Lizard Varanus Exanthematicus Research Articles

Locomotor rib kinematics in two species of lizards and a new hypothesis for the evolution of aspiration breathing in amniotes

Most lizards walk and run with a sprawling gait in which the limbs are partly advanced by lateral undulation of the axial skeleton. Ribs and vertebrae are integral to this locomotor mode, but 3D motion of the axial skeleton has not been reported for lizard locomotion. Here, we use XROMM to quantify the relative motions of the vertebrae and ribs during slow treadmill locomotion in three savannah monitor lizards (Varanus exanthematicus) and three Argentine black and white tegus (Salvator merianae). To isolate locomotion, we selected strides with no concurrent lung ventilation. Rib rotations can be decomposed into bucket-handle rotation around a dorsoventral axis, pump-handle rotation around a mediolateral axis, and caliper rotations around a craniocaudal axis. During locomotion, every rib measured in both species rotated substantially around its costovertebral joint (8–17 degrees, summed across bucket, pump and caliper rotations). In all individuals from both species, the middle ribs rotated cranially through bucket and pump-handle motion during the propulsive phase of the ipsilateral forelimb. Axial kinematics during swing phase of the ipsilateral forelimb were mirror images of the propulsive phase. Although further work is needed to establish what causes these rib motions, active contraction of the hypaxial musculature may be at least partly responsible. Unilateral locomotor rib movements are remarkably similar to the bilateral pattern used for lung ventilation, suggesting a new hypothesis that rib motion during locomotion may have been an exaptation for the evolution of costal aspiration breathing in stem amniotes.

Responses by Juvenile Savannah Monitor Lizards (Varanus exanthematicus) to Chemical Cues from Animal Prey, Plants Palatable to Herbivores, and Conspecifics

Varanid lizards often tongue-flick in feeding and social contexts, but little is known regarding their abilities to identify a variety of prey using only chemical cues or to detect pheromones. We studied responses by juvenile Varanus exanthematicus to surface chemical stimuli from several animal taxa, two plant species palatable to herbivorous lizards, and conspecifics, using diluted cologne and deionized water as pungency and odorless controls. In 60-sec trials with stimuli presented on cotton swabs, lizards showed stronger responses to prey stimuli from mouse, cricket, earthworm, and a gekkonid lizard than to control stimuli. These findings suggest that the lizards are able to locate and identify prey from a wide variety of taxa, which would be adaptive for a generalist predator. Only mouse and cricket stimuli induced a greater proportion of individuals to bite swabs than control stimuli. Because these prey were the laboratory diet, biting frequency may depend on familiarity with the prey. Like other tested insectivores and carnivores, V exanthematicus showed no signs of discriminative responses to plant chemicals. The lizards tongue-flicked in response to conspecific cues at a higher rate than to the odorless control but at a lower rate than to cues from a gekkonid lizard, indicating that conspecific cues were detected and discriminated from prey cues.

Patterns of cardiovascular and ventilatory response to elevated metabolic states in the lizard Varanus exanthematicus.

The principal function of the cardiopulmonary system is the precise matching of O(2) and CO(2) transport to the metabolic requirements of different tissues. In some ecothermic vertebrates (amphibians and reptiles), vdot (O2) increases dramatically following feeding. Factorial increments in vdot (O2) range from 1.7 to 44 times above resting rates, and in some cases vdot (O2) approaches or even exceeds values measured during physical activity. There is virtually no information on the cardiopulmonary response during the postprandial period in these animals or how the pattern of cardiopulmonary support compares with that during activity. In our experiments, pulmonary ventilation ( vdot e), heart rate (fh), systemic blood flow ( qdot (sys)), rate of oxygen consumption ( vdot (O2)) and rate of carbon dioxide production ( vdot (CO2)) were measured at 35 degrees C in the lizard Varanus exanthematicus for 24 h prior to the ingestion of meals of various sizes and measured continuously for up to 72 h during the postprandial period. The results of this study were compared with previously published values for treadmill exercise in the same experimental animals. The change in fh and stroke volume (V(S)) for a given increment in vdot (O2) did not differ during exercise and digestion. In contrast, the ventilatory response was very dependent on the nature of the elevated metabolic state. During digestion, an increase in vdot (O2) resulted in a relative hypoventilation in comparison with resting values, whereas hyperventilation characterized the response during activity. During exercise, breathing frequency (f) increased 10- to 40-fold above resting values accompanied by large reductions in tidal volume (V(T)). In contrast, postprandial increases in vdot (O2) resulted in relatively minor changes in f and V(T) almost doubled. These results indicate that, in these lizards, the cardiac response to elevated vdot (O2) is stereotyped, the response being predictable irrespective of the source of the metabolic increment. In contrast, the ventilatory response is flexible and state-dependent, not only in pattern but also in its frequency and volume components.

Herpetofaunal communities at Muni lagoon in Ghana

A herpetofaunal survey of Muni-Pomadze Lagoon, during the main rainy season (May–June), recorded a total of 32 species (13 amphibians and 19 reptiles). Three species are the first records for coastal habitats in Ghana: Kinixys homeana, Calabaria reinhardti, and Bothrophthalmus lineatus. None of the surveyed species are restricted to Ghana. The most diverse herpetofaunal community occurs in grassland thicket, with 26 species (81% of the sampled herpetofauna). Freshwater ponds include 12 species, while only three species (all amphibians) occur in brackish lagoons. Herpetofaunal conservation efforts at these sites should focus on protecting and monitoring grassland coastal thicket and freshwater ponds. Currently, freshwater pond habitats appear to be stable, but coastal thicket is being lost to provide new agricultural land at Muni. Hyperolius reedfrogs, pythons (Python regius) and monitor lizards (Varanus exanthematicus and V. niloticus) appear to offer the greatest potential for undertaking long-term monitoring of the coastal lagoon herpetofauna, because they can be more readily surveyed, and are likely to be sensitive to a broad range of environmental stressors.

Primary Structure of Hemoglobin from Monitor Lizard(Varanus exanthematicus albigularis -Squamata)

The primary structure of the major hemoglobin component from the Monitor Lizard Varanus exanthematicus albigularis is presented. The polypeptide subunits were separated by reversed-phase high-performance liquid chromatography on Nucleosil C-4 column. The amino-acid sequence was established by automatic Edman degradation of the native polypeptide and its tryptic and hydrolytic cleavage products in a spinning cup sequencer. The structural data are discussed with reference to other reptiles.

Synaptic connections between primary trigeminal afferents and accessory abducens motoneurons in the monitor lizard, Varanus exanthematicus.

We studied the anatomical pathway underlying the nictitating reflex in the monitor lizard Varanus exanthematicus by the anterograde degeneration technique combined with retrograde transport of horseradish peroxidase (HRP) and electron microscopy. After application of HRP to the abducens nerve, retrogradely labeled neurons were observed in the ipsilateral principal and accessory abducens motor nuclei. The transection, in the same experiments, of the root of the trigeminal nerve resulted in massive degeneration of myelinated fibers in the descending trigeminal tract. In the ipsilateral accessory abducens nucleus, we observed electron-dense degenerating axon terminals that formed asymmetric synaptic contacts with the primary and secondary dendrites of large neurons retrogradely labeled with HRP. A few of the degenerating terminals could be traced in serial sections to myelinated axons. No terminal degeneration was found in the contralateral accessory abducens nucleus or in the ipsilateral and contralateral principal abducens nuclei. The present results are complementary with the findings of previous light microscopic experimental tracing studies (Barbas-Henry, H.A., and A.H.M. Lohman, J. Comp. Neurol. 1986, 254:314-329; see also J. Comp. Neurol. 1988, 267:370-386), and strongly suggest the existence in Varanus of a monosynaptic, unilateral reflex pathway in which trigeminal fibers, presumably originating from the cornea, synapse with motoneurons of the bursalis and retractor bulbi muscles, which are located in the accessory abducens nucleus. This monosynaptic pathway may mediate a rapid unilateral eyeball retraction and nictitating membrane extension.

The fasciculus longitudinalis medialis in the lizard Varanus exanthematicus. 2. Vestibular and internuclear components.

In the present study the vestibular components of the fasciculus longitudinalis medialis (flm) were investigated in the lizard Varanus exanthematicus with various tracing techniques: anterograde transport of horseradish peroxidase to study vestibulo-oculomotor and vestibulospinal projections, the multiple retrograde fluorescent tracer technique for the cells of origin of such projections. Internuclear projections between the oculomotor and abducens nuclei could also be studied in this way. Rather extensive vestibulo-ocular projections passing via the flm were demonstrated. Mainly ipsilateral ascending projections arise in the dorsolateral vestibular nucleus, mainly contralateral ascending projections in the ventromedial vestibular nucleus and adjacent parts of the ventrolateral and descending vestibular nuclei. Furthermore, distinct bilateral ascending projections of the nucleus prepositus hypoglossi were demonstrated. Extensive vestibulospinal projections pass via the flm and form the medial vestibulospinal tract. This largely contralateral descending pathway arises predominantly in the ventromedial and descending vestibular nuclei. Terminal structures presumably arising in the ventromedial and descending vestibular nuclei were found on contralateral neurons, probably motoneurons innervating neck muscles. Vestibular neurons with both ascending (presumably to extra-ocular motoneurons) and descending projections to the spinal cord are present in all vestibular nuclei, although preferentially in the ventromedial vestibular nucleus and adjacent parts of the ventrolateral and descending vestibular nuclei. However, also in the dorsolateral vestibular nucleus a substantial number of double labeled neurons were found. These vestibular neurons with both vestibulomesencephalic and vestibulospinal projections are probably involved in combined movements of eyes and head. Evidence for reciprocal internuclear connections between the oculomotor and abducens nuclei was found. Neurons in the dorsal part of the oculomotor nucleus probably project to the ipsilateral abducens nucleus, while neurons in the abducens nucleus most likely project to the contralateral oculomotor nucleus. These reciprocal internuclear connections between the oculomotor and abducens nuclei probably play an important role in conjugate horizontal eye movements.

Distribution of serotonin in the brain stem and spinal cord of the lizard Varanus exanthematicus: An immunohistochemical study

The distribution of serotonin-containing nerve cell bodies, fibers and terminals in the lizard Varanus exanthematicus was studied with the indirect immunofluorescence technique, using antibodies to serotonin. Most of the serotonin-containing cell bodies were found in the midline, in both of the raphe nuclei, i.e. the nuclei raphes superior and inferior. A considerable number of more laterally shifted serotonergic neurons was found particularly at three levels of the brain stem, viz. in the caudal mesencephalic tegmentum, at the isthmic level, and over a long distance in the medulla oblongata. These laterally situated serotonin-positive neurons were partly found within the confines of the substantia nigra, the nucleus reticularis superior and the lateral part of the nucleus reticularis medius and ventrolateral part of the nucleus reticularis inferior, respectively. No serotonergic cell bodies were found in the spinal cord. In the brain stem a dense serotonergic innervation was observed in all of the motor nuclei of the cranial nerves, in two layers of the tectum mesencephali, in the nucleus interpeduncularis pars ventralis, the nucleus profundus mesencephali pars rostralis, the periventricular grey, the nucleus parabrachialis, the vestibular nuclear complex, the nucleus descendens nervi trigemini, the nucleus raphes inferior, and parts of the nucleus tractus solitarii. Descending serotonergic pathways could be traced into the spinal cord via the dorsolateral, ventral and ventromedial funiculi, and were found to innervate mainly three parts of the spinal grey throughout the spinal cord, i.e. the dorsal part of the dorsal horn, the motoneuron area in the ventral horn, and the intermediate zone just lateral to the central canal. The results obtained in the present study suggest a close resemblance of the organization of the serotonergic system in reptiles and mammals, especially as to the serotonergic innervation of the spinal cord.

Distribution of catecholamines in the brain stem and spinal cord of the lizard Varanus exanthematicus: An immunohistochemical study based on the use of antibodies to tyrosine hydroxylase

Antibodies to tyrosine hydroxylase were used to study the distribution of nerve cells, fibers and terminals, containing catecholamines, in the lizard Varanus exanthematicus, by means of the indirect immunofluorescence technique. Tyrosine hydroxylase-containing cell bodies occurred in the hypothalamus, the ventral and dorsal tegmentum mesencephali, the substantia nigra, the isthmic reticular formation, in and ventrolaterally to the locus coeruleus, in the nucleus tractus solitarii and in a lateral part of the nucleus reticularis inferior. In addition tyrosine hydroxylase-containing cell bodies were found throughout the spinal cord, ventral to the central canal. Tyrosine hydroxylase-immunoreactive terminal areas in the brain stem were seen in the nucleus interstitialis of the fasciculus longitudinalis medialis, the nucleus raphes superior, the locus coeruleus, several parts of the reticular formation and the nucleus descendens nervi trigemini. Ascending catecholaminergic pathways could be traced from the ventral mesencephalic tegmentum as well as from the dorsal isthmic tegmentum rostralwards, through the lateral hypothalamus. These pathways correspond to the mesostriatal and isthmocortical projections respectively, as described in mammals. Furthermore, ascending catecholaminergic fibers could be traced from the catecholaminergic cell groups in the medulla oblongata to the isthmus, where they intermingle with the locus coeruleus neurons. These pathways correspond to the medullohypothalamic projection and to the dorsal periventricular system in mammals. Descending catecholaminergic fibers to the spinal cord pass via the dorsomedial part of the lateral funiculus, and mainly terminate in the dorsal horn. The results obtained in the present study have been placed in a comparative perspective, which illustrates the constancy of catecholaminergic innervation throughout phylogeny.

The fasciculus longitudinalis medialis in the lizard Varanus exanthematicus. 1. Interstitiospinal, reticulospinal and vestibulospinal components.

With the horseradish peroxidase (HRP) technique the various descending components of the medial longitudinal fasciculus (flm) have been studied in the lizard Varanus exanthematicus. After wheat germ agglutinin conjugated HRP injections at the spinomedullary border, retrogradely labeled fibers passing via the flm could be traced to various parts of the magnocellular rhombencephalic reticular formation, the descending and ventromedial vestibular nuclei and the interstitial nucleus of the flm. By implanting HRP slow-release gels into the flm the trajectory and site of termination of various components of the flm have been analysed. The interstitiospinal tract passes via the dorsal part of the flm. Reticulospinal fibers arising in the nucleus reticularis superior and nucleus reticularis medius take a position ventral to the interstitiospinal fibers. Vestibulospinal projections via the flm are found in its ventral part and arise mainly in the contralateral ventromedial and descending vestibular nuclei. A strong vestibulocollic projection to cervical motoneurons should be noted. The positional relations of the various fiber components within the flm found in a lower vertebrate such as the lizard Varanus exanthematicus are comparable to those in mammals.

Ultrastructure of the exocrine pancreas in a sahelian reptile (Varanus exanthematicus) during starvation.

During the sahelian dry season (November to June) the lizard Varanus exanthematicus fasts, and during these 8 months its pancreatic acinar cells lack zymogen granules and show an inactive Golgi body and damaged mitochondria. The main peculiarity can be observed in the granular endoplasmic reticulum (GER): Each acinar cell posesses a great number of GER vesicles (mean diameter 0.15 μm) and a large spheroid GER resulting from either the nesting of some cisternae or the rolling up of a single cisternae on itself. Attention is focused on the possible relationship between this ultrastructure and alteration of protein metabolism.

Brainstem afferents to the thalamus in a lizard, Varanus exanthematicus.

HRP was injected into various thalamic nuclei in order to investigate the brainstem projections to the thalamus in the lizard Varanus exanthematicus. Nucleus dorsomedialis receives afferents from the septal area, nucleus entopeduncularis anterior, nucleus periventricularis hypothalami, area triangularis, nucleus raphes superior, nucleus reticularis inferior, and locus coeruleus. Nucleus dorsolateralis receives afferents from septal area, nucleus dorsomedialis, nucleus entopeduncularis anterior, nucleus periventricularis hypothalami, and the torus semicircularis. Nucleus rotundus receives an input from the tectum mesencephali, the pretectal area, and from the mesencephalic reticular formation. Nucleus intermedius dorsalis receives afferents from the dorsal column nuclei and nucleus periventricularis hypothalami. Nucleus ventrolateralis receives afferents from the dorsal column nuclei, the trigeminal complex, locus coeruleus, and the reticular formation. Nucleus ventromedialis also receives afferents from the trigeminal complex and the reticular formation. Afferents to the habenula have been demonstrated from the septal area, nucleus entopeduncularis anterior, triangular area, nucleus periventricularis hypothalami, nucleus interpeduncularis, nucleus raphes superior, locus coeruleus, nucleus isthmi, nucleus dorsalis motorius nervi vagi, and the mesencephalic tegmentum. The laminar part of the torus semicicularis projects to nucleus medialis.

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.

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.

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.

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.