C-fos mRNA expression associated with PGF 2α-induced nest-building behaviour in female pigs

Abstract

Domestic pigs, Sus scrofa, build a maternal nest on the day before parturition. A model for nest building has been established in pigs, in which exogenously administered prostaglandin (PG) F 2α may be used to elicit nesting behaviour in cyclic, pseudopregnant and pregnant pigs. The central mechanisms mediating this response are unknown. The present study determined regional brain activity using semi-quantitative analysis of c-fos mRNA, after induction of nest-building behaviour by PGF 2α in Large White pseudopregnant pigs. 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 pens (2.8×1.7 m) containing straw. On the test day (day 46 or 47 of pseudopregnancy) animals were injected with 3 ml saline ( n=5) or 15 mg of PGF 2α (Lutalyse, Upjohn; n=6) intramuscularly. Pigs treated with PGF 2α, but not saline, displayed bouts of rooting, pawing and gathering straw, which we interpret as nest building behaviour. The pigs were killed 65 min after treatment, which was 30 min after peak nest building activity, and the brain, uterus and ovaries removed for processing using in situ hybridisation. Saline-treated pigs had elevated levels of c-fos mRNA, compared to background, in the pituitary, corpus luteum and uterus, and a lower, but elevated, level of expression in cerebellum, cortex, hippocampus and olfactory bulb. PGF 2α-treated pigs had significantly higher levels of c-fos mRNA expression than saline-treated pigs in the parvocellular and magnocellular regions of the hypothalamic paraventricular nucleus, the supraoptic nucleus (including the pars dorso-medialis), the neural lobe of the pituitary gland and the cerebellum. PGF 2α-treated pigs also had significantly higher c-fos induction in corpus luteum. These data show that the pattern of c-fos mRNA expression in specific brain areas is different between pigs that show PGF 2α-induced nest building and saline-injected controls.