Why Does Germfree Rearing Eliminate the Odors of Individuality in Rats But Not in Mice?
The Major Histocompatibility Complex (MHC) appears to provide the genetic basis for an individuality marker in the urine of rats and mice (Brown, Singh and Roser, 1987; Brown, Roser and Singh, 1990; Yamazaki et al., 1991). Recent findings suggest that commensal bacteria are also involved in the production of individually distinct urine odors in rats. Using a habituation-dishabituation task, Singh et al. (1990) determined that rats could not discriminate between the urine of germfree MHC congenic rats (PVG vs. PVG.R1). When donors were moved to conventional housing, their urines could be discriminated. Also, rats trained in a go-no go operant task in an olfactometer made more errors in learning to discriminate between urines of germfree MHC congenic rats than between urines of conventionally housed MHC congenic rats (Schellinck, Brown and Slotnick, 1991). Urine odors from conventionally housed MHC congenic rats were readily discriminated; the discrimination was remembered from session to session and no drop in performance was observed when the samples were changed to different donors of the same MHC type in midsession. Although the rats were able to discriminate between urine samples from individual germfree MHC congenic rats, they consistently performed at chance at the beginning of each session. One explanation of this inability to retain the information from session to session could be that constant cues were not being used to discriminate between the urine samples from germfree rats. Moreover, when the urine samples from germfree rats were changed to others of the same strain in midsession, performance was also disrupted.
KeywordsMajor Histocompatibility Complex Urine Sample Major Histocompatibility Complex Locus Urine Odor Conventional Housing
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