The role of NMDA and non-NMDA glutamate receptors in long-term potentiation has been intensely investigated, yet recent evidence on the dynamics of synaptic depolarization suggests that the original view should be extended. NMDA receptor-mediated currents, apart from their Ca2+ permeability, show a marked voltage dependence, consisting of current increase and slowdown during membrane depolarization. During high-frequency synaptic transmission, NMDA current increase and slowdown are primed by non-NMDA receptor-dependent depolarization and proceed regeneratively. Thus, NMDA receptors make a decisive contribution to membrane depolarization and spike-firing. From the data obtained at the mossy fibergranule cell synapse of the cerebellum, we propose that the electrogenic role of NMDA receptors is functional to LTP induction. Moreover, during LTP, both NMDA and non-NMDA receptor currents are potentiated, thus establishing a feed-forward mechanism that ultimately enhances spike firing. Thus, NMDA receptors exert an integrated control on signal coding and plasticity. This mechanism may have important implications for information processing at the cerebellar mossy fibergranule cell relay.

Animals↗

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Endocrine studies in children with myelomeningocele.

Pituitary-hypothalamic abnormalities due to impaired cerebrospinal fluid circulation have long been recognized. The aim of this study was to assess pituitary, thyroid, adrenal, and gonadal function in 46 prepubertal (22 M and 24 F) and 10 pubertal (4 M and 6 F) subjects with myelomeningocele (MMC). Basal serum levels of FT3, FT4, TSH, PRL, LH, FSH, T or E2, cortisol, 17-OH-P and DHEA-S were measured by routine radio-immunoassay methods. Twenty-two prepubertal patients had a TRH test for TSH and PRL evaluation, and eight underwent a GnRH test. Three patients presented with precocious puberty. Six subjects had modest elevations of serum TSH together with normal free thyroid hormone levels. In three cases, TSH responses to TRH were significantly exaggerated and prolonged: in two patients, TSH responses were delayed. The mean basal plasma FSH level in females with ventriculo-peritoneal shunt was significantly higher than in controls. In six cases FSH responses to GnRH were significantly higher than in controls. Both basal and stimulated PRL levels were elevated in patients with shunts; in patients without shunts, basal PRL was normal, but peak PRL levels following TRH stimulation were elevated. Our data show an abnormal hypothalamic-pituitary function in MMC subjects. These findings reinforce the importance of physical examination, hormonal evaluation and follow-up of pubertal development in patients with myelomeningocele.

Adolescent↗

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Rapid, sensitive, microscale determination of phosphate in water and soil.

A rapid and sensitive analysis of inorganic and organic phosphorus (P) is needed to analyze water and soil extracts at submicromolar concentrations. The proposed method, based on the complexation of malachite green with phosphomolybdate under acidic conditions, was adapted to a 96-well microtiter plate format, and was tested for matrix interferences using 15 soils and some common extractants, including water, KCI, CaCl2, NaOH, and HCl. The accuracy of P determination was affected when CaCl2 and HCl concentrations were greater than 0.1 M and when NaOH concentration exceeded 0.4 M. Potassium chloride concentration up to 1 M did not interfere with P determination. The molar absorptivity was 46 841 M(-1) cm(-1) and the reagent blank absorbance was 0.071+/-0.003 (n = 10). At the 99% confidence limit, the method detection limit was calculated to be 0.006 mg P L(-1). Recovery of added inorganic P in different types of soils and extracts ranged between 95 and 112% with an average of 102%. The proposed microplate method allows P to be determined rapidly in a wide range of soil types and extracts and requires limited volume (20-200 microL). The procedure uses limited quantities (40 microL) of two stable reagents (>1 yr), and generates low amounts of hazardous waste.

Chemistry Techniques, Analytical↗

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Synaptic mechanisms in long-term potentiation.

Long-term potentiation (LTP) is a robust form of synaptic enhancement that far outlasts the duration of active stimulus. LTP represents the most intriguing form of synaptic memory, mainly due to its long duration and associative properties, and is held to be involved in learning processes at the behavioural level. Advances in the understanding of central synaptic functions are now extending interest in LTP to the fine detail of its synaptic mechanisms.

Animals↗

PubMedDate not supplied

Excitatory amino acid regulation of neuronal functions.

Excitatory amino acids (EAAs), usually glutamate, activate the greatest excitatory system in the vertebrate brain. EAAs mediate synaptic transmission and control the stability and efficiency of synaptic connections. Moreover, EAAs provide the postsynaptic neurone with chemical cues for survival and maturation. Improper activation of EAA receptors can lead to neurotoxicity and be involved in the pathogenesis of certain neurological diseases.

Amino Acids↗

PubMedDate not supplied

Glutamate metabolism, release, and quantal transmission at central excitatory synapses: implications for neural plasticity.

Glutamate is thought to act as a neurotransmitter at several excitatory synapses in the brain. Available knowledge reveals complex intercompartmental dynamics of glutamate, which is synthesized, accumulated and released by presynaptic elements, activates postsynaptic receptors, and is eventually re-uptaken and interconverted to glutamine by the participation of surrounding glial cells. The postsynaptic reactions to physiological release of glutamate during neurotransmission are considered in relation to the quantal approach, which is revealing unsuspected complexity in central synaptic mechanisms. This issue is particularly important in view of its implications in the study of long-term synaptic modifications.

Animals↗

PubMedDate not supplied