Signal transmission through the dark-adapted retina of the toad (Bufo marinus). Gain, convergence, and signal/noise.

Responses to light were recorded from rods, horizontal cells, and ganglion cells in dark-adapted toad eyecups. Sensitivity was defined as response amplitude per isomerization per rod for dim flashes covering the excitatory receptive field centers. Both sensitivity and spatial summation were found to increase by one order of magnitude between rods and horizontal cells, and by two orders of magnitude between rods and ganglion cells. Recordings from two hyperpolarizing bipolar cells showed a 20 times response increase between rods and bipolars. At absolute threshold for ganglion cells (Copenhagen, D.R., K. Donner, and T. Reuter. 1987. J. Physiol. 393:667-680) the dim flashes produce 10-50-microV responses in the rods. The cumulative gain exhibited at each subsequent synaptic transfer from the rods to the ganglion cells serves to boost these small amplitude signals to the level required for initiation of action potentials in the ganglion cells. The convergence of rod signals through increasing spatial summation serves to decrease the variation of responses to dim flashes, thereby increasing the signal-to-noise ratio. Thus, at absolute threshold for ganglion cells, the convergence typically increases the maximal signal-to-noise ratio from 0.6 in rods to 4.6 in ganglion cells

The zinc for the common cold review by Singh and Das has a number of problems which should be considered when the review is next time updated : [Feedback on Cochrane review "Zinc for the common cold"]

Feedback to the following Cochrane review: Singh M & Das RR: Zinc for the common cold. Cochrane Database Syst Rev. 2011 Jan 18;1:CD008965 http://www.ncbi.nlm.nih.gov/pubmed/21328251Non peer reviewe

Duration of the common cold and similar continuous outcomes should be analyzed on the relative scale : a case study of two zinc lozenge trials

Background: The relative scale has been used for decades in analysing binary data in epidemiology. In contrast, there has been a long tradition of carrying out meta-analyses of continuous outcomes on the absolute, original measurement, scale. The biological rationale for using the relative scale in the analysis of binary outcomes is that it adjusts for baseline variations; however, similar baseline variations can occur in continuous outcomes and relative effect scale may therefore be often useful also for continuous outcomes. The aim of this study was to determine whether the relative scale is more consistent with empirical data on treating the common cold than the absolute scale. Methods: Individual patient data was available for 2 randomized trials on zinc lozenges for the treatment of the common cold. Mossad (Ann Intern Med 125:81-8, 1996) found 4.0 days and 43% reduction, and Petrus (Curr Ther Res 59:595-607, 1998) found 1.77 days and 25% reduction, in the duration of colds. In both trials, variance in the placebo group was significantly greater than in the zinc lozenge group. The effect estimates were applied to the common cold distributions of the placebo groups, and the resulting distributions were compared with the actual zinc lozenge group distributions. Results: When the absolute effect estimates, 4.0 and 1.77 days, were applied to the placebo group common cold distributions, negative and zero (i.e., impossible) cold durations were predicted, and the high level variance remained. In contrast, when the relative effect estimates, 43 and 25%, were applied, impossible common cold durations were not predicted in the placebo groups, and the cold distributions became similar to those of the zinc lozenge groups. Conclusions: For some continuous outcomes, such as the duration of illness and the duration of hospital stay, the relative scale leads to a more informative statistical analysis and more effective communication of the study findings. The transformation of continuous data to the relative scale is simple with a spreadsheet program, after which the relative scale data can be analysed using standard meta-analysis software. The option for the analysis of relative effects of continuous outcomes directly from the original data should be implemented in standard meta-analysis programs.Peer reviewe

Random-Effects Assumption in Meta-analyses

Non peer reviewe

Vitamin C and sex differences in respiratory tract infections

In their systematic review of sex differences in respiratory tract infections (RTIs), Falagas et al. concluded that males develop RTIs more frequently than females, in particular lower RTIs, and the course of the infection is often more severe in males than in females. ... It is obvious that the findings of the common cold trials with British males and pneumonia trials with males cannot be extrapolated to the general population of the western countries. Nevertheless, further vitamin C trials are warranted among males with low dietary vitamin C intake.Peer reviewedPeer reviewe

Vitamin C and Infections

In the early literature, vitamin C deficiency was associated with pneumonia. After its identification, a number of studies investigated the effects of vitamin C on diverse infections. A total of 148 animal studies indicated that vitamin C may alleviate or prevent infections caused by bacteria, viruses, and protozoa. The most extensively studied human infection is the common cold. Vitamin C administration does not decrease the average incidence of colds in the general population, yet it halved the number of colds in physically active people. Regularly administered vitamin C has shortened the duration of colds, indicating a biological effect. However, the role of vitamin C in common cold treatment is unclear. Two controlled trials found a statistically significant dose-response, for the duration of common cold symptoms, with up to 6-8 g/day of vitamin C. Thus, the negative findings of some therapeutic common cold studies might be explained by the low doses of 3-4 g/day of vitamin C. Three controlled trials found that vitamin C prevented pneumonia. Two controlled trials found a treatment benefit of vitamin C for pneumonia patients. One controlled trial reported treatment benefits for tetanus patients. The effects of vitamin C against infections should be investigated further.Peer reviewe

Vitamin C may shorten ICU stay : [eLetter]

The paper by Sheikh and Horner [1] does not properly describe the context for vitamin C. Fourteen trials have investigated the effect of vitamin C against post-operative AF (POAF), and significant heterogeneity has appeared between studies carried out in the USA and outside of the USA [2]. In 9 non-US studies vitamin C decreased the incidence of POAF on average by 46% (P<0.00001), but no benefit was seen in 5 US studies.Non peer reviewe

Vitamin C, neutrophils and the symptoms of the common cold : [Letter]

Non peer reviewe

Vitamin C and SARS coronavirus

Non peer reviewe

Zinc acetate lozenges may shorten common cold duration by up to 40% : [eLetter]

Other name of article: Zinc acetate lozenges may shorten common cold duration by up to 40%The systematic review by Dr. Science et al. has a number of problems. ... Even though we need further research to find out what the optimal lozenge compositions and treatment strategies are, the great benefit and the minimal adverse effects in the zinc acetate trials gives a strong rationale for physicians to suggest common cold patients to test zinc acetate lozenges (about 80 mg/day of zinc).Non peer reviewe