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Disorders of the bulbospongiosus muscle (Bsm) are associated with male sexual dysfunction, such as premature ejaculation. We determined the effect of sucrose-water consumption during pregnancy-lactation and postnatal on reflex responses and morphology of Bsm fibers in adult male Wistar rat offspring. Female rats were mated and grouped into consumed tap water mothers and sucrose-water (5 %) mothers during pregnancy-lactation to obtain experimental groups. Male pups were weaned and assigned into four groups (n = 12; each group). Those from control mothers who continued drinking tap water (CM-CO group) or sucrose water (CM-SO group), and those from sucrose mothers who drank tap water (SM-CO group) or continued drinking sucrose water (SM-SO group) until adult life. In male rat offspring (n = 6 per group) was recorded the electrical activity of Bsm was recorded during penile stimulation and urethrogenital reflex (UGR). Other male rat offspring were designated for histological analysis (n = 6 per group). Sucrose consumption during prenatal stages increased the frequency of the Bsm during UGR, while pre and postnatal consumption modified muscle fiber cross-sectional area and increased the collagen content, suggesting that a combination of a diet with pre- and postnatal sucrose changes the Bsm morphophysiology possibly causing male sexual dysfunctions., Competing Interests: Declaration of Competing Interest No conflicts of interest, financial or otherwise, are declared by the authors., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Individual-level sibling interactions in the litter huddle have been studied extensively, especially in the domestic rabbit (Oryctolagus cuniculus). However, little is known about inter-litter differences in pup activity patterns during early postnatal life, in particular regarding the drivers of such variation. In our study on 2-3-day-old rabbit pups, we predicted lower locomotor activity in litters with lower mean body masses on the day of birth (starting body mass) and with lower daily milk intake per pup, possibly constituting a behavioral strategy of pups to cope with associated energetic constraints. For an automatized assessment of pup locomotor activity in the litter huddle, we successfully developed and validated a method based on the quantification of dissimilarities between consecutive frames of video footage. Using this method, we could confirm a U-shaped time course of litter-level locomotor activity, with maximum values shortly before and after the once-daily nursing typical for the rabbit. As predicted, between-litter variation in mean starting body mass and in daily milk intake affected the degree of locomotor activity in the litter huddle, in an interactive way. That is, in litters with heavier starting body masses, pup locomotor activity was greater in pups with an initially higher milk intake, suggesting that only pups with better body condition and a higher energy intake could afford higher levels of activity. This interaction was exclusively apparent during the middle phase of the 24 h inter-nursing interval, when litter activity was low. Shortly before nursing, when pups show higher levels of locomotor behavior in anticipation of the mother's arrival, and shortly after nursing when the pups were more active possibly due to adjustments of their positions in the huddle, activity levels were decoupled from pups' starting body mass and previous milk intake. Our findings highlight the importance of pup body mass and daily energy intake, two parameters known to be related to maternal characteristics, in shaping inter-litter differences in pup locomotor activity., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

In mammals, body mass at birth is an important predictor of early postnatal growth and survival. Within litters, heavier young are more successful in competing for limited resources and show higher rates of growth and survival than their lighter sibs. In the present study, we investigated the contribution of two aspects of the intrauterine environment to within-litter differences in birth mass, growth and survival in the rabbit (Oryctolagus cuniculus): implantation site along the uterine horns and number of adjacent male fetuses. We used unilaterally ovariectomized mothers in order to infer relative sites of implantation from the birth order of pups from the single functional uterine horn. Pups from the extremities of the horn were significantly heavier at birth and weaning than their siblings from more central positions and had a higher probability of survival. The effect on body mass was still apparent 3 weeks after weaning in pups that had occupied positions at the ovarian end of the horn. The number of adjacent male fetuses did not affect individuals' growth or survival, and there were no differences between females and males. There were also no significant interactions between the different variables considered, indicating that the effects of implantation site on individuals' birth mass, growth and survival relative to littermates were independent of number of male neighbors, sex or litter size. Our study clearly demonstrates that in the rabbit, the site of implantation along the uterine horns is a major contributor to individual differences among littermates in early postnatal growth and survival., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The altricial young of the European rabbit (Oryctolagus cuniculus) are not brooded by the mother, and although they are born into an underground nest, depend importantly on the warmth and insulation provided by littermates for their early growth and survival. Consistent with previous studies, heavier pups occupied more central, thermally advantageous positions in the litter huddle, maintained higher body temperatures, obtained more milk, were more efficient at converting it to body mass, and consequently grew faster than their lighter sibs occupying the periphery of the huddle. In the present study we measured the expression of uncoupling protein 1 (UCP-1), which is essential for the metabolism of brown adipose tissue to generate body heat in response to cold. In nine litters of domestic rabbits maintained for the first four postnatal days at temperatures below their critical thermoneutral temperature, peripheral pups showed greater expression of UCP-1 than intermediate pups, and these greater expression than central pups. This suggests that during early development littermates of the rabbit experience differing degrees of activation of the sympathetic nervous system as a consequence of exposure to different thermal environments associated with different positions in the litter huddle. Whether this is associated with long term differences in the physiological response to cold and perhaps in the manner of responding to other environmental challenges is currently under investigation., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Many aspects of an animal's early development might potentially contribute to long-term individual differences in physiology and behavior. Here we asked whether differences among littermates of the domestic rabbit in the position in the litter huddle that they occupy during the early nest period might contribute to the development of distinct behavioral and physiological phenotypes. In each of 12 litters we determined the pup occupying the most peripheral, the most central, and an intermediate position in the huddle during the first postnatal week. We then tested the responses of these same individuals as nestlings, juveniles and young adults when confronted by a range of age-appropriate environmental challenges. Two behavioral tests appeared particularly discriminatory in identifying differences associated with early position in the huddle; latency of pre-weaning pups to jump down from a shelf, and the response of young adults to the fearful screams of a conspecific. In both cases animals that had occupied the periphery of the huddle showed behavioral responses indicative of a more proactive behavioral style than their "intermediate" or "central" littermates. We conclude that while consistent long-term differences in behavioral style associated with early position in the litter huddle exist in rabbits, future work is needed to confirm the causal nature of this association, to identify underlying mechanisms, and to refine methods of behavioral and physiological testing across the life span., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Birth mass can vary considerably among mammalian littermates. Heavier pups often show higher growth rates than their lighter siblings, which might positively affect fitness-relevant parameters during later life. Such a correlation between birth mass and pre-weaning growth within litters was confirmed by our study of wild-type and domestic European rabbits (Oryctolagus cuniculus) living in a semi-natural environment and under laboratory housing conditions, respectively. Our study indicates that at least two main mechanisms account for this relationship in our study species: heavier pups had a higher milk intake and also showed a more efficient conversion of milk into body mass. Furthermore, our study suggests that the better milk conversion by heavy pups was driven by three synergistic mechanisms: heavier pups had comparatively more huddling partners in the nest, they did not need to perform large amounts of proactive behavior in order to reach and remain in a central position within the litter huddle, and they could maintain a comparatively higher body temperature most probably due to their more favorable surface area to volume ratio. In conclusion, our study of European rabbits provides strong evidence that both under natural conditions and in the laboratory, within-litter differences in birth mass are maintained and may even increase during pups' early postnatal development.

The European rabbit, both in its wild and domesticated forms, has been a pioneer species in the study of mammalian chemical communication, and illustrates well the difficulty of understanding the functional significance of these often complex signals. Here we investigate the performance of one of the rabbit's most conspicuous chemical signaling behaviors, chin marking (chinning), and the hypothesis that this expresses social dominance. In tests of 21 chinchilla-strain sexually mature males we predicted 1) that animals would show marked and stable individual differences in the frequency of chinning, 2) that these differences would correlate with behaviors associated with dominance such as intrasexual mounting, and 3) that individual differences in the frequency of chinning and dominance-related behaviors would correlate with individual differences in a commonly used physiological indicator of dominance, concentration of serum testosterone. Supporting these predictions and consistent with previous reports, animals showed large and stable individual differences in the frequency of chinning which correlated with the behavioral indicators of dominance and less strongly, with serum testosterone. As our animals had been kept in single cages and without direct contact with other males since weaning, these findings raise the question as to how and when during development such differences among individuals arise. We are currently investigating the possible relation between pups' intrauterine position, postnatal competition among littermates for milk and thermally advantageous positions in the litter huddle, and later differences in indicators of dominance such as those reported here.

Rabbits (Oryctolagus cuniculus), like many small mammals, have a marked postpartum estrus, and during the breeding season, are often both pregnant and lactating. We examined reproductive performance and allocation of resources by rabbit mothers with overlapping litters under presumably optimal conditions of unrestricted food, standardized litter size, and young reproductive age. Even under these conditions, females raising overlapping litters incurred higher costs in terms of greatly increased food intake and pup mortality than females raising nonoverlapping litters. Despite such costs, females with overlapping litters raised a larger total number of young to weaning than females without the load of simultaneous lactation and pregnancy. By more than doubling food intake during lactation, females maintained a stable baseline body weight throughout the study, suggesting that this, in a species with low fat reserves, might have priority over the short-term raising of a maximum number of young. Contrary to the expectation that females with overlapping litters would allocate more resources to their senior young, no appreciable difference in number, growth, or survival between pups of senior and junior litters was found either at birth or weaning. While this might reflect a strategy in this opportunistic breeder of distributing reproductive chances similarly between senior and junior litters, it is now necessary to investigate females' breeding strategy when resources are limited., (Copyright 2004 Elsevier Inc.)

Little information is available on the participation of the perineal striated muscles in female reproductive processes. Here, we describe the gross anatomy and innervation of two striated perineal muscles in the female rabbit, the bulbospongiosus (BSM) and ischiocavernosus (ISM), and analyze their reflex electromyographic (EMG) activity in response to stimulation of the perigenital skin and vaginal tract. Twenty-four mature chinchilla-breed rabbit does were used: 12 to describe the anatomy and innervation of the muscles, 9 to determine reflex EMG activity of the muscles in response to stimulation of the perigenital skin and specific levels of the vaginal tract and 3 to analyze the effect of contraction of the muscles on intravaginal pressure. Both muscles were well developed, with their fibers originating at the ischiadic arch and inserting onto the ligamentum suspensorium clitoridis. Branches of the clitoral and perineal nerves innervated the BSM and ISM, respectively. Bilateral electrical stimulation of these nerves provoked retraction of the clitoral sheath and an increase in intravaginal pressure at the level of the perineal vagina. Whereas neither muscle responded to stimulation of the perigenital skin, both were reflexively activated during mechanical stimulation of the inner walls of the perineal vagina. Prolonged cervical stimulation inhibited this reflex. Thus, in reproductive processes such as copulation and/or parturition, the contraction of these muscles may be induced during stimulation of the perineal vagina.

Although the rabbit (Oryctolagus cuniculus) continues to play an important role in the study of parturitional processes, a detailed behavioral description of birth in this species, necessary for accurately assessing the effects of experimental manipulation, is lacking. It is the aim of this report to provide such a description and to compare it with corresponding behavior in the better-studied rat. Ten pregnant chinchilla-breed rabbits and 10 pregnant Wistar rats were placed in glass-bottomed observation cages 2 days before term, and their behavior recorded on closed-circuit video, viewing the animals from below. All aspects of parturition were accomplished much faster in rabbits than rats; latency to birth of first pup, rate of delivery, duration of vaginal retention, time spent by mothers eating placentas, and in licking and nursing pups. In contrast to rat pups, rabbits were usually born separated from the placenta and already free from membranes. They were much more active, and well able to cast off any remaining membranes, suckle, and survive, whether directly attended to by the mother or not. We conclude that the tight temporal organization of events in the rabbit provides an unusually sensitive assay for investigating mechanisms underlying mammalian parturition.

In the rat the pelvic nerve consists of a viscerocutaneous (sensory) branch which receives information from pelvic viscera and the midline perineal region, and a somatomotor (muscular) branch which innervates the ilio- and pubococcygeous muscles. To investigate the contribution of these branches to the parturition process, the length of gestation and course of delivery were closely monitored in 43 pregnant, Wistar-strain rats randomly assigned to five groups: untreated control animals, animals in which the somatomotor branch of the pelvic nerve was bilaterally sectioned on Day 14 of gestation, animals in which the viscerocutaneous branch of the pelvic nerve was bilaterally sectioned on Day 14 of gestation, animals treated similarly to the previous group but with young delivered by C-section at term, and sham-operated controls. Sectioning the viscerocutaneous branch seriously disrupted parturition and resulted in major dystocia and a high percentage of stillbirths in all females. In contrast, sectioning the somatomotor branch had no apparent effect on parturition and no significant differences were found between females of this group and sham or control dams on any of the measures recorded. It is concluded that the viscerocutaneous branch of the pelvic nerve is vital for the normal course of parturition in the rat but that the somatomotor branch plays little role, if any.

Responsiveness to pain was determined in female rats across the whole reproductive cycle using the tail-flick test. When tested immediately after mating, pain thresholds were unaltered, whereas 10 min later animals typically demonstrated hyperalgesia (Experiment 1). They also demonstrated hyperalgesia during most of pregnancy, and had significantly lower pain thresholds than the unmated controls except for the 24 h before parturition, when a sudden increase in tail-flick latencies was recorded (Experiment 2). Pain thresholds were also significantly lower throughout the nursing period but increased significantly when dams were separated from their litters for 6 h, and returned to premating baseline values within 24 h of weaning (Experiment 3). These findings confirm and extend earlier reports that female reproductive state may significantly modify responsiveness to noxious stimuli, and it is suggested that differences between the results of this and previous studies may be at least partly explained by the relatively stress-free test procedure adopted here.

Pain threshold was determined in female rats using the tail flick test. Latency to respond depended on the locus of the tail heated, with the most distal sites resulting in the shortest response times (Experiment 1). Tail flick latency also varied according to the time of day, with shorter response times recorded around the middle of the dark phase than near its beginning or after its end. This was the case for intact, for ovariectomized, and for ovariectomized, estradiol-treated rats (Experiment 2). However, response times also varied across the estrous cycle, with significantly shorter latencies recorded during estrus and metestrus. Ovariectomy abolished these fluctuations, and whereas administration of estradiol increased response times, progesterone had little effect (Experiment 3). These results suggest that site of tail heating, time of day, and presence of ovarian hormones can influence tail flick latency independently, thus demonstrating the complexity of the mechanisms that may contribute to pain threshold even within the same paradigm.

The role of the pelvic nerve branches in the mediation of copulatory behavior was investigated. The somatomotor or the viscerocutaneous branch of the pelvic nerve was bilaterally sectioned in sexually experienced male rats. Somatomotor branch surgery had no detectable effect. Viscerocutaneous branch transection altered copulatory parameters that reflect impairments in penile erection and seminal plug emission. The altered behavioral parameters approached or reached presurgical and sham values 21 days after transection, indicating that the damage to erectile and ejaculatory function was transient. It is suggested that animals with viscerocutaneous branch transection recover copulatory efficiency through a compensatory plastic mechanism, possibly involving the hypogastric nerve.

The behavior of freely moving cats was assessed in an observation chamber during prolonged periods of time. Four patterns of behavior were consistently scored during the mid-day period: a) exploration, b) attention, c) grooming and d) drowsiness. Intracerebroventricular injections of crustacean neurodepressing hormone (NDH) greatly extended the time spent in drowsiness. The threshold dose of NDH for this effect was 300 units. The effect was established a few minutes after the injections and lasted for several hours. During this time the animals sat quietly and showed complete or semicomplete closure of the eyelids. Conspicuous changes in brain electrical activity were also observed under NDH. At low doses, the predominant electrophysiological pattern matches the activity recorded under spontaneous lapses of drowsiness, i.e., spindle bursts in trains of 8-16 Hz in cortical areas and mesencephalic reticular formation. At higher doses, the brain electrical activity changes into a nonconvulsive spiking activity in limbic areas. The time course of the effects differs in the various structures recorded. These results suggest a multiple substrate of NDH activity.