Both volatile and nonvolatile molecules are involved in chemosensory communication in rodents. Volatile odors from physically inaccessible estrous females induced increased numbers of c-Fos-positive cells in the preoptic area (POA) and in the cortical nucleus of the amygdala (CoA) of male rats. The numbers of c-Fos-positive cells in the medial nucleus of the amygdala (MeA) increased in response to the nonvolatile odors of bedding soiled with the excreta of estrous females. In an alternate choice paradigm, male rats carrying ibotenic acid lesions in either the MeA or the CoA--or a combination of both--distinguished the odors of estrous females from those of males, although the time spent sniffing the stimuli was diminished. Males with POA lesions showed complete loss of this capability. Males carrying either of the lesions did not detect differences between estrous and anestrous females or between intact and orchidectomized males. Lesions in the POA or MeA severely impaired male sexual behavior, whereas a CoA lesion had no effects. Thus, c-Fos-positive cells in the CoA might be involved in chemosensory transmission relevant to certain social contexts, but not in the execution of male sexual behavior. The POA is indispensable for both olfactory preferences and sexual behavior. The residual olfactory preference in males with MeA or CoA lesions or the combination of both could reflect an additional route for chemosensory transmission from the main olfactory bulb to the POA.
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