Projections of the optic tectum and the mesencephalic nucleus of the trigeminal nerve in the tegu lizard (Tupinambis nigropunctatus)

Summary Fibers undergoing Wallerian degeneration following tectal lesions were demonstrated with the Nauta and Fink-Heimer methods and traced to their termination. Four of the five distinct fiber paths originating in the optic tectum appear related to vision, while one is related to the mesencephalic nucleus of the trigeminus. The latter component of the tectal efferents distributes fibers to 1) the main sensory nucleus of the trigeminus, 2) the motor nucleus of the trigeminus, 3) the nucleus of tractus solitarius, and 4) the intermediate gray of the cervical spinal cord.The principal ascending bundle projects to the nucleus rotundus, three components of the ventral geniculate nucleus and the nucleus ventromedialis anterior ipsilaterally, before it crosses in the supraoptic commissure and terminates in the contralateral nucleus rotundus, ventral geniculate nucleus and a hitherto unnamed region dorsal to the nucleus of the posterior accessory optic tract.Fibers leaving the tectum dorso-medially terminate in the posterodorsal nucleus ipsilaterally and the stratum griseum periventriculare of the contralateral tectum. The descending fiber paths terminate in medial reticular cell groups and the rostral spinal cord contralaterally and in the torus and the lateral reticular regions ipsilaterally. The ipsilateral fascicle also issues fibers to the magnocellular nucleus isthmi.     

Microanatomy of the lung parenchyma of a tegu lizard Tupinambis nigropunctatus

The combined techniques of light microscopy, scanning (SEM) and transmission (TEM) electron microscopy were used for the first time to study the structure of unicameral lungs of a Tegu lizard (Tupinambis nigropunctatus). The lungs are prolate spheroid bags with blood supplied by superficial branches of a dorsal pulmonary artery and returned by diffuse, more deeply located veins. The primary bronchus enters the medial aspect near the apex of the lung. The lung wall is composed of trabeculae: (1) arranged in a faviform pattern, (2) forming individual faveoli (gas exchange chambers) which appear deepest in the cranial one-half of the lung, (3) all of which have a smooth muscle core overlain by either a ciliated or nonciliated epithelium. A ciliated epithelium lines the luminal surfaces of the large primary trabeculae and parts of smaller secondary trabeculae; it is composed of cone-shaped cells with ciliated-microvillous surfaces, and of columnar serous secreting cells. Nonciliated epithelium covers the luminal surface of portions of some secondary trabeculae, abluminal surfaces of primary and secondary trabeculae and all surfaces of the small tertiary trabeculae forming the faveoli. The nonciliated epithelium overlies an extensive superficial capillary network. The blood-gas barrier (0.7-1.0 μm thick) is composed of a thin cytoplasmic flange of Type I pneumonocytes, a thick homogeneous basal lamina and an attenuated endothelial cytoplasm. Numerous surfactant-producing Type II pneumonocytes are closely associated with the Type I pneumonocytes. The nonrespiratory ciliated epithelium may function in humidification of air and clearing of the lungs.     

Terminal distribution of retinal fibers in the tegu lizard (Tupinambis nigropunctatus)

Summary The retinal projections in the tegu lizard were traced using degeneration-silver methods. Bilateral projections were found to the dorsolateral geniculate and the posterodorsal nuclei. Unilateral, crossed projections were traced to the suprachiasmatic nucleus, the ventrolateral geniculate nucleus, the mesencephalic lentiform nucleus, nucleus geniculatus praetectalis, the ectomammillary nucleus, and the optic tectum. Some of these connections are distinctly different from those reported in other reptiles and suggest that important interspecific variations occur among reptiles.     

Ventilatory response to inspired CO2 in the lizard, Tupinambis nigropunctatus

Elevating inspired levels of CO2 (1-4%) in Tupinambis nigropunctatus leads to an increase in tidal volume, mean expiratory flow, mean inspiratory flow, duration of the non-ventilatory period, inspiratory duration, expiratory duration and end inspiratory lung volume. Minute ventilation is variable and end expiratory volume decreases. An increase or decrease in CO2 concentration surrounding the head affects the duration of the non-ventilatory period before the altered CO2 concentration is inspired into the lungs. The change in duration of the non-ventilatory period before altered CO2 concentration is inspired into the lungs is probably mediated by CO2 sensitive receptors located in the mouth, nose or on the head surface.     

Efferent connections of the striatum in Tupinambis nigropunctatus

The striatum of the lizard Tupinambis nigropunctatus lies in the lateral wall of the telencephalon and consists of two major subdivisions: the dorsal striatum and the ventral striatum. Electrolytic lesions were placed in all parts of the striatal complex and in adjacent areas and the subsequent anterograde degeneration was studied using the Nauta-Gygax and Fink-Heimer techniques. Lesions in the dorsal striatum cause terminal degeneration in the ventral striatum both ipsi- and contralaterally. In addition, projections have been found to the lateral amygdaloid nucleus and to parts of the dorsal striatum not affected by the lesion. Following lesions in the ventral striatum fiber degeneration could always be observed in the ventral peduncle of the lateral forebrain bundle. Corresponding terminal degeneration was found in the anterior and posterior entopeduncular nuclei, the tegmentum mesencephali, the substantia nigra, the prerubral area, the mesencephalic central grey and the lateral cerebellar nucleus. When the large celled part of the ventral striatum was involved in the lesion additional degeneration could be traced to the nucleus rotundus via the dorsal peduncle of the lateral forebrain bundle.     

Structure of the posthepatic septum and its influence on visceral topology in the tegu lizard, Tupinambis merianae (Teiidae: Reptilia)

The posthepatic septum (PHS) divides the body cavity of Tupinambis merianae into two parts: the cranial one containing the lungs and liver and the caudal one containing the remaining viscera. The PHS is composed of layers of collagenous fibers and bundles of smooth muscle, neither of which show systematic orientation, as well as isolated blood vessels, lymphatic vessels, and nerves. Striated muscle of the abdominal wall does not invade the PHS. The contractions of the smooth muscles may stabilize the pleurohepatic cavity under conditions of elevated aerobic needs rather than supporting breathing on a breath-by-breath basis. Surgical removal of the PHS changes the anatomical arrangement of the viscera significantly, with stomach and intestine invading the former pleurohepatic cavity and reducing the space for the lungs. Thus, the PHS is essential to maintain the visceral topography in Tupinambis.     

Intrinsic organization of the medial cerebral cortex of the lizard Lacerta pityusensis: A golgi study

The morphology of cells and the organization of axons were studied in Golgi-Colonnier and toluidine blue stained preparations from the medial cerebral cortex of the lizard Lacerta pityusensis. In the medial cortex, six strata were distinguished between the superficial glial membrane and the ependyma. Strata I and II formed the outer plexiform layer, stratum III formed the cellular layer, and strata IV go VI the inner plexiform layer. The outer plexiform layer contained smooth bipolar neurons; their dendrites were oriented anteroposteriorly and their axons were directed towards the posterior zone of the brain. Five neuronal types were observed in the cellular layer. The spinous pyramidal neurons had well-developed apical dendrites and poorly developed basal ones. Their axons entered the inner plexiform layer and gave off collaterals oriented anteroposteriorly. The small, sparsely spinous pyramidal neurons had poorly developed dendrites and their axons entered the inner plexiform layer. The spinous bitufted neurons had well-developed apical and basal dendritic tufts. Their axons gave off collaterals that reached the outer and inner plexiform layers of both the dorsomedial and dorsal cortices. The sparsely spinous horizontal neurons had dendrites restricted to the outer plexiform layer. Their axons entered the inner plexiform layer. The sparsely spinous, multipolar neurons had their soma close to stratum IV and their axons entered the outer plexiform layer. In stratum V of the inner plexiform layer were large, spiny polymorphic neurons; they had dendrites with long spines, and their axons reached the cellular layer. On the basis of these results, we have subdivided the medial cortex into two subregions: the superficial region, which contains the neurons of the cellular layer and their dendritic domains, and the deep region, strata V and VI, which contains the large, spiny polymorphic neurons. The neurons in the medial cortex of these lizards resembles those in the area dentata of mammals. On this basis, the superficial region may be compared to the dentate gyrus and the deep region to the hilar region of the hippocampus of mammals.     

Effects of season, temperature, and body mass on the standard metabolic rate of tegu lizards (Tupinambis merianae)

Abstract This study examined how the standard metabolic rate of tegu lizards, a species that undergoes large ontogenetic changes in body weight with associated changes in life-history traits, is affected by changes in body mass, body temperature, season, and life-history traits. We measured rates of oxygen consumption (Vo(2)) in 90 individuals ranging in body mass from 10.4 g to 3.75 kg at three experimental temperatures (17 degrees , 25 degrees , and 30 degrees C) over the four seasons. We found that standard metabolic rate scaled to the power of 0.84 of body mass at all experimental temperatures in all seasons and that thermal sensitivity of metabolism was relatively low (Q(10) approximately 2.0-2.5) over the range from 17 degrees to 30 degrees C regardless of body size or season. Metabolic rates did vary seasonally, being higher in spring and summer than in autumn and winter at the same temperatures, and this was true regardless of animal size. Finally, in this study, the changes in life-history traits that occurred ontogenetically were not accompanied by significant changes in metabolic rate.     

GFAP-immunoreactive perivascular glia in the chick optic tectum.

Immunocytochemical staining of the glial fibrillary acidic protein (GFAP) was utilized to characterize the processes of the astrocytes enveloping the vessel wall in the central nervous system. The study was carried out in the mesencephalic lobes of 18 and 20 incubation-day chick embryos and of 20 day chickens. A perivascular GFAP positivity was mainly detectable in the vessel portions running within the tectum white layers, while it was scarce, or absent, in the grey ones. The perivascular GFAP negativity in the tectum cellular layers was not considered result of the absence of astrocytic endfeet since our previous electronmicroscopical studies evidenced an almost complete perivascular astrocytic ring throughout the tectum layers at hatching time. Present data rather suggest that the expression of the GFAP-made intermediate filaments in developing astrocytes might be controlled by the surrounding microenvironment.     

The use of the tongue and hyoid apparatus during feeding in lizards (Ctenosaura similis and Tupinambis nigropunctatus)

The use of the tongue and hyoid is examined in cineradiographic and electromyographic investigations of feeding in two species of lizards, Ctenosaura similis (Iguanidae) and Tupinambis nigropunctatus (Teiidae). In both animals food is transported through the oral cavity by regular cycles of the tongue. Tongue movements correlate with jaw and hyoid movement. Similarities between the two animals in the use of the tongue in food transport, lapping, pharyngeal packing, and pharyngeal emptying are detailed. Mechanisms of tongue protrusion are examined and it is shown that the tongue in Tupinambis is relatively more protrusible than in Ctenosaura. This difference is complementary with data on the greater reliance of Tupinambis on the tongue as a sensory organ. Tupinambis further differs from Ctenosaura in possessing a greater mobility of the hyoid. In many features of tongue use in food transport, lizards resemble mammals, supporting postulations of a basic pattern of intra-oral food transport. However, whether this pattern can be attributed to convergence or a common, primitive neural pattern of control cannot be distinguished. Lizards lack two major characteristics of mammalian food transport: regular masticatory cycles and an internal swallowing mechanism.     

Lineage of radial glia in the chicken optic tectum.

In many parts of the central nervous system, the elongated processes of radial glial cells are believed to guide immature neurons from the ventricular zone to their sites of differentiation. To study the clonal relationships of radial glia to other neural cell types, we used a recombinant retrovirus to label precursor cells in the chick optic tectum with a heritable marker, the E. coli lacZ gene. The progeny of the infected cells were detected at later stages of development with a histochemical stain for the lacZ gene product. Radial glia were identified in a substantial fraction of clones, and these were studied further. Our main results are the following. (a) Clones containing radial glia frequently contained neurons and/or astrocytes, but usually not other radial glia. Thus, radial glia derive from a multipotential progenitor rather than from a committed radial glial precursor. (b) Production of radial glia continues until at least embryonic day (E) 8, after the peak of neuronal birth is over (approximately E5) and after radial migration of immature neurons has begun (E6-7). Radial glial and neuronal lineages do not appear to diverge during this interval, and radial glia are among the last cells that their progenitors produce. (c) As they migrate, many cells are closely apposed to the apical process of their sibling radial glia. Thus, radial glia may frequently guide the migration of their clonal relatives. (d) The population of labelled radial glia declines between E15 and E19-20 (just before hatching), concurrent with a sharp increase in the number of labelled astrocytes. This result suggests that some tectal radial glia transform into astrocytes, as occurs in mammalian cerebral cortex, although others persist after hatching. To reconcile the observations that many radial glia are present early, that radial glia are among the last offspring of a multipotential stem cell, and that most clones contain only a single radial glial cell, we suggest that the stem cell is, or becomes, a radial glial cell.     

Chemical constituents of the femoral gland secretions of male tegu lizards (Tupinambis merianae) (Family teiidae)

In spite of the importance of chemical signals (pheromones) in the reproductive behaviour of lizards, the chemical compounds secreted by their femoral glands, which may be used as sexual signals, are only known for a few lizard species. Based on mass spectra, obtained by GC-MS, we found 49 lipophilic compounds in femoral gland secretions of male tegu lizards (Tupinambis merianae) (fam. Teiidae), including a very high proportion of carboxylic acids and their esters ranging between n-C8 and n-C20 (mainly octadecanoic and 9,12-octadecadienoic acids), with much less proportions of steroids, tocopherol, aldehydes, and squalene. We discuss the potential function of these compounds in secretions, and compare the compounds found here with those documented for other lizard species.     

Vasculogenesis in the chick embryo optic tectum

The initial formation and further development of the intraneural blood vessel network in the tectum opticum of the chick from the 4th to the 14th incubation day have been analyzed and some quantitative data morphometrically recorded. Vessels have been filled by intracardial injection of India ink in vivo. As inferred from our previous investigations on the vasculogenesis of several districts of the central and peripheral nervous system in the chick embryo, also in the developing optic tectum growth and distribution pattern of the vessels seem to unfold step by step under the local influence of earlier occurring morpho-histogenetic processes of the corresponding neural substratum.