We have analyzed the role of glutamate and its receptors (GluRs) in regulating the development of oligodendrocytes. Activation of AMPA-preferring GluRs with selective agonists inhibited proliferation of purified cortical oligodendrocyte progenitor (O-2A) cells cultured with different mitogens, as measured by [3H]thymidine incorporation or bromodeoxyuridine staining. In contrast, activation of GABA or muscarinic receptors did not affect O-2A proliferation. Cell viability and apoptosis assays demonstrated that the inhibition of O-2A proliferation was not attributable to a cytotoxic action of GluR agonists, and was reversible. Activation of GluRs prevented lineage progression from the O-2A (GD3+/nestin+) stage to the prooligodendroblast (O4+) stage, but did not affect O-2A migration. Additional experiments examined the membrane ionic channels mediating these GluR activation effects. We found that proliferating O-2A cells expressed functional delayed rectifier K+ channels, which were absent in pro-oligodendroblasts. GluR agonists and the K+ channel blocker tetraethylammonium (TEA) strongly inhibited delayed rectifier K+ currents in O-2A cells. TEA reproduced the effects of GluR activation on O-2A proliferation and lineage progression in the same concentration range that blocked delayed rectifier K+ currents. These results indicate that glutamate regulates oligodendrogenesis specifically at the O-2A stage by modulating K+ channel activity.

No abstract

Although widespread neural atrophy is an inevitable consequence of normal aging, not all cognitive abilities decline as we age. For example, spoken language comprehension tends to be preserved, despite atrophy in neural regions involved in language function. Here, we combined measures of behavior, functional activation, and gray matter (GM) change in a younger (19–34 years) and older group (49–86 years) of participants to identify the mechanisms leading to preserved language comprehension across the adult life span. We focussed primarily on syntactic functions because these are strongly left lateralized, providing the potential for contralateral recruitment. In an functional magnetic resonance imaging study, we used a word-monitoring task to minimize working memory demands, manipulating the availability of semantics and syntax to ask whether syntax is preserved in aging because of the functional recruitment of other brain regions, which successfully compensate for neural atrophy. Performance in the older group was preserved despite GM loss. This preservation was related to increased activity in right hemisphere frontotemporal regions, which was associated with age-related atrophy in the left hemisphere frontotemporal network activated in the young. We argue that preserved syntactic processing across the life span is due to the shift from a primarily left hemisphere frontotemporal system to a bilateral functional language network.

The neurotrophins brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) were compared for their effects in promoting the survival and/or regulation of expression of phenotypic markers of dopaminergic and GABAergic neurons in cultures derived from embryonic rat ventral mesencephalon. Dopaminergic neuron number and phenotypic expression were monitored by tyrosine hydroxylase (TH) immunocytochemistry, and measurement of high-affinity dopamine uptake activity and dopamine content, respectively. High-affinity GABA uptake, glutamic acid decarboxylase (GAD) activity, and endogenous GABA content were used to detect GABAergic neurons. Seven days of treatment with either BDNF or NT-3 resulted in dose-dependent increases in the number of TH-positive neurons, with maximal responses of 3-fold and 2.3- fold, respectively. Dopamine uptake activity and dopamine content were similarly increased. The effects of BDNF and NT-3 on dopamine uptake activity showed no additivity. NT-4/5 treatment elicited the greatest increase (7-fold) in the number of TH-positive neurons, as well as a 2.6-fold increase in dopamine content. In marked contrast to BDNF or NT- 3, NT-4/5 had no effect on dopamine uptake capacity. BDNF, NT-3, or NT- 4/5 also produced dose-dependent elevations of 2–3-fold in GABA uptake activity. These effects were not additive. GAD activity was increased by BDNF (1.8-fold) and NT-3 (threefold) treatment, but not by NT-4/5, whereas GABA content was increased to a similar extent by all three neurotrophins. NGF had no effect on any of the parameters measured in this study. Northern analyses indicated that the mRNAs encoding TrkB and TrkC, the functional high-affinity receptors for BDNF and NT-4/5, and NT-3, respectively, are expressed in the substantia nigra of adult rat brain, as well as in cultures of developing ventral mesencephalon. Taken together, our results indicate that BDNF and NT-3 have broadly similar effects in promoting the survival and differentiated phenotype of both dopaminergic and GABAergic neurons of the developing substantia nigra. Although BDNF and NT-4/5 are thought to act through the same high-affinity receptor, TrkB, it is evident that these two neurotrophins have distinct as well as overlapping actions toward mesencephalic dopaminergic or GABAergic neurons.

For the past 150 years, neurobiological models of language have debated the role of key brain regions in language function. One consistently debated set of issues concern the role of the left inferior frontal gyrus in syntactic processing. Here we combine measures of functional activity, grey matter integrity and performance in patients with left hemisphere damage and healthy participants to ask whether the left inferior frontal gyrus is essential for syntactic processing. In a functional neuroimaging study, participants listened to spoken sentences that either contained a syntactically ambiguous or matched unambiguous phrase. Behavioural data on three tests of syntactic processing were subsequently collected. In controls, syntactic processing co-activated left hemisphere Brodmann areas 45/47 and posterior middle temporal gyrus. Activity in a left parietal cluster was sensitive to working memory demands in both patients and controls. Exploiting the variability in lesion location and performance in the patients, voxel-based correlational analyses showed that tissue integrity and neural activity—primarily in left Brodmann area 45 and posterior middle temporal gyrus—were correlated with preserved syntactic performance, but unlike the controls, patients were insensitive to syntactic preferences, reflecting their syntactic deficit. These results argue for the essential contribution of the left inferior frontal gyrus in syntactic analysis and highlight the functional relationship between left Brodmann area 45 and the left posterior middle temporal gyrus, suggesting that when this relationship breaks down, through damage to either region or to the connections between them, syntactic processing is impaired. On this view, the left inferior frontal gyrus may not itself be specialized for syntactic processing, but plays an essential role in the neural network that carries out syntactic computations.

Although previous functional brain imaging studies have found that the insula responds selectively to facial expressions of disgust, it remains unclear whether the insula responds selectively to disgust-inducing pictures. In this fMRI study, healthy volunteers viewed pictures of contamination, human mutilation, attacks and neutral scenes during scanning, and then rated pictures for the 'basic' emotions. The anterior insula responded to contamination and mutilation but not attacks, while the ventral visual areas responded to attacks and mutilations more strongly than contamination. The above activations were predicted by disgust and arousal ratings respectively. Additionally, mutilations uniquely activated the right superior parietal cortex. These results support selective disgust processing at the insula, and suggest distinct neural responses to contamination and mutilation.

Selected for its high relative abundance, a protein spot of MW approximately 75 kDa, pI 5.5 was cored from a Coomassie-stained two-dimensional gel of proteins from 2850 zona-free metaphase II mouse eggs and analyzed by tandem mass spectrometry (TMS), and novel microsequences were identified that indicated a previously uncharacterized egg protein. A 2.4-kb cDNA was then amplified from a mouse ovarian adapter-ligated cDNA library by RACE-PCR, and a unique 2043-bp open reading frame was defined encoding a 681-amino-acid protein. Comparison of the deduced amino acid sequence with the nonredundant database demonstrated that the protein was approximately 40% identical to the calcium-dependent peptidylarginine deiminase (PAD) enzyme family. Northern blotting, RT-PCR, and in situ hybridization analyses indicated that the protein was abundantly expressed in the ovary, weakly expressed in the testis, and absent from other tissues. Based on the homology with PADs and its oocyte-abundant expression pattern, the protein was designated ePAD, for egg and embryo-abundant peptidylarginine deiminase-like protein. Anti-recombinant ePAD monospecific antibodies localized the molecule to the cytoplasm of oocytes in primordial, primary, secondary, and Graafian follicles in ovarian sections, while no other ovarian cell type was stained. ePAD was also expressed in the immature oocyte, mature egg, and through the blastocyst stage of embryonic development, where expression levels began to decrease. Immunoelectron microscopy localized ePAD to egg cytoplasmic sheets, a unique keratin-containing intermediate filament structure found only in mammalian eggs and in early embryos, and known to undergo reorganization at critical stages of development. Previous reports that PAD-mediated deimination of epithelial cell keratin results in cytoskeletal remodeling suggest a possible role for ePAD in cytoskeletal reorganization in the egg and early embryo.

The TrkB and TrkC receptor tyrosine kinases have been identified as high-affinity receptors for the neurotrophic factors brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) and NT-3 respectively. These receptor classes were identified and mapped by the in situ hybridization of antisense riboprobes complementary to portions of the intracellular (tyrosine kinase) or extracellular (ligand-binding) domains of trkB and trkC mRNA, and by the distribution of high-affinity [125I]BDNF, [125I]NT-4/5 and [125I]NT-3 binding sites in adjacent rat brain sections. Both methods showed that TrkB and TrkC receptors are abundant and widely expressed throughout the brain. Kinase or extracellular domain trkC probes labelled neuronal somata in a qualitatively similar manner in virtually every major area of the forebrain. Neither trkC probe labelled non-neuronal cells except for elements within cerebral arteries and arterioles. The kinase domain trkB probe hybridized exclusively to neurons. Neurons expressing trkB were even more widely distributed than those expressing trkC. The extracellular domain trkB probe labelled neurons with the same relative distribution as the trkB kinase domain probe, but also hybridized extensively with non-neural cells, particularly astrocytes, ependyma and choroid epithelium cells. The distribution of [125I]NT-3 binding sites generally resembled that of trkC hybridization, particularly in the neocortex, striatum and thalamus. [125I]BDNF and [125I]NT-4/5 binding sites were more widely distributed and denser than those for [125I]NT-3, and resembled the trkB hybridization pattern. These patterns are consistent with the preferential binding in the brain of TrkC receptors by [125I]NT-3 and of TrkB receptors by [125I]BDNF and [125I]NT-4/5. That the predominantly neuronal patterns of hybridization obtained with kinase and extracellular domain probes for trkC are qualitatively indistinguishable suggests that truncated and full-length forms of TrkC are expressed within extensively overlapping populations of neurons. In marked contrast to TrkC, expression of the full-length and truncated forms of TrkB appears to be largely segregated, being expressed principally on neurons and non-neuronal cells respectively. The abundant and widespread neuronal distribution of full-length, signal-transducing forms of TrkB and TrkC predict that their cognate ligands, BDNF, NT-4/5 and NT-3, may exert direct effects on a large proportion of neurons within the mature brain.