Drift barriers in the postcartilaginous development of the mammalian otic capsule

Summary Postcartilaginous development of the otic capsule was studied in undecalcified histological material from rabbits following sequential fluorochromic time labeling of mineralizing tissues, using combined microradiography, fluorescence microscopy and osteoid staining. Early fetal bone formation was monitored by labeling of the experimental animals in utero. In contrast to the normal pattern of drift movements displayed by long bones and extracapsular cranial bone, capsular bone inside a zone immediately surrounding the perilymphatic space developed as a separate functional unit in which growth and modeling was absent. Bone tissue behavior appeared to depend on its spatial relation to the membranous labyrinth rather than histological characteristics. These findings suggest the role of inner ear tissues as a functional matrix in control of capsular bone dynamics beyond fetal life.     

环境镉污染对儿童健康影响的调查

调查结果表明：（１）冶炼厂周围受污染的Ａ、Ｂ两所小学空气、饮用水、灌溉水、土壤、大米、蔬菜中镉的含量均明显高于对照Ｃ小学。（２）对儿童发镉和生长发育的身高、体重、胸围、肺活量等指标调查，发现受污染的Ａ、Ｂ两所小学儿童发镉没有差别，而与对照Ｃ小学有显著差异。（３）受污染的Ａ、Ｂ两所小学儿童生长发育水平较对照组Ｃ小学落后。在体格发育匀称度方面，Ａ小学匀称型百分率低于Ｂ和Ｃ小学，不匀称体型中以粗壮型为多。     

豚鼠耳蜗外毛细胞的共聚焦图像

建立了用激光扫描共聚焦显微镜观察豚鼠耳蜗外毛细胞生理变化及细胞形态的方法。以荧光染料Ｆｌｕｏ－３作胞内Ｃａ￣（２＋）指示剂，用共聚焦显微镜观察了乙酰胆碱（ＡＣｈ）、ＡＴＰ、高钾引起的外毛细胞（ＯＨＣ）胞内Ｃａ￣（２＋）浓度的变化。三种物质均引起Ｃａ￣（２＋）升高，但升高的幅度、时相及所在细胞部位不同。高钾还引起ＯＨＣ短缩、偏折。利用共聚焦显微镜“光学切片”的特性，对Ｆｌｕｏｒｅｓｃｅｉｎ荧光素染色的活的ＯＨＣ形态及碘化吡啶（ＰＩ）染色的细胞核形态进行了三维重建。讨论了共聚焦显微镜在ＯＨＣ生理及形态学研究中的应用前景。     

双醋酸荧光素－碘化丙啶双染色法鉴别豚鼠外毛细胞活性

为提供一种准确判断单离细胞活性的方法，采用双醋酸荧光素（ＦＤＡ）－碘化丙啶（ＰＩ）双染色，荧光显微镜观察，鉴别了豚鼠耳蜗单个外毛细胞的活性。在激发光下染色后的活细胞显绿色，失活细胞核呈红色。在室温下计数５只豚鼠（１０侧听泡）在断头１、２、３、５和７ｈ后的单离细胞平均存活百分率分别为８５．０％、７８．０％、７０．０％、２３．５％和０。本方法为一种鉴别细胞活性的客观可靠的方法。     

Energy dispersive X-ray microanalysis of individual yestibular hair cells

Summary Microprobe analysis was performed at the cellular and subcellular levels of type I and type II vestibular hair cells. In principle the same types of elemental histograms were found in the two types of hair cells studied. High concentrations of Cl and K were detected in stereocilia, whereas calcium was found when analyzing stereocilia and the supranuclear cytoplasm.Supported by grants from the Swedish Medical Research Council (12X-720 and 12X-7305), the Swedish Society for Medical Sciences, the Foundation Tysta Skolan, and the Ragnar and Torsten Söderberg Foundation     

Volume and length changes in outer hair cells of the guinea pig after potassium-induced shortening

Summary Measurements of volume and length were made on isolated guinea pig cochlear outer hair cells (OHCs) in an attempt to establish whether OHC shortening was accompanied by changes in cell volume. A sustained shortening in response to an isotonic 100 mM KCl solution was found to be accompanied by a significant increase in OHC volume. The application of hypotonic solutions had a similar effect. When testing solutions with unchanged or reduced [K⁺] [Cl^–] products in order to avoid loading the cells with chloride ions and producing concomitant water influx, the most frequent response was a rapid shortening followed by an elongation beyond the original cell length. These findings of a sustained and a spontaneously reversible shortening suggest that the potassium-induced response may consist of two components: a rapid one, which may be reversible in the presence of the stimulus, and a second, slower, component resulting in sustained shortening.     

Age-related hair cell loss in spontaneously hypertensive and normotensive rats

In the spontaneously hypertensive (SH) rat, a hereditary form of hypertension and widespread vascular abnormalities develop. In the present study the inner ear degeneration pattern in SH and normotensive (N) rats not exposed to noise was investigated and correlated with frequency-specific auditory brainstem response (ABR) thresholds. Rats of both strains were found to have a spontaneous loss of apical hair cells, but this was slightly more pronounced in SH. In SH rats, but not in those of the N strain, there was an age-related progressive loss of outer hair cells in the region 3–5 mm from the stapes, and a slight additional loss at the most basal end. According to available frequency maps, the hair cell loss should correspond to hearing loss between 6 and 24 kHz. In the SH rats hearing loss was not observed in the whole of this range, only at 16 and 20 kHz. It cannot be determined to what extent the localized spontaneous loss of hair cells is caused by vascular factors and what other mechanisms are involved, but vascular factors probably only play a minor role.     

Development of an optrode for intramural multisite optical recordings of Vm in the heart

INTRODUCTION: Optical mapping of transmembrane potential (Vm) is an important tool in the investigation of impulse propagation in the heart. It provides valuable information about spatiotemporal changes of Vm that cannot be obtained by other techniques, but it presently is limited to measurements from the heart surfaces. Therefore, the goal of this work was to develop a technique for intramural multisite optical measurements of Vm using fiberoptic technology. METHODS AND RESULTS: An optrode, a bundle of thin optical fibers, was developed for measuring intramural optical signals at multiple sites in the heart. The optrode consisted of seven fibers with diameter of 225 microm arranged in a hexagonal pattern that were used to deliver excitation light to the myocardium, to collect the emitted fluorescence, and to project the light onto a 16 x 16 array of photodiode detectors. Rabbit hearts were stained with the Vm-sensitive dye RH-237. Fluorescence was excited using a 100-W Hg lamp. Intramural action potentials were recorded at multiple sites separated by 2 mm inside the left ventricle. Signal-to-noise (RMS) ratio was 21.2 +/- 12 (n = 7) without averaging or ratiometry and with negligible cross-talk (<1.9%) between the neighboring photodiodes. The size of the recording area for an individual fiber was estimated at approximately 0.8 mm. CONCLUSION: These data demonstrate feasibility of multisite transmural measurements of Vm without signal averaging and ratiometry. This technique might become useful in studies of transmural impulse conduction during arrhythmias and defibrillation.     

Role of Emx2 in the development of the reciprocal connectivity between cortex and thalamus

Emx2 knockout mice appear to show a shift in the areal identity in the cerebral cortex , which is matched with altered distribution of thalamocortical projections (Bishop et al. [2000] Science 288:344-349; Mallamaci et al. [2000] Nat Neurosci. 3:679-686) [corrected]. We have examined the early establishment of these projections to understand how the altered Emx2 expression results in changes in their cortical targeting. We used carbocyanine dye tracing to visualize thalamocortical and corticofugal projections as well as immunohistochemistry for L1 and TAG-1, respective markers of the two axonal systems, in wild-type, heterozygote, and null mutant for Emx2 at embryonic (E) ages ranging from E13.5 to E18.5. These tracing studies demonstrated that, in Emx2 knockout mice, a large proportion of early thalamocortical projections were misrouted at the border between the diencephalon and telencephalon. This abnormality was associated with displaced connectivity of the internal capsule cells at the diencephalic-telencephalic junction. Interestingly, most of the aberrant thalamic projections compensated for the ventral entry to the telencephalon and still ascended to the cortex. Although this early targeting abnormality is associated with the altered Emx2 expression pattern in the cortex, it most probably occurs independently from it, and is related to earlier guidance defects at the diencephalic-telencephalic boundary. These defects might result in the altered and delayed arrival of thalamic projections to the cortex and, thus, contribute to the shifted thalamocortical matching previously observed in the Emx2 knockout mice.