

CAPILLARITY AND FIBRE TYPES IN LOCOMOTORY MUSCLES OF WILD YELLOW-LEGGED GULLS (LARUS CACHINNANS)

This study analyzes the Capillarity and fibre‐type distribution of six locomotory muscles of gulls. The morphological basis and the oxygen supply characteristics of the skeletal muscle of a species with a marked pattern of gliding flight are established, thus contributing to a better understanding of the physiology of a kind of flight with low energitic requirements. The four with muscles studied (scapulotriceps, pectoralis, scapulohu meralis, and extensor metacrpi) exhibited higher percentages of fast oxidative glycolytic fibres (>70%) and lower percent‐ages of slow oxidative fibres (>16%) than the muscles involved in nonflight locomotion (gastrocnemius and iliotibialis). Capil‐lary densities ranged from 816 to 1,233 capillaries mm‐2, having the highest value in the pectoralis. In this muscle, the fast oxidative glycolytic fibres had moderate staining for succingate dehydrogenase and relatively large fibre sizes, as deduced from the low fibre densities (589‐665 fibres mm‐2). All these findings are seen as an adaptive response for gliding, when the wing is held outstretched by isometric contractions. The leg muscles studied a considerable population of slow oxidative fibres (>14% in many regions),which suggests thatthey are adapted to postural activities. Regional variations in the relative distributions of fibre types in muscle gastrocnemius may reflect different functional demands placed on this muscle during terrestrial and aquatic locomotion. The predominance of oxidative fibres and capillary densities under 1,000 capillaries mm02 in leg muscles is probably a consequence of an adapta‐tion for slow swimming and maintenance of the posture on land rather than for other locomotory capabilities, such as endurance or sprint activities.

Hemorheology and oxygen transport in vertebrates. A role in thermoregulation

We studied the effect of temperature on blood rheology in three vertebrate species with different thermoregulation and erythrocyte characteristics. Higher fibrinogen proportion to total plasma protein was found in turtles (20%) than in pigeons (5.6%) and rats (4.2%). Higher plasma viscosity at room temperature than at homeotherm body temperature was observed in rats (1.69 mPa·s at 20 °Cvs. 1.33 mPa·s at 37 °C), pigeons (3.40 mPa·s at 20 °Cvs. 1.75 mPa·s at 40 °C), and turtles (1.74 mPa·s at 20 °Cvs. 1.32 mPa·s at 37°C). This fact allow us to hypothesize that thermal changes in protein structure may account for an adjustement of the plasma viscosity. Blood viscosity was dependent on shear rate, temperature and hematocrit in the three species. A different behaviour in apparent and relative viscosities between rat and pigeon at environmental temperature was found. Moreover, the blood oxygen transport capacity seems more affected by a reduction of temperature in rats than in pigeons. Both findings indicate a greater influence of temperature on mammalian erythrocyte than on nucleated red cells, possibly as a consequence of differences in thermal sensitivity and mechanical stability between them. A comparison between the three species revealed that apparent blood viscosity measured at homeotherm physiological temperature was linearly related to the hematocrit level of each species. However, when measured at environmental temperature, rat blood showed a higher apparent viscosity than those found in species with non-nucleated red cells, thus indicating a higher impact of temperature decrease on blood viscosity in mammals. This suggest that regional hypothermia caused by cold exposure may affect mammalian blood rheological behaviour in a higher extent than in other vertebrate species having nucleated red cells and, consequently, influencing circulatory function and oxygen transport.ResumenSe estudia el efecto de la temperatura sobre la reología sanguínea en tres especies de vertebrados con diferente termorregulación y características eritrocitarias. Se encuentra que la relación fibrinógeno/proteínas plasmáticas es mayor en tortugas (20%), que en palomas (5.6%) y ratas (4.2%). Se observa mayor viscosidad plasmática a temperatura ambiente que a la corporal en rata (1,69 mPa·s a 20 °Cvs. 1,33 mPa·s a 37 °C), paloma (3,40 mPa·s a 20 °Cvs. 1,75 mPa·s a 40 °C) o tortuga (1,74 mPa·s a 20 °Cvs. 1,32 mPa·s a 37 °C). Esto sugiere que los cambios térmicos afectan a la estructura de las proteínas y causan un ajuste de la viscosidad plasmática. La viscosidad sanguínea depende del gradiente de velocidad, de la temperatura y del hematocrito, en las tres especies. Se observa un comportamiento diferente en la viscosidad aparente y relativa entre rata y paloma a temperatura ambiente. Sin embargo, la capacidad transportadora de oxígeno por la sangre parece más afectada por una reducción de la temperatura sanguínea en ratas que en palomas. Ambos hallazgos apuntan a un mayor efecto térmico sobre los eritrocitos de mamífero que en los nucleados, indicando diferente sensibilidad térmica y estabilidad mecánica. La comparación entre las tres especies revela que la viscosidad aparente sanguínea a temperatura fisiológica en homeotermos presenta una relación lineal con el hematocrito. A temperatura ambiental, la sangre de ratas mostró una viscosidad aparente mayor de la esperada por su hematocrito, indicando un mayor impacto del descenso de temperatura sobre la viscosidad sanguínea. Esto sugiere que la hipotermia regional debida a la exposición al frío puede alterar la reología de la sangre de los mamíferos en mayor medida que en otras especies de vertebrados con eritrocitos nucleados y, en consecuencia, afectar la función circulatoria y el transporte de oxígeno.

A combined myosin ATPase and acetylcholinesterase histochemical method for the demonstration of fibre types and their innervation pattern in skeletal muscle

An improved, combined staining method for myofibrillar ATPase (m-ATPase) and for acetylcholinesterase activity is described. This method allows the observations, on the same slide, of the classical histochemical m-ATPase profile following the Brooke and Kaiser technique and the neuromuscular junction morphology. Thus the pattern of innervation, nerve ending structure and number of nerve endings along the fibres is shown simultaneously for the basic differentiation between slow and fast fibres. The use of acidic and alkaline preincubation allows better visualization of endplate morphology and avoids the masking effect of a positive m-ATPase reaction. The technique has been validated on skeletal muscles from avian and mammalian species.

CAPILLARITY AND FIBER TYPES IN LOCOMOTORY MUSCLES OF WILD COMMON COOTS, FULICA ATRA

Six locomotory muscles of wild common coots, Fulica atra, were analyzed histochemically. Capillarity and fiber‐type distributions were correlated to the functional implications and physiological needs of each muscle. Leg muscles exhibit three unevenly distributed fiber types, a pattern that reflects the great variety of terrestrial and aquatic locomotory performances that coots are able to develop. Aerobic zones are presumably recruited during steady swimming and diving, while regions with anaerobic characteristics may be used for bursts of activity such as sprint swimming or during take off, when coots run along the waters surface. Fiber types and capillarization in wing muscles have a marked oxidative trend. High wing beat frequencies, short and broad wings, and the long distance migrations that these birds perform indicate that the presence of high numbers of oxidative fibers and the well developed capillary supply are needed for enhanced oxygen uptake. The pectoralis muscle, except in its deep part, has exclusively fast oxidative fibers with a very high staining intensity for succinate dehydrogenase assay as compared to the same fiber type of other muscles. Its predominant role in flapping flight justifies these characteristics that are typical of fibers with high aerobic metabolism. The deep part of the pectoralis muscle presents a low proportion of an unusual slow anaerobic fiber type. These fibers could play a role during feeding dives when the bird presses the air out of the feathers by tightening the wings against the body. A linear relationship between capillary and fiber densities in all coot muscles studied reflects an adjustment between fiber diameter and vascularization in order to obtain the oxygen for mitochondrial supply. This strategy seems a suitable way to cope with the rigid aerobic constraints that flying and diving impose upon the coots physiology. J. Morphol. 237:147–164, 1998.