Discrimination of Male Social Status by Female Hamsters

This study was conducted to determine whether urinary ol-factants were capable of communicating information about a male's dominance status to females. Voided urine was collected from pairs of dominant and subordinate males. These odors were simultaneously presented to females in a Y-maze olfactometer. Females in estrus spent more time in proximity to the area infused with the odors associated with dominant males. Females, when tested while in diestrus, apparently preferred the odors of submissive males. It is hypothesized that male urinary odors influence male attractiveness and might provide the female with a basis for mate selection.

Attack priming in female Syrian golden hamsters is associated with a c-fos-coupled process within the corticomedial amygdala

Allowing a resident hamster a single "priming" attack on a conspecific induces a transient aggressive arousal as indicated by a reduction in the latency and increase in the probability of attack on a second intruder presented within the next 30 min. We present two lines of evidence identifying the corticomedial amygdala as an important locus mediating this effect. (1) Attack priming significantly increases the number of neurons expressing immunocytochemically identified Fos protein in the corticomedial amygdala, but not elsewhere. Pursuit and biting of an inanimate object does not induce corticomedial amygdala c-fos expression of the same pattern or magnitude. The corticomedial amygdala contribution to the priming effect involves more than a non-specific arousal, since corticomedial amygdala c-fos expression does not correlate with locomotor activity, a standard indicator of such arousal. (2) Radiofrequency lesions of the corticomedial amygdala reduce aggression, the greatest reduction occurring with the more anterior lesions. Other behaviors, including a priming-like locomotor practice effect in a running wheel, are unaffected by corticomedial amygdala lesions. These findings suggest that attack priming is an aggression-specific effect resulting from a Fos-coupled change within neural circuitry of which the corticomedial amygdala is a part. From a theoretical point of view, these experiments suggest a new approach to the analysis of the mechanisms underlying aggressive behavior and the persistence of aggressive arousal. We present a sketch of a quantitative neurobehavioral model which relates attack probability to neural activation within the corticomedial amygdala. From a methodological viewpoint, these experiments extend the utility of mapping c-fos expression as a technique for localizing endogenous, behavior-specific processes within the central nervous system.

Female discrimination of male dominance by urine odor cues in hamsters

Female hamsters have been found to differentially respond to the odors of dominant as opposed to subordinate males. This study reexamined these responses in an olfactometer allowing the females to choose between urinary odors obtained from males differing in dominance status and clean air source. The behavior of the estrous females was consistent with previous research which indicated that such females exhibit a preference for stimuli obtained from dominant males. Contrary to previous findings in a two-choice apparatus, diestrous females failed to prefer the odors of subordinates. These females spent significantly more time in the area infused with unscented air. These data emphasize the importance of odor cues as they relate to male attractivity and possibly mate choice. They also underscore the need to allow animals to avoid conspecific odors in order to reduce the possibility of forcing animals into an unrealistic choice situation.

The attractiveness of Harderian gland smears to sexually naive and experienced male golden hamsters

The Harderian gland of the golden hamster shows pronounced sexual dimorphism in histology and products. Sexually experienced or inexperienced males were attracted to fresh smears of female and male Harderian gland as opposed to a control. Female smears were investigated significantly more than male smears. Control smears of quadriceps muscle proved unattractive. Neither category of male preferred oestrus to mid-cycle Harderian smears, and attractiveness did not correlate with protoporphyrin content. Males were unattracted to protoporphyrin solution. Cephalic olfactory cues, such as Harderian secretions, may be of importance in tunnel-dwelling rodents.

Olfactory stimulation and olfactory bulb removal: effects on territorial aggression in male Syrian golden hamsters

The Syrian golden hamster exhibits territorial aggression in a laboratory setting, attacking much more when in the home cage than in the cage of another hamster. In expt. 1 it was found that female hamster vaginal discharge (FHVD) greatly inhibits the territorial aggression of males. In expt. 2 it was found that hamster territorial aggression is almost completely eliminated by bilateral olfactory bulbectomy but is unaffected by unilateral olfactory bulbectomy. However, bilateral olfactory bulbectomized (BOB) hamsters fought back normally if attacked first. Blinding increased the territorial aggression of male hamsters. In expt. 3 a peripheral means of impairing olfaction was used. The results suggest that it is the olfactory impairment, rather than the loss of some hypothetical non-sensory functions of the olfactory bulbs, that causes the elimination of territorial aggression after olfactory bulbectomy. Because of the extensive secondary and tertiary olfactory projections to the limbic forebrain and hypothalamus, and because most laboratory mammals are macro-osmatic, the nature and degree of olfactory control should be an important consideration in studies on the neural basis of social behavior.