Contribution of retinoic acid receptor beta isoforms to the formation of the conotruncal septum of the embryonic heart

To investigate the relative contribution of retinoic acid receptor (RAR)beta isoforms in conotruncal septation, RAR beta 1 and beta 3 were inactivated in the mouse. Mice lacking RAR beta 1 and beta 3 appear normal. Disruption of these isoforms in RAR alpha or RAR gamma null genetic backgrounds results in a high postpartum lethality. However, except for ocular defects found in RAR beta 1-3/RAR gamma compound mutants, the double null mutants display only abnormalities seen in single null mutants. This probably reflects a functional redundancy with other RARs, most notably with RAR beta 2 which is five- to sixfold more abundant than RAR beta 1 and beta 3 and whose domain of expression is largely overlapping. The conotruncal ridges form normally in retinoid X receptor (RXR)alpha/RAR beta compound mutants but fail to fuse, apparently as a result of excessive apoptosis of mesenchymal cells. Additionally, many cardiomyocytes in the conotruncal wall of these mutants appear necrotic. Although RAR beta 1 and beta 3 are expressed specifically in the conotruncal ridges, failure of fusion of these structures is not more frequent in RXR alpha/RAR beta 1-3 double null mutants than in RXR alpha single null mutants. Similarly, the disruption of the sole RAR beta 2 isoform in a RXR alpha null genetic background does not result in an increase of the frequency of conotruncal septum agenesis. However, this agenesis is fully penetrant in RXR alpha/RAR beta +/- mutants, which reflects distinct role of RXR alpha:RAR beta 1 (and beta 3) and RXR alpha:RAR beta 2 heterodimers in promoting the survival of conotruncal mesenchymal cells. Unexpectedly, we discovered that, in wild-type embryos, the conotruncal mesenchyme is a major site of morphogenetic cell death and that conotruncal myocytes are occasionally necrotic. Thus, excessive cell death in the conotruncus is a potential cause of ventricular septal defects in humans.     

Two new species of nematodes (Rhabditida: Diplogasteridae and Rhabditidae) parasites of Gryllodes laplatae (Orthoptera: Gryllidae) in Argentina

Cephalobium magdalensis n. sp. (Rhabditida: Diplogasteridae) found in Magdalena, Buenos Aires, and Cruznema lincolnensis n. sp. (Rhabditida: Rhabditidae) found in Lincoln, Buenos Aires, parasitizing the cricket Gryllodes laplatae (Orthoptera: Gryllidae) are described and illustrated. C. magdalensis n. sp. is characterized by having the excretory pore between the pseudobulb and the basal bulb and seven pairs of postanal papillae in the male. C. lincolnensis n. sp. can be distiguished by having meanly two pairs of preanal papillae, one pair of adanal papillae and six pairs of postanal papillae in the male.     

Entry of US medical school graduates into family practice residencies: 1997-1998 and 3-year summary

This is the 17th report prepared by the American Academy of Family Physicians (AAFP) on the percentage of each US medical school's graduates entering family practice residency programs. Approximately 16.6% of the 15,894 graduates of US medical schools between July 1996 and June 1997 were first-year family practice residents in October 1997, compared with 15.9% in 1996 and 14.6% in 1995. This is the highest percentage since this series of studies began in 1980-1981 (12.8%). Medical school graduates from publicly funded medical schools were almost twice as likely to be first-year family practice residents in October 1997 than were residents from privately funded schools, 19.8% compared with 11.8%. The Mountain region reported the highest percentage of medical school graduates who were first-year residents in family practice programs in October 1997 at 25.8%; the Middle Atlantic and New England regions reported the lowest percentages at 11.7% and 10.7%, respectively. Nearly half of the medical school graduates (48.1%) entering a family practice residency program as first-year residents in October 1997 entered a program in the same state where they graduated from medical school. The percentages for each medical school have varied substantially from year to year since the AAFP began reporting this information. This article reports the average percentage for each medical school for the last 3 years. Also reported are the number and percentage of graduates of colleges of osteopathic medicine who entered Accreditation Council for Graduate Medical Education-accredited family practice residency programs, based on estimates provided by the American Association of Colleges of Osteopathic Medicine.     

Phonetic profiles of toddlers with specific expressive language impairment (SLI-E)

Spontaneous language samples of 30 24-month-old toddlers diagnosed with Specific Expressive Language Impairment (SLI-E) were compared with samples produced by an age-matched group of 30 typically developing toddlers. Vocalization patterns, phonetic inventories, and syllable formation patterns were compared. Toddlers with SLI-E vocalized significantly less often than their typically developing peers, had proportionately smaller consonantal and vowel inventories, and used a more restricted and less mature array of syllable shapes. Although the mean incidence of phoneme usage varied significantly in all comparisons, profiles of consonant usage were similar between the two groups for initial phoneme usage, but considerably different for final consonant closure. Such patterns of vocal and phonetic behavior confirm earlier reports of phonetic delay in SLI-E, and suggest that nongrammatical factors contribute to the development of expressive language deficits in toddlers. We further propose a bidirectional model for the expressive deficits in SLI-E, in which the child's limited phonetic capacity interacts with propensities in caretaker interaction to further reduce opportunities for expressive language learning and practice.     

Production of low-pour diesel fuels by hydroisomerization of middle distillates from eastern medium-sulfur crudes

Summary Processes have been developed for catalytic hydrotreating and isomerization of n-paraffins to produce wintergrade diesel fuels from middle distillates.In the single-stage process on sulfur-resistant hydrotreating catalysts promoted with halogens, thorough drying of the feedstock and the hydrogen-rich recycle gas is required, along with promotion of the catalyst with the halogen and protection of the equipment against hydrogen halide corrosion.The yield of winter-grade diesel fuel conforming to specification GOST 305-62 (solid point –35C, cloud point –25C) is 85% by weight.In the two-stage process, the first stage is a thorough hydrotreating operation, the second stage hydroisomerization of the n-paraffins. The yield of winter-grade diesel fuel conforming to the requirements of GOST 4749-49 (solid point –45C, cloud point –35C) is 70% by weight. Also formed in the process is some 21–24% naphtha cut with a clear octane number of 76 by the motor method.Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 9, pp. 22–25, September, 1973.     

Sex and age differences in pulmonary mechanics in normal nonsmoking subjects

This study was performed to determine whether stimulation of the carotid chemoreceptors increases total or regional cerebral blood flow and whether activation of arterial chemoreceptors contributes to cerebral vasodilation during systemic hypoxemia. In anesthetized and ventilated dogs, carotid chemoreceptors were stimulated with nicotine or hypoxic and hypercapnic blood. To measure total and regional cerebral blood flow, we used labeled 15-mu microspheres. Stimulation of chemoreceptors did not increase cerebral blood flow or produce significant redistribution of cerebral blood flow, even though the chemoreflex was intact in these animals (as manifested by vasoconstriction in muscle, kidney, and small bowel) and the cerebral vessels dilated in response to systemic hypercapnia. In other studies in anesthetized, ventilated dogs and rhesus monkeys, cerebral vasodilator responses to systemic hypoxemia were observed before and after denervation of carotid and aortic chemoreceptors. Systemic hypoxemia produced large and equivalent increases in cerebral blood flow before and after chemodenervation. We conclude that stimulation of carotid chemoreceptors does not produce cerebral vasodilation and that chemoreceptors do not contribute significantly to cerebral vasodilation during systemic hypoxemia.     

Mixed infection with tularemia and Omsk hemorrhagic fever in experiments on aquatic field mice

The authors carried out an experimental study of some aspects of the pathogenesis of mixed tularemia and Omsk hemorrhagic fever infection in Arvicola terrestris L. The results obtained reflected the dynamics of development of the pathological process of the mixed infection, peculiarities of distribution of Francisella tularensis and of the viral antigen in different organs, the character of pathomorphological changes in the organism at different periods after the administration of the causative agent.