Brain research. Developmental brain research最新文献

The expression of vertebrate homeoproteins has been extensively studied in a variety of normal and cancerous tissues, but little is known on the role of vertebrate homeoproteins in the proliferation and differentiation of cells from these tissues. In the present study, we investigate the relationship between Quox 1 protein (a quail homeodomain containing protein) expression and the proliferation and differentiation of quail dorsal root ganglia (DRG) and neural crest cells. In vivo [3H]TdR labeling experiments demonstrate that the postmitotic sensory neuroblasts appear before the formation of the ganglion, and that more than half of sensory neuroblasts from DRG have already terminated their proliferation in embryos of 2 days of incubation (E2). All DRG neurons have completely ceased to proliferate from E6.5 onwards. By means of immunocytochemistry, we observe that Quox 1 protein is accumulated exclusively in all bipolar neurons in culture of DRG from E9-E11, and in all postmitotic sensory-like neuroblasts during in vitro cell differentiation of the neural crest. The Quox 1 immunoreactive neurons express simultaneously neurofilaments or substance P, and they are never labeled by anti-bromodeoxyuridine. These observations together with the morphology of Quox 1 positive cells, demonstrate that Quox 1 protein is expressed in the postmitotic sensory neurons of DRG. Our previous experiments have shown that between E4 and E6, the accumulation of Quox 1 protein increases in DRG in vivo, but decreases in the central nervous system in which cell proliferation decreases (Xue et al., (1993) Mech. Dev. 43, 149-158). Taken together, our results show that the accumulation of Quox 1 protein in DRG is tightly linked to the increase in the number of postmitotic neurons, whereas in the central nervous system the level of expression of Quox 1 seems concomitant with the extent of cell proliferation.

Indomethacin-sensitive mechanisms involved in inducible heat shock protein 70 (iHSP 70) synthesis were investigated at 6 h after global cerebral ischemia in parietal cortex and hippocampus. In anesthetized piglets, increased intracranial pressure was used to produce 5 or 10 min of cerebral ischemia. Brain regions were sampled for immunoblot analysis, immunohistochemistry and morphology. Immunoblots revealed differential expression of iHSP 70 in untreated brains. Cerebellum contained substantial amounts of iHSP 70 while lower levels were present in parietal cortex and hippocampus. Detectable increases in iHSP 70 were observed at 2 h after ischemia in parietal cortex and hippocampus. Using immunoblot data, calculation of percent change from control at 6 h after ischemia revealed significant (p < 0.05) increases in iHSP 70 of 111 +/- 39% (x +/- sem) (n = 6) in parietal cortex and 195 +/- 69% (n = 8) in hippocampus. Increased iHSP 70 immunoreactivity occurred primarily in the granular/subgranular area of the dentate gyrus 6 h after ischemia. Histological staining revealed little cellular injury at 6 h after ischemia in the granular/subgranular region injury whereas the CA3 region, which lacked iHSP 70 staining, displayed modest cellular injury. Cellular injury was also observed in cortical layers II/III and VI. At 6 h after ischemia, indomethacin pretreatment (5 mg/kg, i.v.) attenuated the iHSP 70 increases in parietal cortex and hippocampus (7 +/- 30% and 89 +/- 30%, respectively n = 5; p < 0.05 compared to ischemia). Also, the increase in iHSP 70 immunoreactivity and appearance of cellular injury were not detected with indomethacin pretreatment. Thus, prior administration of indomethacin is associated with attenuation of ischemia-induced increases in iHSP 70 and cellular injury.

We have employed a collagen-gel co-culture system to evaluate the influence of the hindbrain floor-plate on initial axon outgrowth from the cochlear nucleus. After 2 days in vitro, cochlear nucleus explants exhibited directed outgrowth towards co-cultured floor-plate explants. Comparisons with co-cultures of cochlear nucleus/forebrain or cochlear nucleus/midbrain explants or with cochlear nucleus explants cultured alone suggest that the floor-plate has a specific chemoattractant effect on the outgrowth of the pioneer fibers of the hindbrain auditory commissure. Fiber outgrowth was not directed towards a recombinant source of the chemoattractant molecule netrin suggesting that floor-plate-directed outgrowth in the cochlear nucleus is not solely dependent on netrin. In the present report, we present evidence for the first time that the floor-plate is a chemotropic source in pathfinding of second-order auditory fibers from the cochlear nucleus in the hindbrain.

The present studies were designed to study the interrelationships between GABAergic, serotoninergic and excitatory amino acids systems (EAAs) in the control of gonadotropin secretion in prepubertal female rats. For this purpose we determined the effects of N-methyl-d-aspartate (NMDA), an exogenous agonist of EAAs receptors, on LH and FSH secretion in 16-day-old female rats in which the GABA-A and GABA-B receptors were blocked by bicuculline and baclofen or serotonin (5-HT) depleted by p-choloroamphetamine (PCA). In addition the effects of the GABAergic and serotoninergic systems on LH and FSH secretion were evaluated in animals treated with dibenzocycloalkenimine (diocilpine MK-801), an antagonist of NMDA neurotransmission. While muscimol, a GABA- A agonist, induced a significant increase in LH and FSH levels (P<0.01), baclofen, a GABA-B agonist, had an inhibitory effect on these hormones (P<0.01). MK 801, a NMDA receptor antagonist, not only suppressed the stimulatory effect of NMDA on LH and FSH but also blocked the stimulatory effect of muscimol without modifying the inhibitory action of baclofen on both gonadotropins. Bicuculline, a GABA-A receptor antagonist, did not modify the release effect of NMDA on LH and FSH. 5-HTP, a precursor of 5-HT that increases the levels of this neurotransmitter in the central nervous system significantly increased (P<0.01) the plasma levels of LH and FSH, and this effect was blocked by the NMDA receptor antagonist MK-801. We conclude that the stimulatory effects of GABAergic and serotoninergic systems in prepubertal female rats are connected with the activation of EAA neurotransmission, while the stimulatory effects of NMDA appear to be independent of serotoninergic and GABAergic actions on LH and FSH secretion. Since both GABA and serotonin systems change their effects on LH and FSH during sexual maturation from a stimulatory action in prepubertal to an inhibitory action in adult rats and since NMDA neurotransmission has a stimulatory effect on gonadotropin secretion both in prepubertal and adult rats, it is clear that the interrelationships between GABAergic and serotoninergic systems with EAAs in the gonadotropin control are different in prepubertal and in adult rats.

The developmental absence of brain-derived neurotrophic factor (BDNF) in null mutant mice caused three interrelated defects in the vallate gustatory papilla: sparse innervation, a reduction in the area of the gustatory epithelium, and fewer taste buds. On postnatal day 7, the stunted vallate papilla of bdnf null mutant mice was 30% narrower, the trench walls 35% reduced in area, and the taste buds 75% less abundant compared with wild-type controls. Quantitative assessment of innervation density was carried out to determine if the small trench walls and shortage of taste buds could be secondary consequences of the depletion of gustatory neurons. The diminished gustatory innervation was linearly associated with a reduced trench wall area (r=+0.94) and fewer taste buds (r=+0.96). Residual taste buds were smaller than normal and were innervated by a few surviving taste neurons. We conclude that BDNF-dependent taste neurons contribute to the morphogenesis of lingual gustatory epithelia and are necessary for both prenatal and postnatal mammalian taste bud formation. The gustatory system provides a conspicuous example of impaired sense organ morphogenesis that is secondary to sensory neuron depletion by neurotrophin gene null mutation.

Embryonic ventral midbrains from GFAP-lacZ transgenic mice were xenografted into the dopamine-depleted striata of adult rats. This transgenic line harbors a nuclear-targeted bacterial beta-galactosidase (beta-gal) reporter gene under transcriptional control of the human glial fibrillary acidic protein (GFAP) promoter sequence. Five weeks post-transplantation, graft-derived astrocytes and dopaminergic neurons were visualized by dual immunocytochemistry for beta-gal and tyrosine hydroxylase (TH), respectively. This report describes the advantages associated with the use of GFAP-lacZ transgenic mice to study astrocyte fate in embryonic neural grafts.

We studied the ontogeny of concentration and in vitro phosphorylation of an 85 kDa Triton-insoluble protein from cerebral cortex of 7, 15, 21 and 90 day old rats. The Triton-insoluble cytoskeletal fraction contains an 85 kDa basic phosphoprotein different from synapsin 1, as determined by nonequilibrium pH gradient electrophoresis and phosphopeptide mapping with V8 protease. The concentration of the 85 kDa cytoskeletal associated phosphoprotein was analyzed during development. Results indicated that the concentration of this protein oscillated during suckling, presenting a maximal value at day 15 and decreasing again to stabilize at values near those of 7 day old rats, remaining constant in 21 and 90 day old animals. However, in vitro 32P incorporation, expressed as cpm/microgram, presented a developmentally regulated pattern, with maximal values in young rats, declining with age to negligible values in 90 day old animals. The endogenous phosphorylating system responsible for in vitro 32P incorporation into the 85 kDa protein was determined by the addition of specific activators of second-messenger protein kinases (cAMP, Ca2+/ calmodulin and Ca2+/phosphatidylserine/phorbol ester) and a protein phosphatase inhibitor (okadaic acid) to the incubation system. Results suggested that the in vitro phosphorylation system is composed of protein kinase A, Ca2+/calmodulin dependent protein kinase and protein phosphatase 1.

In the present study we have characterized the postnatal (PN) development of the retina in the Brazilian opossum, Monodelphis domestica. Monodelphis, a small, pouchless marsupial, undergoes a protracted period of postnatal development. Using bromodeoxyuridine immunohistochemistry, we have investigated postnatal neurogenesis of the retina. In addition, we have examined the differentiation of the retina by using antibodies directed against the presynaptic terminal-associated proteins synaptotagmin, Rab3A, synaptophysin and synaptosomal-associated protein-25 (SNAP-25), and have characterized their spatial and temporal distribution during postnatal development. This study is the first systematic comparison of the developmental expression of multiple presynaptic terminal-associated proteins in relation to retinal neurogenesis and differentiation. At birth (1PN), the Monodelphis retina was relatively undifferentiated morphologically and birthdating analysis revealed mitotically active cells throughout the retina. The 8PN retina was organized into two cellular layers: an outer region of mitotically active neuroepithelial cells and an inner region of postmitotic cells. The inner plexiform layer formed between 5PN and 10PN, and exhibited unique patterns of immunoreactivity with the antibodies used in this analysis. By 25PN the retina was well laminated, and synaptotagmin-, Rab3A-, synaptophysin- and SNAP-25-like immunoreactivities exhibited distinct and specific patterns within the plexiform layers, although they had not yet achieved their mature, adult patterns. These results indicate that each of these proteins exhibits developmentally regulated changes in its cellular localization, and therefore may play important roles during morphogenesis and synaptogenesis of the vertebrate retina.