Showing papers in "Annual Review of Neuroscience in 1997"
TL;DR: A review of recent studies showing that the encoding of intentions to make movements is also among the cognitive functions of the posterior parietal cortex is reviewed.
Abstract: Recent experiments are reviewed that indicate that sensory signals from many modalities, as well as efference copy signals from motor structures, converge in the posterior parietal cortex in order to code the spatial locations of goals for movement. These signals are combined using a specific gain mechanism that enables the different coordinate frames of the various input signals to be combined into common, distributed spatial representations. These distributed representations can be used to convert the sensory locations of stimuli into the appropriate motor coordinates required for making directed movements. Within these spatial representations of the posterior parietal cortex are neural activities related to higher cognitive functions, including attention. We review recent studies showing that the encoding of intentions to make movements is also among the cognitive functions of this area.
1,394 citations
TL;DR: The release of several different neurotransmitters from the brain stem, hypothalamus, basal forebrain, and cerebral cortex results in a depolarization of thalamocortical and thalamic reticular neurons and an enhanced excitability in many cortical pyramidal cells, thereby suppressing the generation of sleep rhythms and promoting a state that is conducive to sensory processing and cognition.
Abstract: Thalamocortical activity exhibits two distinct states: ( a) synchronized rhythmic activity in the form of delta, spindle, and other slow waves during EEGsynchronized sleep and (b) tonic activity during waking and rapid-eye-movement sleep. Spindle waves are generated largely through a cyclical interaction between thalamocortical and thalamic reticular neurons involving both the intrinsic membrane properties of these cells and their anatomical interconnections. Specific alterations in the interactions between these cells can result in the generation of paroxysmal events resembling absence seizures in children. The release of several different neurotransmitters from the brain stem, hypothalamus, basal forebrain, and cerebral cortex results in a depolarization of thalamocortical and thalamic reticular neurons and an enhanced excitability in many cortical pyramidal cells, thereby suppressing the generation of sleep rhythms and promoting a state that is conducive to sensory processing and cognition.
1,248 citations
TL;DR: The findings support the hypothesis that olfactory transduction and neural processing in the peripheral Olfactory pathway involve basic mechanisms that are universal across most species in most phyla.
Abstract: ▪ Abstract Olfaction begins with the transduction of the information carried by odor molecules into electrical signals in sensory neurons. The activation of different subsets of sensory neurons to different degrees is the basis for neural encoding and further processing of the odor information by higher centers in the olfactory pathway. Recent evidence has converged on a set of transduction mechanisms, involving G-protein-coupled second-messenger systems, and neural processing mechanisms, involving modules called glomeruli, that appear to be adapted for the requirements of different species. The evidence is highlighted in this review by focusing on studies in selected vertebrates and in insects and crustaceans among invertebrates. The findings support the hypothesis that olfactory transduction and neural processing in the peripheral olfactory pathway involve basic mechanisms that are universal across most species in most phyla.
1,066 citations
TL;DR: It appears that this fronto-parietal network functions as a visuomotor controller-one that makes computations based on proprioceptive, visual, gaze, attentional, and other information to produce an output that reflects the selection, preparation, and execution of movements.
Abstract: The dorsal premotor cortex is a functionally distinct cortical field or group of fields in the primate frontal cortex Anatomical studies have confirmed that most parietal input to the dorsal premotor cortex originates from the superior parietal lobule However, these projections arise not only from the dorsal aspect of area 5, as has long been known, but also from newly defined areas of posterior parietal cortex, which are directly connected with the extrastriate visual cortex Thus, the dorsal premotor cortex receives much more direct visual input than previously accepted It appears that this fronto-parietal network functions as a visuomotor controller-one that makes computations based on proprioceptive, visual, gaze, attentional, and other information to produce an output that reflects the selection, preparation, and execution of movements
940 citations
TL;DR: The role of apoptotic cell death in the development of the nervous system and as a response to neuronal injury is discussed and the evidence for a role for these cell death regulators in neuronal death decisions is discussed.
Abstract: A growing family of genes that share homology with the bcl-2 proto-oncogene is involved in the regulation of cell death Many of these proteins show widespread expression and are expressed in the nervous system in developing and adult organisms A physiologic role for Bcl-2 and Bcl-x in neuron survival has been shown In addition, these proteins have been shown to protect neurons from a wide array of toxic insults In this review, we discuss the Bcl-2 family of proteins with regard to their structure and interactions We then discuss the role of apoptotic cell death in the development of the nervous system and as a response to neuronal injury Lastly, we discuss the evidence for a role for these cell death regulators in neuronal death decisions
600 citations
TL;DR: Structural similarities are evident for the pore-forming alpha subunits and for the beta subunits, which could potentially regulate channel activity according to the level of energy and/or reducing power of the cell.
Abstract: Potassium channels contribute to the excitability of neurons and signaling in the nervous system. They arise from multiple gene families including one for voltage-gated potassium channels and one for inwardly rectifying potassium channels. Features of potassium permeation, channel gating and regulation, and subunit interaction have been analyzed. Potassium channels of similar design have been found in animals ranging from jellyfish to humans, as well as in plants, yeast, and bacteria. Structural similarities are evident for the pore-forming alpha subunits and for the beta subunits, which could potentially regulate channel activity according to the level of energy and/or reducing power of the cell.
519 citations
TL;DR: This review presents recent data on the structural and functional characterization of Pax-6 homologues from species of different animal phyla and discusses the implications of these findings for the understanding of the development and evolution of eyes and nervous systems.
Abstract: Pax-6 is a member of the Pax gene class and encodes a protein containing a paired domain and a homeodomain. The molecular characterization of Pax-6 genes from species of different animal phyla and the analysis of Pax-6 function in the developing eyes and central nervous system of vertebrates, Drosophila melanogaster, and Caenorhabditis elegans suggest that Pax-6 homologues share conserved functions. In this review, we present recent data on the structural and functional characterization of Pax-6 homologues from species of different animal phyla. We discuss the implications of these findings for our understanding of the development and evolution of eyes and nervous systems.
480 citations
TL;DR: Elaborate studies have significantly enhanced knowledge of the functional anatomy of G-protein-coupled receptors, and the concept has emerged that receptor function can be modulated with high specificity by coexpressed receptor fragments and may have significant clinical impact in the future.
Abstract: A prerequisite for the maintenance of homeostasis in a living organism is finetuned communication between different cells. The majority of extracellular signaling molecules, such as hormones and neurotransmitters, interact with a threeprotein transmembrane signaling system consisting of a receptor, a G protein, and an effector. These single components interact sequentially and reversibly. Considering that hundreds of G-protein-coupled receptors interact with a limited repertoire of G proteins, the question of coupling specificity is worth considering. G-protein-mediated signal transduction is a complex signaling network with diverging and converging transduction steps at each coupling interface. The recent realization that classical signaling pathways are intimately intertwined with growth-factor‐signaling cascades adds another level of complexity. Elaborate studies have significantly enhanced our knowledge of the functional anatomy of G-protein-coupled receptors, and the concept has emerged that receptor function can be modulated with high specificity by coexpressed receptor fragments. These results may have significant clinical impact in the future.
327 citations
TL;DR: Physiological activation of the mag nocellular hypothalamo-neurohypophysial system induces a coordinated astrocytic withdrawal from between the magnocellular somata and the parallel-projecting dendrites of the supraoptic nucleus, which results in interneuronal coupling increases that are capable of being modulated synaptically via second messenger-dependent mechanisms.
Abstract: ▪ Abstract Physiological activation of the magnocellular hypothalamo-neurohypophysial system induces a coordinated astrocytic withdrawal from between the magnocellular somata and the parallel-projecting dendrites of the supraoptic nucleus. Neural lobe astrocytes release engulfed axons and retract from their usual positions along the basal lamina. Occurring on a minutes-to-hours time scale, these changes are accompanied by increased direct apposition of both somatic and dendritic membrane, the formation of dendritic bundles, the appearance of novel multiple synapses in both the somatic and dendritic zones, and increased neural occupation of the perivascular basal lamina. Reversal, albeit with varying time courses, is achieved by removing the activating stimuli. Additionally, activation results in interneuronal coupling increases that are capable of being modulated synaptically via second messenger–dependent mechanisms. These changes appear to play important roles in control and coordination of oxytocin and...
315 citations
TL;DR: This review examines the hypothesis that the modular structure of the vertebrate cerebellum is strongly analogous to this earlier scheme and presents the case that a variety of molecular markers expressed in specific subdivisions reveal distinct boundaries that partition the cerebellity into true developmental compartments.
Abstract: The concept of developmental compartments originated in studies of Drosophila embryogenesis. This review examines the hypothesis that the modular structure of the vertebrate cerebellum is strongly analogous to this earlier scheme. The pattern of cerebellar development, the adult circuitry, a variety of molecular markers expressed in specific subdivisions, and the phenotypes of several neurological mutations all provide abundant evidence that the vertebrate cerebellum is organized into modules. We present the case that, as a group, these markers reveal distinct boundaries that partition the cerebellum into true developmental compartments. Although this reductionist viewpoint advances our understanding of cerebellar organization, the relationship between these compartments and the functional behavior of the cerebellum remains a mystery.
303 citations
TL;DR: Molecular cloning of vesicular monoamine transporters shows sequence similarity to bacterial antibiotic resistance proteins, supporting a role for transport in detoxification and defining a novel mammalian gene family that now also includes a transporter for acetylcholine.
Abstract: ▪ Abstract Classical neurotransmitters are synthesized in the cytoplasm, so they require transport into secretory vesicles for regulated exocytotic release. Previous work has identified distinct vesicular transport activities for the different classical transmitters, and all depend on the H+-electrochemical gradient across the vesicle membrane but differ in the extent to which they rely on the chemical and electrical components of this gradient. Drugs that interfere with vesicular amine transport have implicated this activity in psychiatric disease. Selection for a cDNA encoding vesicular amine transport in the neurotoxin MPP+ also implicates the activity in Parkinson's disease. Molecular cloning of vesicular monoamine transporters shows sequence similarity to bacterial antibiotic resistance proteins, supporting a role for transport in detoxification and defining a novel mammalian gene family that now also includes a transporter for acetylcholine. Current work focuses on the mechanism of transport and the...
TL;DR: This review discusses how studies of mutant mice have helped elucidate the mechanisms that underlie synaptic plasticity and the relationship of these synaptic mechanisms to the activity-dependent phase of neural development and learning and memory.
Abstract: Recently, dozens of mutant mice generated with gene targeting or transgenic technologies have been shown to exhibit a distinct set of impairments in the brain and behavior. In this review, we discuss how studies of mutant mice have helped elucidate the mechanisms that underlie synaptic plasticity and the relationship of these synaptic mechanisms to the activity-dependent phase of neural development and learning and memory. We focus on the recent progress in the analysis of whisker-related pattern formation, elimination of climbing fibers, long-term potentiation, long-term depression, and various learning and memory tasks in mutant mice.
TL;DR: The predicted amino acid sequence suggests that ARIA is synthesized as a transmembrane precursor protein and that it is a member of a family of ligands that activate receptor tyrosine kinases related to the epidermal growth factor receptor.
Abstract: ▪ Abstract Motor neurons influence the expression and the distribution of acetylcholine receptors in skeletal muscle. Molecules that mediate this carefully choreographed interaction have recently been identified. One of them, ARIA, is a polypeptide purified from chicken brain on the basis of its ability to stimulate the synthesis of muscle acetylcholine receptors. The predicted amino acid sequence suggests that ARIA is synthesized as a transmembrane precursor protein and that it is a member of a family of ligands that activate receptor tyrosine kinases related to the epidermal growth factor receptor. Certain features of the ligand family (the neuregulins) and their receptors (erbBs) are reviewed. Evidence that ARIA plays an important role at developing and mature neuromuscular junctions is discussed.
TL;DR: The mechanisms by which human speech is processed in the brain are reviewed from both behavioral and neurobiological perspectives, and the separation of speech processing as a complex acoustic-processing task versus a linguistic task is separated.
Abstract: The mechanisms by which human speech is processed in the brain are reviewed from both behavioral and neurobiological perspectives. Special consideration is given to the separation of speech processing as a complex acoustic-processing task versus a linguistic task. Relevant animal research is reviewed, insofar as these data provide insight into the neurobiological basis of complex acoustic processing in the brain.
TL;DR: Genetic screens for touch-insensitive nematodes or flies promise to identify the proteins that constitute a mechanosensory apparatus in eukaryotes, which includes a "degenerin" channel tethered to specialized extracellular and intracellular structural proteins.
Abstract: ▪ Abstract Mechanosensation, the transduction of mechanical forces into a cellular electrochemical signal, enables living organisms to detect touch; vibrations, such as sound; accelerations, including gravity; body movements; and changes in cellular volume and shape. Ion channels directly activated by mechanical tension are thought to mediate mechanosensation in many systems. Only one channel has been cloned that is unequivocably mechanically gated: the MscL channel in bacteria. Genetic screens for touch-insensitive nematodes or flies promise to identify the proteins that constitute a mechanosensory apparatus in eukaryotes. In Caenorhabditis elegans, the mec genes thus identified encode molecules for a candidate structure, which includes a “degenerin” channel tethered to specialized extracellular and intracellular structural proteins. In hair cells of the inner ear, evidence suggests that an extracellular tip link pulls on a channel, which attached intracellularly to actin via a tension-regulating myosin ...
TL;DR: A review of factors involved in the specification of neural fate within the frame of the default model of neural induction focuses on factors with direct neural-inducing ability.
Abstract: ▪ Abstract During early vertebrate development, the cells of the ectoderm choose between two possible fates: neural and epidermal. The process of neural induction was discovered nearly 70 years ago in vertebrates, and molecular analyses in recent years using Xenopus laevis embryos have identified several secreted factors with direct neural-inducing ability. There is considerable evidence that the mechanism of neuralization by these inducing factors is under inhibitory control and involves derepression. This review focuses on factors involved in the specification of neural fate within the frame of the default model of neural induction.
TL;DR: Mechanisms of regulating cell phenotype in the cortex that are common to all parts of the neuraxis are suggested.
Abstract: Regionalization of the cerebral cortex occurs during development by the formation of anatomically and functionally discrete areas of the brain. Descriptive evidence based on expression of molecules and structural features suggests that an early parcelation of the cerebral wall may occur during fetal development. Experimental strategies using tissue transplants and cell culture models have explored the nature of the timing of areal specification. New signaling systems displaying the sensitivity of precursor cells to environmental cues that define the fate of neurons destined for specific areas of the cortex have been discovered. Studies in the field now suggest mechanisms of regulating cell phenotype in the cortex that are common to all parts of the neuraxis.
TL;DR: This highly selective review of the song system of zebra finches discusses the important role of sex steroid hormones and of neurotrophins in creating a male-typical neural song circuit (which can learn to produce complex vocalizations) instead of a reduced, female-Typical song circuit that does not produce learned song.
Abstract: The neural substrate underlying learned vocal behavior in songbirds provides a textbook illustration of anatomical localization of function for a complex learned behavior in vertebrates. The song-control system has become an important model for studying neural systems related to learning, behavior, and development. The song system of zebra finches is characterized by a heightened capacity for both neural and behavioral change during development and has taught us valuable information regarding sensitive periods, rearrangement of synaptic connections, topographic specificity, cell death and neurogenesis, experience-dependent neural plasticity, and sexual differentiation. The song system differs in some interesting ways from some well-studied mammalian model systems and thus offers fresh perspectives on specific theoretical issues. In this highly selective review, we concentrate on two major questions: What are the developmental changes in the song system responsible for song learning and the restriction of learning to a sensitive period, and what factors explain the highly sexually dimorphic development of this system? We discuss the important role of sex steroid hormones and of neurotrophins in creating a male-typical neural song circuit (which can learn to produce complex vocalizations) instead of a reduced, female-typical song circuit that does not produce learned song.
TL;DR: This review examines recent studies employing simultaneous recording of ten or more individual neurons in the mammalian brain and discusses whether ensemble information content reconstructed from single-neuron recordings may be underestimated if compared to ensembles where those same neurons were recorded simultaneously.
Abstract: The development of techniques to record from populations of neurons has made it possible to ask questions concerning the encoding of task-relevant information in awake, behaving animals. The issue of how groups of neurons within different brain structures register and retrieve representations of behaviorally significant events can now be addressed using multineuron-recording techniques. This review examines recent studies employing simultaneous recording of ten or more individual neurons in the mammalian brain. A major issue discussed is whether ensemble information content reconstructed from single-neuron recordings may be underestimated if compared to ensembles where those same neurons were recorded simultaneously. The mechanics of ensemble information encoding in the hippocampus is illustrated from population statistical analyses of ensemble activity during performance of a delay task. Detailed descriptions of methods of extracting ensemble information, as well as cross-correlational analyses, are discussed in the context of emergent issues regarding interpretation of ensemble data.
TL;DR: By bringing the endocrine system under the control of the brain, it allows access to external environmental inputs, learned behavior patterns, and the whole of the central integrative machinery needed for the bodily functions to be sensitively and optimally adapted to the ever-changing challenges and opportunities in the outside world.
Abstract: Geoffrey Harris is responsible for our view that the brain controls the endocrine system by an exquisitely regulated pattern of synthesis and release of individual members of a family of peptide hormones. These hormones are carried through a portal vascular system that passes from the hypothalamus to the pituitary gland, where they selectively regulate the secretion of the six anterior pituitary hormones. This family of hypothalamic hormones is highly conserved in all vertebrates, including humans. They are essential for all aspects of reproduction—courtship, mating, pregnancy and young rearing—and they are responsible for the seasonal regulation of breeding. The hypothalamic control mechanism for reproduction is sexually dimorphic, with a basic female pattern that becomes masculinized under the influence of specific steroid hormones acting during development. Other members of the hypothalamic hormone family specifically regulate the secretion of pituitary growth hormone and the anterior pituitary hormones controlling the functions of the thyroid and adrenal glands. The secretion of the hypothalamic hormones is itself regulated by the feedback of the target gland hormones (such as estrogen and progesterone), which concurrently act on the brain to elicit appropriate behavior patterns. The hypothalamo-hypophysial axis plays a crucial role in the struggle for the survival of the species. By bringing the endocrine system under the control of the brain, it allows access to external environmental inputs, learned behavior patterns, and the whole of the central integrative machinery needed for the bodily
TL;DR: As molecular mechanisms of inheritance are elucidated, it will be important to consider the ethical implications of genetic testing in a clinically and genetically complex disorder such as manic depressive illness.
Abstract: Manic depressive illness is a common and frequently debilitating familial psychiatric disorder. Efforts to understand the mechanisms of inheritance have been hindered by the complexity of the phenotype, which may range from benign mood swings to chronic psychosis, and by apparently nonmendelian modes of transmission. Early reports of linkage to chromosomal loci have fallen into doubt; however they have helped encourage the development of more sophisticated methods for analyzing complex phenotypes. Using such methods, linkage of manic depressive illness to loci on chromosome 18 has been reported and apparently replicated, and work is proceeding to identify genes associated with what is probably a genetically heterogeneous set of disorders. As molecular mechanisms of inheritance are elucidated, it will be important to consider the ethical implications of genetic testing in a clinically and genetically complex disorder such as manic depressive illness.