摘要:

AbstractThe neuromuscular junction in the myotomes of larval and adult lampreys,Lampetra japonica, was studied with the electron microscope. In larval lampreys of 26 days after artificial insemination, the myotome consists of triangular lamellae of muscle cell with their bases laterally and apexes medially oriented and placed one on the other. The lateral aspect of the myotome is covered by a layer of flattened cell, and the other aspect is covered by an external lamina which does not extend into the intercellular space between adjacent cells within a myotome. A bundle of thin axons was found in a depression at the middle of medial edge (apex) of each muscle lamella of the myotome and neuromuscular junction was formed here. No nerve endings were found at the myoseptal ends or at the lateral borders of the muscle lamellae. Enlarged axon terminals contained numerous clear vesicles with a few cored vesicles, mitochondria and neurofilaments. The presynaptic axolemma was separated from the postsynaptic sarcolemma by an interspace (50–55 mμ wide) with an interposed external lamina.In the trunk musculature of adult lampreys, nerve endings were found on the surface of the parietal fibers whereas they were seen on both the myoseptal ends near the myotendinous junction along the medial border of each central fiber. Thickening and enhancement in the electron density and accumulation of filamentous material on the sarcoplasmic surface of the postsynaptic sarcolemma were noted in both the larval and adult lampreys. Any other specific alterations were not found on both the pre‐ and postsynaptic membrane in the neuromuscular junctions of larval and adult lampreys.A brief comment was made on the relationship in development of the characteristic muscle units and patterns of the motor innervation in the larval and adult lampreys. The significance of the neuromuscular junction in the very young larvae reported here was also discussed in respect to the evolution of the neuromuscular junction, particularly in lower chordates, and it was presumed to be the most primitive pattern of innervation in the vertebrate skeletal mu

ISSN:0092-7317    

DOI:10.1002/cne.901650102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractIndividual ganglia of the cockroach embryo (Periplaneta americana) were explanted on clean glass coverslips immersed in a chemically defined liquid medium and incubated for periods up to eight weeks. Substantial, straight interganglionic connections were formed between: (1) rows of ganglia arranged in the normal in vivo configuration; (2) rows of ganglia placed in abnormal orders; (3) rows of ganglia which never form connections in vivo because they occur singly in the embryo; and (4) rows of ganglia in natural sequences but which have had their rostro‐caudal axes rotated 90° in relation to the line of the row. Therefore fascicles and interganglionic connectives were formed without regard to normal in vivo relationships.Daily observations with a Nomarski microscope indicated that several processes are involved in connective formation. (1) Initial outgrowth is in a random, radial pattern. (2) Intersecting fibers from adjacent ganglia are deflected toward each others' perikarya. (3) Initially bowed fiber connectives are straightened, perhaps by increases in fiber tension or by fiber shortening which may be brought about by neuronal or extraneuronal (glial) processes. (4) Outgrowing fibers follow already established fiber pathways.The present results indicate that fiber‐fiber and fiber‐target interactions play a significant role in the formation of interganglionic connectives. In this system, the spatial relationships between ganglia determine the patterns and varieties of permissible neuronal connections. Thus, major, straight nerve trunks may be formed between adjacent ganglia which are growing out fibers on a glass surface submerged in a liquid medium which offers minimal orientation cues and provides a growth substrate vastly different and simpler than that encountered by outgrowing fibers i

ISSN:0092-7317    

DOI:10.1002/cne.901650103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractIn neonate and infant rats the area of the cerebellum was irradiated with different schedules of single or multiple doses of low‐level X‐ray. One set of schedules allowed the early recovery of the external germinal layer and the differentiation of all the postnatally‐forming cell types while the other selectively prevented the acquisition of basket cells. The first schedule did not interfere with the development of normally oriented and arborizing Purkinje cells. The second schedule led to the growth of twisted and entwined stem dendrites even when, in association with the recovered granule cells, parallel fibers were present in the molecular layer together with Purkinje cell spiny branchlets. Evidence was presented that the alignment of Purkinje cell perikarya in a monolayer does not guarantee the normal growth of Purkinje cell stem dendrites which may be dependent on the presence of basket cells. The problem was discussed whether cell differentiation in the cerebellar cortex is governed by a chronological or sequential prin

ISSN:0092-7317    

DOI:10.1002/cne.901650104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractIn Long‐Evans rats the area of the cerebellum was X‐irradiated with two schedules beginning on day 8 by which time the bulk of basket cells were formed. The shorter schedule of four successive daily doses of 200 r between 8–11 days was designed to allow some cell recovery, the longer schedule between 8–15 days was expected to prevent it. Neither of the schedules interfered with the differentiation of basket cells. Purkinje cells remained aligned in a monocellular layer and formed singularly long, upright stem dendrites which were surrounded by the descending collaterals of basket cell axons. This supported the hypothesis that the directed growth of Purkinje cell stem dendrite is promoted by morphogenic interaction with basket cells. The upright stem dendrites had few or no smooth branches where cell recovery was prevented or had few such branches where recovery occurred. It was postulated that the outgrowth of smooth branches is dependent on interaction with stellate cells which form after the acquisition of basket cells. The absence or scarcity of smooth branches did not prevent the formation of spiny branchlets which grew downward to establish synaptic contacts with the spared parallel fibers of granule cells formed before the start of irradiation. In the group with some granule cell recovery, spiny branchlets grew to a limited extent upward into the pile of parallel fibers formed after the irra

ISSN:0092-7317    

DOI:10.1002/cne.901650105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractIn Long‐Evans rats the area of the cerebellum was irradiated with multiple doses of low‐level X‐ray beginning on day 12 after the bulk of stellate cells were acquired. The treatment spared basket, stellate and early‐forming granule cells but led to a substantial reduction in the total granule cell population and a correlated miniaturization of the cerebellar cortex. Nevertheless most Purkinje cells had normally shaped planar dendritic arbors, with an upward directed stem dendrite, several smooth branches and a multitude of spiny branchlets. The frequent piling up of spiny branchlets near the surface was attributed to the truncation of the bed of parallel fibers by this radiation schedule.In this last paper of the series the accumulated results are summarized and evaluated. The hypothesis is offered that while the growth of the Purkinje cell perikaryon is an autonomous process, the oriented perpendicular growth of a single stem dendrite depends on the presence of basket cell axons, the outgrowth of smooth branches on the presence of stellate cell axons, and the proliferation of spiny branchlets on interaction with parallel fibers. The parallel fibers are responsible for the orthogonal, planar growth of the dendritic arbor and a hypothesis is offered about the mechanisms i

ISSN:0092-7317    

DOI:10.1002/cne.901650106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractSpontaneously metamorphosing bullfrog tadpoles and those induced to metamorphose by injections of thyroid stimulating hormone (TSH) were given a single intraperitoneal injection of thymidine‐3H (10 μCi/g body weight). The brains were dissected out at various periods 3 hours to 14 days later, and processed for autoradiography. At the 3‐hour interval after thymidine‐3H injection, ependymal cells were labelled, but not the external granular layer (EGL) cells. Furthermore, in all the metamorphosing tadpoles intense labelling was restricted to the ependyma of the marginal region of the cerebellar plate. At 48 hours, labelled cells were seen in the EGL of the marginal region. At the 4‐day interval, most of the EGL was labelled, and labelled cells were also seen migrating from the EGL into the internal granular layer (IGL). By 14 days, several labelled cells were seen in the IGL. Although the sequence of cerebellar histogenesis in the frog is similar to the general pattern described in other vertebrate groups, the results indicate that the EGL of the frog cerebellum does not serve the function of a secondary proliferat

ISSN:0092-7317    

DOI:10.1002/cne.901650107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractRetinofugal projections in the blind cave fish A.Hubbsiand in the highly visualA. Mexicanuswere studied with both reduced silver and autoradiographic methods. Contrary to what has been reported for other teleosts, ipsilateral, as well as the generally accepted contralateral, projections were found inA. Mexicanus. Bilateral retinofugal projections were traced to the dorsolateral thalamic nucleus and area pretectalis. Contralateral projections were traced to the lateral geniculate nucleus, nucleus pretectalis, accessory optic nucleus, nucleus corticalis, nucleus opticus hypothalamicus and the superficial layers of the optic tectum (strata opticum, fibrosum and griseum superficiale, and the cellular zone of griseum centrale).Retinal efferents in the blindfish,A. Hubbsi, are sparse and totally crossed. Areas receiving a retinal projection include nucleus opticus hypothalamicus, lateral geniculate and the superficial layers of the medial third of the optic tectum. Preliminary behavioral studies are described and discussed in relation to the possible visual potential of this teleost.

ISSN:0092-7317    

DOI:10.1002/cne.901650108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractSuction lesions were placed in the optic tecta of 36 blind cave fish. Three main bundles of tectal efferents were observed. A large, caudally directed fascicle distributes to the ipsilateral torus semicircularis, nucleus isthmi, and lateral tegmental areas of the mesencephalon and pons via the ipsilateral tectobulbar tract. Contralaterally, this fascicle descends to pontine levels as the contralateral tectobulbar tract.A second, rostrally directed bundle exits from the tectum at two levels. A small fascicle leaves from the caudal tectum and ascends rostrally as the commissura transversa. This bundle then joins with more rostrally exiting fibers and the combined fascicles collect in the area of the medial optic tract. They remain in this position until the level of the postoptic commissure where they decussate. Subsequently, this bundle moves caudally and enters the contralateral tectum at its most rostral extreme.The third bundle of tectofugal efferents leaves the tectum medially, at the level of the lesion, and enters the tectal commissure, through which it is distributed to the ipsilateral torus longitudinalis and contralateral optic tectum.

ISSN:0092-7317    

DOI:10.1002/cne.901650109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901650101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY