Developmental psychobiology: prenatal, perinatal, and early postnatal aspects of behavioral development.
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Adaptation, Physiological↗
Biomedical subjects
W G Hall
Publications and source records attributed to W G Hall.
The ontogeny of independent ingestion in mice: or, why won't infant mice feed?
Unlike infant rats, which show deprivation-related ingestion in several different test situations, infant mice appeared to be relatively unwilling to feed independently of suckling until 12 days of age. We tested mouse pups that were deprived (of food, water, suckling, and maternal care) for 1, 7, or 24 hr in ingestive tests in which a milk diet was spread on the floor of their test container (Experiment 1). Pups at 3, 6, and 9 days of age consumed small amounts of the diet and showed little increase in intake when deprivation was increased. In contrast (and like rat pups of all ages), mouse pups 12 and 15 days of age actively ingested the diet and increased their intake with increased deprivation. Six-day-old mouse pups were similarly unwilling to ingest a 5% sucrose solution, though 12-day-old pups showed deprivation-related intake (Experiment 2). Cellular dehydration (produced by hypertonic saline injection), a potent stimulus for ingestion in infant rats, did not stimulate ingestion in mice younger than 12 days of age (Experiment 3). Finally, when ingestion was tested with diet infusions made through oral cannulas, mouse pups at 6 and 9 days of age showed only a slight increase in intake with increased deprivation. However, by 12 days of age, pups' ingestion increased markedly with deprivation (Experiment 4). Thus, mouse pups seem to be very different from rat pups with respect to the early existence of ingestive systems. The neural substrates for the ingestive responses that subserve independent ingestion are only minimally present in infant mice or are somehow inhibited.
Aging↗
Ontogeny of glucose inhibition of independent ingestion in preweanling rats.
Rat pups that have been maternally and nutritionally deprived will vigorously ingest diet infused directly into the mouth. The development of nutritive controls in this form of ingestion was examined by administering nutritive and non-nutritive gastric preloads to 6- and 15-day-old pups. In 6 day-old pups, nutritive gastric preloads (0.6 M glucose in distilled H2O or saline) and vehicle preloads were followed by similar intakes; only the change in hydrational state caused by distilled H2O loads appeared to affect intake. By 15 days of age, intake following nutritive preloads was less than intake following non-nutritive preloads. Also, at 15 days, stomach volume at the termination of intake was less following nutritive preloads. In a separate experiment with 6-day-old pups, gastric preloads of an alternative energy source, the ketone beta-hydroxybutyrate, also failed to inhibit intake when given at a dose that did not cause excessive gastric distension. These results indicate that a nutritive control of intake termination in rats is not present at 6 days of age but develops by 15 days of age.
3-Hydroxybutyric Acid↗
Unilateral olfactory conditioning in 6-day-old rat pups.
The potential that early olfactory learning might be laterally organized in the brain was investigated in 6-day-old rats. This hypothesis is based on the finding that the commissural systems that subserve bilateral olfactory communication do not mature until the second week of postnatal life. Pups were trained with pairings of cedar odor and intraoral infusions of milk while one nostril was occluded. Animals expressed a conditioned orientation towards cedar if tested with the trained nostril open. No such conditioning was observed if the untrained nostril was open during testing. Further, when individual pups received cedar odor/milk pairings with one nostril open and orange odor/milk pairings with the other open, they expressed a conditioned preference for orange when tested with the orange-trained nostril open, and a preference for cedar when tested with the cedar-trained nostril open. Classically conditioned oral responses (mouthing) also appeared to be lateralized. However, no such unilateral conditioning occurred with respect to behavioral activation, which is also conditioned in this paradigm. Increases in activity to the odor CS were observed regardless of whether the trained or untrained nostril was open during testing. These results suggest that in developing rodents, olfactory memories may be partly represented in structures that can be unilaterally accessed during training and testing. They provide a starting point for isolation of neural substrates of the olfactory conditioning process.
Age Factors↗
Control of ingestion in 6-day-old rat pups: termination of intake by gastric fill alone?
Six-day-old rat pups, tested away from the dam, vigorously ingested orally infused milk for up to 90 min when the ingested milk was allowed to drain through a gastric fistula. Total intake in pups with unplugged fistulas was more than double that consumed by littermates with plugged fistulas. This persistent feeding could not be due to the absence of postgastric cues because blocking movement of the milk into the intestine with a closed pyloric noose resulted in less intake than when the noose was open. Furthermore, a 5% body weight gastric preload of milk or nonnutritive saline suppressed intake in pups with either open or closed pyloric nooses by an amount equal to the preload. Regardless of noose or preload condition, ingestion stopped when stomach content reached approximately 6.5% of body weight. Thus level of gastric fill appeared critical for intake control. When gastric fistulas were unplugged after pups had ingested milk until they stopped, vigorous ingestion followed, with total intakes of up to 20% body weight. Intake termination in young rat pups thus appears to be controlled exclusively by gastric fill level; pregastric signals alone appear insufficient, and postgastric signals appear unnecessary for termination of intake.
Animals↗
What we know and don't know about the development of independent ingestion in rats.
Because suckling behavior differs in many ways from later ingestive behavior, the development of feeding and drinking in rats is best studied apart from the normal suckling situation. Newborn rat pups, separated from their mothers, will actively ingest diet infused into their mouths or spread on the floor beneath them. Such "independent" ingestion resembles the ingestive behavior of adult animals, but it also undergoes developmental changes in organization and control during the pre- and post-weaning periods: When young, deprived pups are fed, they show generalized, non-directed behavioral excitement; but with increasing age, this generalized responding matures into directed and focused ingestive activity. Early independent ingestion depends on a warm test environment; but with development, other familiar environmental and social cues come to influence responding. The internal controls of ingestion also change. Only gastric distension and hydrational status seem to be involved in controlling intake volume during early ingestion, with other ingestive controls emerging later in development. Thus ingestion, independent of suckling from the mother, is a system undergoing revealing developmental changes. These changes offer opportunities for studying ingestion, its controls, and its neural basis at its simplest organizational stage in the newborn, and at higher levels of complexity as maturation adds new components to the feeding system.
Animals↗
Appetitive conditioning in neonatal rats: conditioned ingestive responding to stimuli paired with oral infusions of milk.
Components of rat pups' ingestive responses to orally infused milk came to be elicited by a novel odor conditioned stimulus (cedar) that had been repeatedly paired with milk infusions (Experiment I). Pups responded specifically to one odor, and they did not generalize their conditioned responding to either another odor or an unscented airstream (Experiment II). Ingestive responses could also be conditioned to a vibrotactile CS paired with milk, although levels of conditioned responding were lower than were obtained with an odor CS (Experiment III). Pups' internal state determined the effectiveness of training, in that pups that were removed from their dam for 24 hr showed reliable conditioned responding, while nondeprived pups and dehydrated pups did not (Experiment IV). Finally, pups showed retention of conditioned responding for at least several days after training (Experiment V).
Animals↗
Inhibitory controls of ingestion in 6-day-old rat pups.
The ability of gastric preloads of milk, water, and isotonic saline to inhibit ingestion was studied in deprived 6-day-old rat pups being fed through oral cannulas. Preloads were delivered through gastric cannulas or by gavage, and both the volume of the load and the interval between the preload and testing were varied in order to assess the relative contributions of pre- and post-absorptive cues from the loads. Pups' willingness to initiate ingestion in short (10 min) tests (appetite) was unaffected by the degree of gastric filling produced by a load but was depressed by post-absorptive changes in hydrational state. On the other hand, pups terminated ingestion in long (30 min) tests (satiety) in response to gastric filling. Cessation of intake in long tests was only slightly influenced by post-absorptive factors. These results reveal two distinct phases of ingestion in infant rats and show that each is controlled in a different manner.
Animals↗
Appetitive conditioning in neonatal rats: conditioned orientation to a novel odor.
These experiments document a form of early appetitive learning in rats obtained using classical conditioning procedures. Some of the special determinants of this conditioning are described, as well as ontogenetic changes in the effectiveness of training procedures. Learning was apparent when deprived 3- and 6-day old rats oriented to and maintained contact with a novel and normally aversive odor after this odor had been paired with oral infusions of milk (Experiment I). The effectiveness of the conditioning procedures depended on the temperature at which pups were trained (Experiment IB). Moreover, the reinforcing properties of milk infusions depended on deprivation (Experiment IC). This conditioned change in responsiveness to odor was specific to the odor that had been paired with milk (Experiment II) and was retained for at least 24 hr (Experiment III).
Age Factors↗
Olfactory contributions to dehydration-induced anorexia in weanling rats.
By 20 days of age, dehydration produces a clear anorexia, even though weanling rats have had only limited feeding and drinking experience. Their lack of ingestive experience makes weanlings good subjects for studying the physiological mechanisms subserving anorexic phenomena because learned contributions are unlikely to add significant complications. Twenty-day-old rats dehydrated by hypertonic saline injection were anorexic when offered milk or solid food (rat chow), but not when offered sucrose solutions (Experiment I). However, when the scent of almond was associated with sucrose solutions, or with water, intake of these solutions was depressed by dehydration (Experiment II). Thus for dehydrated rats, olfactory stimulation may help produce dehydration-induced anorexia. Making rats anosmic by intransal lavage with ZnSO4 (Experiment III) eliminated the anorexia to almond-scented water and partially eliminated that to milk. For these fluids, an odor cue seems a requirement for the occurrence of dehydration-anorexia. In Experiment IV, we found that dehydration-anorexia did not occur when milk was infused directly into pups' mouths. This finding suggests that the inhibitory process mediating dehydration-anorexia influences the approach to food and not the actual consumatory response that occurs once food is in the mouth. The inhibition of feeding produced by dehydration, therefore, may depend largely on olfactory cues, and seems to operate at a distance, as rats locate and approach food.
Animals↗
Metabolic neural mapping in neonatal rats.
Functional neural mapping by 14C-deoxyglucose autoradiography in adult rats has shown that increases in neural metabolic rate that are coupled to increased neurophysiological activity are more evident in axon terminals and dendrites than neuron cell bodies. Regions containing architectonically well-defined concentrations of terminals and dendrites (neuropil) have high metabolic rates when the neuropil is physiologically active. In neonatal rats, however, we find that regions containing well-defined groupings of neuron cell bodies have high metabolic rates in 14C-deoxyglucose autoradiograms. The striking difference between the morphological appearance of 14C-deoxyglucose autoradiograms obtained from neonatal and adult rats is probably related to developmental changes in morphometric features of differentiating neurons, as well as associated changes in type and locus of neural work performed.
3-Hydroxybutyric Acid↗
The ontogeny of feeding in rats: IV. Taste development as measured by intake and behavioral responses to oral infusions of sucrose and quinine.
Infusions of sucrose or quinine were delivered through cannulas implanted in rat pup's mouths. Intake was measured, and behavioral responses were scored. Responsiveness to sweet and bitter tastes emerged over the first 2 wk of postnatal life. Pups showed discrimination between water and sucrose in their mouthing behavior and general activity from 3 days of age, but in their intake only from 6 days of age. Discrimination between water and quinine was not shown until 9 days of age in either behavior or intake. Even then, the stereotypic aversion reactions (paw treading, chin scraping) that characterize the adult response to quinine were not apparent until 12 days. By 15 days of age, preferences for sucrose and aversions to quinine were robust. They resembled those of adult rats and did not depend on previous experience with either solution.
Aging↗
The ontogeny of feeding in rats: V. Influence of texture, home odor, and sibling presence on ingestive behavior.
Terry-cloth texture, home odor, and the presence of siblings modulate the ingestive behavior of infant rats. Unlike warmth, which affects ingestion in pups until at least 15 days of age, the relative importance of these other cues varies with the age of the pup. At 3 days, ingestion is dependent on warmth but is not influenced by the other cues. At 6 days, texture and home odor enhance ingestive behavior (intake, activity, mouthing, and probing), but the presence of siblings has no effect. Home odor or terry-cloth texture did not alter the ingestive behavior of 12-day-olds, but the presence of siblings enhanced milk intake. Thus, during development, the external sensory controls for ingestion become progressively more complex. Warmth serves as a primary permissive cue for ingestion in developing pups, but as pups grow older, other types of cues (such as odor, texture, or social stimuli) also gain significance.
Aging↗
The ontogeny of nipple-shifting behavior in albino rats: mechanisms of control and possible significance.
Nipple-shifting behavior was studied in rats 3--30 days old in 4 experimental paradigms. The incidence of nipple-shifting of rats tested in groups of 3 on their nonlactating, anesthetized mother was age-related. Rats 12 days of age and younger did not leave the nipple first suckled during the 2-hr test period. Starting by Day 15, however, nipple-shifting increased and reached its maximum in 24-day-old rats. This behavior's incidence was directly related to maternal (and, therefore, nutrient and water) deprivation (Experiment I). Milk letdown reduced the incidence of nipple-shifting behavior at all ages studied and synchronized its occurrence, as almost all shifts occurred immediately aftet letdown and almost none during the 15-min interval between successive milk letdowns (Experiment II). Testing rats individually on the nonlactating, anesthetized mother produced age-related effects. Shifting was virtually eliminated in 15-day-old rats, markedly reduced in 21-day-old rats, and not affected in 27-day-old rats tested individually (Experiment III). Rats 27 and 30 days of age, upon leaving a nipple, ate and did not return to suckle. Rats 15 days old never ate and always returned to suckle (Experiment IV). Twenty-one-day-old rats suckled, and many ate in the mother's presence. The significance of these findings relates to maximizing milk intake and facilitating the process of weaning.
Aging↗
Ontogeny of oral behavior induced by tail pinch and electrical stimulation of the tail in rats.
In sated adult rats, a mild tail pinch induces stimulation-bound eating. Experiment 1 showed that during preweaning development the response to tail pinch changes in (a) type, from mouth opening to licking, gnawing, and eating; (b) duration, from intermittent to stimulation-bound; (c) direction, from indiscriminate licking to focused on food pellets; and (3) intensity of stimulation required to elicit it, from high to low. These changes were also observed with electrical stimulation of the tail (Experiment 2). In Experiment 3, tail stimulation did not induced suckling, which suggests that it does not activate all the behavioral patterns available to the pup or potentiate its responsiveness to all environmental stimuli. Furthermore, in contrast to food deprivation, it did not induce licking of milk in 5-day-old pups. It seems, therefore, that tail stimulation reveals a mode of control over ingestive response patterns that is different from the one exerted by food deprivation.
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Appetitive learning in 1-day-old rat pups.
One-day-old rat pups learned to probe upward into a terry-cloth-covered paddle when they were rewarded with small infusions of milk into their mouths. In the presence of two paddles, discriminable on the basis of odor and position in the test container, the pups learned to probe into the paddle that provided them with milk. These experiments demonstrate (i) that milk may serve as a reinforcer to deprived rat pups and (ii) that pups as young as 1 day are capable of appetitive learning.
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Feeding and behavioral activation in infant rats.
Three-day-old rats that were separated from their mothers and deprived of food were found to be capable of feeding either from small puddles of milk or when milk was infused into the front of their mouths. Such feeding was accompanied by a dramatic increase in behavioral activity and only occurred in a warm environment. These data demonstrate that neural systems for ingestive behavior are present at birth and suggest the existence of feeding-related arousal or motivational systems.
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Developmental changes in the suckling behavior of hamster pups: a comparison with rat pups.
The suckling behavior of hamster pups was observed to undergo several transitions during the preweaning period. Pups 10 days of age and younger attached to the nipples of their anesthetized mothers and suckled. After 10 days of age, however, only animals which had been deprived of suckling (and food and water) reliably attached to their mothers' nipples. By 25 days of age, deprived pups no longer suckled. The pattern of response after nipple attachment also changed during development: pups younger than 5 days of age remained on 1 nipple after initial attachment, whereas older pups shifted from 1 nipple to another. The development of suckling in hamster pups resembles that in rat pups, although certain changes or transitions occur at different ages in the 2 species. These changes may provide important markers for neural and behavioral development in each species and for comparisons between the two.
Aging↗