Separate origin of the main components of the left coronary artery in Syrian hamsters (Mesocricetus auratus).

This study describes a rare congenital coronary artery anomaly in the Syrian hamster; namely, the separate origin of the obtuse marginal and left circumflex arteries which are the main components of the left coronary artery. The hearts of nine affected animals were examined by means of a corrosion-cast technique and histology. The hamsters belonged to a laboratory inbred family with a high incidence of coronary artery anomalies and bicuspid aortic valve. The aortic valve was tricuspid in three hamsters and bicuspid in the other six hamsters. In all cases, the right coronary artery was normal, whereas the left coronary artery main trunk was absent. The present anomalous coronary artery patterns could be classified into two main entities: (i) ectopic origin of the obtuse marginal artery from the right aortic sinus or from the right coronary artery, with the left circumflex artery arising from the left side of the aortic valve; and (ii) ectopic origin of both the obtuse marginal artery from the right aortic sinus or from the right coronary artery and left circumflex artery from the dorsal aortic sinus. In all cases, the obtuse marginal artery coursed to the right side of the heart through the ventral wall of the right ventricular outflow tract. When the left circumflex artery arose from the dorsal aortic sinus, it formed an acute angle with the aortic wall. This report seems to be the first to describe the separate origin of the main components of the left coronary artery in a non-human mammalian species. In man, the congenital coronary artery and aortic valve defects reported herein may entail the risk of clinical complications. However, none of the affected hamsters showed signs of disease.

New embryological evidence for the formation of quadricuspid aortic valves in the Syrian hamster (Mesocricetus auratus).

A Syrian hamster embryo, aged 11 days and 4 h post-coitus, had a developing quadricuspid aortic valve. The septation of the cardiac outflow tract was confined to the distal part of the conotruncus. There was a conspicuous recess in the anlage that normally gives rise to the left aortic valve cushion. Globular endothelial cells arranged in several layers were present at the luminal side of the recess. The present findings support the hypothesis that in the Syrian hamster, quadricuspid aortic valves result from the division of one of the three mesenchymal anlagen that give rise to normal aortic valves. In addition, they indicate that the division of the anlage is due to the invagination of the endothelial layer that covers its luminal side. The invagination of the endothelium starts at a very early stage of the valvulogenesis, namely, when the conotruncal ridges begin to fuse at the distal portion of the embryonic cardiac outflow tract.

Anatomy and formation of congenital bicuspid and quadricuspid pulmonary valves in Syrian hamsters.

BACKGROUND: Congenital bicuspid and quadricuspid pulmonary valves have received little attention because of their limited clinical relevance. However, knowledge of the mechanisms by which these anomalous valves develop is essential to obtain a more accurate survey of the etiological factors implicated in the malformations of the cardiac outflow tract in mammals. The present study was designed to assess the anatomical features of bicuspid and quadricuspid pulmonary valves in Syrian hamsters as well as to elucidate the mechanisms involved in the formation of these defective valves. METHODS: The sample examined consisted of 206 adults and 28 embryos belonging to a laboratory-inbred family of Syrian hamsters with a high incidence of congenital anomalies of the pulmonary and aortic valves. The study was carried out using histological techniques for light microscopy, semithin sections, and scanning electron microscopy. RESULTS: The pulmonary valve was tricuspid in 140 of the 206 adult hamsters, and in 124 of these tricuspid valves the dorsal commissure was more or less extensively fused. Another 45 hamsters possessed a bicuspid pulmonary valve with the sinuses oriented ventrodorsally. In 43 of these bicuspid valves, a raphe was located in the dorsal pulmonary sinus. The pulmonary valve was quadricuspid in a further nine specimens. The remaining 12 hamsters had a tricuspid pulmonary valve with a raphe-like ridge located in the right pulmonary sinus. In seven of these valves, the dorsal commissure showed a more or less extensive fusion. The embryos examined, aged between 11 days, 3 hours and 12 days, 6 hours postcoitum, were at the beginning of the valvulogenesis. In five of the 28 embryos, the pulmonary valve consisted of three mesenchymal valve cushions, right, left, and dorsal. In a further 17 embryos, the right and left valve cushions were more or less fused toward the lumen of the pulmonary artery. In the remaining six embryos, the left and dorsal valve cushions were normal, whereas the right cushion was divided into two lobes. CONCLUSIONS: The present findings suggest that in the Syrian hamster: (1) bicuspid pulmonary valves result from the extensive fusion of the right and left pulmonary valve cushions at the beginning of the valvulogenesis, (2) the partial fusion of the right and left pulmonary valve cushions leads to the formation of tricuspid pulmonary valves with a more or less extensive fusion of the dorsal commissure, (3) quadricuspid pulmonary valves result from the partition of one of the three valve cushions at a very early stage of the valvulogenesis, and (4) the partial division of the right pulmonary valve cushion may lead to the development of tricupsid pulmonary valves with a raphe-like ridge located in the right pulmonary sinus. In addition, the present findings, together with previous observations in Syrian hamsters, indicate that in this species the mechanisms by which bicuspid and quadricuspid pulmonary valves develop are similar to those by which bicuspid and quadricuspid aortic valves form, respectively. However, the primary factor or factors that induce the malformations of the pulmonary valve operate independently from those inducing the malformations of the aortic valve.

An inner ear anomaly in golden hamsters.

A new mutation of the inner ear was discovered in golden hamsters raised in our laboratories. Although scanning electron microscopy showed a normal arrangement of individual stereocilia on the first row of outer hair cells, the entire bundle of stereocilia were irregular in orientation and scattered in several directions. Seventy per cent to 85% of the stereociliary bundles were found to be abnormal throughout the cochlea, with no apparent difference between the right and left sides. Transmission electron microscopy showed that the cuticles of the first row of the outer hair cells were dislocated, but no dislocation due to this mutation was apparent in the lower portions. This mutation of the inner ear was already present in the basal turn four days after birth. The kinocilium was located outside of the stereocilia in the first row of outer hair cells, but sensory hairs were scattered in every direction, as in the adult animals. A comparison of auditory brainstem response tests revealed no difference between the abnormal and normal hamsters.