骨髓间充质干细胞对免疫介导再生障碍性贫血的治疗

背景：骨髓间充质干细胞具有免疫调节作用,可以影响淋巴细胞和其他免疫细胞的功能,同时其分泌的因子尚有支持造血的作用。而再生障碍性贫血的发生、发展与T细胞功能亢进引起的造血干、祖细胞凋亡密切相关。 目的：比较骨髓间充质干细胞和全骨髓细胞治疗免疫介导再生障碍性贫血小鼠的疗效。 方法：建立BALB/C小鼠免疫介导再生障碍性贫血模型。将BALB/C小鼠随机分成正常组、对照组、注射骨髓间充质干细胞和注射全骨髓细胞组。观察骨髓间充质干细胞和全骨髓细胞对实验动物的疗效及骨髓的造血组织容量、脂肪细胞和血窦结构。 结果与结论：再生障碍性贫血模型小鼠至第20天,对照组全部死亡,骨髓间充质干细胞组4例死亡,全骨髓细胞组1例死亡。②骨髓间充质干细胞组和全骨髓细胞组存活小鼠,其体质量变化趋势、血细胞计数、骨髓造血功能恢复均无显著性差异。③检测骨髓间充质干细胞组和全骨髓细胞组脾脏CD4+T细胞、CD8+T细胞、CD4+/CD8+的比值示无差异,与正常小鼠相比,骨髓间充质干细胞组外周血CD4+T细胞、CD8+T细胞水平有下降趋势。全骨髓细胞组CD8+T细胞水平明显下降。提示,单独使用骨髓间充质干细胞治疗能够使部分再生障碍性贫血模型小鼠症状改善、造血恢复。骨髓间充质干细胞治疗有效率不如全骨髓细胞,但两组无显著性差异。     

人羊膜间充质干细胞支持造血的体外实验

背景：骨髓是目前间充质干细胞的主要来源，但由于取材不便、细胞数量受年龄限制等原因，其应用具有一定局限性。近年来，羊膜作为间充质干细胞的新来源受到越来越广泛的关注。 目的：探讨人羊膜来源间充质干细胞在体外对造血干细胞的扩增是否有支持作用，以及怎样提高羊膜间充质干细胞和造血干细胞共移植成功率。 方法：利用组织块培养法，从足月分娩的人羊膜中分离培养羊膜间充质干细胞。密度梯度离心法分离脐血单个核细胞，采用免疫磁珠分选技术分选其中CD34+细胞。分别用脐血单个核细胞和CD34+细胞与羊膜间充质干细胞共培养，连续4周，每周计悬浮细胞浓度，并以骨髓间充质干细胞组及无滋养层组作为对照。采用集落形成实验，把扩增的脐血单个核细胞和CD34+细胞分别接种至甲基纤维素半固体培养基中，14 d后根据典型形态特征计数造血集落数。 结果与结论：羊膜间充质干细胞可促进人脐血单个核细胞和CD34+细胞扩增，扩增后两者在甲基纤维素半固体培养基中能够形成造血祖细胞集落，其造血支持作用与骨髓间充质干细胞相似，两者对比无明显统计学差异。提示，羊膜间充质干细胞体外具有与骨髓间充质干细胞相似的造血支持作用，有可能为造血干细胞体外扩增及临床间充质干细胞与造血干细胞联合移植、提高造血干细胞移植成功率提供一种更加理想的间充质干细胞新来源。     

小鼠脂肪源间充质干细胞在重型再生障碍性贫血中的应用

背景：骨髓间充质干细胞联合造血干细胞移植是最有希望解决造血重建缓慢的策略之一，但临床实施中，抽取骨髓进而分离、扩增间充质干细胞尚不能为大部分健康供者所接受。 目的：探讨小鼠脂肪源间充质干细胞对异基因重型再生障碍性贫血模型鼠造血功能的影响。 设计、时间及地点：细胞学体内实验，于2007-05/11在河南省肿瘤医院中心实验室完成。 材料：雄性6~8周龄BALB/c（H-2Kd）小鼠20只，雌性7~8周龄C57BL/6（H-2Kb）小鼠50只，均购于河南省实验动物中心。 方法：贴壁法体外分离培养20只雄性BALB/c小鼠脂肪源间充质干细胞；反复吹打20只雌性C57BL/6（H-2Kb）小鼠骨髓细胞，加入EDTA-NH4Cl液去除红细胞，即为骨髓有核细胞。剩余30只雌性C57BL/6（H-2Kb）小鼠均给予一次全身3.0 Gy 60Co-γ照射，照射后第4，5，6天皮下注射环磷酰胺及氯霉素，建立重型再生障碍性贫血模型。模型鼠随机分为3组，联合组经尾静脉输入骨髓有核细胞2×107个+脂肪源间充质干细胞3×106个，骨髓有核细胞组单纯输入骨髓有核细胞2×107个，对照组输入生理盐水0.2 mL，10只/组。 主要观察指标：定期检测外周血和股骨有核细胞数以及巨噬细胞/粒细胞集落形成单位数的变化，PCR法鉴定Y染色体，流式细胞仪检测移植小鼠骨髓及脾脏CD3和H-2Kd阳性表达情况。 结果：细胞移植后第2周，联合组外周血有核细胞数、股骨有核细胞数、巨噬细胞/粒细胞集落形成单位数均明显高于骨髓有核细胞组（P < 0.05），且随移植时间的延长，各种细胞数量逐渐恢复（P < 0.05）。细胞移植后第4周（即造血恢复期），联合组外周血可特异性地扩增Y染色体的SRY基因片段，移植小鼠骨髓及脾脏中CD3和H-2Kd双阳性细胞达6.66%，提示在受体小鼠体内有供体细胞的存在。 结论：脂肪源间充质干细胞能够重建重型再生障碍性贫血小鼠的造血功能，促进小鼠造血系统的恢复。     

干细胞生长因子和粒细胞集落刺激因子与心肌梗死大鼠体内骨髓间充质干细胞的迁移*

背景：外周静脉移植间充质干细胞只有1%~5%的移植细胞能归巢到心肌梗死区域。 目的：观察干细胞生长因子、粒细胞集落刺激因子对骨髓间充质干细胞归巢的影响。 方法：采用贴壁培养法分离培养SD大鼠骨髓间充质干细胞,取传至3~5代细胞。建立SD大鼠急性心肌梗死模型,干细胞生长因子组、粒细胞集落刺激因子组、干细胞生长因子+粒细胞集落刺激因子组在骨髓间充质干细胞移植前3 d和移植后3 d单独或混合皮下注射干细胞生长因子、粒细胞集落刺激因子,骨髓间充质干细胞组不注射细胞因子。 结果与结论：荧光显微镜下观察,骨髓间充质干细胞迁移至心肌梗死组织,骨髓间充质干细胞组、干细胞生长因子组、粒细胞集落刺激因子组迁移至心肌梗死区的骨髓间充质干细胞数量没有明显的区别(P > 0.05),干细胞生长因子+粒细胞集落刺激因子组的骨髓间充质干细胞数量明显高于其他3组(P < 0.05)。免疫荧光组织化学显示,植入的部分骨髓间充质干细胞表达心肌特异蛋白cTnI。结果说明干细胞生长因子和粒细胞集落刺激因子两种细胞因子联合应用可以促进骨髓间充质干细胞归巢至心肌梗死区域,在体内微环境的诱导下,骨髓间充质干细胞能够转化为心肌样细胞。     

表皮生长因子干预小鼠非黏附骨髓间充质干细胞成纤维细胞集落形成及向神经元样细胞的分化**

背景：非黏附骨髓间充质干细胞在体外可以不断形成成纤维细胞集落形成单位，并且可诱导分化为脂肪细胞、成骨细胞和软骨细胞，表现出一定的多分化潜能。 目的：探讨表皮生长因子对非黏附骨髓间充质干细胞形成成纤维细胞集落的影响，及其在体外向神经细胞分化的能力。 方法：分离小鼠双侧股骨、胫骨，全骨髓法分离总骨髓细胞，采用反复转移非黏附的骨髓细胞培养法纯化非黏附骨髓间充质干细胞。取第5代总骨髓细胞和非黏附骨髓间充质干细胞，加入含表皮生长因子、碱性成纤维细胞生长因子的神经细胞诱导液培养2周。观察非黏附骨髓细胞产生成纤维细胞集落形成单位的能力，表皮生长因子对成纤维细胞集落形成单位的影响，甲苯胺蓝和免疫细胞化学染色鉴定相关蛋白的表达。 结果与结论：总骨髓细胞、反复转移的非黏附骨髓间充质干细胞均能够不断产生成纤维细胞集落形成单位。给予表皮生长因子处理后，非黏附骨髓间充质干细胞成纤维细胞集落形成单位的效率明显增高。诱导2周后，免疫细胞化学染色显示，总骨髓细胞和非黏附骨髓间充质干细胞均表达神经细胞特异性蛋白NeuN和NF-200；经甲苯胺蓝染色在部分细胞中可见神经元特异性标记尼氏体。证实表皮生长因子可有效促进小鼠非黏附骨髓间充质干细胞形成成纤维细胞集落形成单位的效率，经反复转移的非黏附骨髓间充质干细胞能够诱导分化为神经细胞。     

混合骨髓移植后过继免疫治疗小鼠白血病**☆

背景：急性白血病自体造血干细胞移植后复发率高,异基因造血干细胞移植后移植相关病死率高,混合造血干细胞移植及移植后过继免疫治疗有可能取长补短,提高疗效。 目的：观察自体骨髓混合H-2半相合异体骨髓移植后供体淋巴细胞输注+白细胞介素2治疗对小鼠白血病的疗效。 方法：将Balb/c小鼠经直线加速器照射3 Gy后分为白血病模型组、白血病模型照射组、混合移植组、自体骨髓移植组,均尾静脉注射5×105 K562(GFP+/NeoR+)或K562(GFP-/NeoR-)细胞。7 d后6 Gy照射,自体骨髓移植组移植自体骨髓细胞或联合白细胞介素2治疗;混合移植组移植小鼠自体骨髓细胞混合1/10的H-2半相合异体骨髓细胞后应用白细胞介素2或联合供体淋巴细胞输注治疗。4周后行小鼠外周血及骨髓细胞形态检查,外周血细胞亚群、GFP及NeoR基因测定,肝、脾匀浆细胞GFP和NeoR基因测定。 结果与结论：白血病模型组小鼠因骨髓造血功能衰竭于20 d内全部死亡,白血病模型照射组小鼠因造血功能衰竭于14 d内全部死亡;自体骨髓移植组、混合移植组均有多少不等小鼠无白血病存活超过28 d,且混合骨髓移植后及自体骨髓移植后应用白细胞介素2治疗可提高白血病小鼠长期无病生存率,在此基础上联合供体淋巴细胞输注可更进一步提高白血病小鼠长期无病生存率。     

小鼠非黏附骨髓间充质干细胞移植到缺血性脑损伤部位向神经元样细胞的分化**

背景：小鼠非黏附骨髓间充质干细胞在体外可以不断形成成纤维细胞集落形成单位,并且可诱导分化为脂肪细胞、成骨细胞和软骨细胞,表现出一定的多分化潜能。 目的：探讨小鼠非黏附骨髓间充质干细胞移植到缺血损伤脑内后分化为神经细胞的能力。 方法：取β-Gal转基因小鼠,分离双侧股骨、胫骨,全骨髓法分离总骨髓细胞,采用反复转移非黏附的骨髓细胞培养法收集纯化后的第5代非黏附骨髓间充质干细胞,调整细胞浓度为1×1012 L-1备用。两组C57BL/6J小鼠均建立大脑中动脉阻塞模型,造模后7 d,细胞移植组将第5代非黏附骨髓间充质干细胞悬液3 μL定向移植到小鼠脑损伤处,模型组注射等量生理盐水。移植8周后观察供体细胞在缺血脑内微环境中的存活、分布及分化能力。 结果与结论：LacZ组织化学染色发现,8周后供体细胞仍可以表达β-Gal蛋白,在缺血侧供体细胞能够存活。免疫组织化学单染和双染后发现,在缺血模型的坏死区及坏死边缘区均可检测到β-Gal阳性的供体细胞,部分细胞还同时表达神经细胞特异性蛋白NeuN及神经胶质细胞特异性标记GFAP。提示小鼠非黏附骨髓间充质干细胞在缺血动物模型的脑内能够存活、迁移,部分细胞还能分化为成熟的神经元样细胞或神经胶质细胞,参与脑损伤修复。     

Flk-1+骨髓间充质干细胞移植上调白细胞介素6水平：是否同时加重了胶原诱导性关节炎小鼠的症状？**☆

背景：间充质干细胞的免疫调节作用是被大家普遍认可的,在以往实验中也对Flk-1+骨髓间充质干细胞体外抑制T/B淋巴细胞增殖的能力进行了确认。 目的：验证Flk-1+骨髓间充质干细胞对胶原诱导性关节炎小鼠的治疗作用。 方法：健康10周龄雄性DBA-1(H-2Kq)小鼠18只,随机分为3组：初次免疫后细胞移植组、加强免疫后细胞移植组、模型对照组,3组小鼠均通过尾皮下注射牛Ⅱ型胶原进行初次免疫,21 d后同法进行加强免疫,建立胶原诱导性关节炎模型。密度梯度离心法和贴壁筛选法体外分离DBA-1(H-2Kq)小鼠Flk-1+骨髓间充质干细胞,初次免疫后细胞移植组小鼠在初次免疫后立即经尾静脉输注Flk-1+骨髓间充质干细胞(1~2)×106个/只,加强免疫后细胞移植组小鼠在加强免疫时同法输注等量Flk-1+骨髓间充质干细胞,模型对照组小鼠于初次免疫后0或21 d尾静脉输注等量生理盐水。观察初次免疫后和加强免疫后各组小鼠的爪垫增厚情况、临床评分,检测小鼠关节病理学变化及血清因子质量浓度的动态变化。 结果与结论：与模型对照组比较,初次免疫后细胞移植组爪垫增厚程度及平均临床疾病得分均无明显差异(P > 0.05),均可见明显的滑膜组织损伤和炎症细胞浸润,各血清细胞因子质量浓度基本相似;而加强免疫后细胞移植组爪垫明显增厚(P < 0.01),平均临床疾病得分高达3.35分,滑膜损伤严重,毛细血管增生,在初次免疫后28 d白细胞介素6血清浓度急剧上升(P < 0.1),初次免疫后35 d白细胞介素6血清浓度又明显下降(P < 0.1)。提示在胶原诱导性关节炎小鼠模型中,Flk-1+骨髓间充质干细胞移植不但未取得预期的治疗效果,还在加强免疫后细胞移植组观察到显著地关节炎症状恶化现象,其可能通过上调白细胞介素6血清浓度加重类风湿关节炎小鼠的行为症状。     

骨髓间充质干细胞对慢性哮喘小鼠血清白细胞介素12和白细胞介素4水平的影响

背景：研究显示,骨髓间充质干细胞移植通过减轻炎症程度来改善急性肺损伤的病情,而骨髓间充质干细胞移植对哮喘疾病的研究甚少。 目的：观察慢性哮喘小鼠移植同种异体骨髓间充质干细胞后,其血清白细胞介素12和白细胞介素4水平的变化。 方法：取40只雌性BALB/c小鼠,随机分为4组,正常对照组和骨髓间充质干细胞对照组以PBS致敏及激发小鼠,于第21天激发前气管内注射PBS或骨髓间充质干细胞 30 μL。哮喘模型组和骨髓间充质干细胞治疗组用鸡卵白蛋白制备慢性哮喘模型,于第21天激发前气管内注射PBS或骨髓间充质干细胞 30 μL。采用ELISA法检测各组小鼠血清炎症因子水平。 结果与结论：病理提示哮喘模型组支气管上皮黏膜脱落,同时上皮黏膜有杯状细胞增生,部分管腔内大量黏液栓塞;气道、血管旁有大量炎性细胞浸润以及气道平滑肌细胞增生和肥大。正常对照组及骨髓间充质干细胞对照组无气道炎症及气道重塑的表现,而骨髓间充质干细胞治疗组气道炎症及气道重塑明显减轻。对比骨髓间充质干细胞对照组及正常对照组,哮喘模型组白细胞介素12明显减低,白细胞介素13 和白细胞介素4明显增高;而骨髓间充质干细胞治疗组较哮喘模型组白细胞介素12明显升高,白细胞介素4明显降低。结果表明骨髓间充质干细胞治疗哮喘可能通过降低白细胞介素4水平,提高体内白细胞介素12水平,从而改善气道炎症及气道重塑的程度。     

Sca-1+造血干/祖细胞重建致死剂量辐射小鼠造血功能的作用**☆

背景：近年来,造血干细胞移植在国内外已广泛开展,移植的造血干细胞能否有效重建造血成为造血干细胞移植领域的研究热点问题之一。 目的：观察Sca-1+造血干/祖细胞(hematopoietic stem/progenitor cell,Sca-1+HSC/HPC)对造血衰竭小鼠造血功能重建的作用。 方法：雌性C57BL/6受体鼠给予致死剂量60Coγ射线照射后分2组,对照组：输注无菌PBS;移植组：移植免疫磁性分选法分离纯化的同系雄性C57BL/6小鼠Sca-1+HSC/HPC;检测受体鼠生存时间;外周血白细胞、红细胞比容、血小板的变化;脾湿质量及脾集落数;PCR检测Y染色体(Sry基因)表达确定受体小鼠重建造血的细胞来源。 结果与结论：移植组受体鼠30 d存活率、白细胞、红细胞比容、血小板、脾湿质量及脾集落数均明显高于对照组(P < 0.05);Y染色体PCR分析,证实雌性受体小鼠重建造血的细胞来源于雄性供体。提示Sca-1+HSC/HPC移植后能重建造血衰竭小鼠造血功能。     

Growth of the mouse corpus callosum

Brains of BALB/cCF inbred mice were examined at 15 ages ranging from 16.5 to 50.5 days from conception and cross-sectional areas of major forebrain fibre tracts at the midsagittal plane were measured. The anterior commissure appeared prior to the corpus callosum (CC), which was first seen at midplane at 17.0 days, and both tracts underwent a very rapid increase in size in the prenatal and early postnatal period, reaching the adult range of size at about 1 week after birth or several days prior to the onset of myelination. The growth spurt of these fibre tracts was much more pronounced than that of whole brain. By comparing BALB/c mice with hybrid mice that always have normal CC, it was found that some BALB/c mice at 18.5 days of age which have very small or absent CC do so because the growth of the whole brain is retarded whereas others have CC that is small for the brain size. Evidence also suggested that many mice with no CC but normal brain size at 18.5 days prenatally do eventually acquire at least a small CC. Observations at 3 postnatal ages of BALB/c mice weighed and marked at birth revealed that the 'runts' with low birth weight, which were presumably retarded prenatally, either die or catch up with mice of normal birth weight and do not have unusually small adult CC.     

Immunocytochemical analysis of the mouse retina

Transgenic mice provide a new approach for studying the structure and function of the mammalian retina. In the past, the cellular organization of the mammalian retina was investigated preferentially in primates, cats, and rats but rarely in mice. In the current study, the authors applied 42 different immunocytochemical markers to sections of the mouse retina and studied their cellular and synaptic localization by using confocal microscopy. The markers applied were from three major groups: 1) antibodies against calcium-binding proteins, such as calbindin, parvalbumin, recoverin, or caldendrin; 2) antibodies that recognize specific transmitter systems, such as glycine, gamma-aminobutyric acid, or acetylcholine; and 3) antibodies that recognize transmitter receptors and show their aggregation at specific synapses. Only a few markers labeled only one cell type: Most antibodies recognized specific groups of neurons. These were analyzed in more detail in double-labeling experiments with different combinations of the antibodies. In light of their results, the authors offer a list of immunocytochemical markers that can be used to detect possible changes in the retinal organization of mutant mice.     

Histogenesis of the cochlear nucleus of the mouse

In Nissl-stained preparations of the cochlear nucleus there are nine recognizable cell types. These cells are born during three periods of histogenesis prenatally. On gestation days 10.0, 10.5, and 11.0 the pyramidal, giant, and dark-staining cells are born. The spherical, globular, multipolar, and horizontal cells are formed on gestation days 12.0, 12.5, and 13.0 and small cells follow on gestation day 14.5. The onset of granule cell formation is gestation day 14.5 and continues to birth on gestation day 19. At birth, and for at least the first 2 postnatal weeks, glial cells are born. There are no regional gradients in cell birth dates, cells from all birth dates being intermixed. Cell birth proceeds in an orderly sequence that is related only to cell size. Although there were no apparent spatiotemporal patterns, some clustering of labeled cells was evident. These observations do not support the hypothesis that Golgi Type I cells precede Golgi Type II cells in their order of birth since both large and small neurons project beyond the nucleus. There is, nonetheless, a sequential pattern in the onset of cell birth for the auditory system, with cochlear nucleus neurons preceding cochlear neurons.     

Production of the butyrylcholinesterase knockout mouse

The butyrylcholinesterase (BChE [EC 3.1.1.8]) knockout mouse is a model for BChE deficiency in humans. The existence of genetic variants of human BChE was discovered after a new muscle relaxant, succinylcholine, was introduced into the practice of medicine in the late 1950s. People with the atypical variant were unable to breathe for 2 h after receiving a dose intended to paralyze for 3-5 min (Kalow and Gunn, 1957, 1959). The atypical variant was later found to have a single-amino-acid mutation at Asp-70 (McGuire et al., 1989), which decreased the affinity of BChE for all positively charged compounds. Though the atypical BChE mutant is the one most commonly encountered in cases of succinylcholine apnea, an additional 58 mutations in the BChE coding sequence have been reported. The frequency of BChE mutations in the American population is known (Lockridge, 1990). One person out of 25 carries one atypical allele (D70G), whereas 1 out of 2500 is homozygous for D70G. The most frequent mutation, A539T, is carried by 1 person out of every 4 and is found in homozygous form in 1 person out of 69 (Bartels et al., 1992). The homozygous A539T form is associated with a 33% decrease in plasma BChE activity. Some people have no detectable BChE activity in plasma, owing to a mutation that truncates the protein, or inactivates it. The frequency of silent BChE is 1 out of 160 for carriers, and 1 out of 110,000 for homozygotes. The BChE knockout mice are models for silent BChE in humans. The literature contains no documentation of the health of people with silent BChE, other than to say they are healthy. We know nothing about their life expectancy, fertility, risk of cognitive impairment, risk of heart disease, or susceptibility to toxins. The BChE knockout mouse will allow us to test the hypothesis that the function of BChE is to detoxify poisons and will allow us to test the role of BChE in other physiological functions.     

Nicotine abstinence in the mouse

We present evidence that intermittent administration of nicotine, 2 mg/kg s.c., four times daily to mice for 14 days produces a somatic abstinence syndrome after discontinuing treatment. The nicotine abstinence was mild and protracted, lasting more than 92 h. The constellation of abstinence signs was characterized by rearing, jumping, shakes, abdominal constrictions, chewing, facial tremor and scratching. No autonomic symptomatology was observed. Nicotine abstinence was attenuated with a single dose of nicotine administered at 24 or 48 h into withdrawal. The nicotinic antagonist mecamylamine, 3 mg/kg, induced a small increase in the total abstinence score when given 60 min after the last nicotine injection. Nicotine-abstinent mice displayed reduced locomotor activity. Finally, mice lost weight during the nicotine treatment which was not recovered during the withdrawal. Along with the rat nicotine abstinence model, the mouse model of intermittent nicotine administration and abstinence might be useful for studying the pharmacological and biochemical mechanisms of nicotine addiction and tobacco use.     

小鼠小脑皮质的生长发育

目的：探讨小鼠小脑皮质的组织发生过程。方法：应用光镜和电镜技术对胚胎和生后小脑皮质进行形态学观察,对各层厚度和细胞密度进行测量。结果：胚胎12d（E12）小脑原基有室管膜层、套层和边缘层构成,约出生当日（P0）出现外颗粒层、分子层、Purkinje细胞层和内颗粒层。外颗粒层P6／7达最厚,至P20消失。P0至P30内颗粒层细胞逐步分化发育成熟,Purkinje细胞树突树逐渐形成,约P7时Purkinje细胞排列成单层。结论：E12至P0片层化小脑主要经历了细胞增殖、分化与迁移;P0至P30片层化结构逐渐发育成熟,外颗粒层消亡以细胞迁移和凋亡为主,其他各层细胞主要经历了分化发育与凋亡。     

Tenascin-C in the cochlea of the developing mouse

Tenascin-C is a glycoprotein of the extracellular matrix that acts in vitro as both a permissive and a nonpermissive substrate for neurite growth. We analyzed, by immunocytochemistry, the distribution of tenascin-C along neural growth pathways in the developing mouse cochlea. In the spiral lamina, tenascin-C coexists in a region where nerve bundles arborize. In the organ of Corti, tenascin-C lines the neural pathways along pillar and Deiters' cells before and during the time of nerve fiber ingrowth. By embryonic day 16, tenascin-C is abundant on the pillar side of the inner hair cell but does not accumulate on the modiolar side until about birth, a time after the arrival of afferent fibers. The synaptic zones beneath outer hair cells are strongly labeled during the time when early events in afferent synaptogenesis are progressing but not during the time of efferent synaptogenesis. At the age when most neural growth ceases, tenascin-C immunoreactivity disappears. Faint tenascin-C immunolabeling of normal hair cells, strong tenascin immunolabeling in pathological hair cells of Bronx waltzer (bv/bv) mice, and staining for beta-galactosidase, whose gene replaces tenascin in a "knockout" mouse, indicate that hair cells supply at least part of the tenascin-C. The changing composition of the extracellular matrix in the synaptic region during afferent and efferent synaptogenesis is consistent with a role for tenascin in synaptogenesis. The presence of tenascin-C along the growth routes of nerve fibers, particularly toward the outer hair cells, raises the possibility that growth cone interactions with tenascin-C helps to guide nerve fibers in the cochlea.