Mercury delays cerebellar development in a model songbird species, the zebra finch.

Mercury exposure can disrupt development of the cerebellum, part of the brain essential for coordination of movement through a complex environment, including flight. In precocial birds, such as fowl, the cerebellum develops embryonically, and the chick is capable of leaving the nest within hours of hatching. However, most birds, including all songbirds, are altricial, and spend weeks in the nest between hatching and fledging. The objective of this study was to describe the normal development of the cerebellum in a model altricial songbird so as to determine the effect of exposure to mercury on cerebellar maturation. Adult zebra finch (Taeniopygia guttata) pairs were fed either a control diet, or a diet augmented with one of four treatment-levels of methylmercury (0.3-2.4 µg/g wet weight), and their offspring, the subjects of this study, were fed the same diet by parents. We documented, for the first time, the schedule of cerebellar development in an altricial bird, and compared stages of development among methylmercury-exposed groups. For all treatments of methylmercury, the age of completion of cellular migration was later than for control zebra finches, indicating a delay in cerebellar maturation. Displaced (heterotopic) Purkinje neurons, a pathology typical of methylmercury exposure in developing vertebrate brains, were more numerous in methylmercury-exposed birds, and persisted at least until the age of independence. Delays in maturation of the cerebellum could delay fledging in altricial bird species, with potential serious implications for the fitness of exposed individuals, as predation rates in the nest are often very high.

Cerebellar abnormalities typical of methylmercury poisoning in a fledged saltmarsh sparrow, Ammodramus caudacutus.

A fledged, 12-15 day-old saltmarsh sparrow, Ammodramus caudacutus, was collected from an accidental kill on Cinder Island, Long Island, NY, USA. The sparrow was assessed for feather mercury levels and the brain analyzed for cerebellar abnormalities by microscopic examination. In humans, fetal Minamata disease is caused by maternal ingestion of mercury. It is characterized by disrupted and disordered cerebellar neuronal migration in the fetus or infant. Results from this sparrow show cerebellar abnormalities typical of Minamata disease. It is the first known avian or mammalian specimen taken from the wild to show the abnormalities typical of the human fetal syndrome.

Traditional and virtual microscopy compared experimentally in a classroom setting.

The technology known as virtual microscopy is now widely available to medical students. A number of medical school histology and pathology course directors, including those at the Eastern Virginia Medical School, are exploring the question of how best to make use of this new tool. The current study compared the efficacy of teaching and testing one unit of histology, bone and cartilage, using two technologies, namely, virtual microscopy and traditional microscopy. Additionally, the study examined whether low, moderate, high moderate, or high achieving students perform more effectively in any of the learning/testing formats. In a completely randomized block design, 96 first semester, first-year medical students were grouped by previous exam quartiles then subsequently randomly assigned to one of four groups. Using identical laboratory exercises with highly comparable slides for each experimental group, half of the subjects learned the exercise with traditional microscopy and half learned with virtual microscopy. Subjects were further randomly subdivided into virtual or actual testing groups. The authors found no significant differences in test scores when they examined effects by learning group or by testing group, nor were there significant interaction effects. Student performance evaluated by previous exam quartile was significant (P < 0.001). That is, students who had scored in a particular quartile on a previous test tended to score in the same quartile on the bone and cartilage test regardless of learning or testing method. In a short opinion survey, students were polled to evaluate their experience. Student preferences for both learning and testing method varied widely.