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At least 415 records · Page 23Linked to original sources
PubMed1985

Parietalectomy does not affect testicular growth in photoregulating lizards.

The testicular response of male anoles maintained at a constant 32 degrees C was similar in both parietalectomized and sham-parietalectomized lizards exposed to either constant light (40 lux intensity) or to photic gradients (40-300 lux). The results support the hypothesis that the acceleration of gonadal growth in parietalectomized lizards noted by others depends on the ability of lizards to self-regulate exposure to thermal, but not photic, stimuli.

Animals↗
PubMed1993

Regional differences in the dopaminergic regulation of cyclic AMP formation within the rat nucleus accumbens: comparison with the striatal complex of the lizard Gekko gecko.

Effects of dopamine D2 receptor activation on the forskolin or D1 receptor stimulated formation of cyclic adenosine monophosphate (cyclic AMP) were investigated in tissue slices of two subregions of the rat nucleus accumbens and in the striatal complex of a lizard. Cyclic AMP production in the tissue was estimated by measuring the conversion of [3H]adenine in a superfusion system. Activation of a D2 receptor appeared to inhibit the D1 receptor agonists or forskolin stimulated formation of cAMP in the rostrolateral but not in the caudomedial part of the rat nucleus accumbens. In the striatal complex of the lizard the formation of cAMP was dramatically stimulated by forskolin, but only marginally by dopamine. Neither the forskolin, nor the dopamine stimulated cyclic AMP formation could be inhibited by activation of D2 receptors. These findings are compatible with previously obtained functional data indicating that especially the caudomedial part of the rat nucleus accumbens has much in common with the striatal complex of the lizard.

Animals↗
PubMed1984

Fatty acid composition of lizard tissue lipids and the effects of estradiol on serum free fatty acids.

Fatty acid analyses of lipids from lizard fat bodies, carcass, and blood serum were performed by GLC. Principal fatty acids from all three tissues were palmitate (16:0), stearate (18:0), oleate (18:1), and linoleate (18:2). Administration of estradiol to vitellogenic or non-vitellogenic lizards increased serum levels of non-esterified fatty acids, but had no effect on the fat body wet weights. Lizards receiving estradiol had a higher proportion of arachidonate and a lower proportion of oleate in their serum non-esterified fatty acids.

Acclimatization↗
PubMed1991

Vitellogenin diversity in tropical lizards (Anolis pulchellus): identification and partial characterization.

1. Three size-classes of vitellogenin polypeptides were detected by electrophoretic and radiolabeling techniques in 32Pi-labeled plasma of vitellogenic female lizards but not in male animals. Based on their apparent Mr, the polypeptides were designated as VTG-226-201K, VTG-169-153K and VTG-116-123K. 2. Structural differences were found between VTG-169-153K and VTG-116K by partial proteolysis with S. aureus V8 protease and radiolabeling techniques. 3. Autoradiography of a 3-10% native gradient gel revealed three different species of VTG in 32Pi-labeled plasma of stimulated males: VTG-I (Mr = 850,000), VTG-II (Mr = 750,000) and VTG-III (Mr = 610,000). By 2D PAGE, it was shown that VTG-169K and VTG-116K are components of VTG-I, while VTG-153K and VTG-116K comprise VTG-III. These results suggest an oligomeric structure for native VTG. 4. Amino acid analysis, 32Pi incorporation, electrophoretical behavior and Mr estimation demonstrated homology between VTG-116K and the S1-lipovitellin from the lizard egg. 5. These results strongly indicate an unusual multiplicity of VTG forms in tropical lizards when compared to other egg-laying vertebrates.

Amino Acids↗
PubMed1995

Reactive neurogenesis during regeneration of the lesioned medial cerebral cortex of lizards.

This study reports that lesion of the adult lizard medial cortex (lizard hippocampal fascia dentata) induces a short period of intensive neurogenesis which we have termed reactive neurogenesis; a cell proliferation event that occurs in the subjacent ependyma. Specific lesion of the medial cortex was achieved by intraperitoneal injection of the neurotoxin 3-acetylpyridine and proliferating cells were detected using tritiated thymidine or 5-bromodeoxiuridine pulse labelling. After lesion, granule neurons in the lizard medial cortex cell layer appeared pyknotic and died; they were then removed and progressively replaced by a set of new neurons. These neurons were mostly generated from the second to the seventh day post-lesion. A dramatic temporal increment of labelled ependymal cells was detected when either tritiated thymidine or 5-bromodeoxiuridine pulses were delivered in that period. The maximum of about five thousand labelled cells per hemisphere was reached by the fourth day after the lesion. Beyond the seventh day post-lesion, the numbers of labelled cells returned to a level of about four hundred per hemisphere, similar to that of the control specimens. Electron microscopy revealed that the recently generated cells were neuroblasts or immature neurons with a characteristic pattern of chromatin condensation and a high number of ribonucleic granules.

Animals↗
PubMed1985

Involvement of platelet activating factor in physiological stress in the lizard, Anolis carolinensis.

Platelet activating factor (PAF) and 1-O-alkyl-linked choline-containing phosphoglycerides have been identified in the blood of the lizard, Anolis carolinensis. The level of PAF in the blood of chronically stressed lizards is 250% higher than in that of controls; the blood contains sufficient 1-O-alkyl-linked choline-containing phosphoglycerides to support the synthesis of PAF. Incorporation of PAF is higher in the liver than in the blood; control animals incorporate more PAF than chronically stressed animals. "Lyso"-PAF is the major metabolite in the blood; whereas, in the liver both "lyso"-PAF and "acyl"-PAF are predominant products. 1-Alkyl-2-acetyl-sn-glycero-3-phosphocholine:acetylhydrolase activity in the chronically stressed or corticosterone-implanted lizards is increased 2- to 3-fold over the control. Involvement of PAF in the physiological response to psychological stress is indicated.

Animals↗
PubMed2006

Calcium signaling in lizard red blood cells.

The ion calcium is a ubiquitous second messenger, present in all eukaryotic cells. It modulates a vast number of cellular events, such as cell division and differentiation, fertilization, cell volume, decodification of external stimuli. To process this variety of information, the cells display a number of calcium pools, which are capable of mobilization for signaling purposes. Here we review the calcium signaling on lizards red blood cells, an interesting model that has been receiving an increasing notice recently. These cells possess a complex machinery to regulate calcium, and display calcium responses to extracellular agonists. Interestingly, the pattern of calcium handling and response are divergent in different lizard families, which enforces the morphological data to their phylogenetic classification, and suggest the radiation of different calcium signaling models in lizards evolution.

Animals↗
PubMed2006

Some vaguely explored (but not trivial) costs of tail autotomy in lizards.

Lizard tail autotomy is considered an efficient anti-predator strategy that allows animals to escape from a predator attack. However, since the tail also is involved in many alternative functions, tailless animals must cope with several costs following autotomy. Here we explicitly evaluate the consequences of tail autotomy for two costs that have been virtually unexplored: 1. we test whether the anatomical change that occurs after tail loss causes a reduction in the role of the tail as a distraction mechanism to predators; 2. we analyzed whether tail synthesis comprises an energetically costly process in itself, by directly comparing the cost of maintenance before and after autotomy. We found that original tails displace further and at greater velocity than regenerated tails, indicating that the anti-predation responses of a lizard probably changes according to whether its tail is original or regenerated. With regard to the energetic cost of tail synthesis, we observed a significant increase in the standard metabolic rate, which rose 36% in relation to the value recorded prior to tail loss. This result suggests that the energetic cost of tail synthesis itself could be enough to affect lizard fitness.

Animals↗
PubMed2006

Seasonal effects on circulating leptin in the lizard Sceloporus undulatus from two populations.

Characterizing leptin's structure and function in mammals has been the subject of thousands of studies since 1994. Recently, the study of leptin has expanded to include its distribution in non-mammalian taxa, and the role that leptin plays in the reproductive axis. We demonstrated in a previous study that Sceloporus undulatus, fence lizards (ectotherms), express a leptin-like protein. In the current study we quantified seasonal variation in this putative leptin among free-ranging fence lizards from two populations characterized by early and late reproductive maturation (after one or two years, respectively). Immunoblots were performed on whole blood samples to detect leptin and estimate its titer. Leptin titers were higher in the reproductive population of S. undulatus (early maturing: 2.5+/-0.2 microg/mL; late-maturing 2.2+/-0.3 microg/mL; mean+/-2 S.E.), but both populations showed the same seasonal pattern. Leptin titers were lowest in fall when fat stores are expected to be highest (spring: 2.6+/-0.3 microg/mL; summer: 2.6+/-0.3; microg/mL; fall: 1.8+/-0.3 microg/mL), consistent with findings of seasonal variation in free-ranging mammals. Our data support previous work asserting that lizards express leptin and that it has a similar physiological function in endotherms and ectotherms. Our long-term goal is to use leptin to manipulate age at maturity and to test fundamental questions in the evolution of life-history strategies.

Aging↗
PubMed2005

Circadian expression of the clock gene Per2 is altered in the ruin lizard (Podarcis sicula) when temperature changes.

When exposed to the cold, the body temperature of the ruin lizard (Podarcis sicula), an ectothermic vertebrate, comes into equilibrium with that low environmental temperature. During this time, the behavioral output of the circadian clock, locomotor activity, disappears. We tested the activity of the circadian clockwork at low temperature (6 degrees C) by following the expression of one of its essential components, the Period2 (Per2) gene. Here we show that lizard Per2 (lPer2) expression, which is rhythmic and paralleling the behavioral rhythm of locomotor activity at higher temperature (29 degrees C), becomes constantly high at low temperature. When lizards are re-exposed to high temperature, rhythmic lPer2 expression is re-established after 2 days of adaptation and coincides with onset of locomotor activity. The alteration of the lPer2 expression pattern at low temperature indicates that the activity of the molecular feedback loop is modified under these conditions.

Analysis of Variance↗
PubMed2004

Behavioral sensitivity to corticosterone in juveniles of the wall lizard, Podarcis muralis.

Reptiles exposed to stressful conditions respond with increases in plasma levels of corticosterone (CORT). The outcome of such hormonal fluctuations can affect the organism's physiology and behavior; however, relatively few studies in reptiles have progressed past the effects of stress on the plasma levels of CORT. The purpose of this study was to investigate the effects of CORT on lizard behavior. We focused on activity and thermoregulation of juveniles of the wall lizard, Podarcis muralis. Juveniles with experimentally elevated plasma CORT concentrations showed a higher moving rate and spent a greater amount of time moving. They also spent more time being involved in attempts to escape from a terrarium. This enhanced locomotor activity was associated with significant changes in thermoregulatory behavior, as CORT-increased individuals had reduced thermoregulatory activity than the controls. The same pattern of results was obtained in nature and under laboratory conditions. Thus, CORT levels appear to mediate an important trade-off between locomotor activity and thermoregulation. To our knowledge, this is the first time that the effect of CORT on lizard thermoregulation has been examined.

Activity Cycles↗
PubMed2004

Glucocorticoid-induced thymocyte apoptosis in wall lizard Hemidactylus flaviviridis.

The aim of the present study is to demonstrate the phenomenon and mechanism of GC-induced cell death of thymocytes in wall lizard Hemidactylus flaviviridis. Lizard thymocytes were treated in vitro with different concentration of corticosterone (CS) for varying durations and the genomic DNA was analyzed both by agarose gel electrophoresis and flow cytometry. Corticosterone induced DNA fragmentation in a dose-dependent manner, as the DNA laddering was more prominent at 10(-14) M than at lower concentrations. However, CS could activate the programmed cell death of thymocytes only when incubated for 48 h and not at 3, 6, 12, or 24 h. Similar results were obtained following the flow cytometric analysis. The highest apoptotic cell death was noted at 10(-14) M concentration. CS-induced programmed cell death was decreased dramatically when the thymocytes were preincubated with RU 486 (10(-9) ng /ml) for 24 h, suggesting the classical receptor-mediated genomic pathway of glucocorticoid action in inducing apoptosis of thymocytes in wall lizard H. flaviviridis.

Animals↗
PubMed2006

Effect of hypernatraemia and the neurohypophysial peptide, arginine vasotocin (AVT) on behavioural thermoregulation in the agamid lizard, Ctenophorus ornatus.

Hypernatraemia induced by chronic injections of sodium chloride provokes thermal depression in the agamid lizard, Ctenophorus (formerly Amphibolurus) ornatus, with a fall of two degrees Celsius in the mean body temperature selected behaviourally in a photo-thermal gradient. The placement of an electrolytic lesion in the base of the hypothalamus, designed to eliminate secretion of the neuropeptide arginine vasotocin (AVT), did not affect the lizards' thermoregulatory behaviour and their Preferred Body Temperature (PBT) was not significantly different from that of unoperated controls. Saline loading, however, did not induce thermal depression in these tract-operated individuals and their PBT was significantly higher than that of salt-loaded intact individuals. When AVT was injected into operated, salt-loaded, animals, however, thermal depression was observed, supporting the hypothesis that thermal depression brought about by hypernatraemia is mediated through the action of AVT. AVT similarly significantly depressed the PBT of injected intact individuals by 3.2 degrees C when compared with hydrated controls. Immunostaining for AVT confirmed that the lesions placed in the region of the median eminence virtually eliminated AVT located in the neurohypophysial tract, and the pars nervosa. This is the first report of an effect of this peptide on behavioural thermoregulation in a lizard.

Analysis of Variance↗
PubMed2006

Serotonergic modulation of male-like pseudocopulatory behavior in the parthenogenetic whiptail lizard, Cnemidophorus uniparens.

Hormone-neurotransmitter interactions form an important link through which hormones influence a variety of behavioral processes. Typically, sexual behavior is dimorphic with males mounting receptive females. In the all-female lizard species Cnemidophorus uniparens, individuals display both male-like pseudocopulation and female-like receptivity. These respective behavioral states are correlated with high circulating concentrations of progesterone following ovulation and of estrogen preceding it. In sexual species, serotonin is involved in male-typical mounting, and, as reported here, in male-like pseudosexual behavior in this unisexual species. In the first study, C. uniparens were ovariectomized and treated systemically with exogenous androgen, a hormonal regimen that results in individuals displaying only male-like pseudosexual behavior. An increase in serotonin levels in the preoptic area coupled with the suppression of male-like pseudocopulation was observed in androgen-treated lizards injected with 5-hydroxytryptophan (the precursor of serotonin) and clorgyline (a monoamine oxidase inhibitor) compared to vehicle-treated controls. Our second experiment involved ovariectomizing lizards and either injecting them with estradiol or implanting them with either an empty (Blank) or a progesterone- or testosterone-containing Silastic capsule. Treatment with para-chlorophenylalanine (an inhibitor of tryptophan hydroxylase) facilitated male-like pseudosexual behavior depending on the circulating hormonal milieu and decreased serotonin levels in the preoptic area. Our data suggest that serotonin is inhibitory to male-like pseudosexual behavior in C. uniparens but more importantly that the hormonal environment modulates the serotonin system at the level of the preoptic area, with the serotonergic system then establishing behavioral thresholds that allow for this behavior to be "gated".

Animals↗
PubMed2005

Comparing alignment methods for inferring the history of the new world lizard genus Mabuya (Squamata: Scincidae).

The rapid increase in the ability to generate molecular data, and the focus on model-based methods for tree reconstruction have greatly advanced the use of phylogenetics in many fields. The recent flurry of new analytical techniques has focused almost solely on tree reconstruction, whereas alignment issues have received far less attention. In this paper, we use a diverse sampling of gene regions from lizards of the genus Mabuya to compare the impact, on phylogeny estimation, of new maximum likelihood alignment algorithms with more widely used methods. Sequences aligned under different optimality criteria are analyzed using partitioned Bayesian analysis with independent models and parameter settings for each gene region, and the most strongly supported phylogenetic hypothesis is then used to test the hypothesis of two colonizations of the New World by African scincid lizards. Our results show that the consistent use of model-based methods in both alignment and tree reconstruction leads to trees with more optimal likelihood scores than the use of independent criteria in alignment and tree reconstruction. We corroborate and extend earlier evidence for two independent colonizations of South America by scincid lizards. Relationships within South American Mabuya are found to be in need of taxonomic revision, specifically complexes under the names M. heathi, M. agilis, and M. bistriata (sensu, M.T. Rodrigues, Papeis Avulsos de Zoologia 41 (2000) 313).

Animals↗
PubMed2006

Molecular evidence for a species complex in the patagonian lizard Liolaemus bibronii and phylogeography of the closely related Liolaemus gracilis (Squamata: Liolaemini).

The lizard genus Liolaemus is endemic to temperate South America and includes 190 species. Liolaemus bibronii has a large geographic distribution and inhabits a great diversity of habitats, including the Monte, Steppe, and high Andean grassland environments. Liolaemus gracilis has a similar body size and shape to L. bibronii; the two are parapatrically distributed, and L. gracilis is also widely distributed. Here we use the mtDNA cytb sequence data of these two species to investigate lizard phylogeographic patterns in southern South America. L. bibronii is paraphyletic with respect to L. gracilis, Liolaemus ramirezae, Liolaemus robertmertensi and Liolaemus saxatilis; it is composed of many genetically different allopatric haploclades, some of which are reciprocally monophyletic. We also found evidence for introgression between L. bibronii and L. gracilis in the same area that introgression was hypothesized in the Liolaemus darwinii complex. We discuss the distribution of the major haploclades with inferences of their population histories, the concordance of these clades' distributions and histories with other lizard complexes studied with the same markers and methods, and taxonomic implications of these results.

Animals↗
PubMed2003

Shift from noradrenaline to adrenaline production in the adrenal gland of the lizard, Podarcis sicula, after stimulation with vasoactive intestinal peptide (VIP).

The aim of this study was to investigate the distribution and function of VIP in the adrenal gland of the lizard, Podarcis sicula. We have shown by immunohistochemistry that VIP fibers were localized exclusively around clusters of chromaffin cells in the dorsal ribbon of the lizard adrenal gland. Moreover, a strong positivity for this peptide was observed within ganglial cells and within most chromaffin cells of the gland. To investigate the effects of VIP on the adrenal gland, we have treated lizards with several doses of this peptide and we have shown that injections of exogenous VIP increased plasma levels of catecholamines and corticosteroids, but not of ACTH. This probably suggests a direct effect of VIP on the control of adrenal hormone secretion without the involvement of the hypothalamo-hypophyseal axis. Our results also establish that the increased levels of the hormones were modulated in a time- and dose-dependent manner. Therefore, our morphological studies showed a clear increased function of steroidogenic cells. In the medullary region, VIP administration induced not only a functional enhancement of adrenaline release from adrenergic cells, but also a shift of noradrenaline cells to adrenaline ones.

Adrenal Cortex Hormones↗
PubMed2003

Environmental and endocrine correlates of tactic switching by nonterritorial male tree lizards (Urosaurus ornatus).

Animals often exhibit individual variation in their behavioral responses to the same stimuli in the biotic or abiotic environment. To elucidate the endocrine mechanisms mediating such behavioral variation, we have been studying a species of lizard with two distinct male phenotypes. Here we document behavioral variation across years in one of the two male phenotypes of the tree lizard, Urosaurus ornatus, and present hormone data that support an endocrine mechanism underlying this behavioral variation. Nonterritorial male tree lizards appear to be nomadic rovers in some years and sedentary satellites in others, whereas territorial males are always territorial. This behavioral variation by nonterritorial males was correlated with environmental conditions. In environmentally harsher years (as assessed by rainfall), nonterritorial males appear to behave as nomads, whereas in more benign years they are more site-faithful. A between-year comparison of levels of corticosterone and testosterone for the two male phenotypes supports a model for how hormones underlie the males' reproductive tactics, particularly the nonterritorial males' behavioral plasticity. In an environmentally harsher (drier) year, both types of males had higher corticosterone levels than in a milder (wetter) year, but only nonterritorial males had lower testosterone in the relatively harsher year. We propose that disruptive selection for individual variation in hormonal responses to environmental cues may be a common mechanism underlying the evolution of alternative male reproductive tactics in this and other species.

Animals↗