C.L Gilbert

Naloxone prevents interruption of parturition and increases plasma oxytocin following environmental disturbance in parturient sows

Experiments in rodents have suggested that environmental disturbance can disrupt parturition through an opioid-mediated inhibition of oxytocin secretion. To test this hypothesis in a large animal model, 14 primiparous female pigs were allowed to commence parturition in a strawed pen. Five of these gilts were allowed to continue parturition undisturbed in this pen, while the remainder were moved to a farrowing crate immediately after the birth of the first piglet. At this time, pigs were injected subcutaneously with either the opioid antagonist naloxone (n = 4; dose 1 mg/kg body weight) or saline (n = 5). Whereas the undisturbed pigs all gave birth to a second piglet within 53 min, in three of the five disturbed and saline-treated pigs no further births occurred for 2 h, at which time oxytocin was administered subcutaneously to restart parturition. By contrast, all of the naloxone-treated pigs gave birth spontaneously within 2 h, although mean interbirth intervals were still prolonged compared to undisturbed pigs. In a second experiment, nine primiparous female pigs with chronic catheters preplaced in the external jugular vein were similarly moved after the birth of their first piglet and either injected with naloxone (n = 5) or saline (n = 4). Again, parturition was interrupted in three out of four saline-treated animals for at least 2.5 h, but resumed promptly when exogenous oxytocin was administered. Plasma concentrations of oxytocin in these pigs were significantly lower than in naloxone-treated pigs, five out of six of which gave birth spontaneously to one or more piglets within 2.5 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Prepartum plasma estradiol and postpartum cortisol, but not oxytocin, are associated with interindividual and breed differences in the expression of maternal behaviour in sheep

Consistent, individual differences in the expression of maternal behaviour have been described in several species including the sheep. The neuroendocrine mechanisms underlying the onset of maternal behaviour in the sheep have been described, although the relationship between hormonal events and individual differences in behaviour has yet to be determined. In this study, we examined whether the individual differences in plasma estradiol, progesterone, oxytocin and cortisol concentrations were related to observed individual and breed differences in maternal behaviours in two breeds of sheep (Scottish Blackface and Suffolk) known to differ in maternal behavioural expression. Maternal estradiol concentration increased rapidly before parturition and was higher in Blackface ewes than Suffolk ewes. Plasma progesterone declined before parturition and was higher in Suffolk than Blackface ewes. Prepartum estradiol, but not progesterone, was related to individual differences in maternal grooming of the lamb. Plasma oxytocin did not differ between breeds in late gestation. There was a tendency for oxytocin to be higher in Blackface than Suffolk ewes immediately after birth. However, there were no significant relationships between prepartum or postpartum oxytocin and any maternal behaviours. Plasma cortisol was higher in Blackface than Suffolk ewes in the last days of pregnancy but rose in both breeds over the last 24 h before parturition and did not differ at delivery. Cortisol peripartum was negatively related to individual differences in maternal affiliative behaviours. These data suggest that estradiol, and potentially cortisol, may mediate individual differences in maternal behaviour in sheep.

Gene expression profiling in porcine maternal infanticide: A model for puerperal psychosis†

The etiology of mental disorders remains largely unclear. Complex interactions between genetic and environmental factors are key to the development of such disorders. Puerperal psychosis is the most extreme form of postnatal mood disorder in women. Similarly, parturition in the pig can trigger extreme behavioral disturbances, including maternal infanticide. In this study, we have used a targeted cDNA microarray approach using the pig as a model to understand the genes and genetic pathways that are involved in these processes. Two subtracted cDNA libraries from porcine hypothalamus were constructed, which were enriched for genes that were over‐expressed and under‐expressed in the aberrant behavioral phenotype, compared to the matched control. In addition to this, a normalized library was constructed from hypothalamus and pituitary samples taken from pigs in a variety of reproductive states. The libraries were partially sequenced and combined represented approximately 5,159 different genes. Microarray analysis determined differences in gene expression between hypothalamus samples from nine matched pairs of infanticidal versus control animals, using a common reference design. Microarray analysis of variance (MAANOVA) identified 52 clones as being differentially expressed (P ≤ 0.002) in the infanticide phenotype, a second analysis with friendly statistics package for microarray analysis (FSPMA) identified 9 genes in common to MAANOVA, and a further 16 genes. A rapid cross‐species screen onto a human oligonucleotide array confirmed 3 genes and highlighted 61 more potential candidates. Some of these genes and the pathways in which they are involved were also implicated in a parallel QTL study on maternal infanticide.

The effects of chronic environmental stress on parturition and on oxytocin and vasopressin secretion in the pig

Previous work has suggested that an acute behavioural confinement in mid-partum can inhibit oxytocin secretion and prolong delivery in the pig, an effect that is opioid mediated. The present experiment investigated the effect of longer-term (chronic) behavioural confinement, that has previously been shown to elevate total plasma cortisol, on speed of delivery and on plasma oxytocin and lysine vasopressin concentrations during the peri-parturient period in primiparous pigs (gilts). Five days before their expected parturition (farrowing) date, gilts with preplaced jugular catheters were either confined to farrowing crates that severely restricted maternal behaviour, or housed in pens that permitted free movement and maternal behaviour (e.g. nest building). Blood samples were taken continuously from 24 h before the birth of the first piglet (BFP) to 6 h post-BFP, and for oxytocin on Days 1, 2, and 7 following parturition (Days P1, P2, P7). Both oxytocin and vasopressin were strongly influenced by parturition (P<0.001). There was no overall effect of chronic crating on either hormone, but crated and penned gilts did show significant differences with respect to the pattern of both oxytocin and vasopressin concentrations over time (P<0.05 in both cases). Oxytocin and vasopressin first increased in crated and penned gilts from 3 h pre-BFP (P<0.05). Crated gilts subsequently showed greater increases in both oxytocin and vasopressin over the first hour of delivery than penned gilts (mean oxytocin (pmol 1−1): 53.3±8.5 vs. 39.7±5.0 for crated vs. penned gilts; mean vasopressin (pmol l−1):4.4±0.7 vs. 2.0±04 for crated vs. penned gilts; both P<0.05). For oxytocin, crated gilts then showed subsequent declining concentrations relative to penned gilts (P<0.05). For vasopressin, penned gilts reached similar concentrations as crated gilts in the third hour post-BFP before vasopressin concentrations in both groups declined. Crated gilts also gave birth to piglets faster in the early stages of delivery (e.g. mean interval between Piglets 2 and 3 (min): 9.6±2.5 vs. 25.6±8.54 for crated and penned gilts, respectively: P<0.02). We conclude that confinement of gilts to a farrowing crate for 5 days neither adversely affects the progress of delivery in the primiparous pig nor the secretion of posterior pituitary hormones involved in parturition.

Prostaglandin F2α-Induced Nest-Building in Pseudopregnant Pigs. I. Effects of Environment on Behaviour and Cortisol Secretion

Pigs may be susceptible to stress when they are strongly motivated to nest-build in a space-restricted environment. This study aimed to explore whether nest-building behaviour could be induced by prostaglandin F2alpha (PG) administration to pseudopregnant gilts and to determine whether induced behaviour and cortisol output differed between animals chronically placed in either farrowing crates or pens. Jugular vein catheters were placed on Day 39 of pseudopregnancy and blood samples collected daily from Day 40 to Day 48. On Day 42, gilts were either restricted to farrowing crates 1.6 x 0.6 m with no straw (C: n = 11) or left in pens 2.8 x 1.74 m with straw (P: n = 11). On Day 47, blood and behaviour sampling was from 90 min pre-PG (Dinoprost; Lutalyse, Upjohn, Kalamazoo, MI) to 6 h post-PG. PG injection successfully induced nest-building behaviour in P gilts within 15 min of injection. Penned gilts engaged in more straw/floor-directed behaviour than C gilts (p < 0.01), whereas attempts in C gilts seemed partial or incomplete. Conversely, C gilts showed increased (p < 0.05) amounts of fixture-directed behaviour, whereas P gilts did not post-PG. For both groups, cortisol increased significantly (p < 0.05) post-PG compared to pre-PG values. Cortisol concentrations in C gilts were significantly greater than in P gilts prior to and after PG (p < 0.05) on Day 47, whereas there were no significant differences in concentrations of cortisol between C and P on other days. These results demonstrate that PG can induce nest-building behaviour in the absence of foetal signals. Whereas the pseudopregnant gilt seemed to chronically adapt to the imposition of a farrowing crate, gilts subsequently attempting to nest-build showed increases in cortisol output when compared to their penned counterparts, suggesting that a stress was imposed by the space-restricted environment.

Porcine Maternal Infanticide as a Model for Puerperal Psychosis

Childbirth is a period of substantial rapid biological and psychological change and a wide range of psychotic disorders can occur ranging from mild ‘baby blues’ to severe episodes of psychotic illnesses. Puerperal psychosis is the most extreme form of postnatal psychosis, occurring in 1 in 1,000 births. In this study, we have used the pig as an animal model for human postnatal psychiatric illness. Our aim was to identify quantitative trait loci (QTL) associated with maternal (infanticide) sow aggression. This is defined by sows attacking and killing their own newborn offspring, within 24 hr of birth. An affected sib pair whole genome linkage analysis was carried out with 80 microsatellite markers covering the 18 porcine autosomes and the X chromosome, with the aim of identifying chromosomal regions responsible for this abnormal behavior. Analysis was carried out using the non‐parametric linkage test of Whittemore and Halpern, as implemented in the Merlin software. The results identified 4 QTL mapping on Sus scrofa chromosomes 2 (SSC2), 10 (SSC10), and X (SSCX). The peak regions of these QTL are syntenic to HSA 5q14.3‐15, 1q32, Xpter‐Xp2.1, and Xq2.4‐Xqter, respectively. Several potential candidate genes lie in these regions in addition to relevant abnormal behavioral QTL, found in humans and rodents.

Prostaglandin F2α-Induced Nest-Building in Pseudopregnant Pigs. II. Space Restriction Stress Does Not Influence Secretion of Oxytocin, Prolactin, Oestradiol or Progesterone

We have previously shown that prostaglandin F2alpha (PG) is capable of inducing nest-building behaviour in pseudopregnant gilts and established a protocol. This experiment examined which reproductive endocrine systems might mediate these behavioural responses, in the presence or absence of a space restriction stress. Pseudopregnancy was induced with 5 mg/day i.m. (intramuscular) injections of oestradiol valerate (OV) on Days 11-15 of the oestrous cycle, jugular vein catheters were placed on Day 39 of pseudopregnancy, and blood samples were collected daily from Day 40 to Day 48. On Day 42, gilts were either space restricted to farrowing crates 1.6 x 0.6 m (C: n = 11) or left in pens 2.8 x 1.74 m (P: n = 11). On Day 47, blood samples were collected from all animals every 15 min from 90 min prior to a single i.m. injection of 15 mg of prostaglandin F2alpha (PG: Lutalyse, Upjohn, Crowley, West Sussex) to 120 min post-PG and then hourly for 4 h and assayed for oxytocin, prolactin, progesterone, and oestradiol. Results showed that mean daily concentrations of prolactin and progesterone were significantly lower (p < 0.05 respectively) in C than P gilts from Day 42 to Day 46 of pseudopregnancy. There were no significant differences in mean daily concentrations of oxytocin and oestradiol between C and P gilts during this time. For both groups, oxytocin, prolactin, and progesterone concentrations increased significantly (p < 0.05) post-PG when compared to their respective pre-PG values. However, for both groups, oestradiol concentrations were unaffected by PG injection. The prostaglandin-induced increases in oxytocin, prolactin, and progesterone concentrations did not differ between groups. We conclude that coincident changes in oestradiol secretion does not influence nesting behaviour and that space restriction stress associated with nest-building does not influence secretion of oxytocin, prolactin, oestradiol, or progesterone.

Release of oxytocin and prostaglandin F2α around teasing, natural service and associated events in the mare.

Mating has been shown in many species to provoke the release of oxytocin (OT). In our study, various stimuli were applied to mares to study release of OT and prostaglandin F(2alpha) (PGF(2alpha)) associated with mating. Blood samples were collected from mares around the time of teasing both in oestrus and dioestrus and at mating. For comparison, blood samples were also collected at the time of manual manipulation of the genital tract and after intrauterine infusion of 500 ml phosphate buffered saline (PBS). Additional samples were collected 16 to 18 h after mating. Mating caused a significant increase in OT in all mares and teasing caused a significant OT response in 6 of 10 oestrous and 3 of 5 dioestrous mares. However, mating and teasing had no significant effect on concentrations of 15-keto-13,14-dihydro-PGF(2alpha) (PGFM). Manual manipulation of the clitoris, vagina and cervix caused significant OT release in all mares and intrauterine infusion of 500 ml PBS caused significant OT release in three of the five mares. However, only one mare had a significant PGF(2alpha) response during manual manipulation and only one responded positively to intrauterine infusion of 500 ml PBS. We concluded that events around mating, including stimulation of the genital tract and uterine distension, often caused an increase in circulating concentrations of OT but only rarely in PGFM.

Deprivation of straw bedding alters PGF2α-induced nesting behaviour in female pigs.

Sows are highly motivated to build a maternal nest on the day preceding parturition. A model for nest building has been established in pigs, in which exogenously administered prostaglandin F-2 alpha (PGF(2 alpha)) may be used to elicit nesting behaviour in cyclic, pseudopregnant and pregnant pigs. The aim of this experiment was to examine the effects of deprivation of straw bedding on PGF(2 alpha)-induced nest building in pseudopregnant Large White gilts. Oestradiol valerate injections (5 mg/day) were given on days 11-15 of the oestrous cycle to induce pseudopregnancy. The pigs were housed individually in a pen (2.8 x 1.7 m) and provided with 2-kg fresh straw each day. On the test day, on day 46 or 47 of pseudopregnancy, half of the pigs were deprived of straw (substrate effect) and they were injected intramuscularly with saline or 15 mg of PGF(2 alpha) (Lutalyse, Upjohn) (treatment effect) allocated in a Latin-square design. Behaviour was recorded onto video tapes for 1 h either side of treatment for analysis using a computerised event recorder. PGF(2 alpha)-treated pigs housed in bare or strawed pens showed significantly higher frequencies of pawing and rooting, and stood for longer than saline-treated controls. This treatment effect has been previously shown to be comparable to pre-partum nest building. The removal of straw significantly reduced the frequency of pawing and the duration of rooting by PGF(2 alpha)-treated pigs. The results demonstrate that nesting behaviour can be initiated by exogenously administered PGF(2 alpha) and is further modified by the provision of straw. This suggests that PGF(2 alpha)-induced nesting behaviour is subject to environmental feedback

Effects of oestrogen supplementation and space restriction on PGF2α-induced nest-building in pseudopregnant gilts

This study examined the role of oestrogen supplementation on PGF2alpha-induced nest-building in pseudopregnant gilts. Oestradiol valerate (5 mg/day) injections were given on Days 11-15 of the oestrous cycle to induce pseudopregnancy. A further series of injections of either oestradiol valerate (5 mg/day) or vehicle were given on days 44-46 of pseudopregnancy to reflect more closely the hormone profile seen in pregnancy. Nest-building was induced by a single intramuscular injection of 15 mg of PGF2alpha (Lutalyse) on Day 47 of pseudopregnancy. The gilts were housed in pens (2.8 x 1.7 m) containing straw in experiment 1 or chronically confined in crates (0.6 x 1.7 m) that did not contain straw on days 44-48 of pseudopregnancy for experiment 2. Oestrogen supplemented gilts had significantly higher concentrations of circulating 17beta-oestradiol on day 47 of pseudopregnancy but there were no significant differences between treatments for circulating levels of prolactin, progesterone, cortisol or oxytocin, or for any behavioural measure in either experiment. These results indicate that there is no direct effect of supplementing already pseudopregnant gilts with oestradiol valerate on PGF2alpha-induced nest-building. The results also show that the pre-partum environment has a pronounced effect on nest-building behaviours and that non-pregnant pigs might be a useful model for pre-partum nest-building in this species.