H3 and H4 Lysine Acetylation Correlates with Developmental and Experimentally Induced Adult Experience-Dependent Plasticity in the Mouse Visual Cortex.

Histone posttranslational modifications play a fundamental role in orchestrating gene expression. In this work, we analyzed the acetylation of H3 and H4 histones (AcH3-AcH4) and its modulation by visual experience in the mouse visual cortex (VC) during normal development and in two experimental conditions that restore juvenile-like plasticity levels in adults (fluoxetine treatment and enriched environment). We found that AcH3-AcH4 declines with age and is upregulated by treatments restoring plasticity in the adult. We also found that visual experience modulates AcH3-AcH4 in young and adult plasticity-restored mice but not in untreated ones. Finally, we showed that the transporter vGAT is downregulated in adult plasticity-restored models. In summary, we identified a dynamic regulation of AcH3-AcH4, which is associated with high plasticity levels and enhanced by visual experience. These data, along with recent ones, indicate H3-H4 acetylation as a central hub in the control of experience-dependent plasticity in the VC.

Neurotoxicity of cadmium on immature hippocampus and a neuroprotective role for p38 MAPK.

The developing brain is very sensitive to damage by toxic agents, many of which only manifest in adulthood. Cadmium [Cd(II)] is an environmental pollutant which is widely used in industry and is a constituent of tobacco smoke. Exposure to Cd(II) has been linked to detrimental effects on mammalian cells including neural cells. We have investigated the action of Cd(II) on immature hippocampus by assessing cell viability and modulation of AKT/PKB and mitogen-activated protein kinase (MAPK) family members including extracellular signal-regulated kinase (ERK)-1/2, p38 MAPK and c-Jun N-terminal kinases (JNK). Hippocampal slices from immature rats (postnatal day 14; PN14) were incubated with Cd(II) (5-200 microM) for 3h and the effects on protein phosphorylation were analyzed by western blotting. Phosphorylation of p38(MAPK) was enhanced by Cd(II) at all doses tested. Cd(II) also stimulated the phosphorylation of ERK1/2 in a concentration-dependent manner. However, the phosphorylation of JNK and AKT was not altered by the metal. Moreover, Cd(II) reduced cell viability, as measured by MTT reduction. Inhibition of p38 MAPK by SB203580 aggravated the acute Cd(II)-induced impairment of cell viability, whereas inhibition of MEK by PD98059 did not alter the effects of Cd(II). The present data suggest that in immature hippocampal cells p38 MAPK may be a part of signaling pathway that counteracts acute Cd(II) neurotoxicity. In conclusion, our results showed that Cd(II) impairs cell viability and disturbs MAPKs pathways in an important developmental stage for synaptic organization.

The transporters GlyT2 and VIAAT cooperate to determine the vesicular glycinergic phenotype.

The mechanisms that specify the vesicular phenotype of inhibitory interneurons in vertebrates are poorly understood because the two main inhibitory transmitters, glycine and GABA, share the same vesicular inhibitory amino acid transporter (VIAAT) and are both present in neurons during postnatal development. We have expressed VIAAT and the plasmalemmal transporters for glycine and GABA in a neuroendocrine cell line and measured the quantal release of glycine and GABA using a novel double-sniffer patch-clamp technique. We found that glycine is released from vesicles when VIAAT is coexpressed with either the neuronal transporter GlyT2 or the glial transporter GlyT1. However, GlyT2 was more effective than GlyT1, probably because GlyT2 is unable to operate in the reverse mode, which gives it an advantage in maintaining the high cytosolic glycine concentration required for efficient vesicular loading by VIAAT. The vesicular inhibitory phenotype was gradually altered from glycinergic to GABAergic through mixed events when GABA is introduced into the secretory cell and competes for uptake by VIAAT. Interestingly, the VIAAT ortholog from Caenorhabditis elegans (UNC-47), a species lacking glycine transmission, also supports glycine exocytosis in the presence of GlyT2, and a point mutation of UNC-47 that abolishes GABA transmission in the worm confers glycine specificity. Together, these results suggest that an increased cytosolic availability of glycine in VIAAT-containing terminals was crucial for the emergence of glycinergic transmission in vertebrates.

Exposure of C6 glioma cells to Pb(II) increases the phosphorylation of p38(MAPK) and JNK1/2 but not of ERK1/2.

Pb(II) is a neurotoxic pollutant that produces permanent cognitive deficits in children. Pb(II) can modulate cell signaling pathways and cell viability in a variety of cell types. However, these actions are not well demonstrated on glial cells, which represent an important target for metals into the central nervous system. The present work was undertaken to determine the ability of Pb(II) in modulating the activity of mitogen activated protein kinases (MAPKs) in cultures of C6 rat glioma cells, a useful functional model for the study of astrocytes. Additionally, cell viability was analyzed by measurement of MTT reduction. Cells were exposed to lead acetate 0.1, 1, 10 microM for 24 and 48 h. MAPKs activation - in particular ERK1/2, p38(MAPK) and JNK1/2 - were analyzed by western blotting. Results showed that 10 microM Pb(II) treatment for 24 h caused a discrete stimulation of p38(MAPK) phosphorylation. However, 1 and 10 microM Pb(II) treatment for 48 h provoked a significant stimulation in the phosphorylation state of p38(MAPK) and JNK1/2. The phosphorylation state of ERK1/2 was not modified by any Pb(II) treatment. Moreover, data indicate that at 48 h treatment even 1 microM Pb(II) can be cytotoxic, causing impairment on cell viability. Therefore, depending on a long incubation period, a significant concomitant activation of p38(MAPK) and JNK1/2 by Pb(II) took place in parallel with the impairment of C6 glioma cells viability.

Antidepressant-like effect of lectin from Canavalia brasiliensis (ConBr) administered centrally in mice.

This study investigates the action of the central administration of the lectins isolated from Canavalia brasiliensis seeds (ConBr) and from Canavalia ensiformes seeds, (Concanavalin A, ConA) in the forced swimming test (FST) in mice. ConBr (1-10 micro g/site, i.c.v.), but not ConA, produced a decrease in the immobility time in the FST (observed at the time points 15, 30, 60 and 120 min after the injection), without changing the locomotor activity in the open-field test. The effect of ConBr in the FST was dependent on its protein structure integrity. ConBr (0.1 micro g/site, i.c.v.) caused a potentiation of the action of fluoxetine, a selective 5-HT reuptake inhibitor. The anti-immobility effect elicited by ConBr (10 micro g/site, i.c.v.) in the FST was prevented by the pretreatment of mice with pindolol (32 mg/kg, a 5-HT(1A/1B) receptor/beta-adrenoceptor antagonist), NAN-190 (0.5 mg/kg, a 5-HT(1A) receptor antagonist), ketanserin (5 mg/kg, a 5-HT(2A/2C) receptor antagonist), sulpiride (50 mg/kg, a D(2) receptor antagonist) or yohimbine (1 mg/kg, an alpha(2)-adrenoceptor antagonist), but not with SCH 23390 (0.05 mg/kg, a D(1) receptor antagonist) or prazosin (1 mg/kg, an alpha(1)-adrenoceptor antagonist). These results indicate that the antidepressant-like effect of ConBr in the FST is dependent on its interaction with the serotoninergic (via 5-HT(1A) and 5-HT(2)), noradrenergic (via alpha(2)-adrenoceptors) and dopaminergic (via D(2) receptors) systems. Considering the presence of lectins in the brain and based on the results, it will be important to determine a possible role of endogenous lectins in the modulation of the central nervous system function.

Abnormal functional organization in the dorsal lateral geniculate nucleus of mice lacking the beta 2 subunit of the nicotinic acetylcholine receptor.

Spontaneous activity patterns in the developing retina appear important for the functional organization of the visual system. We show here that an absence of early retinal waves in mice lacking the beta2 subunit of the nicotinic acetylcholine receptor (nAChR) is associated with both gain and loss of functional organization in the dorsal lateral geniculate nucleus (dLGN). Anatomical studies show normal gross retinotopy in the beta2(-/-) dLGN but suggest reduced topographic precision in the retinogeniculate projection. Physiological recordings reveal normal topography in the dorsoventral visual axis but a lack of fine-scale mapping in the nasotemporal visual plane. In contrast, unlike wild-type mice, on- and off-center cells in the beta2(-/-) dLGN are spatially segregated. The presence of the beta2 subunit of the nAChR in the CNS is therefore important for normal functional organization in the retinogeniculate projection.

Subunit composition of functional nicotinic receptors in dopaminergic neurons investigated with knock-out mice.

Nicotinic acetylcholine receptors (nAChRs) expressed by dopaminergic (DA) neurons have long been considered as potential therapeutic targets for the treatment of several neuropsychiatric diseases, including nicotine and cocaine addiction or Parkinson's disease. However, DA neurons express mRNAs coding for most, if not all, neuronal nAChR subunits, and the subunit composition of functional nAChRs has been difficult to establish. Immunoprecipitation experiments performed on mouse striatal extracts allowed us to identify three main types of heteromeric nAChRs (alpha4beta2*, alpha6beta2*, and alpha4alpha6beta2*) in DA terminal fields. The functional relevance of these subtypes was then examined by studying nicotine-induced DA release in striatal synaptosomes and recording ACh-elicited currents in DA neurons fromalpha4, alpha6, alpha4alpha6, and beta2 knock-out mice. Our results establish that alpha6beta2* nAChRs are functional and sensitive to alpha-conotoxin MII inhibition. These receptors are mainly located on DA terminals and consistently do not contribute to DA release induced by systemic nicotine administration, as evidenced by in vivo microdialysis. In contrast, (nonalpha6)alpha4beta2* nAChRs represent the majority of functional heteromeric nAChRs on DA neuronal soma. Thus, whereas a combination of alpha6beta2* and alpha4beta2* nAChRs may mediate the endogenous cholinergic modulation of DA release at the terminal level, somato-dendritic (nonalpha6)alpha4beta2* nAChRs most likely contribute to nicotine reinforcement.

Selective activation of central subtypes of the nicotinic acetylcholine receptor has opposite effects on neonatal excitotoxic brain injuries.

The incidence of neurological disabilities ascribable to perinatal injury is rising in Western countries, raising ethical and financial problems. No curative treatments are available. The pathophysiology of brain lesions of hypoxic-ischemic or inflammatory origin involves various neurotransmitters or neuromodulators. Among these, glutamate plays a key role. By overactivating N-methyl-D-aspartate receptors, it triggers the excitotoxic cascade. Although addictive, nicotine prevents excitotoxic neuronal death in adult animals. Its potential neuroprotective effects have not been evaluated in neonates. We found that nicotine is neuroprotective in vivo, in a murine model of neonatal excitotoxic brain injury, and in vitro, in primary cultures of cortical neurons. We investigated the respective roles in nicotine-related neuroprotection of the two dominant nicotinic acetylcholine receptor (nAChR) isoforms, namely, alpha4beta2 (heteropentameric) and alpha7 (homopentameric). Inhibition of alpha4beta2, either pharmacological (i.e., an alpha4beta2 nAChR antagonist) or molecular (beta2-/- knockout mice), abolished the protective effect of nicotine in vivo and in vitro, suggesting the involvement of alpha4beta2 nAChR in neonatal nicotine-related neuroprotection. In contrast, activation of alpha7 nAChR, which is protective in adult animals, was deleterious in our neonatal model, whereas its blockade, either pharmacological or molecular (alpha7-/- knockout mice) provided neuroprotection. Neuroprotective strategies must consider these opposite properties of distinct nAChR isoforms in neonates.