Arturs Vitums

Light-microscope studies of the cytology of the adenohypophysis of the white-crowned sparrow, Zonotrichia leucophrys gambelii

SummaryAdenohypophyses from more than two hundred white-crowned sparrows of both sexes and different ages, and from different periods of their annual reproductive cycle, have been used for this investigation. In addition to examination of these normal birds, we have also studied the adenohypophyses of 23 castrates and 24 controls held in different photoperiodic conditions.Cytologically the pars distalis of the adenohypophysis of the white-crowned sparrow is typically avian with distinct cephalic and caudal lobes, each with characteristic cell-types.Four basic cell-types, the acidophils, basophils, amphophils, and chromophobes, have been identified in the pars distalis by means of Matsuo tetrachrome and Matsuo modified PAS-methyl blue staining methods.Three types of acidophils, orange, red, and small, are confined to the caudal lobe of the pars distalis. Their possible functions are discussed.Light basophils (PAS-light red cells) and deep basophils (PAS-deep red cells) are equally distributed in both lobes. It is suggested that basophils may be involved in gonadotropic function since their appearance correlates well with the annual gonadal cycle and photoperiodic stimulation of gonadal growth and with the results of castration.The amphophils or PAS-purple cells (aldehyde-fuchsin positive) are found only in the cephalic lobe. Their probable function is discussed.Two types of chromophobes, specific and ordinary chromophobes, have been observed. The specific chromophobes are found only in the cephalic lobe and are similar to the “Kernhaufen” described by Romeis (1940). The ordinary chromophobes are similar to those of the pars distalis of other avian species and of mammals.The castration cells are found in both lobes of the photosensitive castrates under natural photoperiodic conditions as well as in those subjected artificially to photostimulation (20-hour daily photoperiods). Similar cells have also been observed in the pars tuberalis of the castrated photostimulated birds.The relations of the rostral and caudal groups of the portal vessels to the cell-types found in the cephalic and caudal lobes are discussed.

The development of the hypophysial portal system in the White-crowned Sparrow, Zonotrichia leucophrys gambelii

SummaryThe development of the hypophysial portal system has been studied in 35 embryos and 45 nestlings of the White-crowned Sparrow. The primordium of the hypophysis is vascularized by the infundibular (primary) capillary plexus, supplied by the right and left infundibular arteries, which, in the embryo, are constant branches of the right and left internal carotid arteries.The cellular proliferation and differentiation of the pars distalis into rostral and caudal lobes is accompanied by a penetration of portal vessels from the infundibular (primary) capillary plexus into these lobes beginning on the fifth day of incubation. The cellular proliferation of the rostral lobe of the pars distalis and development of the rostral group of the portal vessels precedes that of the caudal lobe of the pars distalis and the development of the caudal group of the portal vessels.The periglandular vessels, which originate in younger embryos from the infundibular (primary) capillary plexus, apparently become a part of the portal vessels.The portal vessels are the sole blood supply to the developing pars distalis of the White-crowned Sparrow; there is no evidence of a direct arterial supply at anytime during embryonic development. The neural-lobe artery appears at the end of incubation as a secondary branch of the right and left infundibular arteries. The rostral and caudal groups of the portal vessels are well-developed at the end of incubation (17–29 mm CRL) when aldehyde-fuchsin positive neurosecretory material first appears in the supraoptic and paraventricular nuclei, in the median eminence and in the neural lobe.The differentiation of the median eminence into rostral and caudal divisions begins at the end of the nestling period although its adult form is not achieved until later. The formation of the portal zone begins at the end of incubation (17–29 mm CRL) and is completed by the time of fledging.

Development and transformation of the aortic arches in the equine embryos with special attention to the formation of the definitive arch of the aorta and the common brachiocephalic trunk

SummaryThe development and transformation of the aortic arches were studied in 84 equine embryos (5 to 35 mm CRL; approximately 21–49 days of gestation). The arch of the aorta and the vessels which originate from it were also examined in several fetuses (41–335 mm CRL) and in a full-term fetus.There are six pairs of aortic arches that originate from the ventral aortic root. The first and second aortic arches regress very early, while the fifth pair appears in a vestigial form relatively late in the development, when the truncus arteriosus divides into the aortic and pulmonary channels. The development of the cervical intersegmental arteries is described and the formation of the subclavian arteries is discussed. The primitive arch of the aorta appears at the earliest in the 14–15.5 mm CRL equine embryos (approximately 35 days of gestation). The segments of the aortic arches system which are incorporated in the formation of the definitive arch of the aorta are discussed.Three vessels, the innominate (brachiocephalic) artery, the left common carotid artery, and the left subclavian artery, originate from the primitive arch of the aorta. This arrangement of the vessels is regarded as the primitive mammalian pattern.Two more stages precede the development of the definitive arch of the aorta and the common brachiocephalic trunk in the equine embryos, at approximately 42 days of gestation. The secondary changes, which occur in the process of formation of the arch of the aorta and the common brachiocephalic trunk, are described and discussed. Certain anomalies of the arrangement of the vessels from the arch of the aorta are also discussed.

Atresia of the Right Atrioventricular Orifice with Complete Transposition of the Great Arteries in a Horse

The heart of a 6‐week old Arabian filly with a history of poor health and exercise intolerance revealed at postmortem examination, multiple cardiac malformations which included atresia of the right atrioventricular orifice (tricuspid atresia, with associated atrial and ventricular septal defects), complete transposition of the great arteries, anomalous drainage of the venae cavae and coronary sinus into the left atrium, coarctation of the aorta, and a small but patent ductus arteriosus. The course of blood through the heart was suggested and discussed.

The Embryonic Development of the Equine Heart

Equine cardiogenesis was studied in embryos of approximately 21 to 49 days of gestation, with particular attention to the partitioning of the ventricular outflow channel. Timing of several morphogenetic events associated with this partitioning was recorded in Table 1. Present investigation indicated that partitioning of the ventricular outflow channel into the pulmonary trunk and aorta was already completed at about 36th to 38th day of gestation. Results of this study may aid in better understanding of the congenital malformations, especially those associated with great vessels of the equine heart.

Development of the equine hypophysis cerebri, with a reference to its blood supply.

The development of the equine hypophysis and its blood supply was investigated in embryos and fetuses from ca. the 22nd to 270th day of gestation. The developing equine primary capillary plexus was supplied by the right and left rostral (ventral and dorsal) infundibular arteries, which were constant branches of the right and left internal carotid arteries, or their terminal rami, respectively. The early cellular proliferation and differentiation of Rathkes pouch were accompanied by penetration of vessels from the primary capillary plexus into the developing pars tuberalis. These vessels represented the primitive portal vessels. The development of the ventral group of portal vessels preceded that of the dorsal group of portal vessels. In the fetuses at the terminal half of gestation, the primary capillary plexus, with its superficial and deep components of the ventral and dorsal walls of the median eminence, and the ventral and dorsal groups of portal vessels, resembled that of the postnatal animals. The caudal infundibular artery (single or paired) appeared as a branch of the arteria intercarotica caudalis relatively late in the development and supplied the neural lobe. The portal vessels were the sole blood supply to the developing equine pars distalis; there was no evidence of a direct arterial supply to the pars distalis at any time during embryonic and fetal development. The early appearance and differentiation of the equine portal system suggested the onset of its function in the fetal life.

Observations on the Equine Hypophysial Portal System

The blood supply to the equine pituitary gland, with special attention to its portal system, was studied by the aid of vascular injections and histological serial sections. The primary capillary plexus of the median eminence was supplied by the rostroventral and rostrodorsal infundibular arteries, which were branches of the internal carotid arteries and the ramus communicans caudalis, respectively. The neural lobe was supplied by the caudal infundibular arteries, which originated from the arteria intercarotica caudalis. Dorsal and ventral groups of the portal vessels were described. Their regional distribution into the sinusoidal capillaries of the pars distalis was discussed. Results of this investigation indicated that the portal vessels were the sole supply to the equine pars distalis. No direct arterial supply to this part of the adenohypophysis was observed.

Development of the venous drainage of the equine hypophysis cerebri.

The development of the venous drainage from the equine hypophysis cerebri was investigated in embryos and fetuses ca. 22nd to 270th day of gestation. The early venous drainage was represented by the right and left retrohypophysial veins which were tributaries of the primary head veins. In later development an anastomosis was formed between the contralateral retrohypophysial veins. This anastomosis was named the retrohypophysial sinus which was identical with the caudal intercavernous sinus of the postnatal animals. The development of the rostral intercavernous sinus was not observed. The right and left cavernous sinuses developed secondarily from the retrohypophysial sinus. The venous drainage was directed rostrolaterad into the ophthalmic veins. In addition to the rostrolateral route, a caudoventral route, represented by the right and left ventral petrosal sinuses, developed from the retrohypophysial sinus relatively late in the fetal period. Both the rostrolateral and caudoventral routes joined eventually the external jugular system basically resembling postnatal conditions.

Malformations of the great arteries and heart in Arabian foals

Summary The data recorded from the clinical and physiological examinations of three male Arabian foals exhibiting cyanosis, depression and exercise intolerance are presented. The foals ranged in age from 10 days to 8 months. All displayed tachycardia and tachypnea and had loud pansystolic or continuous heart murmurs which were auscultable on both sides of the thorax but loudest on the left. Electrocardiography, blood gas analysis and right-sided cardiac catheterization were performed on each foal. Angiocardiograms were performed in two instances. An interventricular septal defect (VSD) was indicated in each case by a right ventricular pO2 which was greater than that in the right atrium. Samples taken from the right ventricular outflow tract demonstrated a further step-up in pO2, suggesting the existence of a great vessel which was common to both ventricles. Pressure recordings indicated the presence of right-sided hypertension and the absence of a systolic pressure gradient across the semilunar valve. No evidence of a normal pulmonary trunk wave form could be obtained. When quality radiographs were obtained, angiocardiography was of use in making the best possible premortem diagnosis. In each foal, a VSD and dextroposed aorta was diagnosed in conjunction with either a common truncus arteriosus, a pseudotruncus arteriosus or a tetralogy of Fallot. At necropsy, a variant of the tetralogy of Fallot — pulmonary atresia, patent ductus arteriosus, dextroposed aorta and VSD was found in each foal.

Development of the Equine Venous Sinuses of the Dura Mater

The equine dorsal sinus system of the dura mater develops from the dural venous plexuses. In early development, venous blood from these plexuses is drained into the primary head vein, which together with the stem of the caudal dural plexus joins the primitive internal jugular vein. After involution of the primary head vein new channels, the transverse and sigmoid sinuses, develop which empty into the internal jugular vein. The temporal sinus develops secondarily and coexists with the sigmoid sinus. After regression of the sigmoid sinus and internal jugular vein, the temporal sinus represents the sole channel in the equine fetuses, by which venous blood from the brain is drained through the emissary vein of the retroarticular foramen into the external jugular system.