Arousal thresholds during human tonic and phasic REM sleep

The goal of the present study was to investigate arousal thresholds (ATs) in tonic and phasic episodes of rapid eye movement (REM) sleep, and to compare the frequency spectrum of these sub‐states of REM to non‐REM (NREM) stages of sleep. We found the two REM stages to differ with regard to behavioural responses to external acoustic stimuli. The AT in tonic REM was indifferent from that in sleep stage 2, and ATs in phasic REM were similar to those in slow‐wave sleep (stage 4). NREM and REM stages of similar behavioural thresholds were distinctly different with regard to their frequency pattern. These data provide further evidence that REM sleep should not be regarded a uniform state. Regarding electroencephalogram frequency spectra, we found that the two REM stages were more similar to each other than to NREM stages with similar responsivity. Ocular activity such as ponto‐geniculo‐occipital‐like waves and microsaccades are discussed as likely modulators of behavioural responsiveness and cortical processing of auditory information in the two REM sub‐states.     

ERP and behavioral changes during the wake/sleep transition

Event-related potentials (ERPs) following infrequent and frequent stimuli were studied as subjects moved from wakefulness to sleep. Subjects were instructed to respond to the infrequent “target” stimuli (attend condition) or to ignore the stimuli (ignore condition). Parietal P300, prominent following target ERPs in wakefulness under the attend condition, disappeared in association with reduced behavioral responsiveness and emergence of a central negativity (N350). The N350 and preceding and following positivities (P220 and P450) became the dominant feature of both target and nontarget ERPs under both attend and ignore conditions. The P220-N350-P450 complex was larger and peak latencies were shorter under the attend condition. Peak amplitudes tended to be larger following targets, especially under the attend condition. The findings suggest that, although the processes under-lying P300 are less likely to be engaged, processing of stimulus deviance and task relevance continues in sleepiness and sleep, and is reflected by variance in N350 and related activity.     

Subchronic Feeding Study of the Mycotoxin Fumonisin B1 in B6C3F1 Mice and Fischer 344 Rats

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium moniliforme,a common fungus which occurs naturally on corn, and other Fusariumspecies. FB1 and other fumonisins are now recognized as havingpotentially important animal and human health implications.However, few toxicological data are currently available. Maleand female B6C3F1 mice and Fischer 344 rats were fed diets containing0, 1, 3, 9, 27, or 81 ppm FB1 (98% purity) for 13 weeks. Nodifferences in behavior or appearance, body weight or food consumptionbetween control and FB1-fed groups were found. In mice, hepatopathyand altered serum chemical profiles indicative of hepatotoxicitywere found in females fed the 81 ppm diet. No adverse effectswere found in female mice fed 27 ppm FB1 or in male mice atany dietary level studied. In rats, nephrosis involving theouter medulla was found in males fed 9 ppm and, to a lesserdegree, in females fed 81 ppm FB1, while decreased kidney weightwas found in both sexes at dietary levels 9 ppm FB1. Althoughthe liver is a target organ of FB1 in rats, hepatotoxicity wasnot found in rats fed diets containing up to 81 ppm FB1 for90 days. Thus, FB1 was toxic to both species following subchronicoral exposure, although significant interspecies differencesin the no observed effect levels and organ-specific responseswere found.