Impaired long-term potentiation induction in dentate gyrus of calretinin-deficient mice

Calretinin (Cr) is a Ca2+ binding protein present in various populations of neurons distributed in the central and peripheral nervous systems. We have generated Cr-deficient (Cr−/−) mice by gene targeting and have investigated the associated phenotype. Cr−/− mice were viable, and a large number of morphological, biochemical, and behavioral parameters were found unaffected. In the normal mouse hippocampus, Cr is expressed in a widely distributed subset of GABAergic interneurons and in hilar mossy cells of the dentate gyrus. Because both types of cells are part of local pathways innervating dentate granule cells and/or pyramidal neurons, we have explored in Cr−/− mice the synaptic transmission between the perforant pathway and granule cells and at the Schaffer commissural input to CA1 pyramidal neurons. Cr−/− mice showed no alteration in basal synaptic transmission, but long-term potentiation (LTP) was impaired in the dentate gyrus. Normal LTP could be restored in the presence of the GABAA receptor antagonist bicuculline, suggesting that in Cr−/− dentate gyrus an excess of γ-aminobutyric acid (GABA) release interferes with LTP induction. Synaptic transmission and LTP were normal in CA1 area, which contains only few Cr-positive GABAergic interneurons. Cr−/− mice performed normally in spatial memory task. These results suggest that expression of Cr contributes to the control of synaptic plasticity in mouse dentate gyrus by indirectly regulating the activity of GABAergic interneurons, and that Cr−/− mice represent a useful tool to understand the role of dentate LTP in learning and memory.

Regulation of the human ether-a-gogo related gene (HERG) K+ channels by reactive oxygen species

Human ether-a-gogo related gene (HERG) K+ channels are key elements in the control of cell excitability in both the cardiovascular and the central nervous systems. For this reason, the possible modulation by reactive oxygen species (ROS) of HERG and other cloned K+ channels expressed in Xenopus oocytes has been explored in the present study. Exposure of Xenopus oocytes to an extracellular solution containing FeSO4 (25–100 μM) and ascorbic acid (50–200 μM) (Fe/Asc) increased both malondialdehyde content and 2′,7′-dichlorofluorescin fluorescence, two indexes of ROS production. Oocyte perfusion with Fe/Asc caused a 50% increase of the outward K+ currents carried by HERG channels, whereas inward currents were not modified. This ROS-induced increase in HERG outward K+ currents was due to a depolarizing shift of the voltage-dependence of channel inactivation, with no change in channel activation. No effect of Fe/Asc was observed on the expressed K+ currents carried by other K+ channels such as bEAG, rDRK1, and mIRK1. Fe/Asc-induced stimulation of HERG outward currents was completely prevented by perfusion of the oocytes with a ROS scavenger mixture (containing 1,000 units/ml catalase, 200 ng/ml superoxide dismutase, and 2 mM mannitol). Furthermore, the scavenger mixture also was able to reduce HERG outward currents in resting conditions by 30%, an effect mimicked by catalase alone. In conclusion, the present results seem to suggest that changes in ROS production can specifically influence K+ currents carried by the HERG channels.

Selectively enhanced contextual fear conditioning in mice lacking the transcriptional regulator CCAAT/enhancer binding protein δ

CCAAT/enhancer binding protein δ (C/EBPδ) is a transcriptional regulator implicated in the hepatic acute phase response and in adipogenic and myeloid cell differentiation. We found that C/EBPδ is widely expressed in the peripheral and central nervous systems, including neurons of the hippocampal formation, indicating a role in neural functions. To examine the role of C/EBPδ in vivo, we generated mice with a targeted deletion of the C/EBPδ gene. This mutation does not interfere with normal embryonic and postnatal development. Performance in a battery of behavioral tests indicates that basic neurological functions are normal. Furthermore, performance in a Morris water maze task suggests that C/EBPδ mutant mice have normal spatial learning. However, in the contextual and auditory-cue-conditioned fear task, C/EBPδ null mice displayed significantly more conditioned freezing to the test context than did wild-type controls, but equivalent conditioning to the auditory cue. These data demonstrate a selectively enhanced contextual fear response in mice carrying a targeted genomic mutation and implicate C/EBPδ in the regulation of a specific type of learning and memory.

The area code hypothesis revisited: Olfactory receptors and other related transmembrane receptors may function as the last digits in a cell surface code for assembling embryos

Recent evidence emerging from several laboratories, integrated with new data obtained by searching the genome databases, suggests that the area code hypothesis provides a good heuristic model for explaining the remarkable specificity of cell migration and tissue assembly that occurs throughout embryogenesis. The area code hypothesis proposes that cells assemble organisms, including their brains and nervous systems, with the aid of a molecular-addressing code that functions much like the country, area, regional, and local portions of the telephone dialing system. The complexity of the information required to code cells for the construction of entire organisms is so enormous that we assume that the code must make combinatorial use of members of large multigene families. Such a system would reuse the same receptors as molecular digits in various regions of the embryo, thus greatly reducing the total number of genes required. We present the hypothesis that members of the very large families of olfactory receptors and vomeronasal receptors fulfill the criteria proposed for area code molecules and could serve as the last digits in such a code. We discuss our evidence indicating that receptors of these families are expressed in many parts of developing embryos and suggest that they play a key functional role in cell recognition and targeting not only in the olfactory system but also throughout the brain and numerous other organs as they are assembled.

Identification and characterization of a melanin-concentrating hormone receptor

Melanin-concentrating hormone (MCH), a neuropeptide expressed in central and peripheral nervous systems, plays an important role in the control of feeding behaviors and energy metabolism. An orphan G protein-coupled receptor (SLC-1/GPR24) has recently been identified as a receptor for MCH (MCHR1). We report here the identification and characterization of a G protein-coupled receptor as the MCH receptor subtype 2 (MCHR2). MCHR2 has higher protein sequence homology to MCHR1 than any other G protein-coupled receptor. The expression of MCHR2 has been detected in many regions of the brain. In contrast to MCHR1, which is intronless in the coding region and is located at the chromosomal locus 22q13.3, the MCHR2 gene has multiple exons and is mapped to locus 6q21. MCHR2 is specifically activated by nanomolar concentrations of MCH, binds to MCH with high affinity, and signals through Gq protein. This discovery is important for a full understanding of MCH biology and the development of potential therapeutics for diseases involving MCH, including obesity.

An ATP-activated, ligand-gated ion channel on a cholinergic presynaptic nerve terminal.

ATP has recently been identified as a fast neurotransmitter in both the central and peripheral nervous systems. Several studies have suggested that ATP can also affect the release of classical neurotransmitters, including acetylcholine with which it is co-released. We have searched for ATP receptors on a cholinergic presynaptic nerve terminal using the calyx-type synapse of the chicken ciliary ganglion. ATP was pulsed onto the terminals under voltage clamp and induced a short latency cation current that exhibited inward rectification and marked desensitization. This current was not seen with adenosine but was mimicked by several sterically restricted ATP analogs and was blocked by suramin. ATP-activated single ion channels exhibited prominent flickering and had a conductance of approximately 17 pS. Our results demonstrate a ligand-gated P2X-like purinergic receptor on a cholinergic presynaptic nerve terminal.

Molecular cloning of a preprohormone from sea anemones containing numerous copies of a metamorphosis-inducing neuropeptide: a likely role for dipeptidyl aminopeptidase in neuropeptide precursor processing.

Neuropeptides are an important group of hormones mediating or modulating neuronal communication. Neuropeptides are especially abundant in evolutionarily "old" nervous systems, such as those of cnidarians, the lowest animal group having a nervous system. Cnidarians often have a life cycle including a polyp, a medusa, and a planula larva stage. Recently, a neuropeptide, < Glu-Gln-Pro-Gly-Leu-Trp-NH2, has been isolated from sea anemones that induces metamorphosis in a hydroid planula larva to become a hydropolyp [Leitz, T., Morand, K. & Mann, M. (1994) Dev. Biol. 163, 440-446]. Here, we have cloned the precursor protein for this metamorphosis-inducing neuropeptide from sea anemones. The precursor protein is 514-amino acid residues long and contains 10 copies of the immature, authentic neuropeptide (Gln-Gln-Pro-Gly-Leu-Trp-Gly). All neuropeptide copies are preceded by Xaa-Pro or Xaa-Ala sequences, suggesting a role for dipeptidyl aminopeptidase in neuropeptide precursor processing. In addition to these neuropeptide copies, there are 14 copies of another, closely related neuropeptide sequence (Gln-Asn-Pro-Gly-Leu-Trp-Gly). These copies are flanked by basic cleavage sites and, therefore, are likely to be released from the precursor protein. Furthermore, there are 13 other, related neuropeptide sequences having only small sequence variations (the most frequent sequence: Gln-Pro-Gly-Leu-Trp-Gly, eight copies). These variants are preceded by Lys-Arg, Xaa-Ala, or Xaa-Pro sequences, and are followed by basic cleavage sites, and therefore, are also likely to be produced from the precursor. Thus, there are at least 37 closely related neuropeptides localized on the precursor protein, making this precursor one of the most productive preprohormones known so far. This report also shows that unusual processing sites are common in cnidarian preprohormones.

Cloning of a sodium channel alpha subunit from rabbit Schwann cells.

Overlapping cDNA clones spanning the entire coding region of a Na-channel alpha subunit were isolated from cultured Schwann cells from rabbits. The coding region predicts a polypeptide (Nas) of 1984 amino acids exhibiting several features characteristic of Na-channel alpha subunits isolated from other tissues. Sequence comparisons showed that the Nas alpha subunit resembles most the family of Na channels isolated from brain (approximately 80% amino acid identity) and is least similar (approximately 55% amino acid identity) to the atypical Na channel expressed in human heart and the partial rat cDNA, NaG. As for the brain II and III isoforms, two variants of Nas exist that appear to arise by alternative splicing. The results of reverse transcriptase-polymerase chain reaction experiments suggest that expression of Nas transcripts is restricted to cells in the peripheral and central nervous systems. Expression was detected in cultured Schwann cells, sciatic nerve, brain, and spinal cord but not in skeletal or cardiac muscle, liver, kidney, or lung.

Interleukin 1 beta up-regulates the expression of sulfoglucuronosyl paragloboside, a ligand for L-selectin, in brain microvascular endothelial cells.

Treatment of cultured bovine brain microvascular endothelial cells (BMECs) with interleukin 1 beta (IL-1 beta), an inflammatory cytokine, was shown to induce the accumulation of sulfoglucuronosyl paragloboside (SGPG), a glycolipid bearing the HNK-1 epitope. This resulted in the attachment of a greater number of human lymphocytes to the treated than to the untreated BMEC monolayers. Attachment of human lymphocytes to the IL-1 beta-activated BMEC cells could be blocked either by incubation of the human lymphocytes with an anti-L-selectin antibody or by application of an anti-SGPG antibody to the BMECs. These results suggest that SGPG may act as an important ligand for L-selectin for the regulation of the attachment of activated lymphocytes and their subsequent invasion into the nervous system parenchyma in inflammatory disorders of the central and peripheral nervous systems.

Conference on neurological disorders and commercial drivers. Final report.

Federal Highway Administration, Office of Motor Carriers, Washington, D.C.

Human physiology /

v. 1-2 edited by Dr. M. Camis; v. 3-4, by Gordon M. Holmes; v.5, by M.S. Pembrey.

Distinct types of glial cells populate the Drosophila antenna

Background: The development of nervous systems involves reciprocal interactions between neurons and glia. In the Drosophila olfactory system, peripheral glial cells arise from sensory lineages specified by the basic helix- loop- helix transcription factor, Atonal. These glia wrap around the developing olfactory axons early during development and pattern the three distinct fascicles as they exit the antenna. In the moth Manduca sexta, an additional set of central glia migrate to the base of the antennal nerve where axons sort to their glomerular targets. In this work, we have investigated whether similar types of cells exist in the Drosophila antenna. Results: We have used different P( Gal4) lines to drive Green Fluorescent Protein ( GFP) in distinct populations of cells within the Drosophila antenna. Mz317:: GFP, a marker for cell body and perineural glia, labels the majority of peripheral glia. An additional similar to 30 glial cells detected by GH146:: GFP do not derive from any of the sensory lineages and appear to migrate into the antenna from the brain. Their appearance in the third antennal segment is regulated by normal function of the Epidermal Growth Factor receptor and small GTPases. We denote these distinct populations of cells as Mz317- glia and GH146- glia respectively. In the adult, processes of GH146- glial cells ensheath the olfactory receptor neurons directly, while those of the Mz317- glia form a peripheral layer. Ablation of GH146- glia does not result in any significant effects on the patterning of the olfactory receptor axons. Conclusion: We have demonstrated the presence of at least two distinct populations of glial cells within the Drosophila antenna. GH146- glial cells originate in the brain and migrate to the antenna along the newly formed olfactory axons. The number of cells populating the third segment of the antenna is regulated by signaling through the Epidermal Growth Factor receptor. These glia share several features of the sorting zone cells described in Manduca.

Theoretical foundations of neural networks

Neural networks have often been motivated by superficial analogy with biological nervous systems. Recently, however, it has become widely recognised that the effective application of neural networks requires instead a deeper understanding of the theoretical foundations of these models. Insight into neural networks comes from a number of fields including statistical pattern recognition, computational learning theory, statistics, information geometry and statistical mechanics. As an illustration of the importance of understanding the theoretical basis for neural network models, we consider their application to the solution of multi-valued inverse problems. We show how a naive application of the standard least-squares approach can lead to very poor results, and how an appreciation of the underlying statistical goals of the modelling process allows the development of a more general and more powerful formalism which can tackle the problem of multi-modality.

Elements of molecular neurobiology:instruction manual to 2r.e

Extensively updated, revised and illustrated this unique introductory text presents a molecular account of the structure, function and development of the brain and nervous systems. This book describes the latest research in neurobiology made possible by modern molecular biology techniques. The author synthesizes this new knowledge and demonstrates how an understanding at the molecular level can contribute towards a theory of the brain in health and disease.

Origins of molecular neurobiology:The role of the physicists

The revolution in the foundations of physics at the beginning of the twentieth century suggested to several of its most prominent workers that biology was ripe for something similar. In consequence, a number of physicists moved into biology. They were highly influential in initiating a molecular biology in the 1950s. Two decades later it seemed to several of these migrants, and those they had influenced, that the major problems in molecular biology had been solved, and that it was time to move on to what seemed to them the final problem: the nervous system, consciousness, and the age-old mind-body problem. This paper reviews this "double migration" and shows how the hopes of the first generation of physicist-biologists were both realized and dashed. No new physical principles were discovered at work in the foundations of biology or neuroscience. On the other hand, the mind-set of those trained in physics proved immensely valuable in analyzing fundamental issues in both biology and neuroscience. It has been argued that the outcome of the molecular biology of the 1950s was a change in the concept of the gene from that of "a mysterious entity into that of a real molecular object" (Watson, 1965, p.6); the gates and channels which play such crucial roles in the functioning of nervous systems have been transformed in a similar way. Studies on highly simplified systems have also opened the prospect of finding the neural correlatives of numerous behaviors and neuropathologies. This increasing understanding at the molecular level is invaluable not only in devising rational therapies but also, by defining the material substrate of consciousness, in bringing the mind-body problem into sharper focus. Copyright © Taylor & Francis Inc.