ISSN:0022-104X    

DOI:10.1002/jez.1402610302

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

年代:1992

数据来源: WILEY

摘要:

AbstractOur goal is to understand the molecular mechanisms that govern the formation of the central nervous system. In particular, we have focused on the development of a small group of neurons and glia that lie along the midline of theDrosophilaCNS. These midline cells possess a number of unique attributes which make them particularly amenable to molecular, cellular, and genetic examinations of nervous system formation and function. In addition, the midline cells exhibit distinctive ontogeny, morphology, anatomical position, and patterns of gene expression which suggest that they may provide unique functions to the developing CNS. Thesingle‐mindedgene encodes a nuclear protein which is specifically expressed in the midline cells and has been shown to play a crucial role in midline cell development and CNS formation. Genetic experiments reveal thatsimis required for the expression of many CNS midline genes which are thought to be involved in the proper differentiation of these cells.In order to identify additional genes which are expressed in some or all of the midline cells at different developmental stages, a technique known as enhancer trap screening was employed. This screen led to the identification of a large number of potential genes which exhibit various midline expression patterns and may be involved in discrete aspects of midline cell development. Further molecular, genetic, and biochemical analyses ofsimand several of the enhancer trap lines are being pursued. This should permit elucidation of the genetic hierarchy which acts in the specification, differentiation, and function of these CNS midline cell

ISSN:0022-104X    

DOI:10.1002/jez.1402610303

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe technique of steroid hormone autoradiography has been used to study the cellular distribution of ecdysteroid binding sites in the ventral nervous system of the tobacco hornworm moth,Manduca sexta.The ligand was 26‐[125I]iodoponasterone. Tissue was examined from the subesophageal ganglia, thoracic ganglia, and abdominal ganglia of larvae at two times during the larval‐pupal transition: the 2nd day of wandering and the prepupal stage. The patterns of neuronal binding seen were compared with those found in earlier autoradiographic studies of hormone binding in tissue sampled on the 1st day of wandering, in the pharate adult, and in the 4‐day‐old moth (Fahrbach and Truman, '89). The pattern of binding was reproducible but dependent upon developmental stage: whereas only a subset of neurons exhibited nuclear accumulation of radiolabeled ecdysteroids on the 1st day of wandering, less than 24 hours later nearly every neuron in the ventral nervous system was labeled. A limited pattern of binding, however, was seen again in the prepupal nervous system. Thus, the insect nervous system is able to use a single hormone both as a general cue for metamorphic developmentandas a signal targeted to stage‐specific subsets of neurons by alternating periods of ubiquitous expression of receptor with periods during which the capacity to bind the steroid hormone is highly r

ISSN:0022-104X    

DOI:10.1002/jez.1402610304

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

年代:1992

数据来源: WILEY

摘要:

AbstractFrom the initial studies of Sperry (Am. J. Physiol, 144:735–741, 1945) to more recent investigations, the regenerative capacity of the VIIIthcranial nerve in nonmammalian vertebrates has been noted for its robust and accurate recovery of functional connections after transection. The VIIIthcranial nerve contains nerve fibers that link functionally distinct sensory epithelial to various areas within the central nervous system (CNS), yet after transection these multiple components of the nerve navigate back to their original central target areas, without innervating inappropriate nuclei. A number of factors may be required to establish and direct VIIIthnerve regeneration. Cellular interactions appear to be necessary for the initiation of outgrowth and the maintenance of neural connections. The release of chemotropic substances from target cells has been postulated as the most likely mechanism guiding the reinnervation of central targets. Furthermore, the growth characteristics of these neurons in tissue culture, without target cells present, indicates that intrinsically regulated growth features may also contribute to the process of VIIIthnerve regeneratio

ISSN:0022-104X    

DOI:10.1002/jez.1402610305

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

年代:1992

数据来源: WILEY

摘要:

AbstractWe have examined the cellular and synaptic mechanisms underlying the genesis of alternating motor activity in the developing spinal cord of the chick embryo. Experiments were performed on the isolated lumbosacral cord maintained in vitro. Intracellular and whole cell patch clamp recordings obtained from sartorius (primarily a hip flexor) and femorotibialis (a knee extensor) motoneurons showed that both classes of cell are depolarized simultaneously during each cycle of motor activity. Sartorius motoneurons generally fire two bursts/cycle, whereas femorotibialis motoneurons discharge throughout their depolarization, with peak activity between the sartorius bursts. Voltage clamp recordings revealed that inhibitory and excitatory synaptic currents are responsible for the depolarization of sartorius motoneurons, whereas femorotibialis motoneurons are activated principally by excitatory currents. Early in development, the dominant synaptic currents in rhythmically active sartorius motoneurons appear to be inhibitory so that firing is restricted to a single, brief burst at the beginning of each cycle.In E7‐E13 embryos, lumbosacral motor activity could be evoked following stimulation in the brainstem, even when the brachial and cervical cord was bathed in a reduced calcium solution to block chemical synaptic transmission. These findings suggest that functional descending connections from the brainstem to the lumbar cord are present by E7, although activation of ascending axons or electrical synapses cannot be eliminated.Ablation, optical, and immunocytochemical experiments were performed to characterize the interneuronal network responsible for the synaptic activation of motoneurons. Ablation experiments were used to show that the essential interneuronal elements required for the rhythmic alternation are in the ventral part of the cord. This observation was supported by real‐time Fura‐2 imaging of the neuronal calcium transients accompanying motor activity, which revealed that a high proportion of rhythmically active cells are located in the ventrolateral part of the cord and that activity could begin in this region. The fluorescence transients in the majority of neurons, including motoneurons, occurred in phase with ventral root or muscle nerve activity, implying synchronized neuronal action in the rhythm generating network.Immunocytochemical experiments were performed in E14‐E16 embryos to localize putative inhibitory interneurons that might be involved in the genesis or patterning of motor activity. The results revealed a pattern similar to that seen in other vertebrates with the dorsal horn containing neurons with γ‐aminobutyric acid (GABA)‐like immunoreactivity and the ventral and intermediate regions containing neurons with glycine‐like im

ISSN:0022-104X    

DOI:10.1002/jez.1402610306

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

年代:1992

数据来源: WILEY

摘要:

AbstractSpinally transected lamprey recovery locomotor function within 3–6 weeks, and recovery is due, in part, to functional regeneration of neural pathways in the central nervous system (CNS). Our data demonstrate for the first time in the lamprey that descending axons arising from brainstem command neurons can functionally regenerate and restore locomotor initiationbelowa healed spinal transection site. Immediately after behavioral recovery (3–6 weeks) the locomotor pattern was incomplete but returned to normal during the remainder of the recovery period (6–40 weeks). Initially, the extent of regeneration of descending axons was limited but increased to at least 30–50 mm at recovery times of 24–40 weeks. Regenerated giant Muller axons do not contribute significantly to recovery of locomotor function; rather, regenerated axons of smaller reticulospinal neurons appear to restore locomotor initiation. The restoration of locomotor coordinationacrossa spinal lesion is dependent on two mechanisms: regeneration of spinal coordinating neurons and mechanosensory inputs. Comparisons are made to spinal cord regeneration in other lower vertebrates and to the relative lack of CNS regeneration and behavioral recovery in higher ve

ISSN:0022-104X    

DOI:10.1002/jez.1402610307

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

年代:1992

数据来源: WILEY

摘要:

AbstractIt is feasible to study the anatomical, physiological, and biochemical properties of identifiable neurons in lobster embryos. To exploit fully the advantages of this preparation and to lay the foundation for single‐cell studies, our recent goals have been to 1) establish a quantitative staging system for embryos, 2) document in detail the lobster's embryonic development, 3) determine when uniquely identifiable neurons first acquire their transmitter phenotypes, and 4) identify particular neurons that may serve developmental functions. Behavioral, anatomical, morphometric, and immunocytochemical studies have led to a detailed characterization of the growth and maturation of lobster embryos and to the adoption of a percent‐ staging system based upon the eye index of Perkins (Fish. Bull., 70:95–99, 1972). It is clear from these studies that the lobster nauplius molts at approximately 12% embryonic development (E12%) into a metanauplius, which subsequently undergoes a complete molt cycle within the egg. This molt cycle climaxes with the emergence of the first‐stage larva shortly after hatching.Serotonin and proctolin, neurohormones widely distributed in the lobster nervous system, appear at different times in development. Serotonin immunoreactive neurons begin to appear at approximately E10%, with the adult complement being established by E50%. In contrast, proctolin immunoreactive neurons appear later and attain their full complement over a protracted period including larval and juvenile stages. The development of serotonergic deutocerebral neurons and their targets, the olfactory and accessory lobes in the brain, are also examined. The olfactory lobes are forming by E10% and have acquired their glomerulur organization by E50%, whereas the formation of the accessory lobes is delayed; the early rudiments of the accessory lobes are seen by E50%, and glomeruli do not form until the second larva

ISSN:0022-104X    

DOI:10.1002/jez.1402610308

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe swimmerets in the abdomen of the lobsterHomarus americanusare paired external appendages whose back and forth propulsive movements are brought about largely by a group of power and return stroke muscles located in the lateral abdominal cavity. We find functional innervation of these muscles by several excitatory axons and a single inhibitor in embryonic and stage 1 larval lobsters before the external appendages are even formed. This early innervation is via a few nerve bundles in which branches of the motor axons are intertwined in a complex manner. As the swimmerets develop to maturity in later larval and juvenile stages, the innervation consisting usually of several excitor and a single inhibitor synaptic terminals becomes localized to individual muscles. Patterned synaptic activity in these muscles was not seen in the embryonic and larval stages but has been shown in early juvenile stages, when it coincides with the onset of rhythmic movement of the swimmerets. Consequently, such early innervation of the swimmeret muscles may be influential in establishing the central circuitry for the generation of patterned activity, a possibility that was discounted in a previous study (Proc. Natl. Acad. Sci. USA, 70:954–958

ISSN:0022-104X    

DOI:10.1002/jez.1402610309

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

年代:1992

数据来源: WILEY

ISSN:0022-104X    

DOI:10.1002/jez.1402610310

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

年代:1992

数据来源: WILEY

摘要:

AbstractSuckling is the form of feeding unique to infant mammals. The mechanism used by infant mammals to withdraw liquid from the nipple is the subject of considerable debate. Suckling has been examined in two species of infant mammals: miniature pigs and long‐tailed macaques. In both species radio‐opaque markers were inserted into the tongue and jaws; the movements of the jaw and tongue (and also of specific regions within the tongue) plus the movement of milk containing barium were studied by high‐speed cineradiography (100 and 150 frames/sec). In the case of macaques, simultaneous pressure transducer recordings were also made. In both species, liquid moved out of the nipple as the intraoral space was expanded by a combination of tongue movement (negative pressure pumping) coupled with jaw opening. There was no evidence for expression (positive pressure on the nipple) in either species, strongly supporting the view that a suction mechanism is responsible for acquisition of milk from the nipple. Subsequent intraoral transport was different in the two species. The pigs used a second pump mechanism at the base of the tongue to transport liquid through the pillars of the fauces into the valleculae. The monkeys used a “squeeze‐back” mechanism similar to the transport mechanism documented for adult macaques. Further work with other species can test our tentative hypothesis that all mammals use a negative pressure suction for acquisition, but, as is true for adult mammals, infants may use different transport mechanisms to form and mov

ISSN:0022-104X    

DOI:10.1002/jez.1402610311

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

年代:1992

数据来源: WILEY