Thyrotropin releasing hormone in the pancreas of newborn rats from streptozotocin-treated mothers

The effect of maternal diabetes (induced by i.p. injections of 40-50 mg/kg BW Streptozotocin on the day of mating) on TRH in the pancreas of newborn rats was studied. Determination of peptide alpha amidation activity and TRH precursor level on the day of birth revealed decreased biosynthesis of TRH resulting in profoundly (10 times) lower pancreatic TRH and TRH-OH concentrations in pups of diabetic rats. Pancreatic His-Pro-diketopiperazine (His-Pro-DKP) remained unaffected by maternal diabetes. The depression of pancreatic TRH was less profound 24 h later, and even elevated TRH was measured in the pancreas of pups of diabetic mothers on postnatal day 5. Short term postnatal starvation or nursing of intact pups by the diabetic foster mother did not affect pancreatic TRH. It could be postulated that postnatal TRH development in the rat pancreas is retarded by maternal diabetes, while His-Pro-DKP remains unaltered.     

Postnatal recruitment of brown adipose tissue is induced by the cold stress experienced by the pups. An analysis of mRNA levels for thermogenin and lipoprotein lipase.

In order to investigate the postnatal recruitment process, gene expression in the brown adipose tissue of rat pups was followed during the first 20 h of life. In normal pups, the level of mRNA coding for the uncoupling protein thermogenin increased markedly but gradually within the first 24 h. Lipoprotein lipase and actin mRNA levels were relatively low and remained constant. In pups exposed to thermoneutral temperature (35 degrees C) for the first 12 h after birth, no increase in thermogenin mRNA or lipoprotein lipase mRNA was observed, whereas in pups exposed to 28 degrees C a clear increase in both thermogenin and lipoprotein lipase mRNA levels was found. Actin mRNA levels were not affected by the environmental temperature under these circumstances. It was concluded that the postnatal recruitment in brown adipose tissue is a consequence of the cold stress experienced by the newborn pups. Thus, postnatal recruitment is not ontogenically predetermined.     

Promoting effect of bombesin on the cell proliferation in the rat endocrine pancreas during the early postnatal period

The present work investigated whether orally administered bombesin influences cell proliferation in the endocrine pancreatic islets of rats during the suckling period and after weaning. Four series of pups were given bombesin diluted in milk (20 micrograms/kg, 3 times daily) or milk alone for 5 days during either the first, second, third or fourth postnatal week of life. Oral administration was used because bombesin-like peptides have been identified in the breast milk of mammals. 45 min before death, animals were given a single [3H]thymidine pulse injection. Tissue sections were processed for radioautography; DNA labeling and mitotic indices were estimated after counting at least 1000 endocrine cells per rat pancreas. In control rats, the labeling and mitotic indices in pancreatic islets dropped regularly from the first week to the fourth week of life (3.6% +/- 0.2% versus 1.9% +/- 0.1% and 0.46% +/- 0.09% versus 0.08% +/- 0.02%, respectively). Orogastric bombesin administration significantly increased the DNA labeling and mitotic indices at the end of the first week (+20% and +62%, respectively) and second week of life (+37.5% and +49%, respectively) (P less than 0.05 to P less than 0.005), but did not modify these parameters for the third and subsequent weeks of life. Therefore, this study provides evidence that bombesin stimulates DNA synthesis and cell division in pancreatic endocrine cells during the developmental period.     

The reactivity of neonatal rabbits to the mammary pheromone as a probe for viability

Newborn rabbits depend on a daily nursing interaction with the mother to gain milk and to survive. During this interaction, they localise and seize the nipples displaying a typical behaviour triggered by maternal odour cues. The mammary pheromone constitutes such a signal in domestic rabbits: it elicits sucking-related movements in more than 90% of the pups. However, some newborns remain unresponsive to the presentation of the pheromone, even pups apparently healthy and highly motivated to suck. The main goal of the present study was therefore to explore the link between the unresponsiveness of rabbit pups to the mammary pheromone and their growth and survival in breeding conditions. To that end, 293 newborns from 30 litters were tested for their head searching-oral grasping responses to the mammary pheromone on days 1 and 3, and their milk intake and mortality were followed up from days 1 to 21. It was hypothesised that unresponsive newborns would have subsequent difficulties in finding nipples, sucking and surviving. Early weight and success in milk intake were further considered as mediating factors in growth and viability. The results showed that pups that were unresponsive to the mammary pheromone on day 1 were less successful in gaining milk and had a higher rate of mortality than the responsive pups. However, this impact was modulated by the weight of pups: it appeared only in the lightest newborns. Moreover, this impact vanished on day 3. On the other hand, the pup weight and sucking success on days 1 to 3 strongly influenced viability and growth during the period extending from days 1 to 21. Taken together, the results show that the day-1 responsiveness of rabbit pups to the mammary pheromone can be considered as an indicator of individual viability in pups having a small weight (<48 g on day 1). The predictive validity of the pups’ pheromonal reactivity seems however time-limited as it works only during the first, but crucial, postnatal days.     

Essential role for polyamine biosynthesis in thyroxine stimulated pancreatic development in neonatal rats.

Administration of thyroxine to rat pups leads to precocious development of the pancreas. The role of ornithine decarboxylase (ODC) and polyamines in thyroxine-induced pancreatic maturation was examined. Rat pups (aged 5 days) were given daily subcutaneous injection of thyroxine (0.1 micrograms/g body wt.) until the day before death. Serial ODC activities were measured in pancreatic homogenates after 1, 2, 3, 4, 5, 6, 7 and 10 days of thyroxine treatment. There was a biphasic induction of ODC activities by thyroxine: an early peak appeared on day 2 of treatment followed by a decrease on day 4; a second peak was evident on day 5 and then a decrease to control values by day 7. Significant increases in tissue concentrations of putrescine and spermidine were observed concomitant with two peaks of ODC activity. Pancreatic amylase concentration, DNA and protein also showed a significant increase after thyroxine treatment. Difluoromethyl ornithine (DFMO), a specific ODC inhibitor, given orally (8% in drinking water) to nursing dams at postnatal day 5 for 5 days caused an 83% inhibition of pancreatic ODC activity in thyroxine-treated pups when compared to thyroxine-treated pups not exposed to DFMO. Concomitantly, the thyroxine-induced increases in pancreatic weight, protein and amylase activity were suppressed. Our results suggest that increases in ODC activities and polyamine levels are critical intermediary steps in the precocious induction of pancreatic development by thyroxine.     

Development of lipase in nursing piglets

This experiment was designed to investigate the development of gastric lipase and pancreatic lipase in nursing piglets. During the nursing period, the lipase activity was measured at one, 7, 14, 21 and 28 days of age. The results showed that the gastric mucosa weight, pancreas weight, body weight, the specific activity of gastric lipase and pancreatic lipase, and the total activity of gastric lipase and pancreatic lipase increased with the age of the piglets. The development of the specific activity of gastric lipase slowed before the nursing piglets reached 3 weeks of age, but the total activity of gastric lipase at day 28 was significantly higher than that at day 21. The specific activity and total activity of pancreatic lipase were at low levels during the first two weeks of life and then developed quickly from days 21 to 28. It was observed that the specific activity and total activity of gastric lipase were lower than those of pancreatic lipase.     

Treatment of newborn rats with a VEGF receptor inhibitor causes pulmonary hypertension and abnormal lung structure

To determine whether disruption of vascular endothelial growth factor (VEGF)-VEGF receptor (VEGFR) signaling in the newborn has long-term effects on lung structure and function, we injected 1-day-old newborn rat pups with a single dose of Su-5416, a VEGFR inhibitor, or vehicle (controls). Lungs from infant (3-wk-old) and adult (3- to 4-mo-old) rats treated with Su-5416 as newborns showed reductions in arterial density (82 and 31%, respectively) and alveolar counts (45 and 29%) compared with controls. Neonatal treatment with Su-5416 increased right ventricle weight to body wt ratios (4.2-fold and 2.0-fold) and pulmonary arterial wall thickness measurements (2.7-fold and 1.6-fold) in infant and adult rats, respectively, indicating marked pulmonary hypertension. We conclude that treatment of newborn rats with the VEGFR inhibitor Su-5416 impaired pulmonary vascular growth and postnatal alveolarization and caused pulmonary hypertension and that these effects were long term, persisting well into adulthood.     

Differential metabolism of brown adipose tissue in newborn rabbits in relation to position in the litter huddle

Competition for resources can contribute importantly to the early development of individual differences in behavioral and physiological phenotypes. In newborn rabbits, littermates compete for thermally favorable positions within the litter huddle. As brown adipose tissue (BAT) is the principal site of thermogenesis in such altricial young, we investigated differences in rabbit pups’ growth and morphological differences in BAT associated with position within the huddle. We formed three treatment groups (7 litters/group): GI—birth (pups killed at birth); GII—chronic thermal challenge (pups killed after exposure to a moderately cold environmental during postnatal days 1–3); GIII—acute thermal challenge (as for GII but pups killed after an additional 30 min exposure to a very cold environment on postnatal day 3). Interscapular BAT was removed at death for histological analysis, and triglyceride concentrations measured in serum. Pups occupying central positions in the huddle had higher skin temperatures, obtained more milk, and were more efficient at converting this into body mass, than pups occupying peripheral positions. There was no significant difference in BAT morphology or triglyceride concentrations between pups at birth, nor between central and peripheral pups chronically exposed to moderate cold until postnatal day 3. However, during acute cold exposure at this age, peripheral pups were less able to maintain their body temperature, they depleted BAT fat reserves almost completely, and they had lower serum concentrations of triglycerides than central pups. These findings confirm the contribution of early sibling relations to individual differences in growth and metabolic processes associated with thermoregulation in newborn rabbits.     

Demonstration of a quiescent period for feeding controls in the developing rat

Feeding behaviour of rats during development was assessed by weighing pups before and after a 4 h feeding session. During the first postnatal week, fasted pups gained significantly more weight than fed pups. This difference disappeared during the second week, but reappeared during the third week and persisted through the fourth week. In another series, pups were weighed at 2 and 4 h after beginning feeding. This showed that fasted pups aged 6 days compensate by suckling longer than fed pups. At 10 and 14 days of age there were no differences between fed and fasted pups at either 2 or 4 h, but from 16 days onward, fasted pups had eaten significantly more than fed pups at both times. A control experiment showed that the lack of compensation by fasted pups aged 10-14 days did not reflect lack of availability of milk. Video-analysis of suckling behaviour at ages 6, 10 and 15 days provided further evidence for lack of feeding controls during the second postnatal week: at 6 and 15 days fasted pups spent more time actively sucking than did fed pups. Whereas at 10 days, there were no differences between fed and fasted pups. It is concluded that feeding controls are present during the first postnatal week, become quiescent during the second week and reappear during the third week.     

Thyroxine-induced changes in the glycosylation pattern and in brain and serum levels of rat alpha-fetoprotein

We have studied the effect of thyroid disfunction during the postnatal period, on the serum and brain levels of rat alpha-fetoprotein (AFP) and albumin. Hypothyroidism was induced by treatment of pregnant rats and their newborn pups with 2-mercapto-1-methylimidazole(methimazole). Hyperthyroidism was provoked in newborns by daily injections of thyroxine (0.25 micrograms/g body wt) from the 3rd postnatal day weaning. Impaired growth, lower brain size, altered behaviour and morphological features observed were according to an altered thyroid status. Hypothyroid rats showed a significantly reduction in serum AFP concentration (78% of control values at 8 days of age) and a slight increase in that of albumin. level could be appreciated. Thyroxine supplementation (0.2 micrograms/rat/day) corrected most of these alterations. Hyperthyroidism induced a drastic fall in both serum and brain AFP levels (about 48% of the corresponding control values). Albumin concentration in serum was augmented significantly from the 12th postnatal day, but its brain levels did not change significantly. In hyperthyroid rats, a significant reduction (37% relative to controls) in the concanavalin A-non reactive microform of AFP, was observed. This alteration of the glycosylation pattern of AFP could be due to the inhibition by thyroxine of the activity of the hepatic enzyme GlcNAc-transferase III.     

Body and organ size and composition during late foetal and postnatal development of rat

Development induced deep anatomical changes and tissue composition alterations in the rat. To determine the extent of these changes, the organ weight and size of 19 and 21 day rat foetuses and of 1, 5, 10, 20 and 30 day old Wistar rat pups have been studied and compared with adults. Different tissues showed varying rates of cell and tissue growth as well as tissue cellularity during development. Tail length is not a good index of skeletal growth. Brain growth was much slower from late intrauterine life to adulthood than most other organs. Skin weight increased more than 3-fold between days 19 and 21 of intrauterine life. Striated muscle proportion to body weight remained practically constant throughout all postnatal life studied.     

Characterizing the functional significance of the neonatal rat vibrissae prior to the onset of whisking

The present series of experiments assessed how information from the whiskers controls and modulates infant rat behavior during early learning and attachment. Passive vibrissal stimulation can elicit behavioral activity in pups throughout the first two postnatal weeks, although orienting to the source of stimulation is evident only after ontogenetic emergence of whisking. In addition, while pups were capable of demonstrating learning in a classical conditioning paradigm pairing vibrissa stimulation with electric shock, no corresponding changes were detected in the anatomy of the barrel cortex as determined by cytochrome oxidase (CO) staining. Finally, the role of whiskers in a more naturalistic setting was determined in postnatal day (PN)3-5 and PN11-12 pups. Our results showed that both nipple attachment and huddling were disrupted in whisker-clipped PN3-5 pups but only marginally altered in PN11-12 pups. Together, these results suggest that the neonatal whisker system is behaviorally functional and relevant for normal mother-infant interactions, though it lacks the sophistication of a mature whisker system that evokes very specific and directed responses.     

Chronic intermittent hypoxia reduces ventilatory long-term facilitation and enhances apnea frequency in newborn rats

Ventilatory long-term facilitation (LTF; defined as gradual increase of minute ventilation following repeated hypoxic exposures) is well described in adult mammals and is hypothesized to be a protective mechanism against apnea. In newborns, LTF is absent during the first postnatal days, but its precise developmental pattern is unknown. Accordingly, this study describes this pattern of postnatal development. Additionally, we tested the hypothesis that chronic intermittent hypoxia (CIH) from birth alters this development. LTF was estimated in vivo using whole body plethysmography by exposing rat pups at postnatal days 1, 4, and 10 (P1, P4, and P10) to 10 brief hypoxic cycles (nadir 5% O2) and respiratory recordings during the following 2 h (recovery, 21% O2). Under these conditions, ventilatory LTF (gradual increase of minute ventilation during recovery) was clearly expressed in P10 rats but not in P1 and P4. In a second series of experiments, rat pups were exposed to CIH during the first 10 postnatal days (6 brief cyclic exposures at 5% O2 every 6 min followed by 1 h under normoxia, 24 h a day). Compared with P10 control rats, CIH enhanced hypoxic ventilatory response (estimated during the hypoxic cycles) specifically in male rat pups. Ventilatory LTF was drastically reduced in P10 rats exposed to CIH, which was associated with higher apnea frequency during recovery. We conclude that CIH from birth enhances hypoxic chemoreflex and disrupts LTF development, thus likely contributing to increase apnea frequency.     

Characterizing the functional significance of the neonatal rat vibrissae prior to the onset of whisking

The present series of experiments assessed how information from the whiskers controls and modulates infant rat behavior during early learning and attachment. Passive vibrissal stimulation can elicit behavioral activity in pups throughout the first two postnatal weeks, although orienting to the source of stimulation is evident only after ontogenetic emergence of whisking. In addition, while pups were capable of demonstrating learning in a classical conditioning paradigm pairing vibrissa stimulation with electric shock, no corresponding changes were detected in the anatomy of the barrel cortex as determined by cytochrome oxidase (CO) staining. Finally, the role of whiskers in a more naturalistic setting was determined in postnatal day (PN)3-5 and PN11-12 pups. Our results showed that both nipple attachment and huddling were disrupted in whisker-clipped PN3-5 pups but only marginally altered in PN1I 1-12 pups. Together, these results suggest that the neonatal whisker system is behaviorally functional and relevant for normal mother-infant interactions, though it lacks the sophistication of a mature whisker system that evokes very specific and directed responses.     

Correlation between (3H)dopamine specific uptake and (3H)GBR 12783 specific binding during the maturation of rat striatum

The development of the specific uptake of dopamine in the rat striatum during the early postnatal period is compared with the ontogenetic changes of the specific binding of (3H)GBR 12783 to the site of uptake inhibition. During maturation, the increase in the specific binding of (3H)GBR 12783 parallels the increase in the specific uptake of dopamine. (3H)GBR 12783 specific binding sites increase in number from day 1 postpartum until 40 days, when they reach the adult level. In 40 day-old rats, the weight of the striatum represents 80% of adult values. The affinity of (3H)GBR 12783 for the inhibition site is similar in membrane preparations obtained from 6 day-old pups and adults; this results in a same ability of the inhibitor to block the specific uptake of dopamine into synaptosomes obtained from pups or adult rats. These data support the hypothesis of the existence of a single molecular entity including both the inhibition site and the carrier itself.     

Influence of adenosine A(1)-receptor blockade and vagotomy on the gasping and heart rate response to hypoxia in rats during early postnatal maturation.

Failure to autoresuscitate from apnea has been suggested to play a role in sudden infant death. Little is known, however, about factors that influence the gasping and heart rate response to severe hypoxia that are fundamental to successful autoresuscitation in the newborn. The present experiments were carried out on 184 rat pups to investigate the influence of the parasympathetic nervous system, as well as adenosine, in mediating the profound bradycardia that occurs with the onset of hypoxic-induced primary apnea and in modulating hypoxic gasping. On days 1 to 2, days 5 to 6, and days 10 to 11 postpartum and following bilateral cervical vagotomy (VAG) or administration of a selective adenosine A(1) receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine; DPCPX), each pup was exposed to a single period of severe hypoxia produced by breathing an anoxic gas mixture (97% N(2)-3% CO(2)). Exposure to severe hypoxia resulted in an age-dependent decrease in heart rate (P < 0.001), accentuated with increasing postnatal age, that was attenuated in all age groups by DPCPX but not by VAG. Furthermore, DPCPX but not VAG decreased the time to last gasp but increased the total number of gasps in the 1- to 2-day-old and 5- to 6-day-old pups but not in the 10- to 11-day-old pups during exposure to severe hypoxia. Thus our data provide evidence that adenosine acting via adenosine A(1) receptors plays a role in modulating hypoxic gasping and in mediating the profound bradycardia that occurs coincident with hypoxic-induced primary apnea in rats during early postnatal life.     

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in prenatal stage on the dopamine system in the postnatal mouse brain.

A dopaminergic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP), administered to a pregnant female was found to affect postnatally the catecholamine metabolism of the pups. MPTP (5 mg/kg body weight/day) was administered to pregnant C57 Black BYA mice daily for 7 days between the 12th and 18th day of gestation. Dopamine levels and tyrosine hydroxylase (TH) activity were measured in the whole brain from the pups sacrificed after birth. In MPTP-treated pups at 7 days of age, TH total activity (TH activity/brain) did not change (92% of the control value), while TH specific activity (TH activity/mg protein) was increased to 163% of that in control mice. Thus, TH homospecific activity (TH activity/mg TH protein) doubled compared to the control mice. At 28 days of age, both the total activity and the specific activity of TH in the brains of postnatal mice were reduced to 50% and 78% of the control, respectively. Dopamine concentration in the striatum was also reduced significantly. Reduction in the TH activity and dopamine concentration were also observed at the age of 12 weeks. These data suggest that the prenatal exposure to MPTP induced a prolonged reduction of TH activity in the brains of mice with a transient increase of TH homospecific activity during the postnatal period.     

Oxygen consumption and survival prediction in neonatal rats exposed to prenatal hypervitaminosis A

Fetal exposure to excess vitamin A results in a highly variable degree of lung pathology and high neonatal mortality in the Long-Evans rat. The present study evaluated O2 consumption in newborn of vitamin A-treated, vehicle-treated, and untreated pregnancies on five consecutive postnatal days beginning with the day of delivery (D0). Pregnant female rats were treated by gavage with 160,000 USP units of retinyl acetate dissolved in 0.5 ml corn oil on days 15 through 19 of gestation. Vehicle and undisturbed controls were run concurrently. All animals delivered spontaneously, and the pups were tattooed and individually tested in a closed system consisting of three chambers submerged within a thermostatically controlled water bath at 33 degrees C. Vitamin A-exposed pups, as a group, have significantly lower QO2 (ml O2 consumed/min/kg body weight) values than controls through postnatal day 2 (p less than 0.05). By days 3 and 4 of age, the mean QO2 values of surviving vitamin A-treated pups were similar to those of controls. A QO2 of 30 or greater on day 0 appears to be critical for early neonatal survival of vitamin A-exposed pups, as 87% of the pups with initial QO2 less than 30 died prior to day 4. Oxygen consumption rates in teratogen-exposed pups exhibiting low QO2 on day 0 rarely reached normal levels. In contrast, the occasional control pup with such low initial levels were well within normal limits (means +/- 1 SD) by the following day.(ABSTRACT TRUNCATED AT 250 WORDS)     

Perinatal development of endothelial nitric oxide synthase-deficient mice

The purpose of this study was to evaluate the influence of endothelial nitric oxide synthase (eNOS) deficiency on fetal growth, perinatal survival, and limb development in a mouse model with a targeted mutagenesis of the Nos3 gene. Wild-type (Nos3+/+) and eNOS-deficient fetuses (Nos3-/-) were evaluated on Gestational Day (E)15 and E17, and newborn pups were observed on Day 1 of life (D1). The average term duration of pregnancy was 19 days. For the evaluation of postnatal development, a breeding scheme consisting of Nos3+/- x Nos3+/- and Nos3-/- x Nos3-/- mice was established, and offspring were observed for 3 wk. Southern blotting was used for genotyping. No significant differences in fetal weight, crown-rump lengths (CRL), and placental weight were seen between Nos3+/+ and Nos3-/- fetuses on E15. By E17, Nos3-/- fetuses showed significantly reduced fetal weights, CRL, and placental weights. This difference in body weight was also seen throughout the whole postnatal period. In pregnancies of Nos3-/- females, the average number of pups alive on D1 was significantly decreased compared to either E15 or E17. Placental histology revealed no abnormalities. On E15, E17, and D1, Nos3(-/-) fetuses demonstrated focal acute hemorrhages in the distal limbs in 0%, 2.6%, and 5.7%, respectively, of all mutant mice studied on the respective days. Bone measurements showed significantly shorter bones in the peripheral digits of hindpaws of Nos3-/- newborns. We conclude mice deficient for eNOS show characteristically abnormal prenatal and postnatal development including fetal growth restriction, reduced survival, and an increased rate of limb abnormalities. The development of this characteristic phenotype of eNOS-deficient mice dates back to the prenatal development during the late third trimester of pregnancy.