Nipple-search Behavior Research Articles

Olfactory guidance of nipple attachment and suckling in kittens of the domestic cat: Inborn and learned responses

In 60 kittens (11 litters) from free-ranging domestic cats we investigated the role of chemical cues in facilitating nipple attachment and suckling during the first month of postnatal life when kittens are totally dependent on the mother's milk. Kittens were tested both together and individually on sedated females in different reproductive states. We found (1) that newborn kittens with no suckling experience responded to the ventrum of lactating but not to the ventrum of nonlactating females with search behavior and attached to nipples within minutes; (2) that even in older kittens, nipple attachment depended on females' reproductive state, with virtually no attachments on nonreproducing females, some on pregnant females, the greatest number on early-lactating females, followed by a decline on late-lactating females; and (3) that kittens could locate their particular, most used nipple on their mother but not on a female of similar lactational age, even after eye opening. We suggest that kittens respond from birth with efficient nipple-search behavior to inborn olfactory cues on the mother's ventrum, that emission of these is under hormonal control, but that kittens also quickly learn olfactory cues specific to their own mother and to their own particular nipples.

Rabbit pup response to the mammary pheromone: From automatism to prandial control

Rabbit pups display nipple-search behavior in response to maternal odor cues such as the Mammary Pheromone (MP). Here, we assessed in 3 steps whether the activity of the MP is influenced by prandial and/or rhythmic factors during early development. To address this point, the activity of the MP was tested in 690 pups varying in age (day 0, 2, 5 or 10), prandial state (sucked or un-nursed) and period of their 24-h cycle (− 6 to + 12 h after the daily sucking). In Experiment 1, the responsiveness of d0 pups was high and stable during the whole day, whether they are nursed or deprived of sucking. The MP activity was thus unaffected by colostrum ingestion. Experiment 2 revealed that some differences appear the next days: whereas the responsiveness of d2 pups was also very high during the 24-h cycle (> 94%), it decreased in d5–d10 pups immediately after sucking (< 48%), with a rapid recuperation in d5 pups. Experiment 3 showed that this postprandial drop in response to the MP disappeared in d5–d10 pups that missed the daily nursing, suggesting that it resulted from post-ingestive/post-absorptive events rather than from rhythm activity-related factors. Taken together, the results show a progressive change in the circadian dynamics of the MP-induced orocephalic response as a function of age modulated by prandial state. This indicates a transition from an automatic response to the MP to a response regulated by physiological factors associated with satiation.

Do whiskers contribute to nipple-search and suckling behavior in newborn rabbits ( Oryctolagus cuniculus)?

Rabbit pups are only nursed for about 3 min once a day. They depend on a pheromone on the mother's ventrum to locate nipples and on tactile stimulation of the muzzle to grasp them. In a continuing study of the sensory input guiding suckling behavior we investigated the whisker array in newborn pups and the possible contribution of the whiskers to suckling. Rabbits are born with approximately 76 whiskers arranged in seven to nine rows and increasing in length from rostral to caudal. No significant difference was found between pups with whiskers cut and intact controls in latency to perform the stereotyped nipple-search behavior, latency to attach to nipples, time spent on nipples, milk ingested, or in the strength of conditioning to a novel odor paired with suckling. Thus, the whiskers do not seem important for suckling in newborn rabbits.

Sucking, not milk, is important for the rapid learning of nipple-search odors in newborn rabbits.

Newborn rabbits are only nursed once a day for 3 to 4 min and are completely dependent on a pheromone on the mother's ventrum for the release of nipple-search behavior and sucking. However, if the mother's ventrum is perfumed, pups can be conditioned in just one 3-min nursing session to respond with nipple searching to the novel odorant. To define more precisely the reinforcing properties of the nursing situation supporting such rapid learning, odor conditioning was conducted in independent groups of 2-day-old pups after successively eliminating potential reinforcing stimuli such as the doe's behavior, milk ingestion, nipple-search behavior, or sucking nipples. All experimental groups showed significant conditioning compared to control groups subjected to similar treatments on unscented does, with the strength of conditioning indicating that behavior of the doe, milk consumption, or arousal during performance of the search behavior were not major reinforcers, but rather the opportunity to suck nipples. Thus, this study suggests intraoral stimulation associated with sucking to be an important reinforcer in this paradigm, as for early olfactory learning in other young mammals.

Learning of suckling odors by newborn rabbits declines with age and suckling experience

After being nursed just once for 4-5 min by an artificially scented doe, newborn rabbits show the full pattern of nipple-search behavior when placed on a fur scented with the same odor as their mother. It was the aim of the present study to test whether such rapid learning is dependent on age. In Experiment 1 in which normally raised pups were nursed by a scented doe either on Days 1, 3 or 5, conditionability was found to decline markedly by postnatal Day 5. In Experiment 2 conditionability was maintained in pups deprived of suckling experience by bottle feeding from Days 1-4, but not in hand-raised pups allowed to search on a doe for 4 min daily without milk intake. Possible mechanisms underlying the decline in conditionability to suckling odors, as well as the potential functional significance of this early learning for immediate postnatal and later life are discussed.

Prolactin Stimulates Emission of Nipple Pheromone in Ovariectomized New Zealand White Rabbits1

Using ovariectomized New Zealand white rabbits and the nipple-search behavior of pups as a bioassay, we evaluated the capacity of prolactin to stimulate the emission of an odor signal that allows newborn pups to locate the mother's nipples and suckle. Whereas emission of this so-called nipple pheromone was minimal in untreated, ovariectomized does, emission was stimulated by the administration of progesterone (1 mg/day) to estrogen-treated does (0.5 microgram estradiol benzoate/day) and decreased after withdrawal of progesterone despite continuous administration of estrogen. However, substituting ovine prolactin (1.5 mg/day) for progesterone, under continuous estrogen administration, resulted in an increase in pheromone emission to near-maximal levels. This stimulatory effect of prolactin was not progesterone-dependent since it also occurred in does pretreated with estrogen alone and, to a lesser extent, even in females without estrogen priming. From these and previous data, we propose that emission of nipple pheromone in the rabbit is induced during pregnancy by the combined action of estrogen and progesterone, and maintained during lactation by the dual action of estrogen and prolactin.

Rapid odor conditioning in newborn rabbits: Amnesic effect of hypothermia

Rabbit pups are completely dependent on a maternal pheromone for the release of suckling behavior. However, if the mother is perfumed prior to nursing, pups will learn to respond to the novel odor with the characteristic nipple-search behavior in just one 3–4-min nursing episode. In a first investigation of the processes underlying this recently developed learning paradigm, time-dependent effects of hypothermia on retention of the task could be demonstrated. Thus pups whose whole body was cooled to a mouth temperature of 7°C immediately after conditioning (n = 10) and tested 24 h later for 3 min on a perfumed fur did not differ significantly in their search response from naive, untreated controls (n = 10). In contrast, pups cooled 4 h after conditioning (n = 10) demonstrated clear retention of the learned response and searched as vigorously as conditioned but uncooled animals (n = 10). As pups of all groups demonstrated normal nipple-search behavior when tested on a lactating doe, the deficits associated with immediate cooling appear to have been specific to the learning task and time of treatment.

Pheromonal release of suckling in rabbits does not depend on the vomeronasal organ

Newborn rabbits are completely dependent on a pheromone present on the mother's belly for the release of the highly stereotyped nipple-search behavior and for nipple attachment. Surgical removal of the vomeronasal organ had no effect on pups' ability to respond to the pheromone when tested on a lactating female, nor on their ability to obtain milk in the normal nursing situation. Lesioned pups could also learn to associate the odor of citral with nipple-search behavior when nursed by a citral-scented doe. In contrast, irrigating the nasal mucosa with ZnSO 4 completely eliminated responsiveness both to the pheromone and to the conditioned odor of citral. This is of particular interest given the important role attributed to the accessory olfactory system in pheromonal perception. However, it might be necessary to distinguish between pheromones associated with suckling and therefore peculiar to mammals, and other pheromones.

Do newborn rabbits learn the odor stimuli releasing nipple‐search behavior?

Rabbit pups do not need to learn postnatally the pheromonal cues releasing nipple-search behavior. Pups delivered by caesarean section were able to attach to nipples as quickly as normally delivered controls in their first encounter with a lactating doe (Experiment I), and pups hand raised to Day 5 without postnatal experience of the nipple-search pheromone even showed an improvement in their reactivity to it similar to normally raised controls (Experiment II). However, 1-day-old pups could be conditioned during the first nursing episode to respond with nipple-search behavior to artificial odors painted on the mother's ventrum (Experiment III). Finally, pups conditioned on Day 1 but subsequently raised by hand or normally nursed showed retention of the conditioned responsiveness when tested on Day 5 (Experiment IV). These experiments suggest that although rabbit pups are capable of rapidly associating odors with suckling, they do not appear to depend on this ability under normal nursing conditions.