The Medial Amygdala Controls the Coital Access of Female Rats: A Possible Involvement of Emotional Responsiveness

Abstract

Partner preference and paced mating tests were accomplished in ovariectomized female rats 10 following bilateral radiofrequency lesions in the medial amygdala. Open field behavior and passive avoidance learning were also examined to investigate the underlying behavioral mechanism. Partner preference was determined in a chamber located between castrated and sexually active males. Airborne olfactory cues were presented to the female through small holes on the partition. The lesion diminished preference for the odor of sexually active males over that of castrated males, even after injection with 15 high-dose of estrogen. On the other hand, in a paced mating test, the lesioned females without estrogen treatment showed a significantly shorter latency for entering the male's compartment in a two-compartment apparatus, which allowed the females, but not the males, to cross the barrier through a narrow opening at the bottom. However, administration of estrogen and progesterone reduced the effect. The lesion had no effect on emotionality or exploratory behavior in an open field test, but impaired passive avoidance learning 20 capability. We suggest that a male poses an inherent threat to a female. The seemingly incompatible results of partner preference and paced mating tests can be compromised if the male is inherently aversive to the female; this emotional response can be removed by the medial amygdala lesion. [The Japanese Journal of Physiology 55(6), 2005, in press] Key words: female sexual behavior, partner preference, paced mating, medial amygdala, estrogen. 25In the wild rat, sexual interactions are initiated and paced by females in estrus through patterns of approach toward and withdrawal from sexually active males [15]. Although some components of female sexual behavior imply the appetitive aspect, the initiative by females, however, is obscured by male active pursuit when tested in ordinary laboratory situation such as in an aquarium. To solve this problem, several researchers are directing attention to paced mating situation, mimicking wild environment [14, 38]. In the 30 paced mating, female rats can stay a place inaccessible for males and visit a compartment for mating with stimulus males. The situation allows females to regulate their own copulatory pacing without disturbance by males. Pacing behavior, then, is thought to reflect their sexual motivation.Olfactory preference toward sexually active males is also affected by female sexual motivation. When presented odors of sexually active and inactive males, sexually motivated females spend longer time to 35 explore odors from sexually active males. This test also measures female sexual motivation without influence by stimulus male behavior [43].Since the body of our knowledge on neural circuits for female sexual behavior has been accumulated by studying lordosis, a reflexive component of female rat sexual behavior, some researchers start on reevaluation of the regulatory mechanisms of female sexual behavior by means of these test paradigms [16, 4...

Disruption of urinary odor preference and lordosis behavior in female mice given lesions of the medial amygdala

“…In general, the present data corroborate previous reports of olfactory deficits after Me lesions in female hamsters [33] and rats [34]. Male hamsters that received lesions targeted at either the anterior or posterior Me showed a reduced preference for volatiles from female-soiled over male-soiled bedding in Y-maze tests [17].…”

“…It was concluded that such high levels of investigation toward both stimuli reflected males' inability to categorize the relevance of odor stimuli. Furthermore, it has been observed in rats that lesions of the entire Me diminished the preference for testes-intact over castrated male volatiles in females in which air was blown over a stimulus male into the female compartment [34]. In the present study, female mice that received anterior Me lesions did not spend more time investigating both odors when compared to sham females.…”

Estrogen-Induced Sexual Incentive Motivation, Proceptivity and Receptivity Depend on a Functional Estrogen Receptor α in the Ventromedial Nucleus of the Hypothalamus but Not in the Amygdala

“…This structure receives projections both from the main and accessory olfactory systems, and olfactory stimuli are crucial for the activation of approach behaviors [reviewed in [22]]. Lesion of the medial posterodorsal amygdala (MePDA) reduces these behaviors in female rats [23,24]. Furthermore, there is a substantial projection from the amygdala to the VMN [25], suggesting that olfactory stimulation reaches the VMN via the amygdala.…”

6-Hydroxydopamine lesions of the anteromedial ventral striatum impair opposite-sex urinary odor preference in female mice

“…These salient chemosignals (often referred to as pheromones) are detected by the main (MOS) and accessory olfactory systems (AOS) and relayed to the medial amygdala (Me). The Me is critical for odor-guided courtship and reproductive behaviors in female rodents [2–4]. It sends axonal projections to several downstream targets including the bed nucleus of the stria terminalis (BNST), the medial preoptic area (MPA), ventromedial (VMHvm), and ventrolateral (VMHvl) divisions of the ventromedial hypothalamus, and to numerous ventral striatal targets, including the nucleus accumbens core (AcbC) and shell (AcbSh), ventral pallidum (VP), medial olfactory tubercle (mOT) and islands of Calleja (ICj) [5–7].…”