Erythropoietin concentration in developing harbor seals (Phoca vitulina)

Tissue hypoxia elicits the production of erythropoietin (Epo), a hormone that stimulates red blood cell production. In young diving mammals, oxygen is stored primarily in the blood, and blood oxygen stores increase significantly during the first weeks of life. In an effort to establish the role of Epo during this period of blood development, this study measured Epo concentration in plasma of 134 harbor seal (Phoca vitulina) pups and adults. Concurrent measurements of hematocrit (Hct), hemoglobin concentration [Hb], and red blood cell (RBC) counts allowed the evaluation of the effect of Epo on blood oxygen store capacity. Erythropoietin and most blood parameters varied with age. At birth, neonatal [Hb], Hct, and RBC were elevated, possibly due to the rapid expansion of plasma volume associated with growth rates of 0.5 kg/day. In contrast, Epo concentration increased from 6.64 +/- 0.83 mU/ml in newborns to 9.53 +/- 0.86 mU/ml in early nursing pups. Erythropoietin concentration remained elevated above newborn and adult concentration (5.71 +/- 0.79 mU/ml) through weaning, suggesting that Epo was responding to tissue hypoxia brought on by early anemia. Since similar changes in erythropoietin have been documented in terrestrial mammals, it appears that Epo plays a similar role in the blood development of harbor seals.     

Modeling intervertebral articulation: The rotule à doigt mechanical joint (RAD) in birds and mammals

The vertebrate skeleton is composed of articulated bones. Most of the articulations are classically described using mechanical joints, except the intervertebral joint. The aim of this study was to identify a joint model with the same mechanical features as the cervical joints. On the neck vertebrae, six articular surfaces participate in the joint: the cranial part of the centrum and the facets of the two prezygapophyses of a vertebra articulate on the caudal part of the centrum and the two articular facets of the postzygapophyses of the previous vertebra. We used the intervertebral joints of the birds neck to identify the mechanical joint representing intervertebral linkage. This link was described in the literature as a joint allowing two or three rotations and no translation. These features correspond to the rotule à doigt (RAD) joint, a ball and socket joint with a pin. We compared the RAD joint to the postaxial intervertebral joints of the avian neck and found it a suitable model to determine the geometrical features involved in the joint mobility. The difference in the angles of virtual axes linking the geometrical center of the centrum to the zygapophysis surfaces determines the mean dorsoventral flexion of the joint. It also helps to limit longitudinal rotation. The orientation of the zygapophysis surfaces determines the range of motion in both dorsoventral and lateral flexion. The overall system prevents dislocation. The model was validated on 13 joints of a vulture neck and 11 joints of a swallow neck and on one joint (C6–C7) in each of three mammal species: the wolf (Canis lupus), mole (Talpa europaea), and human (Homo sapiens). The RAD mechanical joint was found in all vertebral articulations. This validation of the model on different species shows that the RAD intervertebral joint model makes it possible to extract the parameters that guide and limit the mobility of the cervical spine from the complex shape of the vertebrae and to compare them in interspecific studies.     

Large basolateral processes on type II hair cells are novel processing units in mammalian vestibular organs

Sensory receptors in the vestibular system (hair cells) encode head movements and drive central motor reflexes that control gaze, body movements, and body orientation. In mammals, type I and II vestibular hair cells are defined by their shape, contacts with vestibular afferent nerves, and membrane conductance. Here we describe unique morphological features of type II vestibular hair cells in mature rodents (mice and gerbils) and bats. These features are cytoplasmic processes that extend laterally from the hair cell base and project under type I hair cells. Closer analysis of adult mouse utricles demonstrated that the basolateral processes of type II hair cells vary in shape, size, and branching, with the longest processes extending three to four hair cell widths. The hair cell basolateral processes synapse upon vestibular afferent nerves and receive inputs from vestibular efferent nerves. Furthermore, some basolateral processes make physical contacts with the processes of other type II hair cells, forming some sort of network among type II hair cells. Basolateral processes are rare in perinatal mice and do not attain their mature form until 3–6 weeks of age. These observations demonstrate that basolateral processes are significant signaling regions of type II vestibular hair cells and suggest that type II hair cells may directly communicate with each other, which has not been described in vertebrates. J. Comp. Neurol. 522:3141–3159, 2014. © 2014 Wiley Periodicals, Inc.     

Mercury and neurochemical biomarkers in multiple brain regions of five Arctic marine mammals

Mercury is a neurotoxic chemical that represents one of the greatest pollution threats to Arctic ecosystem health. Evaluating the direct neurotoxic effects of mercury in free ranging wildlife is challenging, necessitating the use of neurochemical biomarkers to assess potential sub-clinical neurological changes. The objective of this study was to characterize the distribution and speciation of mercury, as well as exposure-associated changes in neurochemistry, across multiple brain regions (n = 10) and marine mammal species (n = 5) that each occupy a trophic niche in the Arctic ecosystem. We found consistent species differences in mean brain and brain region-specific concentrations of total mercury (THg) and methyl mercury (MeHg), with higher concentrations in toothed whales (narwhal, pilot whales and harbour porpoise) compared to fur-bearing mammals (polar bear and ringed seal). Mean THg (μg/g dw) in decreasing rank order was: pilot whale (11.9) > narwhal (7.7) > harbour porpoise (3.6) > polar bear (0.6) > ringed seal (0.2). The higher THg concentrations in toothed whales was associated with a marked reduction in the percentage of MeHg (<40 %) compared to polar bears (>70 %) that had lower brain THg concentrations. This pattern in mercury concentration and speciation corresponded broadly to an overall higher number of mercury-associated neurochemical biomarker correlations in toothed whales. Of the 226 correlations between mercury and neurochemical biomarkers across brain regions, we found 60 (27 %) meaningful relationships (r>0.60 or p < 0.10). We add to the growing weight of evidence that wildlife accumulate mercury in their brains and demonstrate that there is variance in accumulation across species as well as across distinct brain regions, and that some of these exposures may be associated with sub-clinical changes in neurochemistry.     

Postnatal development of primary visual projections in the tammar wallaby (Macropus eugenii)

The time course and pattern of retinal innervation of primary visual areas was traced in pouch-young wallabies. Tritiated proline was injected into one eye of animals ranging in age from 1 to 72 days after birth. These results are compared to the 11 primary visual areas found in the adult wallaby, seven of which receive binocular input while four are monocular. At birth retinal ganglion cell axons have not reached any visual areas. Two to 4 days after birth, all of the axons are crossing to the contralateral optic tract. Nine to 12 days after birth axons begin to invade the contralateral lateral geniculate nucleus, the superior colliculus, and the medial terminal nucleus. Twenty to 21 days after birth, ipsilateral axons invade the lateral geniculate nucleus and superior colliculus. The contralateral projection precedes the ipsilateral projection in all binocular visual areas. By 25 days, ipsilateral and contralateral afferents share common territory in the lateral geniculate nucleus; however, afferents from each eye are initially concentrated in appropriate areas. Between 52 and 72 days, afferents to the dorsal lateral geniculate nucleus are gradually segregated into nine terminal bands. Four are contralateral while five are ipsilateral. By 72 days, the ipsilateral component to the superior colliculus is clustered beneath the contralateral projection a deeper layer. Projections to four monocular visual areas--lateral posterior nucleus, dorsal terminal nucleus, lateral terminal nucleus, and nucleus of the optic tract--are established later than binocular visual areas, except the suprachiasmatic nucleus. The suprachiasmatic nucleus is the last to be bilaterally innervated even though it is situated closest to the optic chiasm. At the light microscope level a mature pattern of visual development is emerging by 72 days, although the eyes do not open until 140 days.     

Gap junctions on CA3 pyramidal cells of guinea pig hippocampus shown by freeze-fracture

In freeze-fracture replicas of the hippocampus of guinea pig, gap junctions were found on membranes identified as belonging to the apical dendrites or somata of the CA3 pyramidal cells. The junctions were not part of mixed synapses. It is concluded that adjacent pyramidal cells, which in places lacked an interposed glial sheath are electrically coupled.     

The action of 5-hydroxytryptamine on neuronal membranes and synaptic transmission in area CA1 of the hippocampus in vitro

Cell membrane properties and synaptic transmission were examined by intracellular recording from the CA1 region of hippocampal slices during application of 5-hydroxytryptamine (5-HT). Seventeen cells (50%) showed an inhibitory response to 5-HT. The cells were hyperpolarized with decreased spontaneous activity and increased membrane conductance. The increase may be in potassium or chloride conductance. Synaptic transmission was not involved since Mg2+, Co2+ or Mn2+ did not block the response. 5-HT inhibited dendritic EPSPs by local postsynaptic effect. Four cells (11%) showed an excitatory response. They were depolarized while the spontaneous activity increased and the conductance decreased. The decrease may be in the potassium or chloride conductance. Two cells (6%) showed a mixed type of response with an early excitation and late inhibition. This respons may be a mixture of the two other responses or associated with a third type of 5-HT receptor. Eleven cells (33%) did not respond to 5-HT, but only in 3 of these 5-HT was applied in the soma region. In conclusion, 5-HT may inhibit dendritic excitatory synapses and decrease recurrent inhibition in hippocampus.     

云南大理市小型哺乳动物种群结构的研究

目的 :研究云南省大理市小兽类种群结构。方法 :2 0 0 0年 10月至 2 0 0 2月 5月 ,在不同生境采用捕鼠笼、鼠夹、电子捕鼠器等工具捕捉小兽 ,研究小兽种群结构。结果 :捕获小兽 3目 6科 13属 2 3种 ,共 113 2只。室外生境捕获小兽 3目 2 3种 ,以齐氏姬鼠和大绒鼠为常见种 ,分别占 2 7.3 8%和 16.15 %。室内生境捕获小兽 2目 3种 ,褐家鼠为优势种 ,占 72 .2 0 % ,黄胸鼠次之 ,为 2 7.41%。结论 :室内、室外生境小兽的种群结构有很大差别     

Light responses of primate and other mammalian cones

Retinal cones are photoreceptors for daylight vision. For lower vertebrates, cones are known to give monophasic, hyperpolarizing responses to light flashes. For primate cones, however, they have been reported to give strongly biphasic flash responses, with an initial hyperpolarization followed by a depolarization beyond the dark level, now a textbook dogma. We have reexamined this primate-cone observation and, surprisingly, found predominantly monophasic cone responses. Correspondingly, we found that primate cones began to adapt to steady light at much lower intensities than previously reported, explainable by a larger steady response to background light for a monophasic than for a biphasic response. Similarly, we have found a monophasic cone response for several other mammalian species. Thus, a monophasic flash response may in fact be the norm for primate and other mammalian cones as for lower-vertebrate cones. This revised information is important for ultimately understanding human retinal signal processing and correlating with psychophysical data.Previous suction-pipette recordings have demonstrated that, unlike the typically monophasic flash responses of lower-vertebrate cones (1–8), those of monkey and human cones are distinctly biphasic (9–13). This surprising finding has raised an unanswered question of how retinal circuitry would process such biphasic responses (14). In contrast, rods of mammals and nonmammals alike show monophasic flash responses. More recently, human data extracted from paired-flash electroretinographic (ERG) recordings in conjunction with modeling have suggested, albeit indirectly, that in situ primate-cone responses may actually be monophasic (15, 16). Accordingly, we have reexamined this important question directly with single-cell, suction-pipette recordings, which is the same experimental method as used in previous work (9–13).