RESUMEN
We investigated the role of prolactin and suckling stimulation in the expression of maternal behaviour of primiparous rabbits. Bromocriptine (1 mg/kg/day), given to intact mothers across postpartum days 1-5, decreased serum concentrations of prolactin to undetectable levels, reduced crouching, and increased time inside the nest. Failure of maternal nest-building, provoked by bromocriptine injections from pregnancy day 26 to parturition or to postpartum day 5, correlated with a stronger reduction in crouching and an increased time inside the nest, measures of disturbed maternal behaviour, on postpartum days 3 and 5. Preventing suckling by thelectomy did not prevent prolactin release but reduced crouching incidence and increased the time spent inside the nest on postpartum days 3 and 5. Bromocriptine, injected in thelectomized mothers across postpartum days 1-5, further reduced the incidence of crouching and increased the time spent inside the nest on postpartum days 3 and 5. We conclude that prolactin acting prepartum facilitates maternal behaviour initiation in rabbits and, together with pup stimulation, maintains this behaviour across lactation.
Asunto(s)
Conducta Materna/fisiología , Preñez/fisiología , Prolactina/fisiología , Conejos/fisiología , Animales , Bromocriptina/farmacología , Femenino , Antagonistas de Hormonas/farmacología , Trabajo de Parto/fisiología , Lactancia/efectos de los fármacos , Conducta Materna/efectos de los fármacos , Actividad Motora/efectos de los fármacos , Comportamiento de Nidificación/efectos de los fármacos , Comportamiento de Nidificación/fisiología , Pezones/fisiología , Feromonas/fisiología , Embarazo , Preñez/sangre , Prolactina/sangre , Factores de TiempoRESUMEN
Injection of the serotonergic agonist, 8-hydroxy-2-(di-n-propylamino-tetralin (8-OH-DPAT) (0.5 mg/kg ip) produced a clear anxiolytic-like effect (as measured in the burying behavior test), after parturition, which remains until day 6 of lactation. Thereafter 8-OH-DPAT completely lacked action. In order to analyze whether lactation prevented the action of 8-OH-DPAT, dams were separated from their pups for five consecutive days. The blockade of the anxiolytic effect of 8-OH-DPAT does not disappear by isolation of the mothers from their offspring or from neighboring pups. Finally, to investigate the possible role of maternal behavior in the blockade of the anxiolytic effect of 8-OH-DPAT a third experiment was made in which ovariectomized females were rendered maternal by the sensitization procedure. These females respond normally to the antianxiety actions of 8-OH-DPAT. Results suggest that a long-term clue triggered by lactation, possibly related to prolactin secretion, interferes with the anxiolytic effect of 8-OH-DPAT.
Asunto(s)
8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Ansiolíticos/farmacología , Nivel de Alerta/efectos de los fármacos , Lactancia/efectos de los fármacos , Conducta Materna/efectos de los fármacos , Agonistas de Receptores de Serotonina/farmacología , Animales , Femenino , Masculino , Prolactina/sangre , Ratas , Ratas Wistar , Aislamiento SocialRESUMEN
Estradiol, progesterone, and prolactin regulate digging, carrying straw, and plucking hair for maternal nest-building in rabbits. To explore whether external factors also modulate this process, we assessed whether shaved pregnant rabbits with straw nests would collect their own, male, or synthetic hair for nest-building. Pregnant (but not estrous) does collected and used all hair types, indicating that hair-plucking can be bypassed and a nest constructed with "alternative" hair. Unshaved pregnant does with straw nests also collected synthetic hair, indicating that this behavior is not triggered by the absence of maternal hair. Yet, if hair-plucking/nest-building had occurred, hair-collecting was prevented, suggesting that an internally triggered "drive" was turned off by perceiving a built nest. When given only straw or hair, shaved pregnant does collected and used the material provided, indicating that nest-building is internally driven and accomplished by using any available elements. When given both materials, increasingly more shaved does built straw nests across prepartum days 7 to 2. Straw-carrying declined thereafter, suggesting that perceiving a straw nest limits the collection of such material. Hair-collecting was postponed until prepartum day 1 to postpartum day 2, indicating that: (a) mothers distinguish between straw and hair and (b) hormonal factors regulate the sequential selection of straw and then hair and when the change from straw to hair occurs. Maternal behavior was normal at parturition and for the next 4 days in a similar proportion of does among all experimental groups. We conclude that hormones and external factors regulate nest-building by acting as "on/off/on" signals.
Asunto(s)
Estrógenos/fisiología , Conducta Materna/fisiología , Comportamiento de Nidificación/fisiología , Preñez/fisiología , Conejos/fisiología , Animales , Femenino , Cabello , Remoción del Cabello , Masculino , EmbarazoRESUMEN
Maternal nest-building in rabbits, expressed across the last third of pregnancy, consists of: digging a burrow, collecting straw and shaping it into a nest inside the burrow, plucking body hair and lining the straw nest with it. The sequential expression of these activities is correlated with specific changes in the plasma concentration of estradiol, progesterone (P), and prolactin (PRL). To further substantiate the participation of these hormones in the control of maternal nest-building we explored in ovariectomized (ovx) New Zealand white rabbits the capacity of several combinations of such hormones to stimulate digging, straw-carrying, and hair-pulling. Does given estradiol benzoate (EB; 5 micrograms/day from days 3 to 21) plus P (2 or 10 mg/day from days 4 to 16) dug into a substrate from the fourth day of the P treatment until withdrawal of this hormone. The intensity of this effect was greater in the group treated with the high dose of P. Straw-carrying and hair-pulling occurred after P withdrawal in a dose-response way. Food intake, which declines in pregnant females shortly before parturition, decreased to the same extent in both groups of ovx EB-treated does after P withdrawal. A significant increase in PRL plasma levels was observed on day 9 in does given EB plus 2 mg P/day and at two days following P withdrawal in does given EB plus 10 mg P/day. When such ovx EB/P-treated does were given bromocriptine to block PRL release (1 or 3 mg/Kg/day, from days 11 to 21) the expression of digging was unmodified. By contrast, bromocriptine abolished the display of straw-carrying and hair-pulling, and also prevented the decline in food intake normally following P withdrawal. The addition of ovine PRL to ovx EB/P-treated does given bromocriptine reduced the expression of digging, did not restore straw-carrying or hair-pulling, and provoked a sharp decline in food intake. The possible mechanisms of interaction between PRL and steroid hormones for the regulation of specific aspects of the pregnant doe's physiology and behavior are discussed.
Asunto(s)
Estradiol/farmacología , Conducta Materna/fisiología , Comportamiento de Nidificación/fisiología , Progesterona/farmacología , Prolactina/farmacología , Animales , Conducta Animal/efectos de los fármacos , Conducta Animal/fisiología , Bromocriptina/farmacología , Estradiol/sangre , Femenino , Antagonistas de Hormonas/farmacología , Conducta Materna/efectos de los fármacos , Comportamiento de Nidificación/efectos de los fármacos , Ovariectomía , Progesterona/sangre , Prolactina/sangre , ConejosRESUMEN
Several parameters associated with maternal behavior were quantified under laboratory conditions in New Zealand white rabbits. Digging behavior appeared earliest (8-6 days prepartum), its decline preceding the onset of straw carrying (3-1 days prepartum). Hair pulling consummated the construction of the maternal nest. Food intake significantly decreased on days 2 and 1 prepartum. On parturition day, all females spent 300-500 s with the litter while, for the rest of lactation, nursing bouts lasted 199 +/- 7 s. Milk yield increased linearly up to lactation day 19, declining thereafter. Pup weight increased linearly throughout lactation despite the decline in milk yield. Plasma estradiol (E) levels did not significantly vary across pregnancy: 60 +/- 2 pg/ml (days 10-25) and 75 +/- 6 pg/ml (day 30). The testosterone (T) levels at these times were: 200 +/- 10 and 308 +/- 0.03 pg/ml, respectively. Testosterone significantly declined from pregnancy day 30 to lactation day 1 (202 +/- 0.02 pg/ml). Progesterone (P) levels significantly declined from pregnancy day 20 (9 +/- 1 ng/ml) onwards. Progesterone levels were negligible across lactation. Thus, mother rabbits display a sequence of motor patterns and somatic events correlated with changes in plasma levels of T and P against a background of E.