Low‐frequency conductivity tensor of rat brain tissues inferred from diffusion MRI

Conductivity tensor maps of the rat brain were obtained using diffusion magnetic resonance imaging (MRI). Signal attenuations in the cortex and the corpus callosum were measured using the stimulated echo acquisition mode (STEAM) sequence with b factors up to 6000 s/mm². Our previously published method was improved to infer 3 × 3 conductivity tensor at the low‐frequency limit. The conductivity tensor of the tissue was inferred from the fast component of the diffusion tensor and a fraction of the fast component. The mean conductivity (MC) of the cortex and the corpus callosum was 0.52 and 0.62 S/m, respectively. Diffusion‐weighted images were obtained with b factors up to 4500 s/mm². Conductivity tensor images were calculated from the fast diffusion tensor images. Tissues with highly anisotropic cellular structures, such as the corpus callosum, the internal capsule, and the trigeminal nerve, exhibited high anisotropy in conductivity. The resulting values corresponded to conductivities at the low‐frequency limit because our method assumed electric currents flowing only through extracellular fluid. Bioelectromagnetics 30:489–499, 2009. © 2009 Wiley‐Liss, Inc.     

Contribution of terrestrial invertebrates to the annual resource budget for salmonids in forest and grassland reaches of a headwater stream

1. The annual input, contribution to the diet of salmonids, and quantitative input of terrestrial invertebrates to four reaches with contrasting forest (n=2) and grassland riparian vegetation (n=2) were compared in a Japanese headwater stream.
2. The annual input of terrestrial invertebrates falling into the forest reaches (mean±1 SE=8.7×10³±0.3×10³ mg m^?2 year^?1) was 1.7 times greater than that in the grassland reaches (5.1×10³±0.8×10³ mg m^?2 year^?1), with clear seasonality in the daily input of invertebrates in both vegetation types. The daily input, however, differed between the vegetation types only in summer, when it rose to a maximum in both vegetation types.
3. Fish biomass also differed among the seasons in both vegetation types, being less in the grassland reaches. The contribution of terrestrial invertebrates to the salmonid diet in the forest and grassland reaches was 11 and 7% in spring, 68 and 77% in summer, 48 and 33% in autumn, and 1 and 1% in winter, respectively. The prey consumption rate of fish, which was similar between the vegetation types, increased with stream temperature and was highest in summer. Terrestrial invertebrates supported 49% (mean±1 SE=5.3×10³±0.4×10³ mg m^?2 year^?1) of the annual, total prey consumption (10.9×10³±1.7×10³ mg m^?2 year^?1) by salmonids in the forest and 53% (2.0×10³±0.3×10³ mg m^?2 year^?1) (3.8×10³±0.6×10³ mg m^?2 year^?1) in the grassland reaches.
4. Salmonids were estimated to consume 51 and 35% of the annual total (falling plus drift) input of terrestrial invertebrates in the forest and grassland reaches, respectively. The input of terrestrial invertebrates by drift, however, was almost equal to the output in both vegetation types, suggesting that the reach‐based, in‐stream retention of terrestrial invertebrates almost balanced these falling in.
5. Difference in the riparian vegetation, which caused spatial heterogeneity in the input of terrestrial invertebrates, could play an important role in determining the local distribution of salmonids.     

Behavioral impacts of disentanglement of a right whale under sedation and the energetic cost of entanglement

Protracted entanglement in fishing gear often leads to emaciation through reduced mobility and foraging ability, and energy budget depletion from the added drag of towing gear for months or years. We examined changes in kinematics of a tagged entangled North Atlantic right whale (Eg 3911), before, during, and after disentanglement on 15 January 2011. To calculate the additional drag forces and energetic demand associated with various gear configurations, we towed three sets of gear attached to a load‐cell tensiometer at multiple speeds. Tag analyses revealed significant increases in dive depth and duration; ascent, descent and fluke stroke rates; and decreases in root mean square fluke amplitude (a proxy for thrust) following disentanglement. Conservative drag coefficients while entangled in all gear configurations (mean ± SD C_d,e,go = 3.4 × 10^?3 ± 0.0003, C_d,e,gb = 3.7 × 10^?3 ± 0.0003, C_d,e,sl = 3.8 × 10^?3 ± 0.0004) were significantly greater than in the nonentangled case (C_d,n = 3.2 × 10^?3 ± 0.0003; P = 0.0156, 0.0312, 0.0078, respectively). Increases in total power input (including standard metabolism) over the nonentangled condition ranged from 1.6% to 120.9% for all gear configurations tested; locomotory power requirements increased 60.0%–164.6%. These results highlight significant alteration to swimming patterns, and the magnitude of energy depletion in a chronically entangled whale.     

Seasonality of Antarctic minke whale (Balaenoptera bonaerensis) calls off the western Antarctic Peninsula

The Antarctic minke whale (Balaenoptera bonaerensis) is a difficult species to study because of its low visual detectability and preference for living within the sea ice habitat, accessible only by ice‐strengthened vessels. Recent identification of the Antarctic minke whale as the source of the seasonally ubiquitous bio‐duck call has allowed the use of this sound, as well as downsweeps, to investigate seasonality trends and diel patterns in Antarctic minke whale call production, and their relationship to sea ice cover. Passive acoustic data were collected using an autonomous Acoustic Recording Package (ARP) off the western Antarctic Peninsula. Bio‐duck calls were classified into four distinct call variants, with one variant having two subtypes. Bio‐duck calls were detected between April and November, with increasing call duration during the austral winter, indicating a strong seasonality in call production. Downsweeps, which were also attributed to Antarctic minke whales, were present throughout most months during the recording period, with a peak in July, and an absence in March and April. Both bio‐duck and downsweeps were significantly correlated with sea ice cover. No diel patterns were observed in bio‐duck calls or in downsweep call production at this site.     

The brain of the horseshoe crab (Limulus polyphemus) II. Architecture of the corpora pendunculata

The corpora pedunculata, or mushroom bodies, of the horseshoe crab, Limulus polyphemus, form a bulbous ventral hemisphere composed of two internal lobes that are highly branched like a cauliflower. This organ is clothed with a deep layer of small association neurons called globuli or Kenyon cells. In an animal that is 50 mm in width, they number 3.7 × 10⁶, a value that rises to about 1 × 10⁸ in an adult (250 mm width). The neuropil of each corpus pedunculatum converges from its peripheral lobules toward several major peduncles, which are in communication with the protocerebral neuropil by a narrow stalk containing about 5000 fibers in a 50 mm animal. The numerical relations suggest that presumptive second-order chemosensory fibers enter the corpora pedunculata and synapse divergently onto Kenyon cells. The axons of Kenyon cells, in turn, converge onto efferent fibers that leave through the stalk.     

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Lateral impacts correlate with falx cerebri displacement and corpus callosum trauma in sports-related concussions

Corpus callosum trauma has long been implicated in mild traumatic brain injury (mTBI), yet the mechanism by which forces penetrate this structure is unknown. We investigated the hypothesis that coronal and horizontal rotations produce motion of the falx cerebri that damages the corpus callosum. We analyzed previously published head kinematics of 115 sports impacts (2 diagnosed mTBI) measured with instrumented mouthguards and used finite element (FE) simulations to correlate falx displacement with corpus callosum deformation. Peak coronal accelerations were larger in impacts with mTBI (8592 rad/s² avg.) than those without (1412 rad/s² avg.). From FE simulations, coronal acceleration was strongly correlated with deep lateral motion of the falx center (r = 0.85), while horizontal acceleration was correlated with deep lateral motion of the falx periphery (r > 0.78). Larger lateral displacement at the falx center and periphery was correlated with higher tract-oriented strains in the corpus callosum body (r = 0.91) and genu/splenium (r > 0.72), respectively. The relationship between the corpus callosum and falx was unique: removing the falx from the FE model halved peak strains in the corpus callosum from 35% to 17%. Consistent with model results, we found indications of corpus callosum trauma in diffusion tensor imaging of the mTBI athletes. For a measured alteration of consciousness, depressed fractional anisotropy and increased mean diffusivity indicated possible damage to the mid-posterior corpus callosum. Our results suggest that the corpus callosum may be sensitive to coronal and horizontal rotations because they drive lateral motion of a relatively stiff membrane, the falx, in the direction of commissural fibers below.

     

Brain connections: interhemispheric fiber systems and anatomical brain asymmetries in humans.

The present review summarizes some results of a research program oriented to determine the anatomical substrates of interhemispheric communication in humans, as seen in postmortem material. One main finding is a sensible pattern of histological differentiation along the corpus callosum, indicating specific properties of interhemispheric conduction for axonal fibers involved in different brain functions. Callosal regions that connect primary and secondary sensory and motor areas are characterized by a large proportion of fast-conducting, large-diameter fibers, while regions connecting the so-called association areas and prefrontal areas bear a high density of slow-conducting, lightly myelinated and thin fibers. These findings are interpreted in a functional context, suggesting that the fast-conducting fibers connecting sensory and motor areas contribute to fuse the two hemirepresentations in each hemisphere. It has also been determined that an increased callosal area indicates an increased number of callosal fibers, a finding that validates previous morphometric studies done in several laboratories. No sex differences in callosal size, shape, or in callosal fiber composition were found. Finally, an inverse relation was found between the anatomical asymmetries in the size of the Sylvian fissure and the size and number of fibers in specific segments of the corpus callosum. There were sex differences in terms of the particular callosal regions showing a significant correlation with asymmetries, and in terms of the fiber types that were correlated with asymmetries.     

Transient cellular structures in developing corpus callosum of the human brain

The corpus callosum connects two cerebral hemispheres as the most voluminous fiber system in the human brain. The developing callosal fibers originate from immature pyramidal neurons, grow through complex pathways and cross the midline using different substrates in transient fetal structures. We analyzed cellular structures in the human corpus callosum on postmortem brains from the age of 18 weeks post conception to adult, using glial fibrillary acidic protein, neuron-specific nuclear protein, and chondroitin sulphate immunocytochemistry. We found the presence of transient cellular structures, callosal septa, which divide major fiber bundles and ventrally merge with subcallosal zone forming grooves for callosal axons. The callosal septa are composed of glial fibrillary acidic protein reactive meshwork, neurones and the chondroitin sulphate immunoreactive extracellular matrix. The developmental window of prominence of the callosal septa is between 18-34 weeks post conception which corresponds to the period of most intensive growth of callosal axons in human. During the early postnatal period the callosal septa become thinner and shorter, lose their neuronal and chondroitin sulphate content. In conclusion, transient expression of neuronal, glial and extracellular, growing substrate in the callosal septa, as septa itself, indicates their role in guidance during intensive growth of callosal fibers in the human brain. These findings shed some light on the complex morphogenetic events during the growth of the corpus callosum and represent normative parameters necessary for studies of structural plasticity after perinatal lesions.     

Estimated absorbance spectra of the visual pigments of the North Atlantic right whale (Eubalaena glacialis)

To assess the spectral sensitivities of the retinal visual pigments from the North Atlantic right whale (Eubalaena glacialis), we have cloned and sequenced two exons from the rod opsin gene and two exons from the middle‐wavelength sensitive (MWS) cone opsin gene in order to determine the amino acids at positions known to be key regulators of the spectral location of the absorbance maximum (λ_max). Based on previous mutagenesis models we estimate that the right whale possesses a rod visual pigment with a λ_max of 499 nm and a MWS cone visual pigment with a λ_max of 524 nm. Although the MWS cone visual pigment from the right whale is blue‐shifted in its spectral sensitivity like those from odontocetes, the spectral sensitivity of the right whale rod visual pigment is similar to those from terrestrial mammals.     

Two specific populations of GABAergic neurons originating from the medial and the caudal ganglionic eminences aid in proper navigation of callosal axons

The corpus callosum (CC) plays a crucial role in interhemispheric communication. It has been shown that CC formation relies on the guidepost cells located in the midline region that include glutamatergic and GABAergic neurons as well as glial cells. However, the origin of these guidepost GABAergic neurons and their precise function in callosal axon pathfinding remain to be investigated. Here, we show that two distinct GABAergic neuronal subpopulations converge toward the midline prior to the arrival of callosal axons. Using in vivo and ex vivo fate mapping we show that CC GABAergic neurons originate in the caudal and medial ganglionic eminences (CGE and MGE) but not in the lateral ganglionic eminence (LGE). Time lapse imaging on organotypic slices and in vivo analyses further revealed that CC GABAergic neurons contribute to the normal navigation of callosal axons. The use of Nkx2.1 knockout (KO) mice confirmed a role of these neurons in the maintenance of proper behavior of callosal axons while growing through the CC. Indeed, using in vitro transplantation assays, we demonstrated that both MGE‐ and CGE‐derived GABAergic neurons exert an attractive activity on callosal axons. Furthermore, by combining a sensitive RT‐PCR technique with in situ hybridization, we demonstrate that CC neurons express multiple short and long range guidance cues. This study strongly suggests that MGE‐ and CGE‐derived interneurons may guide CC axons by multiple guidance mechanisms and signaling pathways. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 73: 647–672, 2013     

Rorqual whale (Balaenopteridae) surface lunge‐feeding behaviors: Standardized classification,repertoire diversity,and evolutionary analyses

Rorqual whales (Family: Balaenopteridae) are the world's largest predators and sometimes feed near or at the sea surface on small schooling prey. Most rorquals capture prey using a behavioral process known as lunge‐feeding that, when occurring at the surface, often exposes the mouth and head above the water. New technology has recently improved historical misconceptions about the natural variation in rorqual lunge‐feeding behavior yet missing from the literature is a dedicated study of the identification, use, and evolution of these behaviors when used to capture prey at the surface. Here we present results from a long‐term investigation of three rorqual whale species (minke whale, Balaenoptera acutorostrata; fin whale, B. physalus; and blue whale, B. musculus) that helped us develop a standardized classification system of surface lunge‐feeding (SLF) behaviors. We then tested for differences in frequency of these behaviors among the three species and across all rorqual species. Our results: (1) propose a unified classification system of six homologous SLF behaviors used by all living rorqual whale species; (2) demonstrate statistically significant differences in the frequency of each behavior by minke, fin, and blue whales; and (3) provide new information regarding the evolution of lunge‐feeding behaviors among rorqual whales.     

Analysis of the C4 genes in baleen whales using a human cDNA probe

We have used a human C4 cDNA probe to investigate the complement component C4 gene in four members of the family Balaenopteridae: fin whale (Balaenoptera physalus), sei whale (B. borealis), minke whale (B. acutorostrata), and bryde's whale (B. edeni). Restriction mapping of genomic DNA from the first three species suggests the presence of only one locus in these species, and also shows that the C4 genes in the three species are very similar. We have used 14 restriction endonucleases to investigate the restriction fragment length polymorphism (RFLP) of fin whales, 13 enzymes for sei whales, and 8 enzymes for the minke whale. No polymorphism was seen in DNA from the five minke whale samples, but Rsa I and Taq I restriction enzymes gave polymorphism in fin and sei whales whereas Hind III and Msp I restriction enzymes showed polymorphism in sei whales only. Only one bryde's whale sample was available for investigation. The study of DNA available from mother-fetus pairs from the two polymorphic species demonstrated a simple, two-allele transmission of RFLP alleles.     

Tractography of the Spider Monkey (Ateles geoffroyi) Corpus Callosum Using Diffusion Tensor Magnetic Resonance Imaging

The objective of this research was to describe the organization, connectivity and microstructure of the corpus callosum of the spider monkey (Ateles geoffroyi). Non-invasive magnetic resonance imaging and diffusion-tensor imaging were obtained from three subjects using a 3T Philips scanner. We hypothesized that the arrangement of fibers in spider monkeys would be similar to that observed in other non-human primates. A repeated measure (n = 3) of fractional anisotropy values was obtained of each subject and for each callosal subdivision. Measurements of the diffusion properties of corpus callosum fibers exhibited a similar pattern to those reported in the literature for humans and chimpanzees. No statistical difference was reached when comparing this parameter between the different CC regions (p = 0.066). The highest fractional anisotropy values corresponded to regions projecting from the corpus callosum to the posterior cortical association areas, premotor and supplementary motor cortices. The lowest fractional anisotropy corresponded to projections to motor and sensory cortical areas. Analyses indicated that approximately 57% of the fibers projects to the frontal cortex and 43% to the post-central cortex. While this study had a small sample size, the results provided important information concerning the organization of the corpus callosum in spider monkeys.     

Myotube production in fast myotomal muscle is switched-off at shorter body lengths in male than female Atlantic halibut Hippoglossus hippoglossus (L.) resulting in a lower final fibre number

A sampling method is described to determine accurately the number of fast myotomal muscle fibres (N_F) in a large flatfish species, the Atlantic halibut Hippoglossus hippoglossus. An unusual feature of the fast myotomal muscle is the presence of internalized strips of slow muscle fibres. In fish of 1·5–3·5 kg (n = 24), the total cross‐sectional area (A_TC) of fast muscle was 18% greater in the dorsal than ventral myotomal compartments (P < 0·05), whereas there was no significant difference between left‐ and right‐hand sides of the body. Due the bilateral asymmetry, muscle blocks (5 × 5 × 5 mm) were prepared to systematically sample each myotomal quadrant (dorsal, ventral, left‐ and right‐side) and the diameters of 150 fast fibres measured per block. Smooth non‐parametric probability functions were fitted to a minimum of 800 measurements of fibre diameter per quadrant (n = 5). There were no significant differences in the distribution of muscle fibre diameters between myotomal compartments and therefore N_F could be estimated from a single quadrant. The number of blocks required to estimate N_F with a repeatability of ±2·5% increased from six at 300 g body mass to 17 at 96·5 kg, caused by variation within and between blocks. Gompertz curves were fitted to measurements of fibre number and fork length (L_F). The estimated final fibre number was 8·96 × 10⁵ (7·99–9·94 × 10⁵, 95% CI) for males and 1·73 × 10⁶ (1·56–1·90 × 10⁶, 95% CI) for female fish. The estimated L_F for cessation of fibre recruitment in the fast muscle of female fish (1775 mm) was almost twice that in males (810 mm), reflecting their greater ultimate body size.     

Estimation of minke whale abundance from an acoustic line transect survey of the Mariana Islands

The minke whale is one of the most abundant species of baleen whales worldwide, yet is rarely sighted in subtropical waters. In the North Pacific, they produce a distinctive sound known as the “boing,” which can be used to acoustically localize individuals. A vessel‐based survey using both visual and passive acoustic monitoring was conducted during the spring of 2007 in a large (616,000 km²) study area encompassing the Mariana Islands. We applied line transect methods to data collected from a towed hydrophone array to estimate the abundance of calling minke whales in our study area. No minke whales were sighted, but there were hundreds of acoustic detections of boings. Computer algorithms were developed to localize calling minke whales from acoustic recordings, resulting in over 30 independent localizations, a six‐fold increase over those estimated during the survey. The two best estimates of abundance of calling minke whales were determined to be 80 and 91 animals (0.13 and 0.15 animals per 1,000 km2, respectively; CV = 34%). These are the first density and abundance estimates for calling minke whales using towed hydrophone array surveys, and the first estimates for this species in the Mariana Islands region. These are considered minimum estimates of the true number of minke whales in the study area.     

Flow injection chemiluminescence determination of 6‐mercaptopurine based on a new system of potassium permanganate–thioacetamide–sodium hexametaphosphate

A novel chemiluminescence method for the determination of 6‐mercaptopurine was established based on 6‐mercaptopurine inhibition of the chemiluminescence emission of potassium permanganate–thioacetamide–sodium hexametaphosphate system. The peak height was proportional to log 6‐mercaptopurine concentration in the range 7.0 × 10^?10 to 1.0 × 10^?7 g/mL and the detection limit was 1.9 × 10^?11 g/mL (S/N = 3). The relative standard deviation was 1.5% for the determination of 8.0 × 10^?8 g/mL 6‐mercaptopurine (n = 11). The proposed sensor was successfully applied to the analysis of 6‐mercaptopurine in human serum samples. Copyright © 2009 John Wiley & Sons, Ltd.     

DIFFERENCES IN THE NUCLEAR RIBONUCLEIC ACID CONTENT IN DIFFERENT AREAS OF THE HUMAN ADULT AND FOETAL BRAIN*

Abstract— Four different areas of ten brains from adults in the age group between 44 and 74 years and two areas of six foetal brains were studied. The cellular density was similar in the different areas of the brain of adult man; it averaged 11.9 × 10⁷/g wet tissue. The number of neurons per g wet tissue varied from 2.22 × 10⁷ in the cortex to 0.15 × 10⁷ in the centrum semiovale. In the brain of adults the overall RNA content of nuclei was higher for the cortex than for the corpus callosum or the centrum semiovale. The RNA content of neuronal nuclei was higher than that of non-neuronal nuclei. In the brain of foetuses the nuclear density was higher than in adults. The DNA content of a nucleus in foetal brain was 2–3 times as high as in adult brain and it approached adult values with increasing maturity.     

Myotropic activity and immunolocalization of selected neuropeptides of the burying beetle Nicrophorus vespilloides (Coleoptera: Silphidae)

Burying beetles (Nicrophorus sp.) are necrophagous insects with developed parental care. Genome of Nicrophorus vespilloides has been recently sequenced, which makes them interesting model organism in behavioral ecology. However, we know very little about their physiology, including the functioning of their neuroendocrine system. In this study, one of the physiological activities of proctolin, myosuppressin (Nieve? MS), myoinhibitory peptide (Trica-MIP-5) and the short neuropeptide F (Nicve-sNPF) in N. vespilloides have been investigated. The tested neuropeptides were myoactive on N. vespilloides hindgut. After application of the proctolin increased hindgut contraction frequency was observed (EC50 value was 5.47 x 10-8 mol/L). The other tested neuropeptides led to inhibition of N. vespilloides hindgut contractions (Nicve-MS: IC50 = 5.20 x 10~5 mol/L;Trica-MIP-5: IC50 = 5.95 x 10-6 mol/L;Nicvc-sNPF: IC50 = 4.08 x 10-5 mol/L). Moreover, the tested neuropeptides were immunolocalized in the nervous system of N. vespilloides. Neurons containing sNPF and MIP in brain and ventral nerve cord (VNC) were identified. Proctolin-immunolabeled neurons only in VNC were observed. Moreover, MIP-immunolabeled varicosities and fibers in retrocerebral complex were observed. In addition, our results have been supplemented with alignments of amino acid sequences of these neuropeptides in beetle species. This alignment analysis clearly showed amino acid sequence similarities between neuropeptides. Moreover, this allowed to deduce amino acid sequence of N. vespilloides proctolin (RYLPTa), Nicve-MS (QDVDHVFLRFa) and six isoforms ofNicve-MIP (Nicve-MIP-1一 DWNRNLHSWa;Nicve-MIP-2—AWQNLQGGWa;Nicve-MIP-3—AWQNLQGGWa;Nicve-MlP-4—AWKNLNNAGWa;Nicve-MIP-5—SEWGNFRGSWa;Nicve-MIP-6— DPAWTNLKGIWa;and Nicve-sNPF—SGRSPSLRLRFa).