Developmental basis for hind-limb loss in dolphins and origin of the cetacean bodyplan.

Among mammals, modern cetaceans (whales, dolphins, and porpoises) are unusual in the absence of hind limbs. However, cetacean embryos do initiate hind-limb bud development. In dolphins, the bud arrests and degenerates around the fifth gestational week. Initial limb outgrowth in amniotes is maintained by two signaling centers, the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA). Our data indicate that the cetacean hind-limb bud forms an AER and that this structure expresses Fgf8 initially, but that neither the AER nor Fgf8 expression is maintained. Moreover, Sonic hedgehog (Shh), which mediates the signaling activity of the ZPA, is absent from the dolphin hind-limb bud. We find that failure to establish a ZPA is associated with the absence of Hand2, an upstream regulator of Shh. Interpreting our results in the context of both the cetacean fossil record and the known functions of Shh suggests that reduction of Shh expression may have occurred approximately 41 million years ago and led to the loss of distal limb elements. The total loss of Shh expression may account for the further loss of hind-limb elements that occurred near the origin of the modern suborders of cetaceans approximately 34 million years ago. Integration of paleontological and developmental data suggests that hind-limb size was reduced by gradually operating microevolutionary changes. Long after locomotor function was totally lost, modulation of developmental control genes eliminated most of the hind-limb skeleton. Hence, macroevolutionary changes in gene expression did not drive the initial reduction in hind-limb size.

Morbillivirus infection in stranded common dolphins from the Pacific Ocean.

From August 1995 to August 1997, six of 18 common dolphins (Delphinus delphis) that stranded along beaches of southern California (USA) tested antibody positive for dolphin morbillivirus (DMV). Titers ascertained by virus neutralization ranged from 1:50 to 1:910 while those determined by ELISA ranged from 1:80 to 1:195. The first individual to strand survived and was released back into the Pacific Ocean 14 mo later. Histopathologic examination of tissues from the other five dolphins did not reveal lesions characteristic of morbilliviral disease; however, morbilliviral RNA was detected in three of the five by reverse transcriptase-polymerase chain reaction testing. This is the first report of morbilliviral infection in any marine mammal species in the northern hemisphere of the Pacific Ocean. These data indicate that DMV, or a closely related morbillivirus, is present in the Pacific Ocean and infection of common dolphins may not be associated with morbillivirus disease.

Thermoregulation in the mouths of feeding gray whales.

Vascular structures for heat conservation in the tongue of the gray whale (Eschrichtius robustus) are reported here. Numerous individual countercurrent heat exchangers are found throughout the massive tongue. These converge at the base of the tongue to form a bilateral pair of retia. Temperature measurements from the oral cavity of a live gray whale indicate that more heat may be lost through the blubber layer over the body than through the tongue, despite the fact that the tongue is far more vascularized and has much less insulation. These heat exchangers substantially reduce heat loss when these whales feed in cold waters.

Levamisole in the treatment of recurrent aphthous stomatitis.

In a pilot study as well as in a double-blind placebo-controlled study, 21 patients suffering from recurrent aphthous stomatitis were treated with the immunotherapeutic agent, levamisole. The results obtained confirm previous studies that levamisole has a beneficial effect on the symptoms of recurrent aphthous stomatitis and is well-tolerated.

Cholesteatoma of the middle ear in human patients. An ultrastructural study.

The structure of middle ear cholesteatoma obtained at surgical interventions in 12 patients was investigated by light and electron microscopy. Keratinizing squamous epithelium with underlying granulomatous, partly necrotic tissue showing signs of an acute or chronic inflammatory reaction was observed. Cholesterol clefts were only observed in two specimens in which a chronic hemorrhage was present. It is proposed that a cholesteatoma starts by immigration of epidermal tissue from the tympanic membrane. Destruction of the middle ear components and of the neighboring osseous walls results from invasion of squamous epithelium, underlying necrotizing connective tissue, and keratin.