Type of Document Dissertation Author Westberry, Jenne Mitchell Author's Email Address email@example.com URN etd-11132003-205641 Title Categorization of Pheromonal Chemosignals by Medial Amygdala Degree Doctor of Philosophy Department Biological Science, Department of Advisory Committee
Advisor Name Title Michael Meredith Committee Chair Keywords
- Vomeronasal Organ
Date of Defense 2003-11-03 Availability unrestricted AbstractIndividual members of many species use chemical signals detected by the vomeronasal system to communicate with other members of the same species. Over the past two decades, research in the chemical senses field has focused on peripheral detection and processing of chemosensory signals by the vomeronasal organ (VNO). Not as much focus has been placed on central processing of these signals once they are detected and communicated to the accessory olfactory bulb (AOB). The studies included in this dissertation were designed to investigate neuronal activation in the medial amygdala, an area of the brain that gets direct input from the accessory olfactory bulb (AOB). Based on immediate early gene (IEG) expression in activated neurons, I found that the medial amygdala responded differently to pheromonal chemosignals from animals that were conspecific (same species) versus heterospecific (different species). The anterior medial amygdala (MeA) responded to both, but posterior medial amygdala (MeP) responded only to conspecific stimuli and was suppressed during responses to heterospecific stimuli or artificial (non-biological) stimuli. These data provide the first report of categorical discrimination of chemosensory signals in the medial amygdala. This categorization was not apparent in the AOB so it appears to reflect a second level of sensory analysis. Additional studies indicated a reciprocal relationship between activation in MeP and in adjacent inhibitory intercalated nucleus (ICN) cells. MeP is the brain area that only responded to conspecific stimuli. Its lack of activation in MeP with heterospecific stimuli is accompanied by selective suppression in MeP neurons expressing GABA-a Receptor and occurs concurrently with significant activation in GABA immunoreactive cells of the adjacent ICN. The ability of neurons in medial amygdala to show a discrimination between conspecific and heterospecific stimuli was not dependent on main olfactory input and MeA is the first place in the vomeronasal pathway where all the information from rostral and caudal accessory olfactory bulb comes together. Immediate early gene expression does not reveal all the neural activity of the brain, but within the limits of this method all indications are that discrimination occurs in the anterior medial amygdala.
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