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PubMed1964

THE EFFECTS OF ALKALI METAL CATIONS AND COMMON ANIONS ON THE FROG SKIN POTENTIAL.

The effects on the potential difference across isolated frog skin (R. catesbeiana, R. pipiens) of changing the ionic composition of the bathing solutions have been examined. Estimates of mean values and precision are presented for the potential changes produced by substituting other alkali metal cations for Na at the outside border and for K at the inside border. In terms of ability to mimic Na at the outside border of bullfrog skin, the selectivity order is Li > Rb, K, Cs; at the outside border of leopard frog skin, Li > Cs, K, Rb. In terms of ability to mimic K at the inside border of bullfrog and leopard frog skin: Rb > Cs > Li > Na. Orders of anion selectivity in terms of sensitivity of the potential for the outside border of bullfrog skin are Br > Cl > NO(3) > I > SO(4), isethionate and of leopard frog skin are Br, Cl > I, NO(3), SO(4). An effect of the solution composition (ionic strength?) on the apparent Na-K selectivity of the outside border is described. The results of the investigation have been interpreted and discussed in terms of the application of the constant field equation to the Koefoed-Johnsen-Ussing frog skin model. These observations may be useful in constructing and testing models of biological ionic selectivity.

Animals↗
PubMed1999

Comparison of isometric contractile properties of the tongue muscles in three species of frogs, Litoria caerulea, Dyscophus guinetti, and Bufo marinus.

Previous studies show that anurans feed in at least three different ways. Basal frogs have a broad tongue that shortens during protraction and emerges only a short distance from the mouth. Some frogs have long, narrow tongues that elongate dramatically due primarily to inertia from mouth opening, which is transferred to the tongue. A few species have a hydrostatic mechanism that produces tongue elongation during protraction. This functional diversity occurs among frogs that share the same two pairs of tongue muscles. Our study compares the isometric contractile properties of these tongue muscles among three frog species that represent each feeding mechanism. Nerves to the paired protractors and retractors were stimulated electrically in each species to record the force properties, contraction speeds, and fatigabilites of these muscles. Few differences were found in the isometric contractile properties of tongue muscles, and the greatest differences were found in the retractors, not the protractors. We propose that the unique arrangement of the tongue muscles in frogs results in a retractor that may also be coactivated with the protractor in order to produce normal tongue protraction. Inertial effects from body, head, and jaw movements, along with clear differences that we found in passive resistance of the tongues to elongation, may explain much of the behavioral variation in tongue use among species.

Animals↗
PubMed1975

Unmyelinated preganglionic fibers in frog ventral roots.

It has been suggested that the preganglionic visceral fibers in the frog are unmyelinated. To obtain further evidence for this suggestion: (1) the percentages of unmyelinated fibers and the myelinated fiber histograms were done for all frog ventral roots, (2) the number of unmyelinated fibers were counted on either side of a chronic section of the seventh ventral root and (3) compound action potentials were obtained for roots 7-10. The results are that slightly more than 80% of the unmyelinated fibers in the seventh ventral root arise in the spinal cord and are presumably unmyelinated preganglionic efferents. Furthermore, a C fiber volley could be followed from the seventh ventral root into caudal parts of the sympathetic chain. Thus this data provides confirmation for the idea that many frog preganglionic fibers are unmyelinated. This study also shows that 24% of the ventral root axons in the frog are unmyelinated and that, on the basis of percentages of unmyelinated fibers and myelinated fiber histograms, there are five categories of frog ventral roots.

Action Potentials↗
PubMed1985

Regeneration of lumbar dorsal root axons into the spinal cord of adult frogs (Rana pipiens), an HRP study.

Lumbar dorsal roots of adult frogs were crushed or cut and reanastomosed. Following survival times of up to 75 days, the regenerating dorsal roots were recut and anterogradely injury-filled with horseradish peroxidase. This revealed that in the adult frog, regenerating axons re-enter the spinal cord. Comparison of the distribution of these axons with that of normal dorsal root axons showed that there is a partial restoration of the segmental distribution in the gray matter. However, the long ascending sensory tract of the dorsal funiculus was not restored. The dorsal funiculus was markedly gliotic and had relatively few labelled, regenerated axons. The labelled axons that were seen in the dorsal funiculus either extended longitudinally for a distance just beneath the pia, apparently in association with the glia limitans, or traversed the region to enter the dorsal gray matter. Most of the large and small diameter axons that entered the gray matter did so by passing through the region of the dorsolateral fasciculus. Within the gray matter, small diameter, regenerated axons arborized in the region of the dorsal terminal field, a region that has been shown in the normal frog to receive cutaneous afferents only. Many large diameter axons, presumably muscle afferents, arborized in the ventral terminal field, a region shown in the normal frog to receive muscle afferents exclusively. However, many of these large diameter axons had arborizations that extended to both terminal fields, thus suggesting that some abberant connections are made during dorsal root regeneration in the adult frog.

Animals↗
PubMed1990

Quantitative study of the tectally projecting retinal ganglion cells in the adult frog: I. The size of the contralateral and ipsilateral projections.

The proportion of ganglion cells connected to the several central targets of the retinal projection varies in different species. In the frog, the retinotectal projection is clearly the largest branch of the optic pathway and the relative size of the tectally projecting population can be expected to be correspondingly great. However, there have been no studies aimed at quantifying the size of this population and at partitioning its contralateral and ipsilateral components. We injected the tectum with horseradish peroxidase (HRP) dried onto fine needles to count the numbers of retinal ganglion cells labeled by retrograde transport. The retinas were prepared as flat-mounts to facilitate the cell counting. The tecta were injected either unilaterally or bilaterally in mirror-symmetric loci. Specimens included completely normal frogs and frogs which had undergone unilateral optic nerve regeneration, although only normal retinas are presented in the current study. The retrograde transport interval was varied progressively (from 3 to 5 days), and single or multiple injections of HRP were placed singly or as clusters, in order to increment the cell counts toward a level of saturation. Approximately 70.9% of the neurons in the ganglion cell layer could be labeled by this method. Correcting for the presence of displaced amacrine cells, estimated to comprise approximately 16% of the neurons in the ganglion cell layer (Scalia et al., '85, Brain Res. 344:267-280), we calculate that approximately 84.4% of the retinal ganglion cells project contralaterally to the optic tectum. Flat-mounted retinas ipsilateral to unilaterally injected tecta of completely normal frogs were also examined for labeled cells. The results of injections in the rostrolateral, caudomedial, and caudolateral tectum were studied. We found that ipsilaterally labeled cells comprised no more than 2.3% of the overall population of ganglion cells in the ganglion cell layer. The ipsilaterally projecting cells were found in loci which were approximately mirror-symmetric to the regions of maximal cell labeling in the contralateral retinas from the same animals. The ipsilateral population was always displaced toward the periphery of the retina with respect to the contralateral population, regardless of whether the contralateral locus was centered in the temporal, ventronasal, or dorsonasal sector of the retina. Because the ipsilaterally projecting ganglion cells form such a minor population, and because they exist in the monocular as well as the binocular parts of the retina, it seems likely that they may not play a significant role in visual function in the frog.

Afferent Pathways↗
PubMed1989

Two-dimensional correlated spectroscopy (COSY) of intact frog muscle: spectral pattern characterization and lactate quantitation.

Two-dimensional scalar-correlated 1H spectra (COSY) were recorded from a model solution containing varying amounts of lactate and a fixed concentration of carnosine as the reference compound. The integrated volume of the lactate methyl to methine cross peak in the magnitude-calculated spectra showed a linear increase with respect to lactate concentration. Accordingly, the COSY cross-peak integral volume should be a useful parameter for the quantitative study of metabolism in intact tissue. We have tested this assumption in excised gastrocnemius frog muscle. Lactate, carnosine, and creatine/phosphocreatine cross peaks have been assigned in the spectrum of summer frog muscle. The change in concentration of lactate and phosphorylated compounds upon anaerobic storage of excised frog muscle has been followed by interleaving one-dimensional (1D) 1H and 31P spectra with 2D homonuclear 1H COSY spectra. The lactate concentration in the excised muscle derived from COSY agreed well with that determined from muscle extracts. Qualitative changes in the COSY pattern of the excised muscles under caffeine-induced contracture were detected. Furthermore, seasonal variations were observed in the COSY spectral pattern: winter frog muscle was found to differ from summer frog muscle by the appearance of cross peaks from phosphodiesters and mobile fatty acids.

Animals↗
PubMed2005

Ancient gill and lung oscillators may generate the respiratory rhythm of frogs and rats.

Though the mechanics of breathing differ fundamentally between amniotes and "lower" vertebrates, homologous rhythm generators may drive air breathing in all lunged vertebrates. In both frogs and rats, two coupled oscillators, one active during the inspiratory (I) phase and the other active during the preinspiratory (PreI) phase, have been hypothesized to generate the respiratory rhythm. We used opioids to uncouple these oscillators. In the intact rat, complete arrest of the external rhythm by opioid-induced suppression of the putative I oscillator, that is, pre-Bötzinger complex (PBC) oscillator, did not arrest the putative PreI oscillator. In the unanesthetized frog, the comparable PreI oscillator, that is, the putative buccal/gill oscillator, was refractory to opioids even though the comparable I oscillator, the putative lung oscillator, was arrested. Studies in en bloc brainstem preparations derived from both juvenile frogs and metamorphic tadpoles confirmed these results and suggested that opioids may play a role in the clustering of lung bursts into episodes. As the frog and rat respiratory circuitry produce functionally equivalent motor outputs during lung inflation, these data argue for a close homology between the frog and rat oscillators. We suggest that the respiratory rhythm of all lunged vertebrates is generated by paired coupled oscillators. These may have originated from the gill and lung oscillators of the earliest air breathers.

Action Potentials↗
PubMed2005

Seasonal changes in frequency tuning and temporal processing in single neurons in the frog auditory midbrain.

Frogs rely on acoustic signaling to detect, discriminate, and localize mates. In the temperate zone, reproduction occurs in the spring, when frogs emerge from hibernation and engage in acoustically guided behaviors. In response to the species mating call, males typically show evoked vocal responses or other territorial behaviors, and females show phonotactic responses. Because of their strong seasonal behavior, it is possible that the frog auditory system also displays seasonal variation, as evidenced in their vocal control system. This hypothesis was tested in male Northern leopard frogs by evaluating the response characteristics of single neurons in the torus semicircularis (TS; a homolog of the inferior colliculus) to a synthetic mating call at different times of the year. We found that TS neurons displayed a seasonal change in frequency tuning and temporal properties. Frequency tuning shifted from a predominance of TS units sensitive to intermediate frequencies (700-1200 Hz) in the winter, to low frequencies (100-600 Hz) in the summer. In winter and early spring, most TS neurons showed poor, or weak, time locking to the envelope of the amplitude-modulated synthetic call, whereas in late spring and early summer the majority of TS neurons showed robust time-locked responses. These seasonal differences indicate that neural coding by auditory midbrain neurons in the Northern leopard frog is subject to seasonal fluctuation.

Acoustic Stimulation↗
PubMed1999

Liver freezing response of the freeze-tolerant wood frog, Rana sylvatica, in the presence and absence of glucose. I. Experimental measures.

In this study, two methods are used to assess the equilibrium and dynamic cell volumes in Rana sylvatica liver tissue during freezing in the presence and absence of a cryoprotectant (glucose). The first is a "two-step" low-temperature microscopy (equilibrium and dynamic) freezing method and the second is a differential scanning calorimeter (DSC) technique. These two techniques were used to study (i) the in vitro architecture of R. sylvatica frog liver tissue and to measure its characteristic Krogh cylinder dimensions; (ii) the "equilibrium" (infinitely slow) cooling behavior and the osmotically inactive cell volume (V(b)) of R. sylvatica liver cells; and (iii) the dynamic water transport response of R. sylvatica liver cells in the presence and absence of the CPA (glucose) at a cooling rate of 5 degrees C/min. Stereological analysis of the slam frozen (>1000 degrees C/min) micrographs led to the determination that 74% of the liver tissue in control frogs was cellular versus 26% that was extracellular (vascular or interstitial). Mapping the stereological measurements onto a standard Krogh cylinder geometry (Model 1) yielded distance between adjacent sinusoid centers, DeltaX = 64 microm; original sinusoid (vascular) radius, r(vo) = 18.4 microm; and length of the Krogh cylinder, L = 0.71 microm (based on an isolated frog hepatocyte cell diameter of 16 microm). A significant observation was that approximately 24% of the frog hepatocyte cells are not in direct contact with the vasculature. To account for the cell-cell contact in the frog liver architecture a modified Krogh cylinder geometry (Model 2) was constructed. In this model (Model 2) a second radius, r(2) = 28.7 microm, was defined (in addition to the original sinusoid radius, r(vo) = 18.4 microm, defined above) as the radius of the membrane between the adjacent cells (directly adjacent to vascular spaces) and embedded cells (removed from vascular spaces). By plotting the two-step equilibrium cooling results on a Boyle-van't Hoff plot, the osmotically inactive cell volume, V(b) was obtained as 0.4. V(o) (where V(o) is the isotonic cell volume). The two-step dynamic micrographs and the heat release measurements from the DSC were used to obtain water transport data during freezing. The DSC technique confirmed that R. sylvatica cells in control liver tissue do not dehydrate completely when cooled at 5 degrees C/min but do so when cooled at 2 degrees C/min.

Animals↗
PubMed1999

Freeze-induced alterations of translatable mRNA populations in wood frog organs.

To investigate the roles that gene expression and new protein synthesis play in freezing survival by the wood frog, Rana sylvatica, we compared the in vitro translation products made from mRNA isolated from six tissues (liver, brain, heart, muscle, kidney, gut) of control (5 degrees C), frozen (24 h at -2.5 degrees C), and thawed (24 h at 5 degrees C after 24 h frozen) frogs. [(35)S]Methionine-labeled proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and located by fluorography. Results indicated specific changes in the translatable populations of mRNA in tissues of freezing-exposed frogs that were largely reversed upon thawing. Differential protein expression was greatest in the comparison of liver from control versus frozen frogs with proteins ranging from 45 to 14.8 kDa identified as enhanced or unique to the frozen state. One unique protein appeared in skeletal muscle (116 kDa) of freeze-exposed frogs while another (52.5 kDa) was enhanced. Analysis of brain and heart each revealed the presence of one protein unique to the frozen state in each (58.9 and 5.9 kDa, respectively) whereas no change in the pattern of in vitro translation products was seen in gut (stomach + intestine combined) or kidney between the three experimental states. These freeze-induced alterations in the populations of translatable mRNA suggest that changes in the complement of specific proteins underlie various adaptive responses that contribute to the freezing survival of this amphibian.

Adaptation, Biological↗
PubMed1999

Hormonal control of "tissue" transglutaminase induction during programmed cell death in frog liver.

In this study, we show that sex hormones (testosterone, estradiol, and progesterone) act as physiological modulators of programmed cell death (PCD) during the frog liver involution observed postvitellogenesis. PCD in parenchymal cells is paralleled by the specific induction of the "tissue" transglutaminase (tTG) gene. tTG protein specifically accumulates in hepatocytes showing the morphological features of apoptosis. The hormone-dependent increase of both PCD and tTG was reproduced in ovariectomized frogs. Treatment of castrated animals with testosterone, estradiol, and progesterone inhibited the induction of both tTG and PCD, thus indicating that in vivo the drop in the circulating sex hormone is the signal favoring the involution phase of the maternal frog liver after mating. Although an affinity-purified polyclonal antibody raised against mammalian transglutaminase reacts in frog liver with a 55- to 60-kDa protein, concomitant with the onset of PCD, tTG cleavage products were detected, suggesting a proteolytic processing of the enzyme protein. These results represent the first evidence indicating that the physiological involution occurring postvitellogenesis of frog liver takes place by programmed cell death and that this, together with the concomitant induction of tTG gene expression, is regulated by sex hormones.

Animals↗
PubMed1993

Further studies on the influence of GnRH on the biosynthesis of gonadotropins in female frogs (Rana pipiens).

To further investigate the action of gonadotropin-releasing hormone (GnRH) on pituitaries of female frogs (Rana pipiens), gonadotropin (Gth) secretion and synthesis was measured following either the in vivo or in vitro exposure to GnRH. Treating frogs with a GnRH-agonist (GnRHa) in vivo for either 2 or 5 days led to an elevation in plasma Gth compared to that of saline-injected controls. In general, the pattern of Gth secretion in vitro paralleled changes observed in their plasma levels. GnRHa-treated frogs also had depressed pituitary content of Gth as compared to controls. Pituitaries from frogs treated with GnRHa for 5 days had higher levels of Gth synthesis than those of controls; however Gth synthesis in females treated with GnRHa for only 2 days was not elevated. After 30 hr of continuous exposure to 100 ng/ml GnRH in vitro, glands from females secreted markedly higher levels of LN and FSH than glands not exposed to the secretagogue. The levels of LH and FSH contained within pituitaries exposed to GnRH were significantly less than those of control glands. Prolonged exposure to GnRH elevated both the secretion of radiolabeled Gth as well as increased the total synthesis of Gth (compared to those of controls). These results indicate that GnRH can stimulate the biosynthesis of Gth in pituitaries of female frogs; however these results differ from those previously obtained with males. It appears that female glands require a much longer duration of GnRH stimulation than males before Gth synthesis is elevated.

Animals↗
PubMed2000

Effects of osmotic and light stimulation on 3H-taurine efflux from isolated rod outer segments and synthesis of tauret in the frog retina.

After injection of 3H-taurine into eyeballs of frogs and maintenance for 3 h in darkness by a gentle shaking, an almost homogenous fraction of rod outer segments (ROS) was prepared. About a 22% decrease in tonicity caused by reducing NaCl in isotonic 225 mOsm normal solution caused a rapid increase in the rate coefficient of efflux of 3H-taurine from the ROS fraction. The peak level of increased efflux rate coefficient was 7-times higher than the basal isotonic level. This indicates that taurine could contribute essentially to the volume regulation, either via selective channels or a carrier transporter-mediated pathways. For further clarifying if taurine fluxes in the ROS are sensitive to the light, other experiments were performed. Neither light stimulation of dark-adapted ROSs fractions or dark stimulation of weakly illuminated ROSs revealed any detectable changes in the efflux rate coefficient of 3H-taurine. These results indicate that light-induced taurine efflux, if present in the ROS, must be small, compared with hypoosmotic induced efflux. Thus the question of light-induced release of taurine from ROS still remains to be clarified. In the second part of this study, using TLC (thin layer chromatography) in combination with 3H-taurine measurements we have tried to clarify whether frogs (Rana ridibunda) eye structures can synthesize tauret (retinylidenetaurine). In isolated retinal preparations almost no any noticeable radioactivity was detected compared with background level. The capability of the eye structures to synthesize tauret from 3H-taurine was revealed in the second whole eye injection experiment. About 0.3% of the total 3H-taurine pool taken up was converted into 3H-tauret in the dark-adapted frog retina. In the retina of frogs adapted to light compared with those which were dark adapted tauret quantities were remarkable lower--on average about half. These results are in agreement with our recent data obtained by HPLC, which indicate tauret levels several times higher in the dark-adapted frog retinae compared with those after long lasting light adaption. Taking into account these results one can conclude that the main structure able to synthesize 3H-tauret is probably pigment epithelium rather than retina.

Animals↗
PubMed1993

Do frogs use retinal elevation to measure the distance of a barrier?

Grass frogs, Rana pipiens, will detour around a barrier to reach prey on the other side. However, if the distance between prey and barrier is short, frogs attempt to push through the barrier and reach the prey directly. The relationship between the probability of detouring and the distance between prey and barrier is the same whether the frog's starting position is 4 cm or 8 cm from the barrier. This suggests that frogs measure the absolute separation between the two objects. To discover whether the retinal elevation of the bottom of the barrier contributes to measuring this distance, the relationship between the frequency of detouring and barrier-prey distance was examined in several experiments in which the retinal position of the bottom of the barrier was manipulated. No evidence was obtained that the barrier's retinal elevation helps in gauging distance. On the other hand, retinal elevation influences strongly how far a frog lunges to reach its prey. It is suggested that different cues to distance are applied to the two classes of object because, under natural circumstances, it is difficult to judge where a barrier emerges from the ground. A barrier may be hard to detect below the horizon because of the low contrast between it and the ground, or because vegetation and ground litter mask where the barrier meets the ground. In contrast, the prey's movements make it easily detectable against a stationary background and the prey's short height means that partial occlusion will have little effect on its apparent vertical position in the visual field.

Animals↗
PubMed1994

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog.

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2-4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di- and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs (> or = 60 days) with a pre- or postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with pre- or postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.

Animals↗
PubMed1993

Three-dimensional kinematic analysis of frog hindlimb movement in reflex wiping.

The three-dimensional kinematics of the hindlimb back-wipe were examined in spinal frogs. The component movements were identified and the relationship between stimulus position and hindlimb configuration was assessed. The planes of motion of the hindlimb were examined throughout the movement. The back-wipe comprises three essential phases: a placing phase (I), in which the foot is drawn over the back of the frog and placed in a position near to the stimulus; a pre-whisk phase (II), in which the endpoint of the foot moves away from the stimulus; and a whisk/extension phase (III), in which the stimulus is removed. The pre-whisk phase contributes to force production for the whisk/extension (III). In the placing phase a systematic relationship was found between limb endpoint position and stimulus position in the rostro-caudal direction. The hip, knee and metatarsal joint angles were related to the position of the endpoint in the rostro-caudal direction. However, different frogs tended to adopt different strategies to remove the stimulus. In one strategy, when the knee angle was strongly related to the rostro-caudal stimulus position, the metatarsal angle was weakly related and vice versa. Other strategies were observed as well. There was no adjustment in limb endpoint position for stimulus placement in the medial-lateral direction. Consistent with this finding, the point on the foot at which stimulus contact occurred changed systematically as a function of medial-lateral stimulus placement. Thus, in order to remove the stimulus in different medial-lateral positions, the frog used a different part of the foot rather than moving the foot in the direction of the stimulus. In two frogs a relationship was observed between the elevation of the femur and the medial-lateral stimulus position. The motion planes of the hindlimb were studied by examining the instantaneous plane of motion of the endpoint and the planes of motion of adjacent limb segments. The motion of the endpoint was found not to be planar in any phase of the wipe. In contrast, planar motion of the femur and tibia was observed for all phases. Systematic changes in the orientation of these planes characterized the different phases. The position of the hindlimb was found to be variable prior to the placing phase. This variability was not related to stimulus position. However, in trials with multiple wipes, once an initial limb configuration was assumed, the limb returned to this configuration before each wipe in the sequence. Evidence for motor equivalence was sought in two ways.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

Qualitative and quantitative freeze-fracture studies on olfactory and nasal respiratory structures of frog, ox, rat, and dog. I. A general survey.

A comparative study using freeze-fracturing has been made of surface structures of olfactory and nasal respiratory epithelia of frog, ox, rat and dog. Special attention has been paid to cilia and microvilli present at these surfaces, although the observations include various other structures such as small intracellular vacuoles present in the olfactory receptor endings and infrequent brush cells. Within the mucus overlying the olfactory epithelium membranous vesicles, often attached to olfactory cilia, are seen. Some of these show intramembranous particle distributions similar to those of the rest of the cilia, whereas others are devoid of particles. Smooth vesicles are also found in the mucus of other types of epithelium (respiratory epithelium and Bowman's glands). The freeze-fracture morphology of intracellular secretory vacuoles present in olfactory supporting, Bowman's and respiratory glandular cells of the frog is similar in all these epithelia. Quantitative comparisons are made of the different structures of interest. When corrected for cilia which were not observed, mammalian receptor endings bear 17 cilia on average, whereas frog receptor endings have 6 cilia. The relative magnitudes of the diameters of the cilia and microvilli are, except for frog, the same for all species studied. Dimensions of other structures, e.g., axons, dendrites and dendritic endings are compared in the various species. Freeze-fracture diameters are usually larger than those seen by techniques using dehydration. Dendritic ending densities range from 4.5 X 10(6) (frog) to 8.3 X 10(6) (dog) endings per cm2. Possible sex-dependent differences are only found for these densities and dendritic ending diameters.

Animals↗
PubMed1994

Post-freeze recovery of peripheral nerve function in the freeze-tolerant wood frog, Rana sylvatica.

We investigated the restoration in peripheral nerve function and simple neurobehavioral reflexes in the freeze-tolerant wood frog (Rana sylvatica). Thirty-two specimens, allowed to freeze for 39 h and ultimately cooled to -2.2 degrees C, were sampled at various time intervals up to 60 h after thawing at 5 degrees C was initiated. The sciatic nerves of treated frogs were initially unresponsive to stimulation, but usually regained excitability within 5 h. Except for a slight reduction in nerve excitability, characteristics of the compound action potentials of treated frogs were indistinguishable from those of control frogs. Recovery times for the hindlimb retraction and righting reflexes were 8 h and 14 h, respectively. Concentrations of the cryoprotectant glucose increased 8.2-fold in the sciatic nerve and 10.5-fold in the underlying semimembranosis muscle of treated frogs, and remained elevated for at least 60 h after thawing was initiated. These organs lost 47.2% and 15.9%, respectively, of their water during freezing, but were rehydrated within 2 h of the onset of thawing. The accumulation of glucose and the withdrawal of tissue water apparently are cryoprotective responses which enable this species to survive freezing.

Action Potentials↗