Navigating at night: fundamental limits on the sensitivity of radical pair magnetoreception under dim light.

Night-migratory songbirds appear to sense the direction of the Earth's magnetic field via radical pair intermediates formed photochemically in cryptochrome flavoproteins contained in photoreceptor cells in their retinas. It is an open question whether this light-dependent mechanism could be sufficiently sensitive given the low-light levels experienced by nocturnal migrants. The scarcity of available photons results in significant uncertainty in the signal generated by the magnetoreceptors distributed around the retina. Here we use results from Information Theory to obtain a lower bound estimate of the precision with which a bird could orient itself using only geomagnetic cues. Our approach bypasses the current lack of knowledge about magnetic signal transduction and processing in vivo by computing the best-case compass precision under conditions where photons are in short supply. We use this method to assess the performance of three plausible cryptochrome-derived flavin-containing radical pairs as potential magnetoreceptors.

What effect has pneumococcal vaccination had on acute mastoiditis?

BACKGROUND: Streptococcus pneumoniae is a frequent cause of acute mastoiditis. Despite the recent (2005) introduction of pneumococcal vaccination, mastoiditis incidence and severity may be increasing. This study aimed to assess the incidence, severity and microbiology of acute mastoiditis over an 11-year period. METHODS: Retrospective review of paediatric acute mastoiditis cases seen at our institution (2000-2010), comparing patients seen prior to vaccination introduction (period one, 2000-2004), around the time of vaccine introduction (period two, 2005-2007) and post-vaccination (period three, 2008-2010). RESULTS: We reviewed 84 children. In periods one, two and three, respectively: mean annual case load was 8.4, 5 and 9 children; pneumococcal isolates were seen in 40.5, 6.7 and 29.6 per cent of cases; highest recorded fever was 38.6, 38.9 and 38.2°C and highest leukocyte count 18.9, 15.0 and 15.6 × 109/l; incidence of intracranial complications was 11.9, 0 and 7.4 per cent; mean duration of intravenous antibiotics was 6.0, 4.1 and 4.2 days; proportion treated surgically was 71.4, 60.0 and 48.1 per cent; and mean length of in-patient stay shortened. CONCLUSION: Pneumococcal mastoiditis admission rates appeared to fall when vaccination was introduced, with concomitant reduction in overall mastoiditis incidence and intracranial complications; subsequently, however, admission rates rapidly returned to pre-vaccination levels.