Normal and abnormal nasolabial morphogenesis in the rat

Mediation of muscular control of rhinarial motility in rats by the nasal cartilaginous skeleton

The rhinarium is the rostral-most area of the snout that surrounds the nostrils, and is hairless in most mammals. In rodents, it participates in coordinated behaviors, active tactile sensing, and active olfactory sensing. In rats, the rhinarium is firmly connected to the nasal cartilages, and its motility is determined by movements of the rostral end of the nasal cartilaginous skeleton (NCS). Here, we demonstrate the nature of different cartilaginous regions that form the rhinarium and the nasofacial muscles that deform these regions during movements of the NCS. These muscles, together with the dorsal nasal cartilage that is described here, function as a rhinarial motor plant.

Pathogenesis of median facial clefts in mice treated with methotrexate

Methotrexate (MTX), administered as a single 20 mg/kg intraperitoneal dose to C57Bl/6J mice on their 9th day of pregnancy results in high incidences of median facial clefts in the surviving gestational-day-18 fetuses. We have shown the presence of dilated and congested blood vessels in the frontonasal prominences (FNP) of embryos from treated mothers as early as 3 hours following drug administration. Within 24 hours, large vascular blebs are located in the FNP and the neural tubes appear somewhat distended. By 32 hours after treatment, distention of the neural tube is marked while blebs have become less evident. Subsequent to these changes, FNP mesenchymal deficiency as well as neural tube distention lead to the formation of median facial clefts. It is hypothesized that, as with a number of other teratogenic agents (especially hypoxia), initial fluid imbalance is the primary teratogenic insult.

Morphogenesis of median facial clefts in mice treated with diazo-oxo-norleucine (DON)

The morphogenesis of median facial clefts induced in mice by treatment with diazo-oxo-norleucine (DON) was studied. Following maternal treatment with 0.4 mg/kg DON on the 11th gestational day, 23.1% of fetuses recovered at the 18th day exhibited median facial clefts, which were characterized by a separation in the midline of normal midfacial components, i.e., the premaxilla, nasal bones, and nasal capsule. Malformed embryos could first be identified grossly 24 hr after DON administration by the presence of an abnormally wide separation between the two narrowed medial nasal processes. Evidence of cellular degeneration was observed in the mesenchyme of the nasal processes of DON-treated embryos 8 and 12 hr after treatment, but little or no pyknotic debris remained at 24 hr post-injection. Loss of cells due to cell death was reflected in decreased cell density observed in all areas of facial mesenchyme examined 24 hr after DON administration. It is suggested that DON-induced median facial clefts may be caused by a reduction in tissue volume, particularly in the midline, or by an interference with normal facial growth resulting in increased facial width and consequent failure of merging of the medial nasal processes.

Normal and abnormal midfacial development in the cadmium-treated hamster

Clefts of the midface ranging in severity from a notched lip to complete facial disorganization were observed in the offspring of golden hamsters injected with cadmium chloride on the morning of the eighth day of gestation. Other malformations frequently observed were microphthalmia, anophthalmia, and diencephalic encephaloceles. Histologic examination of embryos on the 10th, 11th, 12th, and 13th days of gestation revealed a marked deficiency of mesenchyme in the frontonasal process, which led to a foreshortened and deformed nasal septum. These data confirm that the teratogenicity of cadmium is highly specific for the region of the anterior neural segment on the eighth day of gestation. The deficiency of mesenchyme in the frontonasal process may be the result of disruption in neural crest cell development in this region.

Rapid nasal pit formation in mouse embryos stimulated by ATP-containing medium

The primary palate in the mouse is composed of epithelium and mesenchyme. Most studies on primary palate formation have concentrated on the role of the mesenchyme based upon the hypothesis that mesenchymal accumulation elevated the sides of the nasal placodes, thereby creating the depressed nasal pits. This study demonstrates that the epithelium is actively participating in formation of the nasal pits. Mouse heads from embryos of 14 to 24 paris of body somites were placed in medium 199 and photographed. The medium was replaced with medium containing 1.0 mM ATP and 0.05% Triton-X. Within 5 minutes, the placodes either thickened or invaginated. Control heads exposed to medium 199 containing only Triton-X or ATP did not show any invaginations. The rapid thickening and invagination stimulated by ATP-containing medium demonstrates that the epithelium is the dominant tissue in nasal put formation. Although mesenchymal accumulation certainly contributes to the formation of the primary palate, it is the placodal epithelial invagination that appears to shape the nasal pits.

Effects of aspirin and acetaminophen on fetal and placental growth in rats

Aqueous suspensions of aspirin or acetaminophen (125 and 250 mg/kg/day) were administered orally to pregnant Sprague-Dawley rats on Days 8-19 of gestation Day 20, each rat was sacrificed and the uterus was examined in situ. Each fetal-placental unit was resected and examined. Fetuses from rats given 125 or 250 mg/kg/day of aspirin were shorter and weighed less than those obtained from control rats. In animals receiving the higher dose of aspirin, the placentas were smaller and the number of fetal resorptions was increased. Acetaminophen (250 mg/kg/day) did not affect fetal length or weight or the incidence of resorption. Acetaminophen interfered less with the normal growth of the rat fetus and placenta than did aspirin.