Adaptive reproductive behavior requires the ability to recognize and approach possible mating partners in the environment. Syrian hamsters (Mesocricetus auratus) provide a useful animal model by which to study the neural processing of sexual signals, as mate recognition in this species relies almost exclusively on the perception of social odors. In the laboratory, male hamsters prefer to investigate female odors compared to male odors, and this opposite-sex odor preference provides a sensitive measure of the underlying neural processing of sexual stimuli. In addition to chemosensory cues, reproductive behavior in hamsters also requires sufficient levels of circulating gonadal steroid hormones, which reflect the reproductive state of the animal. These chemosensory and hormone signals are processed within an interconnected network of ventral forebrain nuclei, and within this network, the posteromedial cortical amygdala (PMCo) and medial amygdala (MA) are the only nuclei that both receive substantial chemosensory input and are also highly sensitive to steroid hormones. Although a large body of evidence suggests that the MA is critical for generating attraction to sexual odors, the specific role of the PMCo in regulating odor-guided aspects of male reproductive behavior has never been directly tested. Furthermore, detailed analyses of the MA suggest that separate, but interconnected sub-regions within this nucleus process odors differently. Specifically, the anterior MA (MeA) receives the majority of chemosensory input and responds to a variety of social odors, whereas the posterodorsal MA (MePD) receives less chemosensory input but contains the vast majority of steroid receptors. In order to further elucidate how the PMCo and/or MA process sexual odors, this dissertation addressed the following research questions: (1) Is the PMCo required for the expression of either opposite-sex odor preferences or male copulatory behavior? (2) Are functional interactions between MeA and MePD required for the expression of opposite-sex odor preferences? (3) How do MeA and MePD regulate odor responses within the MePD and MeA, respectively? (4) Are odor and/or hormone cues conveyed directly between MeA and MePD? Together, these experiments provide a comprehensive analysis of the functional and neuroanatomical substrates by which the brain processes sexual odors and generates appropriate behavioral responses to these stimuli.

「匂い」は私たちの生活を豊かにする感覚である。しかし、匂い情報が最初に大脳皮質に届く場である嗅皮質において、高次情報がどのように表現・分配されているのかは、不明である。本研究は、匂いを手掛かり刺激とした行動課題遂行中のラット・マウスを対象に、4つの嗅皮質亜領域から神経活動を記録した。そして、各領域のニューロンが異なる高次情報を表現することを発見し、それぞれが独自の機能を発揮する仮説を立案した。 / The olfactory cortex (OC), which consists of some distinct subareas, receives both olfactory sensory signals from the olfactory bulb and top-down signals from higher-order regions. However, it remains unknown as to how each area of the OC encodes for sensory- and behavior-related information. We addressed this issue in rodents, particularly focusing on four subareas of the OC. Using electrophysiological recordings in the OC subareas with an odor-guided go/no-go task, we found that each area showed unique behavioral state signals that were predicted by the cue odors (i.e., moving to the reward port, waiting for the reward, and drinking reward state). / 博士(理学) / Doctor of Philosophy in Science / 同志社大学 / Doshisha University