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J. Reynolds and E. B. Keverne

Summary. Mice were grouped to induce suppression of oestrus and subjected to removal of the vomeronasal organs or treatment with CB 154 which lowers prolactin levels. Both treatments overcame the suppression of oestrus after 72 h. Oestrus suppression was induced in lesioned mice by haloperidol treatment which raises plasma prolactin, and oestrus returned some 72 h after withdrawal of haloperidol treatment.

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D. E. Lomas and E. B. Keverne

Summary. Young female mice were grouped on Day 21 after birth and subjected to removal of the vomeronasal organ. Soiled bedding from intact adult males failed to advance the onset of first oestrus in these lesioned mice compared to the various control groups. Vomeronasal organ lesions of prepubertal females also prevented increases in uterine weight following exposure to soiled bedding for 48 h on Day 23 when compared to controls. Lowering prolactin by injections of bromocriptine for 48 h on Day 26, but not Day 23, advanced the onset of puberty in intact and vomeronasal organ-lesioned females. Elevating prolactin by injections of domperidone were without effect on the early onset of oestrus when compared to sham-injected controls. It is concluded that marked similarities exist in both the receptor system and neuroendocrine mechanism of male pheromone action observed in prepubertal females and that seen in the adult.

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R. P. MICHAEL and E. B. KEVERNE

Many mammalian species breed seasonally and alterations in the physical environment provide the necessary stimulation. Zuckerman (1932) stated the case for the existence of an uninterrupted sexual life in monkeys and apes, but evidence has since accumulated that establishes breeding with annual rhythmicity in several primate species (Lancaster & Lee, 1965). In the rhesus monkey, a peak of births has been reported between March and May both in North India (Southwick, Beg & Siddiqi, 1961; Prakash, 1962; Lindburg, 1967) and also in the islands near Puerto Rico (Altmann, 1962; Koford, 1965). A survey of the breeding activity of rhesus monkeys in the laboratory shows different findings in different colonies (Ponce de Lugo, 1964), but there is considerable agreement that a similar birth peak occurs in captivity between March and April (Hartman, 1931; Rowell, 1963; Wisconsin data, 1966, quoted by Eckstein & Kelly, 1966). The existence of an annual (here we avoid the term 'seasonal') rhythm in sexual performance and motivation has been difficult to establish with certainty because of the annual disturbance caused by

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A. E. Rosser, C. J. Remfry and E. B. Keverne

Summary. Exposure of recently mated female mice to strange male urine revealed that exposure for 8 h was sufficient to produce pregnancy block providing exposure is for two 4-h periods coincident with prolactin surges. Exposure for 8 h between prolactin surges or one 4-h exposure coincident with either the nocturnal or the diurnal prolactin surge was without effect. When bromocriptine, a dopamine agonist, was given coincident with the nocturnal and diurnal prolactin surges, it was equally effective, but the opiate antagonist (naltrexone) administered in a similar manner was without effect. This result indicates that pheromonal action is through excitation of the tuberoinfundibular neurones rather than by inhibition of β-endorphin neurones. Further evidence for dopamine involvement in pregnancy block is demonstrated by showing DOPA accumulation in the medio-basal hypothalamus following exposure to male urinary pheromones after dihydroxybenzylhydrazine (DHBH) administration, which blocks the enzyme DOPA-decarboxylase. Taken together, this series of experiments provides convincing evidence for the dopamine inhibition of prolactin release being the final pathway for pheromone action in the context of pregnancy block.

Keywords: pheromones; pregnancy block; critical exposure time; dopamine; mouse

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J. F. Bellringer, Hester P. M. Pratt and E. B. Keverne

Summary. Pregnancy block caused by exposure of mated female mice to a strange male was significantly reduced by bilateral destruction of the vomeronasal organ. Treatment of newly mated females with α-bromocriptine also produced pregnancy block. Pregnancy block also occurred in mated females exposed to strange male odours, but the blastocysts which had failed to implant were still present in the uterus and were viable for up to 15 days after mating. Implantation was induced in such mice by administration of exogenous progesterone and oestradiol.