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M H Bernstein

Publications and source records attributed to M H Bernstein.

At least 19 recordsLinked to original sources
PubMed1998

Fiber capillarization and ultrastructure of pigeon pectoralis muscle after cold acclimation.

We investigated the effect of 2 months of exposure to cold conditions (0-5 C) on capillarization and on fiber size, distribution and ultrastructure in the pectoralis muscle of nine pigeons (Columbia livia; mean body mass 700 31 g) and compared the results with measurements from four control birds (mean mass 715 42 g) kept at normal ambient temperature (22-23 C) for the same period. Superficial and deep portions of the muscles, taken from the central area of the right or left pectoralis major muscle, were perfusion-fixed in situ, processed for electron microscopy and analyzed by morphometry. Aerobic fibers represented the vast majority of fibers (93 1 %, mean s.e.m.) in all samples. After cold-acclimation, fiber sectional area was reduced and capillary density increased proportionally. There was no change in the degree of orientation (anisotropy) of capillaries, capillary-to-fiber ratio or fiber type distribution compared with controls. The volume density of mitochondria and lipid droplets in aerobic fibers and capillary diameter increased in response to cold, while the linear relationship between capillary length per fiber volume and fiber mitochondrial volume density remained unchanged. Capillary surface area, intrafiber lipid deposition and fiber mitochondrial volume density were all correlated in cold-acclimated pigeons. The results indicate a close match between the aerobic capacity of the highly aerobic fibers of the pectoralis muscle and their vascularization to meet the increased energetic demand of shivering.

Acclimatization↗
PubMed1995

Intrapulmonary CO2-rise time and ventilation in ducks.

Many investigators have reported finding intrapulmonary chemoreceptors (IPCs) in several species of birds and reptiles; however, the role of IPCs in ventilatory control in birds has not been identified. This study was undertaken to assess the role of intrapulmonary CO2 dynamics on the control of breathing. Ducks were unidirectionally ventilated, and their breathing was monitored with a pneumotachograph connected to a personal computer. A gas-mixing system controlled by the computer adjusted the rate of rise of airway CO2 concentration ([CO2]). On inspiration, the computer removed CO2 from the ventilating gas for 1.5 s, followed by a controlled [CO2] rise. Breathing frequency was directly related to the rate of rise of airway [CO2]. Tidal volume, however, was not correlated with CO2-rise time but was related to the peak airway [CO2]. This response is likely mediated by IPCs because preventing airway [CO2] from falling during inspiration immediately altered that breath. An increase in CO2 production (as in exercise) will lead to an increase in the rate of CO2 excretion into the lung. The resulting alteration of breathing frequency would thus maintain acid-base balance. The observed response, therefore, may represent a link between ventilation and metabolism.

Acetazolamide↗
PubMed1994

Effect of flying activity on capillary-fiber geometry in pigeon flight muscle.

The effect of flying activity on capillary density and geometry was investigated in pectoralis muscle of 4 wild-caught (W) pigeons (BW 233-348 g) perfusion-fixed in situ and processed for electron microscopy. Morphometric analysis revealed both differences and similarities with similar sampling sites (superficial and deep in central area of right or left pectoralis major muscle, approximately midway along cranio-caudal and lateral axis) in sedentary (S) pigeons. Differences were the greater fractional cross-sectional area of aerobic fibers (W, 82 +/- 2%; S, 63 +/- 6%; p = 0.006) and the greater volume density of mitochondria per volume of fiber (W, 22.0 +/- 1.3%; S, 15.7 +/- 1.7%; p = 0.011) in wild-caught pigeons. While glycolytic fibers were significantly narrower in W, the size of the majority of fibers comprising the muscles, i.e. aerobic fibers, was similar in the two groups. Other similarities were found in capillary-to-fiber ratio (W, 2.0 +/- 0.2; S, 2.1 +/- 0.2) and in the degree of orientation of capillaries in the two groups. In addition, both capillary density at a given fractional cross-sectional area of aerobic fibers and capillary length per fiber volume at a given mitochondrial volume density were similar in the two groups, indicating a proportional increase in capillarity and muscle aerobic capacity in W compared with S. Comparison of capillary numbers around aerobic fibers at a given mitochondrial volume per microns length of fiber showed no difference between W and S groups nor with previous data in muscles with wide differences in fiber size and mitochondrial density such as rat soleus, bat muscles and hummingbird flight muscles. This supported the notion of a tight correlation between capillary numbers around individual fibers and mitochondrial volume per unit length of fiber in aerobic muscles. It also supported the idea that it is the number of capillaries around the fibers rather than diffusion distance which determines O2 flux rates in highly aerobic muscles.

Animals↗
PubMed1991

Mannose-sensitive HRP endocytosis by the retinal pigment epithelium.

Mannose-sensitive endocytosis by rat retinal pigment epithelium (RPE) explants was characterized using the mannose-rich glycoprotein horseradish peroxidase (HRP). The number of HRP-containing endosomes in the RPE was morphologically quantitated by light microscopy while the amount of HRP ingested was biochemically quantitated by enzyme assay. HRP internalized via a mannose-sensitive receptor was differentiated from fluid-phase uptake in competitive inhibition studies using D-mannose. Morphological results showed that most HRP-containing endosomes formed within the first 15 min of incubation and showed little increase in number during 4 hr of continued incubation with HRP. In contrast, the biochemical assay showed a steady increase in the amount of HRP in RPE endosomes measured over time. The addition of 10 mM D-mannose to the incubation medium was associated with a significant decrease in both the number of HRP-containing endosomes and the amount of HRP ingested by RPE explants. Values indicate that half of the total uptake of HRP is mediated by a mannose-sensitive receptor while the balance is ingested via non-specific fluid-phase endocytosis.

Animals↗
PubMed1987

Posthatching development of the rete ophthalmicum in relation to brain temperature of mallard ducks (anas platyrhynchos).

In posthatching mallard ducks (Anas platyrhynchos), brain cooling improves with growth. To determine whether this may be correlated with growth-related changes in morphology of the rete ophthalmicum, we studied the development of this rete in immature mallards from hatching to 29 days of age. We found that the number of arteries and veins was fixed at hatching. The rete continued to grow, however, in length and vessel diameter during body and brain growth. The vascular surface area for heat exchange in the rete therefore also increased with body and brain mass. The increase in retial heat-exchange area was faster than the simultaneous increase in brain mass. The increase in body-to-brain temperature difference (delta T) described previously occurred nearly in direct proportion to heat-exchange area, such that the ratio of delta T to exchange area was nearly constant at about 0.1 degrees C per mm2 during growth. It is concluded that the increase in heat-exchange area of the rete ophthalmicum plays a major role in the development of brain cooling capacity of posthatching ducks.

Animals↗
PubMed1985

Effects of temperature and PCO2 on O2 affinity of pigeon blood: implications for brain O2 supply.

Bird heads contain paired countercurrent heat exchangers, the ophthalmic retia, which function in brain temperature regulation. Blood, cooled by evaporation from the nasal and buccal mucosa and the ocular surfaces, flows to the venous side of each rete and there gains heat from arterial blood flowing countercurrent to it. The cooled arterial blood then flows to the brain. To ascertain whether characteristics of the blood reaching the cooling surfaces and the retia favor O2 and CO2 exchange, as well as heat exchange, we studied blood O2 affinity in relation to temperature (T) and CO2 tension (PCO2) in six pigeons (Columba livia). O2 tension (PO2) at half-saturation (P50, Torr) was measured at various combinations of T and PCO2 from 36 to 44 degrees C and 9 to 33 Torr. pH was uncontrolled. O2 half-saturation of hemoglobin (P50) varied according to P50 = 1.049T + 0.573PCO2-19.444. We propose that shifts in blood O2 affinity, associated with T and PCO2 at the mucosa and eyes and in the retia, would enhance the brain O2 supply by an exchange of O2 and CO2 between air and blood at moist cephalic surfaces, thereby augmenting O2 and reducing CO2 in the venous return to the retia and diffusion of O2 from veins to arteries in the retia. This mechanism might have particular importance at high altitude; we calculate that at 7,000 m above sea level both O2 saturation and PO2 could double in blood flowing from the retia to the brain.

Animals↗
PubMed1985

Blood respiratory properties in pigeons at high altitudes: effects of acclimation.

Many birds thrive at high altitudes where environmental temperatures are low. Previous studies have shown that tolerance of and acclimation to hypoxia involve cardiopulmonary and hematological adaptations. We investigated blood respiratory properties during exposure to simulated high altitude (hypobaric hypoxia) and low temperature in unanesthetized resting pigeons (Columbia livia, mean mass 0.38 kg). A control group (C) and a group acclimated to 7 km above sea level (ASL) in a hypobaric chamber at 25 degrees C (HA group) were used. All were acutely exposed to altitudes through 9 km ASL at 5 or 25 degrees C. Arterial and mixed venous blood gas tensions and O2 and CO2 content during steady state decreased with increased altitude, whereas blood lactate increased in both groups at both temperatures. Acute high-altitude exposure did not affect hematocrit, hemoglobin concentrations, or O2 carrying capacity, but at any altitude these were all greater in HA than in C birds. At 5 degrees C blood pH increased with altitude in controls but remained unchanged in HA birds. At 25 degrees C in both groups mean intracellular pH did not change, averaging 6.97, whereas extracellular (venous) pH increased with altitude. At the highest altitudes tissue O2 extraction was virtually complete in both groups. Acclimation changed blood O2 and CO2 combining properties in ways likely to improve gas transport at high altitudes. The previously unreported shifts in blood respiratory and acid-base properties with acclimation indicate that innate extrapulmonary adaptations contribute to avian hypoxia tolerance.

Acid-Base Equilibrium↗
PubMed1985

Effect of estrogen on the affinity of malachite green for staining cardiac lipid inclusions in mice.

The effect of estradiol-17-beta on lipids of the ventricular myocardium of mice has been studied with a cytochemical technique in which malachite green was added to glutaraldehyde. This malachite green-glutaraldehyde fixative enhances the visualization of certain phospholipid-related elements. Estrogen induces an affinity of ventricular cardiac lipid inclusions for the cationic dye malachite green. The staining affinity is evidenced only in the estrous female, not in diestrus. In oophorectomized animals, malachite green staining is seen only following estradiol injection, but this effect is blocked by progesterone. In the male, ventricular lipids do not stain, nor do they develop malachite green affinity with estrogen stimulation. These results imply a blockade of the estradiol-mediated dye affinity by progesterone and testosterone. This reinforces the concept of the heart as a target organ for sex steroids and expands the previously described estrogen effects on myocardium.

Animals↗
PubMed1985

The interphotoreceptor matrix and the interphotoreceptor space of the vertebrate retina.

The interphotoreceptor space (IPS) of the vertebrate retina is the adult corollary of the lumen within the embryonic optic vesicle. The inner limit of the IPS is formed by the intercellular junctions of Muller cells and photoreceptors forming the external limiting membrane (ELM). The apical surface of the retinal pigment epithelium (RPE) is the outer limit of the IPS. Most of the volume of the IPS is occupied by the inner and outer segments of the photoreceptors, with the microvillous processes of the RPE, and the small microvilli of the Muller cells filling lesser portions. SEM of samples fixed in glutaraldehyde containing 0.5% ruthenium red show the interstitial spaces are filled with interphotoreceptor matrix (IPM). Biochemical studies and our enzyme digestion studies suggest this extracellular material is enriched in glycoproteins and glycosaminoglycans. The carbohydrates are two-thirds sulfated, 25% sialic acid enriched, and about 10% hyaluronic acid. Most of the IPM proteins can be identified as products of adjacent cells.

Animals↗
PubMed1984

Extrapulmonary gas exchange enhances brain oxygen in pigeons.

Blood in mouth, nose, and eye tissues of birds cools by evaporation, then flows to a cephalic vascular heat exchanger, the ophthalmic rete. There, acting as a heat sink, blood from the evaporative surfaces cools arterial blood flowing counter-current to it toward the brain. The brain thus remains cooler than the body core. Data for unanesthetized domestic pigeons (Columba livia) suggest that in addition to losing heat, blood perfusing the evaporative surfaces also exchanges oxygen and carbon dioxide with air. In the heat exchanger, this blood apparently gives up oxygen to, and gains carbon dioxide from, arterial blood. The consequent increase in oxygen and decrease in carbon dioxide in the brain's arterial blood enhance diffusion of these gases in, and oxygen supply to, the brain. Such events may help birds maintain the brain's oxygen supply during the high systemic demand of exercise and at the reduced oxygen availability of high altitude.

Animals↗
PubMed1983

Gas exchange and energy cost of flight in the white-necked raven, Corvus cryptoleucus.

Energy expenditure during steady-state, wind tunnel flights was estimated from O2 and CO2 exchange in five white-necked ravens (Corvus cryptoleucus, mean mass, 0.48 kg) at air speeds of 8-11 m/s. Power input was closely similar to allometric predictions based on data from other species of smaller birds. It increased significantly with air speed and flight angle above horizontal, and decreased with increasing angles below horizontal. Maximum power input reached seven times the preflight value measured under resting but not basal conditions, 14 times the previously measured basal values and three times the calculated maximum for a similar sized running mammal. Energy cost to travel 1 km decreased with increasing air speed. These trends are similar to those previously observed in smaller birds.

Animals↗
PubMed1982

Regulation of brain temperature in pigeons: effects of corneal convection.

The effect of direct ventilation of the eyes on cooling in the brain was investigated in domestic pigeons (Columba livia, mean mass 0.27 kg) with thermocouples chronically implanted in the hypothalamus and anterior eye chamber. During conductive heating in still air body-brain temperature difference (delta T) was 2.6 degrees C. During exclusive ventilation of ocular surfaces, with air flowing at about flight speed, delta T increased to 3.5 degrees C and returned to preventilation values on cessation of ventilation. When the eyes were sealed then ventilated, delta T was not different from that in still air. Administration of phenylephrine caused iridial vasoconstriction and a significant decrease in intraocular temperature, but no changes in brain temperature. This suggests that compensation may occur via other evaporating cranial surfaces. Our findings suggest that the eyes contribute to the control of brain temperature by dissipating heat. Blood cooled while flowing through the ocular vasculature apparently contributes to the venous flow through the ophthalmic rete, serving as a heat sink for arterial blood flowing to the brain.

Animals↗