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PubMed2001

Vesicle-associated membrane protein isoforms in the tiger salamander retina.

Vesicle associated membrane protein (VAMP; also known as synaptobrevin) is a key component of the core complex needed for docking and fusion of synaptic vesicles with the presynaptic plasma membrane. Recent work indicates that the precise complement of presynaptic proteins associated with transmitter release and their isoforms vary among synapses, presumably conferring specific functional release properties. The retina contains two types of vesicular synapses with distinct morphologic, functional, and biochemical characteristics: ribbon and conventional synapses. Although the precise complement of presynaptic proteins is known to differ between conventional and ribbon synapses and among conventional synapses, the distribution of VAMP isoforms among retinal synapses has not been determined. The expression and localization of VAMP isoforms in the salamander retina, a major model system for studies of retinal circuitry, was examined by using immunocytochemical and immunoblotting methods. Both methods indicated that at least two VAMP isoforms were expressed in salamander retina. One isoform, recognized by an immunoglobulin M antibody that recognizes both mammalian VAMP-1 and VAMP-2, was associated with photoreceptor and bipolar cell terminals as well as many conventional synapses, and probably corresponds to mammalian VAMP-2. A different VAMP isoform associated with a subset of amacrine cells, was recognized only by antibodies directed against the N-terminus of mammalian VAMP-2. An antiserum directed against the N-terminus of mammalian VAMP-1 did not specifically recognize any salamander VAMPs in either immunocytochemical or immunoblotting experiments. Heterogeneous distribution of VAMP isoforms among conventional retinal synapses was confirmed by double labeling for synapsin I, a marker for conventional synapses. These studies indicate that VAMP isoforms are expressed heterogeneously among retinal synapses but cannot account for the differences in transmitter release characteristics at ribbon and conventional synapses. These results also corroborate previous studies in Xenopus indicating that the N-terminus of nonmammalian VAMP isoforms differs from their mammalian counterparts.

Ambystoma↗
PubMed2003

Localization of GABAA receptor subunits alpha 1, alpha 3, beta 1, beta 2/3, gamma 1, and gamma 2 in the salamander retina.

Electrophysiological studies have demonstrated that gamma-aminobutyric acid receptors type A (GABA(A)) mediate important information processing in the retinas of salamander and other vertebrates. The pharmacology and physiology of GABA(A) receptors depend on their subunit composition. We studied the localization of GABA(A) receptor subunit isoforms alpha(1), alpha(3), beta(1), beta(2/3) (antibody BD-17 and 62-3G1), gamma(1), and gamma(2) in salamander retina with immunocytochemical methods. All three beta-subunit antibodies labeled similarly in the outer retina, especially the inner segments and synaptic terminals of rod photoreceptors (identified with protein kinase C). Somatic labeling was observed in cell bodies of some horizontal cells, bipolar cells, amacrine cells, and cells in the ganglion cell layer (GCL). Puncta were present throughout the inner plexiform layer (IPL) for beta(1) and 62-3G1, but not for BD-17. alpha(1)-immunoreactivity (IR) stained a population of presumed OFF rod-dominated bipolar cells, including dendrites, soma, and axon terminals in the distal IPL. A subtype of GABAergic amacrine cell also expressed alpha(1)-IR, with puncta sparsely distributed at the distal and proximal margins of the IPL. Both the OPL and IPL were labeled throughout for alpha(3)-IR, as opposed to the narrow distribution of alpha(1)-IR in the IPL, suggesting that the two alpha-subunits are localized at different synaptic sites. Punctate gamma(1)-IR was observed in the OPL and IPL, whereas gamma(2) was most prominent in cone photoreceptors (identified with calbindin), including the terminal telodendria, in cell bodies of some horizontal cells, amacrine cells, cells in the GCL, and less intensely in the IPL. In addition, several subunits were present in Müller cells. The differential labeling suggests the existence of GABA(A) receptor subtypes with different subunit compositions that mediate multiple GABAergic functions in salamander retina.

Ambystoma↗
PubMed2004

Connexin35/36 gap junction proteins are expressed in photoreceptors of the tiger salamander retina.

Photoreceptors in the vertebrate retina are electrically coupled with one another. Such coupling plays important roles in visual information processing. Physiological properties of rod-rod and rod-cone coupling have been best studied in the salamander retina, yet the cellular and molecular basis of these electrical synapses has not been established. Recently, connexin35/36 (Cx35/36) gap junction proteins were found to be highly expressed in brain and retina, suggesting that it may mediate photoreceptor coupling. To test this idea, we examined the cellular distribution of Cx35/36 in the salamander retina. Western blot analysis showed the expression of Cx35/36 proteins, and confocal microscopy revealed characteristic punctate Cx35/36 immunoreactivity in both synaptic layers. In addition, Cx35/36-positive plaques were detected in the outer nuclear layer (ONL) between neighboring rods, and these plaques outlined the mosaic of the rod network at a level distal to the external limiting membrane. Moreover, although Cx35/36 plaques were detected between some cones and their adjacent rods, the number and size of these plaques was smaller, and their staining intensity was diminished compared with the plaques between adjacent rods. Furthermore, Lucifer yellow injection together with confocal microscopy revealed that Cx35/36-puncta were colocalized with finlike structures of rod cell membrane, with the ultrastructure of gap junctions between paired rod fins having been found by electron microscopy. Therefore, our findings demonstrate that Cx35/36 expression in photoreceptors is primarily located between rods and to a lesser extent between rods and cones, suggesting that Cx35/36 may participate in electrical coupling between rods and between rods and cones in the salamander retina.

Animals↗
PubMed2001

Immunohistochemical localization of atrial natriuretic factor and autoradiographic distribution of atrial natriuretic factor-binding sites in the brain of the cave salamander Hydromantes genei (Amphibia, Plethodontidae).

The distribution of atrial natriuretic factor (ANF)-like immunoreactivity in the central nervous system of the cave salamander Hydromantes genei (Amphibia, Plethodontidae) was investigated by using antisera raised against rat and human ANF(1-28). Concurrently, the location of ANF-binding sites was determined by autoradiography, using radioiodinated human ANF(1-28) as a tracer. In several regions of the brain, including the olfactory bulb, the preoptic area, the ventral thalamus, the tectum of the mesencephalon, and the choroid plexuses inside the ventricles, a good correlation was observed between the distribution of ANF-immunoreactive elements and the location of ANF-binding sites. Mismatching was found in the habenular nucleus, the commissura habenularis, the fasciculum retroflexus, and the interpeduncular nucleus, which contained high levels of binding sites but were devoid of ANF-immunoreactive structures. In contrast, a few other regions, such as the pineal gland and the subcommissural organ, showed a high concentration of ANF-like immunoreactivity but did not contain ANF-binding sites. This study provides the first localization of ANF-like immunoreactivity and ANF-binding sites in the brain of an urodele amphibian. The results show that the ANF peptidergic system in the cave salamander has an organization more simple than the organizations described for the brain of frog or other vertebrates. This feature is probably related to the expression of highly pedomorphic characters in plethodontids. The anatomical distribution of ANF-immunoreactive elements and ANF-binding sites suggests that ANF-related peptides may act as hypophysiotropic hormones as well as neurotransmitters and/or neuromodulators in the salamander brain.

Animals↗
PubMed2004

Somatostatin in the brain of the cave salamander, Hydromantes genei (Amphibia, Plethodontidae): immunohistochemical localization and biochemical characterization.

The distribution of somatostatin-like immunoreactivity in the brain of the cave salamander Hydromantes genei (Amphibia, Plethodontidae) was investigated by using two distinct antisera raised against somatostatin-14. Most somatostatin-positive cells were detected in the ependymal cell layer surrounding the ventricles. These cells possessed the typical morphological characteristics of tanycytes or radial glial cells. Double-labeling with an antiserum against somatostatin and a monoclonal antibody against glial fibrillary acidic protein showed that somatostatin-immunoreactive cells lining the ventricles also exhibited GFAP-like immunoreactivity. Injection of the neurotracer biocytin into the lateral ventricle revealed that neurons lining the ventricles did not contain somatostatin-like immunoreactivity. In the telencephalon, somatostatin-like immunoreactivity was confined to radial glial cells. In the diencephalon, in addition to somatostatin-immunoreactive cells in the ependyma, positive cell bodies were also found in the periventricular preoptic nucleus, the infundibular nucleus, the epiphysis, and the subcommissural organ. In the metencephalon, positive cell bodies were found in the auricula cerebelli, whereas in the rhombencephalon numerous somatostatin-immunoreactive cells were seen lining the ventricular cavity. Immunoreactive nerve fibers were observed in the hypothalamus-median eminence complex. In the pituitary, a discrete group of somatostatin-positive cells was found in the pars distalis. High-performance liquid chromatography analysis of brain extracts revealed that the immunoreactive material coeluted with somatostatin-14. The present results show that the somatostatin peptidergic system in the brain of the cave salamander has a more simple organization than those described in the brain of frog and other vertebrates. This feature is probably related to the expression of high pedomorphic characters in plethodontids. The distribution of somatostatin-like immunoreactivity suggests that, in the cave salamander, somatostatin may act as a neurotransmitter and/or neuromodulator, a central regulator of fluid homeostasis, and a hypophysiotropic neurohormone.

Animals↗
PubMed1988

Topography and cytoarchitecture of the motor nuclei in the brainstem of salamanders.

The organization of the motor nuclei of cranial nerves V (including mesencephalic nucleus), VI, VII, IX, and X is described from HRP-stained material (whole mounts and sections) for 25 species representing five families of salamanders, and the general topology of the brainstem is considered. Location and organization of the motor nuclei, cytoarchitecture of each nucleus, and target organs for nuclei and subnuclei are described. The trigeminal nucleus is separated distinctly from the facial and abducens nuclei and consists of two subnuclei. The abducens nucleus consists of two distinct subnuclei, one medial in location, the abducens proper, and the other lateral, the abducens accessorius. The facial nucleus has two subnuclei, and in all but one species it is posterior to the genu facialis. The facial nucleus completely overlaps the glossopharyngeal nucleus and partially overlaps that of the vagus. In bolitoglossine plethodontid salamanders, all of which have highly specialized projectile tongues, the glossopharyngeal and vagus nuclei have moved rostrally to overlap extensively and intermingle with the anterior and posterior subnuclei of the facial nerve. In the bolitoglossines there is less organization of the cells of the brainstem nuclei: dendritic trunks are less parallel and projection fields are wider than in other salamanders. Some aspects of function and development are discussed; comparisons are made to conditions in anurans; and phylogenetic implications are considered.

Abducens Nerve↗
PubMed1988

Organization of the motor nuclei in the cervical spinal cord of salamanders.

The distribution and cytoarchitecture of motor nuclei of the cervical spinal cord were studied by using HRP techniques (whole mounts and sections) in 22 species of salamanders (families Hynobiidae, Dicamptodontidae, Ambystomatidae, Salamandridae, and Plethodontidae) representing a wide variety of life histories and functional modes of feeding. The nucleus of the first spinal nerve extends from the level of, or slightly caudad to, the root of the tenth cranial nerve, almost to the ventral root of the second spinal nerve. Approximately one-half of this nucleus is situated in the brainstem. This anterior extension is longest in bolitoglossine plethodontids. The nucleus of the second spinal nerve extends from the root of the first spinal nerve to the dorsal root of the second spinal nerve. The nuclei of the first and second spinal nerves in all species except bolitoglossines have motor neurons arranged in two columns: a lateral one containing large spindle-shaped cells and a medial one containing pear-shaped or polygonal smaller cells. The primary dendrites of these lateral and medial cells are parallel and their arborization is relatively narrow. In contrast, bolitoglossines lack the lateral motor column. The nucleus of the first spinal nerve consists only of a medial band of pear-shaped and sometimes polygonal cells, and the nucleus of the second spinal nerve is a wider band of pear-shaped and polygonal cells which are always situated inside the periventricular gray matter. The arrangement of the somata in bolitoglossines is less organized and the primary dendrites are less parallel and have a broader arborization than in other salamanders. In all species, cells in the second spinal nucleus are arranged in a less orderly manner than those in the first. All salamanders studied possess a spinal accessory nerve whose motor neurons are located in the cervical spinal cord; the axons leave the brainstem with fibers of the vagus nerve. The rostrocaudal extent of this nucleus differs markedly among species. In bolitoglossines the nucleus is more or less restricted to the region of the nucleus of the second spinal nerve. In all other species studied, the accessory nucleus extends from the obex to the caudal end of the nucleus of the third spinal nerve. In the tribe Plethodontini the cytoarchitecture of the accessory nucleus is similar to that of the second spinal. In desmognathine and hemidactyliine plethodontids as well as in all nonplethodontid species studied the nucleus consists of pear-shaped and cone-shaped cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Accessory Nerve↗
PubMed1993

Amphibian-specific regulation of polysialic acid and the neural cell adhesion molecule in development and regeneration of the retinotectal system of the salamander Pleurodeles waltl.

Antibodies specific to the neural cell adhesion molecule (NCAM-total), the 180 x 10(3) M(r) component of NCAM (NCAM-180) and polysialic acid (PSA) were used in immunohistochemistry and Western blots to detect the spatiotemporal dynamics of these molecules in development and regeneration of the retinotectal system of Pleurodeles waltl. NCAM-total and NCAM-180 are continuously expressed in the retina, optic nerve, and tectum of the developing and adult salamander. This is also found for the 140 x 10(3) M(r) component of NCAM in Western blots of the retina. In the larval retina, PSA is present in the inner plexiform layer (IPL) and a few cells in all nuclear layers. At metamorphosis, PSA expression in the retina strongly increases in the layer of cone photoreceptor somata. Several cells in the inner nuclear layer and Müller cell processes also begin to express PSA. This pattern persists into adulthood. The optic nerve and the tectum are strongly PSA-immunoreactive throughout development. In the adult optic nerve and optic fiber pathway in the brain, PSA expression is selectively downregulated. In the crush-lesioned adult optic nerve, regenerating fibers are NCAM-180-positive but PSA-negative. This demonstrates a molecular difference between growing nerve fibers of Pleurodeles in development and in regeneration. PSA regulation is closely correlated with metamorphosis, thus suggesting that PSA expression may be under hormonal control. Some aspects of PSA and NCAM isoform expression patterns in the retinotectal system of salamanders differ considerably from that of other vertebrates. The sustained expression of NCAM isoforms in adult salamanders might be due to secondary simplification (paedomorphosis).

Animals↗
PubMed2005

Limb chondrogenesis of the seepage salamander, Desmognathus aeneus (amphibia: plethodontidae).

Salamanders are infrequently mentioned in analyses of tetrapod limb formation, as their development varies considerably from that of amniotes. However, urodeles provide an opportunity to study how limb ontogeny varies with major differences in life history. Here we assess limb development in Desmognathus aeneus, a direct-developing salamander, and compare it to patterns seen in salamanders with larval stages (e.g., Ambystoma mexicanum). Both modes of development result in a limb that is morphologically indistinct from an amniote limb. Developmental series of A. mexicanum and D. aeneus were investigated using Type II collagen immunochemistry, Alcian Blue staining, and whole-mount TUNEL staining. In A. mexicanum, as each digit bud extends from the limb palette Type II collagen and proteoglycan secretion occur almost simultaneously with mesenchyme condensation. Conversely, collagen and proteoglycan secretion in digits of D. aeneus occur only after the formation of an amniote-like paddle. Within each species, Type II collagen expression patterns resemble those of proteoglycans. In both, distal structures form before more proximal structures. This observation is contrary to the proximodistal developmental pattern of other tetrapods and may be unique to urodeles. In support of previous findings, no cell death was observed during limb development in A. mexicanum. However, apoptotic cells that may play a role in digit ontogeny occur in the limbs of D. aeneus, thereby suggesting that programmed cell death has evolved as a developmental mechanism at least twice in tetrapod limb evolution.

Animals↗
PubMed1998

Geographical variation in agonistic behaviour in a ring species of salamander, Ensatina eschscholtzii.

Ensatina eschscholtzii is a plethodontid salamander with several geographical races distributed in a ring-like series throughout the coastal mountains and inland Sierra Nevada mountains of California. Populations of these salamanders show genetic and morphological divergence, and in this study, we examined divergence in overt aggressive, passive aggressive/exploratory, avoidance and sensory behaviours in four populations. Two of the populations represent a zone of secondary contact between coastal and inland lineages of Ensatina. We recorded behaviour of resident salamanders paired with same-sex intruders during the non-courtship season. The residents' behaviour was affected independently by the population of the resident and the population of the intruder but not by the interaction between the resident population and the intruder population. Levels of agonistic and sensory behaviour showed a high degree of constraint among the populations. These behaviours also showed divergence among coastal and inland populations, and the geographical variation in behaviour is consistent with the phylogenetic history of Ensatina. Convergent evolution of behaviour appears to have occurred at the zone of secondary contact between the coastal and inland lineages. Variation in agonistic and sensory behaviour among the populations observed and between the sexes suggests that there may be geographical and sexual variation in territoriality or competition. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Fate and the biochemical effects of 2,4,6-trinitrotoluene exposure to tiger salamanders (Ambystoma tigrinum).

Biotransformation, metabolic enzyme profiles, and the glutathione antioxidant system in tiger salamanders (Ambystoma tigrinum) from a 14-day exposure to 2,4,6-trinitrotoluene (TNT) in situ were examined. Concentrations of parent compound and metabolites were measured in skin, kidney, and liver tissue. In addition, cytochrome P450 (P450) and cytochrome b5 content and their dependent isozyme activities, ethoxyresorufin O-dealkylation, pentoxyresorufin O-dealkylation, and the glutathione antioxidant system in the skin, liver, lung, kidneys, and blood were evaluated. Considerable differences were found in relative concentrations of TNT and its metabolites in the skin, relative to the liver and kidney. Trace amounts of TNT were detected only in the skin and liver of exposed animals while one of the secondary reduction metabolites, 2,6-diaminonitrotoluene, was found only in liver and kidney. Differences in the metabolite concentrations between systemic organs (liver, kidneys) and the skin suggest that the skin may be important in the primary reduction of TNT. In addition, measurable levels of these basal enzyme indicators were detected; yet of those evaluated only hepatic P450 content was affected by TNT exposure. The qualitative and quantitative differences in TNT and its metabolites in tissues suggest the fate and metabolism of the TNT in salamanders. Furthermore, results indicate that tiger salamanders possess considerable levels of xenobiotic metabolizing and antioxidant enzymes in these tissues but are not sensitive indicators of TNT exposure.

Ambystoma↗
PubMed1996

Courtship behavior and plasma levels of androgens and corticosterone in male marbled salamanders, Ambystoma opacum (ambystomatidae).

We measured plasma levels of testosterone, dihydrotestosterone (DHT), and corticosterone for male marbled salamanders (Ambystoma opacum) collected during the breeding season. Our goal was to ascertain whether steroid levels changed in response to particular reproductive behaviors or laboratory confinement. Six groups of salamanders were examined: (a) MIGRATING, males migrating toward the pond basin during the breeding season; (b) LABORATORY, males kept under confined conditions in the laboratory for 10 days; (c) LAB-FIELD, laboratory males that were later released into seminatural enclosures in the field; (d) COURTING, males from male-female pairs in which the male actively courted the female (and deposited at least one spermatophore); (e) SOLO, males that were individually isolated from conspecifics; and (f) MALE-MALE, males that were placed together in pairs, and in which one male actively courted the other male. In three groups (COURTING, SOLO, and MALE-MALE), salamanders were placed in containers for observation and each male was observed for at least 2 hr prior to a plasma sample being taken. Circulating levels of testosterone, DHT, and corticosterone did not differ significantly for males in these groups. The similarity of androgen levels among the three groups indicated a lack of behaviorally evoked change under experimental conditions designed to reveal a behavior-androgen response. Male A. opacum differ taxonomically from other amphibians showing a behavior-androgen response (three species of toads in the genus Bufo) and also lack amplexus and male-male combat during competition for mates. The effects of confinement were indicated by levels of testosterone and DHT in LABORATORY males that were significantly lower than average levels of males in the following groups: MIGRATING, LAB-FIELD, and MALE-MALE. We inferred that LAB-FIELD males, following their release to seminatural enclosures, were able to regain plasma androgen levels typical of migrating males. This increase is one of very few demonstrations for amphibians of an increase in androgen levels upon release from laboratory confinement. Levels of corticosterone did not differ significantly between males that were active in the field and males that were kept in the laboratory. The similarity of corticosterone levels among these groups differs from the typical pattern of elevated corticosterone and depressed androgen levels in captive amphibians. Maximal corticosterone levels in breeding male A. opacum may act differently than in other species in which chronic elevations inhibit the pituitary-gonadal axis.

Ambystoma↗
PubMed1985

Trends in the functional morphology and sensorimotor control of feeding behavior in salamanders: an example of the role of internal dynamics in evolution.

Organisms are self-producing and self-maintaining, or "autopoietic" systems. Therefore, the course of evolution and adaptation of an organism is strongly determined by its own internal properties, whatever role "external" selection may play. The internal properties may either act as constraints that preclude certain changes or they open new pathways: the organism canalizes its own evolution. As an example the evolution of feeding mechanisms in salamanders, especially in the lungless salamanders of the family Plethodontidae, is discussed. In this family a large variety of different feeding mechanisms is found. The authors reconstruct this evolutionary process as a series of "bifurcation points" of either constraints or opportunities forming a sequence of preconditions for the formation of a high-speed projectile tongue characteristic of tropical salamanders. Furthermore, it is shown how parallel evolution of seemingly unrelated domains within an organism such as respiratory physiology, life history biology and pattern of ontogeny has rather direct relevance to the feeding biology, thus demonstrating that organisms always evolve as wholes.

Animals↗
PubMed1984

The projection from the olfactory epithelium to the olfactory bulb in the salamander, Ambystoma tigrinum.

Odor quality may be represented as a "topographic" code of responses of receptor cells throughout the olfactory epithelium, with this code conveyed to the central nervous system by a topographic projection from the olfactory epithelium to the olfactory bulb. There is good evidence for topographic differences in odor-induced receptor cell activity in the tiger salamander but there is no evidence for a topographic epithelium-to-bulb projection in this species. In the present study 3H-leucine autoradiography was used to trace the projections of olfactory receptor neurons in the tiger salamander. Thirteen animals received small injections of tritiated leucine into different regions of the dorsal or the ventral olfactory epithelium, or into the ventrolateral, "vomeronasal organ". The results show that the anterior-to-posterior axes in the dorsal and ventral epithelia are represented along the ventral-to-dorsal axis in the rostral end of the olfactory bulb. The "vomeronasal organ" projects to the caudal end of the bulb. We conclude that the central projection of the olfactory epithelium in the tiger salamander is topographically organised only along the antero-posterior axis and not the medio-lateral axis. Thus epithelial receptor cell activity along the anteroposterior axis would be represented in the glomerular layer of the bulb by activity along its ventro-dorsal axis.

Ambystoma↗
PubMed1986

Olfactory responses of aquatic and terrestrial tiger salamanders to airborne and waterborne stimuli.

Electro-olfactograms (EOGs) were used to assess olfactory responding by aquatic larval and terrestrial adult tiger salamanders (Ambystoma tigrinum) to airborne volatile compounds, and volatile and non-volatile compounds in aqueous solution. Both forms of salamander showed saturation effects to presentations of airborne stimuli (Fig. 2). Saturation was not observed, however, to stimulus presentations in aqueous solution (Figs. 2, 3). When threshold values and concentration-response curve parameters were compared, non-volatile amino acids in solution were more potent stimuli for larvae while airborne volatiles were more potent stimuli for adults (Tables 1, 2). We infer that metamorphosis in the tiger salamander is accompanied by changes in olfactory response characteristics, due possibly to changes in receptor population, changes in perireceptor properties (e.g. mucus) or to changes in stimulus access.

Ambystoma↗
PubMed2001

Immunocytochemical demonstration of visual pigments in the degenerate retinal and pineal photoreceptors of the blind cave salamander (Proteus anguinus).

Visual pigments in the regressed eye and pineal of the depigmented neotenic urodele, the blind cave salamander (Proteus anguinus anguinus), were studied by immunocytochemistry with anti-opsin antibodies. The study included light- and electron-microscopic investigations of both the eye and the pineal organ. A comparison was made with the black pigmented subspecies Proteus anguinus parkelj (black proteus), which has a normal eye structure. In the retina of the black proteus, we found principal rods, red-sensitive cones and a third photoreceptor type, which might represent a blue- or UV-sensitive cone. Photoreceptors in the regressed eye of the blind cave salamanders from the Planina cave contained degenerate outer segments, consisting of a few whorled discs and irregular clumps of membranes. The great majority of these outer segments showed immunolabelling for the red-sensitive cone opsin and only a few of them were found to be positive for rhodopsin. An even more pronounced degeneration was observed in the photoreceptors of the animals derived from the Otovec doline, which are completely devoid of an outer segment, most of them not even possessing an inner segment. Even in some of these highly degenerate cells, the presence of rhodopsin could be detected in the plasma membrane; however, immunoreactions with antibodies recognizing cone visual pigment were negative. In the pineals of all studied animals, the degenerate photoreceptor outer segments were recognized exclusively by the antibody against the red-sensitive cone opsin. The presence of immunopositive visual pigments indicates the possibility of a retained light sensitivity in the blind cave salamander photoreceptors.

Animals↗
PubMed1993

Quantitative analyses of the coexistence of gamma-aminobutyric acid in substance P-amacrine cells of the larval tiger salamander retina.

The present study was performed as part of a systematic examination of gamma-aminobutyric acid's (GABA) coexistence with other classical transmitters and neuropeptides in neuronal populations of the larval tiger salamander retina. Substance P immunocytochemistry was combined with either GABA immunocytochemistry or autoradiography of high-affinity GABA uptake to examine for the presence of GABA in substance P-amacrine cells of the larval tiger salamander retina. Double-label analyses revealed two populations of substance P-amacrine cells that express both markers of GABA activity. One population was situated in the innermost cell row of the inner nuclear layer, while the other population was located in the ganglion cell layer. In both cases, these double-labelled cells accounted for approximately 10% of substance P-amacrine cells in their respective layers. The present study demonstrates, therefore, that substance P-amacrine cells in the larval tiger salamander retina can be categorized on the basis of their coexisting/non-coexisting relationships with GABA and suggests a possible functional diversity in the population of substance P-amacrine cells.

Ambystoma↗