Influence of adult castration on the olfactory sensitivity of the male rat: a signal detection analysis.
The effect of adult castration on the male rat's ability to detect ethyl acetate odor was measured with high-precision olfactometry and a go-no-go signal detection task. Castration was found to significantly mitigate the tendency observed in sham castrates to improve detection performance across an l8-week postoperative test period. No significant castration-related alterations on the responsivity or s+ response latency measures were observed. These findings indicate that castration influences the male rat's ability to improve odor detection performance over time, although it is not known whether this effect is attributable to sensory or to memory mechanisms. Although numerous studies have noted that castration decreases the preference of male rats for conspecific estrous odor (cf. Brown, 1977; Carr, Loeb, & Dissinger, 1965; LeMagnen, 1952a), the influence of this operation on olfactory sensitivity per se has received little attention. The sole study on this topic (Carr , Solberg, & Pfaffmann, 1962) found no influence of castration performed at 22 days of age on detection thresholds for estrous urine in 3-month-old male rats. Unfortunately, this pioneering study was limited by a relatively short postcastration testing interval and by the lack of repeated postcastration tests. A more definitive test of the influence of castration on olfactory sensitivity would be to repeatedly assess smell function across a somewhat longer postcastration interval, because the influences of castration on some behavioral parameters can be delayed. For example, the ability to mount and ejaculate can be maintained for a number of postcastration months (Davidson, 1966), even though some morphological changes occur within a day or two of castration (e.g., regressive changes in the sexual accessory glands; cf. Price & Williams-Ashman, 1961 ). The purpose of the present study was to examine, using high-precision olfactometry and a go-no-go operant signal detection task, the effects of adult castration on signal detection measures of olfactory sensitivity and response bias in male rats repeatedly tested across a relatively long postcastration period.