Journal of Neurochemistry

doi: 10.1111/jnc.12878pmid: N/A

Front cover: Immature oligodendrocytes show complex morphology as revealed by Rip immunostaining. Oligodendrocyte progenitor cells were prepared from P1 rat forebrain and were differentiated into immature oligodendrocytes under defined medium condition. Cells were immunostained with anti‐oligodendrocyte (Rip) antibody (green), nuclei were counter‐stained with propidium iodide (red) (original micrograph G of the lower panel in Figure 3). Images were acquired by a QICLICK monochrome digital camera attached to an Olympus BX60 fluorescence microscope with 40x objective lens. J. Neurochem. 2015, vol. 133 (4), pp. 532–543. Read the full article on doi: 10.1111/jnc.12988

doi: 10.1111/jnc.12876pmid: N/A

doi: 10.1111/jnc.12877pmid: N/A

Tai, Leon M.; Ghura, Shivesh; Koster, Kevin P.; Liakaite, Vaiva; Maienschein‐Cline, Mark; Kanabar, Pinal; Collins, Nicole; Ben‐Aissa, Manel; Lei, Arden Zhengdeng; Bahroos, Neil; Green, Stefan J.; Hendrickson, Bill; Van Eldik, Linda J.; LaDu, Mary Jo

doi: 10.1111/jnc.13072pmid: 25689586

Mo, Jiwon; Kim, Chong‐Hyun; Lee, Dongmin; Sun, Woong; Lee, Hyun Woo; Kim, Hyun

doi: 10.1111/jnc.13077pmid: 25708312

The homeostatic regulation of neuronal activity in glutamatergic and GABAergic synapses is critical for neural circuit development and synaptic plasticity. The induced expression of the transcription factor early growth response 1 (Egr‐1) in neurons is tightly associated with many forms of neuronal activity, but the underlying target genes in the brain remained to be elucidated. This study uses a quantitative real‐time PCR approach, in combination with in vivo chromatin immunoprecipitation, and reveals that GABAA receptor subunit, GABRA2 (α2), GABRA4 (α4), and GABRQ (θ) genes, are transcriptional targets of Egr‐1. Transfection of a construct that over‐expresses Egr‐1 in neuroblastoma (Neuro2A) cells up‐regulates the α2, α4, and θ subunits. Given that Egr‐1 knockout mice display less GABRA2, GABRA4, and GRBRQ mRNA in the hippocampus, and that Egr‐1 directly binds to their promoters and induces mRNA expression, the present findings support a role for Egr‐1 as a major regulator for altered GABAA receptor composition in homeostatic plasticity, in a glutamatergic activity‐dependent manner. The early growth response 1 (Egr‐1) is an inducible transcription factor to mediate rapid gene expression by neuronal activity. However, its underlying molecular target genes and mechanisms are not fully understood. We suggest that GABAA receptor subunits, GABRA2 (α2), GABRA4 (α4), and GABRQ (θ) genes are transcriptional targets of Egr‐1. Neuronal activity‐dependent up‐regulation of Egr‐1 might lead to altered subtypes of GABAA receptors for the maintenance of homeostatic excitatory and inhibitory balance for the regulation of synaptic strength.

Hang, Chong Yee; Kitahashi, Takashi; Parhar, Ishwar S.

doi: 10.1111/jnc.13084pmid: 25727787

Zebrafish possess two isoforms of vertebrate ancient long (VAL)‐opsin, val‐opsinA (valopa) and val‐opsinB (valopb), which probably mediate non‐visual responses to light. To understand the diurnal and light‐sensitive regulation of the valop genes in different cell groups, the current study used real‐time quantitative PCR to examine the diurnal changes of valopa and b mRNA levels in different brain areas of adult male zebrafish. Furthermore, effects of the extended exposure to light or dark condition, luminous levels and the treatment with a melatonin receptor agonist or antagonist on valop transcription were examined. In the thalamus, valop mRNA levels showed significant diurnal changes; valopa peaked in the evening, while valopb peaked in the morning. The diurnal change of valopa mRNA levels occurred independent of light conditions, whereas that of valopb mRNA levels were regulated by light. A melatonin receptor agonist or antagonist did not affect the changes of valop mRNA levels. In contrast, the midbrain and hindbrain showed arrhythmic valop mRNA levels under light and dark cycles. The differential diurnal regulation of the valopa and b genes in the thalamus and the arrhythmic expression in the midbrain and hindbrain suggest involvement of deep brain VAL‐opsin in time‐ and light‐dependent physiology. We show diurnal expression changes of vertebrate ancient long (VAL) opsin genes (valopa and valopb), depending on brain area, time of day and light condition, in the adult male zebrafish. Differential regulation of the valop genes in the thalamus and arrhythmic expression in the midbrain and hindbrain suggest their involvement in time‐ and light‐dependent physiology to adjust to environmental changes.

Albiñana, Elisa; Segura‐Chama, Pedro; Baraibar, Andres M.; Hernández‐Cruz, Arturo; Hernández‐Guijo, Jesus M.

doi: 10.1111/jnc.13055pmid: 25683177

We characterized the ionic currents underlying the cellular excitability and the Ca2+‐channel subtypes involved in action potential (AP) firing of rat adrenal chromaffin cells (RCCs) preserved in their natural environment, the adrenal gland slices, through the perforated patch‐clamp recording technique. RCCs prepared from adrenal slices exhibit a resting potential of −54 mV, firing spontaneous APs (2–3 spikes/s) generated by the opening of Na+ and Ca2+‐channels, and terminated by the activation of voltage and Ca2+‐activated K+‐channels (BK). Ca2+ influx via L‐type Ca2+‐channels is involved in reaching threshold potential for AP firing, and is responsible for activation of BK‐channels contributing to AP‐repolarization and afterhyperpolarization, whereas P/Q‐type Ca2+‐channels are involved only in the repolarization phase. BK‐channels carry total outward current during AP‐repolarization. Blockade of L‐type Ca2+‐channels reduces BK‐current ~60%, whereas blockade of N‐ or P/Q‐type produces little effect. This study demonstrates that Ca2+ influx through L‐type Ca2+‐channels plays a key role in modulating the threshold potential from RCCs in situ. This study demonstrates that Ca2+ influx through L‐type Ca2+ channels plays a key role in modulating the threshold potential for action potential firing and activating BK channels contributing to repolarization and afterhyperpolarization from rat adrenal chromaffin cells in situ.

Taylor, I. Mitch; Nesbitt, Kathryn M.; Walters, Seth H.; Varner, Erika L.; Shu, Zhan; Bartlow, Kathleen M.; Jaquins‐Gerstl, Andrea S.; Michael, Adrian C.

doi: 10.1111/jnc.13059pmid: 25683259

Dopamine (DA), a highly significant neurotransmitter in the mammalian central nervous system, operates on multiple time scales to affect a diverse array of physiological functions. The significance of DA in human health is heightened by its role in a variety of pathologies. Voltammetric measurements of electrically evoked DA release have brought to light the existence of a patchwork of DA kinetic domains in the dorsal striatum (DS) of the rat. Thus, it becomes necessary to consider how these domains might be related to specific aspects of DA's functions. Responses evoked in the fast and slow domains are distinct in both amplitude and temporal profile. Herein, we report that responses evoked in fast domains can be further classified into four distinct types, types 1–4. The DS, therefore, exhibits a total of at least five distinct evoked responses (four fast types and one slow type). All five response types conform to kinetic models based entirely on first‐order rate expressions, which indicates that the heterogeneity among the response types arises from kinetic diversity within the DS terminal field. We report also that functionally distinct subregions of the DS express DA kinetic diversity in a selective manner. Thus, this study documents five response types, provides a thorough kinetic explanation for each of them, and confirms their differential association with functionally distinct subregions of this key DA terminal field. The dorsal striatum is composed of five significantly different dopamine domains (types 1–4 and slow, average ± SEM responses to medial forebrain bundle (MFB) stimulation are shown in the figure). Responses from each of these five domains exhibit significantly different ascending and descending kinetic profiles and return to a long lasting elevated dopamine state, termed the dopamine hang‐up. All features of these responses are modeled with high correlation using first‐order modeling as well as our recently published restricted diffusion model of evoked dopamine overflow. We also report that functionally distinct subregions of the dorsal striatum express selective dopamine kinetic diversity.

Fan, Lir‐Wan; Bhatt, Abhay; Tien, Lu‐Tai; Zheng, Baoying; Simpson, Kimberly L.; Lin, Rick C. S.; Cai, Zhengwei; Kumar, Praveen; Pang, Yi

doi: 10.1111/jnc.12988pmid: 25382136

Serotonin (5‐hydroxytryptamine, 5‐HT) has been implicated to play critical roles in early neural development. Recent reports have suggested that perinatal exposure to selective serotonin reuptake inhibitors (SSRIs) resulted in cortical network miswiring, abnormal social behavior, callosal myelin malformation, as well as oligodendrocyte (OL) pathology in rats. To gain further insight into the cellular and molecular mechanisms underlying SSRIs‐induced OL and myelin abnormalities, we investigated the effect of 5‐HT exposure on OL development, cell death, and myelination in cell culture models. First, we showed that 5‐HT receptor 1A and 2A subtypes were expressed in OL lineages, using immunocytochemistry, Western blot, as well as intracellular Ca2+ measurement. We then assessed the effect of serotonin exposure on the lineage development, expression of myelin proteins, cell death, and myelination, in purified OL and neuron‐OL myelination cultures. For pure OL cultures, our results showed that 5‐HT exposure led to disturbance of OL development, as indicated by aberrant process outgrowth and reduced myelin proteins expression. At higher doses, such exposure triggered a development‐dependent cell death, as immature OLs exhibited increasing susceptibility to 5‐HT treatment compared to OL progenitor cells (OPC). We showed further that 5‐HT‐induced immature OL death was mediated at least partially via 5‐HT2A receptor, since cell death could be mimicked by 5‐HT2A receptor agonist 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane hydrochloride, (±)‐2,5‐dimethoxy‐4‐iodoamphetamine hydrochloride, but atten‐uated by pre‐treatment with 5‐HT2A receptor antagonist ritanserin. Utilizing a neuron‐OL myelination co‐culture model, our data showed that 5‐HT exposure significantly reduced the number of myelinated internodes. In contrast to cell injury observed in pure OL cultures, 5‐HT exposure did not lead to OL death or reduced OL density in neuron‐OL co‐cultures. However, abnormal patterns of contactin‐associated protein (Caspr) clustering were observed at the sites of Node of Ranvier, suggesting that 5‐HT exposure may affect other axon‐derived factors for myelination. In summary, this is the first study to demonstrate that manipulation of serotonin levels affects OL development and myelination, which may contribute to altered neural connectivity noted in SSRIs‐treated animals. The current in vitro study demonstrated that exposure to high level of serotonin (5‐HT) led to aberrant oligodendrocyte (OL) development, cell injury, and myelination deficit. We propose that elevated extracellular serotonin levels in the fetal brain, such as upon the use of selective serotonin reuptake inhibitors (SSRIs) during pregnancy, may adversely affect OL development and/or myelination, thus contributing to altered neural connectivity seen in Autism Spectrum Disorders. OPC = oligodendrocyte progenitor cell.

Lim, Juhee; Choi, Hueng‐Sik; Choi, Hyun Jin

doi: 10.1111/jnc.13085pmid: 25727910

The orphan nuclear receptor estrogen‐related receptor gamma (ERRγ) is highly expressed in the nervous system during embryogenesis and in adult brains, but its physiological role in neuronal development remains unknown. In this study, we evaluated the relevance of ERRγ in regulating dopaminergic (DAergic) phenotype and the corresponding signaling pathway. We used retinoic acid (RA) to differentiate human neuroblastoma SH‐SY5Y cells. RA induced neurite outgrowth of SH‐SY5Y cells with an increase in DAergic neuron‐like properties, including up‐regulation of tyrosine hydroxylase, dopamine transporter, and vesicular monoamine transporter 2. ERRγ, but not ERRα, was up‐regulated by RA, and participated in RA effect on SH‐SY5Y cells. ERRγ over‐expression enhanced mature DAergic neuronal phenotype with neurite outgrowth as with RA treatment; and RA‐induced increase in DAergic phenotype was attenuated by silencing ERRγ expression. ERRγ appears to have a crucial role in morphological and functional regulation of cells that is selective for DAergic neurons. Polo‐like kinase 2 was up‐regulated in ERRγ‐over‐expressing SH‐SY5Y cells, which was involved in phosphorylation of glycogen synthase kinase 3β and resulting downstream activation of nuclear factor of activated T cells. The likely involvement of ERRγ in regulating the DAergic neuronal phenotype makes this orphan nuclear receptor a novel target for understanding DAergic neuronal differentiation. We propose the relevance of estrogen‐related receptor gamma (ERRγ) in regulating dopaminergic neuronal phenotype: ERRγ is up‐regulated by retinoic acid in SH‐SY5Y cells, and enhances dopaminergic phenotypes and induces neurite outgrowth; Polo‐like kinase 2 (PLK2) and glycogen synthase kinase 3 beta/nuclear factor of activated T cells (GSK3β/NFAT) signaling are responsible for the ERRγ effect. Our findings provide the first insights into the role of ERRγ in the brain, as a novel approach toward understanding dopaminergic differentiation.