Maternal deprivation and prolonged suckling in the absence of milk alter the frequency and intensity of sucking responses in neonatal rat pups.
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Animals↗
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Surgical manipulation of the uterine environment of rat fetuses.
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Acyclic Monoterpenes↗
Milk taken by human babies from the first and second breast.
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Breast Feeding↗
Arousal a prerequisite for suckling in the conscious rabbit?
Electrocorticographic activity (ECoG) was recorded from the frontal cortex of unanaesthetized, lactating rabbits, and analysed in relation to the suckling behaviour of the animals. Suckling lasted 2--5 minutes each day and was always associated with a desynchronized ECoG. Milk ejection was never seen during slow wave sleep. Mild sedation of the doe caused a dose-dependent block of milk yield but did not affect her willingness to suckle and the ECoG was desynchronized during nursing. In contrast to the rat, but similar to the pig, sleep is not a prerequisite for reflex milk ejection in the rabbit. Evidence presented implies that ECoG arousal may be important for this reflex in the rabbit.
Animals↗
In utero taste/odor aversion conditioning in the rat.
Rat fetuses exposed to a taste-odor stimulus and an aversive stimulus in utero showed an aversion to the taste/odor stimulus when tested 16 days postnatally. Fetuses which received various control treatments in utero did not show an aversion. These data show that rat fetuses at 20 days of gestation are capable of associative learning which can be demonstrated more than two weeks postnatally.
Animals↗
Odor aversion learning by the rat fetus.
Rat fetuses were exposed to an odor stimulus on day 20 of gestation via amniotic injection and then injected with LiCl. In a CER paradigm, 10 day old pups were trained to approach an anesthetized dam in a runway for suckling reinforcement. When running speeds had stabilized the odor stimulus experienced in-utero was introduced into the test chamber. This odor took on aversive properties as a function of its pairing with LiCl, as evidenced by a decrease in running speed on CER trials and increases in the number of trials that were terminated because pups failed to traverse the runway. These data indicate that the fetal rat is capable of odor aversion learning.
Animals↗
A method for recording and analyzing intra-oral negative pressure in suckling rat pups.
A method for recording and analyzing intra-oral negative pressure in suckling rat pups is described. The technique is capable of detecting changes in sucking frequency, rate and amplitude. Three separate patterns of sucking are defined on the basis of these measures.
Animals↗
Effects of undernutrition during suckling on novelty-induced analgesia in young and adult rats.
The effects of undernutrition on novelty-induced analgesia were investigated in young and adult rats. Rats were undernourished by feeding their dams an 8% casein diet from birth until weaning (21 days of age). Rats were exposed to an open field (novelty) for 2 min and the nociception was measured by the tail-flick method. At adult age, only well-nourished rats presented novelty-induced analgesia, suggesting that early undernutrition abolishes this response. At 21 days of age, the exposure to the open field had no effect on nociception of both nutritional groups, suggesting that some developmental factor is necessary for the emergence of novelty-induced analgesia.
Age Factors↗
Age-related stimulatory and inhibitory effects of suckling regulate lactation in rabbits.
Milk production and the duration of lactation were compared between control rabbits nursing their own pups and those whose litters were replaced by younger, i.e., 4-6 days old, or older pups (20-23 days old) starting at pp days 4, 10 or 15. In rabbits whose pups were exchanged on pp day 4 by older pups, an early decline of milk secretion was induced and similar yields to those of late-lactating controls were produced during mid lactation. Conversely, yields similar to those of mid-lactating controls were produced in late-lactating mothers nursing young pups continuously since pp day 10 and high yields were maintained in these animals until pp day 45. When litter exchanges, by either older or younger pups, were delayed until pp day 15, yields were not significantly different from controls. These results indicate that qualitative changes in suckling stimulation develop as the litter grows older, i.e., young pups stimulate milk secretion, whereas old pups inhibit it. Thus, suckling itself may determine the overall pattern of milk secretion in these species.
Age Factors↗
Prolactin and propranolol prevent the suckling-induced inhibition of lactation in rabbits.
The normal once-a-day frequency of suckling in the rabbit was increased on day 31 (late lactation) by the addition of two extra sucklings (8 and 16 hr after) the daily suckling. In confirmation of previous data, two additional sucklings significantly decreased milk yield acutely on day 31 in comparison with the average 4-day milk yield before and after day 31. The decrease in milk secretion after the two additional sucklings was prevented by a single injection of 3 mg prolactin (given 24 hr before the two extra sucklings) and/or by injections of the beta-adrenergic-blocking drug, propranolol (100 micrograms/kg b. wt. given 30 min before each additional suckling). Since prolactin secretion is decreased in these species and the mammary gland is less responsive to the hormone during late lactation, the present results suggest that in addition to these factors, suckling-induced activation of sympathetic influences may contribute to the decline in milk production at this stage of lactation. Taken together, these results suggest that suckling may regulate lactation in the rabbit through antagonistic mechanisms at different stages of lactation.
Animals↗
Pharmacological blockade of blood pressure and heart rate increases following milk ingestion in 15-day-old SHR and WKY rat pups.
The effects of hexamethonium, a ganglionic blocker, on blood pressure (BP) and heart rate (HR) responses to milk ingestion were assessed in awake, 15-day-old spontaneously hypertensive rats (SHR) and their normotensive progenitor strain, Wistar-Kyoto rats (WKY) using two methods of milk delivery. SHRs had larger increases in BP compared to WKYs, but WKYs exhibited larger increases in HR following milk ingestion from an anesthetized dam. BP responses to milk ingestion from a tongue cannula were also larger in SHRs. Administration of hexamethonium prior to milk delivery resulted in a drop in BP following milk ingestion in both milk delivery situations for each strain. The results suggest that SHRs exhibit exaggerated sympathetic activation to milk ingestion compared to WKYs, and that in both strains, cardiovascular responses to feeding are modulated by the presence of the dam.
Animals↗
Cocaine-exposed newborns show an exaggerated sucking response to sucrose.
The sucking responses of 16 newborn infants exposed to cocaine just prior to birth and 16 control newborns were recorded when offered a fluidless sucrose-flavored nipple and a comparable nonsweet nipple. Cocaine-exposed infants showed a significantly greater preference for sweet taste: Compared with control infants, the cocaine group sucked more frequently when offered the sweet nipple and less frequently when presented with the nonsweet nipple. This heightened response to sweet stimulation might reflect (i) a coping mechanism for the perinatal distress of intrauterine cocaine-exposure since sweet taste appears to alleviate distress via an opioid mechanism; and/or (ii) altered dopaminergic activity in a common neuronal pathway that mediates the rewarding aspects of both cocaine and sweet taste.
Cocaine↗
Analysis of walking locomotion in adult female rats undernourished as sucklings.
Suckling rats were undernourished from birth by underfeeding their mothers. They were refed from 3 weeks of age. Detailed analyses were made of the walking locomotion of previously undernourished and well-fed control female rats at 10 weeks, using electronic, computer, and TV techniques. Previously undernourished rats were found to deploy shorter stride times resulting in greater forward velocities. The shorter stride times were attained by reductions in stance time, while swing time was unaffected. No changes in stride length or width were observed, and the relationships between stride time and velocity, swing, or stance times were unaffected.
Animals↗
Nursing-induced changes in pain sensitivity, prolactin, and somatotropin in the pig.
Suckling by piglets led to increases in prolactin and somatotropin in the sow. Failed nursing attempts, which did not result in milk ejection, also led to elevations of prolactin and somatotropin, suggesting that massage of the udder is sufficient and milk ejection is not necessary for these hormonal changes to occur. Prior treatment with the opioid antagonist, naloxone, blocked the nursing-induced increases in prolactin and somatotropin. Tail-flick latencies of the sows were significantly elevated after a nursing, suggesting reduced pain sensitivity. This was blocked by naloxone, suggesting that nursing directly increases endogenous opioid activity. Removing piglets for 2 h led to a drop in prolactin and somatotropin. When the piglets were returned, the nursing-induced increase in prolactin and somatotropin tended to be higher than following a normal nursing interval (1 h). However, prolactin concentrations remained at a significantly lower level following the extended nursing interval. A reduction in nursing frequency seems likely to lead to reduced prolactin levels and altered patterns of somatotropin secretion.
Animals↗
Metabolic correlates of behaviour in the newborn infant.
Twenty-four infants were submitted to behavioural observation 0.5 and 3.5 h after birth. Blood samples were collected from the umbilical cord and from the infant immediately following observation, for the determination of glucose, insulin, cholecystokinin (CCK), and free fatty acids (FFA). It was found that 88% of the infants were awake and 83% performed sucking movements 0.5 h after birth; these findings were associated to a decrease in the plasma glucose concentration (p = 0.05). Eighty-eight percent of the infants were asleep and only 12% exhibited sucking movements 3.5 h after birth; at this time point there was an increase in the plasma concentrations of both CCK (p = 0.05) and FFA (p = 0.01). The infants' plasma insulin concentrations remained unchanged during the time course. It is suggested that the initial behavioural pattern of the newborn, characterized by the appearance of sucking movements, may be due to the rapid decrease of the circulating glucose concentration. The successive increase in the blood concentrations of both CCK and FFA might be two of the factors contributing to the cessation of sucking and to the establishment of a sleeping state.
Arousal↗
Dopamine D1 and D2 effects on fetal mouthing responses to milk.
Rat fetuses exhibit prompt responses to an intraoral infusion of milk, including mouthing movements and an increase in motor activity. Two experiments examined the involvement of dopamine D1 and D2 receptors in mediating these fetal responses to milk. The D1 agonist SKF-38393 and the D2 antagonist sulpiride diminished fetal mouthing responses. Mouthing responses appeared normal in fetuses treated with the D2 agonist quinpirole or the D1 antagonist SCH-23390. These findings suggest that activity in the dopamine system may inhibit mouthing within 30 s of milk infusion.
2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
Sucking in the newborn infant during the first hour of life.
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Birth Weight↗
The 5-HT1A agonist 8-OH-DPAT increases attachment maintenance but decreases suckling-related intake in 17-18-day-old rat pups.
Deprived and nondeprived preweanling (17-18 days of age) Sprague-Dawley rat pups were injected with 0, 0.03, 0.06, 0.1, or 0.5 mg/kg of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and observed in a suckling test using a milk replete anesthetized dam, with milk let-downs being intermittently precipitated via IV infusions of oxytocin. In experiment 1, the 0.5 mg/kg dose of 8-OH-DPAT was observed to increase the proportion of nondeprived animals which attached to a nipple; no dose effect was seen in deprived animals, who generally all attached. Deprived pups given the 0.5-mg/kg dose exhibited a lower frequency of nipple disattachment/reattachment following milk let-downs and had significantly lower percent body weight gains when compared with saline controls. In experiment 2a, the 0.5-mg/kg dose of 8-OH-DPAT was observed to decrease the overall incidence of nipple disattachment/reattachment as well as to suppress nipple shifting per se in both deprived and nondeprived 17-18-day-old rat pups; this dose also suppressed body weight gains in both the deprived and nondeprived pups. The suppression in weight gain by 8-OH-DPAT does not appear to be primarily related to a drug-induced reduction in nipple shifting. In experiment 2b, where pups were given access to only one nipple, an 8-OH-DPAT-related reduction in body weight gain was still evident. These experiments, which demonstrate that attachment maintenance and suckling ingestion are altered in opposite ways by 8-OH-DPAT, provide strong evidence that these two suckling-related phenomena are subject to different physiological controls.
8-Hydroxy-2-(di-n-propylamino)tetralin↗