Effect of intrauterine positions on fetal brain development in the rat.

The effect of the position on the horn on fetal brain development was studied in 2276 rats (248 litters), by assessing the intrauterine location of those fetuses which had the highest values ('maximal fetuses') of the following parameters: body weight, brain weight, brain DNA (cell number), brain protein and the ratios brain weight/body weight and brain protein/brain DNA. The fetuses were at term (21 days) or at 16-18 days postcoitum. The total numbers of animals in the right and in the left uterine horn were essentially the same: 4.64 and 4.54, respectively. For each parameter, the locations of maximal fetuses were, on the average, symmetrical with respect to the center of each horn. The distributions of maximal fetuses along each horn followed specific patterns, which were different for each horn but showed similar locations of peaks and depressions for various parameters. However, the differences between the peaks and depressions were not statistically significant. It is concluded that both horns are equipotent, and all the positions on the horn are also essentially equipotent for production of animals maximal with respect to parameters studied. This also suggests that occasional cases of outstanding high fetal brain development occur from causes other than a favorable position on the uterine horn.

Litter size, maternal parameters, and brain and body parameters of neonatal rats.

The present work is concerned with the effect of natural litter size in the rat on the brain and body parameters of individual newborns, with particular reference to those newborns that were 'outstanding' (i.e., had parameters higher than mean +/- 2 SD). Correlations between litter size on one side, and length of gestation, number of stillborns, maternal weight at conception and maternal food consumption were also studied. To our knowledge, no previous report presented a similar integrated study on such a large number of rats (288 litters, 2,725 newborns) and wide range of litter size (2-17).

Effects of prenatal and chronic undernutrition on aging and survival in rats.

The effect on aging and survival of mild (2/3 of ad lib) chronic prenatal and postnatal undernutrition over 10 generations, or prenatal undernutrition only has been studied in rats. Both regimes of undernutrition used decreased body weights of animals as compared to the controls. Both undernourished groups had lower cholesterol levels and tumor incidence than the controls. The effects on survival depended not only on the time period of undernutrition but also on the age of the animals examined: chronic undernutrition resulted in lower survival of young adult animals (4-8 months) but higher survival than the controls in old age. Prenatal undernutrition only had no effect on young adult animals, gave higher survival than the controls at ages 8-18 months but considerably lower survival than controls in the old age: the underdevelopment of vital organs whose cells proliferate only before birth might have been the cause of such decreased longevity.

Quantitative study of fetal brain development in individual rats.

The development of cerebral hemispheres was quantitatively studied in twenty 15-day-old rat fetuses from two liters. Thicknesses, areas and mitotic counts (per mm length of ependyma) were not different of left and right hemispheres (parasagittal paraffin sections). On the other hand, among individual fetuses of the same litter, and areas of cerebral hemispheres differed as much as 2 standard deviations, and these values were not correlated with fetal weights (age). It appears that individual fetuses of the same litter and age may differ in the extent of their brain development.

Distribution of nutrients between fetal brain body during rat development.

During prenatal development, the distribution of nutrients between brain and body is influenced by many factors. Fetal and neonatal ratios may serve as indices of the final outcome; brain weight/body weight (Rw), brain DNA/body DNA (RDNA) and brain protein/body protein (Rprot; similar to Rw). These ratios decrease with fetal age but this dependence on age disappears towards term. Within one age, these ratios show considerable variability (up to 14%), from litter to litter, and within litters. The variability is not due to variation in water contents ( less than 1%). An extensive study of 2,089 normal newborns revealed that 7.5% had Rw values significantly higher than the mean for the population. Of these, 35% had normal body weights but significantly higher brain weights. Thus, they do not represent previously studied cases of general (brain and body) overdevelopment; rather, they represent cases of favorable brain versus body growth, i.e. distribution of nutrients between brain and body that is more favorable for the brain. Such a favorable distribution may be caused by maternal factors if it affects entire litters (3% of all affected) or by fetal factors, if it affects only individuals within a litter (49%).

Morphological development of the brain stem reticular core in prenatally undernourished rats.

The development of brain stem reticular core neurons in prenatally undernourished rats was investigated using the Golgi technique to determine the effect of immediate postnatal nutritional rehabilitation. Quantitative measurements of dendritic extent of branching and of cell size were compared in experimental and control neurons. An assessment of developmental dendritic status was achieved by counting numbers of dendritic protospines and varicosities on proximal and distal segments of dendrite. The protein and DNA content of the brain stem was also examined. The deficit of brain stem cell number at birth was rapidly restored by 11 days of age as was the delay of dendritic development. The number of dendritic protospines was comparable to control levels by 20 days but dendritic varicosities were more numerous on proximal segments. The dendritic extent increased during this period with rehabilitation though not as greatly as in control cells. The pattern of dendritic branching and size of somata were restored. Cell replication with rehabilitation probably represents a return of glial numbers which may impede distal dendritic growth of reticular core dendrites. Proximal growth is enhanced and the afferent supply to the reticular core may be increased during this time.

Prenatal undernutrition: effects on behavior, brain chemistry and neuroanatomy in rats.

The behavior and cerebral effects of prenatal protein-calorie undernutrition were investigated in newborn and postweanling rat pups. At birth, prenatally undernourished (PU) animals showed a deficit in body weight; however, by day 15 the difference was diminished and not significant. On days 13-18, PU pups required more trials for reversal learning of a water-escape response in a T-maze than control (C) pups; however, on days 31-35, there were no difference between groups when trained to learn an active-avoidance response. Assessment of brain development showed that at birth, DNA and protein content was severely reduced in PU animals; however, normalization was noted in regional sections of the brain at 35 days of age. Brainstem reticular cells from PU pups at birth show less dendritic arborization and less terminal branching cells from C pups. The results are discussed in terms of a delayed rate of maturation.

Transient and persistent changes in rabbit blood vessels associated with maintained elevation in arterial pressure.

Arteries and veins of hypertensive rabbits were examined 8 weeks after partially constricting the abdominal aorta above both kidneys, and compared with those from sham-operated animals. Structural and functional changes in blood vessels after 2 weeks, when the arterial pressure first attained a new elevated level, have been described previously, and are now compared with changes 6 weeks later. The increase in blood vessel mass could be correlated with an increase in deoxyribonucleic acid (DNA) content. In contrast to the status at 2 weeks postoperatively, there was no increased uptake of 3H-thymidine, 3H-proline, or 3H-lysine at 2 months. Furthermore, at this time cell nuclei labeled with 3H-thymidine were infrequent. Some vessels showed evidence of change in the physical characteristics of their wall. Only minimal changes were observed in those parameters of adrenergic nerve function measured -- neuronal 3H-norepinephrine uptake and vessel wall catecholamine content -- that had been markedly changed at 2 weeks. The results of this work, together with those of other studies of this model, suggest two phases of response of the arterial wall to pressure rise: an initial dynamic proliferative cellular response mainly of vascular smooth muscle associated with changes in adrenergic neuronal parameters, and a subsequent equilibrium phase characterized by an increased number of smooth muscle cells, some changes in the extracellular components, and minimal changes in the adrenergic innervation.

An 8 month longitudinal study of changes in elastic and muscular arteries and veins of the rabbit with sustained hypertension after abdominal aorta constriction.

1. Long-term changes in the function and structure of arteries and veins in response to an elevation in arterial pressure have been studied in the rabbit after partial abdominal aorta constriction. 2. Transient changes occur in the vasculature in association with the rise in arterial pressure. 3. The dominant change seen after arterial pressure elevation has been maintained for 8 months is an increase in arterial wall mass, including an increase in vascular smooth muscle cell number, and in some arteries an increase in internal diameter. 4. It may be inferred from this limited study of elastic and muscular arteries that structural alteration represents the over-riding response of the vasculature to an elevation in intramural pressure.

The effect of progesterone on fetal and placental development in normal and protein-energy-restricted rats.

Maternal protein-energy restriction (25% of the ad libitum intake) during the first 10 days of pregnancy resulted in severely altered fetal growth rates. Fetal development was assessed by body weight, brain weight, brain DNA, and brain protein content on fetal days 16, 18, 20 and at term. The individual placentas were also examined (weight, DNA and protein content) on each of these fetal days. Progesterone was administered commencing with day 3 of pregnancy until the day Caesarian section was done, in an attempt to rehabilitate placental development. This treatment did not improve placental development on fetal days 16 or 18. However, fetal development was significantly improved on day 16 and day 20, as compared to the dietary-restricted group without progesterone.

The effects of chronic undernutrition over generations on rat development.

Experimental rats were fed 2/3 (10g/24 hours) of adlibitum diet throughout pregnancy and post-weaning, thus far for six generations; their brain and body development was compared with those of controls fed ad libitum (15.5 g/24 hours). As expected from previous reports, neonatal F1 offspring exhibited highly significant decreases in body weight, cerebral wet weight, cerebral DNA and cerebral protein. However, neonatal decreases were not greater in F2 through F6 than in F1 indicating that there was no cumulative effect of this undernutrition on offspring's parameters over generations. Maternal body weight at mating (90 days) and percentage of females that did not litter steadily decreased over generations. The observed high mortality in F1 through F6 and the resulting strong natural selection in favor of best mothers and weanlings could explain these findings. The phenomena contributing to high mortality are multiple and involve maternal factors during pregnancy and before weaning, as well as offspring factors.

Alterations in the rate of fetal and placental development as a consequence of early maternal protein/calorie restriction.

The in utero growth rates have been determined for the body, brain, and the placenta in the rat. The accumulation of cell number (DNA content) and protein content in the cerebrum and the placenta were investigated during normal development. When rats were exposed to a severe reduction in protein/calorie intake during the first 10 days of pregnancy and the fetal growth rates were compared to those of the normal control animals, highly significant differences were observed. Pregnant rats, which were restricted in their protein/calorie intake during the early part of pregnancy, significantly prolonged the gestation time. When this increase of in utero time is taken into consideration and the offspring are compared at the time of natural birth, the data presented demonstrate the possibility of in utero catch up growth. The variations, in fetal development within the same litter and across litters, demonstrate a considerable plasticity during normal development in utero.

Hyperplasia of vascular smooth muscle in experimental hypertension in the rabbit.

Evidence for smooth muscle cell hyperplasia was sought in elastic and muscular vessels of rabbits 2 weeks after hypertension had been induced by partial constriction of the abdominal aorta above both kidneys. In those arteries taken from the circulation proximal to the constriction, specifically the common carotid artery and the aorta, vessel length, wall thickness, weight, and deoxyribonucleic acid content were increased in proportion to the rise in arterial pressure. There was no change in the extracellular space of muscular arteries as measured by [14C]inulin. [3H]Thymidine uptake measured in a gastric artery increased in proportion to the rise in arterial pressure. As demonstrated by light microscope autoradiography, [3H]thymidine was incorporated into cells in all layers of the artery wall but predominantly into the smooth muscle cells. There was no change in the size of arteries below the ligature where the arterial pressure was within normal limits. The data demonstrated that the increase in vessel wall dimensions in this animal model of hypertension is due in part, during the acute phase, to an increase in the number of cells, particularly vascular smooth muscle cells.

Experimental intrauterine growth retardation.

The effects of experimental intrauterine growth retardation on subsequent fetal development, especially with respect to brain development, were studied in a new animal model. The rabbit was chosen since it has a perinatal pattern of brain development similar to that of the human. Experimental ischemia was induced during the last trimester by ligation of spiral arterioles and the differential effects on fetal development at term (30th gestational day) are reported. Specific brain regions were examined for wet weight, total cell number (DNA) and total protein content. Highly significant decreases in all these parameters were found in both the cortex and cerebellum following experimental intrauterine growth retardation; these two organs were differentially affected. The prospects and advantages of using this animal model for the study of the postnatal "catch-up growth" are discussed.