A circadian clock regulates rod and cone input to fish retinal cone horizontal cells.

In the vertebrate retina, the light responses of post-receptor neurons depend on the ambient or background illumination. Using intracellular recording, we have found that a circadian clock regulates the light responses of dark-adapted fish cone horizontal cells. Goldfish were maintained on a 12-hr light/12-hr dark cycle. At different times of the day or night, retinas were superfused in darkness for 90 min ("prolonged darkness"), following which horizontal cells were impaled without the aid of any light flashes. In some of the experiments, fish were kept in constant darkness for 3-48 hr prior to surgery. After prolonged darkness during the night, but not during the day, the light responses of L-type cone horizontal cells resembled those of rod horizontal cells with respect to threshold, waveform, intensity-response functions, and spectral sensitivity. Following light sensitization during the night and day, the light responses of rod and cone horizontal cells were clearly different with respect to threshold, waveform, intensity-response functions, and spectral sensitivity. Under conditions of constant darkness for two full light/dark cycles, average responses of cone horizontal cells to a bright light stimulus during the subjective day were greater than during the subjective night. Prior reversal of the light/dark cycle reversed the 24-hr rhythm of cone horizontal cell responses to bright lights. In addition, following one full cycle of constant darkness, average cone horizontal cell spectral sensitivity during the subjective night closely matched that of rod horizontal cells, whereas average cone horizontal cell spectral sensitivity during the subjective day was similar to that of red (625 nm) cones. These results indicate that the effects of dark adaptation depend on the time of day and are regulated by a circadian clock so that cone input to cone horizontal cells predominates in the day and rod input predominates in the night.

Potentiation of proton transfer function by electrostatic interactions in photosynthetic reaction centers from Rhodobacter sphaeroides: First results from site-directed mutation of the H subunit.

The x-ray crystallographic structure of the photosynthetic reaction center (RC) has proven critical in understanding biological electron transfer processes. By contrast, understanding of intraprotein proton transfer is easily lost in the immense richness of the details. In the RC of Rhodobacter (Rb.) sphaeroides, the secondary quinone (QB) is surrounded by amino acid residues of the L subunit and some buried water molecules, with M- and H-subunit residues also close by. The effects of site-directed mutagenesis upon RC turnover and quinone function have implicated several L-subunit residues in proton delivery to QB, although some species differences exist. In wild-type Rb. sphaeroides, Glu L212 and Asp L213 represent an inner shell of residues of particular importance in proton transfer to QB. Asp L213 is crucial for delivery of the first proton, coupled to transfer of the second electron, while Glu L212, possibly together with Asp L213, is necessary for delivery of the second proton, after the second electron transfer. We report here the first study, by site-directed mutagenesis, of the role of the H subunit in QB function. Glu H173, one of a cluster of strongly interacting residues near QB, including Asp L213, was altered to Gln. In isolated mutant RCs, the kinetics of the first electron transfer, leading to formation of the semiquinone, QB-, and the proton-linked second electron transfer, leading to the formation of fully reduced quinol, were both greatly retarded, as observed previously in the Asp L213 --> Asn mutant. However, the first electron transfer equilibrium, QA-QB <==> QAQB-, was decreased, which is opposite to the effect of the Asp L213 --> Asn mutation. These major disruptions of events coupled to proton delivery to QB were largely reversed by the addition of azide (N3-). The results support a major role for electrostatic interactions between charged groups in determining the protonation state of certain entities, thereby controlling the rate of the second electron transfer. It is suggested that the essential electrostatic effect may be to "potentiate" proton transfer activity by raising the pK of functional entities that actually transfer protons in a coupled fashion with the second electron transfer. Candidates include buried water (H3O+) and Ser L223 (serine-OH2+), which is very close to the O5 carbonyl of the quinone.

Transcription of tufA and other chloroplast-encoded genes is controlled by a circadian clock in Chlamydomonas.

Levels of mRNA for the chloroplast-encoded elongation factor Tu (tufA) showed a dramatic daily oscillation in the green alga Chlamydomonas reinhardtii, peaking once each day in the early light period. The oscillation of tufA mRNA levels continued in cells shifted to continuous light or continuous dark for at least 2-3 days. Run-off transcription analyses showed that the rate of tufA transcription also peaked early in the light period and, moreover, that this transcriptional oscillation continued in cells shifted to continuous conditions. The half-life of tufA mRNA was estimated at different times and found to vary considerably during a light-dark cycle but not in cells shifted to continuous light. Light-dark patterns of transcription of several other chloroplast-encoded genes were examined and also found to persist in cells shifted to continuous light or dark. These results indicate that a circadian clock controls the transcription of tufA and other chloroplast-encoded genes.

Habituation of an invertebrate escape reflex due to modulation by higher centers rather than local events.

Learning is widely thought to result from altered potency of synapses within the neural pathways that mediate the learned behavior. Support for this belief, which pervades current physiological and computational thinking, comes especially from the analysis of cases of simple learning in invertebrates. Here, evidence is presented that in one such case, habituation of crayfish escape, the learning is more due to onset of tonic descending inhibition than to the intrinsic depression of circuit synapses to which it was previously attributed. Thus, the altered performance seems to depend at least as much on events in higher centers as on local plasticity.

Electrogenic light reactions in photosystem I: resolution of electron-transfer rates between the iron-sulfur centers.

Flash-induced voltage changes (electrogenic events) in photosystem I particles from spinach, oriented in a phospholipid layer, have been studied at room temperature on a time scale ranging from 1 micros to several seconds. A phospholipid layer containing photosystem I particles was adsorbed to a Teflon film separating two aqueous compartments. Voltage changes were measured across electrodes immersed in the compartments. In the absence of added electron donors and acceptors, a multiphasic voltage increase, associated with charge separation, was followed by a decrease, associated with charge recombination. Several kinetic phases were resolved: a rapid (<1 micros) increase, ascribed to electron transfer from the primary electron donor P700 to the iron-sulfur electron acceptor FB, was followed by a slower, biphasic increase with time constants of 30 and 200 micros. The 30-micros phase is assigned to electron transfer from FB to the iron-sulfur center FA. The voltage decrease had a time constant of 90 ms, ascribed to charge recombination from FA to P700. Upon chemical prereduction of FA and FB the 30- and 200-micros phases disappeared and the decay time constant was accelerated to 330 micros, assigned to charge recombination from the phylloquinone electron acceptor (A1) or the iron-sulfur center FX to P700.

The location of the Spanish technological centers

Paper submitted to the 42nd Congress of ERSA, Dortmund, August 27th–31st 2002.

Smart Monitoring Embedded Service for Energy-Efficient and Sustainable Management in Data Centers

Information technologies (IT) currently represent 2% of CO2 emissions. In recent years, a wide variety of IT solutions have been proposed, focused on increasing the energy efficiency of network data centers. Monitoring is one of the fundamental pillars of these systems, providing the information necessary for adequate decision making. However, today’s monitoring systems (MSs) are partial, specific and highly coupled solutions. This study proposes a model for monitoring data centers that serves as a basis for energy saving systems, offered as a value-added service embedded in a device with low cost and power consumption. The proposal is general in nature, comprehensive, scalable and focused on heterogeneous environments, and it allows quick adaptation to the needs of changing and dynamic environments. Further, a prototype of the system has been implemented in several devices, which has allowed validation of the proposal in addition to identification of the minimum hardware profile required to support the model.

Post-H1N1 Flu Vaccination Narcolepsy in Switzerland: A Retrospective Survey in the 30 Sleep-Certified Swiss Centers

Narcolepsy-cataplexy is a sleep-wake disorder and suggested to be immune-mediated, involving genetic and environmental factors. The autoimmune process eventually leads to a loss of hypocretin neurons in the lateral hypothalamus. Epidemiological studies in several countries proved an increased incidence of narcolepsy after H1N1 flu vaccination and infection. This survey in 30 sleep centers in Switzerland led to the identification of 9 H1N1-vaccinated children and adults as newly diagnosed narcolepsy. Clinical features included the abrupt and severe onset of sleepiness, cataplexy and sleep fragmentation.

Preliminary human factors guidelines for traffic management centers.

Federal Highway Administration, ITS Joint Program Office, Washington, D. C.

Directory of content specialists of the national research centers & regional educational laboratories.

Mode of access: Internet.

Complications incurred because of delays in transferring patients to VA spinal cord injury treatment centers; report to the Congress [on the] Veterans Administration [and] Department of Defense by the Comptroller General of the United States.

"B-133044."

A supplement to area health education centers : a directory of Federal, State, local and private decentralized health professional education programs /

Mode of access: Internet.

Export refining centers of the World /

"A (ER) 75-66."

Comparable systems analysis: evaluation of ten command centers as potential sites.

Turner-Fairbank Highway Research Center, McLean, Va.