Peripheral arterial chemoreceptors monitor the levels of arterial blood gases and adjust ventilation and perfusion to meet metabolic demands. These chemoreceptors are present in all vertebrates studied to date but have not been described fully in reptiles other than turtles. The goals of this study were to (1) identify functional chemosensory areas in the South American rattlesnake (Crotalus durissus), (2) determine the neurochemical content of putative chemosensory cells in these areas and (3) determine the role each area plays in ventilatory and cardiovascular control. To this end, rattlesnakes were instrumented with transonic flow probes, arterial catheters and subcutaneous impedance electrodes to measure shunt fraction, heart rate, blood pressure and ventilation. The catheters were placed at three putative chemosensory sites, the bases of the aortic arch and pulmonary artery, and the carotid bifurcation, for site-specific activation with sodium cyanide (NaCN). These same sites were subsequently examined using immunohistochemical markers for acetylcholine, tyrosine hydroxylase (the rate-limiting enzyme in catecholamine synthesis) and serotonin to identify putative oxygen-sensing cells. All three sites were chemosensory and stimulating each led to cardiovascular (shunt fraction and heart rate) and respiratory adjustments although not in an identical fashion. All three chemosensory areas contained cells positive for serotonin; however, cells positive for vesicular acetylcholine transporter (VAChT) were found only in the aorta and pulmonary artery. We found no labelling for tyrosine hydroxylase at any site.

The effects of temperature on breathing pattern and oxygen consumption are being investigated in juvenile tortoises and compared to adults, in order to understand physiological adjustments of the respiratory system as related to body size, especially regarding the energetic expenditure associated with growth. We analyzed the breathing pattern and oxygen consumption of juvenile and adult red-footed tortoises (Chelonoidis carbonarius, Cryptodira: Testudinidae). The animals (N = 9; body mass ranging from 0.03 Kg to 2.5 Kg) were exposed to normoxic-normocarbic conditions using open respirometry in order to determine the breathing pattern and oxygen consumption in three different temperatures (15, 25, 35 °C). The obtained results showed intermittent breathing pattern in all tested temperatures in juveniles and adults. Tidal volume was not affected by changes in temperature, while breathing frequency increased significantly with increasing temperature, leading to a significant increment in minute ventilation between 15 and 35 °C. Mass specific oxygen consumption increased significantly with temperature and juveniles showed greater values when compared to adults. The alterations in the ventilatory response to temperature changes occurred in order to maintain the oxygen supply with increased metabolic activity. The differences between juveniles and adults in breathing frequency lead to juveniles needing a lower ventilation rate to perform gas exchange while extracting more oxygen. While these differences might be attributed to a greater metabolic expenditure during development, scaling effects on respiratory variables might be the main contributors to the found differences.

In humans, physical exercise imposes narrower limits for the heart rate (fH) response of the baroreflex, and vascular modulation becomes largely responsible for arterial pressure regulation. In undisturbed reptiles, the baroreflex-related fH alterations at the operating point (Gop) decreases at elevated body temperatures (Tb) and the vascular regulation changes accordingly. We investigated how the baroreflex of rattlesnakes, Crotalus durissus, is regulated during an activity at different Tb, expecting that activity would reduce the capacity of the cardiac baroreflex neural pathway to buffer arterial pressure fluctuations while being compensated by the vascular neural pathway regulation. Snakes were catheterized for blood pressure assessment at three different Tb: 15, 20 and 30 °C. Data were collected before and after activity at each Tb. Baroreflex gain (Gop) was assessed with the sequence method; the vascular limb, with the time constant of pressure decay (τ), using the two-element Windkessel equation. Both Gop and τ reduced when Tb increased. Activity also reduced Gop and τ in all Tb. The relationship between τ and pulse interval (τ/PI) was unaffected by the temperature at resting snakes, albeit it reduced after activity at 20 °C and 30 °C. The unchanged τ/PI and normalized Gop at different Tb indicated those variables are actively adjusted to work at different fH and pressure conditions at rest. Our data suggest that during activity, the baroreflex-related fH response is attenuated and hypertension is buffered by a disproportional increase in the rate which pressure decays during diastole. This compensation seems especially important at higher Tb where Gop is already low.

To characterise the effect of two common induction agents, propofol and alfaxalone, on mean arterial blood pressure (MAP) and heart rate (HR), we equipped 19 adult South American rattlesnakes (Crotalus durissus) with an indwelling arterial catheter approximately 24 h prior to recording of baseline resting values. Then, seven snakes received alfaxalone (15 mg kg(-1)) intravascularly (IV) through the catheter, while groups two and three (both n = 6) received propofol (15 mg kg(-1) IV). The first two groups were not handled, while the group 3 was manually restrained for 2 min for a mock injection of 0.2 ml saline into the ventral tail vein. Baseline HR was similar in all groups and handling caused a significant tachycardia (p = 0.031) in group three. When given IV to undisturbed animals, both propofol and alfaxalone induced a significant increase in HR (p = 0.0022 and p = 0.0045, respectively) lasting approximately 30 min, but with values only significantly exceeding baseline for the first 5 min for propofol and the first 10 min with alfaxalone. Handling caused a significant increase in MAP (p = 0.0313). Propofol did not affect MAP (p = 0.1064), while alfaxalone caused a marked hypertension (although only significant at 2 min; p = 0.031). Manual restraint significantly increases both HR and MAP, which may lead to a masking of true cardiovascular effects of anaesthetic agents.

Ventilation and gas exchange have been studied in relatively few species of snakes, especially regarding their response to environmental hypoxia or hypercarbia. We exposed Crotalus durissus (N = 6) and Boa constrictor (N = 6) to decreasing levels of oxygen (12, 9, 6, 3 % O2) and increasing levels of carbon dioxide (1.5, 3.0, 4.5, 6.0 % CO2) and analyzed the effect of the different gas mixtures on ventilation and gas exchange using open-flow respirometry. Neither hypoxia nor hypercarbia significantly altered the duration of expiration or inspiration, nor their proportions. Both hypoxia and hypercarbia increased minute ventilation, but the decrease in oxygen had a less pronounced effect on ventilation. Gas exchange under normoxic conditions was low and was not significantly affected by hypoxia, but hypercarbia decreased gas exchange significantly in both species. While B. constrictor maintained its respiratory exchange ratio (RER) under hypercarbia between 0.5 and 1.0, C. durissus showed a RER above 1.0 during hypercarbia, due to a significantly greater CO2 excretion. The overall responses of both species to hypercarbia and especially to hypoxia were very similar, which could be associated to similar lifestyles as ambush hunting sit-and-wait predators that are able to ingest large prey items. The observed differences in gas exchange could be related to respiratory systems with macroscopically different structures, possessing only a tracheal lung in C. durissus, but two functional lungs in B. constrictor.

When snakes digest large meals, heart rate is accelerated by withdrawal of vagal tone and an increased non-adrenergic-non-cholinergic tone that seems to stem from circulating blood-borne factors exerting positive chronotropic effects. To investigate whether this tonic elevation of heart rate impairs the ability for autonomic regulation of heart during digestion, we characterised heart rate responses to pharmacological manipulation of blood pressure in the snake Boa constrictor through serial injections of sodium nitroprusside and phenylephrine. Both fasting and digesting snakes responded with a robust tachycardia to hypotension induced by sodium nitroprusside, with digesting snakes attaining higher maximal heart rates than fasting snakes. Both fasting and digesting snakes exhibited small reductions of the cardiac chronotropic response to hypertension, induced by injection of phenylephrine. All heart rate changes were abolished by autonomic blockade with the combination of atropine and propranolol. The digesting snakes retained the capacity for compensatory heart rate responses to hypotension, despite their higher resting values, and the upward shift of the barostatic response curve enables snakes to maintain the cardiac limb of barostatic regulation for blood pressure regulation.

Vascular tone in the reptil-ian pulmonary vasculature is primarily under cholinergic, muscarinic control exerted via the vagus nerve. This control has been ascribed to a sphincter located at the arterial outflow, but we speculated whether the vascular control in the pulmonary artery is more widespread, such that responses to acetylcholine and electrical stimulation, as well as the expression of muscarinic receptors, are prevalent along its length. Working on the South American rattlesnake (Crotalus durissus), we studied four different portions of the pulmonary artery (truncus, proximal, distal, and branches). Acetylcholine elicited robust vaso-constriction in the proximal, distal, and branch portions, but the truncus vasodilated. Electrical field stimulation (EFS) caused contrac-tions in all segments, an effect partially blocked by atropine. We identified all five subtypes of muscarinic receptors (M1-M5). The expression of the M1 receptor was largest in the distal end and branches of the pulmonary artery, whereas expression of the musca-rinic M3 receptor was markedly larger in the truncus of the pulmonary artery. Application of the neural tracer 1,1'-dioctadecyl-3,3,3',3'- tetramethylindo-carbocyanine perchlorate (DiI) revealed widespread innervation along the whole pulmonary artery, and retrograde trans-port of the same tracer indicated two separate locations in the brainstem providing vagal innervation of the pulmonary artery, the medial dorsal motor nucleus of the vagus and a ventro-lateral location, possibly constituting a nucleus ambiguus. These results revealed parasympathetic innervation of a large portion of the pulmonary artery, which is responsible for regulation of vascular conductance in C. durissus, and implied its integration with cardiorespiratory control.

Reptiles typically heat faster than they cool, and this thermal hysteresis is believed to derive from physiological mechanisms that modulate heat exchange with the environment through changes in thermal conductance. The vascular system, by means of autonomic regulation, is proposed to affect thermal conductance of reptiles by two mechanisms: (1) adrenergic (i.e., sympathetic) control of the peripheral vasculature through n-adrenergic receptors is suggested to be of paramount importance by increasing skin perfusion during heating and reducing perfusion during cooling; (2) cholinergic (i.e., parasympathetic) control of pulmonary blood flow through the vagus nerve supposedly serves to shunt blood away from pulmonary circulation to avoid heat loss over respiratory surfaces. We investigated the efficacy of heat exchange during warming and cooling in South American rattlesnakes (Crotalus durissus) before and after pharmacological n-adrenergic blockage through phentolamine injection, as well as with and without the ability to control pulmonary blood flow. Snakes were free to thermoregulate throughout the whole experiment using an intermittent heating source (on:off = 12:12 h) in a walk-in climatic chamber at a constant room temperature of 16=C (thermal gradient when heating source was turned on was 18 degrees C). All snakes warmed faster than they cooled and behaviorally thermoregulated to maintain body temperature (T-b) at approximately 28-30 degrees C. Neither sympathetic modulation of peripheral vascular resistance nor cardiac shunt control caused differences in warming and cooling rates. In a parallel experiment, coiling behavior was demonstrated to have a small but significant effect on snake thermal dynamics, albeit insufficient to explain the large thermal hysteresis observed. These results indicate that thermal hysteresis in rattlesnakes is not significantly affected by autonomic regulation of blood flow distribution. However, other physiological mechanisms must be important components of body temperature regulation in the South American rattlesnake.

Embryonic turtles have four distinct vascular beds that separately perfuse the developing embryo's body and the extra-embryonic yolk sac, amnion and chorioallantoic membrane (CAM). The mechanisms enabling differential regulation of blood flow through these separate beds, in order to meet the varying demands of the embryo during development, is of current interest. The present investigation followed the changes in blood flow distribution during an acute exposure to hypoxia and after α-adrenergic blockade. We monitored heart rate (fH), mean arterial pressure (Pm), and determined relative blood flow distribution (%Q̇sys) using colored microspheres. At 70% and 90% of the incubation period hypoxia elicited a bradycardia without changing Pm while %Q̇sys was altered only at 70%, increasing to the CAM and liver. Blockade of α-adrenergic responses with phentolamine did not change fH or Pm but increased %Q̇sys to the shell. These results show the capacity of embryos to redistribute cardiac output during acute hypoxia, however α-adrenergic receptors seemed to play a relatively small role in embryonic cardiovascular regulation.

Orthostatic hypotension is a phenomenon triggered by a change in the position or posture of an animal, from a horizontal to a vertical head-up orientation, characterised by a blood pooling in the lower body and a reduction in central and cranial arterial blood pressure (PA). This hypotension elicits systemic vasoconstriction and tachycardia, which generally reduce blood pooling and increase PA. Little is known about the mediation and importance of such cardiovascular adjustments that counteracts the haemodynamic effects of orthostasis in ectothermic vertebrates, and some discrepancies exist in the knowledge available on this subject. Thus, we sought to expand the knowledge on this issue by investigating it in a more elaborate way, through an in vivo pharmacological approach considering temporal circulatory changes during head-up body inclinations in unanaesthetised Boa constrictor. To do so, we analysed temporal changes in PA, heart rate (fH) and cardiac autonomic tones associated with 30° and 60° inclinations, before and after muscarinic blockade with atropine, double blockade with atropine and propranolol, and α1-adrenergic blockade with prazosin. Additionally, the animals’ fH variability was analysed. The results revealed that, in B. constrictor: (1) the orthostatic-tachycardia is initially mediated by a decrease in cholinergic tone followed later by an increase in adrenergic tone, a pattern that may be evolutionarily conserved in vertebrates; (2) the orthostatic-tachycardia is important for avoiding intense decrease in PA at the beginning of body inclinations; and (3) α1-adrenergic orthostatic vasomotor responses are important for the maintenance of PA in satisfactory values during long-term inclinations.

Embryonic staging tables provide information to standardize embryological investigations and to subsidize discussions about evolution. We have established a developmental staging table for Iguana iguana iguana . The sample was composed of 142 embryos, incubated at a constant temperature and collected at regular intervals. Morphological features as pharyngeal arches, craniofacial structures, eyes, limbs, claws, pigmentation, scales and egg tooth were evaluated to determine development stages. The normal staging table includes 17 stages from oviposition to hatching, based on chronology and morphological external features. Stages from 1 to 27 occur before oviposition. Stage 28 was the first described, because all embryos presented limb bud anlage, key feature of the previous stage. We used pharyngeal arches and limb buds to describe the first stages; claws, genital papilla and scales to describe the middle stages; and pigmentation, size and egg tooth to describe the last stages. Incubation lasted approximately 2 months in a controlled environment. The results were similar to the data from other lizards, confirming the embryonic conservative pattern of the group.

The sequence method is an alternative to the traditional pharmacological approach (i.e., the Oxford technique) used to calculate baroreflex gain (G) in mammals. Although the sequence method assesses baroreflex by measuring spontaneous events of blood pressure regulation, the pharmacological method relies on the injection of vasoactive drugs that impact the baroreflex mechanism itself. The sequence method might be relevant for dynamic measurement of baroreflex modulation but it was never validated for vertebrates with low heart rate. Hence, we tested the sequence method in three species of reptiles and compared the results with those provided by the classic pharmacological method. G was similar between both methods and values correlated when parameters for the sequence method were set at delay 0 or 1 (i.e., the baroreflex system responds immediately to blood pressure changes or after 1 heartbeat). Calculation of the baroreflex effectiveness index was adequate at a minimum of 300 cycles and a delay of 1 for the three species. Therefore, the sequence method has been validated to investigate baroreflex regulation in reptiles, enabling studies during dynamic alterations in homeostasis.

Using long-term, remote recordings of heart rate (fH) on fully recovered, undisturbed lizards, we identified several components of heart rate variability (HRV) associated with respiratory sinus arrhythmia (RSA): 1.) A peak in the spectral representation of HRV at the frequency range of ventilation. 2.) These cardiorespiratory interactions were shown to be dependent on the parasympathetic arm of the autonomic nervous system. 3.) Vagal preganglionic neurons are located in discrete groups located in the dorsal motor nucleus of the vagus and also, in a ventro-lateral group, homologous to the nucleus ambiguus of mammals. 4.) Myelinated nerve fibers in the cardiac vagus enabling rapid communication between the central nervous system and the heart. Furthermore, the study of the progressive recovery of fH in tegu following anesthesia and instrumentation revealed that 'resting' levels of mean fH and reestablishment of HRV occurred over different time courses. Accordingly, we suggest that, when an experiment is designed to study a physiological variable reliant on autonomic modulation at its normal, resting level, then postsurgical reestablishment of HRV should be considered as the index of full recovery, rather than mean fH.

The electrocardiogram (ECG) reveals that heart chamber activation and repolarization are much faster in mammals and birds compared to ectothermic vertebrates of similar size. Temperature, however, affects electrophysiology of the heart and most data from ectotherms are determined at body temperatures lower than those of mammals and birds. The present manuscript is a review of the effects of temperature on intervals in the ECG of ectothermic and endothermic vertebrates rather than a hypothesis-testing original research article. However, the conclusions are supported by the inclusion of original data (Iguana iguana, N = 4; Python regius, N = 5; Alligator mississippiensis, N = 4). Most comparisons were of animals of approximately 1 kg. Compared to mammals and birds, the reptiles at 35-37 degrees C had 4 fold lower heart rates, 2 fold slower atrial and ventricular conduction (longer P- and QRS-wave durations), and 4 fold longer PR intervals (atrioventricular delay) and QT intervals (total ventricular repolarization). We conclude that the faster chamber activation in endotherms cannot be explained by temperature alone. Based on histology, we show that endotherms have a more compact myocardial architecture. In mammals, disorganization of the compact wall by fibrosis associates with conduction slowing and we suggest the compact tissue architecture allows for faster chamber activation. The short cardiac cycle that characterizes mammals and birds, however, is predominantly accommodated by shortening of the atrioventricular delay and the QT interval, which is so long in a 1 kg iguana that it compares to that of an elephant. (C) 2018 Elsevier Ltd. All rights reserved.

This study investigated the oxygen consumption of the putative oxygen conformer marbled swamp eel Synbranchus marmoratus during progressive hypoxia. Earlier studies have not reached an agreement on whether S. marmoratus is a conformer or a regulator. Our results support the view that S. marmoratus is an oxygen regulator, like most bony fishes.

The structure and function of crocodilian lungs are unique compared with those of other reptiles. We examined the extent to which this and the semi-aquatic lifestyle of crocodilians affect their respiratory mechanics. We measured changes in intratracheal pressure in adult and juvenile caiman (Caiman yacare) during static and dynamic lung volume changes. The respiratory mechanics of juvenile caiman were additionally measured while the animals were floating in water and submerged at 30, 60 and 90 deg to the water's surface. The static compliance of the juvenile pulmonary system (2.89 +/- 0.22 ml cmH(2)O(-1) 100 g(-1)) was greater than that of adults (1.2 +/- 0.41 ml cmH(2)O(-1) 100 g(-1)), suggesting that the system stiffens as the body wall becomes more muscular and keratinized in adults. For both age groups, the lungs were much more compliant than the body wall, offering little resistance to air flow (15.35 and 4.25 ml cmH(2)O(-1) 100 g(-1) for lungs, versus 3.39 and 1.67 ml cmH(2)O(-1) 100 g(-1) for body wall, in juveniles and adults, respectively). Whole-system dynamic mechanics decreased with increasing ventilation frequency (f(R)), but was unaffected by changes in tidal volume (V-T). The vast majority of the work of breathing was required to overcome elastic forces; however, work to overcome resistive forces increased proportionally with f(R). Work of breathing was higher in juvenile caiman submerged in water at 90 deg because of an increase in work to overcome both elastic and flow resistive forces. The lowest power of breathing was found to occur at high f(R) and low V-T for any given minute ventilation ((V) over dot(E)) in caiman of all ages.

A criação de crocodilianos possui grande potencial econômico. O presente estudo investigou a viabilidade econômica da criação de crocodilianos no estado de São Paulo em diferentes cenários (venda de 40 a 100 animais ao ano), com o objetivo de produzir matrizes e reprodutores para a renovação/formação de plantel de outras criações, através de análise de sensibilidade e também estocástica (simulação de Monte Carlo). Os resultados da análise de sensibilidade não mostraram favorabilidade desta atividade num horizonte de 15 anos, apresentando Valor Presente Lí­­quido (VPL) de R$-202.804,18. Contudo, a projeção de variáveis para uma análise de riscos (estocástica) possibilitou a sobrevivência da criação de crocodilianos sem grandes mudanças e baixos custos para o produtor rural, revelando uma atividade de baixo risco e apontando a probabilidade elevada de retorno econômico.

Background.Ventilatory parameters have been investigated in several species of Testudines, but few species have had their ventilatory pattern fully characterized by presenting all variables necessary to understand changes in breathing pattern seen under varying environmental conditions.Methods.We measured ventilation and gas exchange at 25°C in the semi-aquatic turtle Trachemys scripta and the terrestrial tortoise Chelonoidis carbonarius under normoxia, hypoxia, and hypercarbia and furthermore compiled respiratory data of testudine species from the literature to analyze the relative changes in each variable.Results.During normoxia both species studied showed an episodic breathing pattern with 2-3 breaths per episode, but the non-ventilatory periods (T NVP ) were 3-4 times longer in T. scripta than in C. carbonarius.Hypoxia and hypercarbia significantly increased ventilation in both species and decreased T NVP and oxygen consumption in T. scripta but not in C. carbonarius.Discussion.Contrary to expectations, the breathing pattern in C. carbonarius did show considerable non-ventilatory periods with more than one breath per breathing episode, and the breathing pattern in T. scripta was found to diverge significantly from predictions based on mechanical analyses of the respiratory system.A quantitative analysis of the literature showed that relative changes in the ventilatory patterns of chelonians in response to hypoxia and hyperbarbia were qualitatively similar among species, although there were variations in the magnitude of change.

Body mass is one of the most influencing factors of metabolic rate and gas exchange of animals, and also related to activity pattern and occupancyof ecological niches. This study aimed to understand the relationships between body mass (MB) and morpho-functional features ofthe lungs of Iguana iguana, through morphological and morphometric characterization of the structural elements of the respiratory system.Iguana iguana has lungs of the transitional type, the heterogeneously distributed parenchyma being faveolar in cranial and medial regionsand trabecular in the caudal region. Within the parenchyma, 43.6 ± 25.5% corresponds to faveoli, 18.0 ± 5.9% to interfaveolar septa, and38.7 ± 31.6% to trabeculae. Within the interfaveolar septa, 9.4 ± 4.0% corresponds to blood capillaries, 4.4 ± 1.0% to type I pneumocytes And 3.9 ± 1.1% to type II pneumocytes. Allometric analyses showed that lung (MB 0.8949) and parenchymal volume (MB 1.030) scale with MB in I. iguana just as in other lizards with unicameral or transitional lungs, which was unexpected for lung volume, since reptilian lung volume is generally considered to scale as MB 0.75. The functional orphology of the lungs in I. iguana seems to play an important role to meet the metabolic demands through ontogenetic growth.