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The cytoskeleton has a central role in eukaryotic biology, enabling cells to organize internally, polarize, and translocate. Studying cytoskeletal machinery across the tree of life can identify common elements, illuminate fundamental mechanisms, and provide insight into processes specific to less-characterized organisms. Red algae represent an ancient lineage that is diverse, ecologically significant, and biomedically relevant. Recent genomic analysis shows that red algae have a surprising paucity of cytoskeletal elements, particularly molecular motors. Here, we review the genomic and cell biological evidence and propose testable models of how red algal cells might perform processes including cell motility, cytokinesis, intracellular transport, and secretion, given their reduced cytoskeletons. In addition to enhancing understanding of red algae and lineages that evolved from red algal endosymbioses (e.g., apicomplexan parasites), these ideas may also provide insight into cytoskeletal processes in animal cells.

We describe a new octoploid species of African clawed frog (Xenopus) from the Lendu Plateau in the northern Albertine Rift of eastern Democratic Republic of the Congo. This species is the sister taxon of Xenopus vestitus (another octoploid), but is distinguished by a unique morphology, vocalization and molecular divergence in mitochondrial and autosomal DNA. Using a comprehensive genetic sample, we provide new information on the species ranges and intra-specific diversity of African clawed frogs from the Albertine Rift, including the details of a small range extension for the critically endangered Xenopus itombwensis and previously uncharacterized variation in Xenopus laevis. We also detail a new method for generating cytogenetic preparations in the field that can be stored at room temperature for up to 3 weeks. While extending our understanding of the extant diversity in the Albertine Rift, this new species highlights components of species diversity in ancestral African clawed frogs that are not represented by known extant descendants.

Summary Forests in the Ozark Mountains of northern Arkansas recently experienced a widespread oak decline event. Armillaria, a root rot fungus, has been associated with other oak decline events and may have been an important contributing factor to tree mortality in this event. Although Armillaria has been identified from the Ozark Mountains in Missouri, it has never been investigated in the Arkansas Ozarks. Molecular diagnostic techniques were used in this study to identify species of Armillaria present on roots removed from dead trees of two common oak species, northern red oak, Quercus rubra L., and white oak, Q. alba L., from three geographic areas and on three topographic positions – ridges, south- and west-facing benches. Armillaria(A. mellea, A. gallica or A. tabescens) was identified from 31% of root samples taken from 102 trees in seven of nine sample plots. Armillaria mellea, occurred most often (20 samples, both oak species on seven plots) followed by A. gallica (10 samples, northern red oak only on four plots), and A. tabescens occurred twice (on northern red oak in a single plot). Thus, all three Armillaria species occurred on northern red oaks while A. mellea was the only species recovered from white oaks. Results varied by topographic position with samples from tree roots on ridges having the fewest positive identifications, one of 29. West-facing benches had the highest positive samples with 20 of 41 testing positive and trees on south-facing benches were intermediate with 11 of 32 samples from infected trees. This study documents the occurrence of three species of Armillaria in the Arkansas Ozarks and their association with oak mortality resulting from an oak decline event coupled with a red oak borer, Enaphalodes rufulus, outbreak. Further, it documents some potential variation in host/pathogen combinations and forest site conditions.

Vernal pool soils in California's Mediterranean climate experience extremes in pedogenesis driven by prolonged saturation to extended desiccation. Four northern California vernal pool soil catenas (summit, rim, and basin) were assessed to determine how soil properties and hydric soil indicators vary in response to duration of standing water and landscape position. Each catena had differences in parent material or degree of soil development. Soil properties differed subtly across each microtopographic sequence. In the well-developed soils, the geochemical signature of horizons overlying the duripans changed sharply compared with horizons below the restrictive layers, suggesting polygenic origins of the soil profiles. The presence and abundance of redoximorphic features (RMFs) in profiles corresponded poorly with the duration of standing water at the four sites. Instead, the abundance of RMFs coincided better with the thickness of the soil above the restrictive horizons in all settings with duripans. Hydric soils were identified in the basin positions of each catena. Most rim positions contained hydric soils and most summit positions had soils that were not hydric. Indicators F8 (redox depressions) and TF2 (test indicator for red parent materials) were most commonly applied. None of the vernal pool catena soils met F9 (vernal pools hydric soil indicator), thus the hydric soil criteria for vernal pools may need to be revised.

Xenopus laevis is an aquatic anuran with a complex vocal repertoire. Unlike terrestrial frogs, vocalizations are independent of respiration, and a single muscle group—the laryngeal dilators—produces underwater calls. We sought to identify the premotor neural network that underlies vocal behaviors. Vocal patterns generated by premotor networks control laryngeal motor neurons in cranial nucleus (n.) IX-X. Glottal motor neurons, active during respiration, are also present in n.IX-X. We used horseradish peroxidase (HRP), Lucifer yellow, and fluorescently conjugated dextrans to characterize the organization of n.IX-X and to trace premotor neuron projections. Premotor nuclei include the inferior reticular formation (Ri) adjacent to n.IX-X and the pretrigeminal nucleus of the dorsal tegmental area of the medulla (DTAM), the primary descending input to n.IX-X. Intramuscular HRP injections revealed a spatially segregated pattern, with glottal motor neurons in anterior n.IX-X and laryngeal motor neurons in the caudal portion of the nucleus. Dextran injections identified commissural n.IX-X neurons that project to the contralateral motor nucleus and DTAM-projecting n.IX-X neurons. Both neuronal types are clustered in anteromedial n.IX-X, closely associated with glottal motor neurons. Ri neurons project to ipsilateral and contralateral DTAM. Projections from DTAM target n.IX-X bilaterally, and all four identified subtypes receive DTAM input. In contrast, Ri neurons receive little input from DTAM. We hypothesize that connectivity between neurons in n.IX-X, Ri and DTAM may provide mechanisms to generate laryngeal and glottal activity patterns and that DTAM may coordinate vocal and respiratory motor pools, perhaps acting to switch between these two mutually exclusive behaviors. J. Comp.

Sexually differentiated calling patterns of Xenopus laevis are conveyed to the vocal organ by a dedicated neuromuscular system. Here, we define afferents to vocal motor neurons and determine whether the connectivity of the vocal pathway is sexually differentiated. The use of fluorescent dextran amines and the isolated brain preparation readily permitted identification of anterograde and retrograde connectivity patterns. The whole-mount preparation allowed us to observe projections in their entirety, including cells of origin of a projection (for retrograde projections), terminal fields (for anterograde connections), and fiber tracts. Major findings are the confirmation of a robust and reciprocal connection between cranial nucleus (n.) IX-X and the pretrigeminal nucleus of the dorsal tegmental area of the medulla (DTAM) as well as between DTAM and the ventral striatum (VS). Newly revealed is the extensive connectivity between the rostral subdivision of the dorsal nucleus raphe (rRpd) and candidate vocal nuclei. In contrast to previous results using peroxidase, we did not observe dramatic sex differences in connectivity, although some connections were less robust in female than in male brains. Some retrograde connections previously observed (e.g., anterior preoptic area to DTAM) were not confirmed. Plausible hypotheses are that a set of rhombencephalic neurons located in DTAM, the inferior reticular formation and n.IX-X are responsible for generating patterned vocal activity, that activity is modulated by neurons in rRpd, and that activity in VS (particularly that evoked by conspecific calls), together with effects of steroid hormones at many sites in the vocal circuit, contribute to the initiation of calling. J. Comp. Neurol. 464: 115‐130, 2003. © 2003 Wiley-Liss, Inc. Indexing terms: nucleus ambiguus; frog; song; raphe; parabrachial nucleus

The torus semicircularis of anurans, which is homologous to the inferior colliculus in mammals, is an important area for processing auditory information. In particular, the torus is implicated in the ability to discriminate between different frog calls, which typically vary in beat or click rate (Rose and Capranica, 1983, 1984, 1985; Alder and Rose, 1998). Because neural processing of the temporal features of sounds is poorly understood, the torus provides an attractive target system from both computational and behavioral standpoints. The neuroanatomy of the torus has been extensively studied in terrestrial anurans (Wilczynski, 1981; Wilczynski and Neary, 1983; Feng and Lin, 1991), but in the aquatic anuran Xenopus laevis, data are sparse and conflicting (Paton et al., 1982; Nikundiwe and Nieuwenhuys, 1983; Will et al., 1985b; Lowe, 1986). Unlike adult terrestrial frogs, aquatic anurans maintain an intact lateral line system and this modality is also processed in the torus (Elepfandt, 1996); how lateral line and acoustic information interact is not known. By what pathway does auditory information arrive at the torus? Xenopus has a modified tympanum, located just under the skin on the side of the head, into which the middle ear bones insert (Wever, 1985). Anuran acoustic end organs include the amphibian and basilar papillae, the saccule, and the lagena (Feng et al., 1975; Caston et al., 1977; Baird and Lewis, 1986). Auditory information derived from movement of the sensing membranes and hair cells within the auditory end organs is conveyed to the medulla by means of axons of the 8th nerve, which projects to the dorsal medullary nucleus, or DMN (Matesz, 1979; Wever, 1985; Will et al., 1985a; Will and Fritzch, 1988). The DMN projects to the superior olive and the nucleus of the lateral lemniscus; these together with the DMN, in turn, project to the midbrain auditory region, the torus semicircularis (Wilczynski, 1981; Wilczynski and Capranica, 1984). The anuran torus itself includes three subnuclei: the principal, laminar, and magnocellular (Potter, 1965). The organization of the torus semicircularis in X. laevis superficially resembles that of terrestrial frogs. Neuroanatomic and electrophysiological studies suggested that auditory information goes primarily to the principal nucleus (Will et al., 1985b; Lowe, 1986). However, a 2-deoxyglucose study using deafened and hemideafened male X. laevis suggested instead that auditory information is restricted to the laminar nucleus (Paton et al., 1982). This subnucleus is further distinguished by the presence of cells that concentrate gonadal steroid hormones (Morrell et al., 1975; Kelley, 1980). The torus semicircularis also processes a second sensory modality, the detection of near field changes in water pressure sensed by the lateral line system (Elepfandt, 1996). This input enters the central nervous system by means of the lateral line nerves, which innervate the lateral line nucleus (n.LL) located medial to the DMN (Will et al., 1985a). Cells of the n.LL project to the torus directly (Plassmann, 1980; Altman and Dawes, 1981; Lowe, 1986). In Xenopus, the lateral line system remains intact into adulthood, whereas in terrestrial frogs, the lateral line system degenerates during metamorphosis and is absent in the adult. Which subnuclei of the torus receive lateral line input has not been studied extensively; Lowe’s results (1986) suggest input to the magnocellular nucleus (as per Will et al., 1985b). In any case, the maintenance of a functional lateral line system in adults complicates the organization of the torus in Xenopus relative to terrestrial Anura. Whether the laminar nucleus receives any direct input from either sensory system is also unclear. To determine which subnuclei of the torus receive auditory input and lateral line input, respectively, in Xenopus laevis, we carried out a detailed neuroanatomic study of the torus. We injected tracers into each subnucleus of the torus specifically and mapped their respective afferents and efferents. In addition, we used the method of Golgi to characterize the dendritic arborization patterns of neurons in each subnucleus. The information thus obtained will be helpful in understanding temporal processing of auditory and lateral line information in Xenopus laevis.

This research examined removals of Giardia and Cryptosporidium by clarification either dissolved-air flotation [OAF] or lamella [plate] sedimentation) and by dual-media filtration following clarification. Studies were conducted for challenge conditions of cysts and oocysts (i.e., high influent concentrations) and for process design detention times and hydraulic loadings. To evaluate the effect of water temperature on performance, sets of experiments were performed for winter and spring seasons. DAF clarification performed better than lamella sedimentation and consistently resulted in lower turbidity levels and particle counts Overall log removals of Giardia and Cryptosporidium by clarification and filtration were about the same for DAF versus lamella sedimentation. Although DAF is not recognized under the Surface Water Treatment Rule or the Interim Enhanced Surface Water Treatment Rule, the authors argue that based on these findings, DAF plants should receive Giardia and Cryptosporidium removal credits at least equal to those received by sedimentation plants.

In Xenopus laevis, the laryngeal motor nucleus (n. of cranial nerves IX-X) is part of a sexually differentiated, androgen sensitive neuromuscular system devoted to vocalization. Adult males have more n. IX-X neurons than females; however, during development of n. IX-X, the rate of neurogenesis does not appear to differ between the sexes. In this study, we explored the role of naturally occurring cell death in the development of this nucleus and asked whether cell death might be involved in establishing the sex difference in neuron number. Counts of n. IX-X neurons reveal that at tadpole stage 56, males and females have similar numbers of n. IX-X neurons, but by stage 64 male neuron numbers are greater. This sex difference arises owing to a greater net loss of neurons in females-males lose approximately 25% of their n. IX-X neurons between stages 56 and 64, while females lose approximately 47%. Sexual differentiation of n. IX-X neuron number coincides with a period of developmental cell death, as evidenced by terminal transferase-mediated dUTP nick-end labeling and the presence of pyknotic nuclei in n. IX-X. A role for gonadal hormones in controlling cell number was examined by treating tadpoles with exogenous androgen and determining the number of n. IX-X neurons at stage 64. Dihydrotestosterone (DHT) treatment from the beginning of the cell death period (stage 54) until stage 64 had no effect on the number of n. IX-X neurons in males but did significantly increase n. IX-X neuron number in females. This increase was sufficient to abolish the sex difference normally observed at stage 64. Although DHT induced increases in female neuron number, it did not induce increases in cell proliferation or addition of newly born neurons to n. IX-X. DHT may therefore have increased neuron number by protecting cells from death. We conclude that androgens can influence the survival of n. IX-X neurons during a period of naturally occurring cell death, and that this action of androgen is critical to the development of sex differences in n. IX-X neuron number.

To shed light on the nature and evolution of structure-function relations in the androgen receptor (AR), we have undertaken a comparative analysis of all available AR and other steroid receptor sequences. We have identified a group of amino acids that "diagnose" the clade of androgen receptors--residues that are strictly conserved among the ARs but not shared with other receptors. We hypothesize that these amino acids, clustered in a few regions of the protein, confer upon the androgen receptor its unique functions, including recognition of specific DNA response elements and affinity for androgens, rather than other steroid hormones. The four domains of the AR display markedly different rates of evolutionary divergence; conserved portions of the sequence, including small stable stretches within otherwise divergent regions, may be essential to receptor function. Current data from experimental, crystallographic, and clinical studies support these hypotheses, which can now be further tested in the laboratory.

Synaptic efficacy at the laryngeal neuromuscular synapse differs markedly in adult male and female Xenopus laevis. Here, we examined the relation between circulating estrogen and synapse strength in developing and adult female frogs. Circulating estrogen levels in males and females during juvenile and adult stages were measured using radioimmunoassays. Synaptic strength was determined by quantal analysis in isolated female larynges. In males, estrogen levels are low (

Xenopus gilli is a vulnerable anuran with a patchy distribution along the south-western coast of the Cape Province, South Africa. This species is sympatric with Xenopus laevis laevis, a widespread relative found over much of southern Africa. We examined the molecular phylogeography and population structure of the contact zone between these species to obtain information about historical biogeography and conservation management of this region. Analyses of the distribution, frequency, and cladistic and phenetic relationships among mitochondrial DNA haplotypes indicate that population subdivision is present in both taxa but that long-term isolation of sets of populations has occurred in X. gilli only. Haplotype and nucleotide diversity are also considerably higher within and among X. gilli ponds than X. l. laevis ponds in this region. We attribute the genetic segregation of X. gilli populations to ancient habitat fragmentation by ocean transgression into X. gilli habitat and to continued habitat alteration by human activity. The lower level of genetic diversity in X. L. laevis in this region is likely a result of a recent arrival of this taxon to the south-western Cape region relative to X. gilli. Population structure in X. l. laevis may be a result of isolation by distance. Clear evidence exists for at least two management units within X. gilli and strongly supports the establishment of protective measures east of False Bay in order to conserve a substantial portion of this species' extant genetic diversity.

Using Northern analysis, in situ hybridization, and nuclease protection assays, the expression and regulation of androgen receptor messenger RNA (AR mRNA) was examined in the CNS of juvenile Xenopus laevis. Only one of the AR mRNA isoforms expressed in X. laevis is transcribed in the CNS as shown by Northern blot analysis. Nuclease protection assays demonstrate that the expression of AR mRNA is higher in the brain stem than in the telencephalon and diencephalon. Although expression of AR mRNA is widespread throughout the CNS, cells of cranial nerve nucleus IX-X (N. IX-X) and spinal cord display the highest in situ hybridization signals in their cytoplasm. Double labeling using horseradish peroxidase and digoxigenin labeled AR probes reveals that laryngeal and anterior spinal cord motor neurons express AR mRNA. More cells express AR mRNA in N. IX-X of males than of females. The number of AR expressing cells in N. IX-X decreases following gonadectomy in both sexes, and dihydrotestosterone (DHT) treatment for 1 month reverses this effect. Increased expression of AR mRNA in the brain of DHT treated animals is also apparent in nuclease protection assays. Sex differences in number of AR expressing cells and hormone regulation of AR mRNA expression in motor nuclei may influence neuromuscular systems devoted to sexually differentiated behaviors. © 1996 John Wiley & Sons, Inc.

Bench-scale studies were used to investigate the effectiveness of dissolved-air flotation (DAF) for the removal of Cryptosporidium parvum oocysts from a drinking water supply. Oocysts were spiked into a natural water at a concentration of 3-4 x 10 5 oocysts/L. Results indicate that DAF achieved a >2-log removal of oocysts under a variety of conditions. In addition, flotation was a superior clarification process to sedimentation for the conditions tested. Coagulation and DAF conditions that minimize residual turbidity and maximize the removals of organic matter are conditions that produce high log removals of Cryptosporidium.

In adult Xenopus laevis, innervation of the vocal organ is more robust in males than in females. This sex difference originates during tadpole development; at stage 56, when the gonads first differentiate, the number of axons entering the larynx is the same in the sexes, but by stage 62, innervation is greater in males. To determine if androgen secretion establishes sex differences in axon number, we treated tadpoles with antiandrogen or androgen beginning at stage 48 or 54 and counted laryngeal nerve axons at stage 62 using electron microscopy. When male tadpoles were treated with the antiandrogen hydroxyflutamide, axon numbers were reduced to female-typical values; axon numbers in females were unaffected by antiandrogen treatment. When female tadpoles were treated with the androgen DHT (dihydrotestosterone), axon numbers were increased to male-like values. These findings suggest that endogenous androgen secretion during late tadpole stages in males is required for the sexual differentiation of laryngeal innervation observed from stage 62 on. Because androgen treatment and laryngeal innervation affect myogenesis in postmetamorphic frogs, numbers of laryngeal dilator muscle fibers were determined for hormonally manipulated tadpoles. At stage 62, vehicle-treated males had more laryngeal axons than females; laryngeal muscle fiber numbers did not, however, differ in the sexes. Both male and female tadpoles, treated from stage 54 with DHT, had more muscle fibers at stage 62 than vehicle-treated controls. Thus, while endogenous androgen secretion during late tadpole stages is subthreshold for the establishment of masculinized muscle fiber numbers, laryngeal myogenesis is androgen sensitive at this time and can be increased by suprathreshold provision of exogenous DHT. A subgroup of tadpoles, DHT treated from stage 54 to 62, was allowed to survive, untreated, until postmetamorphic stage 2 (PM2: 5 months after metamorphosis is complete). Androgen treatment between tadpole stages 54 and 62 does not prevent the ontogenetic decrease in axon numbers characteristic of laryngeal development. In addition, the elevation in stage 62 axon numbers produced by DHT-treatment at late tadpole stages was not associated with elevated numbers of laryngeal muscle fibers at PM2. Juvenile males normally maintain elevated axon numbers (relative to final adult values) through PM2 and the presence of these additional axons may result from-rather than contribute directly to—laryngeal muscle fiber addition. 1994 John Wiley & Sons, Inc.

The genus Johnstonella Brand was published in 1925, as a segregate genus of Cryptantha (Boraginaceae). Brand included two species, J. racemosa and J. inaequata, in his treatment. Johnston, in the same year, indicated J. racemosa as the type of Johnstonella. However, Johnston's publication predated Brand's; therefore, Johnston's typification is not effective. Although Johnstonella has generally not been accepted by taxonomists, it has recently been resurrected based on molecular phylogenetic studies. Because of the need for a type for the genus, we designate the type of Johnstonella racemosa as the type of Johnstonella.

Sex differences in the number of muscle fibers in the larynx of clawed frogs (Xenopus laevis) develop after metamorphosis. In order to examine possible contributions of neural innervation to this process, we prepared sections of the laryngeal nerve from tadpole stage 56, when the sexes can first be distinguished, through adulthood, and counted axons on electron micrographs. The adult number of axons is achieved by a sexually differentiated pattern of axonal addition and loss. Axon numbers are high at tadpole stage 56 and equal for males and females; thereafter, males have more axons. Sex differences are most pronounced at tadpole stage 62 because between stages 59 and 62 the number of laryngeal axons in males increases by an average of 119 per nerve. Ultrastructural evidence is congruent with the hypothesis that new axons are added to the laryngeal nerve between tadpole stages 56 and 62. The loss of axons from the laryngeal nerve is greater for females than for males. Between tadpole stages 56 and adulthood, overall axon number decreases by 47% in males and by 64% in females. Signs of axonal degeneration are present in both sexes before metamorphosis but are rare at juvenile or adult stages. The numbers of axons in juvenile frogs do not differ from those in adults and continue to be greater in males than in females. In contrast to the amount of axon addition and loss, the timing of axon loss and the percentage of myelinated axons is the same for males and females throughout development. Thus sex differences in the innervation of laryngeal muscle originate before metamorphosis and could contribute to the marked sex differences in muscle fiber addition that occur thereafter.

To automate tasks like assembly, disassembly, repair and maintenance, the issues arising from environmental uncertainties must be addressed. An integrated sensing approach which addresses uncertainties is presented for two robot systems equipped with multiple sensors. The target tasks involve the insertion of printed circuit boards into cages. Sensors are used to calibrate the robot to the workspace, locate the supply of printed circuit boards and the destination insertion slots. A fingertip lightbeam sensor is used to refine the location information to the precision required for a successful insertion. Two plausible approaches are explored to test some of the sensing concepts. One approach examines blind system sensing strategies; the other examines vision sensing in conjunction with fuzzy reasoning. A controller which is based on fuzzy logic is used to interpret the forces and torques generated by the wrist-mounted force-torque sensor during the insertion process. These explorations represent the first steps which lead toward the development of integrated sensing skills to perform generic activities such as insert and locate.

A 15-year-old male with unresolved hip pain after minor trauma is presented. The diagnosis of an acetabular labral tear was made using correlative scintigraphic and magnetic resonance (MR) imaging, obviating the more invasive investigations of arthrography or arthroscopy of the hip. The clinical and radiological features of this lesion are reviewed. Undiagnosed, acetabular labral tears may result in considerable morbidity. Appropriate operative or conservative management of the condition usually provides symptomatic relief.

Connections of two telencephalic vocal control nuclei, the hyperstriatum ventrale, pars caudale (HVc), and robust nucleus of the archistriatum (RA), were investigated in adult canaries. Methods used were transport of horseradish peroxidase and 3H-adenosine and silver staining of degenerating axons. Three nuclei project to HVc: medial nucleus magnocellularis of the anterior neostriatum (MAN), nucleus interfacialis (NIf) of midneostriatum, and nucleus uvaeformis (Uva) of the diecephalon. Uva also projects to NIf. NIf and Uva have not been described previously. HVc projects to area X of lobus parolfactorius, to RA, and to field Avalanche of hyperstriatum ventrale. Nucleus RA receives projections from HVc and from lateral MAN. All these projections are ipsilateral. No gross male/female differences were apparent in the projections to and from HVc. Uptake of HRP by cell somata in HVc following localized injections of this substance into RA or HVc suggests that HVc is composed of rostrocaudally organized clusters of cells, with little lateral communication between them.

Autoradiographic techniques for light microscopic examination of sex steroid retention were applied to the brains of male and female Xenopus laevis, and anuran amphibian, after 3H-estradiol administration. Estrogen was concentrated by cells in three telencephalic areas (the ventral striatum, the ventral-lateral septum and the amygdala), the anterior preoptic area, the ventral thalamus, the ventral infundibular nucleus, and in the torus semicircularis. The anterior preoptic area and the ventral infundibular nucleus contained the greatest number of labelled cells. The topography of estrogen-concentrating cells was the same in male and female brains. This fact and comparisons of 3H-estradiol with 3H-testosterone retention in Xenopus suggest that the sex steroid itself, and not the genetic sex of Xenopus determines the pattern of uptake by cells in the brain. The distribution of hormone-concentrating cells in Xenopus has many similarities to that found in birds and mammals. Preoptic, hypothalamic (tuberal), limbic forebrain and specific mesencephalic sites in all these forms contain labelled cells following radioactive sex steroid administration. Findings in Xenopus add to the argument for a phylogenetically stable system of hormone-concentrating nerve cells in limbic, hypothalamic and mesencephalic structures.

In the clawed frog (Xenopus laevis), motor neurons in cranial nerve nucleus IX-X control contraction of laryngeal muscles responsible for sexually dimorphic vocal behaviors. We examined sex differences in dendritic arbors of n.IX-X cells using the Golgi–Cox method. Three morphological classes of somal types (ovoid, triangular, and elongate) are present in similar frequencies in n.IX-X of both males and females. The male n.IX-X neuron is a more complex and hypertrophied version of the female n.IX-X cell. The number of primary dendrites is the same for both sexes, but males have more total dendritic segments. The overall dendritic length of male n.IX-X neurons is two to three times that of the female. Males have longer dendritic segments between all branch points. Male and female frogs differ in levels of circulating androgens; neurons of n.IX-X are targets for androgenic steroids. To determine if androgen can affect dendritic morphology in adult females, we examined Golgi-impregnated cells in n.IX-X from ovariectomized females treated with testosterone for 1 month. The total number of dendritic segments was reduced by androgen treatment due to reduction in the number of higher order dendritic segments; the number of primary dendritic segments was unchanged. Androgen treatment may induce resorption of higher order dendritic branches. The overall dendritic length of androgen-treated female n.IX-X neurons was unchanged, and dendritic segments were longer. Thus, although androgen can alter dendrites of n.IX-X cells in adult females, this short-term treatment does not produce a masculine dendritic architecture.

Anterograde projections of a telencephalic auditory area - field L of the neostriatum - were traced in canaries, Serinus canarius. Field L was defined as the neostriatal projection of nucleus ovoidalis of the thalamus. Using amino acid autoradiography, two efferent projections of field L and adjacent neostriatum were observed: (1) a projection to the medial and ventral borders of nucleus hyperstriatum ventrale, pars caudale (HVc) and (2) a smaller projection to medial paleostriatum augmentatum (PA). When autoradiographic injection sites included neostriatum postero-ventral to field L, a projection to archistriatum outlining the anterior and ventral borders of the nucleus robustus archistriatalis (RA) resulted. Injection sites that included neostriatum antero-lateral to "L" gave rise to projections to the interior of HVc proper. Above background numbers of silver grains were consistently observed over caudal dorso-lateral portions of nucleus ovoidalis. Following lesion of field L and adjacent neostriatum, argyrophilic degeneration was traced to medial PA and to a shelf of neostriatum underlying HVc. All observed anterograde projections were ipsilateral. Two of the nuclei outlined by neostriatal projections in this study, HVc and RA, have important roles in the motor control of canary song (Nottebohm et al., '76). The development of song is dependent on auditory information. Auditory-vocal neural connections described here may be involved in song learning.

South African clawed frogs use sex-specific vocalizations during courtship. In the male, vocalizations are under the control of gonadal androgen. Though females have moderate levels of circulating androgen, they do not give male-typical mate calls. Both muscles of the vocal organ and neurons of the central nervous system (CNS) vocal pathway are sexually dimorphic and androgen-sensitive. Recent studies suggest that the failure of androgen to masculinize adult females results from a male-specific, androgen-regulated developmental program. At metamorphosis the larynx is sexually monomorphic and feminine in morphology, muscle fiber number and androgen receptor content. During the next six months, under the influence of increasing androgen titers and high receptor levels, myoblasts proliferate in the male and muscle fibers increase at an average rate of 100/day. Females have much lower hormone levels, receptor values decline and they display no net addition of fibers. At metamorphosis, both males and females have approximately 4000 muscle fibers. By adulthood, males have eight times the female fiber number. In the CNS, adult laryngeal motor neurons are more numerous with larger somata and dendritic trees in males than in females. Certain connections of neurons in the vocal pathway are also less robust in females. Unlike the periphery, motor neuron number does not appear to be established by androgen-induced proliferation. Our current hypothesis is that androgen acts at the level of laryngeal muscle to produce more muscle fibers and thus provide more target for motor neurons in the male. This process could regulate cell number by ontogenetic cell death. In the CNS, androgen-target neurons become capable of accumulating hormone shortly before metamorphosis. Androgen receptor in laryngeal motor neurons may permit the dendritic growth characteristic of males by increasing sensitivity to afferent stimuli. Such a process could account for the observed differences in CNS vocal "circuitry" in X. laevis and thus behavioral differences between the sexes.

The distribution of hormone-concentrating cells in the brains of South African clawed frogs, Xenopus laevis, was examined autoradiographically after the administration of 3H-dihydrotestosterone. Hormone-accumulating cells were found in cranial nerve nucleus IX-X and adjacent smaller cells, a presumed medullary vestibular nucleus, a presumed sensory nucleus of cranial nerve V, dorsal tegmental area of the medulla, laminar nucleus of the torus semicircularis, ventral thalamus, and anterior pituitary. The pattern of dihydrotestosterone-labelled cells differs from previously reported results following testosterone or estradiol administration. Unlike these latter hormones, dihydrotestosterone does not accumulate in anterior preoptic or ventral infundibular nuclei. Both androgens but not estradiol label medullary motor neurons; limbic telencephalic nuclei appear to concentrate only estradiol. Hormone-concentrating brain nuclei in X. laevis have been implicated in neuro-endocrine regulation and the control of male and female reproductive behaviors.

The aims of this study were to characterize sexual dimorphism in the larynx of adult Xenopus laevis and to determine how sex differences arise during postmetamorphic development. The larger male larynx is a result of greater cell numbers in both cartilage and muscle. The dilator laryngis muscle of the male larynx has 6-7 times more muscle fibers than that of the female. At metamorphosis, the larynx is sexually monomorphic and feminine in phenotype. The DNA content of the male larynx doubles during the first 6 months following metamorphosis; there is no net DNA increase in the female larynx during this time. Both sexes experience a marked increase in laryngeal DNA content and mass between 6 months and adulthood. The number of muscle fibers in the male larynx increases at an average rate of 150 fibers a day during the first 10 months of postmetamorphic development. There is no net change in fiber numbers in the female larynx from metamorphosis to adulthood. Administration of the antiandrogen Flutamide to metamorphic frogs prevents the net addition of laryngeal muscle fibers in males. Thus, we propose that addition of postmetamorphic laryngeal muscle fibers in males is dependent upon the presence of circulating androgens. Exogenous testosterone administration results in an increase in laryngeal mass, DNA content, and cellular proliferation in juvenile frogs. Using [3H]thymidine injections to probe ongoing, as well as testosterone-induced, cell proliferation, we conclude that cellular proliferation is regulated differently in males and females during development. Thus androgen-induced proliferation is one cellular mechanism responsible for the sexual dimorphism observed in adults.

The central projections of individual components of the IX-X nerve complex in the South African clawed frog, Xenopus laevis, were mapped by dye diffusion with Lucifer Yellow in an isolated brain preparation. The method reliably revealed fiber tracts, termination zones, and detailed cell morphology. In addition, motor neurons could be doubly labelled by retrograde transport of horseradish peroxidase from muscle targets followed by backfilling the appropriate nerves with Lucifer Yellow. The most anterior root associated with the nerve IX-X complex, root 1, is composed of lateral line afferents that terminate in the medial medulla. Root 2 contains sensory fibers that terminate in the nucleus tractus solitarii and axons of lateral line efferent neurons. Root 3 is composed of sensory and motor fibers, including a major somatosensory component that terminates in posterior medulla and anterior spinal cord, and axons from cranial nerve nucleus IX-X. The most posterior root of the IX-X nerve complex, root 4, contains axons of laryngeal motor neurons and of general visceral efferent neurons.

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