Stud males

Thus, rather than providing a reproductive benefit to males as traditionally assumed, the Bruce effect may have evolved solely to female advantage. Notably, this response also increases selective pressure on stud males to increase their investment in the territorial defence of nest sites that are preferred by females (Ims 1987). Females may improve their own reproductive success through threat of pregnancy block, compelling stud males to invest more heavily in nest defence. 

Bloch, S. (1974) Observations on the ability of the stud male to block pregnancy in the mouse. J. Reprod. Fertil. 38, 469—471. 

Thomas, K.J. and Dominic, C.J. (1987) Evaluation of the role of the stud male in preventing male-induced implantation failure (the Bruce effect) in laboratory mice. Anim. Behav. 35, 1257-1259. 

The VNO is extremely important in mediating endocrine responses to primer pheromones. Puberty acceleration in female rats by male urine odors can be prevented by electrolytic damage to the vomeronasal nerve. Also, effects of male urine odor such as shortening of the estrus cycle (see Ch. 8) can be eliminated by section of the vomeronasal nerve, or bilateral electrocoagulation of the accessory olfactory bulb (Sanchez-Criado, 1982). In rats, the odor of males stimulates ovulation in females, an effect that is lost if the VNO is extirpated (Johns etal., 1978). Female prairie voles, M. ochrogaster, respond to odors from males with reproductive activation. Surgical removal of the VNO from adult females impedes this reproductive activation by the stud male. The weights of the uterus and the ovaries of these females were lower than those of normal or sham-operated individuals. However, the females without a VNO were still able to locate food by chemical cues (Lepri and Wysocki, 1987). 

The impregnated female mouse retains an olfactory memory of the stud male. This memory depends on cervico-vaginal stimulation at mating (Keverne and de la Riva, 1982). For the effect to occur, the female has to be exposed to the stud male s odor for 4-6 hours (Rosser and Keverne, 1985). The memory for the stud male lasts for about 30 days (Kaba etal., 1992). Memory formation is accompanied by synaptic changes in the accessory olfactory bulb (Kaba et al, 1992). The major urinary proteins, currently subjected to intense study, may provide individual information about the male, in addition to the protein s pheromonebinding role. 

Mature NOD stud male mice are singly housed and mated no more than once each week. Injection of Freund s adjuvant may be given to delay onset of the diabetic phenotype (see Note 2). 

If stud males are not routinely used for mating to superovu-lated females, we find it advantageous to practice mate the stud males to any strain of female on-hand 1-2 weeks prior to the next transgenic NOD experiment. This helps ensure the highest plug and fertility rates when it comes time to mate to superovulated NOD females. 

If mice are obtained commercially, allow them to adjust to their new light/ dark schedule for 3 4 d. To induce super-ovulation, inject female mice 3-6 wk of age with 0.1 mL intraperitoneally (ip) of PMS (50 IU/mL) in normal saline between 1 00 and 2 00 pm (on a standard 5 00 am to 7 00 pm light cycle). Two days later, between noon and 1 00 pm, inject 0.1 mL of hCG (50 IU/mL) in NS ip. Place injected females in cage with stud male and check for plugs the following day. 

Set up a mating between a 6 wk-old female Swiss outbred mouse and a vasecto-mized stud male. Vasectomized males are available commercially from Jackson Labs (Bar Harbor, ME) or vasectomies can be performed as described (16). Check for plugging the next day and use a plugged pseudopregnant female. 

Make sure that stud males are caged alone for several weeks prior to caging with females to prevent suppression of testosterone by dominant males in the same cage, which lowers plugging efficiency. 

In this condition females still respond to pheromones producing the olfactory block to pregnancy, but fail to recognise or become imprinted to pheromones of the male that mated, and consequently the stud male s pheromones block such a pregnancy (Keverne and de la Riva, 1982). Hence, females with noradrenaline depleted from their accessory olfactory bulbs would fail to become pregnant unless they were isolated from all male odours after mating. 

The pine voles used in these experiments were 1st through 4th generation laboratory descendants of wild voles trapped in 1982 and 1983 in apple orchards in Henderson County, North Carolina. Breeding pairs and their offspring were maintained in 36 x 30 x 18-cm plastic cages containing peat moss substrate and fitted with wire lids. Stud males were at least 120 days of age and were individually housed Water and Wayne Lab Blox were available ad libitum a slice of apple, 3-5 g sunflower... 

A preliminary experiment determined the time course of reproductive activation in adult females taken from isolation and paired with stud males for the following number of hours 0, 12, 24, 36, 48, 60, or 72. 

Figure 1. Changes in mean (+ SEM) reproductive organ weights of female pine voles paired with stud males for varying periods of time (n 12 females per treatment).

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