American Journal of Anatomy最新文献

Neuromuscular junctions in the rectus abdominis muscles of normal and developmentally arrested Rana pipiens larvae were studied with freeze fracture and conventional electron microscopy to determine whether structural aspects of junctional maturation depend on metamorphosis. Comparison was made between junctions in premetamorphic larvae 1-3 months old and junctions in larvae that had remained in premetamorphosis for more than a year (more than four times as long as normal). In most respects, junctions from the two groups of larvae were similar. Unlike adult junctions, nerve-muscle contacts in both larval groups were pleomorphic and often involved more than one neuronal process; Schwann cell processes very rarely extended between nerve and muscle. Active zone structure ranged from total disorganization to an adult pattern of highly ordered double rows of particles aligned over junctional folds. Only quantitative analysis revealed differences between junctions in old and young larvae. The older larvae had fewer nerve-muscle contact sites involving multiple neuronal elements and a higher ratio of active zone length to presynaptic membrane area, although the mean active zone length was the same in the two groups. The results indicate that the maturation of junctional shape, the branching pattern of the axons, and the relationship of presynaptic axons to Schwann cells must be directly or indirectly dependent on the hormonal or behavioral changes associated with metamorphosis.

Using polarized light microscopy we were able to observe the mineralization patterns of embryonic and neonatal chick otoconia. We compared preparations of freshly dissected material spread under mineral oil to material that had been treated with various fixatives and dehydration agents. We found that the standard fixation agent, glutaraldehyde, and some immersion oils etched embryonic chick otoconia but that fixation with 70% acetone or 70% alcohol followed by dehydration to 100% acetone or 100% alcohol left the otoconia intact. The size and shape of freshly dissected chick otoconia observed with polarized light microscopy were similar to those of acetone-fixed, critical-point-dried material examined by SEM. Embryonic forms of otoconia were found to have a fluted pattern that was different in morphology from otoconia found in hatched chicks and adults. Embryonic chick otoconia did not exhibit the multifaceted surface morphology seen in embryonic rat otoconia. Comparisons of the same fields of otoconia under phase contrast microscopy and polarized light microscopy indicated that the freshly dissected otoconia of embryos exhibit little or no unmineralized (non-birefringent) material but that glutaraldehyde-fixed otoconia exhibited unmineralized areas where etching had occurred. Size frequency distributions of freshly dissected embryonic and mature otoconia in five ages of embryos and hatched chicks were consistent with a hypothesized developmental sequence of otoconia.

The morphology and numbers of Langerhans' cells vary in epithelia with different patterns of hyperplasia and keratinization. Langerhans' cells stained for ATPase were compared at five phases of the estrous cycle in murine vaginal epithelium. The cells were more dendritic and sparsely distributed with hyperplasia and were less dendritic and more densely distributed with atrophy. Greater numbers of the cells did not accompany keratinization at estrus. Ultrastructurally, three types of Langerhans' cells were discriminated. The first type, active in protein synthesis and phagocytosis, was commonest in sloughing and atrophic epithelium. The second type, containing accumulated and dispersed, electron-dense bodies presumed to be lysosomes, predominated in hyperplastic epithelium. The third, a mature resting cell, was found only after keratinization was complete. This study shows that Langerhans' cells in murine vaginal epithelium vary in morphology and numbers with the epithelial changes of the estrous cycle which may relate to their immunological role, but does not support the contention that their distribution is important for keratinization.

The luminal surfaces of the endothelium lining the two surfaces of the aortic arterial (AAR) and ventricular (AVT), and mitral ventricular (MVT) and atrial (MAT), valve cusps were studied with cationic ferritin (CF) and ferritin (Fer)-conjugated lectins (WGA, RCA, SBA). The arterial (AAR) and ventricular (MVT) surfaces of the aortic and mitral cusps, which are exposed to more turbulent fluid mechanical forces and lower wall shear stresses, had the greatest density of CF labeling. The endothelia of the four surfaces displayed a gradient of decreasing density from the nuclear region to the periphery. Neuraminidase, chondroitinase ABC and AC, heparinase, heparitinase, hyaluronidase (testicular), and pronase E digestions suggested that a significant number of the anionic sites labeled by CF are associated with sialoglycoproteins and glycosaminoglycans such as chondroitin 4/6 sulfates, dermatan sulfates, and heparan sulfates. The localization of WGA receptors on the endothelium of AAR and MVT demonstrated a greater density of sialyl moieties than on the AVT and MAT. There was no binding of Fer-RCA with specificity for D-galactopyranosides or Fer-SBA with affinity for N-acetylglucosamine and D-galactose to the endothelium unless it was first treated with neuraminidase. Hence, sialic acids are shown to be among the more superficial components of this glycocalyx and to be largely responsible for the greater densities over the endothelium of AAR and MVT.

This histological study sought to determine the nature and incidence of developmental abnormalities induced by one of the reportedly least teratogenic of insecticides injected into very young chick embryos. Using techniques to assure rapid contact between injectant and embryo, eggs incubated for 24, 48, or 72 hr were injected with corn oil or 125 micrograms-4.0 mg malathion. The embryos were recovered 48 hr later, paraffin-embedded, serially cross-sectioned, and examined in detail. Structures affected (and the nature of the defects) were as follows: wing level notochord and spinal cord (folded or undulated); trunk/leg level spinal cord (variously, neural folds unfused, roof infolded, canal partitioned, etc.); eye (lens misshapen or severely thinned, optic cup incompletely invaginated); diencephalon (epiphysis bifurcated or off-center, supernumerary outgrowths); cardiovascular structures (atrium and major blood vessels enlarged); and tailbud (curled into hindgut: ourentery). Overall incidence was both dose- and age-related, doubling for each doubling of dose and tripling for each 24 hr less age at exposure. For most (not all) individual structures, incidence was greatest when exposed at 24 hr and nil at 72 hr. Severity of effect was not consistently dose- or age-dependent. We conclude that contrary to previous reports, 24- to 72-hr embryos are highly vulnerable to insecticide exposure, with the youngest the most vulnerable, and many of the defects detected may be attributed to either of two mechanisms: failure in formation of the supportive sheath, or factors that cause epithelial morphogenesis (e.g., microtubules, microfilaments, extracellular material, cell-to-cell adhesion mechanisms). Previous observations that 1- to 3-day embryos are relatively unresponsive to insecticides are probably artifactual owing to imprecise techniques.

The effects of the bisphosphonate HEBP on dentin formation and the structural relationship between the dentin and the developing periodontal attachment apparatus have been studied in the continuously growing mouse incisor. It was observed that HEBP (in doses greater than or equal to 8 mg P/kg b.w/day) not only inhibited the deposition of mineral crystallites in newly formed dentin matrix, but also entirely prevented the formation of a layer of acellular root cementum. It was further noticed that the drug interfered with the deposition of 3H-serine-containing substances at the predentin-dentin border. This was not always accompanied by an inhibition of dentin mineralization, thereby suggesting that 3H-serine-containing proteins (presumably phosphoproteins) do not play a critical role in the deposition of mineral layers onto previously formed ones. The absence of a cementum layer did not prevent the developing periodontal ligament from establishing matrix-to-matrix connections with the root-analogue dentin. Collagen fibrils of the ligament intermingled with those of the mantle dentin, which in contrast to teeth not exposed to the drug were clearly visible and not masked by electron-dense matrix components. Finally, it was found that the drug had distinct effects on the formation of root-analogue and crown-analogue dentin. Whereas during the course of the experiment the odontoblasts along the crown-analogue aspect of the tooth continued to produce circumpulpal dentin matrix, those along the root-analogue aspect of the tooth did so only when the mantle dentin layer had been mineralized prior to HEBP administration. This phenomenon is interpreted as being indicative of fundamental differences between the formation of crown and root dentin.