SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Glial fibrillary acidic protein immunohistochemistry revealed the presence of radial glial cells in the adult salamander brain, forming endfeet on the subpial surface and on blood vessels. In the spinal cord, glial cells are displaced from the ependyma. In mice, antibodies stained astrocytes, and radial glial cells in juveniles.
Enkephalin immunocytochemistry was combined with either glycine immunocytochemistry or autoradiography of high-affinity glycine uptake to examine for colocalization of enkephalin and glycine in amacrine cells of the larval tiger salamander retina. A total of 995 enkephalin-immunoreactive amacrine cells were visualized in double-label preparations. None of the enkephalin-labelled cells was observed to co-label for markers of glycinergic activity.
Dissociated Muller (glial) cells from the neotenous tiger salamander retina respond electrogenically and rheogenically to three putative catecholamine (CA) neurotransmitters, epinephrine, norepinephrine and dopamine. All 3 CAs stimulate a net inward current and an increase in input resistance (Rn). The Muller cell response to the CAs is concentration dependent. At high concentrations ascorbate, an antioxidant used to protect the CAs from oxidation, stimulated a net outward current and a decrease in Rn. When the effects of ascorbate were considered, the CA response at 1 mM was no larger than the response at 100 microM, indicating that 100 microM CA maximally stimulated the Muller cell response.
The voltage and current responses of depolarizing bipolar cells to central illumination were studied by means of whole-cell recording in retinal slices of the larval tiger salamander, Ambystoma tigrinum. To stabilize the responses, it was necessary to limit exchanges between the cytosol and the solution in the patch pipette by reducing the diameter of the pipette tip opening. The current-voltage relationship of the cell membrane in darkness displayed a strong outward rectification, and the inward current evoked by light could be consistently reversed by depolarization only when tetraethylammonium was added to the pipette solution. As a result of the membrane non-linearity, increases in the intensity of bright lights caused relatively smaller amplitude increases in the voltage than in the current responses and the latter had a proportionally smaller after-effect. With larger pipette tip openings, the cytosol equilibrated with the pipette filling solution. Under these conditions the light-evoked responses gradually became slower and acquired an on-off pattern, their final amplitude and polarity being determined by the ratio of the chloride concentrations on each side of the cell membrane. This finding is interpreted as revealing the existence of two response components: a chloride-dependent on-off increase in conductance and a faster depolarizing input that was lost through diffusional exchange. Addition of GTP and ATP to the electrode filling solution had a stabilizing effect on the labile component, whether or not cyclic GMP was also included. Observations on the magnitude of the conductance changes and on diphasic reversals indicate that the labile response component, presumably representing direct input from photoreceptors, is caused by an increase in conductance. The resulting inward current was still present at a low intracellular chloride concentration and may be assumed, therefore, to be carried by a cation influx.
Synaptic transmission between photoreceptors and bipolar cells was studied in dark-adapted tiger salamander retinas. Based on the relative light sensitivity, bipolar cells, either depolarizing (DBC) or hyperpolarizing (HBC), fell into two groups: one receives inputs primarily from rods (rod-dominated bipolar cells, DBCR and HBCR) and the other receives inputs primarily from cones (cone-dominated bipolar cells, DBCC and HBCC). The input-output relations of the rod-DBCR and rod-HBCR synapses were determined by plotting the voltage responses of the rod and DBCR (or HBCR) to dim 500-nm light steps, which polarizes only the rods but not the cones. The slope gains of both synapses were the highest near the dark rod voltage (-2.5 for the rod-DBCR synapse and 4.0 for the rod-HBCR synapse), and they (the absolute values) became progressively smaller at more hyperpolarized rod voltages.
The polyamines spermine and spermidine are present in neural tissue, but their functions there are not well understood. Recent work suggests that the NMDA subtype of glutamate receptors, other glutamate receptor subtypes, and certain K(+)-channels, are neural targets for polyamines. To better understand the neuron-specific roles of polyamines, we have developed antibodies that interact with spermine and spermidine in aldehyde-fixed tissue and used these antibodies in immunocytochemical studies to determine the cellular localization of these polyamines in the tiger salamander retina. The affinity-purified, polyclonal antibodies were highly specific for spermine and spermidine, exhibiting < 1% cross reactivity with putrescine, and virtually no cross-reactivity with GABA, arginine, lysine, or glutaraldehyde. Polyamine labeling was most abundant in cells in the inner half of the inner nuclear layer and in the ganglion cell layer. Some cells in the outer half of the inner nuclear layer are labeled, and there was some labeling in both synaptic layers. Double-labeling experiments indicated (1) all GABAergic amacrine cells were polyamine-positive; and (2) all ganglion cells (identified by back-filling after microinjections of rhodamine in the optic nerve) were polyamine-positive. These results are consistent with a role for polyamines as modulators of NMDA receptor function and channel function in the inner retina.
The presence of kainic (KA) and quisqualic acid (QA) receptors on inner retinal neurones of the axolotl Ambystoma mexicanum has been studied using intracellular recording techniques. In the presence of CoCl2, which blocks neurotransmitter release, KA and QA depolarized the membrane. The minimum concentration of KA that induced a response was 1 microM and a maximum response was obtained with 10 microM (EC50: 3 microM). The operating range of QA was between 0.5 and 5 microM with an EC50 of 1 microM. These data show that inner retinal cells of the axolotl are sensitive to KA and QA. Cis-2,3-piperidine dicarboxylic acid (PDA, 3 mM) completely blocked responses to 5 microM KA, but not those induced by 2 microM QA. This suggests that the KA- and QA-sensitive receptors on inner retinal cells of the salamander are pharmacologically different and that PDA can be a valuable tool in distinguishing KA- and QA-sensitive receptors on these neurones.
Depolarizing overshoot responses at the cessation of a test light step were observed in horizontal cells (HCs) and in a population of photoreceptors (rodCS) in light-adapted retinas of the tiger salamander. An anode break regenerative conductance may contribute to the overshoot responses in rodcS(o-wave). The overshoot responses in HCs consist of two components: a fast alpha-wave whose amplitude and time course follow those of the o-wave; and a slow beta-wave whose amplitude and time course vary with the HC membrane voltage. These results are consistent with the notion that the alpha-wave is a postsynaptic response to the voltage overshoots of the o-waves in rodCS and the beta-wave is mediated by voltage-dependent conductances in the HC membrane. A possible function of the HC overshoot responses is to reset the amplitude of the light-adapted HC responses during repetitive or rapidly changing light stimulation.
Two distinct groups of catecholaminergic neurons were observed by histofluorescence techniques in the spinal cord of the axolotl salamander, only one of which was detected in normal intact cords. These neurons were located in the ventral ependymal zone. When the spinal cord was transected, a second group of catecholaminergic neurons was observed in the lateral portions of the ventral gray matter of the spinal cord caudal to the transection site. These observations suggest that the amount of catecholamine in the somata of the second group of neurons is normally very small and that catecholamines accumulate in the perikarya after transection of their ascending axons.
To elucidate the environmental factors and endocrine mechanisms which are responsible for inducing neoteny in the salamander Hynobius retardatus, the effect of temperature on the growth and metamorphosis of this amphibian, as well as the actions of thyroid hormone and prolactin at low temperature, were studied. (1) The metamorphosis of larvae cultivated at 10 degrees was significantly delayed compared with that of larvae cultivated at 22 degrees, but the metamorphosis was eventually completed. At 4 degrees, metamorphosis never occurred, even after 2 years. (2) Exogenously administered thyroid hormone accelerated metamorphosis at 10 degrees or 22 degrees, but was ineffective in larvae kept at 4 degrees, whether administered by injection or immersion. (3) If a higher concentration of thyroid hormone was given by a single injection to larvae cultured at 4 degrees, an appreciable acceleration of metamorphosis was observed after transferring the larvae to 22 degrees. (4) Unlike thyroid hormone, prolactin promoted growth at 4 degrees.
In order to study the environmental conditions and the endocrine mechanism which induce neotenous characteristics, the fine structure of the thyroid glands of larvae of the salamander Hynobius retardatus were examined. The thyroid glands of larvae exposed to a low temperature (4 degrees) were compared with those of larvae exposed to a higher temperature (20 degrees). At 4 degrees, the follicular lumen was large and its contents of low electron density; the epithelial cells were flat or cuboidal. In contrast, the 20 degrees larvae showed a small dense lumen and tall cylindrical epithelial cells, which may indicate a higher level of activity. No apical vesicles were found in the epithelial cells of the 4 degrees larvae, although they were present in 20 degrees larvae. On the other hand, in 4 degrees larvae the chromatin in the nuclei was scattered, while in 20 degrees larvae it was condensed. In addition, large dense granules occupied 2.4% of the epithelial cytoplasm in 4 degrees larvae and as much as 7.3% in 20 degrees larvae. The structural features observed in larvae exposed to the cold resembled those reported for thyroid glands made inactive by a lack of thyrotropin.
The sensitivity of thyroid glands from the tiger salamander, Ambystoma tigrinum, to bovine thyrotropin (bTSH) was tested in vitro. Thyroids were taken from subjects representing metamorphic stages I (premetamorphic larvae), II (onset of climax), and VII (completion of gill resorption), as well as from captivity control larvae. Exogenous TSH reduced the cumulative uptake of 125I in vitro by thyroids from stage I larvae after 24 and 48 hr. The capacity of thyroids to release thyroxine (T4) in vitro was used subsequently as a measure of their responsiveness to TSH. Baseline levels of T4 release in vitro were variable but did not differ significantly among developmental stages. A low dose of bTSH (5 X 10(-6) IU/ml) did not increase in vitro T4 release compared with that of controls. A larger dose (5 X 10(-4) IU/ml) caused greater increases in T4 release from thyroids of stage II and VII subjects than from those of controls. This dose produced only a small response by thyroids from captivity-control subjects. The results suggest that the thyroids of Ambystoma increase in their capacity to respond to TSH during the process of metamorphosis.
Treatment of male and female tiger salamander larvae with testosterone (0.3 micrograms/g body weight/day) induced precocious formation of ventral cloacal glands and stimulated proliferation and differentiation of mucous and granular (serous) glands in the ventral dermis of the skin. Lower doses of testosterone produced no visible glandular effects but did cause hyperemia and edema in the cloacal region. Prolactin (0.5 micrograms/g body weight/day) enhanced the action of testosterone on the cloacal glands, increasing both the amount of gland induced and the degree of glandular secretion. There was no apparent effect of prolactin alone on cloacal glands or any effect of prolactin with or without testosterone on the dermal glands. The possible homology of the amphibian ventral cloacal gland to the mammalian prostate gland is discussed.
The testis of the salamander, Necturus maculosus, is advantageous for studying biochemical changes during spermatogenesis because germ cells and associated Sertoli and Leydig cells are topographically separated by stage of development. Using extracts of staged tissue samples and [3H]testosterone (T) in a standard binding assay, followed by Sephadex LH-20 or DNA-cellulose chromatography to separate free and bound steroid, we have identified a T-binding protein having physicochemical characteristics of a classical androgen receptor (AR): high affinity (Kd = 10(-9) M), limited capacity (Bmax) = 10(-10) M or 350 fmol/g tissue) and androgen specificity (T = 5 alpha - dihydrotestosterone greater than progesterone = corticosterone greater than estradiol). AR was present in nuclear extracts, where greater than 80% of binding sites were occupied by endogenous ligand, but was not detectable in cytosol. On linear sucrose gradients, nuclear AR sedimented at 3-4 S in both low and high ionic-strength buffers and, by this and other criteria, was distinguishable from the nonreceptor androgen binding protein (ABP) of the same species. The diffuse distribution of AR in germinal and nongerminal (glandular) tissues at all developmental stages is consistent with a dual localization in Sertoli cells and Leydig cells, as previously reported in mammals, and further suggests a regulatory role of androgen throughout spermatogenesis.
Tiger salamanders (Ambystoma tigrinum) were trained to respond to two dissimilar odorants (i.e., cyclohexanone, dimethyl disulfide) but not to a third odorant (n-butanol). When the training criterion was met, the animals were anesthetized and given nasal lavages of saline or odorants in saline. Lavage with cyclohexanone decreased responding to cyclohexanone but not dimethyl disulfide, and vice-versa, in later behavioral tests. Likewise, ethyl acetoacetate lavage produced selective response decrements to cyclohexanone. Lavage with n-butanol had no effect on responding to presentations of either cyclohexanone or dimethyl disulfide. The effects of lavage increased with increasing odorant concentration. Thus, lavage with 0.05 M cyclohexanone or ethyl acetoacetate produced more persistent response decrements than lavage with 0.01 M concentrations of either odorant. Such results are consistent with several testable interpretations, including the possibility the response decrements could reflect the nature of odorant-receptor interactions.
In this investigation, we describe two precise tests of visual function that integrate quasinatural situations with time-lapse video recording and infrared computerized monitoring of activity to assess movement detection and phototaxic tendencies, respectively. Four groups of larvae from A. punctatum, A. tigrinum, A. mexicanum, and a mutant albino axolotl were tested in an alley containing light and dark halves and lined with infrared sensors to monitor their phototaxic response. A. punctatum showed no phototaxic tendency, while the other three groups displayed a strong negative phototaxic response. Enucleation of the eyes in mutant albinos eliminated the negative phototaxis. Visual detection of motion was tested by videorecording the behavior of A. punctatum, A. mexicanum, and the mutant albino axolotl larvae while they explored a large bowl with 6 small vials on the perimeter, one of which contained white worms. A. punctatum rapidly approached the worm vial and engaged in intense predatory behavior. A. mexicanum responded to the presence of worms very slowly and rapidly lost interest. Albino axolotls displayed no visual recognition of the worms. The results indicate that visual function can be precisely determined in larval salamanders utilizing behavioral measures consistent with the animal's natural tendencies.
The standard rate of O2 consumption of various aquatic lunged salamanders is compared for animals breathing water only and for animals breathing both air and water. When submerged and prevented from surfacing in air-equilibrated water, most species studied were capable of survival for periods of at least two weeks. The animals that were allowed to respire bimodally exhibited an increased rate of O2 consumption relative to their submerged counterparts who were denied the use of pulmonary respiration. The standard rate of oxygen consumption is submerged and air-and-water-breathing Siren lacertina was determined over a large range of body size. The rate of the bimodally breathing animals was higher than that of the submerged animals, and the difference increased with increasing body size. These data suggest that it is the oxygen transport capacity of these animals that at least partially regulates the standard rate of O2 consumption rather than all such control being exerted at the cellular level.
In the lungless salamander Desmognathus fuscus, mean body weight 4.5 g, the changes in total body concentration of adenosine triphosphate (ATP), creatine phosphate (CP) and lactate (LA) were measured during exposure to a severely hypoxic atmosphere (PO2 = 25 Torr) for 48 h at 13 degrees C. ATP and CP decreased, reaching a minimum at 3 h of exposure, and LA increased, attaining maximum values after 12 to 24 h of hypoxia. Thereafter recovery was observed and control values of ATP, CP and LA were reached after 48 h of sustained hypoxia. This behavior is attributed to a biochemical adjustment to hypoxia of the metabolic machinery which leads to normalization of chemical energy stores in spite of O2 uptake being persistently reduced to 30% of its normoxic level. The anaerobic energy yield derived from splitting of ATP and CP and from LA formation corresponded to about 2/3 of the oxidative energy deficit during the first 3 h of hypoxia. Thereafter anaerobic mechanisms were responsible for insignificant contributions to the energy balance.