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We have previously shown that medial preoptic area (MPOA) lesions disrupt parental behavior in both male and female California mice (P. californicus). In the present study, we compare the effects of lesions in the MPOA, with those in the basolateral amygdala (BA) and nucleus accumbens (NA) on male and female parental behaviors in the biparental California mouse. A male or multiparous female from each male-female pair was given an electrolytic or sham lesion in the MPOA, BA, or NA and tested for parental responsiveness. Since female P. californicus show postpartum estrus, they were likely pregnant during parental testing. MPOA lesions produced deficits in both male and female parental behaviors, and BA lesions disrupted male, and to a lesser extent, female parental behavior. NA lesions produced mild effects on pup-retrieval in males and no effect on parental behavior in females. However, NA lesions incompletely destroyed the NA shell, the region most relevant for maternal behavior in rats, and should be investigated further. These results support a role for the MPOA and BA in both male and female parental behaviors.

This study directly compared the role of genetic and dietary factors in the production of individual urinary odors in mice by investigating the ability of male Long-Evans hooded rats to discriminate between urine samples from two strains of mice (C57BL/6-H-2Kb/J and C57BL/6-H-2Kbml/ByJ), which differ at only one locus of the major histocompatibility complex (MHC) and which were maintained on two different diets. Groups of rats were trained in an olfactometer on a go/no-go operant task with water as reinforcement to discriminate between one of the following four pairs of mouse urinary odors: individual mice differing at the MHC and maintained on the same diet (task 1), individual mice differing at the MHC and maintained on different diets (task 2), individual mice of the same MHC type maintained on the same diet (task 3), or individual mice of the same MHC type maintained on different diets (task 4). The urinary odors of mice on different diets (tasks 2 and 4) were more readily discriminable than those of mice maintained on the same diet (tasks 1 and 3), irrespective of genetic differences at the MHC. It was more difficult to discriminate between urinary odors of mice on the same diet whether they were genetically identical (task 4) or differed at the MHC (task 1). A second experiment revealed that it was no less difficult for rats to discriminate between the urinary odors of mice that differed at three MHC loci than it was for rats to discriminate between two mice that differed at one MHC locus. Thus, the results from Experiment 1 were not caused by the degree of genetic difference at the MHC. Overall, these results provide further evidence that dietary as well as genetic cues contribute to individual odors in rodents, and demonstrate the ability of rats to make very subtle discriminations between odors when trained in an olfactometer.

Inbred mice of MHC-congenic strains prefer to mate with mice of different MHC types. Mate selection based on MHC-type occurs through the urinary odors specific to each MHC-congenic mouse strain. Both urine and preputial gland odors of male mice have been postulated to act as female attractants and the present study examined the attraction of MHC-congenic female mice (C57BL/6J and B6-AKR.H-2k) to the urine and preputial gland odors of males. Females of both strains showed a greater attraction to the urine odors of intact males of the other MHC type, but did not show a preference for the urine odors of these males after their preputial glands were removed. There was, however, a preference for the preputial fluid of males of the other MHC type. These results indicate that the MHC-specific urinary odors of mice may arise from the preputial glands, and that it is the MHC-specific preputial gland odors of MHC-conspecific males that are used for mate selection by females.

This study investigates whether differences in urinary odors of two major histocompatibility complex (MHC) congenic strains of mice reared in germfree conditions could be detected by male Sprague-Dawley rats in a habituation-dishabituation procedure. Rats were tested for their ability to discriminate between urine odors from one of the following pairs: (a) MHC congenic mice (B6 and B6-H-2k) housed in conventional conditions; (b) MHC congenic mice (B6 and B6-H-2k) raised in a germfree environment; (c) genetically identical mice maintained in conventional housing; or (d) genetically identical mice raised in a germfree environment. The urine odors of mice from the two MHC congenic strains raised in conventional housing were discriminable, but the urine odors of MHC congenic mice raised in a germfree environment were not discriminable. The odors of genetically identical mice, whether housed conventionally or under germfree conditions, were not discriminable. These results indicate that germfree rearing influences the urinary odors of individuality in MHC congenic mice. We discuss the possibility that the disparate findings from previous studies are a result of the methodologies employed.

Male rats which ingest feces of lactating females produce anal excreta which is attractive to pups. This excreta is as attractive as that of lactating females and more attractive than the excreta of males eating a diet of lab chow only. Anal excreta of males which consume feces of lactating females is more attractive to pups than excreta of males that consume feces of nonlactating females. These results suggest that group or colony odors may develop from rats eating feces of other colony members and that infant rats may be more attracted to adults that have an odor which is similar to the maternal odor than adults which have different odors.

The present experiments provide the first evidence that congenic strains of rats, which differ only in the MHC, produce discriminably different urinary chemosignals. Urine from adult male PVG and PVG.R1 rats, which differ only in the A region (class 1) of the MHC, was used in a habituation-dishabituation task, with male PVG-RTlu, Wistar albino, and Lister hooded rats as subjects. Urine from PVG males was easily distinguished from that of PVG.R1 males by all three strains. Individual PVG males were not distinguished by their urine odours, but individual PVG.R1 males appeared to have discriminably different odours. A repetition of this experiment indicated that this discrimination may have been due to impurities in the urine. Odours from serum were not sufficient for discrimination between the two strains, nor was the class 1 molecule purified from the urine. Urine with the class 1 molecule removed (remainder fraction) could, however, be used to distinguish between the strains. The chemicals in the urine which give this distinctive odour may be fragments of the class 1 molecule or small molecules associated with the class 1 molecule. The MHC appears to control the odour cues which are used by mammals for individual recognition and may provide an olfactory basis for kin recognition but the mechanism by which the MHC controls these olfactory signals is unknown.

Long-Evans hooded rat pups were reared with their dam alone, their dam and sire or their dam 12 hrs per day and their sire 12 hrs per day and tested for preferences for anal excreta from adult male and female rats when they were 18 to 20 days of age. In all rearing conditions the anal excreta of the rat's own dam was preferred to that of strange dams and the excreta of both own and strange dams was preferred to that of virgin females. Anal excreta from virgin females was preferred to no odor as was anal excreta of unmated males, strange sires and the rat's own sire. Only rats reared with their dam and sire preferred the odor of their own sire to that of other males. The results suggest that pre-weanling rats may attend to different dimensions of the odors of conspecifics, such as the species odor, maternal odor, and individual odor and that different rearing conditions may influence the odor dimension to which the rat attends.

Three experiments were conducted on the preferences of infant rats for nest odors. Pre-weanling rats preferred their own nest odor to nests of strange litters and showed low preferences for the nest odors of virgin females. Nest odors of unmated males were investigated less than the pup's own nest odor but more than the odors of virgin females. Male and female rats did not differ in odor preferences. Rats reared with both their dam and sire did not differ in their odor preferences from rats reared with their dam alone when tested at 16–20 days of age, but when tested at 33–38 days of age they showed a greater preference for male odors. Post-weanling rats did not show a preference for the nest odors of lactating females and began to show sex differences in their preferences.

Male rats were found to emit 22-kHz pre-ejaculatory vocalizations when approaching females after they had achieved 4 or more ejaculations. The onset of these vocalizations was associated with increases in mounts without intromissions and decreases in intromission rate. On those ejaculatory series with 22-kHz pre-ejaculatory vocalizations, the females showed a lower lordosis intensity and a higher number of agonistic responses than on series with no vocalizations. It is suggested that the pre-ejaculatory vocalizations may serve to inhibit female agonistic behavior and stimulate sexual responsiveness.