Varanus Exanthematicus Research Articles

Energetic Cost of Running With Different Muscle Temperatures in Savannah Monitor Lizards

ABSTRACT The purpose of this study was to determine whether the energetic cost of locomotion was independent of muscle temperature, or if it tripled with a 10 °C increase in temperature, like the cost of generating isometric force in isolated muscle preparations. For a given running speed of Savannah Monitor lizards, the energetic cost of locomotion (the difference between running and resting metabolism) was the same when muscle temperature was 28·5 °C as when it was 38 °C. It was also found that stride frequency and posture did not change with temperature, indicating that the average force exerted by the lizards’ muscles during locomotion at the two temperatures was the same. This suggests that the cost of generating force in vivo is independent of temperature. Several possible explanations of the apparent difference between in vivo and in vitro muscle energetics are discussed.

Afferent connections of the cerebellum in various types of reptiles.

The origin of cerebellar afferents was studied in various types of reptiles, viz., the turtles Pseudemys scripta elegans and Testudo hermanni, the lizard Varanus exanthematicus, and the snake Python regius, with retrograde tracers (the enzyme horseradish peroxidase and the fluorescent tracer "Fast Blue"). Projections to the cerebellum were demonstrated from the nucleus of the basal optic root, the interstitial nucleus of the fasciculus longitudinalis medialis, the vestibular ganglion, and the vestibular nuclear complex, two somatosensory nuclei, viz., the descending nucleus of the trigeminal nerve and the nucleus of the dorsal funiculus, the nucleus of the solitary tract, the reticular formation, and throughout the spinal cord. A distinct bilateral projection to the cerebellum was found to arise in a nucleus previously called nucleus parvocellularis medialis (Ebbesson, '67). In the present study this cell mass is termed the perihypoglossal nuclear complex, considering its comparable position and fiber connections to the perihypoglossal nuclei in mammals. In all reptilian species studied a contralateral cerebellar projection of a cell mass located in the caudal brainstem adjacent to the nucleus raphes inferior was observed. It seems likely that this cell mass represents the reptilian homologue of the mammalian inferior olive. Most of the spinocerebellar fibers appeared to arise in neurons located in area VII-VIII of the gray matter. In this respect the origin of the spinocerebellar projection in reptiles resembles the origin of the rostral and ventral spinocerebellar tracts in mammals. No indications for the existence of a column of Clarke or a central cervical nucleus in the reptilian spinal cord were obtained. On comparison of the cerebellum afferents in reptiles with the known connections of the cerebellum in amphibians, birds, and mammals, a basic pattern of cerebellar afferent projections appears to exist in these vertebrate classes, including retinal, vestibular, precerebellar, somatosensory, and spinal afferents.

The motor nuclei and primary projections of the facial nerve in the monitor lizard Varanus exanthematicus.

The location of the motor nuclei and the projection of the primary afferent fibers of the facial nerve of the reptile Varanus exanthematicus were studied by means of the HRP method and the anterograde degeneration technique. The motor nuclei are located ventrolaterally in the rhombencephalon and are constituted by a medial cell group consisting of large, polygonal cells and a lateral cell group consisting of medium-sized, spindle-shaped, and multipolar cells. From HRP applications to the various branches of the facial nerve it could be concluded that the medial cell group represents the branchiomotor nucleus and the lateral cell group the superior salivatory nucleus. The efferent axons from the motor nuclei course dorsomedially toward the fourth ventricle, where they form a genu, and exit from the brainstem in the ventral fiber bundle of the facial nerve. The primary afferent fibers enter the brainstem in the dorsal bundle of the facial nerve. This bundle courses medially, enters the solitary tract, and diverges into rostrally and caudally running fibers. Part of the caudally directed fibers leave the solitary tract and course laterally toward the descending trigeminal tract. Some fibers enter the nucleus of this tract. There was no noticeable terminal degeneration in the solitary tract or in the descending trigeminal tract or its nucleus.

Ventricular Haemodynamics in the Monitor Lizard Varanus Exanthematicus: Pulmonary and Systemic Pressure Separation

ABSTRACT The haemodynamics of the anatomically undivided ventricle of the monitor lizard Varanus exanthematicus have been examined by measurements of blood pressure and flow. Central blood , and pH were also measured. Intracardiac pressure measurements show the ventricle to be functionally divided throughout systole into a high pressure pump (cavum arteriosum : ‘mean’ pressure 89 cm H2O) perfusing the systemic circulation, and a low pressure pump (cavum pulmonale: ‘mean’ pressure 40 cm H2O) perfusing the pulmonary circulation. Hypoxia produced by asphyxia or N2 breathing changed systolic pressures in the ventricular cava, but never resulted in superimposable pressure waveforms which would have indicated a break-down from ventricular division into two pressure pumps. Diastolic pressures were superimposable in the ventricular cava under all conditions. Analysis of blood and O2 content revealed the potential for nearly complete separation of left and right atrial blood in the ventricle, but both left-to-right and right-to-left shunts of considerable magnitude could also develop. The varanid heart with its systolic pressure separation allows the development of high blood pressure gradients capable of driving a large cardiac output through the high impedance systemic vascular beds. Concurrently, the low impedance pulmonary circuit is perfused at a much reduced blood pressure, circumventing filtration of plasma into the lungs and impairment of gas exchange. Haemodynamically this situation resembles that present in crocodilians and the homeothermic vertebrates.

Ascending projections of the brain stem reticular formation in a nonmammalian vertebrate (the lizard Varanus exanthematicus), with notes on the afferent connections of the forebrain.

In the present study an attempt has been made to analyze the ascending reticular projections in the lizard Varanus exanthematicus by means of the horseradish peroxidase (HRP) technique. Reticular projections ascending to the telencephalon were found to arise in the mesencephalon, but not caudal to the mesorhombencephalic border. HRP injections into the dorsal thalamus have demonstrated retrogradely labeled cells in the mesencephalic reticular formation, particularly at the level of the oculomotor nerve and in the medial magnocellular zone of the rhombencephalic reticular formation, predominantly rostrally. HRP infiltrations at the mesodiencephalic border damaged most of the fibers passing beyond this junction, resulting in the uptake of HRP by the damaged axons and subsequent labeling of the cell bodies or origin of ascending reticular projections to the diencephalon and telencephalon. From a comparison of cell-labeling patterns in cases of HRP injections of, respectively, the dorsal thalamus and the mesodiencephalic border, it seems likely that the nucleus reticularis medius and more sparsely the nucleus reticularis inferior project to ventral diencephalic structures (ventral thalamus and hypothalamus), whereas the midbrain reticular formation and the rostral parts of the rhombencephalic reticular formation (nuclei reticulares isthmi and superior) project to both the dorsal thalamus and more ventral diencephalic structures. Projections arising throughout the rhombencephalic reticular formation, but predominantly in the nucleus reticularis inferior, were found to ascend to the midbrain reticular formation. The present experimental data in the lizard Varanus exanthematicus are comparable to the findings in mammals, with the exception of the reticulo-oculomotor pathways which have not been analyzed so far in reptiles. In addition to the aforementioned ascending reticular projections, the present study has demonstrated projections ascending from monoamine cell groups, various diencephalic structures, as well as from neuronal groups involved in somatosensory, auditory, and gustatory systems. Projections were found from the locus coeruleus and the nucleus raphes superior to the telencephalon, as well as from the substantia nigra and the presumable reptilian homologue of the mammalian ventral tegmental area to the basal forebrain and the dorsal thalamus. Bilateral projections were demonstrated from the principal trigeminal nucleus to the telencephalon, reminiscent of the quintofrontal tract of birds. Ascending projections to the diencephalon were found to originate bilaterally in the descending trigeminal nucleus and the dorsal funicular nucleus. Auditory projections to the midbrain arise bilaterally in the superior olivary complex and in the cochlear nuclear complex. Finally, the ascending gustatory pathway arising in the nucleus of the solitary tract was found to project to the "parabrachial region," which in its turn has extensive projections to the forebrain.

Basal ganglia projections to the brain stem in the lizard Varanus exanthematicus as demonstrated by retrograde transport of horseradish peroxidase

In the present study the cells of origin of basal ganglia projections to the brain stem have been studied with the horseradish peroxidase technique in the lizard, Varanus exanthematicus. Injections of horseradish peroxidase were made at various levels of the brain stem from the mesodiencephalic border to the obex as well as in the tectum mesencephali. Efferent libers from the telencephalon to the diencephalon and the brain stem were found to arise predominantly from the striatum. From the present data it seems likely that the basal ganglia in Varanus exanthematicus as in other reptiles consist of two parts, a rostral ‘striatal’ part with projections mainly to the diencephalon and mesencephalon including the substantia nigra and a caudal ‘pallidal’ part with projections to the intercollicular nucleus and the rhombencephalic reticular formation. Injections of horseradish peroxidase into various parts of the rhombencephalic reticular formation have shown rather extensive projections from diencephalic and mesencephalic structures which receive afferents from the striatum: the posterior entopeduncular nucleus, the intercollicular nucleus and the substantia nigra were found to project as far caudal as the nucleus reticularis inferior. The substantia nigra shows, as regards its fiber connections, striking similarities to the mammalian substantia nigra, whereas the intercollicular nucleus possibly represents the reptilian homologue of the mammalian pedunculopontine nucleus. Injections of horseradish peroxidase into the tectum mesencephali have shown labeled cells in the nucleus of the posterior commissure, the posterior entopeduncular nucleus and the substantia nigra, all centers which are known to receive afferents from the striatum. Thus, the striatum can influence bisynaptically the reptilian homologue of the mammalian superior colliculus. It can be concluded that the striatum of the lizard, Varanus exanthematicus, has extensive direct as well as indirect projections to centers which influence the motor apparatus of the brain stem and spinal cord. Thus in reptiles it seems likely that the striatum exerts its influence on motor activity mainly via descending projections, in contrast to mammals where both descending and ascending striatal efferent pathways occur.

Spinothalamic projections in a lizard, Varanus exanthematicus: an HRP study.

In the present study HRP injections have been placed in various thalamic areas in order to investigate spinothalamic projections in the lizard Varanus exanthematicus. It appeared that the spinal cord projects to three different thalamic areas: nucleus dorsomedialis, nucleus ventrolateralis, and an area that includes both the nucleus dorsolateralis and nucleus intermediodorsalis. Spinal neurons projecting to nucleus dorsomedialis are localized bilaterally at the medial side of the dorsal horn. Following injections in nucleus ventrolateralis, labeled neurons were found bilaterally in area VII and VIII, whereas nucleus dorsolateralis and nucleus intermediodorsalis receive a bilateral input mainly from areas V and VI.

Acid-base regulation during heating and cooling in the lizard, Varanus exanthematicus.

Current concepts of acid-base balance in ectothermic animals require that arterial pH vary inversely with body temperature in order to maintain a constant OH-/H+ and constant net charge on proteins. The present study evaluates acid-base regulation in Varanus exanthematicus under various regimes of heating and cooling between 15 and 38 degrees C. Arterial blood was sampled during heating and cooling at various rates, using restrained and unrestrained animals with and without face masks. Arterial pH was found to have a small temperature dependence, i.e., pH = 7.66--0.005 (T). The slope (dpH/dT = -0.005), while significantly greater than zero (P less than 0.05), is much less than that required for a constant OH-/H+ or a constant imidazole alphastat (dpH/dT congruent to 0.018). The physiological mechanism that distinguishes this species from most other ectotherms is the presence of a ventilatory response to temperature-induced changes in CO2 production and O2 uptake, i.e., VE/VO2 is constant. This results in a constant O2 extraction and arterial saturation (approx. 90%), which is adaptive to the high aerobic requirements of this species.

Evolution of glucose induced hyperglycemia during the annual cycle of a sahelian lizard ( Varanus exanthematicus)

During the ecophysiological cycle of Varanus exanthematicus: 1. 1. Normoglycemia can be defined only by referring to each period of the ecophysiological cycle. 2. 2. Intravenous injection of glucose (0.6 g/kg body weight) induces an immediate and durable hyperglycemia. (a) V. exanthematicus shows a glucose tolerance which can be compared to that reported in other lizards (for a duration of 48 hr). (b) Between the two characteristic periods of the ecophysiological cycle, significant differences have been found at the beginning of the response to induced hyperglycemia: the lizards captured in October (nourishment period) present a glucose cellular assimilation slower and less efficient than that of animals captured in December (beginning of the starvation period) or February (middle period of starvation), (c) The lizards captured in June (transition between starvation and nourishment period) show variables responses. 3. 3. Our results concerning the glycemie regulation in V. exanthematicus are compared to those reported by different authors in other Lizards.

Seasonal variations of immunoreactive glucagon contents in pancreatic extracts of a sahelian lizard ( Varanus exanthematicus)

1. 1. The immunoreactive glucagon contents were estimated in the whole pancreas as well as in the cranial, medial and caudal parts throughout the year. 2. 2. We have determined if there is any relationship between the evolution of the glucagon content and the annual ecophysiological cycle of the animal. We found: A bimodal profile of the pancreatic glucagon levels: the maximal values observed during starvation, the minimal ones during the food intake period. A cephalo-caudal gradient of concentration of the pancreatic glucagon content. A difference in the evolution of dynamic transfers between cranial and medio-caudal parts. 3. 3. The results were compared with those reported for different species and the accent is on the anatomical and functional disparity between the different parts of the pancreas, suggesting a possible interaction between these different parts.

Seasonal variations of immunoreactive insulin contents in pancreatic extracts of a sahelian lizard ( Varanus exanthematicus)

1. 1. The immunoreactive insulin contents are estimated in the whole pancreas as well as in the cranial, medial and caudal parts all over the year. 2. 2. We have tried to determine if there is any relationship between the evolution of the insulin content and the annual ecophysiological cycle of the animal. This has permitted us to find: (a) An unimodal profile of the pancreatic insulin levels: the maximal values can be observed during the nourishment period, the minimal ones during starvation, (b) A cephalo-caudal gradient of concentration of the pancreatic insulin content (the maximal values located in the caudal part). 3. 3. The present results were compared with those reported for different species especially the action of insulin in the reptelian glucidic metabolism.

Cells of origin of pathways descending to the spinal cord in some quadrupedal reptiles.

The cells of origin of pathways descending to the spinal cord have been determined in several quadrupedal reptiles, viz., the turtle Pseudemys scripta elegans and Testudo hermanni and the lizards Tupinambis nigropunctatus and Varanus exanthematicus, following a technique introduced by Kuypers and Maisky ('75). This technique was very effective in producing retrograde transport of HRP to a great many neurons in the hypothalamus and in the brain stem. Projections from the hypothalamus (the nucleus paraventricularis and the nucleus periventricularis hypothalami), the interstitial nucleus of the film, the nucleus ruber, the nucleus of Edinger-Westphal, the locus coeruleus, the subcoeruleus area, a conspicuous cell group comparable to Kuypers and Maisky's (75, '77) lateral pontine area, the magnocellular reticular formation, the ventrolateral, ventromedial, and descending vestibular nuclei, the dorsal motor nucleus of the vagus, and the nucleus of the solitary tract, reach at least as far as the lumbar intumescence. Projections from two somatosensory nuclei, i.e., the nucleus descendens nervi trigemini and the nucleus funiculi dorsalis, as well as the laminar nucleus of the torus semicircularis, have been demonstrated to at least the ninth spinal segment. The two deep cerebellar nuclei, particularly the medial cerebellar nucleus, were found to project contralaterally to the spinal cord, in the lizard Varanus exanthematicus at least as far as the seventh segment; in the turtles studied so far, only projections as far caudal as the fourth spinal segment could be demonstrated. Data on the funicular trajectory of various descending pathways could also be obtained. It seems likely that in the reptiles studied, in addition to rubrospinal and reticulospinal pathways, projections from the hypothalamus, the nucleus of Edinger-Westphal, the cell group comparable to the mammalian lateral pontine area, the locus coeruleus, and subcoeruleus area, and the nucleus of the solitary tract pass via the lateral funiculus. The pathways descending from the hypothalamus and brain stem to the spinal cord in the quadrupedal reptiles studied appear to show remarkable similarities to pathway in mammals as regards their cells of origin as well as their funicular trajectory. It seems likely that some of the projections demonstrated, viz., from the locus coeruleus, at least part of the cell group comparable to the lateral pontine area, as well as the cells in and around the dorsal motor nucleus of the vagus, are noradrenergic pathways.

Chemical control of breathing in the lizard, Varanus exanthematicus

1. 1. In Varanus exanthematicus, alterations of inspired and end-tidal gas pressures resulted in rapid ventilatory responses. This, as well as other physiological characteristics, contributes to a homeostatic ability unusual for a reptile. 2. 2. In contrast to the lizard Lacerta, the varanid showed a positive ventilatory response to hypoxia. 3. 3. Whereas CO 2 breathing depressed breathing frequency in other lizards, both tidal volume and frequency increased in Varanus. 4. 4. End-tidal P co2 increased significantly after feeding, presumably compensating for an alkaline “tide” of digestion. The increased end-tidal P co2 not due to a decrease in ventilation.

Aerobic metabolism of the lizardVaranus exanthematicus: Effects of activity, temperature, and size

Oxygen consumption $$(\dot V_{O_2 } )$$ was measured at rest and during spontaneous activity at body temperatures of 25 and 35°C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25°C and body weight (W) is given by: $$\dot V_{O_2 }$$ (ml O2 STPD·g−1·hr−1)=0.88W −0.43 (Fig. 2). Although statistical comparisons are equivocal, this intraspecific size dependence exceeds that reported for interspecific comparisons among reptiles and other vertebrate groups (Fig 3). A reproducible diurnal pattern of activity was observed in undisturbed animals with minimum values of $$\dot V_{O_2 }$$ between 2400 and 0800 h (Fig. 1). Spontaneous activity and $$\dot V_{O_2 }$$ generally reached peak values between 1200 and 2000 hrs. The average ratio of active aerobic metabolic rate (AMR) to minimum (standard) aerobic metabolic rate (SMR) was 8.2. This voluntary AMR/SMR inVaranus exceeds the AMR/SMR for most reptiles stimulated to exhaustion. The high aerobic capacity is consistent with other evidence for efficient exchange and transport of respiratory gases inV. exanthematicus; e.g., low or absent intracardiac shunt flow resulting in high arterial saturation and low ventilation $$(\dot V/\dot V_{O_2 } )$$ and perfusion $$(\dot Q/\dot V_{O_2 } )$$ requirements.

Estimation of shunting, systemic and pulmonary output of the heart, and regional blood flow distribution in unanaesthetized lizards (Varanus exanthematicus) by injection of radioactively labelled microspheres.

Circulatory parameters in a lizard (Varanus exanthematicus) were determined using the microsphere method. Microspheres (MS) (slightly larger than the erythrocytes and labelled with different gamma-emitting isotopes) were injected into a pulmonary vein or the left atrium for determination of the left-to-right (L-R) shunt and the regional distribution of the ventricular systemic output. Injections were also made into the sinus venosus for determination of the right-to-left (R-L) shunt. The relative blood flow was obtained as the ratio of the MS activity found in the various tissues over the total activity injected. Absolute calibration of the method was performed by introduction of an 'artificial organ' into the circulatory system (Hales, 1973). Ventricular systemic output (VSO), in five animals, averaged 121 ml/ (min.kg) and ventricular pulmonary output 119 ml/(min. kg). The value of VSO was significantly higher than those observed in other lizard species. In all experimental animals both R-L as well as L-R shunting of various extent occurred. The reliability of the microsphere method as applied in lizards is discussed and is considered to be relatively accurate even under conditions of incomplete mixing of shunted and unshunted blood in systemic heart output.

Effects of temperature on respiration and acid-base balance in a monitor lizard

Ventilation, gas exchange, blood gas tensions and arterial pH were measured simultaneously in monitor lizards,Varanus exanthematicus. In contrast to previously studied poikilotherms, the arterial pH is independent of body temperature within the normally encountered temperature range (Fig. 1). This exception to the relative alkalinity concept (Rahn, 1966) is correlated with the finding thatV. exanthematicus maintains a constant ratio of ventilation to oxygen uptake (and CO2 production) at different temperatures (Fig. 3). The increase in arterial $$P_{{\text{CO}}_{\text{2}} }$$ (Fig. 1) is related to an increase in physiological dead space; i.e., alveolar ventilation increases less with temperature than total ventilation (Fig. 4). This may result from the increased frequency of breathing which results in a reduced breath holding time (Fig. 2). Varanid lizards have a higher oxygen requirement than other reptiles. This is reflected in the control of ventilation, the specialized lung morphology, the high arterial saturation due to low intracardiac shunting, pH regulation and other mammal-like features ofVaranus.

Effect of fasting upon insulin secretion in the rat.

Effect of fasting upon insulin secretion in the rat.

FACTORS AFFECTING THE INSULIN CONTENT OF THE PANCREAS

ArticlesFACTORS AFFECTING THE INSULIN CONTENT OF THE PANCREASR. E. HaistR. E. HaistPublished Online:01 Oct 1944https://doi.org/10.1152/physrev.1944.24.4.409MoreSectionsPDF (6 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited BySeasonal variations of immunoreactive insulin contents in pancreatic extracts of a sahelian lizard (Varanus exanthematicus)Comparative Biochemistry and Physiology Part A: Physiology, Vol. 69, No. 4Segmental venous drainage of the canine pancreasJournal of Surgical Research, Vol. 11, No. 11Insulin patterns prior to and after onset of diabetesMetabolism, Vol. 18, No. 9Extractable insulin and glucagon from turtle's (Chrysemys d'orbignyi) pancreasComparative Biochemistry and Physiology, Vol. 27, No. 2Studies in experimental diabetesThe American Journal of Medicine, Vol. 7, No. 5 More from this issue > Volume 24Issue 4October 1944Pages 409-444 https://doi.org/10.1152/physrev.1944.24.4.409History Published online 1 October 1944 Published in print 1 October 1944 Metrics