Blood Oxygen Transport and Delivery in Reptiles

Cenozoic reptiles are characterized by physiological morphologicaland ecological systems with low energy requirements comparedto those of mammals. Ectothermy and low resting rates of metabolismare the primary physiological adaptations of reptiles that producelow energy demand. Adjustments of the oxygen-transport systemto different thermoregulatory characteristics among reptilesmay be reflected in blood viscosity oxygen capacity oxygen affinityand the temperature sensitivity of oxygenation. Other adaptationsreduce the energy cost of oxygen transport. Reptiles have lowhematocrits and large, widely spaced capillaries that contributeto a low fluid resistance in the vascular system but also limitthe oxygen transport capacity. The low oxygen affinity characteristicof the blood of most reptiles appears to facilitate diffusionof oxygen to the tissues, overcoming the intrinsic limitationsimposed by the morphological specializations of the cardiovascularsystem. The low blood oxygen affinity permits virtually allof the oxygen carried by the blood to be delivered to the tissuesduring periods of stress. It may also help to maintain a relativelyhigh arterial Po₂ even when a right-to-left shunt occurs inthe heart. Reptilian erythrocytes are capable of reducing methemoglobinrapidly. The high concentrations of methemoglobin and polymerizedhemoglobin that occur in vivo may indicate that these compoundshave a functional role. In their blood physiology as in otheraspects of their biology reptiles are specialized animals thatreflect selective forces quite different from those that haveshaped the evolution of mammals.     

Slow Breathing and Hypoxic Challenge: Cardiorespiratory Consequences and Their Central Neural Substrates

Controlled slow breathing (at 6/min, a rate frequently adopted during yoga practice) can benefit cardiovascular function, including responses to hypoxia. We tested the neural substrates of cardiorespiratory control in humans during volitional controlled breathing and hypoxic challenge using functional magnetic resonance imaging (fMRI). Twenty healthy volunteers were scanned during paced (slow and normal rate) breathing and during spontaneous breathing of normoxic and hypoxic (13% inspired O₂) air. Cardiovascular and respiratory measures were acquired concurrently, including beat-to-beat blood pressure from a subset of participants (N = 7). Slow breathing was associated with increased tidal ventilatory volume. Induced hypoxia raised heart rate and suppressed heart rate variability. Within the brain, slow breathing activated dorsal pons, periaqueductal grey matter, cerebellum, hypothalamus, thalamus and lateral and anterior insular cortices. Blocks of hypoxia activated mid pons, bilateral amygdalae, anterior insular and occipitotemporal cortices. Interaction between slow breathing and hypoxia was expressed in ventral striatal and frontal polar activity. Across conditions, within brainstem, dorsal medullary and pontine activity correlated with tidal volume and inversely with heart rate. Activity in rostroventral medulla correlated with beat-to-beat blood pressure and heart rate variability. Widespread insula and striatal activity tracked decreases in heart rate, while subregions of insular cortex correlated with momentary increases in tidal volume. Our findings define slow breathing effects on central and cardiovascular responses to hypoxic challenge. They highlight the recruitment of discrete brainstem nuclei to cardiorespiratory control, and the engagement of corticostriatal circuitry in support of physiological responses that accompany breathing regulation during hypoxic challenge.     

Temperature Effects on Locomotion and Activity Bioenergetics of Amphibians, Reptiles, and Birds

1) Large temperature differences have a measurable effect onectothermic power consumption both at rest and during locomotion,yet this question remains to be satisfactorily addressed inecological studies looking at optimal foraging strategy andperformance. 2) Acclimation may influence the enzyme complementpresent in ectotherms and this could influence the energeticcost and efficiency of locomotion for ectotherms. 3) There maybe an optimal temperature for ectothermic locomotion and thismay vary from species to species, yet we measure power consumptionduring locomotion uniformly at 30°C. 4) Endothermic locomotionas demonstrated by birds is temperature sensitive, as was shownby Paladino and King (1984). Although the locomotory cost maynot change, thermoregulatory adaptations allow the bird to usethe heat produced during locomotion in the cold to reduce thermoregulatorypower requirements. 5) Avian hypothermia and inactivity is nota last ditch effort to save energy, but a strategy that allowsendotherms to conserve energy reserves during inactivity orstressful environmental conditions.     

The Effect of Adding CO2 to Hypoxic Inspired Gas on Cerebral Blood Flow Velocity and Breathing during Incremental Exercise

Hypoxia increases the ventilatory response to exercise, which leads to hyperventilation-induced hypocapnia and subsequent reduction in cerebral blood flow (CBF). We studied the effects of adding CO₂ to a hypoxic inspired gas on CBF during heavy exercise in an altitude naïve population. We hypothesized that augmented inspired CO₂ and hypoxia would exert synergistic effects on increasing CBF during exercise, which would improve exercise capacity compared to hypocapnic hypoxia. We also examined the responsiveness of CO₂ and O₂ chemoreception on the regulation ventilation (E) during incremental exercise. We measured middle cerebral artery velocity (MCAv; index of CBF), E, end-tidal PCO₂, respiratory compensation threshold (RC) and ventilatory response to exercise (E slope) in ten healthy men during incremental cycling to exhaustion in normoxia and hypoxia (FIO₂ = 0.10) with and without augmenting the fraction of inspired CO₂ (FICO₂). During exercise in normoxia, augmenting FICO₂ elevated MCAv throughout exercise and lowered both RC onset andE slope below RC (P<0.05). In hypoxia, MCAv and E slope below RC during exercise were elevated, while the onset of RC occurred at lower exercise intensity (P<0.05). Augmenting FICO₂ in hypoxia increased E at RC (P<0.05) but no difference was observed in RC onset, MCAv, or E slope below RC (P>0.05). The E slope above RC was unchanged with either hypoxia or augmented FICO₂ (P>0.05). We found augmenting FICO₂ increased CBF during sub-maximal exercise in normoxia, but not in hypoxia, indicating that the ‘normal’ cerebrovascular response to hypercapnia is blunted during exercise in hypoxia, possibly due to an exhaustion of cerebral vasodilatory reserve. This finding may explain the lack of improvement of exercise capacity in hypoxia with augmented CO₂. Our data further indicate that, during exercise below RC, chemoreception is responsive, while above RC the ventilatory response to CO₂ is blunted.     

Blood Parasites of Some Reptiles of the Pacific Northwest

SYNOPSIS. Three hundred and fifty-seven reptiles belonging to 15 species (11 genera, 7 families) from the Pacific Northwest were examined for haematozoa. Twenty-six (7.3%) had parasites. Eleven (3.1%) were infected with haemogregarines, 6 (1.7%) with microfilariae and 9 (2.5%) with unidentified organisms. Four species of snakes and 4 of lizards were positive. Several forms of haemogregarine from the Pacific gopher snake ( Pituophis melanoleucus catenifer ) are described.     

Wrist Skin Temperature,Motor Activity,and Body Position as Determinants of the Circadian Pattern of Blood Pressure

Although the circadian blood pressure (BP) pattern has been extensively studied, the determinants of this rhythm are not fully understood. Peripheral vasodilatation is a regulatory mechanism for BP maintenance. However, it remains to be established whether the increase of nocturnal distal skin temperature associated with heat loss could also reflect the dipping status. For the first time, this paper investigates the relationship between BP and skin wrist temperature (WT), to evaluate whether the WT circadian rhythm can serve as screening procedure to detect dipping/non-dipping BP patterns. In addition, the authors compare the relationship between WT and other variables previously described as determinants of the BP pattern, such as physical activity and body position. Measurements of WT, motor activity, and body position for 5 d, plus ambulatory BP for 24-h during that span, were obtained from 28 diurnally active normotensive volunteers. WT was negatively correlated, whereas activity and body position were positively correlated, with systolic and diastolic BPs. However, these relationships were stronger during the rest than activity phase. In addition, a 78.6% concordance was detected between the observed dips in BP and the predicted BP pattern calculated based on the WT rhythm. Thus, these results suggest that the increase in WT produced by heat loss during the rest phase through peripheral skin blood vessels is the result of blood vessel vasodilatation reflexes in response to a shift from a standing to a supine position, together with shift in the circadian sympathetic/parasympathetic balance (nocturnal parasympathetic activation). In conclusion, WT could be considered as a potential new screening procedure to implement the diagnosis of non-dipping BP pattern. (Author correspondence: angerol@um.es)     

温度依赖型性别决定在爬行动物中的研究进展

爬行动物性别决定方式主要有遗传依赖型性别决定(genetic sex determination,GSD)和环境依赖型性别决定(environmental sex determination,ESD),而ESD又以温度依赖型性别决定(temperature sex determination,TSD)为主。研究爬行动物TSD有助于人们弄清楚环境条件对物种表型的影响,从而更好地利用环境条件和遗传基础的共同机制来人为的改善或者诱导具TSD型物种的进化方向,以实现自然和人类的最大利益。该篇综述从母系活动、气候变化(全球气候变暖)、类固醇以及TSD机制四个方面总结了近年来关于爬行动物TSD的最新研究。     

Episodic Breathing in Frogs: Converging Hypotheses on Neural Control of Respiration in Air Breathing Vertebrates

SYNOPSIS. The episodic, or intermittent, breathing of frogsand many ectothermic vertebrates results in important fluctuationsof arterial blood gases. This pattern of breathing differs fromthe rhythmic and continuous alternation of inspiration observedin most homeotherms, which maintain O₂ and CO₂ levels withinnarrow ranges. These differences in pattern of breathing indicatethat the respiratory control systems of ectotherms and homeothermsdiffer substantially. The results of recent studies using invitro brainstemspinal cord preparations of adult frogs and premetamorphictadpoles (Rana catesbeiana and Rana pipiens) demonstrate, however,that the mechanisms for rhythm generation and pattern formationdescribed previously for mammals are also key features of therespiratory control system of frogs. These findings thereforesupport the hypothesis that the respiratory control system ishighly conserved amongst air breathing vertebrates, whetherthey breathe continuously or episodically.     

An Intercontinental Analysis of Climate-Driven Body Size Clines in Reptiles: No Support for Patterns, No Signals of Processes

Climatic gradients impose clinal selection on animal ecological and physiological performance, often promoting geographic body size clines. Bergmann’s rule predicts that body size increases with decreasing environmental temperatures given the need to retain body-heat through adjustments of body-mass-to-surface-area ratio. This prediction generally holds for endotherms, but remains controversial for ectotherms. An alternative interpretation, the ‘resource rule’, suggests that food abundance, primary productivity and precipitation (which, unlike temperature, do not necessarily correlate with geography), drive body size clines. We investigate geographic variation in body size within 65 species of lizards and snakes (squamates) based on an intercontinental dataset (6,500+ specimens belonging to 56 Israeli species, and multiple populations of nine Liolaemus species from Argentina and Chile). Bergmann’s rule is only rarely supported by our data (in four species, 6 %), whereas six species (9 %) follow its converse (hence, it is unsupported in 94 % of cases). Similarly, size increases with resource abundance in only 12 species (18 %). Therefore, although neither of the rules is supported, factors suggested by the resource rule are better predictors of body size than temperature. Surprisingly, we show that some measures of the extent of a species’ climatic envelope do not affect the likelihood of it showing a size-climate relationship. We conclude that negative size-temperature associations are an exception rather than a generality among squamates.     

Control of Drosophila Blood Cell Activation via Toll Signaling in the Fat Body

The Toll signaling pathway, first discovered in Drosophila, has a well-established role in immune responses in insects as well as in mammals. In Drosophila, the Toll-dependent induction of antimicrobial peptide production has been intensely studied as a model for innate immune responses in general. Besides this humoral immune response, Toll signaling is also known to activate blood cells in a reaction that is similar to the cellular immune response to parasite infections, but the mechanisms of this response are poorly understood. Here we have studied this response in detail, and found that Toll signaling in several different tissues can activate a cellular immune defense, and that this response does not require Toll signaling in the blood cells themselves. Like in the humoral immune response, we show that Toll signaling in the fat body (analogous to the liver in vertebrates) is of major importance in the Toll-dependent activation of blood cells. However, this Toll-dependent mechanism of blood cell activation contributes very little to the immune response against the parasitoid wasp, Leptopilina boulardi, probably because the wasp is able to suppress Toll induction. Other redundant pathways may be more important in the defense against this pathogen.     

Maximum Body Temperature as a Parameter of Thermoregulation in Reptiles: Experience from a Statistical Evaluation Using the Common Adder (Vipera berus) as an Example

Biology Bulletin - The maximum body temperature has meaning as the upper limit of temperature tolerance. Our statistical analysis made it possible to identify five indicators of the maximum body...     

Voluntary and Involuntary Control of Breathing with Imposed Ventilation Parameters

To clarify the mechanisms of interaction between voluntary and involuntary control of respiratory movements in a waking human, respiratory patterns were studied during self-controlled artificial ventilation used in place of natural breathing. Seven subjects controlled both the duration of artificial inhalations and the flow rate of air at excess pressure, continuously adjusting their actions to obtain the sensation of comfortable breathing. At rest, pulmonary ventilation was higher during self-controlled artificial breathing than during natural breathing. This trend was also noted during exercise. A correlation was observed between the velocity of the movement that started air flow and the artificial ventilation volume (r = 0.91). During self-controlled artificial breathing, the subjects sometimes took natural breaths. Natural inhalations did not influence the beginning or end of an artificial inhalation. Information received from respiratory receptors was assumed to play a certain role in the self-control of artificial breathing.     

Dopaminergic Properties of Cultured Rat Carotid Body Chemoreceptors Grown in Normoxic and Hypoxic Environments

Abstract: Using dissociated carotid body (CB) cultures prepared from neonatal (postnatal days 5–7; P7) or juvenile (postnatal day 19–20; P20) rats, we compared catecholaminergic properties and mechanisms of O₂ sensing in glomus cells grown in normoxic (Nox; 20% O₂) and chronically hypoxic (CHox; 6% O₂) environments for up to 2 weeks. In Nox cultures, basal dopamine (DA) release, determined by HPLC and normalized to the number of tyrosine hydroxylase-positive glomus cells present, was similar for P7 and P20 cultures (∼0.3 pmol/1,000 cells/15 min) and was unaffected by culture duration (2 vs. 12 days). Acute hypoxia (5 and 10% O₂) caused a dose-dependent stimulation (6× and 3× basal, respectively) in DA release, that was inhibited by nifedipine (10 µ M ). DA release was also stimulated by high extracellular K⁺ (30 m M ) and iberiotoxin (200 n M ), a selective blocker of P o ₂-regulated, Ca-dependent K⁺ channel in glomus cells. The stimulatory effect of iberiotoxin was similar to 5% O₂ in P20 cultures, but substantially less (about one-half) in P7 cultures. In contrast, in CHox cultures, basal DA release was substantially elevated, ∼8× Nox levels, although this did not correlate with significant differences in stores. Further, whereas acute hypoxia (5% O₂) and high K⁺ also stimulated DA release in CHox cultures (∼2× and ∼3× basal), iberiotoxin (200 n M ) did not. Thus, after chronic hypoxia in vitro, there is an enhanced basal catecholamine release and an apparent down-regulation of functional Ca-dependent K⁺ channels in CB chemoreceptors. These cellular adaptations may relate to changes in CB chemosensitivity during chronic hypoxemia.