The sensory functions of the cerebellum of the thornback ray,Platyrhinoidis triseriata

Summary Single unit spikes and evoked field potentials were recorded in different parts and depths of the corpus cerebelli and auricle of immobilized rays before and after stimulating with light, electric fields, touch, tail bending and direct shock to mechanoreceptive nerves of the lateral line.Discrete areas of the cerebellum are responsive to these modalities and the areas show limited overlap; they are all distinct from the area reported by Plassmann to be responsive to angular acceleration. The visual and tactile-proprioceptive areas are large; the electric area is small. Most units are excited only by one modality.The tail is represented only in the posterior lobe; trigeminal innervation extends from the posterior onto the anterior lobe, suggesting some topographic projection.The dynamic characteristics of the responses were examined particulary in the visual units. To a flash, units discharge up to six bursts of spikes in 500 ms. This pattern is reduced at repetition rates > 1/s; above ca. 4/s units tend to fire irregularly. Various kinds of units are found in respect to the succession of responses to short trains of flashes. Some units fire much better to objects moving in a limited visual field with a certain direction and rate.Abbreviation EP evoked potential     

The lateral line mechanoreceptive mesencephalic,diencephalic, and telencephalic regions in the thornback ray,Platyrhinoidis triseriata (Elasmobranchii)

Central lateral line pathways were mapped in the thronback ray, Platyrhinoidis triseriata, by analyzing depth profiles of averaged evoked potentials (AEPs), multiunit activity (MUA), and single unit recordings. Neural activity evoked by contra- or ipsilateral posterior lateral line nerve (pLLN) shock is restricted to the tectum mesencephali, the dorsomedial nucleus (DMN) and anterior nucleus (AN) of the mesencephalic nuclear complex, the posterior central thalamic nucleus (PCT), the lateral tuberal nucleus of the hypothalamus, and the deep medial pallium of the telencephalon (Figs. 2, 3, 4, 6, 7). Neural responses (AEPs and MUA) recorded in different lateral line areas differ with respect to shape, dynamic response properties, and/or latencies (Figs. 9, 10 and Table 1). Ipsilaterally recorded mesencephalic and diencephalic AEPs are less pronounced and of longer latency than their contralateral counterpart (Fig. 9 and Table 1). In contrast, AEP recorded in the telencephalon show a weak ipsilateral preference. If stimulated with a low amplitude water wave most DMN, AN, and tectal lateral line units respond in the frequency range 6.5 Hz to 200 Hz. Best frequencies (in terms of least displacement) are 75-150 Hz with a peak-to-peak water displacement of 0.04 micron sufficient to evoke a response in the most sensitive units (Fig. 11A, B, C). DMN and AN lateral line units have small excitatory receptive fields (RFs). Anterior, middle, and posterior body surfaces map onto the rostral, middle, and posterior brain surfaces of the contralateral DMN (Fig. 12). Some units recorded in the PCT are bimodal; they respond to a hydrodynamic flow field--generated with a ruler approaching the fish--only if the light is on and the eye facing the ruler is left uncovered (Fig. 13).     

shape Echinobothrium californiense n. sp. (Cestoda: Diphyllidea) from the thornback ray shape Platyrhinoidis triseriata (Chondrichthyes: Rajoidei) and a key to the species in the genus

Systematic Parasitology - A new cestode, Echinobothrium californiense n. sp., from the spiral intestine of Platyrhinoidis triseriata, taken in California waters is described. The new species is...     

The cerebellar dorsal granular ridge in an elasmobranch has proprioceptive and electroreceptive representations and projects homotopically to the medullary electrosensory nucleus

1. Response properties of neurons in the dorsal granular ridge (DGR) of the little skate, Raja erinacea, were studied in decerebrate, curarized fish. Sensory responses included proprioceptive (426 of 952; 45%) and electroreceptive units (526 of 952; 55%). Electroreceptive units responded to weak electric fields with a higher threshold than lower-order units and had large ipsilateral receptive fields, whose exact boundaries were often unclear but contained smaller, identifiable best areas. Proprioceptive units responded to displacement of the ipsilateral fin and were either position-or movement-sensitive.
2. Both proprioceptive and electroreceptive units showed a progression of receptive fields from anterior to posterior body in the rostral to caudal direction along the length of DGR. Sensory maps in DGR projected homotopically to the electrosensory somatotopy in the dorsal nucleus. Peak evoked potentials and units responding to local DGR stimulation occurred only in areas of the dorsal nucleus with receptive fields located within the composite receptive field at the DGR stimulation site.
3. Single shocks to DGR produced a short spike train followed by a prolonged suppression period in the medullary dorsal nucleus. These results have implications for the role of the parallel fiber system in medullary electrosensory processing.

     

Functional organization of dendritic Ca2+ signals in midbrain dopamine neurons

Dendritic Ca²⁺ plays an important role not only in synaptic integration and synaptic plasticity, but also in dendritic excitability in midbrain dopamine neurons. However, the functional organization of dendritic Ca²⁺ signals in the dopamine neurons remains largely unknown. We therefore investigated dendritic Ca²⁺ signals by measuring glutamate-induced Ca²⁺ increases along the dendrites of acutely isolated midbrain dopamine neurons.Maximal doses of glutamate induced a [Ca²⁺]_c rise with similar amplitudes in proximal and distal dendritic regions of a dopamine neuron. Glutamate receptors contributed incrementally to the [Ca²⁺]_c rise according to their distance from the soma, with a reciprocal decrement in the contribution of voltage-operated Ca²⁺ channels (VOCCs). The contribution of AMPA and NMDA receptors increased with dendritic length, but that of metabotropic glutamate receptors decreased. At low doses of glutamate at which spontaneous firing was sustained, the [Ca²⁺]_c rise was higher in the distal than the proximal regions of a dendrite, possibly due to the increased spontaneous firing rate.These results indicate that functional organization of Ca²⁺ signals in the dendrites of dopamine neurons requires different combination of VOCCs and glutamate receptors according to dendritic length, and that regional Ca²⁺ rises in dendrites respond differently to applied glutamate concentration.     

Functional organization of projection zones of lateral line organs in the midbrain of Raja clavata

The character and distribution of evoked potentials in the midbrain during electrical stimulation of the lateral line nerves were investigated in acute experiments on the ray (Raja clavata). The clearest response was observed on the contralateral side of the dorsal surface. The evoked potentials consisted of several components. The initial high-frequency component is regarded as presynaptic. The principal slow component of the evoked potential corresponds to postsynaptic processes. The lateral line organs have spatially differentiated representation with partial overlapping of the projection zones.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 384–391, July–August, 1973.     

Gill function in an elasmobranch

Summary Highly efficient oxygen uptake in elasmobranchs, as indicated by frequent excess of over has previously been ascribed to the operation of multicapillary rather than counter-current gas exchange by the gills. Analysis of models shows that, at maximum efficiency, a multicapillary system cannot account for values of greater than . In Port Jackson sharks Heterodontus portusjacksoni) commonly exceeds , which indicates the operation of a functional counter-current at the respiratory surface. The anatomical basis of this counter-current is provided by the demonstration that a continuous flow of water passes between the secondary lamellae into septal canals and thence via the parabranchial cavities to the exterior.Queen Elizabeth II Fellow.     

Functional organization of the arctiid moth tymbal (insecta,lepidoptera)

The exoskeletal morphology, muscular organization, and innervation patterns of the tymbals of seven sound-producing species of tiger moths (Arctiidae) were compared with the undifferentiated episterna of two silent species. At least three muscles are involved in sound production: the tymbal muscle, pv2, and the accessory muscles, pvl and/or pv6. All of the tymbal muscles are innervated by the IIIN2a branch of the metathoracic leg nerve, which contains two axons larger than the others. Backfills of the tymbal branch of the IIIN2a reveal a medial sensory neuropil and a population of five ipsilateral motor neurons whose somata are clustered into three groups along the anterior edge of the metathoracic ganglion. The dendritic arborizations of the motor neurons extend to the ganglionic midline but are separate from one part of the auditory neuropil observed in other noctuoids. The study concludes that the arctiid tymbal reveals only minor modifications (e.g., cuticle thinning) of the episterna of silent moths and represents a primitive form of the tymbal compared to those of the Cicadidae.     

Functional organization of the cassava vein mosaic virus (CsVMV) promoter

Cassava vein mosaic virus (CsVMV) is a pararetrovirus that infects cassava plants in Brazil. A promoter fragment isolated from CsVMV, comprising nucleotides -443 to +72, was previously shown to direct strong constitutive gene expression in transgenic plants. Here we report the functional architecture of the CsVMV promoter fragment. A series of promoter deletion mutants were fused to the coding sequence of uidA reporter gene and the chimeric genes were introduced into transgenic tobacco plants. Promoter activity was monitored by histochemical and quantitative assays of -glucuronidase activity (GUS). We found that the promoter fragment is made up of different regions that confer distinct tissue-specific expression of the gene. The region encompassing nucleotides -222 to -173 contains cis elements that control promoter expression in green tissues and root tips. Our results indicate that a consensus as1 element and a GATA motif located within this region are essential for promoter expression in those tissues. Expression from the CsVMV promoter in vascular elements is directed by the region encompassing nucleotides -178 to -63. Elements located between nucleotides -149 and -63 are also required to activate promoter expression in green tissues suggesting a combinatorial mode of regulation. Within the latter region, a 43 bp fragment extending from nucleotide -141 to -99 was shown to interact with a protein factor extracted from nuclei of tobacco seedlings. This fragment showed no sequence homology with other pararetrovirus promoters and hence may contain CsVMV-specific regulatory cis elements.     

Neuronal organization of the periaqueductal gray matter in the cat midbrain

It is shown by the use of Golgi's method in Antonova's modification that the neuronal structure of the periaqueductal gray matter (PGM) in the frontal plane is characterized by the presence of small and medium-sized cells of "reticular type," which can be subdivided into three types: fusiform, triangular, and multipolar. On the basis of the visual distribution of these types of neurons and also of statistical analysis of 800 identified neurons, two regions can be distinguished: medial, directly surrounding the aqueduct of Sylvius, containing small neurons, among which the fusiform kind predominate significantly (P<0.001), and a lateral region with larger neurons, with significantly (P<0.001) more triangular cells. Neurons in the medial region show a characteristic and strong (P<0.001) tendency for their dendrites to be oriented toward the lumen of the aqueduct, and through them the physiologically active substances of the CSF may influence the functional activity of neurons of PGM.Central Research Institute of Reflex Therapy, Moscow City Council Main Health Board, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 773–777, November–December, 1984.     

Functional analysis of the TFIID-specific yeast TAF4 (yTAF(II)48) reveals an unexpected organization of its histone-fold domain

Yeast TFIID comprises the TATA binding protein and 14 TBP-associated factors (TAF(II)s), nine of which contain histone-fold domains (HFDs). The C-terminal region of the TFIID-specific yTAF4 (yTAF(II)48) containing the HFD shares strong sequence similarity with Drosophila (d)TAF4 (dTAF(II)110) and human TAF4 (hTAF(II)135). A structure/function analysis of yTAF4 demonstrates that the HFD, a short conserved C-terminal domain (CCTD), and the region separating them are all required for yTAF4 function. Temperature-sensitive mutations in the yTAF4 HFD alpha2 helix or the CCTD can be suppressed upon overexpression of yTAF12 (yTAF(II)68). Moreover, coexpression in Escherichia coli indicates direct yTAF4-yTAF12 heterodimerization optimally requires both the yTAF4 HFD and CCTD. The x-ray crystal structure of the orthologous hTAF4-hTAF12 histone-like heterodimer indicates that the alpha3 region within the predicted TAF4 HFD is unstructured and does not correspond to the bona fide alpha3 helix. Our functional and biochemical analysis of yTAF4, rather provides strong evidence that the HFD alpha3 helix of the TAF4 family lies within the CCTD. These results reveal an unexpected and novel HFD organization in which the alpha3 helix is separated from the alpha2 helix by an extended loop containing a conserved functional domain.     

Different distribution of serotonin in an elasmobranch (Scyliorhinus stellaris) and in a teleost (Conger conger) fish

1. A comparative quantitative study on the occurrence of 5-HT in several tissues and organs of the elasmobranch Scyliorhinus stellaris and the teleost Conger conger has been carried out. 2. In Scyliorhinus, the richest source of the amine is the brain, in which 5-HT is twice as concentrated as in the teleost brain. Significant levels have been also detected in the intestine, followed by gills and heart. 5-HT is also concentrated in other epithelial organs, such as the rectal gland and the olfactory organ. 3. In Conger, the gills show the highest content of 5-HT, in which, like in the kidney, serotonin is 2-3 times more concentrated than in the corresponding organs of the elasmobranch. 4. These differences are discussed in relation to the distinct phylogenetic and ecophysiological features of the two animals. In addition, the possible functional significance of 5-HT in the fish heart is taken into consideration.     

Observations on the life history and descriptions of coccidia (Apicomplexa) from the western chorus frog,Pseudacris triseriata triseriata,from eastern Nebraska

Two hundred and twenty-four anurans of 6 species (47 adults and 16 tadpoles of Rana blairi, 35 R. catesbeiana, 31 Hyla chrysoscelis, 30 adults and 46 tadpoles of Pseudacris triseriata triseriata, 11 Bufo woodhousii, and 8 Acris crepitans) from Pawnee Lake, Lancaster County, Nebraska, were surveyed for coccidian parasites during March 2001 to May 2002. Of these, 23 of 30 (77%) adults and 4 of 46 (9%) tadpoles of P. t. triseriata shed oocysts of Isospora cogginsi n. sp. Oocysts of I. cogginsi were ovoid, 19.3 x 15.1 (18-23 x 11-20) microm, with a thin, smooth, colorless, single-layered wall, with no micropyle or oocyst residuum. Sporocysts were ovoid, 13.3 x 9.9 (11-15 x 9-13) microm, with a thin, colorless, smooth wall, and Stieda body absent. Sporocyst residuum was present, 5.5 x 5.3 (4-7 x 4-7) microm, consisting of numerous granules. Histological examination of frogs and tadpoles infected with the new species revealed endogenous stages including mature meronts, developing microgamonts, mature microgametes, mature macrogamonts, and young unsporulated oocysts located in the cytoplasm of the epithelial cells of the small intestine. Concurrently, 2 adult P. t. triseriata shed oocysts of Eimeria streckeri. Oocysts of E. streckeri were spherical, 15.7 x 15.4 (14-17 x 14-19) microm, with a thin, smooth, single-layered, colorless wall with an oocyst residuum composed of numerous granules surrounding a large vacuolated area, with a previously undescribed globularlike body present within the vacuole, and no micropyle. Sporocysts were ovoid, 9.1 x 6.1 (7-10 x 5-7) microm, with a thin, colorless, smooth wall with a Stieda body and sporocyst residuum. Our results are the first to document infection of adult and tadpole stages of frogs of the same species with the same species of coccidian, indicating that adult frogs may contaminate breeding ponds with oocysts during their breeding season and infect tadpoles directly by the ingestion of sporulated oocysts.     

Parthenogenesis in an elasmobranch in the presence of conspecific males

Parthenogenesis has been observed in several elasmobranch species, primarily in public aquaria. The majority of cases of parthenogenesis have occurred either when females were held without males or once a male was removed from a female's habitat. Here we report a second instance of parthenogenesis in a zebra shark female that was housed with conspecific mature males. This study calls into question the conditions under which elasmobranch females undergo parthenogenesis.     

Solute effects on mitochondria from an elasmobranch (Raja erinacea) and a teleost (Pseudopleuronectes americanus)

Varying osmolarity with sucrose/KCl media resulted in similar effects on the oxidation of glutamate by mitochondria isolated from the livers of an elasmobranch, Raja erinacea, and a teleost, Pseudopleuronectes americanus. In both species trimethylamine oxide (TMAO) inhibited mitochondrial oxidation of glutamate. Urea penetrated the inner mitochondrial membrane of both species and equilibrated with a ratio ureai/ureao of unity. Urea had little effect on the oxidation of glutamate in both species at concentrations as high as 760 mM. Addition of urea (urea/TMAO, 2:1) did not overcome the detrimental effects of TMAO in the mitochondria of either species. In the case of the elasmobranch, the osmolarity of the urea/TMAO media giving the optimal rate of respiration was hypoosmotic with respect to the intracellular osmolarity. The rate of glutamate oxidation steadily declined as osmolarity increased above this value. Assuming the osmotic profile obtained with the urea/TMAO (2:1) medium resembled most closely the in vivo situation, higher rates of oxidation or organic solutes at low osmolarity would help deplete the cell of these solutes and could contribute to cell volume regulation during hypoosmotic stress. It is suggested that two broad classes of intracellular solutes can be defined based on their effects on mitochondrial respiration. Solutes such as K+, C1-, and TMAO penetrate the inner mitochondrial membrane slowly or not at all. Increasing concentrations of these solutes result in lower rates of oxidation. This capacity may be important in regulating intracellular levels of organic solutes during osmotic stress. Solutes such as urea rapidly penetrate the cell and inner mitochondrial membrane reducing the mitochondrial volume changes associated with osmotic stress. The known detrimental effects of urea on protein structure may prevent its exclusive use as an intracellular osmotic effector.     

A new electroreceptive teleost:Xenomystus nigri (Osteoglossiformes: Notopteridae)

Summary The African knife fish,Xenomystus nigri, is found to be sensitive to weak electric fields by the method of averaged evoked potentials from the brain. Slow waves and spikes were recorded in or near the lateral line area of the medulla and the torus semicircularis of the mesencephalon in response to long pulses (best > 50 ms) and low frequency sine waves (best ca. 10 Hz) of voltage gradients down to < 10 V/cm. Evoked waves in the lateral line area are a sequence of negative and positive deflections beginning with a first peak at ca. 24 ms; in the torus semicircularis the first peak is at ca. 37 ms. Spikes are most likely in the torus between 50 and 80 ms after ON. At each recording locus there is a best axis of the homogeneous electric field and a better polarity. Effects of stimulus intensity, duration and repetition are described. The physiological properties are similar to those of ampullary receptor systems in mormyriforms, gymnotiforms and siluriforms.Confirming Braford (1982),Xenomystus has a large medullary nucleus resembling the nucleus otherwise peculiar to mormyriforms, gymnotiforms and siluriforms and now called the electrosensory lateral line lobe (ELLL; formerly the posterior lateral line lobe). We describe the projections of anterior and posterior lateral line nerves by HRP applied to the proximal stump of a cut nerve. A descending central ramus of the anterior lateral line nerve and a lateral component of the ascending ramus of the posterior lateral line nerve end in part in the ELLL.Electroreception, including the system of discrete central structures mediating it, is for the first time found to be less than an ordinal or even a family character, but apparently a characteristic of the subfamily Xenomystinae. Species of the other subfamily, Notopterinae as well as of the other families of osteoglossiforms (Osteoglossidae, Hiodontidae and Pantodontidae), lack the ELLL.Notopterus andPantodon are found to lack the evoked potential.The positive finding of evoked activity to feeble electric field is found to be the most practical method for searching widely among fishes for the presence of the electrosense modality and its central pathways. The anatomical criterion of an ELLL can now be taken to be a good criterion for the presence of this sensory system. The absence of evoked response correlates well with the absence of an ELLL.Abbreviations ELLL electrosensory lateral line lobe - HRP horseradish peroxidase - TS torus semicircularis     

Functional organization of cerebral microvasculature in a marsupial, the northern quoll (Dasyurus hallucatus)

Capillaries within the central nervous system (CNS) of eutherian mammals form meshworks with numerous anastomoses, whereas capillaries in the CNS of marsupials consist entirely of hairpin-like loops, without anastomotic interconnections. Counter-current blood flow in capillary loops may have been important in the evolutionary development of a cerebral vascular supply. However, loops are not found in eutherian mammals, perhaps because of a limited benefit to the diffusive conductance of gases.     

GABAergic system of the pineal organ of an elasmobranch (Scyliorhinus canicula): a developmental immunocytochemical study

The present immunocytochemical study provides evidence of a previously unrecognized, rich, γ-aminobutyric acid (GABA)-ergic innervation of the pineal organ in the dogfish (Scyliorhinus canicula). In this elasmobranch, the pineal primordium is initially detected at embryonic stage 24 and grows to form a long pineal tube by stage 28. Glutamic acid decarboxylase (GAD)-immunoreactive (-ir) fibers were first observed at stage 26, and by stage 28, thin GAD-ir fibers were detectable at the base of the pineal neuroepithelium. In pre-hatchling embryos, most fibers gave rise to GAD-ir boutons that were localized in the basal region of the neuroepithelium, although a smaller number of labeled terminals ascended to the pineal lumen. A few pale GAD-ir perikarya were observed within the pineal organ of stage 29 embryos, but GAD-ir perikarya were not observed at other developing stages or in adults. In contrast, GABA immunocytochemistry revealed the presence of GABAergic perikarya and fibers in the pineal organ of late stage embryos and adults. Although high densities of GABAergic cells were observed in the paracommissural pretectum, posterior tubercle, and tegmentum of dogfish embryos (regions previously demonstrated to contain pinealopetal cells), the presence of GABA-ir perikarya in the pineal organ strongly suggests that the rich GABAergic innervation of the elasmobranch pineal organ is intrinsic. This contrasts with the central origin of GABAergic fibers in the pineal gland of some mammals. This work was supported by the Spanish Education and Science Ministry and FEDER (BXX2000-0453-C02 and BFU2004-03313/BF1), the Xunta de Galicia (PGIDT99BIO20002), and NIH/NIDCD awards R01 DC01705 and P01 DC01837 (to G.R.H.).