摘要:

AbstractThe postnatal development of benzodiazepine binding sites in the rat brain was studied by quantitative receptor autoradiography using [3H]flunitrazepam. The coupling of these sites to GABA receptors was assessed in 43 cerebral structures by examining the effects ofin vitroaddition of GABA on flunitrazepam specific binding. Benzodiazepine‐specific binding was relatively high at birth and exhibited an heterogeneous distribution pattern, anatomically different from the adult one. Data showed a sequential development of benzodiazepine receptors in relation to the time course of maturation of cerebral structures. A proliferation peak which paralleled rapid brain growth was noticed. High levels of benzodiazepine sites were transiently observed in some areas, e.g. thalamus and hypothalamus, and might be related to maturational events. In every brain structure examined, benzodiazepine binding sites were linked to GABA receptors. However, enhancement of flunitrazepam specific binding by exogenous GABA differed according to the structures studied and decreased during development, suggesting some changes in the control of GABA/benzodiazepine regulation during postnatal maturation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90052-N

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractWe have examined what effect the loss of spontaneous bioelectric activity has on neural network formation in organotypic rat neocortical explants grown under serum‐free culture conditions. Explants were taken from dorsal midline (presumptive visual) and lateral (presumptive auditory) occipital cortex and chronically exposed to tetrodotoxin which blocked all measurable bioelectric activity between change of medium. Extracellular recordings revealed complex, rhythmic spontaneous and evoked multiunit discharges in all explants examined (following tetrodotoxin washout in the experimental group). Control auditory explants had significantly more sites from which electric activity could be recorded compared with control visual explants. Auditory cultures showed no effect of the tetrodotoxin treatment, whereas visual explants showed significant increases over control values, equalling the auditory values. This increased level of spontaneous bioelectric activity was maintained for at least 10 days following transfer of the cultures to control growth medium. There was no significant difference between control visual and auditory explants regarding the number of sites from which evoked activity was seen. Nor did either cortex group show an effect of tetrodotoxin on the number of sites from which evoked activity was seen. The frequency with which spontaneous bioelectric discharges occurred per site increased with age in auditory vs visual cortex. These differences, however, were abolished in the tetrodotoxin‐treated groups. It was concluded that neocortical explants which have experienced chronic suppression of spontaneous electric activity did not suffer deficits in neural network formation, though there is an effect on the incidence and frequency with which such activity is given.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90053-O

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractCulture thickness, numerical density of neurons and neuronal survival were studied in timed series of control and tetrodotoxin‐silenced neocortical cultures to provide information on the role of bioelectric activity on neuronal development. In control cultures, culture thickness and number of surviving neurons decrease during the first weeksin vitro, but remain constant between 2 and 3 weeks indicating that the cultures are essentially mature. In the 4th weekin vitroa further decrease in surviving neurons was observed. In tetrodotoxin‐treated cultures the number of surviving neurons decreased significantly between 1 and 2 weeksin vitro, to remain constant thereafter. However, culture thickness significantly increased at 3 and 4 weeksin vitroafter an initial drop between 1 and 2 weeks. Compared to age‐matched controls at 2 and 3 weeksin vitro, only ca 50% of the neurons survived the loss of bioelectric activity. Similar differences were present between 1 and 2 weeks. Thus, the loss of all measurable bioelectric activity induces neuronal death in neocortical explants, but promotes neuropil formation by the surviving cells.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90054-P

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractChronic depolarization is inimical to neuronal growth and synaptogenesis so that spontaneous action potential generation appears to be required for the normal cytomorphological maturation of neocortical networks. The efficacy of 25 mM K in suppressing spontaneous bioelectric activity was monitored by extra‐ and intracellular recording from the explants. Intracellular recording from individual neurons showed that membrane potentials were reduced to ca −30 mV in potassium cultures but rapidly repolarized to ca −50 mV when returned to normal growth medium. Though action potentials could be readily evoked from these explants, spontaneous discharges and postsynaptic potentials were absent from potassium‐treated cultures. Both spontaneous bioelectric activity and postsynaptic potentials returned to the cultures by 5 days after returning the explants to normal growth medium. Extracellular recordings also showed that the explants were bioelectrically silent in the presence of 25 mM K or 25 mM K plus tetrodotoxin. In contrast to tetrodotoxin alone, bioelectric activity was absent when the cultures (with or without tetrodotoxin) were returned to normal growth medium. The explants gradually began to evince spontaneous bioelectric activity between 3 and 5 days after being returned to normal growth medium. Massive cell death induced by chronic exposure to tetrodotoxin was totally prevented by concomitant addition of 25 mM potassium, though these explants were significantly thinner than controls due to a large decrease in neuropil.We conclude that chronic depolarization of neonatal cortical explants by potassium results in a delayed return of spontaneous bioelectric discharges. Chronic depolarization results in a retardation of network formation in these explants apparently due to a lack of neurite and/or synapse formation. These effects are reversible with function returning to the explants over a period of several days.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90055-Q

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe developmental changes in the β‐adrenergic receptor/cyclic AMP generating system were examined using mouse cerebral cortical neurons in primary culture. During neuronal growthin vitro, the number of binding sites for [3H]dihydroalprenolol (DHA) showed a tendency to increase (Bmax), while the affinity (Kd) for [3H]DHA did not show any noticeable changes. Basal and isoproterenol‐stimulated adenylate cyclase activities as well as the activation of adenylate cyclase by 5′‐guanylylimidodiphosphate (GppNHp), NaF and forskolin showed progressive and parallel increases during neuronal growth on a polylysine‐coated surface. The treatment of primary cultured neurons with islet‐activating protein (IAP), one of the pertussis toxins, attenuated the inhibitory effect of carbachol, a muscarinic agonist, on isoproteronol‐induced activation of adenylate cyclase activity. These results indicate that primary cultured neurons possess a cyclic AMP generating system coupled with β‐adrenergic and muscarinic receptors, which is regulated via stimulatory and inhibitory GTP‐binding proteins, respectively. The results described above also suggest that the β‐adrenergic receptor, stimulatory and inhibitory types of GTP‐binding proteins and adenylate cyclase may develop in a parallel fashion during neuronal growth on a polylysine‐coated surface.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90056-R

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe clustering and level of nicotinic acetylcholine receptor (n‐AChR) in cultured mouse myotubes are negatively controlled by endogenous phospholipase A2(PLA2) (Kimuraet al., Int. J. Devl. Neurosci.5, 127–133, 1987). The effects of PLA2‐related metabolites, prostaglandins, leukotrienes and platelet‐activating factor (PAF) were investigated using fluorescein isothiocyanate‐α‐bungarotoxin. Peak and total fluorescence within a cluster were used as indices of clustering and level of n‐AChR, respectively. Prostaglandin E2(PGE2, 1–10 μm) decreased both indices in a concentration‐dependent manner. Aspirin and indomethacin, cyclooxygenase inhibitors, increased the indices at 1.0 μM and 10–30 nM, and decreased them at higher concentrations of 10–30 μM and 0.1–1 μM, respectively. Prostaglandin F2α(PGF2α, 1–10 μM), nordihydroguaiaretic acid (30 μM), a lipoxygenase inhibitor, and PAF (10 μM) had no effect. These results suggest that the control of endogenous PLA2on the clustering and level of n‐AChR is due to PGE2, but not to PGF2α, leukotrienes or PAF.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90057-S

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractGlutamate, aspartate, GABA, glycine and taurine levels have been measured in rat thalamus and in cerebral cortex at different time intervals (3rd, 7th, 15th, 30th day) after cerebellectomy. A decrease in glutamate, aspartate and GABA was detected at the 7th day after cerebellectomy in the thalamus and at the 15th day in the cerebral cortex; at the 30th day after cerebellectomy the levels of these amino acids in the thalamus and in the cerebral cortex were observed to have recovered to control values. No statistically significant difference in glycine and taurine levels in the thalamus and in the cerebral cortex after cerebellectomy could be seen. These results show that the functional recovery process after cerebellar injury is associated with a complex modification of amino acid levels in thalamus and in cerebral cortex.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90058-T

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractAbout half of the trochlear motor neurons die during the course of normal development. The present study was undertaken to determine whether the afferent synapses form before the onset of motor neuron death and also to determine whether the number of synapses differs between the healthy and degenerating trochlear motor neurons. Brains of duck embryos from days 10 to 20 were prepared for quantitative electron microscopical observations on synaptogenesis. Results indicate that synapses form on the trochlear motor neuron soma before cell death begins suggesting that afferent input is in a position to exert an influence on survival or death of motor neurons. There were no significant differences in the number of synapses between the healthy and dying neurons during the period of cell death. This observation suggests that the mechanism by which afferent synapses could be involved in neuron survival or death is not related to the number of synapses on the cell soma. The number of synapses on the cell process, synaptic transmission and/or molecules released at the synapses are likely candidates for the mechanism of action of afferent input.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90059-U

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThe influence of triiodothyronine (T3) on the level of tubulin and other proteins in primary cultures of neuronal (N) and glial (G) cells from rat brain has been investigated. Quantitation of tubulin by [3H]colchicine binding assay revealed that when cells from 1 day rat brain were cultured for 18 hr with physiological doses (0.5–5 nM) of T3, the hormone elicited 35–40% increase in the soluble (30,000gsupernatant) tubulin content of G cells only. This stimulation was age‐dependent and occurred neonatally at a time corresponding to the onset of synaptogenesis. In mouse and chick brain also, [3H]colchicine binding assay showed a similar selective stimulation of the soluble tubulin content of G cells by T3with virtually no effect on N cells. However, SDS‐polyacrylamide gel electrophoresis of the total proteins in the 30,000gsupernatants from N and C cells of rat brain, labeled for 18 hr with [14C]leucine in the presence of T3, revealed that T3elicited 2–3‐fold enhancement of radiolabeled tubulin in the N cells which is relatively greater than the 1.5‐fold increase seen in the G cells. Analysis of the autoradiograms of these labeled proteins also revealed that in addition to tubulin, T3stimulated the accumulation of radiolabeled actin by 1.5‐ and 2‐fold in N cells and G cells respectively. Similar electro‐phoretic analysis of the solubilized labeled proteins in the 30,000gpellets from N and G cells indicated that the failure to detect the stimulation of tubulin in the 30,000gsupernatants from N cells by [3H]colchicine binding assay could be at least partly due to rapid translocation of the dimeric soluble tubulin into insoluble membrane fractions or due to presence of higher oligometric forms of tubulin which are insensitive to [3H]colchicine binding assay.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90060-Y

出版商:Wiley    

年代:2003

数据来源: WILEY

摘要:

AbstractThis study examined the morphology and the development of inward currents in the course of differentiation of a stem cell toward a neuronal phenotype. Using the P19 embryonal cell line, whole‐cell current profiles of P19 cells before, during and after retinoic acid‐induced differentiation were matched with their morphology as well as with the expression of neuron‐specific enolase‐like immunoreactivity. Prior to and during the initial 48 hr of retinoic acid treatment, P19 cells either lacked detectable currents or expressed a voltage‐dependent outward potassium current, did not display neuron‐like morphology and did not express neuron‐specific enolase‐like immunoreactivity. Upon completion of retinoic acid treatment, the current profile of fully differentiated P19 cells was hallmarked by a large voltage‐dependent inward current which consisted of a sodium current and a smaller cobalt‐sensitive calcium component, in addition to the potassium current observed earlier. Such cells invariably emitted neuntes and displayed neuron‐specific enolase‐like immunoreactivity. Interestingly, coupling was prevalent among P19 cells in the undifferentiated state but was absent in the fully differentiated cultures. In studying cells undergoing neuronal differentiation, these results underscore the importance of taking into account both electrical properties and morphological considerations in determining the degree of differentiation.

ISSN:0736-5748    

DOI:10.1016/0736-5748(91)90061-P

出版商:Wiley    

年代:2003

数据来源: WILEY