First Week Of Postnatal Life Research Articles

The effect of age, growth retardation and asphyxia on ascorbic acid concentrations in developing brain.

Abstract— The concentration of ascorbic acid in whole rat brain during the first week of postnatal life was up to 100 per cent higher than in adult animals. A progressive fall in concentration occurred between 4 and 30 days of age. Corresponding changes did not occur in liver and adrenal gland, two other organs rich in ascorbic acid. Rats subjected to growth retardation during the fetal and suckling periods had, at 25 days of age, levels of ascorbic acid in the cerebellum and brainstem significantly higher than those of control animals. A period of prolonged asphyxia in 5‐day‐old rats resulted in a significant 4 per cent reduction in whole brain ascorbic acid concentration.

Effect of protein-calorie malnutrition on the development of social behavior in rats.

AbstractThe effect of early protein‐calorie malnutrition on the development of social behavior was studied during the first weeks of postnatal life. Activity and social interaction were recorded in groups of young rats either in the rearing cage or in a novel enviornment. The malnourished group had a delayed development of social behavior and smaller number of social contacts in all tests. During the suckling period, the nutritionally deprived pups were also more dependent on the mother, showed no social grooming, but were also more aggressive. On the 49th day, the normal rats showed increased exploration of the social stimulus whereas the malnourished rats were markedly inhibited. Apparently, early nutritional deficiency altered the social structure of the litter and of all individuals from the beginning by disturbing behavior and interactions of all members of the “family”.

Vulnerability of developing brain. II. Effects of early nutritional deprivation on reflex ontogeny and development of behaviour in the rat

During the last two weeks of pregnancy and throughout lactation the food intake of a group of female rats was restricted to about half that of a control group fed ad libitum. The growth, physical maturation and behavioural development of control and undernourished male offspring were compared. At 21 days the body weight of the underfed young was only one-third that of controls. The appearance of 2 out of 3 physical features, and of 4 out of 8 reflexes was significantly delayed in the undernourished group. Generally, characteristics which normally appear in the first week of postnatal life were not significantly affected; whereas most of those appearing later were significantly delayed. When rats were 9, 13, 17 and 21 days old their behaviour in an open field was observed. Exploratory responses were first seen significantly later in undernourished young. Though they moved about the field as much as the controls, they made significantly fewer upward-directed responses on the first 3 days of testing. At 21 days most control rats were able to move round the rim of a plastic beaker to a refuge platform, a feat accomplished by only a few underfed animals.

The development of immunoglobulinlevels in man

Summary The development of IgG, IgA, and IgM levels from birth, through the newborn period, infancy, childhood, and into adulthood has been studied with the use of 1,241 sera from 939 subjects. Rapid synthesis of IgM starts in the first week of postnatal life. This system expands to the adult levels by the age of about 1 year for boys and 2 years for girls. Boys and girls have similar IgM values until age 7, after which girls have higher values. IgA synthesis begins by 2 to 3 weeks of age, increases slowly, and attains adult levels by about 12 years. Rapid IgG synthesis probably begins by the first 4 to 6 weeks of life and adult levels are reached at about age 8 years.

THE X-RAY EXAMINATION OF THE CHEST DURING INSPIRATION IN THE NEWBORN AND DURING INFANCY.

Respiratory disease in early infancy attracts increasing interest (Strang, 1963; Karlberg, 1960; Warley and Gairdner, 1962) and radiological examination is being more frequently applied. However, the radiographs present great difficulty in interpretation and the technical difficulties in producing them are by no means confined to the inevitable lack of co-operation. The anatomical features distinctive of the thoracic viscera in infancy are generally recognised, but less attention has been paid to the different formation of the thorax at birth from that of adult life, and the consequent alteration in the mechanism of normal respiration. In the average adult thorax, the angle of the ribs to the thoracic spine is approximately 45 deg. at the level of the 6th rib in the mild-axillary line. In the foetus the ribs are “horizontal”, this term being used by convention when they are at right angles to that part of the thoracic vertebral column with which they are articulated. This foetal formation persists unchanged for the first weeks of post-natal life, after which, at a very variable rate, the adult shape is assumed. Lateral radiographs of the thorax demonstrate the angulation of the ribs relative to the thoracic vertebral column with an accuracy unobtainable in antero-posterior views because of the practical difficulty of avoiding some degree of lordotic or kyphotic distortion (Figs. 1 and 2).

Changes in the size of germ cell nuclei during the development of the testis of the ram and rat.

The surface areas of the plane of maximum size of germ cell nuclei have been determined at different stages of development of the testis of the ram and rat. The distributions of these surface areas both in the developing and the adult testis were found to be logarithmically rather than arithmetically normal. A basic pattern of change in surface area takes place during the development of the testis in both species of animal. The overall pattern of change consists of nuclear enlargement prior to the onset of spermatogenesis. By the time spermatogenesis has become fully established, germ cell nuclei have diminished in size. The enlargement in the ram testis does not take place until just before the onset of spermatogenesis. In the rat it is obvious during foetal life and continues until the gono- cytes begin to divide at the end of the first week of post-natal life. The enlargement is not, as was believed by previous workers, indicative of degenerative changes taking place in these cells, but is part of the normal differentiation of gonocytes. Abnormally enlarged germ cell nuclei are found in the ram in mid-foetal and particularly in early post-natal life prior to the appearance of prospermatogonia. Excessively enlarged nuclei are also found in the rat in the second week of post-natal life after the gonocytes have begun to divide. The reasons for the abnormal enlargement in both species of animal require further investigation. In both the ram and the rat, the nuclei of type A spermatogonia increase in size prior to dividing to initiate a new spermatogenic cycle.

Changes in the cells of the Sex Cords and Seminiferous Tubules during the development of the Testis of the rat and mouse.

The sex cords of the testis of the foetal rat and mouse are made up of two types of cell- the gonocytes and the indifferent cells. During foetal and early postnatal life, the former undergo a process of maturation involving principally an increase in size and in number of cytoplasmic inclusions. Nuclear enlargement is accompanied by a diminution in staining intensity. Gonocytes are more centrally placed within the sex cords than indifferent cells, and in the later stages of foetal development they cease to divide. In the first week of postnatal life, however, they resume mitotic activity and migrate to the basement membrane of the sex cords. Gonocytes as such disappear and are replaced by smaller daughter cells, the immature type A spermatogonia. The appearance of the latter is followed by the onset of spermatogenesis. As the tubules gradually become filled with the layers of cells of the spermatogenic line, the daughter cells of the gonocytes become flattened against the basement membrane, and come to resemble the type A spermatogonia found in the adult. Indifferent cells, which are always cytologically distinct from gonocytes and spermatogonia, exist as mononucleate units. The pattern of change of these cells during the development of the testis is different from that of the germ cells. Unlike the gonocytes, the indifferent cells continue to divide during foetal and early postnatal life. Little change takes place in these cells until after the onset of spermatogenesis, when they gradually increase in size and become Sertoli cells. The latter are principally mononucleate in form.

THE EFFECTS OF HYPOXIA ON THE RESPIRATION OF NEWBORN INFANTS

The effects of administering atmospheres containing 10 and 12% oxygen to healthy newborn infants of different ages have been studied. Infants under 24 hours of age tended to hypoventilate throughout the period of hypoxia. Infants six to 11 days of age hyperventilated for the first two or three minutes and then showed a decrease, although not so marked as observed in the infants under 24 hours of age. Infants 16 to 48 days of age showed the most marked increase in ventilation, but even in these infants it was poorly maintained as compared to responses seen in adults. Hypoxia produced a slowing of the respiratory rate in all infants except the very oldest. Tidal air was increased at first and then decreased. The increases in tidal air accounted for most of the increase in minute volume seen in the older infants. Hypoxia increased the incidence of periodic breathing in the two older groups of infants, but had very little effect on infants under 24 hours of age. Respiratory patterns did not appear to be altered by the hypoxic conditions employed in this study. It has been postulated that the comparatively weak response to hypoxia made by infants immediately after birth possibly is dependent on relatively poor chemoreceptor reflexes and that the latter increase in strength during the first weeks of postnatal life. It has also been suggested that the relative inability to induce periodic breathing in infants under 24 hours of age as compared to those several weeks old is further evidence indicating that metabolism of the medullary respiratory centers is to a larger extent anerobic than at the later periods of postnatal life.

INFLUENCE OF AGE AND PRESENCE OF THE OVARIES ON REPRODUCTIVE FUNCTION IN RATS INJECTED WITH ANDROGENS1

THE DEVELOPMENT OF REPRODUCTIVE FUNCTION in female rats is materially altered by the injection of testosterone compounds during the first weeks of postnatal life (1–4). When these animals reach adulthood they show abnormalities in several features of reproductive structure and function. They do not display cyclic mating behavior; ovulation and corpus luteum formation do not occur; the uterus differentiates atypically and is not normally responsive to estrogen. When such animals are spayed and injected with estrogen and progesterone estrous behavior is not induced even with 10 times the quantity of hormone (3) which causes heat in control animals. It was concluded from these studies that testosterone propionate in doses from 3 to 36 mg. is effective in suppressing reproductive function when the injections are begun soon after birthOn the other hand, these androgens when given to sexually mature.

Andromimetic Effect of Estrogen upon the Clitoris of the Rat.

SummaryThe administration of estrogen to female rats during the first week of postnatal life produces a defect in the external genital organs characterized by cleavage of the preputial fold, hypertrophy of the glans clitoridis, and a feeble differentiation of erectile tissues. Since these changes resemble, except for extent, those produced by postnatal androgen, it is concluded that estrogen exerts a mild andromimetic effect upon the clitoris of the rat.