哺乳、哺乳-禁乳及哺乳-禁乳后再哺乳对大鼠下丘脑胖素A免疫反应神经元的影响

为观察下丘脑胖素 A在哺乳期摄食增加和能量代谢中的作用,本研究采用脑连续切片之免疫组织化学和图像定量分析技术,对分娩后第 12 天非哺乳、持续哺乳、持续哺乳后禁哺乳过夜和持续哺乳 - 禁哺乳后再急性哺乳大鼠下丘脑胖素A免疫反应神经元的免疫反应性进行了观察和半定量分析。结果表明,分娩后持续哺乳 11 d, 大鼠的日摄食量较同期分娩的非哺乳大鼠明显增加(180%),一夜禁哺乳则明显降低哺乳大鼠的日摄食量(45%); 哺乳12 d, 大鼠下丘脑胖素 A免疫反应神经元的数目和平均染色强度较非哺乳大鼠明显增加(P<0.001,P<0.05); 禁哺乳过夜(15 h)明显降低哺乳大鼠胖素A免疫反应神经元的数目和平均染色强度(P<0.001,P<0.05),与非哺乳大鼠比较无明显差异;禁哺乳过夜后再急性哺乳2 h 明显增加禁哺乳大鼠胖素 A 免疫反应神经元的数目和平均染色强度(P<0.001,P<0.05),急性哺乳 5 h 后,虽亦明显增加禁哺乳大鼠胖素 A免疫反应性(P<0.05),但与急性哺乳 2 h 比较作用减弱。上述结果表明,持续哺乳和禁乳后再哺乳均导致下丘脑胖素A明显增加,提示哺乳期胖素A可能表达上调并可能与哺乳期摄食增加有关, 且吸乳动作与下丘脑胖素A样神经元之间可能存在某种神经或体液性联系途径。     

Investigations on erythropoiesis in newborn rats. Dependence of erythropoiesis in newborn rats on the intensity of the haemopoietic processes in the lactating mothers.

The intensity of haemopoietic processes was investigated in 7, 9, 11, 14 and 19-day-old suckling rats in relation to the intensity of these processes in their mothers. The rate of the haemopoietic processes in newborn rats was determined on the basis of 59Fe incorporation into the blood and haemopoietic organs. The activity of the erythropoietic system in lactating rat females was stimulated by haemorrhage and inhibited by erythrocyte transfusion. Anaemization of lactating rats by haemorrhage did not stimulate erythropoiesis in the suckling rats. Posttransfusion polycythaemia in the lactating mothers inhibited erythropoiesis in the suckling rats beginning with the 9th day of life. This phenomenon became more pronounced with the age of the rats.     

On the quantification of suckling intensity in primates

The inhibitory effect that suckling has on the reproductive function of primate mothers varies as a function of the intensity with which they are suckled. Here we present an easily computed index of one parameter of suckling intensity, namely the temporal patterning of suckling bouts. High intensity suckling is characterized by frequent nursing bouts demarcated by short interbout intervals. Therefore, our suckling index is based on the brevity of observed interbout intervals, more specifically the proportion of such intervals that fail to exceed a criterion length. The index is an appropriate means of making interspecific comparisons of the development of infant suckling and is well suited for application to field data that include interbout intervals that were not observed in their entirety. To demonstrate its utility, we apply the index to field data collected on the suckling behavior of free-ranging rhesus monkey (Macaca mulatta) infants in India. In this context, we demonstrate that, in rhesus, between-infant differences in suckling intensity manifest themselves early in the postpartum period and contribute to between-female differences in the timing of first mating postpartum. Am J Phys Anthropol 105:33–42, 1998. © 1998 Wiley-Liss, Inc.     

Precocious cessation of intestinal macromolecular transport and digestive enzymes development by prostaglandin E2 in suckling rats

The effect of repeated oral administration of prostaglandin analogue (dmPGE₂) on intestinal macromolecular transport and digestive enzymes development were investigated in the suckling rats. By the administration of dmPGE₂ for 7 days, precocious induction of maltase activity, depression of amylase activity and enhancement of trypsin activity in the pancreas occurred. Absorption of bovine IgG was dose dependently depressed by drnPGE₂ treatments. The intestinal cessation was also observed in the adrenalectomized pups, but was not influenced by difluoromethyl ornithine administration. These results suggest that oral administration of PGE₂ induces precocious maturation of the small intestine and exocrine pancreas and that the intestinal cessation is not directly related to ornithine decarboxylase activity in the suckling rats.     

The development of nursing behaviour in swine

Certain aspects of nursing behaviour in the sow have been well documented. This literature has revealed that during parturition, nursing is asynchronous and continuous, while later in the lactation nursing is synchronous and cyclical. Fourteen Yorkshire sows and their litters were observed during the first week of lactation to study the transition from the first type of nursing to the second.The first type of nursing was termed neo-nursing and the second, cyclical nursing. Equivalent designations were assigned to suckling. The transition from neo-nursing to cyclical nursing occurred 10.7 ± 4.5 h following the birth of the first piglet. Using the video-taped behaviour of the sow and her piglets, the first cyclical nursing was defined as the first nursing of less than 30 min duration which was preceded by a period of at least 30 min in which less than one half of the litter was suckling. This transition was easily determined on the video-tapes, with little ambiguity. The transition tended to be fairly abrupt, and was probably due to the cessation of oxytocin release and the consequent cessation of continuous milk flow.     

The response of plasma prolactin to suckling during normal and prolonged lactation in the rat

In dams which had been kept isolated from pups for 8-10 h, the magnitude of the suckling-induced prolactin rise in the plasma was studied in relation to intensity of suckling stimulus and lactational age of the mother. At midlactation the response of prolactin evoked by suckling was enhanced as litter size increased. Suckling of 2 pups induced a greater prolactin rise in dams adjusted to 2 pups than in dams adjusted to 8 pups. Suckling of 8 pups caused a greater prolactin rise in dams which had been adjusted to an 8-pup litter, than in rats with a 2-pup litter. At late and prolonged lactation the rise of prolactin in the plasma induced by the suckling stimulus of 8 pups was significantly lower than at midlactation. Injection of perphenazine after a period of suckling induced a moderate increase of plasma prolactin in dams at midlactation, and a similar increase in dams at late lactation and at day 42 of lactation. It is concluded that in the first half of lactation the number of pups, i.e. the intensity of the suckling stimulus, is an important factor in determining the magnitude of the prolactin response to suckling. The lower response of plasma prolactin to suckling in late lactation is neither caused by a decrease in suckling stimulus from the pups nor by an increase in prolactin clearance; it is probably due to a gradual reduction in prolactin synthesizing and releasing capacity of the pituitary, brought on by a desensitization of the neural or neuroendocrine system to suckling stimuli as lactation proceeds.     

Effects of suckling mode on endocrine control of reproductive activity resumption in Texel ewes lambing in July or November

To study the effects of the overlapping of seasonal and lactation anestrus and the influence of the suckling mode on the resumption of reproductive activity in Texel ewes, two experiments were carried out after the July and November lambings. The frequency and the duration of suckling decreased with the age of the lambs, and the suckling intensity in the lambs that were allowed to suck unrestrictedly was three times higher than in lambs restricted to sucking three times a day. The overlapping of seasonal anestrus and lactation delayed the resumption of ovarian and estrus activity, but no difference was observed between dams suckling single lambs and twins. The resumption of ovarian and estrus activity was much earlier after the November lambing than after the July lambing. Weaning after the November lambing shortened the interval between parturition to first estrus but not to the first luteal function. The reduction of suckling intensity by suckling management had no effect on the resumption of ovarian and estrus activity. In early postpartum, suckling inhibited the luteinizing hormone (LH) pulsatile secretion and consequently the first LH discharge. However, the earlier restoration of gonadotropin stimulation in dry ewes was not immediately followed by ovarian activity. The suckling inhibition may be due to a temporary disturbance in hormonal balance, the rise in prolactin (PRL) and cortisol secretions. Plasma estradiol 17beta (E2) concentrations were higher in dry than in suckling ewes in early postpartum. Follicle stimulating hormone (FSH) secretion was not involved in the process of delaying the resumption of reproductive activity after lambing.     

Precocious cessation of intestinal macromolecular transmission and sucrase development induced by insulin in adrenalectomized suckling rat.

1. The role of insulin in the regulatory mechanisms governing cessation of intestinal absorption of macromolecules and sucrase development was studied in the adrenalectomized suckling rat (ADX rat). 2. Intestinal absorption of bovine immunoglobulin (IgG) infused orally was dose-dependently suppressed to 35-75% in ADX rats repeatedly injected subcutaneously with insulin. 3. When insulin was administered orally, the IgG absorption was also suppressed. 4. Intestinal sucrase activity was also induced precociously by insulin administered subcutaneously and orally. 5. These results suggest that insulin plays a role in the maturation of suppression mechanisms for macromolecular transmission and sucrase development in the small intestine of the suckling rat.     

Postpartum aggression in mice: The influence of suckling stimulation

The influence of suckling stimulation upon postpartum aggression was studied by removing the nipples (thelectomy) of female mice at various times during pregnancy and lactation. Prepartum thelectomy, regardless of whether it was performed prior to mating or shortly before parturition, in combination with the fostering of young, prevented the exhibition of aggression. The aggressive behavior of females thelectomized following either 2 or 5 days of suckling experience was similar to that of normal lactating females. However, only 25% of animals thelectomized following 24 hr of suckling experience exhibited aggressive behavior. The results demonstrate that suckling stimulation is important for the initiation of postpartum aggression but is not essential in animals that have had at least 48 hr of suckling experience.     

Study of 137Cs transfer to the rat offspring with breast milk and a modifying effect of ferrocene on this process

137Cs transfer to the lactating rats' offspring has been investigated following daily administration of the radionuclide to the females. Certain patterns have been established for 137Cs accumulation dynamics in the female rats and their progeny during 30 days of suckling. Radiocaesium accumulation multiplicity in both female rats and offspring, as well as absorbed dose formation and a modifying effect of ferrocinum on these processes have been studied.     

Epidermal growth factor accelerates the intestinal cessation of macromolecular transmission in the suckling rat

1. The effects of EGF administered subcutaneously on the intestinal cessation of macromolecular transmission and sucrase development were investigated in suckling rats and compared with those on hydrocortisone-treated pups. 2. In the EGF-treated pups, intestinal absorptive response of IgG was suppressed 50% whereas, the sucrase activity was not affected. In the hydrocortisone-treated pups, the absorptive response was inhibited completely, while sucrase activity was induced precociously. 3. The characteristics of intestinal cessation was morphologically observed at the jejunal epithelial cells in EGF and hydrocortisone-treated pups. 4. These results suggest that EGF affects the maturation of gastrointestinal function in a manner different from that of glucocorticoid hormones.     

Time course of the insensitivity of prolactin release to morphine administration in the lactating female rat

The effect of morphine on circulating levels of prolactin and growth hormone (GH) in the lactating female model was determined at various time intervals following the termination of suckling. Morphine administration did not produce an increase in prolactin levels when dams remained suckling. Four days after suckling was terminated, 50% of the dams tested showed a morphine induced prolactin increase. The prolactin secretory response to morphine gradually returned in dams, so that after 8 days of non-suckling, all animals tested showed a morphine induced prolactin increase. Consistent with the lack of prolactin stimulation, the tuberoinfundibular dopaminergic (TIDA) neurons, were insensitive to the morphine induced inhibition of activity during lactation. In contrast, circulating levels of GH were increased in these dams following morphine administration. These results suggest that the lactating female rat is insensitive to the mu mediated stimulation of prolactin release while suckling. However, sensitivity begins to return following at least 4 days of non-suckling.     

Pinocytosis persists in the ileum of hypophysectomized rats unless closure is induced by thyroxine or cortisone.

It was previously reported that in rats hypophysectomized at 6 days of age, the apicotubular system that permits the entrance of macromolecules closes spontaneously in the duodenal epithelium. Extending these observations to the ileum, where pinocytosis is nutritionally important in the suckling rat, now reveals that in the absence of the hypophysis, closure of the surface does not occur. Hence, the failure of growth that sets in during the fourth postnatal week appears not to be due to malnutrition consequent on the cessation of intracellular digestion. Treatment of the hypophyseoprivic sucklings with either thyroxine or cortisone from 15 to 23 days causes the disappearance of the apical infoldings, vesicles, and giant vacuole characteristic of the suckling stage. Instead, the cells exhibit all of the ultrastructural features typical of mature ileal epithelium. The effects of the two hormones differed in that cortisone caused a slightly greater lengthening of the microvilli. These results further extend the evidence indicating that either thyroid hormone or glucocorticoid can activate the complete regulatory program that brings about the redifferentiation of the intestinal epithelium from the suckling to the mature type.     

Leaf angle in Chenopodium album is determined by two processes: induction and cessation of petiole curvature

Petiole curvature is important in regulating light interception by the leaf. To dissect the determination processes of leaf angle, we irradiated the lamina or petiole of Chenopodium album L. with either one or two spots of actinic light, after dark adaptation. When the abaxial side of the petiole was irradiated with blue light, the petiole curvature increased, and under continuous irradiation, the curvature continued for up to 6 h. The rate of curvature increased with increasing blue light intensity. The curvature induced by irradiation of the abaxial side with blue light ceased when the adaxial side of the petiole was simultaneously irradiated with either blue or red light. When an inhibitor for photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, was applied to the adaxial side of the petiole, the cessation of curvature caused by blue light was only weakly inhibited, while the cessation caused by red light was markedly inhibited. When the adaxial side of the petiole was irradiated alternately with red and far-red light, the far-red light antagonized the cessation of curvature caused by the red light. These results clearly show that the petiole curvature is controlled by two processes, the induction and the cessation of curvature. At least three photoreceptor systems, blue-light receptor, photosynthesis and phytochrome, are involved in the reactions.     

Angiotensin II-induced release of oxytocin: interaction with norepinephrine and role in lactation

These studies examined the receptors involved in angiotensin II (Ang II) stimulated secretion of systemic oxytocin (OT) and the role of this peptide in release of OT during suckling. Plasma OT concentrations were measured following intracerebroventricular (icv) injection of vehicle, Ang II, or Ang II following pretreatment with a selective AT1 (Losartan) or AT2 (PD 123319) receptor antagonist. Furthermore, we measured Ang II-induced OT release during central alpha-adrenergic receptor blockade (phentolamine). Finally, plasma OT concentrations before and during suckling were evaluated following central administration of Ang II receptor antagonists. The increase in systemic OT following central Ang II was abolished by AT1 receptor blockade and inhibited by the AT2 receptor antagonist. Furthermore, pretreatment with phentolamine significantly diminished systemic OT release in response to icv Ang II. Finally, central Ang II receptor blockade did not alter the increase in circulating OT during suckling. These data demonstrate that Ang II evoked OT release is mediated through activation of both AT1 and AT2 receptors and suggest that a component of Ang II-induced OT stimulation is due to norepinephrine release. Furthermore, central angiotensin systems do not have a direct role in stimulating OT release during suckling.     

Breast-feeding patterns, maternal milk output and lactational infecundity.

Breast feeding can serve as a contraceptive up to 6 months after birth with 98% effectiveness. The so-called suckling reflex arc is a sensitive mechanism conveying messages about nutritional needs of the child, stimulating the release of prolactin responsible for milk production, suppressing ovarian activity by hypothalamic beta-endorphin production leading to reduction in the pulsatile release of gonadotrophic hormones. Increased suckling produces more milk, but only in well-fed women. In Bangladesh, malnourished children required more suckling time than better-fed infants. Increasing the amounts of weaning food lowers feed urgency and suckling intensity thereby relaxing ovarian suppression. Breast-milk consumption can be measured by test weighing the infant before and after feeding, but it is subject to error, especially in developing countries where up to 20 feeds are required to deliver 800 ml of milk. Thus, weighing over 2-5 days is more accurate. The method of giving deuterium oxide tracer to the mother, and measuring its disappearance from the mother's milk and the infant's saliva for 2 weeks is precise and noninvasive. The Doppler ultrasound technique measures milk flow through an artificial teat for research purposes. Manual or mechanical pump measurement of milk transfer separates the mother from the child, thus it is not useful for normal conditions. It can be used for estimating the amount of milk left and the rate of milk secretion by using a breast pump along with oxytocin for full emptying of milk. Accurate estimation of suckling intensity and milk transfer is essential for the determination of the relationship of breast feeding and lactational infecundity.     

Effects of naloxone, metaclopramide and domperidone on plasma levels of prolactin and LH following suckling in the female rabbit

Saline, naloxone, domperidone or metaclopramide was injected into lactating rabbits immediately before suckling. Blood samples were taken prior to injection (0 minutes) and then at 15, 30, 45 and 60 minutes after the start of suckling, after which the samples were assayed for plasma prolactin and LH concentrations. In all the does there was a significant increase in prolactin concentration, which was highest 15 minutes after the start of suckling, and which declined exponentially thereafter to levels significantly higher than before suckling. The increase in prolactin concentration was similar in does given saline and naloxone, but it was significantly enhanced in does given metaclopramide; with domperidone the increase was intermediate and not significantly different from that following treatment with saline. In does given saline, domperidone, and metaclopramide plasma LH concentrations declined slowly during the hour after suckling but the concentration was increased significantly in does given naloxone. The inverse correlations between prolactin and LH were low weak and were not significant.     

Effects of exogenous ovine growth hormone on reproduction, serum hormone profiles and milk characteristics in early-postpartum fine-wool ewes nursing single or twin offspring

After parturition (Day 0), 31 mature spring-lambing, fine-wool ewes were randomly allotted to one of six groups. Treatments were lambs suckled (one or two) and ovine growth hormone (oGH; 0, 5 or 10 mg). Growth hormone was administered subcutaneously daily from Days 6 to 25. Milk characteristics were determined on Day 26. Ewes were observed for estrus beginning on Day 27. Serum insulin did not differ (P > 0.10) between suckling intensity before or after oGH treatment on Days 6, 15 or 25. Likewise, no difference (P > 0.10) in serum insulin was detected among ewes receiving 0, 5 or 10 mg oGH. Ewes suckling twins had higher (P < 0.05) serum growth hormone on Day 6 (before beginning oGH treatment) than ewes suckling single lambs. In ewes receiving 0, 5 and 10 mg oGH, serum growth hormone differed (P < 0.01) in a linear fashion 1 h after treatment was initiated on Day 6 and continued through Hour 6. Serum growth hormone on Days 15 and 25 differed among groups both before and after oGH was administered (P < 0.01). Suckling intensity did not affect (P > 0.10) milk or milk protein and fat yields; however, oGH increased (linear, P < 0.05) fat but did not affect milk or protein yields. Interval from parturition to estrus did not differ (P > 0.20) in ewes suckling single or twin offspring. Likewise, no differences (P > 0.20) in interval length were noted in ewes receiving 0, 5 or 10 mg oGH. Suckling intensity and oGH administration for 20 d had little effect on postpartum interval or milk characteristics during the first 30 d after lambing in fine-wool ewes.     

Fighting During Suckling: Is it Really an Epiphenomenon?

Suckling by piglets and kittens is accompanied by intense fighting among littermates. There are strong arguments that support the fighting for teats as an epiphenomenon, such as there being a sufficient number of mammary glands (teats) that are of equal quality for littermates, as suggested by Hudson and Distel (Ethology, 119, 2013, 353). However, this article presents a possible adaptive explanation for fighting during suckling. To substantiate the adaptive function of suckling fights, the disposability and limitations of colostrum are first considered. Other aspects are also discussed, such as the potential role of social thermoregulation, the stimulation of mammary glands (massage) and milk composition. Adaptive explanations for the absence/presence and intensity of suckling fights across species consider differences in the colostrum and mature milk composition, mechanisms of transferring immunoglobulin that supply passive immunity to neonates, strategies used to compete for teats and litter size. However, agonistic behaviours in the context of suckling should not be simply categorised as an epiphenomenon.     

The relationship of accentuated lines in enamel to weaning stress in juvenile baboons (Papio hamadryas anubis)

Weaning conflict may represent an evolutionary conflict of interest between parent and offspring, an honest signal of need on the part of a weanling, or both. Accentuated lines visible in histological sections of teeth are indicators of stress during enamel formation and have been hypothesised to form in baboon teeth during weaning. We analysed growth increments in 5 tooth sections from 2 Ugandan baboons (Papio hamadryas anubis), using polarised light microscopy, to determine when stresses occurred during the weaning process. Dietary transitions were reconstructed using normalised strontium intensities (Sr/Ca) in enamel. Accentuated lines were cross-matched between teeth from the same animal and plotted by month. The highest frequency of stress was experienced at around 6 months in 1 baboon, coinciding with an inferred reduction in suckling frequency, and at 11 months in another, coinciding with the inferred cessation of suckling. Because accentuated lines appear to indicate weaning stress at dietary transitions, weaning conflict may represent an honest signal of need on the part of the weanling.