摘要:

AbstractThe effect of postnatal age on phosphoinositide metabolismper seand on quisqualate‐stimulated phosphoinositide metabolism was characterized in synaptoneurosomes prepared from nine different regions of the rat nervous system, namely the brainstem, cerebellum, cerebral cortex, colliculi, hippocampus, hypothalamus, olfactory bulb, spinal cord and striatum. In the hippocampus, striatum, cerebellum, cerebral cortex, brainstem, colliculus and spinal cord, the basal levels of inositol phosphate (inositol‐1‐phosphate+inositol‐4,5‐bisphosphate) formation were maximal two days after birth and declined steeply to steady‐state levels from the age of 10 postnatal days. Similarly, in the olfactory bulb, basal inositol phosphate synthesis did not significantly change when measured during the period from postnatal day 10 to 42. The extent of [3H]‐inositol labelling of phosphoinositides as a function of age presented similar profiles when measured in hippocampal, striatal, cerebellar and cerebral cortical synaptoneurosomes, i.e. maximal at perinatal ages and minimal at adult ages. In the hypothalamus, [3H]‐inositol labelling of phosphoinositides showed an increase from postnatal day 12 to higher levels from postnatal days 14 to 18 subsequently followed by a dramatic increase from postnatal day 21 to 42. A similar developmental trend was also obtained for basal inositol phosphate synthesis.On the whole, four types of developmental profiles for quisqualate‐stimulated inositol phosphate formation (expressed as the percentage of the basal level and as the difference between stimulated and basal levels of radioactive inositol phosphates) were obtained depending on the nervous system region studied. In the early, prenatally developed nervous system regions, namely the brainstem and the spinal cord, no postnatal stimulation peaks of quisqualate‐induced inositol phosphate formation were recorded. This was also the case for the colliculi when the stimulation of IP formation was expressed as the difference in basal and stimulated levels of inositol phosphates. Secondly, in the olfactory bulb a region known to possess a continuous capacity for developmental plasticity both structurally and functionally during the first three weeks of postnatal development, a simultaneous sustained high level of quisqualate stimulation of phosphoinositide metabolism (fluctuating around 200% of the basal level) during the early postnatal period was evident. Thirdly, in regions of the central nervous system like the cerebellum, cerebral cortex, hippocampus and the striatum known to undergo intense developmental activity during the first two postnatal weeks, peaks of quisqualate‐stimulated phosphoinositide metabolism were initially detected around the first week after birth in each of these brain areas. Finally, in the hypothalamus where structurally unique postnatal developmental processes are known to take place, quisqualate‐induced inositol phosphate formation progressively increases with age to reach maxima at postnatal day 18. The transient increases in quisqualate responses in the cerebellum, hippocampus and striatum are probably specific to quisqualate since carbachol‐stimulated phosphoinositide metabolism yielded different age‐associated response patterns. Similar increases of carbachol‐ and quisqualate‐mediated phosphoinositide hydrolysis were on the other hand assayed in cerebral cortical and hypothalamic synaptoneurosomes. EC50, values for quisqualate (the quisqualate concentration required to produce 50% of the maximal effect) at postnatal days 6 and 10 were not significantly different in each of four types of synaptoneurosomes: cerebellar, cerebral cortical, hippocampal and striatal. On the basis of these latter results, it was deduced that the peak of quisqualate‐stimulated phosphoinositide metabolism does not materialize on the basis of changes in quisqualate metabotropic receptor affinity. In conclusion, the measurement of inositol phosphate formation in synaptoneurosomes prepared from different regions of the postnatally developing nervous system indicate that there is a temporal correlation between the increased activity of quisqualate‐stimulated phosphoinositide metabolism mediated by specific metabotropic glutamate receptors and region‐specific developmental events. This could suggest a key role for certain metabotropic glutamate receptors in the developmental plasticity of the nervous system.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90090-6

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractPolyamines and the key enzyme for their biosynthesis, ornithine decarboxylase (ODC) play an important role in the control of neuronal proliferation and differentiation. Exposure to agents that interfere with normal cell maturation is expected to result in alteration of neuronal ODC developmental pattern. We have administered to newborn rats, about 6 and 30 hr after birth, 20 mg/kg of methylazoxymethanol acetate (MAM), an agent able to selectively kill dividing cells and we have evaluated ODC activity and polyamine levels in the cerebellum and ODC activity in the olfactory bulbs at various developmental stages starting from postnatal day 4 (PD 4) until PD 28. Cerebellar weight decreased by 22–50% at the different developmental stages in MAM‐treated animals. A decline in ODC specific activity was observed at PD 4 and a decrease of putrescine levels at PD 4 and PD 6 in the cerebellum. At PD 10, however, both ODC activity and putrescine level were increased in MAM‐treated animals. Spermidine levels were never affected by the treatment, while spermine was significantly decreased at PD 6 and PD 8. These results demonstrate that altered ontogenetic patterns of ODC activity and polyamine levels are the consequence of disturbance of the normal process of brain maturation. No significant differences in specific ODC activity were noticed in the olfactory bulbs of MAM‐treated rats. This may be related to the more widespread time‐span of neurogenesis in this region, a fact that is also revealed by the higher ODC activity constitutively expressed at times in which neurogenesis has ended in the rest of the brain.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90091-4

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractOrnithine decarboxylase (ODC) is a growth‐associated enzyme which is critical for cell growth and transformation. ODC activity follows a specific ontogenetic pattern of activity in distinct brain regions according to their developmental stage. Perturbations in the pattern of ODC activity have been associated with brain damage including arrested cerebral growth. Modulations in the pattern of ODC activity were examined in the hippocampus, neocortex and cerebellum of neonatal rats (PND 3, 6, 9, 15) exposed via the dam to 0.2% lead‐acetate (Pb2+prenatally (gestational day 13 to birth), postnatally (PND 1–15) or perinatally (gestational day 13 to PND 15). Prenatal exposure to Pb2+perturbed the profile of ODC activity in all three brain regions examined, while postnatal exposure to Pb2+resulted in prolonged stimulations of ODC activity in the cerebellum. Following prenatal exposure, these effects were manifested as a stimulation of ODC activity in the hippocampus, a repression of activity in the neocortex and a combination of these effects in the cerebellum. Perinatal exposure to Pb2+transiently modulated the pattern of ODC activity similarly in all three brain regions, in a characteristic manner irrespective of their developmental stage. These Pb2+‐induced modulations of ODC activity suggest that polyamine‐dependent processes may play a significant role in the manifestation of Pb2+‐induced neurotoxicity dependent upon developmental factors at specific exposure periods.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90092-2

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe postnatal development of the ligand binding ton‐methyl‐d‐aspartate (NMDA), alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA), and kainate receptor sites was studied in individual layers of rat visual cortex with [3H]MK‐801, [3H]CNQX and [3H]kainate, respectively. The studies were performed by quantitative receptor autoradiography in the different visual cortical layers from normally raised rats and from monocularly deprived animals.In normally raised rats, in all visual cortical layers, [3H]MK‐801 and [3H]CNQX binding increased significantly from birth to around postnatal day 20, at which age already the adult values are reached. In contrast, the increase in [3H]kainate binding from day 1 to day 15 is followed by a significant decrease in binding sites up to day 25; at this age the adult binding level is nearly attained.Monocular deprivation, by unilateral eyelid suture at the age of 11 days onwards, leads to a transient decrease in [3H]CNQX binding in all visual cortical layers, whereas [3H]kainate binding results to a permanent decrease in AMPA receptor sites in cortical layers II to VI in both sides of the cortex. In contrast, only long‐term monocular deprivation until the age of 90 days resulted in decreased [3H]MK‐801 binding levels as compared to age‐matched controls. The data suggest that the laminar development of glutamate receptor subtypes is differentially affected by visual experience during early brain maturation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90093-0

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

Abstractω‐GVIA conotoxin has been used to mark presynaptic N‐type voltage sensitive calcium channels (VSCC).3,13,19,21–23Litzingeret al.9used ω‐conotoxin binding to describe a critical period of neurodevelopment in Swiss Webster mice between postnatal days (PND) 11 and 14, which appears to be important to the initiation of proper final development of the central nervous system. In this study, we compare how three different ω‐conotoxins (i.e. GVIA fromConus geographus, MVIIA fromConus magus, and RVIA fromConus radiatus) mark N‐type VSCC during this critical period in Swiss Webster mouse cortex.125I‐GVIA was bound to Swiss Webster mouse cortex synaptosomal membrane fractions at postnatal days 8 and 14.125I‐GVIA binding displacement curves were obtained by incubating membranes with increasing concentrations of unlabeled GVIA, MVIIA, and RVIA. Displacement curves and IC50were calculated for each of these three ω‐conotoxins, and then compared. At PND 14, GVIA, MVIIA and RVIA were able to displace greater than 95% of125I‐GVIA binding. At PND 8, however, MVIIA was only able to displace 83% of125I‐GVIA binding, and RVIA was only able to block 84%. The IC150does not appear to change significantly during this period of development for any of the ω‐conotoxins. The inability of MVIIA and RVIA to completely block125I‐GVIA binding in pre‐critical period Swiss Webster cortex denotes an alteration in the composition of N‐type VSCC binding sites. With this data, we have suggested the presence of subtypes of the N‐type VSCC in the cortex of pre‐critical period Swiss Webster mouse.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90094-9

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractIn cultures of neonatal rat brain cells, labeled with35S‐methionine in the presence or absence of triiodothyronine (T3), the hormone promoted a significant enhancement of labeled tubulin and actin in the insoluble fraction (30,000gpellet) of cell homogenate. To identify the specific sub‐cellular fraction associated with this induction, organ cultures of 1 day rat cerebra were labelled with35S‐methionine in the presence and absence of T3and the insoluble fraction (30,000gpellet) was subfractionated into mitochondria, plasma membrane and cytoskeleton. Analysis of the labeled proteins by SDS‐PAGE, autoradiography and densitometry revealed a T3‐induced increase of 50–80% for both tubulin and actin, only in the cytoskeleton fraction without any significant effect on the other fractions. Similar results were obtained when plasma membrane or cytoskeleton were isolated directly from labeled cerebrum by conventional methods instead of fractionating from the 30,000gpellet. Analysis of relative stimulation of labeled tubulin and actin by T3in cytoskeleton fraction derived from primary cultures of neuronal (N) and glial (G) cells labeled with35‐methionine show that the stimulatory effect is predominantly on the N cells. Studies on the kinetics of induction of labeled tubulin and actin by T3in the cytoskeleton fraction prepared from cerebra labeled with35S‐methionine for 2, 8 and 18 hrs revealed no significant difference at 2 hrs; at 8 hrs, an increased incorporation into both tubulin and actin was reproducibly seen in the controls relative to T3‐treated samples. However by 18 hrs, this pattern reversed and an enhanced accumulation of both labeled tubulin and actin was observed under the influence of T3. The mechanism of this apparently intriguing effect of T3on the kinetics of association of tubulin and actin with the cytoskeleton has been discussed in the light of the dual effect of the hormone on tubulin viz. enhancing its stability as well as rate of synthesis. The overall results indicate that the thyroid hormones play a major role in the cytoskeletal transport of tubulin and actin from their site of synthesis to that of assembly thus facilitating axodendritic outgrowth and morphological differentiation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90095-7

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractLeptomeningeal and skin fetal (E16‐17) fibroblasts were subculturedin vitroeither in DMEM/F12 basal medium (with or without 10% FCS) or in astroglial conditioned medium (ACM). Both populations were characteristically composed of flat, undifferentiated, fibronectin(+), GFAP(‐)cells where cultured in fetal serum supplemented basal media. When exposed to ACM leptomeningeal cells developed a population of thin, elongated, fibronectin(+) cells with radial type long processes while skin fibroblasts did not show significant changes in their characteristic morphotype. Exposure to db cAMP in basal medium resulted within 3 hr in their transformation to an astrocytic‐like morphotype characterized by a condensed soma and multiple, short processes. Twenty‐four hours later skin fibroblasts had returned to their flat appearance while leptomeningeal ones showed elongated, radial‐like forms. Results indicate the possible existence of different receptors (to ACM factors) and/or cytoskeletal properties, and suggest that ACM‐reactive fibroblasts of leptomeningeal origin represent a different cell type from those of skin origin. The hypothetical role of leptomeningeal cells during brain development is considered.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90096-5

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractNeonatal rats were exposed to parathion, an acetylcholinesterase inhibiting organophosphorus pesticide, during a rapid phase of cholinergic receptor development. Rats were given subcutaneous injections of 1.5 mg/kg/day from postnatal days 8–20. The immediate effects of subchronic developmental exposure were assessed in 21‐day‐old animals and more persistent effects assessed in 36‐day‐old animals. There was a 61% inhibition of acetylcholinesterase and a 27% decrease of muscarinic receptor density in 21‐day‐old treated rats. The reduction in receptor density was dose‐dependent and a significant correlation was found between the level of acetylcholinesterase inhibition produced by parathion and the reduction in receptor density. It was estimated that a minimum of at least 15% prolonged inhibition of forebrain acetylcholinesterase by parathion was necessary to reduce receptor density. Regional analyses of receptor autoradiograms of 21‐day‐old animals indicated muscarinic receptors in the cortex and hippocampus were preferentially lost. The anterior thalamus was notable in having a high density of cholinergic receptors which were unaffected by parathion treatment. No changes were found in the affinity of [3H]QNB for the receptor or in the binding of the agonist, acetylcholine, in competition binding studies. AChE activity and muscarinic receptor density returned to normal after a 16 day recovery period. Parathion treated animals were growth inhibited but, growth retardation induced by undernutrition did not alter receptor density or affinity of QNB for muscarinic receptors. Thus, the transient decrease in receptor density in parathion exposed animals was similar to the response previously observed in adults and was not secondary to growth retardation or undernutrition. Receptor densities and acetylcholinesterase levels were regulated back to normal values after a 16 day recovery period in spite of the perturbation of cholinergic function during cholinergic synapse and receptor development.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90097-3

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractTreatment with mevinolin, a competitive inhibitor of HMGCoAR, the key enzyme of isoprenoid metabolism, causes the arrest of proliferation and the differentiation of a neuroblastoma cell line (N18TG2). Mevalonate and high density lipoproteins partially restore growth.Cholesterol synthesis in the presence of mevinolin remains active, because in these cells the key enzyme HMG‐CoA reductase is not completely inhibited by this drug. The fact that cell growth is reduced, while cholesterogenesis remains active, suggests that mevinolin acts by interfering with the synthesis of some unknown compound, other than cholesterol, which is necessary for proliferation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90098-1

出版商:Wiley    

年代:2003

数据来源: WILEY

ISSN:0736-5748    

DOI:10.1016/0736-5748(94)90099-X

出版商:Wiley    

年代:2003

数据来源: WILEY