摘要:

AbstractBarbiturates are allosteric modulators of the CNS GABAAreceptor, increasing [3H]‐GABA binding to its receptor sites. In the present work we have studied the modulatory effect of the barbiturate pentobarbital on low‐affinity GABA binding sites during ontogenetic development of the chick optic lobe. Our results indicate that [3H]‐GABA binding enhancement by pentobarbital shows a differential profile during development, following a two‐component enhancement model at early stages of development and a single‐component enhancement model in the adult stage. Kinetic analysis performed at different stages of development showed that barbiturate enhancement was invariably due to an increase in [3H]‐GABA binding affinity, while maximal binding capacity remained unchanged. Using GABA antagonists, picrotoxinin and bicuculline, convulsant sensitivity of high‐affinity barbiturate modulatory sites was found at early stages.These data suggest that barbiturate action displays receptor heterogeneity during development, with high‐ and low‐affinity modulatory sites only at early stages, while the high‐affinity sites disappear between hatching and adulthood. Kinetic data indicate that both barbiturate modulatory sites are coupled to the GABAAreceptor at early stages. The presence of high‐affinity modulatory sites at early stages and at hatching suggests a major role during visual pathway maturation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00080-1

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractThe developing noradrenaline‐containing (NA‐C) sympathetic nerves of the rat uterus were analyzed following acute and chronic treatment with oestrogen. Histochemical methods were used in association with nerve density measurements and biochemical assays. For comparative purposes, noradrenaline (NA) levels were measured in the urinary bladder and right auricle following chronic oestrogen treatment. Acute treatment was performed by s.c. administration of a single dose of 40 μg oestradiol cypionate on the 25th day of age. Chronic treatment consisted of four doses of 10 μg oestradiol on days 10, 15, 20 and 25 of postnatal development. Both acute‐ and chronic‐treated animals were killed at 28 days of age. The main biochemical findings were the following: (a) both acute and chronic oestrogen treatment increased the weight of the uterine horn, parametrial tissue and uterine cervix; (b) in the uterine horn, the total content of NA was reduced following both oestrogen treatments. However, the degree of reduction was greater after chronic treatment; (c) in the parametrial tissue, the NA levels were reduced only after chronic treatment; (d) in the cervix, the NA total content was increased after both treatments; (e) in the urinary bladder, there was a parallel increase between organ growth and NA content following chronic oestrogen treatment; (e) in the auricle neither the tissue weight nor the total content of NA were changed by chronic estrogen treatment.Histochemical studies showed that: (a) acute treatment with one single dose of oestradiol, provoked a marked reduction in the density of NA‐C nerves associated with the myometrial and parametrial smooth muscle, without affecting the innervation of blood vessels; (b) following chronic treatment, the only fibers we were able to recognize were those associated with blood vessels. These fibers were thinner and less intensely fluorescent than in controls. Results are interpreted considering the differential sensitivity of uterine nerves to sex hormones. A possible involvement of oestrogen in changes of noradrenergic innervation of the uterus following puberty is discussed.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00079-8

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractOrganotypic transverse medullary slices (obex level) from six‐day‐old rats, cultured for two to four weeks in chemically defined medium contained rhythmically discharging neurones which were activated by CO2and H+. The mechanisms underlying this rhythmicity and the spread of excitation and synaptic transmission within this organotypic tissue were examined by modifying the composition of the external solution. Our findings showed that (1) Exposure to tetrodotoxin (0.2 μM) or to high magnesium (6 mM) and low calcium (0.2 mM) concentrations abolished periodic activity. (2) Neither the blockade of GABAergic potentials with bicuculline methiodide (200 μM) and/or hydroxysaclofen (200 μM) nor the blockade of glycinergic potentials with strychnine hydrochloride (100 μM) abolished rhythmicity. (3) While atropine sulphate (5 μM) was ineffective in modulating periodic discharges nicotine (100 μM) — like CO2— shortened the intervals between the periodic events; hexamethonium (50–100 μM) reduced both periodic and aperiodic activity. (4) Exposure to the NMDA antagonist 2‐aminophosphonovaleric acid (50 μM) suppressed periodic events only transiently. In the presence of 2‐aminophosphonovaleric acid rhythmicity recovered. However, the AMPA‐antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (10–50 μM), abolished periodic activity reversibly within less than 5 min. When 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione and nicotine were administered simultaneously periodic events persisted for up to 10 min. These findings indicate that synaptic excitatory drive is a prerequisite for the generation of rhythmic discharges of medullary neurones in this preparation. This drive may activate voltage‐dependent channels or it may facilitate endogenous cellular mechanisms which initiate oscillations of intracellular calcium concentration. To test the latter possibility (5) calcium antagonists were added to the bath saline. The organic calcium antagonists verapamil and flunarizine (50–100 μM each) and the inorganic calcium antagonists cobalt (2 mM) and magnesium (6 mM) suppressed periodic activity and abolished or weakened the chemosensitivity towards CO2/acidosis. (6) Dantrolene (10 μM), an inhibitor of intracellular calcium release decreased the periodicity, while thapsigargin (2 μM) which blocks endoplasmic Ca2+‐ATPase, transiently accelerated the occurrence of periodic events. (7) Oscillations of intracellular free calcium concentrations in Fura‐2 AM‐loaded cells were weakened or abolished by cobalt (2 mM). The results of (5)–(7) indicate that transmembrane calcium fluxes as well as intracellular Ca2+‐release and ‐clearance mechanisms are a prerequisite for intracellular free calcium oscillations which may be important in the generation of rhythmic discharges in medullary neurones.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00081-X

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractIt has been proposed that neurodegenerative processes of aging are associated with the generation of reactive oxygen species (ROS) during cellular metabolism. These reactive oxygen species are scavenged by antioxidant enzymes in biological systems. The present study was designed to determine the selective distribution of the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase activity and reduced glutathione (GSH) levels in different regions of the C57BL/6N mouse brain and to determine if any alterations occurred with age. Catalase activity did not show any significant change except in cerebellum. Activity of superoxide dismutase was increased with age in all regions of the brain except in hippocampus of 2‐yr‐old mice. The glutathione peroxidase activity in the caudate nucleus increased in all regions of the brain, however, the activity did not change at one, six and 12 months. A significant increasing pattern of glutathione content was found in the cerebellum and brain stem with age. These data demonstrate that although the level of antioxidant enzymes varied in different regions of the brain, overall the enzyme activities tend to increase with age.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00071-2

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractThe inductive signals for the differentiation of motor neurons in the spinal cord have been experimentally shown to arise from cells in the midventral region of the neural tube, often referred to as the floor plate, and from the notochord. Although the prevailing view is that a similar mechanism accounts for the differentiation of motor neurons in the brain stem, supporting experimental evidence is lacking. Here, using the formation of the trochlear nucleus in the midbrain of duck embryos as a model system, we report that the floor plate and the notochord are not necessary for the development of these motor neurons in the brain stem. Early damage to the floor plate or extirpation of the floor plate and notochord does not prevent the development of these cranial motor neurons. Thus, either the inductive signals for the formation of these cranial motor neurons arise from some other structure or the germinal epithelium of the cranial neural tube is intrinsically programmed to form specific cranial motor nuclei.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00077-1

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractPrevious biochemical and histochemical studies have suggested that catechol‐O‐methyltransferase (COMT) is a predominantly glial enzyme in the brain. The aim of this work was to study its localization and molecular forms in primary cultures, where cell types can be easily distinguished with specific markers. COMT immunoreactivity was studied in primary astrocytic cultures from newborn rat cerebral cortex, and in neuronal cultures from rat brain from 18‐day‐old rat embryos using antisera against rat recombinant COMT made in guinea pig. Double‐staining studies with specific cell markers to distinguish astrocytes, neurons and oligodendrocytes were performed. COMT immunoreactivity colocalized with a specific oligodendrocyte marker galactocerebroside in cells displaying oligodendrocyte morphology, flat cells displaying type‐1 astrocyte morphology and glial fibrillary acidic protein, in branched cells displaying type‐2 astrocyte morphology and in cell bodies of neurons, the processes of which displayed neurofilament immunoreactivity. Western blots detected both soluble 24 kDa and membrane‐bound 28‐kDa COMT proteins in neuronal and astrocyte cultures. The results suggest that COMT is synthesized by cultured astrocytes, oligodendrocytes and neurons.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00070-4

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractThis paper describes the development of the serotonergic innervation of the chick tectum opticum as revealed by an immunohistochemical methodology. The development of this innervation was previously described simply as the formation of an irregular network of serotonergic fibers that gradually invades the organ and increases in density.Our results show that the developmental pattern of serotonergic innervation differs significantly through the distinct tectal layers and that it progresses through a characteristic temporospatial pattern related to the lamination process. These findings support the idea that the concept of laminar segregation can be applied to describe the development of the serotonergic innervation. On the other hand, it is clear that the existence of a typical ordered developmental pattern of innervation makes it possible to detect embryonic or post‐hatching alterations. Thus, the tectal serotonergic innervation could be used as a suitable model to investigate possible plastic changes in experimental conditions.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00068-2

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractSeveral ontogenetic studies have been devoted to the structural organization of the developing tectum opticum. They disagree in many respects because they are based on histological preparations performed with differently oriented planes of section. According to our results the differences found in the literature mainly result from the fact that the developmental gradient axis undergoes remarkable positional changes with respect to both optic lobe and neural tube longitudinal anatomical axes during the early stages of development. The present work is a dynamic description of the tectum opticum lamination based on sections coinciding with the developmental gradient. Since this latter displays a curved disposition, several slightly modified planes of section had to be used to obtain a complete picture along the developmental gradient.The development of the tectal architecture proceeds from a relatively simple organization through increasingly complex multilaminated patterns. A dynamic interpretation of successive images of a particular region observed at increasing developmental stages or of images observed at a particular stage along the entire length of the developmental gradient axis, allows us to propose that embryonic laminae are only transient spatial arrangements of cells actively migrating from the sites where they were generated to those where they will definitively reside. These considerations led us to define a nomenclature that establishes clear correlations between the early transient organizations and the definitive one of the fully developed optic tectum. This type of nomenclature could be usefully applied to describe dynamically the development of structures displaying multilaminated patterns such as other cortical zones of the central nervous system.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00069-0

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractThe present study was undertaken to investigate the involvement of NCAM in the neuroteratogenic effects of ethanol demonstrated by us and others. In the first experiment we examined the effect ofin‐ovoethanol exposure on expression of NCAM in various regions of the embryonic CNS throughout development. Chick embryos received ethanol (10 mg/50 μl/day) or saline (control) at days 1–3 of development (E1–E3), were sacrificed at various embryonic ages and whole brain (WB), cerebral hemispheres (CH) and cerebellum (CE) processed for SDS‐polyacrylamide gel electrophoresis. The normal developmental profile of NCAM in the chick brain exhibited the same dynamics as previously reported by others. When compared to age‐matched control brains, an increase was observed in expression of high molecular weight forms of NCAM in cerebral hemispheres between E8 and E10. These bands represented highly sialated (>180 kDa) forms of NCAM. In fact, the NCAM band from ethanol‐treated embryos at E8 migrated at a higher molecular weight than did its control counterpart, indicating an increase in sialic acid content. In contrast, no clear change was observed in NCAM expression in cerebellum from E10 through E20 as a result of ethanol exposure. In the second experiment, we examined the involvement of NCAM in the alterations in neuronal growth patterns observed in ethanol‐exposed cultures. Neuroblast‐enriched cultures derived from three‐day‐old whole chick embryos (E3WE) were maintained on poly‐l‐lysine pre‐coated Petri dishes in DMEM + 5% fetal bovine serum with or without 50 mM ethanol. Cultures were fixed at 3, 6 or 9 DIV and co‐stained for NCAM and neurofilament (160 kDa). E3WE cultures exhibited intense NCAM immunoreactivity at 3 and 6 DIV decreasing by 9 DIV. NCAM positive structures included all neuronal perikarya, neuritic processes and growth cones. Addition of 50 mM ethanol to the medium resulted in profound alterations in growth patterns of developing neurons which continued to exhibit intense NCAM staining. Ethanol‐induced changes in the developmental profile of NCAM expression (i.e. increased sialation) in cerebral hemispheres correspond temporally with the shift in neuronal phenotype from cholinergic to catecholaminergic and GABAergic which we have reported previously. Changes in the normal pattern of cellular contact and interaction as a result of altered NCAM expression may influence establishment of neurotransmitter phenotype. Findings from this study support the view that NCAM may be involved both directly and indirectly in shaping of the CNS during development and we speculate that ethanol neuroembryotoxicity uncouples this relationship.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00065-8

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractProgrammed cell death is a basic cellular process that has aroused much interest in recent years. Like immune cells, cultures of cerebellar granule neurons are very homogeneous and provide a unique opportunity for quantifying by flow cytometry one form of programmed cell death in the CNS, the apoptosis, and for studying its regulation by neurotrophic factors. We found that thyroid hormone promoted postmitotic survival by preventing the apoptosis of newly formed and early differentiated granule neurons in a dose‐dependent manner. This regulation could be through the protein bcl‐2, which is known to prevent cell death. This protein was present at all stages of granule neuron differentiation and appeared to be developmentally regulated. It was underexpressed in apoptotic granule neurons. The protein content of the cerebellum in hypothyroid rats was drastically reduced. In contrast, thyroid hormone caused a marked dose‐dependent increase in the amounts of this protein in granule neuron cultures. The possibility that thyroid hormone may be directly or indirectly required to promote cell survival is discussed, in terms of the hormone control of the local delivery of neurotrophins, such as NGF and NT‐3, as well as the expression of their low affinity receptors, gp75. We suggest that thyroid hormone has a permissive action on the developing CNS.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00057-7

出版商:Wiley    

年代:1999

数据来源: WILEY