Relationship between afferent and central temporal patterns in the locust olfactory system

Odors evoke synchronized oscillations and slow temporal patterns in antennal lobe neurons and fast oscillations in the mushroom body local field potential (LFP) of the locust. What is the contribution of primary afferents in the generation of these dynamics? We addressed this question in two ways. First, we recorded odor-evoked afferent activity in both isolated antennae and intact preparations. Odor-evoked population activity in the antenna and the antennal nerve consisted of a slow potential deflection, similar for many odors. This deflection contained neither oscillatory nor odor-specific slow temporal patterns, whereas simultaneously recorded mushroom body LFPs exhibited clear 20-30 Hz oscillations. This suggests that the temporal patterning of antennal lobe and mushroom body neurons is generated downstream of the olfactory receptor axons. Second, we electrically stimulated arrays of primary afferents in vivo. A brief shock to the antennal nerve produced compound PSPs in antennal lobe projection neurons, with two peaks at an approximately 50 msec interval. Prolonged afferent stimulation with step, ramp, or slow sine-shaped voltage waveforms evoked sustained 20-30 Hz oscillations in projection neuron membrane potential and in the mushroom body LFP. Projection neuron and mushroom body oscillations were phase-locked and reliable across trials. Synchronization of projection neurons was seen directly in paired intracellular recordings. Pressure injection of picrotoxin into the antennal lobe eliminated the oscillations evoked by electrical stimulation. Different projection neurons could express different temporal patterns in response to the same electrical stimulus, as seen for odor-evoked responses. Conversely, individual projection neurons could express different temporal patterns of activity in response to step stimulation of different spatial arrays of olfactory afferents. These patterns were reliable and remained distinct across different stimulus intensities. We conclude that oscillatory synchronization of olfactory neurons originates in the antennal lobe and that slow temporal patterns in projection neurons can arise in the absence of temporal patterning of the afferent input.     

Human brain metabolic response to caffeine and the effects of tolerance

OBJECTIVE: Since there is limited information concerning caffeine's metabolic effects on the human brain, the authors applied a rapid proton echo-planar spectroscopic imaging technique to dynamically measure regional brain metabolic responses to caffeine ingestion. They specifically measured changes in brain lactate due to the combined effects of caffeine's stimulation of glycolysis and reduction of cerebral blood flow. METHOD: Nine heavy caffeine users and nine caffeine-intolerant individuals, who had previously discontinued or substantially curtailed use of caffeinated products because of associated anxiety and discomforting physiological arousal, were studied at baseline and then during 1 hour following ingestion of caffeine citrate (10 mg/kg). To assess state-trait contributions and the effects of caffeine tolerance, five of the caffeine users were restudied after a 1- to 2-month caffeine holiday. RESULTS: The caffeine-intolerant individuals, but not the regular caffeine users, experienced substantial psychological and physiological distress in response to caffeine ingestion. Significant increases in global and regionally specific brain lactate were observed only among the caffeine-intolerant subjects. Reexposure of the regular caffeine users to caffeine after a caffeine holiday resulted in little or no adverse clinical reaction but significant rises in brain lactate which were of a magnitude similar to that observed for the caffeine-intolerant group. CONCLUSIONS: These results provide direct evidence for the loss of caffeine tolerance in the human brain subsequent to caffeine discontinuation and suggest mechanisms for the phenomenon of caffeine intolerance other than its metabolic effects on elevating brain lactate.     

Upper tibial hyperextension fractures in infants: another occult toddler''s fracture

Our study describes a newly designed stapedotomy prosthesis which consists of two components: (1) a platinum ribbon, and (2) a Teflon shaft. The first innovation is a flattened 'tab' on the posterior aspect of the platinum ribbon. The second innovation concerns the dual diameter cylinder-like shaft. Our prosthesis was implanted into 25 individuals, who underwent stapedotomy for stapes fixation, and the results are shown and discussed. Our innovations offer a proper and safe insertion of the prosthesis into the oval window associated with excellent manipulation and handling. At the same time, maximum visualization of the surgical field is achieved, while the stepped-down design of the shaft prevents the prosthesis protruding into the vestibule.     

Combination antiretroviral therapy and recent declines in AIDS incidence and mortality

The reasons for recent declines in AIDS incidence and mortality may include advances in treatment, but these may be confounded by earlier declines in the incidence of human immunodeficiency virus (HIV) infection. To determine whether the declines in AIDS and mortality may, in part, stem from wider use of combination antiretroviral therapy, 622 HIV-positive men with well-characterized dates of seroconversion were followed. In this group, combination therapy came into widespread use in only 1996. In a Cox proportional hazards model, the 1996 calendar period was significantly associated with slower progression to AIDS (relative hazard [RH]=0. 19, 95% confidence interval [CI], 0.05-0.69, P=.01) and death (RH=0. 45, 95% CI, 0.21-0.95, P=.04). Declines in incidence of HIV infection, changes in HIV virulence, and end-point underreporting cannot fully explain the decline in AIDS and death in 1996. The introduction of combination antiretroviral therapy as the standard of care may already have had measurable effects.     

The use of ceramic onlays for restoring the occlusal surface of the teeth

Computer-aided milling of ceramic insertions helped more effectively repair the masticatory surface of teeth, minimize the incidence of errors, rule out the laboratory stage of making the insertions and the technological errors made at this stage, retain physical and mechanical characteristics of ceramics, optimize marginal adherence of the insertion to the tooth, retain the height of the lower part of the face, and thus prevent the maxillodental dysfunction.     

The yeast mic2 mutant is defective in the formation of mannosyl-diinositolphosphorylceramide

Three transmembrane glutamic acid residues play essential roles in the metal-tetracycline/H+ antiporter Tet(K) of Staphylococcus aureus [Fujihira et al., FEBS Lett. 391 (1996) 243-246]. In the putative hydrophilic loop region of the Tet(K) and Tet(L) proteins, six acidic residues are conserved. Asp74, Asp200, Asp318 and Glu381 are located on the putative cytoplasmic side, and Asp39 and Glu345 on the putative periplasmic side. These residues were replaced by a neutral amino acid residue or a charge-conserved one. In contrast to the transmembrane glutamic acid residues, the replacement of the two glutamic acid residues (Glu345 and Glu381) did not affect the tetracycline resistance level. Out of the other four aspartic acid residues, the only essential residue is Asp318, any replacement of which resulted in complete loss of the tetracycline resistance and transport activity. Asp318 is located in cytoplasmic loop 10-11 in the putative 14-transmembrane-segment topology of Tet(K). In the case of the tetracycline exporters of Gram-negative bacteria, the only essential acidic residue in the cytoplasmic loop region is located in loop 2-3 [Yamaguchi et al., Biochemistry 31 (1992) 8344-8348]. It may be a general role for tetracycline efflux proteins that three transmembrane and one cytoplasmic acidic residues are mandatory for the tetracycline transport function.