The tritocerebral commissure ''dwarf'' (TCD): a major GABA-immunoreactive descending interneuron in the locust

Summary The minor branch of the tritocerebral commissure of the locust,Locusta migratoria, contains only two axons which are from interneurons in the brain descending to the ventral cord ganglia. The smaller of these two neurons, the tritocerebral commissure dwarf (TCD), is immunoreactive to GABA, suggesting that it may be an inhibitory interneuron. We have exploited the accessibility of its axon in the commissure, first, to fill it with cobalt to define its morphology, and second, to record its input characteristics. It has a cell body and arborization of fine branches in the deutocerebrum of the brain, its axon passes contralateral through the tritocerebral commissure and it forms bilateral arborizations in the suboesophageal and three thoracic ganglia. It receives mechanosensory input from many regions of the ipsilateral body and head, and it is sensitive to illumination levels, generally showing greater spontaneous activity in the dark.It is one of the largest GABA-immunoreactive descending interneurons in the locust, suggesting it plays a prominent role in behaviour. Since it is easily accessible for physiological recording, its roles in circuits for particular components of behaviour should be amenable to investigation.     

Commissure formation in the embryonic insect brain

The primary axon scaffold of the insect brain is established early in embryogenesis and comprises a preoral protocerebral commissure, a postoral tritocerebral commissure and longitudinal fiber pathways linking the two. In both grasshopper and fly its form is approximately orthogonal and is centered around the stomodeum. We show how pioneer fibers from the protocerebrum and tritocerebrum cross the brain midline directly via their respective commissures. The deutocerebrum, however, lacks its own commissure and we describe how deutocerebral pioneers circumnavigate the gut to cross the midline either via the protocerebral commissure or the tritocerebral commissure. In contrast to all other commissures of the central nervous system, the protocerebral commissure persists, albeit in reduced form, in the commissureless mutation in the fly. Besides the com gene, a further, as yet unidentified, mechanism must regulate this commissure. The formation of the tritocerebral commissure involves labial, a member of the Hox gene group. Genetic rescue experiments in labial mutants reveal that the formation of this commissure can be rescued by all other Hox genes except Abdominal-B. However, only in the labial and Deformed null mutants are the commissures associated with the respective expression domains (tritocerebral, mandibular, respectively) absent. This suggests that the molecular mechanisms regulating postoral brain commissure formation are distinct from those in the neuromeres of the ventral nerve cord.     

A method with three triangular flaps as a secondary operative procedure after reconstruction of the lower lip by Estlander's method.

We have devised a new method for secondary commissuroplasty after reconstruction of the lower lip using Estlander's method with both aesthetically and functionally satisfactory results. This method consists of forming two equilaterally triangular mucosal flaps on the vermilion and a small triangular skin flap in the new position of the commissure and transposing these three flaps to reconstruct the commissure. In the present paper, we reported the procedure and the results. This method produces extremely good results, obtaining favorable commissure form and reconstruction of the mucosa of both upper and lower lips without leaving an unnatural-looking color change in the mucosa or a step deformity in the vermilion. It can be expected that our method will improve the results of Estlander's operations after tumor resection in the lower lip.     

Hippocampal commissure defects in crosses of four inbred mouse strains with absent corpus callosum

It is known that four common inbred mouse strains show defects of the forebrain commissures. The BALB/cJ strain has a low frequency of abnormally small corpus callosum, whereas the 129 strains have many animals with deficient corpus callosum. The I/LnJ and BTBR T+ tf/J strains never have a corpus callosum, whereas half of I/LnJ and almost all BTBR show severely reduced size of the hippocampal commissure. Certain F1 hybrid crosses among these strains are known to be less severely abnormal than the inbred parents, suggesting that the parent strains have different genetic causes of commissure defects. In this study, all hybrid crosses among the four strains were investigated. The BTBR × I/Ln hybrid expressed almost no defects of the hippocampal commissure, unlike its inbred parent strains. Numerous three‐way crosses among the four strains yielded many mice with no corpus callosum and severely reduced hippocampal commissure, which shows that the phenotypic defect can result from several different combinations of genetic alleles. The F2 and F3 hybrid crosses of BTBR and I/LnJ had almost 100% absence of the corpus callosum but about 50% frequency of deficient hippocampal commissure. The four‐way hybrid cross among all four abnormal strains involved highly fertile parents and yielded a very wide phenotypic range of defects from almost no hippocampal commissure to totally normal forebrain commissures. The F2 and F3 crosses as well as the four‐way cross provide excellent material for studies of genetic linkage and behavioral consequences of commissure defects.     

Development of paleocortical projections through the anterior commissure of hamsters adopts progressive, not regressive, strategies

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.     

Development of palecortical projections through the anterior commissure of hamsters adopts progressive,not regressive,strategies

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.     

C. elegans dystroglycan coordinates responsiveness of follower axons to dorsal/ventral and anterior/posterior guidance cues

Neural development in metazoans is characterized by the establishment of initial process tracts by pioneer axons and the subsequent extension of follower axons along these pioneer processes. Mechanisms governing the fidelity of follower extension along pioneered routes are largely unknown. In C. elegans, formation of the right angle‐shaped lumbar commissure connecting the lumbar and preanal ganglia is an example of pioneer/follower dynamics. We find that the dystroglycan ortholog DGN‐1 mediates the fidelity of follower lumbar commissure axon extension along the pioneer axon route. In dgn‐1 mutants, the axon of the pioneer PVQ neuron faithfully establishes the lumbar commissure, but axons of follower lumbar neurons, such as PVC, frequently bypass the lumbar commissure and extend along an oblique trajectory directly toward the preanal ganglion. In contrast, disruption of the UNC‐6/netrin guidance pathway principally perturbs PVQ ventral guidance to pioneer the lumbar commissure. Loss of DGN‐1 in unc‐6 mutants has a quantitatively similar effect on follower axon guidance regardless of PVQ axon route, indicating that DGN‐1 does not mediate follower/pioneer adhesion. Instead, DGN‐1 appears to block premature responsiveness of follower axons to a preanal ganglion‐directed guidance cue, which mediates ventral‐to‐anterior reorientation of lumbar commissure axons. Deletion analysis shows that only the most N‐terminal DGN‐1 domain is required for these activities. These studies suggest that dystroglycan modulation of growth cone responsiveness to conflicting guidance cues is important for restricting follower axon extension to the tracts laid down by pioneers. © 2011 Wiley Periodicals, Inc. Develop Neurobiol, 2012     

Contour correction of the vermilion of the upper lip by island flap of the lower lip

A method is shown to correct contour defects of the upper lip vermilion by an island of vermilion of the lower lip. A muscle bundle of the orbicularis oris is used to carry the island. It is tunneled around the commissure to the upper lip defect. Three cases are shown.     

SALMFamide2 and serotonin immunoreactivity in the nervous system of some acoels (Xenacoelomorpha)

Acoel worms are simple, often microscopic animals with direct development, a multiciliated epidermis, a statocyst, and a digestive parenchyma instead of a gut epithelium. Morphological characters of acoels have been notoriously difficult to interpret due to their relative scarcity. The nervous system is one of the most accessible and widely used comparative features in acoels, which have a so‐called commissural brain without capsule and several major longitudinal neurite bundles. Here, we use the selective binding properties of a neuropeptide antibody raised in echinoderms (SALMFamide2, or S2), and a commercial antibody against serotonin (5‐HT) to provide additional characters of the acoel nervous system. We have prepared whole‐mount immunofluorescent stainings of three acoel species: Symsagittifera psammophila (Convolutidae), Aphanostoma pisae, and the model acoel Isodiametra pulchra (both Isodiametridae). The commissural brain of all three acoels is delimited anteriorly by the ventral anterior commissure, and posteriorly by the dorsal posterior commissure. The dorsal anterior commissure is situated between the ventral anterior commissure and the dorsal posterior commissure, while the statocyst lies between dorsal anterior and dorsal posterior commissure. S2 and serotonin do not co‐localise, and they follow similar patterns to each other within an animal. In particular, S2, but not 5‐HT, stains a prominent commissure posterior to the main (dorsal) posterior commissure. We have for the first time observed a closed posterior loop of the main neurite bundles in S. psammophila for both the amidergic and the serotonergic nervous system. In I. pulchra, the lateral neurite bundles also form a posterior loop in our serotonergic nervous system stainings.     

The nucleus of the posterior pallial commissure in Lacerta sicula (Rafinesque) and its ontogenetic connection to the thalamus]

The nucleus of the posterior pallial commissure of Lacerta sicula originates between the 11th and 18day of incubation. During this time, the developing nucleus shows a distinct and wellformed cellular connection with the rostral, dorsally lying ventral thalamus. The whole connecting nuclear mass lies close to the matrix of the diencephalic and telencephalic ventricle and the connecting foramen interventriculare. It is evident that cells which originate from the the ventral thalamus are possibly delivered to the telencephalic nucleus of the posterior pallial commissure. The cellular connection between thalamus and hemisphere ruptures between the 18th and 19th day of incubation as a result of growth displacement and is no longer visible in later stages.     

A simple neuronal system characterized by a monoclonal antibody to SCP neuropeptides in embryos and larvae of Tritonia diomedea (Gastropoda, Nudibranchia)

SCP-like antigenicity is first present in Tritonia diomedea in small cells of the cerebral ganglia and a single axon crossing the cerebral commissure of 8-day-old embryos. Other axons and neurons become antigenic as the larva develops. At 4-9 days after larvae hatch from the egg mass, 2 additional pairs of neurons are labeled. Axons extend from one pair to the left cerebral ganglion and from the other to the right. A second labeled axon is present across the cerebral commissure. In metamorphically competent larvae the cerebral and pedal neuropils, as well as two neurons in the buccal ganglia with axon(s?) across the commissure, are antigenic. The change in antigenicity as the larva becomes competent is presumably preparatory for juvenile life. The labeled buccal neurons may be B12, which are known to contain SCPs, extend an axon across the buccal commissure, and function in adult feeding behavior. The two large neurons strongly labeled by rabbit polyclonal antibodies against FMRFamide are clearly different from neurons labeled by monoclonal antibody against SCPs. This result supports the contention that different antigens are labeled by these two immune probes.     

Frizzled-3a and slit2 genetically interact to modulate midline axon crossing in the telencephalon

The anterior commissure forms the first axon connections between the two sides of the embryonic telencephalon. We investigated the role of the transmembrane receptor Frizzled-3a in the development of this commissure using zebrafish as an experimental model. Knock down of Frizzled-3a resulted in complete loss of the anterior commissure. This defect was accompanied by a loss of the glial bridge, expansion of the slit2 expression domain and perturbation of the midline telencephalic-diencephalic boundary. Blocking Slit2 activity following knock down of Frizzled-3a effectively rescued the anterior commissure defect which suggested that Frizzled-3a was indirectly controlling the growth of axons across the rostral midline. We have shown here that Frizzled-3a is essential for normal development of the commissural plate and that loss-of-function causes Slit2-dependent defects in axon midline crossing in the embryonic vertebrate forebrain. These data supports a model whereby Wnt signaling through Frizzled-3a attenuates expression of Slit2 in the rostral midline of the forebrain. The absence of Slit2 facilitates the formation of a midline bridge of glial cells which is used as a substrate for commissural axons. In the absence of this platform of glia, commissural axons fail to cross the rostral midline of the forebrain.     

Building the central complex of the grasshopper Schistocerca gregaria: axons pioneering the w, x, y, z tracts project onto the primary commissural fascicle of the brain

The central complex is a major neuropilar structure in the insect brain whose distinctive, modular, neuroarchitecture in the grasshopper is exemplified by a bilateral set of four fibre bundles called the w, x, y and z tracts. These columns represent the stereotypic projection of axons from the pars intercerebralis into commissures of the central complex. Each column is established separately during early embryogenesis in a clonal manner by the progeny of a subset of four identified protocerebral neuroblasts. We report here that dye injected into identified pioneers of the primary brain commissure between 31 and 37% of embryogenesis couples to cells in the pars intercerebralis which we identify as progeny of the W, X, Y, or Z neuroblasts. These progeny are the oldest within each lineage, and also putatively the first to project an axon into the protocerebral commissure. The axons of pioneers from each tract do not fasciculate with one other prior to entry into the commissure, thereby prefiguring the modular w, x, y, z columns of the adult central complex. Within the commissure, pioneer axons from columnar tracts fasciculate with the growth cones of identified pioneers of the existing primary fascicle and do not pioneer a separate fascicle. The results suggest that neurons pioneering a columnar neuroarchitecture within the embryonic central complex utilize the existing primary commissural scaffold to navigate the brain midline.     

Development of the anterior commissure in the opossum: Midline extracellular space and glia coincide with early axon decussation

While the anterior commissure has been shown to be an important route of information transfer in the forebrain, relatively little is known about its anatomical development. Glial substrates and extracellular spaces have been associated with the maturation of other large-fiber tracts, such as the corpus callosum and retinofugal pathway. The present study examined early stages in the maturation of the commissure in the gray short-tailed opossum, Monodelphis domestica. Monodelphis offspring are born after a short 14-day gestation, and, unlike in rats and mice, the anterior commissure develops entirely during the postnatal period. A number of techniques were employed: the carbocyanine dye Dil was used to label early axons in the region, semithin plastic sections were used to examine the extracellular environment of the developing commissure, and immunocytochemistry for glial fibrillary acidic protein (GFAP) was used to characterize glial components. Results suggest that the first commissural fibers that cross the midline pass through a region of large extracellular spaces and may use GFAP-immunoreactive cells and processes as guides during their midline decussation. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 403–414, 1997.     

The corpus callosum as an evolutionary innovation

The corpus callosum (CC) is the major interhemispheric fibre bundle in the eutherian brain and has been described as a true evolutionary innovation. This paper reviews the current literature with regard to functional, developmental and genetic concepts that may help elucidate the evolutionary origin of this structure. It has been suggested that the CC arose in the eutherian brain as a more direct and, therefore, more effective system for the interhemispheric integration of topographically organized sensory cortices than the anterior commissure (AC) and hippocampal commissure (HC) already present in nonplacental mammals. It can also be argued, however, that the ability of the CC to integrate the newly evolving motor cortices of placental mammals may have played a role in the evolutionary fixation of this structure. Investigations into the developmental mechanism involved in the formation of the CC and their underlying patterns of gene expression make it possible to formulate a tentative hypothesis about the evolutionary origin of this commissure. This paper suggests that changes in the developmental patterns of the expression of certain regulatory genes may have allowed a first group of callosal pioneering axons to cross the cortical midline. These pioneering fibres may have used the axons of the HC to find their way across the midline. Additional callosal fibres may then have fasciculated with these pioneers. Once the CC had formed in this way, more complex systems of axonal guidance may have evolved over time, thus enabling a gradual increase in the size and complexity of the CC.     

Remodelling of continuously distributed collagen fibres in soft connective tissues

Extracellular matrix remodelling plays an essential role in tissue engineering of load-bearing structures. The goal of this study is to model changes in collagen fibre content and orientation in soft connective tissues due to mechanical stimuli. A theory is presented describing the mechanical condition within the tissue and accounting for the effects of collagen fibre alignment and changes in fibre content. A fibre orientation tensor is defined to represent the continuous distribution of collagen fibre directions. A constitutive model is introduced to relate the fibre configuration to the macroscopic stress within the material. The constitutive model is extended with a structural parameter, the fibre volume fraction, to account for the amount of fibres present within the material. It is hypothesised that collagen fibre reorientation is induced by macroscopic deformations and the amount of collagen fibres is assumed to increase with the mean fibre stretch. The capabilities of the model are demonstrated by considering remodelling within a biaxially stretched cube. The model is then applied to analyse remodelling within a closed stented aortic heart valve. The computed preferred fibre orientation runs from commissure to commissure and resembles the fibre directions in the native aortic valve.     

伞形科植物芫荽果实发育过程中的解剖结构变化

采用常规石蜡切片法对伞形科(Apiaceae)芹亚科(Apioideae Drude)芫荽属(Coriandrum Linn.)种类芫荽(Coriandrum sativum Linn.)花后幼果发育阶段和果熟发育阶段的果实横切面解剖结构及其变化进行了观察和比较。观察结果表明:芫荽果实的幼果和果熟发育阶段均分为前期、中期和后期3个时期,不同时期果实横切面的形状和大小、果壁厚度和结构以及合生面、果棱、维管束、油管、胚乳和结晶等特征均有明显变化。在芫荽果实发育过程中,果实横切面由近椭圆形逐渐变为近圆形,且分生果长度从1 630μm增加至3 290μm、宽度从860μm增加至1 580μm。合生面长度与分生果长度相等,但合生面逐渐分离,成熟的2个分生果仅由心皮柄维管束和合生面两端的外果壁及中果壁最外侧数层细胞相连,从外形看2个分生果不分离。果壁由薄变厚、再由厚变薄,明显分为4个层次;成熟果实的中果壁大部分由木化细胞构成。果棱可分为主棱和次棱2种,且均不发达;次棱呈角状突起、主棱呈波状弯曲,次棱较主棱明显。维管束包括果壁维管束、心皮柄维管束和种脊维管束3类,其中,果壁维管束不发达且散布于中果壁木化细胞层中。油管仅存在于合生面并被逐渐压扁,而果壁油管消失并转变成大空腔。胚乳逐渐膨大,其形状由元宝形逐渐转变为船形或肾形。此外,在幼果发育阶段,中果壁薄壁细胞、合生面和胚乳细胞中或多或少都含有结晶,胚乳细胞中还含有大量糊粉粒结晶;但在果熟发育阶段结晶消失,仅胚乳细胞中存有糊粉粒结晶。分析结果显示:芫荽果实属隐性双悬果类型且果棱属微果棱型,其部分解剖结构与伞形科芹亚科多数种类的果实有差异。     

A neural network simulation of the vestibular system: implications on the role of intervestibular nuclear coupling during vestibular compensation

 Previous neural network simulations of the vestibular system have been based loosely on known physiology. This research involved the use of a strongly physiologically based neural network model which was used to investigate the role of the vestibular commissure in restoring the bilateral symmetry of the resting rates of the vestibular nuclei during vestibular compensation following unilateral labyrinthectomy. It was found that readjustments in the gain of the vestibular commissure were not primarily responsible for vestibular compensation, as has previously been suggested, but rather that it was modifications in extralabyrinthine sources of tone which mediated the restoration of the central symmetry between the two nuclei. Received: 20 November 1995/Accepted in revised form: 24 July 1996     

伞形科东当归的果实形态和解剖结构

对伞形科(Apiaceae)当归属(Angelica L.)东当归〔A.acutiloba(Sieb.et Zucc.)Kitag.〕的分生果形态特征和解剖结构进行了全面观察。该种分生果的外观呈倒椭圆状长卵形,有三角状萼齿,果棱、棱槽和腹面表面均有黄白色斑点。果实横切面解剖结构具有以下特征:外果皮终止于果棱顶端的腹面处,合生面宽阔,外果皮和中果皮细胞中有大量淡黄色晶体,油管在棱槽和合生面处连续分布等。东当归的这些果实形态及解剖结构明显不同于当归属的其他种类,其分类地位有待重新探讨。