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At least 307 records · Page 17Linked to original sources
PubMed1999

Radial glia and cell debris removal during lesion-regeneration of the lizard medial cortex.

Intraperitoneal injection of the neurotoxin 3-acetylpyridine (3AP) induces a rapid degeneration of the medial cerebral cortex (lizard fascia dentata) granular layer and of its zinc enriched axonal projection (lizard mossy fibres). After 6-8 weeks post-lesion the cell debris have been removed and the granular layer is repopulated by neurons generated in the subjacent ependyma. Both processes, neuron incorporation and debris removal, seem to be crucial for successful regeneration. Scavenging processes in the lesioned mammalian CNS are usually carried out by microglia and/or astrocytes. In the lizard cerebral cortex there are no free astrocytes and the only glial fibrillary acid (GFAP) immunoreactive cells are radial glia-ependymocytes, similar to those present during mammalian CNS development. Ependymocytes, in addition to their help in vertical migrations of just generated immature neurons, built the cortical glial scaffold, insulate the blood capillaries, form the outer glial limiting membrane, thus playing an essential role in the lizard cortical blood-brain barrier. In this study, by means of GFAP-immunocytochemistry and electron microscopy, we have shown that radial glial cells participate actively in the removal/phagocytosis of cellular debris generated in the lesion process: mainly degenerated synapses, but interestingly, also some neuronal somata. Cell debris taken up by ependymocyte lateral processes seem to be progressively transported to either distal (pial) or proximal (ventricular) poles of the cell, where they result in lipofuscin accumulations. The hypothetical subsequent exchange of debris from ependymoglia by microglia/macrophages and Kolmer cells is discussed.

Animals↗
PubMedDate not supplied

Chemical compounds from femoral gland secretions of male Iberian rock lizards, Lacerta monticola cyreni.

In spite of the importance of chemoreception and chemical signals in the social organization of lizards, there are only a few studies examining the chemical composition of secretions of lizards used for scent marking. The secretion of the femoral glands of male Iberian rock lizards (Lacerta monticola cyreni) contains 44 lipophilic compounds, including several steroids (mainly cholesterol), and n-C6 to n-C22 carboxylic acids, and minor components such as esters of carboxylic acids, alcohols, squalene, and one lactone. These compounds were identified on the basis of mass spectra, obtained by GC-MS. Most lipids were detected in all individuals, although relative proportions of each chemical show a high interindividual variability. This variability might be related to the characteristics or physical and health condition of males and might be the basis of female choice based on chemical cues observed in this lizard species.

Animals↗
PubMed1992

Putative steroid-binding receptors and nonreceptor components and testicular activity in the lizard Podarcis sicula sicula.

Labelled testosterone- and oestradiol-binding molecules have been found in the cytosol and nuclei of lizard testes. DNA-cellulose affinity chromatography was used to separate putative sex-steroid-binding receptors (adhering molecules) and nonreceptor components (nonadhering molecules). A putative androgen receptor (Kd: 10(-10) mol l-1; 3-9 fmol g-1 tissue) was found mainly in the nuclei of testicular cells when actively undergoing spermatogenesis. This suggests that, as in higher vertebrates, testosterone is implicated in spermatogenetic step regulation (meiosis and spermiogenesis) in lizard testis. In the cytosol, testosterone-binding molecules (Kd: 10(-9) mol l-1; 384-784 fmol g-1 tissue) with several properties of androgen-binding proteins are present from autumn to spring. The behaviour of these molecules is consistent with the role assigned to androgen-binding proteins as androgen reservoir. A putative oestrogen receptor is present throughout the sexual cycle, except during the culmination phase (breeding). The putative oestrogen receptor may be involved in the regulation of the first spermatogenetic step (spermatogonia multiplication) and in the induction of post-reproductive refractoriness. This phase is present in temperate-zone lizards. These studies show that the evaluation of sex-steroid-binding molecules is useful in considering the relationships between sex hormones and spermatogenetic activity in the testes of lizards.

Analysis of Variance↗
PubMed2002

The lizard cerebral cortex as a model to study neuronal regeneration.

The medial cerebral cortex of lizards, an area homologous to the hippocampal fascia dentata, shows delayed postnatal neurogenesis, i.e., cells in the medial cortex ependyma proliferate and give rise to immature neurons, which migrate to the cell layer. There, recruited neurons differentiate and give rise to zinc containing axons directed to the rest of cortical areas, thus resulting in a continuous growth of the medial cortex and its zinc-enriched axonal projection. This happens along the lizard life span, even in adult lizards, thus allowing one of their most important characteristics: neuronal regeneration. Experiments in our laboratory have shown that chemical lesion of the medial cortex (affecting up to 95% of its neurons) results in a cascade of events: first, massive neuronal death and axonal-dendritic retraction and, secondly, triggered ependymal-neuroblast proliferation and subsequent neo-histogenesis and regeneration of an almost new medial cortex, indistinguishable from a normal undamaged one. This is the only case to our knowledge of the regeneration of an amniote central nervous centre by new neuron production and neo-histogenesis. Thus the lizard cerebral cortex is a good model to study neuronal regeneration and the complex factors that regulate its neurogenetic, migratory and neo-synaptogenetic events.

Animals↗
PubMed2002

Intergenic and external transcribed spacers of ribosomal RNA genes in lizard-infecting Leishmania: molecular structure and phylogenetic relationship to mammal-infecting Leishmania in the subgenus Leishmania (Leishmania).

To establish the relationships of the lizard- and mammal-infecting Leishmania, we characterized the intergenic spacer region of ribosomal RNA genes from L. tarentolae and L. hoogstraali. The organization of these regions is similar to those of other eukaryotes. The intergenic spacer region was approximately 4 kb in L. tarentolae and 5.5 kb in L. hoogstraali. The size difference was due to a greater number of 63-bp repetitive elements in the latter species. This region also contained another element, repeated twice, that had an inverted octanucleotide with the potential to form a stem-loop structure that could be involved in transcription termination or processing events. The ribosomal RNA gene localization showed a distinct pattern with one chromosomal band (2.2 Mb) for L. tarentolae and two (1.5 and 1.3 Mb) for L. hoogstraali. The study also showed sequence differences in the external transcribed region that could be used to distinguish lizard Leishmania from the mammalian Leishmania. The intergenic spacer region structure features found among Leishmania species indicated that lizard and mammalian Leishmania are closely related and support the inclusion of lizard-infecting species into the subgenus Sauroleishmania proposed by Saf'janova in 1982.

Animals↗
PubMed2005

Endocrine roles of D-aspartic acid in the testis of lizard Podarcis s. sicula.

In the lizard Podarcis s. sicula, a substantial amount of D-aspartate (D-Asp) is endogenous to the testis and shows cyclic changes of activity connected with sex hormone profiles during the annual reproductive phases. Testicular D-Asp content shows a direct correlation with testosterone titres and a reverse correlation with 17beta-estradiol titres. In vivo experiments, consisting of i.p. injections of 2.0 micromol/g body weight of D-Asp or other amino acids, in lizards collected during the three main phases of the reproductive cycle (pre-reproductive, reproductive and post-reproductive period), revealed that the testis can specifically take up and accumulate D-Asp alone. Moreover, this amino acid influences the synthesis of testosterone and 17beta-estradiol in all phases of the cycle. This phenomenon is particularly evident during the pre- and post-reproductive period, when endogenous testosterone levels observed in both testis and plasma were the lowest and 17beta-estradiol concentrations were the highest. D-Asp rapidly induces a fall in 17beta-estradiol and a rise in testosterone at 3 h post-injection in the testis and at 6 h post-injection in the blood. In vitro experiments show that testicular tissue converted L-Asp into D-Asp through an aspartate racemase. D-Asp synthesis was measured in all phases of the cycle, but was significantly higher during the reproductive period with a peak at pH 6.0. The exogenous D-Asp also induces a significant increase in the mitotic activity of the testis at 3 h (P < 0.05) and at 6 h (P < 0.01). Induction of spermatogenesis by D-Asp is recognized by an intense immunoreactivity of the germinal epithelium (spermatogonia and spermatids) for proliferation cell nuclear antigen (PCNA). The effects of D-Asp on the testis appear to be specific since they were not seen in lizards injected with other D- or L-forms of amino acids with known excitatory effects on neurosecretion. Our results suggest a regulatory role for D-Asp in the steroido-genesis and spermatogenesis of the testis of the lizard Podarcis s. sicula.

Amino Acid Isomerases↗
PubMed1983

A simple model of cochlear micromechanics in the mammal and lizard.

A model is presented which is a simple representation of cochlear micromechanics in the lizard and mammal. The model is a linear, time-invariant mechanical system, consisting of two coupled mechanical filters. It is capable of a sharply tuned first and second filter, consistent with the sharply tuned basilar membrane and auditory nerve fibers in the mammal. When parameters are adjusted for the alligator lizard (Gerrhonotus multicarinatus), the model generates a sharply tuned second filter without a sharply tuned first filter. In the alligator lizard, the auditory nerve fibers are sharply tuned but the basilar membrane is not. The model supports the hypothesis that cochlear transduction is not fundamentally different in the mammal and the alligator lizard.

Animals↗
PubMedDate not supplied

Body temperature alters the lipid composition of pulmonary surfactant in the lizard Ctenophorus nuchalis.

In any 24-h period the body temperature (Tb) of the central Australian agamid lizard, Ctenophorus nuchalis, may vary from 13 to 45 degrees C; the mean preferred Tb is 37 degrees C. We have analyzed surfactant-type lipids in lizards that underwent rapid changes in Tb from 37 degrees C to 14, 19, 27, or 44 degrees C. Lipids were extracted from lung lavage and lamellar body fractions, and phospholipids and cholesterol components were measured. There was no change in either the total amount or relative proportions of the different classes of phospholipids, but cooling increased the cholesterol content of lavage. An increase in the cholesterol: phospholipid ratio was evident within 2 h of cooling to 19 degrees C and was maintained for at least 48 h. The ratio increased from 8% at 37 degrees C, to 15% after 4 h at 19 degrees C, and 18% after 4 h at 14 degrees C. Possibly the increase in cholesterol promotes fluidity and absorption of surfactant within the alveoli of lizards with low Tb. Cold lizards collapse their lungs during prolonged periods of apnea and the surfactant may prevent the epithelial walls from adhering.

Animals↗
PubMed1998

Gastric cryptosporidiosis in a wild frilled lizard from Australia.

An adult male frilled lizard (Chlamydosaurus kingi) was found dead in Northern Territory (Australia). On physical examination it was found to be severely emaciated. At necropsy the stomach was found to be firm with mild thickening of the gastric mucosa. Gastric rugae were prominent and the mucosa was red with a thin layer of dark red mucus on its surface. Light microscopic examination revealed a mild diffuse gastritis with infiltration of the lamina propria by lymphocytes, plasma cells, and heterophils. Large numbers of small, round amphophilic to basophilic (2 to 4 microns in diameter) organisms morphologically consistent with cryptosporidia were seen on the surface of the mucosal epithelium and free in the gastric lumen. The gastric lesions seen in this frilled lizard did not involve atrophy, as previously described in lizards with gastric cryptosporidiosis, and were similar to those described in snakes. The possibility that more than one species of Cryptosporidium parasitizes reptiles could explain the different lesions. This is the first report of cryptosporidiosis in a frilled lizard.

Animals↗
PubMed2001

Thymic structural changes in relation to seasonal cycle and testosterone administration in wall lizard Hemidactylus flaviviridis (Ruppell).

Light microscopic and ultrastructural studies of thymus in wall lizard showed remarkable season dependent structural changes. In winter, the thymus was involuted and its cortico-medullary differentiation was not distinct. Thymocytes were sparsely distributed. The epithelial cells exhibited atrophic features such as an appreciable decrease in the nuclear-cytoplasmic ratio and accordingly reduction in cell organelles. The reconstruction of thymus commenced during spring and it became fully developed with marked delineation of cortico-medullary regions during summer. The thymus was then densely populated with thymocytes and epithelial cells showed voluminous cytoplasm having numerous cell organelles. The thymus regression started again by the beginning of autumn. The results suggest that the thymic development in wall lizard have inverse relationship with the androgen level, as the testicular steroidogenic activity was seen maximum during winter and least in summer. This assumption gets support by castration and testosterone replacement experiments. Castration of lizards during winter resulted in profound development of thymus with an appreciable increase in thymocytes mainly in the cortex region . The cortex became delineated from the medulla. Following testosterone treatment, the thymus underwent regression and was comparable to testis-intact lizard's thymus during winter season. After withdrawal of testosterone treatment, the thymus exhibited dense lymphoid and thymocyte population with a demarcation of cortico-medullary regions and sub-cortical region was regenerated.

Androgens↗
PubMed2004

Interrelationship among testicular cells in wall lizard Hemidactylus flaviviridis (Rüppell): an ultrastructural seasonal and experimental study.

The present study was aimed at investigating ultrastructure of different testicular cells and their interactions through various junctional specializations during different phases of reproductive cycle in wall lizard H. flaviviridis to develop an integrated approach of cell-cell interaction in control of testicular functions. Specialized steroid synthesizing cell organelles such as smooth endoplasmic reticulum (SER) and long slender mitochondria with tubulo-vesicular cristae were predominantly seen in Leydig as well as Sertoli cells during spermatogenically active phase, suggesting their active involvement in steroid biosynthesis. Peritubular cells also exhibited marked seasonal variations. Multi-layered fibroblast-like peritubular cells during regressed phase became single layered myoid-like during spermatogenically active phase. The presence of various types of junctions, including gap and tight junctions (occluding junctions) and adhering junctions such as desmosomes, septate-like junction, ectoplasmic specializations and tubulo-bulbar complexes, were demonstrated among testicular cells in wall lizard H. flaviviridis. However, the nature and degree of junctional (environmental) interaction varied with the reproductive state of the wall lizard. Further, administration of dihydrotestosterone in wall lizards during regressed phase resulted in increase of lipid droplets in Leydig cells and accumulation of germ cell debris in seminiferous tubules. Some of the Sertoli cells were seen darker in response to testosterone treatment probably due to its inhibitory effect on lipid metabolism. These results suggest that testosterone either directly or via inhibiting pituitary basal gonadotropin secretion has suppressive effect on testicular cells.

Androgens↗
PubMed2006

Field use of maximal sprint speed by collared lizards (Crotaphytus collaris): compensation and sexual selection.

To understand how selection acts on performance capacity, the ecological role of the performance trait being measured must be determined. Knowing if and when an animal uses maximal performance capacity may give insight into what specific selective pressures may be acting on performance, because individuals are expected to use close to maximal capacity only in contexts important to survival or reproductive success. Furthermore, if an ecological context is important, poor performers are expected to compensate behaviorally. To understand the relative roles of natural and sexual selection on maximal sprint speed capacity we measured maximal sprint speed of collared lizards (Crotaphytus collaris) in the laboratory and field-realized sprint speed for the same individuals in three different contexts (foraging, escaping a predator, and responding to a rival intruder). Females used closer to maximal speed while escaping predators than in the other contexts. Adult males, on the other hand, used closer to maximal speed while responding to an unfamiliar male intruder tethered within their territory. Sprint speeds during foraging attempts were far below maximal capacity for all lizards. Yearlings appeared to compensate for having lower absolute maximal capacity by using a greater percentage of their maximal capacity while foraging and escaping predators than did adults of either sex. We also found evidence for compensation within age and sex classes, where slower individuals used a greater percentage of their maximal capacity than faster individuals. However, this was true only while foraging and escaping predators and not while responding to a rival. Collared lizards appeared to choose microhabitats near refugia such that maximal speed was not necessary to escape predators. Although natural selection for predator avoidance cannot be ruled out as a selective force acting on locomotor performance in collared lizards, intrasexual selection for territory maintenance may be more important for territorial males.

Aging↗
PubMed1989

Recognition of cyclic transmission of Sarcocystis stehlinii n. sp. in the Gran Canarian giant lizard.

The transmission of Sarcocystis species via cannibalism seems to be common among lizards of the genus Gallotia that are endemic to the Canary Islands. Gran Canarian giant lizards, Gallotia stehlini, were screened for the presence of sarcosporidian parasites. Sarcocysts, measuring 90-400 micrometers in length and 60-160 micrometers in width, were found in the musculature of the lizards' tails. In their feces the lizards passed sporocysts of 8.5(8.2-9.4) x 6.5(5.9-7.0) micrometers. A series of laboratory infections was carried out to shed light on the life cycle of Sarocystis stehlinii n.sp., proving it to be another dihomoxenous Sarcocystis species.

Animals↗
PubMed1983

Comparative effects of some autonomic drugs on lizard (Agama agama) and tortoise (Kinixys crosa) isolated rectum.

The effects of some cholinomimetic and sympathomimetic drugs have been investigated on the isolated rectal muscles of West African rainbow lizard (Agama agama) and land tortoise (Kinixys crosa). Acetylcholine and its natural or synthetic analogues evoked concentration-related atropine-sensitive contractions of the muscle preparations, whereas all the catecholamines examined relaxed the lizard (and guinea-pig), but not the tortoise, isolated rectum in a dose-dependent fashion. The ganglionic stimulant drugs used, nicotine and DMPP, did not produce any effect on the isolated rectum of the two reptiles, although they contracted the guinea-pig isolated rectum in a concentration-dependent manner. Concentrations of physostigmine, which induced spasms or contractions in the isolated rectum of the guinea-pig, failed to excite reptilian rectal muscle preparations. Histamine induced biphasic responses in the lizard isolated rectum without affecting the isolated rectum of the tortoise. Serotonin (5-HT) which contracted the isolated rectum of the guinea-pig (like histamine) also provoked variable contractions of the lizard rectum but did not affect the tortoise isolated rectum. It is therefore concluded that although the rectal smooth muscles of these two terrestrial West African reptiles possess cholinergic innervation with mainly "muscarinic" cholinoceptors, their autonomic innervation differs from that of a conventional mammalian (e.g. guinea-pig) gastrointestinal tract smooth muscle.

Acetylcholine↗
PubMed1994

Are rostral and caudal parts of the hippocampus of the lizard Gekko gecko related to different types of behaviour?

Spatial orientation is an important function of the hippocampus. In reptiles the medial cortex is the equivalent of the mammalian hippocampus. In this study we compared the structure and connections of the hippocampus of ground-dwelling lizards with those of gekkonid lizards which are able to walk on vertical walls as well as on the ceiling. This last type of locomotor behaviour makes high demands on spatial orientation. It appeared that, in contrast to the ground-dwelling lizards, in geckos the small-celled part of the medial cortex can be divided into a rostral and a caudal part. The rostral part receives visual, auditory, vestibular and proprioceptive information from the dorsolateral thalamic nucleus. The caudal part is connected with the lateral cortex which is the recipient of olfactory information from the main olfactory bulb. Also the efferent connections of the rostral and caudal part of the small-celled part of the medial cortex to the septum, and via the septum to the preoptic and hypothalamic areas remain strictly separated. Since different behavioural aspects are localized in different preoptic and hypothalamic subdivisions it seems likely that the two parts of the hippocampus in gekkonid lizards serve different behavioural functions.

Animals↗
PubMed1993

Electrical resonance of isolated hair cells does not account for acoustic tuning in the free-standing region of the alligator lizard's cochlea.

The cochlea of the alligator lizard is divided into two morphologically and physiologically distinct regions. In the "tectorial region," hair bundles of hair cells are draped by a tectorial membrane, whereas in the "free-standing region," hair bundles are said to be free-standing because there are no overlying tectorial structures. The acoustic tuning of the free-standing region depends at least in part on mechanical resonances of the hair bundles. In the turtle cochlea, in contrast, acoustic tuning depends in large part upon the electrical properties of the hair cells. We have investigated the electrical properties of hair cells isolated from the free-standing region of the alligator lizard's cochlea. When injected with steps of depolarizing current, these "free-standing hair cells" exhibited electrical resonances that were comparable in frequency and quality to electrical resonances in cochlear hair cells from turtles, chicks, and alligators, and in saccular hair cells from frogs and fish. In the lizard's free-standing hair cells, however, the electrical resonance frequencies (< 300 Hz) were a decade below the cells' acoustic characteristic frequencies (between 1 and 4 kHz), showing that the electrical resonance is not likely to contribute to acoustic tuning. The electrical resonances were not apparent at rest. The cells' resting potentials were significantly more negative than the activation voltage (approximately -40 mV) of the Ca(2+)-dependent K+ current upon which the electrical resonance has been shown to depend in other hair cells. At potentials more negative than -50 mV, an inwardly rectifying K+ conductance dominated. Because we observed no electrical tuning above 300 Hz, our results indirectly support a mechanical origin for acoustic tuning in the free-standing region of the alligator lizard cochlea. These results further show that acoustic tuning cannot be inferred solely from the electrical resonances of isolated hair cells.

Animals↗
PubMed1993

Immature Ixodes scapularis (Acari: Ixodidae) parasitizing lizards from the southeastern U.S.A.

Preserved museum specimens of 13 lizard and 3 snake species common in the southeastern U.S.A. were examined for immature Ixodes scapularis Say ticks. Five Eumeces and 4 Ophisaurus lizard species yielded an infestation prevalence of 17.8% for species of Eumeces and 29.0% for species of Ophisaurus. Mean intensity of larvae and nymphs was 7.1 and 2.7, respectively, for species of Eumeces, and 6.3 and 1.4, respectively, for species of Ophisaurus. Collection dates of the lizards ranged from January through December, but most were collected from March through October. The maximum number of immatures found on a single specimen was 193 larvae and 11 nymphs on a specimen of Eumeces and 75 larvae and 7 nymphs on a specimen of Ophisaurus. For species of Eumeces, 75.2% of all nymphs observed were attached in the shoulder area. Larvae were most abundant on the rear legs (53.3%), followed by the front legs (26.3%) and shoulders (12.9%). Larvae and nymphs on species of Ophisaurus were found almost exclusively in the lateral groove area (84.0% and 94.4%, respectively). Three other lizard species (Anolis carolinensis, Sceloporus undulatus, Scincella lateralis) had only a few ticks or none. A fourth species, Cnemidophorus sexlineatus, hosted a total of 3 larvae on 3 specimens (infestation prevalence, 10.7%). Three snake species (Diadophis punctatus, Virginia striatula, Crotalus adamanteus) had none.

Animals↗
PubMed1995

Effects of cyproterone acetate on FSH and testosterone influenced spermatogenesis, steroidogenesis and epididymis in the Indian wall lizard, Hemidactylus flaviviridis (Ruppell).

The effects of FSH, testosterone and either cyproterone acetate (CPA) alone or in combination with FSH or testosterone on testis and epididymis in male lizards were studied histologically and histochemically during recrudescent phase to find out whether the onset of spermatogenesis is androgen dependent or FSH dependent. The testes of control lizards consisted of mainly spermatogonia, a few primary spermatocytes and secondary spermatocytes rarely. The interstitial or Leydig cells were atrophied. FSH treatment induced spermatogenic activity substantially as indicated by increase in number of primary and secondary spermatocytes and transformation of secondary spermatocytes into spermatids and into spermatozoa in a few cases. Besides, steroidogenic activity was also remarkably stimulated as evidences by considerable depletion of sudanophilic lipid and an increase in Delta5-3beta-hydroxysteroid dehydrogenase enzyme activity in Leydig cells. However, testosterone treatment resulted in the inhibition of spermatogenesis. A significant inhibition of spermatogenesis was noted in lizards treated either with CPA alone or in combination with FSH. The inhibitory effect of CPA on spermatogenesis was increased when it was given in combination with testosterone. The results indicate that onset of spermatogenic activity is dependent on FSH (or FSH-like protein), but not on the androgen. The ductus epididymidis in control lizards was regressed with low cuboidal epithelium. The lumen of the tubules was totally devoid of secretory material and spermatozoa. FSH treatment induced a marked hypertrophy in epididymidis. The lumen became filled with secretory material mixed with spermatozoa. The hypertrophy in epididymidis was also recorded after the treatment with testosterone, but the degree of induction was not to that extent as noted in FSH treated ones. However, CPA injected either with FSH or with testosterone resulted in the profound atrophy in epididymidis.

Animals↗