Human CHN1 mutations hyperactivate alpha2-chimaerin and cause Duane's retraction syndrome

Duane's retraction syndrome (DRS) is a complex congenital eye movement disorder caused by aberrant innervation of the extraocular muscles by axons of brainstem motor neurons. Studying families with a variant form of the disorder (DURS2-DRS), we have identified causative heterozygous missense mutations in CHN1, a gene on chromosome 2q31 that encodes alpha2-chimaerin, a Rac guanosine triphosphatase-activating protein (RacGAP) signaling protein previously implicated in the pathfinding of corticospinal axons in mice. We found that these are gain-of-function mutations that increase alpha2-chimaerin RacGAP activity in vitro. Several of the mutations appeared to enhance alpha2-chimaerin translocation to the cell membrane or enhance its ability to self-associate. Expression of mutant alpha2-chimaerin constructs in chick embryos resulted in failure of oculomotor axons to innervate their target extraocular muscles. We conclude that alpha2-chimaerin has a critical developmental function in ocular motor axon pathfinding.     

Axonal proteins of presynaptic neurons during synaptogenesis

Changes occur in the synthesis and axonal transport of neuronal proteins in dorsal-root ganglia axons as a result of contact with cells from the spinal cord during synapse formation. Dorsal-root ganglia cells were cultured in a compartmental cel culture system that allows separate access to neuronal cell bodies and their axons. When cells from the ventral spinal cord were cultured with the dorsal-root ganglia axons, synapses were established within a few days. Metabolic labeling and two-dimensional electrophoresis revealed that four of more than 300 axonal proteins had changed in their expression by the time synapses were established. The highly selective nature of these changes suggests that the proteins involved may be important in the processes of axon growth and synapse formation and their regulation by the regional environment.     

Regeneration in crustacean motoneurons: evidence for axonal fusion

Crayfish motor axons remain excitable for over 100 days after severance from their central cell bodies, and continue to store and release normal amounts of transmitter substance. Evidence indicates that regeneration occurs by fusion of the central process with its surviving peripheral segment.     

Input resistance, electrical excitability, and size of ventral horn cells in cat spinal cord

Experiments on cat lumbosacral alpha motoneurones showed that, in comparison with cells possessing rapidly conducting axons, the cells with slowly conducting axons have the higher input resistance, that they need weaker stimulating currents to reach the threshold for repetitive firing, and that they need a relatively larger increment in current strength for a given increase in firing rate. Measurements of the number and diameters of dendritic trunks gave larger values for the larger cell bodies. The discussion deals with the interrelation between cell geometry, electrical properties, and the reflex action of alpha motoneurones.     

Presynaptic location and axonal transport of beta 1-adrenoreceptors in the rat brain

Interruption of the ascending noradrenergic neurons of the locus coeruleus in the rat forebrain with 6-hydroxydopamine produced a progressive accumulation, proximal to the lesion, of tritiated dihydroalprenolol binding activity over 2 days. This accumulation could be blocked by interrupting the neurons closer to their cell bodies. Competitive binding studies with the beta 2 agonist Zinterol suggested that the accumulated beta-receptors were primarily of the beta 1 subtype. These results suggest that, in the rat brain, some beta 1-adrenoreceptors are located in presynaptic, noradrenergic locus coeruleus neurons and are transported in their axons.     

Substance P activity in the bullfrog retina: localization and identification in several vertebrate species

Immunoreactive substance P is present in the bullfrog retina, possibly in two types of stratified amacrine cells, with their somas in the inner nuclear layer and their neuronal processes entering the inner plexiform layer and ramifying in sublayers 3 or 4 (or both). Occasionally, polygonal somas positive for substance P were found in the ganglion cell layer. Approximately 75 percent of the cell bodies positive for substance P and 65 percent of the radioimmunoassayable substance P were found in the superior half of the frog retina. On the basis of high-performance liquid chromatography, the immunoreactive substance P in the neural retina of the rat, monkey, or chick is similar to synthetic substance P, whereas this is not true of the immunoreactive substance P in the bullfrog or carp retina.     

Human amnion membrane serves as a substratum for growing axons in vitro and in vivo

The epithelial cell layer of human amnion membrane can be removed while the basement membrane and stromal surfaces remain morphologically intact. Such a preparation has been used as a substratum for the in vitro culture of dissociated neurons. Embryonic motor neurons from chick ciliary ganglion attached to both surfaces but grew extensive neurites only on the basement membrane. On cross sections of rolled amnion membranes, regenerating axons of cultured neurons were guided along pathways of basement membrane that were immunoreactive with an antibody to laminin. In addition, when rolled amnion membranes were implanted into a lesion cavity between the rat septum and hippocampus, cholinergic neurons extended axons through the longitudinally oriented implant into the hippocampus. Thus, this amnion preparation can serve as a bridge to promote axonal regeneration in vivo in damaged adult brain.     

Transport of protein by goldfish optic nerve fibers

After tritiated leucine was injected into the eye of goldfish, radio-active protein synthesized by the ganglion cell bodies moved down the optic axons at an average rate of 0.4 mm per day. Radioautograms of the optic tectum in which these axons end show that, as early as 24 hours after the injection, before the radioactivity in the tectal layer containing the optic axons had risen above background level, the layer containing the axon terminals was already heavily labeled. The radioactivity in the terminals reached a maximum about 48 hours after the injection and remained approximately constant for at least 23 days thereafter, whereas the radioactivity in the fiber layer increased significantly during the same interval, as the slowly moving protein component entered it. Thus there appears to be a special mechanism for rapid transport of protein from the cell body to the synaptic terminals, as well as a slower movement of protein down the axon.     

Directional specificity in the regeneration of lamprey spinal axons

After spinal transection in ammocoetes (lamprey larvae) 4 to 5 years old, functional recovery is accompanied by a limited regeneration in which axons grow as far as 5 millimeters beyond the scar. In axotomized giant interneurons labeled intracellularly with horseradish peroxidase 16 to 120 days after transection, 74 percent of regenerating neurites grew in their normal projection pattern, rostal and contralateral to the cell body. One third of the neurites originated anomalously from posterior dendrites. Despite their initial abnormal orientation, 80 percent of these neurites looped contralaterally and rostrally to assume the normal projection path. The directional specificity persisted when giant interneurons were located in islands formed by double simultaneous cord transection. This limited regeneration seems to be characterized by directional selectivity that cannot be attributed to nonspecific influences, such as a tendency of neurites to grow in an already established direction or a trophic effect of the zone of injury.     

柔嫩艾美耳球虫卵囊形成的超微结构

对柔嫩艾美耳球虫卵囊形成的超微结构进行了观察。大配子体系由末代裂殖子侵入盲肠上皮细胞后,长大变圆而形成。大配子体发育、大配子形成、受精、卵囊形成均在带虫空泡内进行,大配子体发育过程的早期,微线、棒状体、椎体、极环等组成的顶复合器消失,随之,首先在大配子体内部形成大量的成囊体 2,成囊体 2有电子稀疏的杆状结构组成,成囊体 2为圆形,外被一层单位膜,结构比较明显,但表面不光滑;成囊体 1较成囊体 2形成晚,其组成成分电子结构十分致密,它也呈圆形,而且表面十分光滑,外被一层不明显的膜;在成囊体形成的同时,支链淀粉和脂肪体也逐渐形成;大配子体和大配子外被单位膜,中央有一个细胞核,核仁不十分明显。卵囊壁形成起始于大配子受精以后,成囊体移向被膜,并且集中于被膜下,首先,成囊体 1解聚,在被膜下形成一层卵囊壁,随后,成囊体 2解聚形成又一层卵囊壁,最后,在内部的合子膜形成第五层囊壁,卵囊形成以后,细胞核位于细胞中央,细胞内有大量的支链淀粉和脂肪体     

Perivascular meningeal projections from cat trigeminal ganglia: possible pathway for vascular headaches in man

Peroxidase-containing cell bodies were found in the ipsilateral trigeminal ganglia after horseradish peroxidase was applied to the proximal segment of the middle cerebral artery in seven cats. Cell bodies containing the enzyme marker were located among clusters of cells that project via the first division. The existence of sensory pathways surrounding large cerebral arteries provides an important neuroanatomical explanation for the hemicranial distribution of headaches associated with certain strokes and migraine.     

Lesions of central norepinephrine terminals with 6-OH-dopamine: biochemistry and fine structure

Intracisternal injections of 6-hydroxydopamine produce rapid and long-lasting depletion of brain catecholamines without effects on serotonin concentrations. Depletion of norepinephrine is greatest in areas containing only nerve terminals and axons and least in areas containing monoamine cell bodies. The norepinephrine loss is accompanied by electron microscopic evidence of nerve terminal degeneration and decreased turnover. Dopamine loss is less marked and is not accompanied by degeneration or alteration of turnover rate.     

Dopamine-accumulating retinal neurons revealed by in vitro fluorescence display a unique morphology

Dopamine is the principal catecholamine neurotransmitter in the vertebrate retina. The shape of retinal neurons that accumulate dopamine has been demonstrated in an in vitro preparation of cat retina. This was achieved by the discovery that the combined uptake of dopamine and the indoleaminergic transmitter analog 5,7-dihydroxytryptamine leads to an intense, catecholamine-like fluorescence in the cell bodies and processes of presumed dopaminergic amacrine cells in the living retina. This fluorescence served as an in vitro marker for these cells, and their detailed morphology was analyzed after intracellular injection of horseradish peroxidase under direct microscopic control. The horseradish peroxidase-filled cells show an unprecedented neuronal morphology: each cell gives rise to multiple, axon-like processes that arise from, and extend for millimeters beyond, the dendritic tree. The unique structure of this type of amacrine cell suggests a function for dopamine in long-range lateral interactions in the inner plexiform layer.     

1-Adamantanamine hydrochloride: inhibition of Rous and Esh Sarcoma viruses in cell culture

I-Adamantanamine hydrochloride, added to chick embryo cells, inhibited focus production upon subsequent inoculation of the cells with Rous and Esh sarcoma viruses. Addition of the chemical to suspensions of Rous and Esh viruses before they were added to chick cell cultures did not inactivate the viruses; and the addition to chick cells did not prevent plaque formation following their inoculation with Newcastle disease virus. This indicates that cells treated with 1-adamantanamine hydrochloride are capable of supporting viral replication, and these observations suggest that the drug inhibits growth of two oncogenic viruses by prevention of virus penetration, but not by a virucidal effect or cell intoxication.     

Assembly of chick brain tubulin onto isolated basal bodies of Chlamydomonas reinhardi

Basal bodies isolated from Chlamydomonas reinhardi will serve as initiation centers for the assembly of chick brain microtubule protein subunits (tubulin) into microtubules. The rate of microtubule assembly is tubulin-concentration dependent; this assembly occurs onto both distal and proximal ends of the basal body mnicrotubules, with distal assembly greatly favored. In vitro assembly of brain tubulin also occurs onto the mid-lateral aspects of the basal bodies, presumably onto the fiber connecting the two basal bodies.     

Conservation of brain amyloid proteins in aged mammals and humans with Alzheimer's disease

The formation of clusters of altered axons and dendrites surrounding extracellular deposits of amyloid filaments (neuritic plaques) is a major feature of the human brain in both aging and Alzheimer's disease. A panel of antibodies against amyloid filaments and their constituent proteins from humans with Alzheimer's disease cross-reacted with neuritic plaque and cerebrovascular amyloid deposits in five other species of aged mammals, including monkey, orangutan, polar bear, and dog. Antibodies to a 28-amino acid peptide representing the partial protein sequence of the human amyloid filaments recognized the cortical and microvascular amyloid of all of the aged mammals examined. Plaque amyloid, plaque neurites, and neuronal cell bodies in the aged animals showed no reaction with antibodies to human paired helical filaments. Thus, with age, the amyloid proteins associated with progressive cortical degeneration in Alzheimer's disease are also deposited in the brains of other mammals. Aged primates can provide biochemically relevant models for principal features of Alzheimer's disease: cerebrovascular amyloidosis and neuritic plaque formation.     

Dopamine-mushroom body circuit regulates saliency-based decision-making in Drosophila

Drosophila melanogaster can make appropriate choices among alternative flight options on the basis of the relative salience of competing visual cues. We show that this choice behavior consists of early and late phases; the former requires activation of the dopaminergic system and mushroom bodies, whereas the latter is independent of these activities. Immunohistological analysis showed that mushroom bodies are densely innervated by dopaminergic axons. Thus, the circuit from the dopamine system to mushroom bodies is crucial for choice behavior in Drosophila.     

Lipoprotein uptake by neuronal growth cones in vitro

Macrophages that rapidly enter injured peripheral nerve synthesize and secrete large quantities of apolipoprotein E. This protein may be involved in the redistribution of lipid, including cholesterol released during degeneration, to the regenerating axons. To test this postulate, apolipoprotein E-associated lipid particles released from segments of injured rat sciatic nerve and apolipoprotein E-containing lipoproteins from plasma were used to determine whether sprouting neurites, specifically their growth cones, possessed lipoprotein receptors. Pheochromocytoma (PC12) cells, which can be stimulated to produce neurites in vitro, were used as a model system. Apolipoprotein E-containing lipid particles and lipoproteins, which had been labeled with fluorescent dye, were internalized by the neurites and their growth cones; the unmetabolized dye appeared to be localized to the lysosomes. The rapid rate of accumulation in the growth cones precludes the possibility of orthograde transport of the fluorescent particles from the PC12 cell bodies. Thus, receptor-mediated lipoprotein uptake is performed by the apolipoprotein B,E(LDL) (low density lipoprotein) receptors, and in the regenerating peripheral nerve apolipoprotein E may deliver lipids to the neurites and their growth cones for membrane biosynthesis.     

Rat brain binds adrenal steroid hormone: radioautography of hippocampus with corticosterone

Tritiated corticosterone injected subcutaneously into adrenalectomized male rats 1 hour before killing produced intense labeling of the hippocampus in radioautograms prepared by a method that reduced or prevented diffusion of the radioactive material. The pyramidal neurons of the cornu ammonis and the granule neurons of the gyrus dentatus contained more radioactivity than did other regions of the brain; however, the intensity of labeling varied among adjacent neurons. The nuclei of many neurons were clearly labeled but radioactivity was relatively sparse in the cytoplasm, in the axons where they branch from cell bodies, and in adjacent neuropil.     

Protein uptake in multivesicular bodies in the molt-intermolt cycle of an insect

Plant peroxidase injected into the hemocoel is taken up in granules by almost all tissues. These granules may become multivesicular bodies or isolation bodies which later breakdown. There is most uptake and breakdown at times in the molt-intermolt cycle when cells are engaged in active syntheses.