The faithful copy neuron

Theoretical and experimental evidence is presented for the presence in nervous tissue of neurons whose firing rate faithfully follow their input stimulus. Such neurons are shown to deliver their spikes with minimum dissipation per spike. This optimal performance is likely accomplished by use of local circuitry that adjusts conductances to match input currents so that the neuron operates near the threshold for firing. This results in an unusual mechanism for neuronal firing that uses background noise to achieve the desired firing rate. This framework takes place dynamically, and the present deliberations apply under time varying conditions. It is shown that an analytically explicit probability distribution function, which depends on one dimensionless parameter, can account for the interspike interval statistics under general time varying conditions. An innovative analysis based on the unsteady firing rate fits data to the appropriate probability distribution function.     

神经元特异性烯醇化酶

神经元特异性烯醇化酶(neuron specific enolase,NsE)是烯醇化酶的一种同工酶,该酶不仅参加糖酵解反应,而且还具有神经营养因子作用,对神经系统疾病和肿瘤的诊断、治疗和预后等也有重要作用.本文将从NSE的理化特性、生物学功能和临床应用等方面对其进行阐述.     

Magnetoencephalography study of right parietal lobe dysfunction of the evoked mirror neuron system in antipsychotic-free schizophrenia

IntroductionPatients with schizophrenia commonly exhibit deficits of non-verbal communication in social contexts, which may be related to cognitive dysfunction that impairs recognition of biological motion. Although perception of biological motion is known to be mediated by the mirror neuron system, there have been few empirical studies of this system in patients with schizophrenia.MethodsUsing magnetoencephalography, we examined whether antipsychotic-free schizophrenia patients displayed mirror neuron system dysfunction during observation of biological motion (jaw movement of another individual).ResultsCompared with normal controls, the patients with schizophrenia had fewer components of both the waveform and equivalent current dipole, suggesting aberrant brain activity resulting from dysfunction of the right inferior parietal cortex. They also lacked the changes of alpha band and gamma band oscillation seen in normal controls, and had weaker phase-locking factors and gamma-synchronization predominantly in right parietal cortex.ConclusionsOur findings demonstrate that untreated patients with schizophrenia exhibit aberrant mirror neuron system function based on the right inferior parietal cortex, which is characterized by dysfunction of gamma-synchronization in the right parietal lobe during observation of biological motion.     

The epileptic neuron: I

Mathematical models of neurons are studied which exhibit spontaneous and repetitive firings in the absence of normally occurring substances. The activity of such neurons could result in the symptoms of epilepsy. The identification of such substances would be important in the treatment of the disease as well as in the understanding of their mode of action. The importance of the geometrical and physical parameters for the generation of spontaneous repetitive discharges is brought out.     

The epileptic neuron: II

Conditions under which a neuron can maintain repetitive discharges are studied with the view that some light may be shed on the problem of epilepsy. It is shown that if there are excitatory and inhibitory substances as well as binding substances in volved, then for repetitive discharges to occur, the formation of the substances must be intracellular. The geometric physical characteristics of the system are also determining factors. The role of a fatigue factor is considered in an attempt to understand the frequency and duration of mild and severe epileptic attacks.     

Developmental patterns of doublecortin expression and white matter neuron density in the postnatal primate prefrontal cortex and schizophrenia

Postnatal neurogenesis occurs in the subventricular zone and dentate gyrus, and evidence suggests that new neurons may be present in additional regions of the mature primate brain, including the prefrontal cortex (PFC). Addition of new neurons to the PFC implies local generation of neurons or migration from areas such as the subventricular zone. We examined the putative contribution of new, migrating neurons to postnatal cortical development by determining the density of neurons in white matter subjacent to the cortex and measuring expression of doublecortin (DCX), a microtubule-associated protein involved in neuronal migration, in humans and rhesus macaques. We found a striking decline in DCX expression (human and macaque) and density of white matter neurons (humans) during infancy, consistent with the arrival of new neurons in the early postnatal cortex. Considering the expansion of the brain during this time, the decline in white matter neuron density does not necessarily indicate reduced total numbers of white matter neurons in early postnatal life. Furthermore, numerous cells in the white matter and deep grey matter were positive for the migration-associated glycoprotein polysialiated-neuronal cell adhesion molecule and GAD65/67, suggesting that immature migrating neurons in the adult may be GABAergic. We also examined DCX mRNA in the PFC of adult schizophrenia patients (n?=?37) and matched controls (n?=?37) and did not find any difference in DCX mRNA expression. However, we report a negative correlation between DCX mRNA expression and white matter neuron density in adult schizophrenia patients, in contrast to a positive correlation in human development where DCX mRNA and white matter neuron density are higher earlier in life. Accumulation of neurons in the white matter in schizophrenia would be congruent with a negative correlation between DCX mRNA and white matter neuron density and support the hypothesis of a migration deficit in schizophrenia.     

The specification of sensory neuron identity in Drosophila

Different types of sense organs are present on the larva of Drosophila. Several genes that specify the type of sense organ that will form at a particular position have been recently identified. Here we review the functional and molecular analyses of these genes, and summarize the evidence which supports a role in the choice of which type of organ will be formed. Most or all of these genes are required for the appropriate specification of adult as well as larval sense organs, suggesting that the larval and adult systems share many gene requirements. Interestingly, the specifying genes identified so far in the peripheral nervous system are also expressed in subsets of cells in the central nervous system, where they might have similar roles.     

The calcium current of Helix neuron

Calcium current, Ica, was studied in isolated nerve cell bodies of Helix aspersa after suppression of Na+ and K+ currents. The suction pipette method described in the preceding paper was used. Ica rises to a peak value and then subsides exponentially and has a null potential of 150 mV or more and a relationship with [Ca2+]o that is hyperbolic over a small range of [Ca2+]o's. When [Ca2+]i is increased, Ica is reduced disproportionately, but the effect is not hyperbolic. Ica is blocked by extracellular Ni2+, La3+, Cd2+, and Co2+ and is greater when Ba2+ and Sr2+ carry the current. Saturation and blockage are described by a Langmuir adsorption relationship similar to that found in Balanus. Thus, the calcium conductance probably contains a site which binds the ions referred to. The site also appears to be voltage-dependent. Activation and inactivation of Ica are described by first order kinetics, and there is evidence that the processes are coupled. For example, inactivation is delayed slightly in its onset and tau inactivation depends upon the method of study. However, the currents are described equally well by either a noncoupled Hodgkin-Huxley mh scheme or a coupled reaction. Facilitation of Ica by prepulses was not observed. For times up to 50 ms, currents even at small depolarizations were accounted for by suitable adjustment of the activation and inactivation rate constants.     

The molecular economics of the long neuron

Summary 1. Nerve cells grow by progressively changing their nucleo-cytoplasmic ratio, whereas growth in other cell types is associated with an increase in number of nuclei or degree of ploidy of a single nucleus in such a way that the nucleo-cytoplasmic ratio is maintained within its original order of magnitude.2. Reasons are given for supposing that the primary factor in maintaining the nucleo-cytoplasmic ratio within its usual order of magnitude lies in the peculiar nature of protein metabolism which is keyed to a fixed number of DNA molecules.3. An input-output model was constructed of a molecular system operating under similar limitations and its properties examined.4. By altering the values under which the system operated it was possible to examine the ways in which the system could grow. Patterns emerged for both limited and indefinite growth, both ultimately depending on the supply of molecules with a short half-life.5. The pattern of indefinite growth which most nearly resembled that of the long neuron was one in which the deficiencies in labile molecules encountered by an extending system were met by transfer of similar molecules from adjacent unextended systems. The extended system, however, became liable to contract molecular debts whose magnitude was related to the degree of extension of the system.6. A series of comparisons were drawn between the properties of the model and the observed morphological, biochemical and physiological characteristics of neural tissue. The coincidences were found to be sufficiently numerous to suggest that models of this type may be useful in correlating morphological and biochemical findings in the nervous system and in the design of experiments.

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Die molekulare Ökonomie der langen Neuronen

Kurzfassung Im Gegensatz zu anderen Zellen ist ein Neuron in der Lage, durch Veränderung der Kern-Plasma-Relation progressiv zu wachsen. Dieses Phänomen wurde untersucht, wobei der Eiweißstoffwechsel einer Zelle als limitierender Faktor für die Erhaltung der normalen Kern-Plasma-Relation angesehen wurde. Es wurde ein Modell eines Systems konstruiert, mit voneinander abhängigen Molekülen verschiedener Halblebenszeiten, welche unter den Bedingungen molekularen Austausches operieren, die den Proteinstoffwechsel zu beherrschen und einzuschränken scheinen. Dann wurde geprüft, auf welche Weise dieses System sich durch Anstieg der Molekülzahlen auszudehnen vermag. In einer weitgehend dem Muster des unbeschränkten Wachstums der langen Neuronen ähnelnden Situation wurde dem Mangel an Molekülen mit kurzer Halblebenszeit (diese wurden in sich ausdehnenden Systemen gefunden) durch Überführung ähnlicher Moleküle aus benachbarten, nicht ausgedehnten Systemen begegnet. Das ausgedehnte System neigte aber dazu, Molekülschulden auf sich zu laden, deren Höhe abhing von dem Ausmaß der Systemausdehnung. Diese Sachverhalte stimmten überein mit vielen beobachteten histologischen, biochemischen und physiologischen Charakteristika der Nervengewebe. Es wurde daher gefolgert, daß Modelle dieser Art nützlich sein können hinsichtlich einer Korrelation morphologischer und biochemischer Befunde und der Planung geeigneter Experimente.