Age-related light scattering in rat lenses observed in a 2-year inhalation toxicity study.

Normal light scattering in the eye is determined primarily by the size of alpha-crystalline molecules. Ageing effects appear as an increase in normal lens light scattering in distinct layers. Subliminal effects of toxins on lens transparency can also cause an increase in light scattering due to protein molecule aggregation before visible opacities appear. Scheimpflug photography of the anterior eye segment with subsequent densitometric image analysis is the method of choice to evaluate such effects. To gain more insight into normal ageing and the potential effects of complex aerosols, a subset of Wistar rats (both sexes) belonging to a larger chronic inhalation toxicity study was documented at baseline and after 2 years with a Topcon SL-45 Scheimpflug camera on Kodak T(max) 400 ISO film. The recording procedure, film development, and microdensitometric image analysis were all performed according to standard protocol. A second group from the same study was documented at the start and after 5 months of a 6-month posttreatment period immediately following the inhalation period. Rats were nose-only exposed for 6 h/day, 7 days/week, for 2 years to low (3 microg/l) or high (10 microg/l) concentrations of room-aged cigarette sidestream smoke or diesel engine exhaust. Control animals were exposed to filtered fresh air. At the baseline examination, there were no relevant differences between groups with respect to corneal density or density of defined layers in the lens capsule (1), epithelium and superficial cortex (2), deep cortex (3), supranuclear layer (4) and nucleus (5). At the 2-year examination, mean corneal density was significantly lower in females than in males. This same trend, although not significant, was also found in most layers of the lens. The most prominent differences in density over time were measured in lens layers 3 and 4, but neither corneal density nor lenticular density showed any consistent treatment-related effects in any of the layers. The data from the posttreatment period confirmed the results of the 2-year study. The depth of the anterior chamber increased constantly over the 2.5-year period, but again, treatment did not affect this. This study provided completely new data on age-related light scattering in the cornea and in defined layers of the lens in long-term toxicity studies in Wistar rats.

Frequency and nature of spontaneous age-related eye lesions observed in a 2-year inhalation toxicity study in rats.

A group of 160 Wistar rats (both sexes) from a larger chronic inhalation toxicity study was monitored at baseline and after 1 and 2 years with a photo-slitlamp microscope and a direct ophthalmoscope to record spontaneous age-related eye lesions and treatment-related eye lesions over a period of 24 months. A second group from the same study was monitored at the start and after 5 months of a 6-month posttreatment period immediately following the inhalation period. Rats were nose-only exposed for 6 h/day, 7 days/week, for 2 years to low (3 microg/l) or high (10 microg/l) total particulate matter concentrations of room-aged cigarette sidestream smoke (RASS) or diesel engine exhaust (DEE). Control animals were exposed to filtered fresh air. All ophthalmological examinations were performed in mydriasis, and relevant observations were documented on color slide film. At baseline, all animals with eye lesions were excluded from the study. After 1 year, only minor lesions were found: retrolental opacities (14%) and a few cases of corneal dryness with reddish lid margins. After 2 years, 23% of the animals had unilateral or bilateral retrolental opacities, but the most frequent eye lesions were posterior subcapsular cataracts (PSC, 32%). Water clefts and spokes were found in 11% of the lenses and mature cataracts in 6%. All other eye lesions observed were much less frequent. There were a few cases of glaucoma, corneal dryness and stromal neovascularization. The frequency and type of lesion in animals monitored from the start of the posttreatment period was comparable to what was seen after 2 years. Toward the end of this period the frequency of mature cataracts went up to 9% and that of (secondary) glaucomas to 5%. None of the eye lesions observed showed any association in frequency or severity of expression to the treatment, either RASS or DEE, or to the sex of the animals. In comparison to the (limited) literature data available, far fewer corneal lesions were found in this study, but PSCs and mature cataracts were more frequent. Strain differences may influence these parameters. This study provided valuable information on the nature and frequency of spontaneous age-related eye lesions (0-56%, depending on the tissue) in long-term toxicity studies in Wistar rats.

Specific sensory detection, discrimination, and hedonic estimation of nicotine enantiomers in smokers and nonsmokers: are there limitations in replacing the sensory components of nicotine?

The aim of this study was to investigate in smokers and nonsmokers (1) the olfactory and trigeminal detection of R(+)- and S(-)-nicotine and (2) the discrimination ability and hedonic estimation of nicotine enantiomers in olfactory and trigeminal concentrations. Thirty healthy male subjects (15 smokers, 15 nonsmokers) participated in the experiments. A randomized sequence of R(+)- and S(-)-nicotine stimuli (seven R(+)- and seven S(-)-nicotine stimuli) were introduced into the right nostril of the subjects using a Kobal-olfactometer. The subjects were instructed to group the stimuli into two categories (A and B). To test the role of the olfactory and the trigeminal system in this discrimination task, the authors studied the olfactory detection threshold for the "odorous" sensation and the trigeminal detection thresholds for the "burning" and "stinging" sensations. Nicotine enantiomers were presented at the individual "olfactory" and "trigeminal" concentration levels. The subjects estimated the hedonic properties using a bipolar visual analog scale (from "very unpleasant" to "very pleasant"). A statistical evaluation (t-test) revealed that the subjects were able to identify R(+)- and S(-)-nicotine at olfactory and trigeminal concentrations (p < or = 0.01, p < or = 0.001, respectively). At concentrations near the detection thresholds, i.e., clearly below subjective pain thresholds, smokers rated both nicotine stereoisomers to be significantly more pleasant than did nonsmokers (t-test, R(+)-nicotine: p < or = 0.05; S(-)-nicotine: p < or = 0.01). Increasing the concentrations to above trigeminal thresholds resulted in a difference in hedonic estimates. Smokers perceived the S(-)-isomer as being less unpleasant than nonsmokers at trigeminal concentrations (t-test, p < or = 0.001). This difference in perception might be explained by the smokers' experience with S(-)-nicotine, which is the natural nicotine enantiomer in tobacco.

Dose-dependent stereoselective activation of the trigeminal sensory system by nicotine in man.

RATIONALE: Nicotine applied to the nasal cavity can evoke 'odorous' sensations in the concentration range near the detection threshold by the activation of the olfactory sensory system and at higher concentrations 'burning' and 'stinging' sensations by the dose-dependent recruitment of C- and Adelta-fibers of the trigeminal sensory system. Neuronal nicotinic acetylcholine receptor (nAchR) subunits are expressed in trigeminal primary afferents and could constitute the receptors involved in nicotine perception. OBJECTIVE: In the present study, we dose-dependently investigated the stereoselective effects of R(+)- and S(-)-nicotine on the trigeminal and olfactory sensory system in man. METHODS: Trigeminal detection thresholds for the 'burning' and 'stinging' sensations and the olfactory detection threshold for the 'odorous' sensation were determined. In order to quantify trigeminal activation, we recorded summated electrical responses from the respiratory nasal mucosa during stimulation with R(+)-and S(-)-nicotine vapor (40, 80, 120, 160 ng/ml; stimulus duration: 250 ms). In addition, subjects rated the intensity of 'odorous', 'burning' and 'stinging' sensations. For chemical stimulation with nicotine enantiomers, a vapor-dilution olfactometer (constant flow rate: 140 ml/s, humidity: 80%, temperature: 37 degrees C, stimulus duration 250 ms) was employed. RESULTS: We found significant stereoselective differences for the trigeminal but not for the olfactory system, i.e. higher summated responses, higher trigeminal intensity estimates, and lower trigeminal detection thresholds for S(-)- compared to R(+)-nicotine. CONCLUSION: Our results clearly demonstrate the different stereoselective activation of the trigeminal sensory system by R(+)-and S(-)-nicotine, indicating the presence of specific stereoselective receptors on trigeminal nociceptive Adelta- and C-fibers.

Recovery of auditory evoked potentials after long-term complete brain ischemia.

Complete cerebral ischemia lasting 20 and 30 min was produced in dog brains. Before and after complete ischemia early and middle latency auditory evoked potentials were recorded simultaneously. In all cases of complete ischemia for 30 min amplitudes of evoked potentials were diminished during the reperfusion period of 8 to 12 hours. In some cases evoked potentials reappeared only temporarily. After complete ischemia of 20 min duration, the amplitude of evoked potentials varied within a wide range. They could reach nearly normal values.