The Lactation Interval in the Mouse

Abstract

The length of the lactation interval in the mice in these experiments is from 20 to 25 days. It is not affected by an artificially induced prolongation of lactation. Removal of the litter at birth, on the 7th day, 14th day, or 21st day of lactation is followed within 2 to 4 days by œstrus in all cases. From a comparative survey of the states of pregnancy, pseudopregnancy, and lactation, it is argued that in all the same hormonal conditions prevail.

Induction by young of prolonged dioestrus in virgin rats behaving maternally

“…In non-lactating women manual stimulation of the breast without manipulating the nipples is able to induce dramatic elevations of plasma prolactin (Kolodny, Jacobs & Daughaday, 1972 The presence of corpora lutea and the decidual response during dioestrus induced by young in nulliparous (the present study) and parous (Selye & McKeown, 1934a, b) rats suggest that these females entered a luteal phase which has characteristics common to the post-partum dioestrus and ordinary pseudopregnancy. In post-partum mothers it is generally agreed, with the exception of one study (van der Schoot, Lankhorst, de Roo&deGreef, 1978), that the dioestrous phase cannot be maintained after removal of young (Crew & Mirskaia, 1930;Ota & Yokoyama, 1965;Moltz et al, 1969;Zarrow et al, 1973;Maneckjee & Moudgal, 1975;present study). In these females prolactin levels are high when young are present and diminish following removal of young (Amenomori, Chen & Meites, 1970), allowing the rapid resumption of oestrous cycles (van der Schoot et al, 1978).…”

“…When suckling is maintained for an extended period, resulting in prolonged lactation, this post-partum dioestrus is followed by cycles with a prolonged dioestrous phase (Parkes, 1926;Crew & Mirskaia, 1930;Selye & McKeown, 1934c;Bruce, 1961;Nagasawa & Yanai, 1976; Tomogane, Ota, Unno & Yokoyama, 1976). Removal of young during the 3-week post-partum dioestrus leads to a rapid resumption of regular oestrous cycles (Crew & Mirskaia, 1930;Ota & Yokoyama, 1965;Moltz, Levin & Leon, 1969;Zarrow, Johnson, Denenberg & Bryant, 1973;Maneckjee & Moudgal, 1975).…”

Molecular conservation of marsupial and eutherian placentation and lactation

“…The tammar wallaby ( Macropus eugenii ), a key model for investigating marsupial reproduction ( Renfree et al, 2011 ), has a 26.5 day pregnancy followed by a 300–350 day period of lactation ( Tyndale-Biscoe and Renfree, 1987 ). By comparison, the mouse has a 20 day pregnancy followed by a 20–24 day period of lactation ( Crew and Mirskaia, 1930 ), relying much less on lactation for offspring success. The tammar placenta is derived from a fusion of the yolk sac and chorion, producing a structure that contains two different tissue types: the avascular bilaminar omphalopleure (BOM) and the vascular trilaminar omphalopleure (TOM).…”

Nail abnormalities identified in an ageing study of 30 inbred mouse strains

“…A variety of abnormalities have been described in mice including long curled nails in animals carrying mutations in the hairless ( Hr ) gene and its genocopies, nail plate abnormalities with separation from the nail bed in some but not all strains of mice with alopecia areata, thin nail plates in nude mice ( Foxn1 nu ) or bone morphogenic protein receptor, type 1A ( Bmpr1a tm2.1Bhr ), destruction of the entire nail unit by trauma in sensory deprivation syndrome, such as mice with null mutations in the nerve growth factor receptor gene ( Ngfr , formerly called p75 ) and many other phenotypes. In most cases, abnormalities can be observed in young mice through adulthood affecting all nails on both front and rear feet.…”