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PubMed2002

The naris muscles in tiger salamander. II. Innervation as revealed by enzyme histochemistry and immunocytochemistry.

The naris muscles control the aperature of the external naris in tiger salamanders, Ambystoma tigrinum, and may contribute to glandular secretion. Autonomic neurons of the palatine ganglion and possibly neurons associated with the nervus terminalis innervate these muscles. To elucidate the neural control of the naris muscles, neurotransmitters in nerve fibers supplying the naris muscles and in neurons of the palatine ganglion were examined using acetylcholinesterase enzyme histochemistry and immunocytochemistry to visualize possible peptide candidates for muscle innervation. The naris muscles, autonomic neurons, and associated nerve fascicles demonstrated strong acetylcholinesterase labeling, and the muscles were innervated by substance P fibers passing through the palatine ganglion from the trigeminal ganglion. Gonadotropin-releasing hormone and molluscan cardioexcitatory peptide-like immunoreactivities were found in secretory cell bodies and/or fibers in the palatine ganglion, and gonadotropin-releasing hormone was found in fiber projection pathways into the muscles. Vasoactive intestinal peptide was found in cell bodies and fibers of the palatine ganglion but appeared to provide a sparse innervation to the naris dilator muscle only. These findings suggest a typical autonomic cholinergic and sensory innervation of the naris muscles with some variations in peptide innervation. The presence of gonadotropin-releasing hormone in palatine ganglion and naris constrictor muscle suggests a potential modulation of autonomic neurons and perhaps even muscle fibers by this neuropeptide. We hypothesize that this reproductive hormone may modulate the activity of the naris constrictor muscle during reproductively appropriate events in order to provide access of pheromones to the vomeronasal organ.

Acetylcholinesterase↗
PubMed1997

5-HT-like immunoreactivity in the brains of plethodontid and salamandrid salamanders (Hydromantes italicus, Hydromantes genei, Plethodon jordani, Desmognathus ochrophaeus, Pleurodeles waltl): an immunohistochemical and biocytin double-labelling study.

The distribution of 5-HT-like-immunoreactive cell bodies and fibres was studied in the brains of the salamanders Hydromantes italicus, H. genei, Plethodon jordani, Desmognathus ochrophaeus (family Plethodontidae), and Pleurodeles waltl (family Salamandridae). In addition, double-labelling experiments with biocytin were carried out to identify the relationship between serotonergic fibres and neurons involved in the processing of sensory and sensorimotor information. In all species, 5-HT-immunopositive somata are found in the ventral thalamus close to the ventricle forming the paraventricular organ. In the hypothalamus, cells are labelled in the ependymal layer around the infundibular recess and at the lateral edge of the periventricular grey. In the pretectum, a few immunoreactive cells are situated dorsolaterally in the grey matter. In the tegmentum and medulla oblongata, cells of the raphe nuclei are regularly distributed along the midline; labelled perikarya are occasionally found in the cervical spinal cord. 5-HT-like-immunoreactive fibres are widely distributed throughout the nervous system. Densely arborizing fibres are found in the olfactory bulb, striatum and amygdala. Distinct fibre projections extend in the ventral thalamus and tectum. Biocytin tracing of striatal and tectal projection neurons and ascending reticular neurons combined with the demonstration of 5-HT suggest that the striatum, the tectum and the ascending activating system are strongly influenced by 5-HT.

Animals↗
PubMed1998

Connectivity of the salamander pretectum: an in-vitro (whole-brain) intracellular tracing study.

The amphibian optic tectum and pretectum have been analyzed in detail anatomically and physiologically, and a specific model for tecto-pretectal interaction in the context of the visual guidance of behavior has been proposed. However, anatomical evidence for this model, particularly the precise pattern of pretectotectal connectivity, is lacking. Therefore, we stained pretectal neurons intracellularly in an in-vitro preparation of the salamanders Plethodon jordani and Hydromantes genei. Our results demonstrate that the projections of neurons of the nucleus praetectalis profundus are divergent and widespread. Individual neurons may project divergently to telencephalic (ipsilateral amygdala and striatum), diencephalic (ipsi-and contralateral thalamus, contralateral pretectum), and mesencephalic (ipsi- and contralateral tectum and tegmentum) centers, and to the ipsi- and contralateral medulla oblongata and rostral spinal cord. The projection of pretectal cells to the optic tectum is bilateral; axonal structures do not show discernible patterns and are present in all layers of the superficial white matter. A classification of pretectal neurons on the basis of axonal termination pattern or dendritic arborization has not been possible. Our results do not support the hypothesis that a distinct class of pretectal neurons projects to a particular subset of tectal cells. Rather, the pretectum appears to influence the tectum indirectly, acting either on retinal afferents or modulating inhibitory interneurons.

Animals↗
PubMed2003

Color change and color-dependent behavior in response to predation risk in the salamander sister species Ambystoma barbouri and Ambystoma texanum.

Although many organisms show multiple types of trait responses to predation risk (e.g., shifts in behavior, morphology, color, chemistry or life history), relatively few studies have examined how prey integrate these multiple responses. We studied the joint expression of color and behavioral responses to predation risk in two sister species of salamander larvae that live in habitats with different selection pressures. We examined responses to predation risk in three situations that differed in availability of refuge and substrate color heterogeneity, and thus availability of behavioral options for reducing risk. Relative to Ambystoma texanum, A. barbouri larvae were darker in color and showed a greater range of color change. With no variation in background color or refuge available, both species exhibited color change to better match the available background. The degree of color change showed by both species, however, did not depend on predation risk. Given the option to choose between light and dark substrates, A. texanum exhibited behavioral background matching (i.e., they preferred substrates that matched their own body color), while A. barbouri's substrate preferences did not depend on their initial body color. Instead, A. barbouri responded to risk by showing a strong preference for dark substrates, followed by a change to a darker body color. With refuge available, A. texanum's refuge use was color-dependent; larvae that were well camouflaged spent less time in refuge. In contrast, A. barbouri showed strong refuge use in response to risk, regardless of their body color. Overall, these results reflect how conflicting selection pressures (predation risk, habitat ephemerality, risk of UV damage) and species differences in mean color and ability to change color can govern the interplay of complementary and compensatory behavioral and color responses to predation risk.

Adaptation, Physiological↗
PubMed2003

A growth/mortality trade-off in larval salamanders and the coexistence of intraguild predators and prey.

Behavioral and morphological traits often influence a key trade-off between resource acquisition and vulnerability to predation, and understanding trait differences between species can provide critical insight into their interactions with other species and their distributions. Such an approach should enhance our understanding of the criteria for coexistence between species that can interact through both competition and predation (i.e. intraguild predators and prey). I conducted a common garden experiment that revealed strong differences between three guild members (larval salamanders Ambystoma laterale, A. maculatum, and A. tigrinum) in behavior, morphology, and growth in the presence and absence of a shared top predator (the larval dragonfly Anax longipes). All three species also reduced their activity and modified their tail fin depth, tail muscle length, and body length in response to non-lethal Anax. Species that act as intraguild predators were more active and could grow faster than their intraguild prey species, but they also suffered higher mortality in laboratory predation trials with Anax. I also used survey data from natural communities to compare the distribution of Ambystoma species between ponds differing in abiotic characteristics and predatory invertebrate assemblages. An intraguild prey species ( A. maculatum) was found more reliably, occurred at higher densities, and was more likely to persist late into the larval period in ponds with more diverse invertebrate predator assemblages. Taken together, these results indicate that top predators such as Anax may play an important role in influencing intraguild interactions among Ambystoma and ultimately their local distribution patterns.

Animals↗
PubMed2003

Mothers influence offspring body size through post-oviposition maternal effects in the redbacked salamander, Plethodon cinereus.

In the terrestrial salamander (Plethodon cinereus), previous work has shown that mother's body size is positively correlated to offspring size at the time of hatching even after controlling for the effects of egg size. This study was designed to determine whether maternal body size affects offspring size via pre-oviposition factors (e.g., yolk quality, jelly coat composition, or maternal genes) or post-oviposition factors (e.g., parental care behaviors, parental modification of environment). Gravid females were captured and induced to lay eggs in experimental chambers in which the environment was standardized. Fifteen clutches were exchanged, or cross-fostered, between female pairs differing in body size. Ten females whose eggs were taken away and then returned served as controls for the crossing treatment. Foster mothers did not significantly differ from control mothers in the time spent with eggs, body position, or number of egg movements during brooding. Average egg mass measured midway through development was not significantly correlated to the body size of either the genetic or foster mother, but was correlated to pre-oviposition oocyte size. At hatching, offspring body length was positively correlated to egg size and the foster mother's body size. This correlation suggests that in P. cinereus post-oviposition maternal effects have a greater impact on offspring size than other maternal factors incorporated into the egg prior to oviposition. While our study showed that larger mothers moved their eggs less often and tended to spend more time in contact with their eggs, further work needs to be done to identify the specific mechanisms through which larger mothers influence the body size of their offspring. This is the first experimental demonstration of post-oviposition maternal effects for any amphibian with parental care.

Animals↗
PubMed1985

Effects of inositol-1,4,5-trisphosphate injections into salamander rods.

Solitary rods were isolated by trituration of salamander (Ambystoma tigrinum) retinas. One barrel of an intracellular, double-barreled micropipette was used to record membrane voltage; the other barrel was used to pressure-inject inositol-1,4,5-trisphosphate. The injection of inositol-1,4,5 -trisphosphate induced a reversible hyperpolarization of the rod membrane. Injections of inositol-1,4,5-trisphosphate decreased the size of receptor potentials induced by dim lights. Conversely, light decreased the responses of the rod to injections of inositol-1,4,5-trisphosphate. These results suggest that inositol-1,4,5-trisphosphate might be involved in the modulation of rod membrane voltage during phototransduction.

Animals↗
PubMed1977

Neuronal transport in salamander nerves and its blockade by colchicine.

Neuronal transport and the effects of colchicine on it has been studied in salamander spinal nerves. Cholinesterase (ChE) accumulation above the cut region of a nerve at 12.5 degrees C was shown to depend upon two processes. One caused a transient increase which declined to zero by 24 h; the other was explained by axoplasmic transport. At 22 degrees C the transient change was not observed, but the rate of accumulation attributable to transport increased. The Q10 for this transport over the range 12.5 degrees C--22 degrees C is approximately three. The ChE accumulation in the sensory component of the mixed nerve was about equal to that in the motor. The rate of fast axoplasmic transport of labeled leucine was 56 mm/day at 22 degrees C; if ChE moves at the same rate, then only 7% of the total enzyme is carried by fast axoplasmic transport. The transport of ChE was reduced by at least 50% when nerves were bathed in a 75 mM solution of colchicine for 30 min; this treatment is known not to cause subsequent degeneration of these nerves. The rate of slow flow of labeled material after bathing the nerve trunk in tritiated colchicine was found to be approximately 0.5 mm/day.

Animals↗
PubMed1977

Analysis of intracellular recordings from salamander olfactory epithelium.

Intracellular recordings have been obtained from provisionally identified olfactory receptor and sustentacular cells in the salamander olfactory epithelium. Two categories of membrane potential transients were recorded intracellularly in response to odor stimulation. The first category of responses, presumably recorded from receptor cell somas, were monophasis positive spikes 10-50 mV in amplitude which were superimposed on a depolarizing slow potential which ranged from 4 to 8 mV in amplitude. Graded and differential responses were recorded in response to odor stimulation. The second category of responses were depolarizing and hyperpolarizing slow membrane potential transients presumably recorded from sustentacular cells. Spiking was not observed in response to odor stimulation. Pysiological criteria and Procion dye marking in several instances have provided evidence that responses in the first category were recorded from olfactory receptors and that certain of the other responses were recorded from sustentacular cells.

Ambystoma↗
PubMed1983

Intracellular recordings from salamander olfactory receptor cells.

Intracellular recordings were obtained from salamander olfactory receptor cells. The occurrence of an intracellular spike in response to the antidromic stimulation of the olfactory fibers was considered as a physiological criterion of a neuronal impalement. The mean resting potential was -56 +/- 9 mV (mean +/- S.D.; n = 70). Fifty-two cells presented a spontaneous spike activity lower than 2 impulses/s. Appropriate olfactory stimulation generally evoked a slow and graded decrease (up to 28 mV) of the intracellular potential. The input resistance of the cell decreased markedly during the response. The slow potential change induced a repetitive firing. Increasing the intensity of the olfactory stimulation increased the instantaneous frequency of firing (up to 25 s-1) and reduced the spike amplitude. The spikes presented an inflexion in the rising phase indicating a two-stage depolarization. With the strongest intensities of stimulation the impulse activity was stopped during the repolarizing phase of the cell response when the membrane potential was still appreciably depolarized.

Animals↗
PubMed1984

Topographic coding of odorant quality is maintained at different concentrations in the salamander olfactory epithelium.

In a recent study in the tiger salamander, Ambystoma tigrinum, were demonstrated topographic patterns of responsivity across the olfactory epithelium which were characteristic for each odorant. The present study was initiated to investigate whether these patterns remain constant when odorant concentration is varied. Odorant-induced electro- olfactograms were recorded from at least 12 sites on each epithelium. The odorants used were pinene, amyl acetate and propanol. Each epithelium was tested with one odorant, delivered at 3 concentrations. For comparison between animals, the epithelia were divided into 3 regions with at least 4 recording sites per region. An analysis of variance model was used to study odorants, concentrations, regions and animals. Odorant-induced regional patterns in responsivity were similar across all concentrations. In particular, the region of highest responsivity at one concentration was the region of highest responsivity at all concentrations. It is concluded that topographic patterns of receptor cell responses may reflect an underlying genetic component in the distribution of receptor cells. This distribution is related to two aspects of receptor cell responses: responsivity to particular odorants (Fig. 4) and general responsivity to all odorants (Fig. 5).

Ambystoma↗
PubMed1984

Localization of cholinesterase activity in the outer plexiform layer of the larval tiger salamander retina.

Acetylcholinesterase activity, which may be indicative of cholinergic synapses, has been ultrastructurally localized in the outer plexiform layer of the larval tiger salamander retina using the cholinesterase staining method of Karnovsky and Roots. In the presence of the butyrylcholinesterase inhibitor, ethopropazine, precipitate is localized to discrete 'stain laminae' about 300 nm in their largest dimension and bounded by a 10 nm wide electron-lucent gap. Stain laminae are predominantly found adjacent to horizontal cell axon terminals which were identified by serial section analysis. Stain precipitate has not been found associated with horizontal cell dendrites and in only one case was a lamina found adjacent to a bipolar cell dendrite. Intracellular deposits of cholinesterase stain precipitate were also observed. In some cases, stain is found adjacent to synaptic ribbons in photoreceptor terminals. Likely artifacts appear to have been ruled out by control experiments in which retinas either were not treated with cholinesterase stain or were treated in the presence of the specific acetylcholinesterase inhibitor, BW284C51. Thus, the stain laminae probably result from specific, highly localized areas of acetylcholinesterase activity. The implications of the present study on current theories of cholinergic function in the vertebrate retina are discussed.

Acetylcholinesterase↗
PubMed1985

Intracellular potentials of salamander mitral/tufted neurons in response to odor stimulation.

Intracellular responses of salamander mitral/tufted neurons to defined odor pulses are described. Responses to odor stimulation, which generally are more complex than responses to olfactory nerve or tract electrical stimulation, show periods of depolarization and hyperpolarization that are influenced by odor concentration and quality. The way these periods coincide with different types of spike patterns in individual cells supports the hypothesis that the temporal patterning of odor responses is generated by differential activation of bulbar circuits.

Animals↗
PubMed1985

Muscarinic cholinergic receptors in the retina of the larval tiger salamander.

The pharmacology and autoradiographic localization of muscarinic cholinergic receptors in retinal slices of the larval tiger salamander have been examined using the muscarinic antagonist [3H]propylbenzilylcholine mustard. Under the conditions of these experiments the binding of this ligand is irreversible. Saturation and maximum specific binding of 270 pM of ligand per gram protein are observed after an incubation of 1 h, and autoradiographic studies show that this does not reflect surface binding alone. Muscarinic but not nicotinic drugs suppress the binding of propylbenzilylcholine mustard at physiologically relevant concentrations; half-maximal suppression of binding by the muscarinic antagonists atropine sulfate and quinuclidinyl benzilate occurs, respectively, at 9.0 and 7.5 X 10(-10) M. Light microscopic autoradiography reveals the discrete localization of the ligand to the sites of synaptic contact, the retinal plexiform layers, predominantly the inner plexiform layer. The implications of the present study on current theories of cholinergic function in the vertebrate retina are discussed.

Ambystoma↗
PubMed1986

Intracellular recordings from salamander olfactory supporting cells.

Stable intracellular potentials were recorded just below the surface of the salamander olfactory epithelium. The site of recording corresponded to the zone of highest density of supporting cell perikarya. The electrophysiological properties of cells recorded in this zone included: neither spontaneous nor evoked spike activity, high resting potential (-96 +/- 10 mV, n = 113) and low input resistance (15 +/- 12 M omega, n = 64). The cells were depolarized to -9 +/- 8 mV when the extracellular potassium concentration was increased from 2 to 100 mM. The membrane potential also changed during activation of the olfactory receptor neurons. Antidromic stimulation of olfactory axons elicited both rapid and slow depolarizations. Odorant stimulation induced graded depolarizations which always lagged behind the electro-olfactogram by more than 1 s. In contrast to the responses of the olfactory receptor neurons, these responses were nearly identical from one cell to another. Compared with the concomitant electro-olfactogram, they had almost the same amplitude, with a reversed polarity. These findings are discussed in the context of the possible auxiliary functions of supporting cells in olfactory processes.

Animals↗
PubMed1987

Odor-elicited activity monitored simultaneously from 124 regions of the salamander olfactory bulb using a voltage-sensitive dye.

In response to controlled, odor pulse stimulation of the olfactory receptor mucosa, large fluorescence signals were recorded simultaneously from 124 contiguous anatomical regions of the salamander olfactory bulb using the potentiometric probe RH 414. The amplitudes and waveforms of the signals varied systematically across the bulbar surface in apparent correspondence with the laminae of the bulbar neurons. Qualitatively similar results were obtained using both intact and decorporate preparations, although fluorescence signals obtained from intact animals were distorted by optical noise generated by mechanical disturbances related to the functioning cardiovascular system. These results indicate that multiple site optical recording can be used to obtain information about spatio-temporal patterning of bulbar electrical activity evoked by physiological odor stimulation of the receptor mucosa. This is the first demonstration that activity elicited by a single, one second odor stimulus at physiological concentration and duration can be measured across many elements in the olfactory bulb. Information provided by this approach, in combination with complementary data derived from 2-deoxyglucose and single unit studies, may yield a better understanding of how the vertebrate central nervous system extracts quality and concentration information from olfactory afferent input.

Action Potentials↗
PubMed1987

Interactions between enkephalin and gamma-aminobutyric acid in the larval tiger salamander retina.

Both double-label and intracellular electrophysiological recording techniques were utilized to investigate the interactions between enkephalin and gamma-aminobutyric acid in the larval tiger salamander retina. Double-label studies revealed that the vast majority (greater than 96%) of enkephalin-immunostained amacrine cells also exhibit high affinity uptake of [3H]gamma-aminobutyric acid. Electrophysiological evidence demonstrated that morphine and gamma-aminobutyric acid exert opposite effects on a population of On-Off ganglion cells. gamma-Aminobutyric acid decreased the activity of these cells, while enkephalin increased their activity. These findings support the idea that opiate-mediated pathways inhibit GABAergic pathways in the vertebrate retina.

Animals↗
PubMed1987

Binocular afferents to the salamander pretectum mediate rotation sensitivity of cells selective for visual background motions.

The majority (85%) of background motion-sensitive pretectal cells in salamanders was found to be binocularly driven. In 70% of the units the binocularity establishes a rotation selectivity with respect to background pattern-movements. This results in a considerable augmentation of the discharge rate when pattern movement is perceived simultaneously in the temporonasal direction by the contralateral eye and nasotemporally by the ipsilateral eye. The response is depressed when the pattern movement is seen in the same direction by both eyes. It is concluded that the rotation-sensitive cells are mainly excited by contralateral retinal afferents selective for temporonasal movements and inhibited by direct or indirect ipsilateral afferents with the same type of direction selectivity.

Afferent Pathways↗