Physiological and behavioral consequences in rats of water recycling during lactation

Tactile stimulation prevents disruptions in male rat copulatory behavior induced by artificial rearing

Early life social interactions in gregarious mammals provide an important source of stimulation required for the development of species-typical behaviors. In the present study, complete deprivation of maternal and littermate contact through artificial rearing was used to examine the role of early social stimulation on copulatory behavior and the ejaculate in adult rats. We found that artificially reared naïve male rats were sexually motivated; nevertheless, they did not acquire the level of sexual experience that typically occurs during copulatory training. Disrupted expression of sexual experience of artificially reared rats was demonstrated by an inconsistent pattern of ejaculatory behavior across training tests. Artificial tactile stimulation applied during isolation prevented this disruption and rats achieved ejaculation in most copulatory tests. Despite the irregularity of ejaculatory behavior in isolated rats, their sperm count and seminal plug were similar to control maternally reared (sexually experienced) and artificially-reared rats that received tactile stimulation. These results suggest that tactile sensory information provided by the mother and/or littermates to the offspring is crucial for the development of copulatory behavior. The absence of social and/or tactile stimulation during early life compromises the ability of male rats to gain sexual experience in adulthood.

Parental Behavior in Rodents

Members of the order Rodentia are among the best-studied mammals for understanding the patterns, outcomes, and biological determinants of maternal and paternal caregiving. This research has provided a wealth of information but has historically focused on just a few rodents, mostly members of the two Myomorpha families that easily breed and can be studied within a laboratory setting (including laboratory rats, mice, hamsters, voles, gerbils). It is unclear how well this small collection of animals represents the over 2000 species of extant rodents. This chapter provides an overview of the hormonal and neurobiological systems involved in parental care in rodents, with a purposeful eye on providing information known or could be gleaned about parenting in various less-traditional members of Rodentia. We conclude from this analysis that the few commonly studied rodents are not necessarily even representative of the highly diverse members of Myomorpha, let alone other rodent suborders, and that additional laboratory and field studies of members of this order more broadly would surely provide invaluable information toward revealing a more representative picture of the rich diversity in rodent parenting.

Influence of gestational exercise practice and litter size reduction on maternal care

Mother-pup interactions are extremely important to offspring survival and growth. The goal of this study was to evaluate the influence of prenatal and neonatal interventions on maternal care, analyzing the effect of maternal exercise, as a healthy intervention, and also the litter size reduction, a model that has been widely used to study early overfeeding in rats. Female Wistar rats were divided into 1) sedentary, and 2) swimming exercise for four weeks, starting one week before mating (5 days/week, 30 min/session). One day after birth, the litter was culled to 8 pups (normal) or 3 pups (small) per dam, yielding control and overfed subgroups for each maternal group, respectively. From postnatal days 2-9 the litter was observed 5 periods a day, to evaluate maternal behavior. Litter reduction caused important alterations in maternal behavior, reducing the total time out of the nest and increasing the frequency of maternal care and lactation in several observation periods, justifying the increased pup's weight gain already demonstrated by this animal model. The practice of maternal exercise did not prevent, but cause the less intensive frequency of non-maternal behavior and lactation in arched-back position, induced by the reduction of litter size. These data demonstrated that small litter size altered maternal behavior, and gestational exercise does not influence significantly these changes.

Maternal behaviour in domestic dogs

Mammalian parental care, in most of the cases, is given by the female, who provides food, warmth, and protection. In domestic dogs, maternal behaviour shown by the dam mainly consists of contact, nursing, grooming/licking, play, punishment, thermoregulation, and motion. Peer-reviewed literature published between 1952 and 2018 was retrieved from CAB Abstracts, PubMed, ISI Web of Knowledge, Scopus and book chapters. Keywords for this search included the following terms: behaviour, bonding, altricial, precocial, offspring, maternal, whelping, nursing, domestic dogs, female dog, aggression, puppies, anogenital licking. In this review, we reported and discussed scientific information about maternal behaviour in domestic bitches, comparing altricial vs precocial species; the importance of the bonding, grooming/licking and nursing, and their impacts on puppies' behaviour; altered maternal behaviours such as aggression, cannibalism, rejection, and also the relation between hormones and maternal care behaviours. We concluded that the level of interactions between the dam and the puppies influences the physiological, cognitive and behavioural development of the litter, and the main hormones in the bitch for inducing maternal care behaviours are estradiol, oxytocin, prolactin and progesterone.

Survival implications of the development of behavioural responsiveness and awareness in different groups of mammalian young

This paper focuses on the development of behaviours that are critical for the survival of newborn and juvenile mammals of veterinary and wider biological interest. It provides an updated, integrated and comparative analysis of how postnatal maturation of sensory, motor and perceptual capacities support and constrain behavioural interactions between mammalian young and the mother, any littermates and the environment. Young that are neurologically exceptionally immature, moderately immature and mature at birth are compared, and include, for example, marsupial joeys, rodent pups and ruminant offspring. Mothers in these three groups exhibit distinctive patterns of birthing and postnatal care behaviours. To secure survival of the young, maternal care must compensate for behavioural inadequacies imposed by the limited sensory capacities the young possess at each stage. These sensory capacities develop in a predictable sequence in most mammals such that before birth the sequence progresses to an extent that parallels the degree of neurological maturity reached at birth. The extent of neurological maturity is likewise reflected in how long it takes after birth for the necessary brain circuit connectivity to develop sufficiently to support cortically based cognitive modulation of behaviour. This takes several months, days-to-weeks or minutes-to-hours in young that are, respectively, neurologically exceptionally immature, moderately immature, or mature at birth. Once achieved, cognitive awareness confers a high degree of behavioural flexibility that allows the young to respond more effectively to the unpredictability of their postnatal environments. It is shown that the onset of this cognitively based flexibility in the young of each group coincides with their first exposure to a variable environment that requires such behavioural flexibility.

Developmental plasticity of coordinated action patterns in the perinatal rat

Some of the most simple, stereotyped, reflexive, and spinal-mediated motor behaviors expressed by animals display a level of flexibility and plasticity that is not always recognized. We discuss several examples of how coordinated action patterns have been shown to be flexible and adaptive in response to sensory feedback. We focus on interlimb and intralimb coordination during the expression of two action patterns (stepping and the leg extension response) in newborn rats, as well as interlimb motor learning. We also discuss the idea that the spinal cord is a major site for supporting plasticity in the developing motor system. An implication of this research is that normally occurring sensory stimulation during the perinatal period influences the typical development and expression of action patterns, and that exploiting the developmental plasticity of the motor system may lead to improved strategies for promoting recovery of function in human infants with motor disorders.

Sensorimotor training during expression of the leg extension response (LER) in 1-day-old rats

In newborn rats, the leg extension response (LER) is a coordinated hyperextension of the hindlimbs that is shown in response to anogenital stimulation. Here we examined the influence of sensorimotor training on LER expression in postnatal day 1 rats. In Experiment 1, we examined if proprioceptive feedback facilitates LER expression. We did this by repeatedly stimulating the pup's anogenital region with a vibrotactile device, to experimentally evoke the LER, thus increasing LER-relevant hindlimb proprioceptive feedback during training. In trained subjects, the LER was evoked every 4 min for 15 trials, followed by a final LER test. Results indicated that proprioceptive feedback on its own did not alter later expression of the LER. In Experiment 2, we examined the effect of both proprioceptive and cutaneous feedback on LER expression, through the use of a range of motion (ROM) restriction during training. During ROM restriction, a Plexiglas plate was placed beneath the pup at 50% of limb length. After the 15th training trial, a final LER test occurred with no ROM restriction in place. Compared to controls, pups that experienced ROM restriction exhibited a significantly shorter LER duration, and smaller hip and ankle angles during the LER test (indicating greater limb flexion). Together these findings show that concurrent proprioceptive and cutaneous feedback, but not proprioceptive feedback alone, has persistent effects on expression of this newborn action pattern.

Maternal and affective behaviors of lactating rats reared in overlapping litters

Postpartum mating in rats gives rise to complex family units consisting of the mother and two overlapping litters. As a consequence, newborn pups of the second litter, since the moment they are born, acquire experience not only from interaction with the mother and age-matched littermates but also from interaction with older siblings. Newborn pups reared in overlapping litters (OLs) receive a different pattern of maternal stimulation compared to those reared in single litters (SL: one litter of same aged pups), as the mothers reduce some maternal behavior components and juvenile pups from the first litter develop maternal behavior. Since there is strong evidence showing that variations in maternal behavior are transmitted throughout generations, we hypothesized that the altered pattern of maternal stimulation received by OL reared females would modify their behavior during motherhood. To test this hypothesis maternal behavior, maternal aggression and experimental anxiety of dams reared under OL and SL conditions during the first postpartum week were compared. No differences were found between the groups in their maternal behavior and aggression. This result may be explained by the maternal behavior of the juveniles that could compensate for the deficits in the caregiving behaviors received by OL litters. However, a subtle temporal reorganization of the licking behavior was found in OL reared mothers, together with an increased anxiety-related behavior in the plus maze test. These results suggest dissociation in the effects provoked by early environmental alterations on different behavioral systems, and more importantly, that independently of their early family composition, both groups can cope effectively with the changing demands of the pups.

Prematurely delivered rats show improved motor coordination during sensory-evoked motor responses compared to age-matched controls

The amount of postnatal experience for perinatal rats was manipulated by delivering pups one day early (postconception day 21; PC21) by cesarean delivery and comparing their motor behavior to age-matched controls on PC22 (the typical day of birth). On PC22, pups were tested on multiple measures of motor coordination: leg extension response (LER), facial wiping, contact righting, and fore- and hindlimb stepping. The LER and facial wiping provided measures of synchronous hind- and forelimb coordination, respectively, and were sensory-evoked. Contact righting also was sensory-evoked and provided a measure of axial coordination. Stepping provided a measure of alternated forelimb and hindlimb coordination and was induced with the serotonin receptor agonist quipazine. Pups that were delivered prematurely and spent an additional day in the postnatal environment showed more bilateral limb coordination during expression of the LER and facial wiping, as well as a more mature righting strategy, compared to controls. These findings suggest that experience around the time of birth shapes motor coordination and the expression of species-typical behavior in the developing rat.

Implications of temporal variation in maternal care for the prediction of neurobiological and behavioral outcomes in offspring

Previous studies in Long-Evans rats demonstrated a significant relationship between variation in pup licking/grooming and arched-back nursing (LG-ABN) and offspring development. However, maternal care is dynamic and exhibits significant temporal variation. In the current study, we assessed temporal variation in LG and ABN in lactating rats across the circadian cycle and determined the impact of these behaviors for the prediction of offspring hypothalamic gene expression, anxiety-like behavior, and responsiveness to a high fat diet (HFD). We find that distinguishing between dams that engage in stable individual differences in maternal behavior (Low, Mid, High) requires assessment across the light-dark phases of the light cycle and across multiple postpartum days. Among juvenile female offspring, we find a positive correlation between maternal LG and mRNA levels of estrogen receptor alpha and beta and the oxytocin receptor (when LG is assessed across the light-dark cycle or in the dark phase). In young adults, we find sex-specific effects, with female High LG offspring exhibiting increased exploration of a novel environment and increased latency to approach HFD, and male High LG offspring displaying increased activity in a novel environment and reduced HFD consumption. Importantly, these effects on behavior were primarily evident when LG was assessed across the light-dark cycle and ABN was not associated with these measures. Overall, our findings illustrate the dissociation between the effects of LG and ABN on offspring development and provide critical insights into the temporal characteristics of maternal behavior that have methodological implications for the study of maternal effects.

Genetic influences on maternal care

The basis of social evolution in mammals is the mother-offspring relationship. It is also the primary and most important instance of indirect genetic effects, where genetic variation in one individual affects phenotypic variation among others. This relationship is so important in mammals that often the major factor determining the life or death of newborns is the environment provided by their mother. Variations in these environments can be due to variations in maternal genotypes. In our work with the intercross of two mouse inbred strains, LG/J and SM/J, we uncovered a very severe variation in maternal performance. These females failed to nurture their offspring and showed abnormal maternal behaviors leading to loss of their litter. Rather than this being due to a single gene variant as in knockout mice, we uncovered a complex genetic basis for this trait. The effects of genes on maternal performance are entirely context dependent in our cross. They depend on the alleles present at the same or other epistatically interacting loci. Genomic locations identified in this study include locations of candidate genes whose knockouts displayed similar aberrant maternal behavior. Behaviors significantly associated with maternal performance in this study include suckling, nest building, placentophagia, pup grooming, and retrieval of pups after disturbance.

Development as adaptation: a paradigm for gravitational and space biology

Adaptation is a central precept of biology; it provides a framework for identifying functional significance. We equate mammalian development with adaptation, by viewing the developmental sequence as a series of adaptations to a stereotyped sequence of habitats. In this way development is adaptation. The Norway rat is used as a mammalian model, and the sequence of habitats that is used to define its adaptive-developmental sequence is (a) the uterus, (b) the mother's body, (c) the huddle, and (d) the coterie of pups as they gain independence. Then, within this framework and in relation to each of the habitats, we consider problems of organismal responses to altered gravitational forces (micro-g to hyper-g), especially those encountered during space flight and centrifugation. This approach enables a clearer identification of simple "effects" and active "responses" with respect to gravity. It focuses our attention on functional systems and brings to the fore the manner in which experience shapes somatic adaptation. We argue that this basic developmental approach is not only central to basic issues in gravitational biology, but that it provides a natural tool for understanding the underlying processes that are vital to astronaut health and well-being during long duration flights that will involve adaptation to space flight conditions and eventual re-adaptation to Earth's gravity.

Paternal care in the social and diurnal striped mouse (Rhabdomys pumilio): laboratory and field evidence

Paternal care is rare in mammals, occurring mainly in carnivores and neotropical primates, in which the difficulties of long generation time and large individuals lead to small sample sizes. Here, the authors show that paternal care can be easily studied in the four-striped mouse (Rhabdomys pumilio) because (a) captive males show all the patterns of parental care as do females, with the obvious exception of nursing; (b) in the field, wild males act amicably toward juveniles and retrieve pups experimentally presented to them; (c) the striped mouse facilitates experimental approaches in captivity because it has a short generation period and can be kept in large numbers; and (d) the striped mouse is diurnal, not only making observations in captivity easier but also enabling direct observations in the field.

NaCl preference increases during pregnancy and lactation: assessment using brief access tests

Pregnancy and lactation are characterized by increases in NaCl intake, as determined by long-term consumption tests, which cannot examine the relative contribution of taste and postingestive factors to this phenomenon. Consequently, in this study, changes in NaCl preference during pregnancy and lactation were studied in nulliparous Long-Evans rats using a brief access test (lickometer). In Experiment 1, rats were maintained on a Na(+)-adequate diet (0.03% Na(+)), habituated to lickometer testing, and subsequently assessed during pregnancy and lactation with three 30-s exposures to each of seven taste solutions: 0.075 M sucrose (base), 0.089 M NaCl in base, 0.158 M NaCl in base, 0.281 M NaCl in base, 0.5 M NaCl in base, 0.158 M NaCl and 0.281 M NaCl. Results indicated higher lick rates to the 0.5 M NaCl in base, 0.158 M NaCl and 0.281 M NaCl solutions during late pregnancy and late lactation (Day 13 and beyond). In Experiment 2, a comparison of two diets differing in sodium content (0.03% vs. 0.3% Na(+)) determined that these changes in NaCl preference during pregnancy and lactation were unrelated to dietary sodium. Thus, the apparent increase in NaCl preference during pregnancy and lactation, independent of dietary sodium, suggests that this change in preference is not in response to physiological sodium need.

Comparison of the parental behavior of pair-bonded female and male prairie voles (Microtus ochrogaster)

The behavior of primiparous lactating prairie voles (Microtus ochrogaster) and their mates individually interacting with pups was continuously assessed for 45 min after a 2-h parent-litter separation on days 3-4 and 10-11 postpartum. Both sexes were highly parental after reunion with the young, and their general pattern of behavior consisted of bouts of quiescence interspersed with bursts of heightened activity. Lactating females spent more time than males in contact with pups, and more time being quiescent, most often in the kyphotic (upright crouched) nursing posture. Even in the absence of nipples upon which the pups could suckle, males also displayed kyphosis, although for shorter durations than females. Males spent more time, however, huddled over the litter in a hunched position than their mates. In accordance with their decreased quiescence, male voles licked and carried pups more and were more exploratory than females. Compared with the first week postpartum, bouts of kyphosis were shorter during the second week postpartum for both sexes, while laying prone on the pups increased. Males spent less time licking and more time carrying older pups than younger ones, and were more exploratory during the second week postpartum. Sex differences in the parental behavior of prairie voles may reflect differences in the somatosensory stimulation that females and males receive from pups. Furthermore, the display of kyphosis by male voles indicates that the sensorimotor organization of this posture in voles differs from that of lactating rats, which require suckling stimulation for its regulation.

Effects of lactation on sodium intake in Fischer-344 and Long-Evans rats

Rats of most strains are attracted to salt in low concentrations, and this attraction is increased by pregnancy and lactation. Nonreproducing Fischer-344 (F344) rats are unusual in that they avoid saline at all concentrations, raising the question of whether lactation alters their sodium appetite. Therefore, lactating and cycling Long-Evans and F344 rats were compared in their relative consumption of water and several concentrations of saline. We found that Long-Evans rats preferred saline, but F344 rats preferred plain water. In comparison with cycling rats, lactating Long-Evans rats markedly increased saline intake whereas F344 rats exhibited only a modest increase. Lactating rats of both strains increased total fluid intake, but this increase was primarily from water in F344 rats and from saline in Long-Evans rats. It was concluded that the aversion to saline characteristic of nonreproducing adult F344 rats continues during lactation. Their aversion to sodium in pup urine may account for the low levels of maternal anogenital licking observed in the F344 strain.

Oral grasping of a surrogate nipple by the newborn rat

Newborn rat pups exhibit oral appetitive behaviors when presented with an artificial nipple. These behaviors include mouthing and licking movements and expression of stereotyped oral grasp response. Caesarean-delivered pups show increased responding to the nipple over the first 5 h after birth that is independent of experience with the nipple. Mimicking maternal licking by stimulating the anogenital region of the newborn rat with a soft paintbrush increases response to the nipple. Pups tested after 24 hr of normal experience respond to the artificial nipple when tested immediately after separation from the mother. However, oral grasping of the nipple is more frequent in 1-day-old pups tested 3 or 5 hr after separation from the mother. Study of behavioral responses to the artificial nipple promises to provide information about sensory and neurochemical controls of the initial suckling episode.

Detrusor-sphincteric dyssynergia in paraplegics compared with the synergia in a brain-dead human by using the single-fibre action potential recording method

(1) Humans with spinal cord lesions often show detrusor-sphincteric dyssynergia of the urinary bladder which is reflected urodynamically in the detrusor pressure and a simultaneous increase in electromyographic pelvic floor activity. (2) The time-course of the increase in the secondary muscle spindle afferent activity, induced by the parasympathetic nervous system in muscle spindles contributing to continence, is very similar to that of detrusor pressure. The detrusor-sphincteric dyssynergia is therefore analysed by comparing the natural impulse patterns of secondary muscle spindle afferents (SP2) and sphincteric motoneurons in a brain-dead human with those in patients with spinal cord lesion. The parasympathetic nervous system was activated by painful bladder catheter pulling. (3) In a brain-dead human the sphincteric motoneurons subserving continence were inhibited at a time, when preganglionic parasympathetic efferents increased their activity for 10 s and an SP2 fibre increased its activity for several minutes. In a paraplegic with a strong bladder dysfunction, the SP2 fibre activity increased, due to parasympathetic activation, lasted for approx. 1 min, showed undulations and its amplitude was smaller than that measured in a brain-dead human. The sphincteric motoneurons were not inhibited. (4) In the brain-dead human, an SP2 fibre showed doublet firing with interspike intervals (IIs) of a duration between 10 and 14 ms for low level parasympathetic activation. For high level parasympathetic activation this single parent spindle afferent fibre showed multi-ending regular firing of up to 6 endings with IIs of a duration of predominantly 15 to 25 ms. In one paraplegic with a strong bladder dysfunction the doublet firing was less regular, even though two II peaks at 10.2 and 11.2 ms occurred in a II distribution similar to the brain-dead human. The multi-ending regular firing was replaced by a repeated burst firing. In a second paraplegic with strong detrusor-sphincteric dyssynergia the burst firing consisted of up to 6 impulses with increasing IIs and a first II of approx. 0.2 ms (transmission frequency 5000 Hz). In a third paraplegic with a lesser dysfunction of the bladder a highly activated SP2 fibre showed an activity pattern intermediate to those of multi-ending regular firing and burst firing. (5) The time constant for the activity decrease of a spindle afferent fibre following parasympathetic activation was to 31 s in a paraplegic and approx. 40 s in a brain-dead human. It is concluded that the muscle spindles are unchanged following spinal cord lesion.(ABSTRACT TRUNCATED AT 400 WORDS)

Caveats in the study of perinatal behavioral development: utility of fetal study

Study of behavior during development presents psychobiologists and neurobiologists with a unique set of problems that should be addressed in the design and analysis of experiments. Some of these caveats have become apparent only with the recent growth in research with subjects around the time of birth. For example, physiological regulation within the maternal-infant dyad, litter effects, the influence of context at the time of testing on performance, and dissociation of age-related change and experience, all are important experimental considerations in developmental study. Manipulation and measurement of behavioral variables in the fetus in vivo can provide one means for circumventing many of the methodological pitfalls that are associated with behavioral study of newborn subjects.

The psychobiology of parenting in mammals

Parental behavior denotes a variety of genetically programmed activities in which parents help their young to survive to maturity. A highly successful research has been devoted to the psychoneuroendocrine bases of parenting in two species, rat and sheep. As a result empirical data along with conceptual formulations have been obtained which provide a model for generating hypothesis for the study of other species. This review was written to draw the attention to this research because of its enormous potential significance for problems pertaining to human infant care. It discusses the current status of research on the physiological bases of parental behavior.

Sex and species differences in the vasopressin innervation of sexually naive and parental prairie voles, Microtus ochrogaster and meadow voles, Microtus pennsylvanicus

To study whether central systems that are implicated in functions associated with reproduction show different changes in males and females that become parental, the central vasopressin (AVP) innervation was compared in two species of voles: prairie voles, in which males and females provide parental care, and meadow voles, in which only females provide parental care. For both species, the densities of AVP-immunoreactive (AVP-ir) fibers in the lateral septum, lateral habenular nucleus, medial preoptic area and paraventricular nucleus of the thalamus were compared in males and females that were sexually inexperienced or had become parents 6 days before sacrifice. The lateral septum and lateral habenular nucleus presumably receive their projections from the bed nucleus of the stria terminalis and medial amygdaloid nucleus, while the other two areas presumably receive their projections from the suprachiasmatic nucleus. Differences between sexually naive and parental animals were found only in the presumed projections of the bed nucleus of the stria terminalis and medial amygdaloid nucleus. In both species, AVP-ir fiber densities in the lateral habenular nucleus and the lateral septum were much greater in males than in females regardless of parental state. In prairie voles, AVP-ir fiber density in the lateral septum and lateral habenular nucleus was reduced in parental males, while no differences were found in females. In parental meadow voles, the AVP-ir fiber density in the lateral septum did not show changes, while the fiber density in the lateral habenular nucleus was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in maternal care and individual differences in play, exploration, and grooming of juvenile Norway rat offspring

Individual differences in two different forms of maternal licking, time in nest and nursing, were measured during the first 2 weeks after birth. Two treatments were imposed to reduce maternal anogenital licking (AGL): peripheral zinc sulfate to interfere with reception of pup chemosignals, and dietary saline to reduce appetite for pup urine. Both treatments reduced AGL but did not affect other maternal licking. Zinc sulfate was more effective than saline during the first week, but was somewhat less selective as it also increased time in nest. Selected behavioral patterns were measured in male and female juveniles and related by multiple regression to the behavior of their mothers. Independent of the method of manipulation, maternal AGL was a significant predictor of play and open-field defecation males and of some forms of activity in the open field in both sexes. The relationships between other maternal variables and juvenile behavior were more modest. These data demonstrate that intervening in the sensory regulation of maternal behavior can produce predictable changes in stimulation provided by the dam, thereby providing a useful means for investigating the effects of protracted differences in early stimulation in otherwise normal developmental contexts.

Unmasking of a neonatal somatovesical reflex in adult cats by the serotonin autoreceptor agonist 5-methoxy-N,N-dimethyltryptamine

In neonatal kittens, micturition is induced by a spinal somatovesical reflex pathway that is activated by the mother cat licking the perigenital region of the kitten. The somatovesical reflex pathway disappears about the time of weaning and is replaced by a vesicovesical reflex pathway that produces micturition via a supraspinal reflex pathway that is activated by distension of the urinary bladder. Furthermore, stimulation of the perigenital region in adult cats actually inhibits the supraspinal vesicovesical micturition reflex. Spinalization prompts the return of the somatovesical reflex, immediately in weaned kittens but over a course of days to weeks in adult cats. The purpose of the present experiments was to determine if the somatovesical reflex could be demonstrated acutely, and reversibly, in adult cats with an intact spinal cord via pharmacological suppression of the serotonergic system. The serotonergic system was suppressed by the intravenous administration of 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), a serotonin agonist that inhibits the firing of serotonergic neurons via activation of inhibitory somatodendritic autoreceptors. 5-MeODMT in low doses (20-50 micrograms/kg) abolished inhibition of the bladder produced by either light tactile stimulation of the perigenital region or by electrical stimulation of the pudendal nerve, which carries the afferent fibers from the perigenital region, in 9 of 10 adult cats. Furthermore, in 8 of the 10 cats, the bladder inhibition was reversed to an excitation of variable amplitudes in each cat. Higher doses of 5-MeODMT (100-1000 micrograms/kg) abolished spontaneous bladder activity but did not inhibit perigenital-induced bladder contractions in those 8 animals in which the drug unmasked the excitatory somatovesical reflex.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventral somatosensory determinants of nursing behavior in Norway rats. I. Effects of variations in the quality and quantity of pup stimuli

By varying the quality and quantity of tactile input that rat dams, between Days 2 and 14 postpartum, received from their pups, we found the following: a) After a 4-hr separation from their litter, mothers continuously display an array of activities, until the onset of nursing, in response to displaced pups and to pups gathered in the nest. b) While the dam hovers over the gathered pups, engaged in an activity such as pup-licking, the young gain access to the dam's ventrum and root for a nipple. c) Pups capable of effective rooting, nipple attachment, and suckling thereby stimulate the dam's immobility (i.e., inhibition of head and limb movements), assumption of the upright crouching posture, and milk ejections. d) Rat dams do not become immobile or crouch in response to pups that are inactive or that are active but incapable of rooting effectively or suckling. e) The likelihood and speed of assuming the quiescent nursing posture, as well as of having milk ejections subsequently, are directly related to the number of effective pups in the nest. We propose that the initiation, maintenance and termination of nursing behavior are related to the spatial and temporal summation of effective ventral somatosensory afferents.

Behavioral analysis of the postnatal development of micturition in kittens

Micturition in neonatal mammals of various species can be induced by a somatovesical reflex that is triggered by the mother licking the perineal region of the neonate. The present study was conducted to ascertain whether neonatal kittens can also urinate via a vesicovesical reflex that is elicited by bladder distension. Initial experiments consisted of isolating kittens from their mothers and observing urine release. Kittens less than 3 weeks of age did not urinate despite the presence of large volumes of urine in their bladders. Kittens older than 3 weeks of age did urinate, completely emptying their bladders. The volumes of urine that induced micturition in the older kittens were generally less than those that were ineffective in inducing micturition at younger ages. Cystometrograms in unanesthetized kittens less than 3 weeks of age revealed that distension of the bladder by saline infusion did not evoke bladder contractions. However, saline infusion in older kittens did produce bladder contractions that were accompanied by squatting and the release of urine from around the bladder cannula. Surprisingly, bladder contractions, which were typically abolished by spinal transection, were observed in kittens less than 3 weeks of age when the kittens were anesthetized with either ketamine or chloralose. This latter finding indicates that the vesicovesical reflex is present in neonatal kittens, but it is being suppressed by anesthetic-sensitive mechanisms. Thus, micturition in neonatal kittens is normally mediated entirely by the somatovesical reflex.

Behavioral responses of infant rats to maternal licking: variations with age and sex

Behavioral interactions of Norway rat pups and their dams during maternal anogenital licking (AGL) were observed. Regularities in posture and orientation that may facilitate AGL were noted, and age-related changes in the pup's postural adjustments that may contribute to the decline of AGL in the 3rd postpartum week were described. It was found that cutaneous stimulation of the perineum, such as that provided by AGL, stimulates a characteristic leg extension response from pups. It was concluded that this response, which includes immobility and extension of all limbs, may permit maternal licking to continue long enough to stimulate the pup to eliminate and to allow the dam to ingest the urine. Males and females were found to exhibit similar responses and similar age-related changes. However, the latency from onset of AGL to performance of the leg extension response was shorter in males.

Maternal behavior in rats and the effects of neonatal progestins given to the pups

This paper reports changes in maternal behavior of rats following progestin treatment of the neonates. There have been recent reports that hormonal treatment of pups can alter maternal behavior, particularly licking of pups, and that such effects might have implications for the later development of those pups. Accordingly, the major objective of the experiments described was to test the hypothesis that the effects of neonatal progestins on later behavioral development that we have previously described (Birke & Sadler, 1983; 1984) might in part be mediated by changes in maternal behavior. This was done by investigating the behavior of dams, including pup-directed behavior, following the hormone treatments that we have used previously. In the first experiment, medroxyprogesterone acetate (MPA), given via maternal milk, was found to increase rates of pup licking by dams. In the second experiment, anogenital licking was increased to litters containing pups that had received either MPA or progesterone by direct injection. No significant changes in licking following pup treatment with the antiserum to progesterone were observed, however. The results are discussed in relation to our previous work on progestin effects on later behavior, and in relation to the suggestion that hormonal effects on sexually dimorphic behaviors might, at least partly, be mediated through interactions with the mother during the neonatal period.

Opiate antagonism reduces placentophagia and pup cleaning by parturient rats

Since endogenous opiate mechanisms are activated during parturition, the present study examined in rats the effects of opiate antagonism on maternal care during and shortly after parturition. Endogenous opiate mechanisms were blocked in late pregnant rats by (1) naltrexone pellet implants (Experiment 1); (2) acute naloxone injections of 10 mg/kg (Experiment 2) or 0.1 mg/kg (Experiment 7); or (3) induction of opiate tolerance (Experiment 3). All methods resulted in a significant decrease in placentophagia and/or in cleaning pups of umbilical cords and birth fluids (Experiment 6). Other aspects of maternal care appeared relatively unaffected and 24 hr pup survival rats were lowered only by induction of morphine tolerance (probably via its effects on the young). In nonpregnant females, naloxone produced a small but significant decrease in placentophagia (Experiment 4) whereas morphine-tolerant nonpregnant females consumed placentas as readily as controls (Experiment 5). Thus the inhibition of placentophagia produced by opiate antagonism may be specific to conditions associated with parturition. These findings suggest that endogenous opiates support placenta eating and pup cleaning during and immediately after birth. Mediation may be via opiate effects on ingestive behavior, and/or via a reduction in the stress of parturition which otherwise can interfere with the female's ability to perform these tasks.

Maternal licking by virgin and lactating rats: water transfer from pups

Rat dams provide water to their young via milk. Dams reclaim much of this water by licking the pups' anogenital areas, stimulating reflexive urination and consuming the pups' urine. Sensitized virgin rats, induced to act maternally do not provide water to pups, but they nevertheless lick them. To determine whether bidirectional transfer of water between the rat mother and her litter mediates maternal licking, water transfer from pups to sensitized virgins was compared with that to lactating dams. We used time-lapse video recordings to measure anogenital licking of pups. Sensitized virgins and lactating dams spent equivalent amounts of time licking the anogenital regions of test litters. We quantified the amount of water transferred from offspring to both virgins and dams by injecting pups with tritiated water and measuring the radioactive label in maternal plasma after interaction with a litter of 5-day-olds. Dams obtained more than twice as much urine from the litter in 4 hr than did the maternal virgins. Differences in the amount of water obtained from pups were due to differences in urine availability caused by the receipt of milk from the dams. When the dams' nipples were ligated, so that their pups received no milk, ligated dams and virgins consumed equivalent amounts of pup urine. Maternal licking and urine consumption are not dependent solely upon the bidirectional exchange of water between the dam and her offspring.

Maternal contributions to the development of masculine sexual behavior in laboratory rats

Maternal licking was manipulated by lining the nasal passages of rat dams with polyethylene tubing to interfere with their olfactory competence. Olfactory cues from pups elicit maternal licking and handling, particularly of anogenital regions, and dams with olfactory deficits were observed to lick their pups less. Mature male and female offspring of these dams and their controls were gonadectomized, treated with testosterone propionate, and tested for masculine sexual behavior. The male offspring of dams that provided less maternal licking had longer ejaculatory latencies, longer post-ejaculatory intromission latencies, and longer inter-intromission intervals than controls. Female offspring of the intubed dams performed fewer mounts and intromissions, had longer intromission latencies, and longer inter-intromission intervals. It was concluded that stimulation from maternal licking contributes toward the development of a mechanism that underlies the timing of copulatory rate.