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1.
Numerous small structures (stellate trichomnes) protrude from the surface of marginal hairs, outer leaf surface, and stem of Dionaea muscipula Ellis. None are present inside the trap. Mechanical stimulation causes small action potentials and eventual closure of the trap, independently of the sensitive trigger hairs. Subthreshold stimulation of these structures appears to sensitize the trigger hairs and facilitate closure of the trap. This suiggests that these structures act as touch sensors or receptors. 相似文献
2.
Axons from eyes transplanted to the tail in Xenopus larvae enter the caudal spinal cord and follow two adjacent tracts rostrally to the level of the cerebellum. When eyes are transplanted to the ear area, optic axons enter the hindbrain and follow the same tracts rostrally and caudally. These sensory pathways normally contain the embryonic sensory system of the Rohon-Beard axons and the descending and ascending tracts of nerve V. We propose that the transplanted optic axons have followed a continuous substrate sensory pathway normally shared by a number of different sensory tracts. 相似文献
3.
Scanning electron microscopy of the organ of Corti 总被引：1，自引：0，他引：1
With the scanning electron microscope we have examined normal cochlear sensory epithelium of the guinea pig and cat and that damaged by noise. The studies demonstrate how the regular surface architecture of the organ of Corti is altered after exposure to noise. The changes include loss of sensory hairs, formation of giant hairs, and complete degeneration of circumscribed areas of the organ of Corti. Our method greatly reduces the artifacts. 相似文献
4.
Transient pioneer neurons are essential for formation of an embryonic peripheral nerve 总被引：6，自引：0，他引：6
In developing nervous systems, many peripheral and central pathways are established by early arising populations of pioneer neurons. The growth cones of these pioneer neurons can migrate while embryonic distances are short and while intervening tissue is relatively uncomplicated. Are these pioneers necessary? In grasshopper embryos, a pair of pioneer neurons arise at the tips of limb buds and extend axons through the limb to the central nervous system. Growth cones of later arising sensory neurons migrate along the pioneer axons. After ingrowth of sensory axons, the pioneer neurons die. If the pioneer neurons are prevented from differentiating by heat shock, then the sensory growth cones that would have migrated along them are blocked and fail to reach the central nervous system. Thus, the pioneer axons are necessary for successful migration of these sensory growth cones. By crossing a segment boundary early in embryogenesis, the pioneers circumvent an incompatibility between differentiated segment boundary cells and growth cone migration. Pioneer neurons may resolve similar problems in many systems. 相似文献
5.
Oury F Murakami Y Renaud JS Pasqualetti M Charnay P Ren SY Rijli FM 《Science (New York, N.Y.)》2006,313(5792):1408-1413
In the mouse trigeminal pathway, sensory inputs from distinct facial structures, such as whiskers or lower jaw and lip, are topographically mapped onto the somatosensory cortex through relay stations in the thalamus and hindbrain. In the developing hindbrain, the mechanisms generating such maps remain elusive. We found that in the principal sensory nucleus, the whisker-related map is contributed by rhombomere 3-derived neurons, whereas the rhombomere 2-derived progeny supply the lower jaw and lip representation. Moreover, early Hoxa2 expression in neuroepithelium prevents the trigeminal nerve from ectopically projecting to the cerebellum, whereas late expression in the principal sensory nucleus promotes selective arborization of whisker-related afferents and topographic connectivity to the thalamus. Hoxa2 inactivation further results in the absence of whisker-related maps in the postnatal brain. Thus, Hoxa2- and rhombomere 3-dependent cues determine the whisker area map and are required for the assembly of the whisker-to-barrel somatosensory circuit. 相似文献
6.
精河县荒漠林鼠害猛禽天敌招引初报 总被引：5，自引：2，他引：5
设立了栖架和人造巢箱招引猛禽防治荒漠林鼠害，初步结果表明：猛禽对栖架的利用率依季节不同，可达40％～90％．栖架下发现大量猛禽的吐物，其中含有害鼠的骨骼和毛发；至少一种猛禽——红隼(Falco tinnunculus)可在人造巢箱中繁殖：初步调查表明在非繁殖季节，猛禽对栖架的利用表现为广利用、低频率的特点，在繁殖季节则表现为高频率、局限性而形成明显巢区。 相似文献
7.
Astrocytes block axonal regeneration in mammals by activating the physiological stop pathway 总被引：15，自引：0，他引：15
Regenerating sensory axons in the dorsal roots of adult mammals are stopped at the junction between the root and spinal cord by reactive astrocytes. Do these cells stop axonal elongation by activating the physiological mechanisms that normally operate to stop axons during development, or do they physically obstruct the elongating axons? In order to distinguish these possibilities, the cytology of the axon tips of regenerating axons that were stopped by astrocytes was compared with the axon tips that were physically obstructed at a cul-de-sac produced by ligating a peripheral nerve. The terminals of the physically obstructed axon tips were distended with neurofilaments and other axonally transported structures that had accumulated when the axons stopped elongating. By contrast, neurofilaments did not accumulate in the tips of regenerating axons that were stopped by spinal cord astrocytes at the dorsal root transitional zone. These axo-glial terminals resembled the terminals that axons make on target neurons during normal development. On the basis of these observations, astrocytes appear to stop axons from regenerating in the mammalian spinal cord by activating the physiological stop pathway that is built into the axon and that normally operates when axons form stable terminals on target cells. 相似文献
8.
Zou DJ Feinstein P Rivers AL Mathews GA Kim A Greer CA Mombaerts P Firestein S 《Science (New York, N.Y.)》2004,304(5679):1976-1979
Axonal projections from the olfactory epithelium to the olfactory bulb are organized into glomeruli according to the expressed odorant receptor. Using gene-targeted mice, we show that glomerular maturation proceeds along different time courses for two similar receptors and requires sensory input during distinct sensitive periods. During early development, some glomeruli are innervated by axons of neurons that do not express the same receptor. These heterogeneous glomeruli normally disappear with age, but they persist in adults deprived of sensory input by unilateral and permanent naris closure. Persistence may be due, in part, to prolonged survival of olfactory sensory neurons. 相似文献
9.
本研究旨在揭示斑马鱼下颌再生中神经和肌肉的关系。通过HE染色技术、免疫荧光组织化学等实验技术分别观察斑马鱼下颌神经和肌肉的再生过程,考察神经和肌肉的关系。研究结果显示,截面附近的神经纤维在剪切后5 h降解,剪切后2 d时完全消失。剪切后3 d,整个芽基所在位置已出现新生的神经纤维。剪切5 d时,芽基上布满大量的神经纤维。肌纤维在剪切后12 h已发生断裂,剪切后5 d形成芽基细胞并分化成各种前体细胞如肌肉前体细胞,剪切后9 d出现新生的肌细胞,剪切后14 d新生的肌细胞与新生的神经纤维建立神经肌肉接头联系,30 d后成为成熟的肌肉组织。结果表明:如果斑马鱼1/3的下颌被人为切除,下颌肌肉可以实现功能性再生,同时神经极可能在肌肉再生中发挥作用。但是如果切除部分超过1/3,则下颌无法再生复原,其原因有待进一步研究。 相似文献
10.
R Schafer 《Science (New York, N.Y.)》1973,180(83):315-317
Acetylcholine is transported along insect chemoreceptor axons at a rate of 12 to 13 centimeters per day after peripheral uptake of choline. Colchicine, vinblastine sulfate, and cytochalasin B all block transport, but transport continues in axons separated surgically from the cell body. These data from an insect are in accord with many studies on vertebrates which have implicated intracellular microtubules in the transport mechanism. The peripheral uptake of choline and its acetylation and transport to nerve terminals in the brain are consistent withthe suggestion that acetylcholine is an antennal sensory transmitter in insects. 相似文献
11.
薄荷叶两种腺毛的发育解剖学研究 总被引：5，自引：0，他引：5
应用扫描电镜及薄切片技术研究薄荷叶的盾状腺毛和头状腺毛的形态发育过程。结果表明,它们的腺毛原始细胞均来源于原表皮,都经二次平周分裂形成1个基细胞、1个柄细胞和1个顶细胞,两者的发生和早期发育相同。以后的发育过程中,由于有的腺毛的柄细胞迅速分化,其顶细胞不再分裂,从而形成单个分泌细胞构成头部的头状腺毛;有的腺毛的柄细胞保持分生组织状态,其顶细胞继续进行多次垂周分裂,从而形成由8个或16个横向扩展的分泌细胞构成头部的盾状腺毛。在腺毛分泌期,盾状腺毛分泌细胞的外壁出现明显的角质层下间隙,其中充满挥发油,而头状腺毛无明显的角质层下间隙。因此。薄荷腺毛发育中丙细胞分化状态决定其腺毛的类型和功能。 相似文献
12.
DNA topoisomerase IIbeta is shown to have an unsuspected and critical role in neural development. Neurogenesis was normal in IIbeta mutant mice, but motor axons failed to contact skeletal muscles, and sensory axons failed to enter the spinal cord. Despite an absence of innervation, clusters of acetylcholine receptors were concentrated in the central region of skeletal muscles, thereby revealing patterning mechanisms that are autonomous to skeletal muscle. The defects in motor axon growth in IIbeta mutant mice resulted in a breathing impairment and death of the pups shortly after birth. 相似文献
13.
Purcell JE 《Science (New York, N.Y.)》1980,209(4460):1045-1047
Collection by divers permitted determination of the natural diets of siphonophore species within II genera. Siphonophores that swim rapidly to spread their tentacles capture small prey, whereas those that swim very weakly capture much larger prey. Nematocyst batteries of two species of weak swimmers closely resemble copepods and fish larvae. Morphology, behavior, and diet suggest that these two species attract large prey by mimicking other zooplankton. 相似文献
14.
The rapid closure of leaves in the Venus flytrap (Dionaea muscipula) involves irreversible cell enlargement, which can be initiated by acidifying the cell walls to pH 4.50 and below. Leaves infiltrated with neutral buffers that keep the pH above 4.50 to 4.75 will not close in response to stimulation of their trigger hairs even though the action potentials that ordinarily cause closure are produced. During the 1 to 3 seconds required for closure about 29 percent of the cellular adenosine triphosphate is lost. It is likely that this adenosine triphosphate is used in very rapid transport of hydrogen ions from the motor cells and that the movement is due to a mechanism of "acid growth." 相似文献
15.
Neurotrophins regulate survival, axonal growth, and target innervation of sensory and other neurons. Neurotrophin-3 (NT-3) is expressed specifically in cells adjacent to extending axons of dorsal root ganglia neurons, and its absence results in loss of most of these neurons before their axons reach their targets. However, axons are not required for NT-3 expression in limbs; instead, local signals from ectoderm induce NT-3 expression in adjacent mesenchyme. Wnt factors expressed in limb ectoderm induce NT-3 in the underlying mesenchyme. Thus, epithelial-mesenchymal interactions mediated by Wnt factors control NT-3 expression and may regulate axonal growth and guidance. 相似文献
16.
Hellal F Hurtado A Ruschel J Flynn KC Laskowski CJ Umlauf M Kapitein LC Strikis D Lemmon V Bixby J Hoogenraad CC Bradke F 《Science (New York, N.Y.)》2011,331(6019):928-931
Hypertrophic scarring and poor intrinsic axon growth capacity constitute major obstacles for spinal cord repair. These processes are tightly regulated by microtubule dynamics. Here, moderate microtubule stabilization decreased scar formation after spinal cord injury in rodents through various cellular mechanisms, including dampening of transforming growth factor-β signaling. It prevented accumulation of chondroitin sulfate proteoglycans and rendered the lesion site permissive for axon regeneration of growth-competent sensory neurons. Microtubule stabilization also promoted growth of central nervous system axons of the Raphe-spinal tract and led to functional improvement. Thus, microtubule stabilization reduces fibrotic scarring and enhances the capacity of axons to grow. 相似文献
17.
Control of sensory fields by stimulation of hypothalamus 总被引：2，自引：0，他引：2
Stimulation of the cat's hypothalamus, which elicits attack, also establishes sensory fields for two reflexes related to biting. Touching a perioral region leads to head movement, bringing the stimulus to the mouth. Touching the lip-line leads to jaw opening. The size of the fields depends on the intensity of stimulation. 相似文献
18.
Del Bene F Wyart C Robles E Tran A Looger L Scott EK Isacoff EY Baier H 《Science (New York, N.Y.)》2010,330(6004):669-673
The optic tectum of zebrafish is involved in behavioral responses that require the detection of small objects. The superficial layers of the tectal neuropil receive input from retinal axons, while its deeper layers convey the processed information to premotor areas. Imaging with a genetically encoded calcium indicator revealed that the deep layers, as well as the dendrites of single tectal neurons, are preferentially activated by small visual stimuli. This spatial filtering relies on GABAergic interneurons (using the neurotransmitter γ-aminobutyric acid) that are located in the superficial input layer and respond only to large visual stimuli. Photo-ablation of these cells with KillerRed, or silencing of their synaptic transmission, eliminates the size tuning of deeper layers and impairs the capture of prey. 相似文献
19.
Implantable electrode assemblies that become penetrated by regenerating axons were used to record signals from single sensory and motor nerve fibers associated with leg movement in unrestrained amphibians (Xenopus laevis). Such neuroimplants may provide a means for establishing the roles of various muscle afferents and efferents in posture and locomotion, and have potential clinical applications. 相似文献
20.
Nociceptive neuronal circuits are formed during embryonic and postnatal times when painful stimuli are normally absent or limited. Today, medical procedures for neonates with health risks can involve tissue injury and pain for which the long-term effects are unknown. To investigate the impact of neonatal tissue injury and pain on development of nociceptive neuronal circuitry, we used an animal model of persistent hind paw peripheral inflammation. We found that, as adults, these animals exhibited spinal neuronal circuits with increased input and segmental changes in nociceptive primary afferent axons and altered responses to sensory stimulation. 相似文献