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Postnatal Maturation (postnatal + maturation)
Selected AbstractsPostnatal maturation of Na+, K+, 2Cl, cotransporter expression and inhibitory synaptogenesis in the rat hippocampus: an immunocytochemical analysisEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002Serge Marty Abstract GABA, a major inhibitory neurotransmitter, depolarizes hippocampal pyramidal neurons during the first postnatal week. These depolarizations result from an efflux of Cl, through GABAA -gated anion channels. The outward Cl, gradient that provides the driving force for Cl, efflux might be generated and maintained by the Na+, K+, 2Cl, cotransporter (NKCC) that keeps intracellular Cl, concentration above electrochemical equilibrium. The developmental pattern of expression of the cotransporter in the hippocampus is not known. We studied the postnatal distribution pattern of NKCC in the hippocampus using a monoclonal antibody (T4) against a conserved epitope in the C-terminus of the cotransporter molecule. We also examined the temporal relationships between the developmental pattern of NKCC expression and the formation of perisomatic GABAergic synapses. This study was aimed at determining, with antivesicular inhibitory amino acid transporter (VIAAT) antibodies, whether perisomatic GABAergic synapses are formed preferentially at the time when GABA is depolarizing. During the first postnatal week, NKCC immunolabelling was restricted to cell bodies in the pyramidal cell layer and in the strata oriens and radiatum. In contrast, at postnatal day 21 (P21) and in adult animals little or no labelling occurred in cell bodies; instead, a prominent dendritic labelling appeared in both pyramidal and nonpyramidal neurons. The ultrastructural immunogold study in P21 rat hippocampi corroborated the light-microscopy results. In addition, this study revealed that a portion of the silver-intensified colloidal gold particles were located on neuronal plasmalemma, as expected for a functional cotransporter. The formation of inhibitory synapses on perikarya of the pyramidal cell layer was a late process. The density of VIAAT-immunoreactive puncta in the stratum pyramidale at P21 reached four times the P7 value in CA3, and six times the P7 value in CA1. Electron microscopy revealed that the number of synapses per neuronal perikaryal profile in the stratum pyramidale of the CA3 area at P21 was three times higher than at P7, even if a concomitant 20% increase in the area of these neuronal perikaryal profiles occurred. It is concluded that, in hippocampal pyramidal cells, there is a developmental shift in the NKCC localization from a predominantly somatic to a predominantly dendritic location. The presence of NKCC during the first postnatal week is consistent with the hypothesis that this transporter might be involved in the depolarizing effects of GABA. The depolarizing effects of GABA may not be required for the establishment of the majority of GABAergic synapses in the stratum pyramidale, because their number increases after the first postnatal week, when GABA action becomes hyperpolarizing. [source] Postnatal maturation of GABAA and GABAC receptor function in the mammalian superior colliculusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2001Mathias Boller Abstract In the stratum griseum superficiale (SGS) of the mammalian superior colliculus, GABAC receptors seem to control the excitability of projection neurons by selective inactivation of local GABAergic interneurons. As the onset of visual responses to SC begins well after birth in the rat, it is possible to study developmental changes in GABAergic mechanisms that are linked to the onset of visual information processing. In order to analyse postnatal changes in inhibitory mechanisms that involve GABA receptor function, we used extracellular field potential (FP) recordings and single cell patch-clamp techniques in slices from postnatal day 4 (P4) to P32 and examined the effects of GABA and muscimol on electrically evoked SGS cell activity. While GABAA receptor activation affected FP amplitudes throughout postnatal development, GABAC receptor activation did not significantly change FP amplitudes until the third postnatal week. Results from patch-clamping single cells, however, clearly demonstrate that GABAC receptors are already functional at P4 , similar to GABAA receptors. Throughout postnatal development, activation of GABAC receptors leads to a strong inhibition of inhibitory postsynaptic activity, indicating that GABAC receptors are expressed by inhibitory interneurons. Furthermore, the proportion of neurons that show decreased excitatory postsynaptic activity during GABAC receptor activation correlates with the proportion of GABAergic interneurons in SGS. Our patch-clamp results indicate that the functional expression of GABAC receptors by GABAergic interneurons does not change significantly during postnatal development. However, our measurements of FP amplitudes indicate that the maturation of the efferent connections of these GABAergic neurons within SGS during the third postnatal week strongly changes GABAC receptor function. [source] Developmental changes in the BDNF-induced modulation of inhibitory synaptic transmission in the Kölliker,Fuse nucleus of ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2007Miriam Kron Abstract The Kölliker,Fuse nucleus (KF), part of the pontine respiratory group, is involved in the control of respiratory phase duration, and receives both excitatory and inhibitory afferent input from various other brain regions. There is evidence for developmental changes in the modulation of excitatory inputs to the KF by the neurotrophin brain-derived neurotrophic factor (BDNF). In the present study we investigated if BDNF exerts developmental effects on inhibitory synaptic transmission in the KF. Recordings of inhibitory postsynaptic currents (IPSCs) in KF neurons in a pontine slice preparation revealed general developmental changes. Recording of spontaneous and evoked IPSCs (sIPSCs, eIPSCS) revealed that neonatally the ,-aminobutyric acid (GABA)ergic fraction of IPSCs was predominant, while in later developmental stages glycinergic neurotransmission significantly increased. Bath-application of BDNF significantly reduced sIPSC frequency in all developmental stages, while BDNF-mediated modulation on eIPSCs showed developmental differences. The eIPSCs mean amplitude was uniformly and significantly reduced following BDNF application only in neurons from rats younger than postnatal day 10. At later postnatal stages the response pattern became heterogeneous, and both augmentations and reductions of eIPSC amplitudes occurred. All BDNF effects on eIPSCs and sIPSCs were reversed with the tyrosine kinase receptor-B inhibitor K252a. We conclude that developmental changes in inhibitory neurotransmission, including the BDNF-mediated modulation of eIPSCs, relate to the postnatal maturation of the KF. The changes in BDNF-mediated modulation of IPSCs in the KF may have strong implications for developmental changes in synaptic plasticity and the adaptation of the breathing pattern to afferent inputs. [source] Proliferative responses to growth factors decline rapidly during postnatal maturation of mammalian hair cell epitheliaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2007Rende Gu Abstract Millions of lives are affected by hearing and balance deficits that arise as a consequence of sensory hair cell loss. Those deficits affect mammals permanently, but hearing and balance recover in nonmammals after epithelial supporting cells divide and produce replacement hair cells. Hair cells are not effectively replaced in mammals, but balance epithelia cultured from the ears of rodents and adult humans can respond to hair cell loss with low levels of supporting cell proliferation. We have sought to stimulate vestibular proliferation; and we report here that treatment with glial growth factor 2 (rhGGF2) yields a 20-fold increase in cell proliferation within sheets of pure utricular hair cell epithelium explanted from adult rats into long-term culture. In epithelia from neonates, substantially greater proliferation responses are evoked by rhGGF2 alone, insulin alone and to a lesser degree by serum even during short-term cultures, but all these responses progressively decline during the first 2 weeks of postnatal maturation. Thus, sheets of utricular epithelium from newborn rats average >,40% labelling when cultured for 72 h with bromo-deoxyuridine (BrdU) and either rhGGF2 or insulin. Those from 5- and 6-day-olds average 8,15%, 12-day-olds average <,1% and after 72 h there is little or no labelling in epithelia from 27- and 35-day-olds. These cells are the mammalian counterparts of the progenitors that produce replacement hair cells in nonmammals, so the postnatal quiescence described here is likely to be responsible for at least part of the mammalian ear's unique vulnerability to permanent sensory deficits. [source] Descending respiratory polysynaptic inputs to cervical and thoracic motoneurons diminish during early postnatal maturation in rat spinal cordEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2005Laurent Juvin Abstract Isolated brainstem-spinal cord preparations were used to explore the coexistence of a direct and an indirect descending drive from the brainstem respiratory centre to cervical and thoracic respiratory motoneurons in the neonatal Sprague,Dawley rat. Polysynaptic spinal relay pathways from the respiratory centre were suppressed by selectively perfusing the cord with mephenesin (1 mm) or a solution enriched with Ca2+ and Mg2+. At birth, both direct and spinally relayed pathways are functional and contribute equally to the global descending respiratory drive. However, during the first postnatal week, significant maturational changes appear in the way the respiratory centre controls its target respiratory motoneurons in the cervical and thoracic spinal cord, with the direct respiratory drive becoming progressively predominant with maturation (from 50% to around 75% of the global descending command). The relative contributions of the monosynaptic and the polysynaptic spinal pathways may therefore have important implications for effective respiratory control during early postnatal development. [source] Modulation of systemic and renal haemodynamics by ,-opioids in conscious lambsEXPERIMENTAL PHYSIOLOGY, Issue 5 2006Wei Qi The purpose of the present study was to determine the cardiovascular effects of the ,-opioid receptor agonist U-50488H at two stages of postnatal maturation under physiological conditions. Experiments were carried out firstly to define systemic and renal haemodynamic responses to ,-opioid receptor activation and, secondly, to determine whether these effects are altered during postnatal maturation. To investigate whether the responses to U-50488H resulted from receptor-dependent effects, responses to U-50488H were also tested in the presence of the specific ,-opioid receptor antagonist 5,-guanidinonaltrindole (GNTI). Experiments were carried out in two groups of conscious, chronically instrumented lambs aged ,1 and ,6 weeks. Mean arterial pressure, mean venous pressure and renal blood flow (RBF) were measured for 30 min before and 90 min after i.v. injection of U-50488H or vehicle. Heart rate increased in both age groups of lambs within 10 min of U-50488H administration. Mean arterial pressure decreased for 50 min following U-50488H administration at 1 week but, in contrast, increased transiently at 10 min in 6-week-old lambs, returning to control levels by 20 min. In both age groups, there was a sustained decrease in RBF following U-50488H. The aforementioned responses to U-50488H were abolished by pretreatment with GNTI. These data provide the first measurements of systemic and renal haemodynamic responses to ,-opioid receptor activation during postnatal maturation. [source] Late postnatal maturation of excitatory synaptic transmission permits adult-like expression of hippocampal-dependent behaviorsHIPPOCAMPUS, Issue 5 2005Theodore C. Dumas Abstract Sensorimotor systems in altricial animals mature incrementally during early postnatal development, with complex cognitive abilities developing late. Of prominence are cognitive processes that depend on an intact hippocampus, such as contextual,configural learning, allocentric and idiocentric navigation, and certain forms of trace conditioning. The mechanisms that regulate the delayed maturation of the hippocampus are not well understood. However, there is support for the idea that these behaviors come "on line" with the final maturation of excitatory synaptic transmission. First, by providing a timeline for the first behavioral expression of various forms of learning and memory, this study illustrates the late maturation of hippocampal-dependent cognitive abilities. Then, functional development of the hippocampus is reviewed to establish the temporal relationship between maturation of excitatory synaptic transmission and the behavioral evidence of adult-like hippocampal processing. These data suggest that, in rats, mechanisms necessary for the expression of adult-like synaptic plasticity become available at around 2 postnatal weeks of age. However, presynaptic plasticity mechanisms, likely necessary for refinement of the hippocampal network, predominate and impede information processing until the third postnatal week. © 2005 Wiley-Liss, Inc. [source] Postnatal downregulation of inhibitory neuromuscular transmission to the longitudinal muscle of the guinea pig ileumNEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2009X. Bian Abstract, Neuromuscular transmission is crucial for normal gut motility but little is known about its postnatal maturation. This study investigated excitatory/inhibitory neuromuscular transmission in vitro using ileal nerve-muscle preparations made from neonatal (,48 h postnatal) and adult (,4 months postnatal) guinea pigs. In tissues from neonates and adults, nicotine (0.3,30 ,mol L,1) contracted longitudinal muscle preparations in a tetrodotoxin (TTX) (0.3 ,mol L,1)-sensitive manner. The muscarinic receptor antagonist, scopolamine (1 ,mol L,1), reduced substantially nicotine-induced contractions in neonatal tissues but not adult tissues. In the presence of N, -nitro- l -arginine (NLA, 100 ,mol L,1) to block nitric oxide (NO) mediated inhibitory neuromuscular transmission, scopolamine-resistant nicotine-induced contractions were revealed in neonatal tissues. NLA enhanced the nicotine-induced contractions in neonatal but not in adult tissues. Electrical field stimulation (20 V; 0.3 ms; 5,25 Hz, scopolamine 1 ,mol L,1 present) caused NLA and TTX-sensitive longitudinal muscle relaxations. Frequency,response curves in neonatal tissues were left-shifted compared with those obtained in adult tissues. Immunohistochemical studies revealed that NO synthase (NOS)-immunoreactivity (ir) was present in nerve fibres supplying the longitudinal muscle in neonatal and adult tissues. However, quantitative studies demonstrated that fluorescence intensity of NOS-ir nerve fibres was higher in neonatal than adult tissues. Nerve fibres containing substance P were abundant in longitudinal muscle in adult but not in neonatal tissues. Inhibitory neuromuscular transmission is relatively more effective in the neonatal guinea pig small intestine. Delayed maturation of excitatory motor pathways might contribute to paediatric motility disturbances. [source] Expression pattern of calcitonin gene-related peptide in the superior colliculus during postnatal development: Demonstration of its intrinsic nature and possible rolesTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 5 2006Inmaculada Gerrikagoitia Abstract Calcitonin gene-related peptide (CGRP) is a widespread neuropeptide with multiple central and peripheral targets. In an analysis on the expression of this peptide throughout the rat brain during postnatal development, we observed a discrepancy between results obtained by immunohistochemistry and by in situ hybridization. In the superior colliculus (SC), only the immunohistochemical signal could be detected (Terrado et al. [1997] Neuroscience 80:951,970). Here we focus our attention on this structure because the temporal pattern of CGRP immunoreactivity observed in the SC suggested the participation of this peptide in the postnatal maturation of the SC. In the present study, we describe in detail the postnatal development of collicular CGRP-immunoreactive structures and their spatiotemporal relationship with cholinergic modules and definitively demonstrate the local expression of CGRP in the SC. CGRP-immunopositive axons and neurons were distributed within the most ventral part of superficial strata and in the intermediate strata of the SC, showing a peak in staining intensity and density at the end of the first postnatal week. At P14, CGRPergic terminal fibers are arranged in small, clearly defined patches in a complementary manner with respect to the cholinergic modules, which start forming at this stage. By using Western blot and RT-PCR analyses, and by means of injections of antisense oligonucleotides, both the presence of CGRP peptide in the SC and the local expression of ,-CGRP transcripts in collicular neurons were demonstrated. A possible role of CGRP is discussed in the context of postnatal modular compartmentalization of collicular afferents. J. Comp. Neurol. 494:721,737, 2006. © 2005 Wiley-Liss, Inc. [source] Impaired development of hippocampal mossy fibre synapses in mouse mutants for the presynaptic scaffold protein BassoonTHE JOURNAL OF PHYSIOLOGY, Issue 12 2010Frederic Lanore Bassoon, a protein highly concentrated at the synaptic active zone, is thought to participate in the organization of the cytomatrix at the site of neurotransmitter release. Bassoon is amongst the first proteins to accumulate at newly formed synaptic junctions, raising the question of the functional role of this protein in the early stages of synaptic development. Here we show that the course of synaptic maturation of hippocampal mossy fibre (MF) synapses (glutamatergic synapses with multiple release sites) is markedly altered during the first 2 weeks of postnatal development in mutant mice lacking the central region of Bassoon (Bsn,/, mice). At postnatal day 7 (P7), Bsn,/, mice display large amplitude MF-EPSCs with decreased paired pulse ratios, an abnormality which may be linked to deficits in the organization of the presynaptic active zone. Surprisingly, 1 week later, decreased MF-EPSCs amplitude is observed in Bsn,/, mice, consistent with the inactivation of a subset of synaptic release sites. Finally, at more mature states a decreased posttetanic potentiation is observed at MF-synapses. These results support the notion that Bassoon is important for organizing the presynaptic active zone during the postnatal maturation of glutamatergic synapses. [source] | ||||||||||||||||||||||