Chemical signals are important for social communication in many rodent species. Detection and processing of these chemosignals is necessary for the production of reproductive and defensive behaviors that are important for species survival. The medial amygdala is the first site of convergence for input regarding these chemosignals, thus it is vital to investigate its role in chemosignal processing. Previous studies using immediate early gene (IEG) expression indicative of neuronal activation have demonstrated a categorical response in the medial amygdala subareas to different types of chemosignals. Both the anterior and posterior medial amygdala (MeA and MeP, respectively) show higher activation after exposure to conspecific odors, while only MeA has a higher response to heterospecific odors. These experiments also suggest that the primarily GABAergic, main intercalated nucleus (m-ICNc) may be involved in modulating the MeP response since there is a negative correlation in the IEG responses between these two areas after exposure to heterospecific odors. These data suggest that the medial amygdala and possibly the m-ICNc are involved in the processing of chemosignals, however little is known about the functional circuitry underlying chemosignal processing within and between these two areas. Using whole-cell patch clamp electrophysiology and immunohistochemical staining, the experiments included in this dissertation investigated the functional circuitry between the medial amygdala areas; the connections between the medial amygdala and m-ICNc; how this circuit may be modulated by input from other brain areas; and the potential involvement of phenotypically distinct subpopulations during chemosignal processing. Consistent with previous tract-tracing studies, I demonstrated functional excitatory and inhibitory connections between the anterior-dorsal (MeAd) and posterior dorsal (MePd) regions of the medial amygdala in electrophysiology experiments. These diverse connections may provide a means by which MeAd can directly affect MePd activity during chemosignal processing consistent with previously published IEG responses. Further electrophysiology experiments provide evidence for an indirect pathway allowing for even further modulation of MePd by MeAd. In these experiments, I found excitatory projections from MeAd to m-ICNc that were strong enough to drive action potential firing in my thin tissue slices. Projections from m-ICNc to MePd were also documented and stimulation of m-ICNc often resulted in hyperpolarization of MePd neurons. The m-ICNc-evoked hyperpolarization of MePd persisted during glutamate receptor blockade suggesting that there are direct inhibitory connections from m-ICNc to MePd. These data suggest that MeAd may also modulate MePd indirectly providing an even greater diversity of medial amygdala output in order to produce appropriate behavioral responses to various chemosignals. The neurotransmitter dopamine may also be involved in chemosignal processing. Dopamine decreased the excitability of m-ICNc neurons and decreased the m-ICNc-evoked hyperpolarization of MePd neurons, suggesting that this indirect pathway may also be modulated by other brain areas. I also found evidence of projections from infralimbic cortex and the localization of mu-opioid receptors to the m-ICNc. These two inputs may provide even further modulation of the circuitry and greater diversity in medial amygdala output depending on the brain state of the animal during chemosignal processing. Lastly, I investigated the potential role of phenotypically distinct subpopulations of presumably GABAergic medial amygdala neurons characterized by expression of calcium binding proteins in chemosignal processing. I found differential expression patterns of parvalbumin, calbindin and calretinin neurons throughout the medial amygdala areas. Parvalbumin was not expressed in the medial amygdala but was found in other amygdalar areas surrounding the medial amygala. Calbindin and calretinin neurons were found throughout the medial amygdala with different densities across subdivisions. Overall, very few calretinin or calbindin neurons were activated (as indicated by IEG expression) after exposure to the female conspecific odors. However, the overall pattern of activation of calbindin and calretinin-immunoreactive neurons was similar to the overall IEG expression, suggesting that these neuronal subpopulations may be involved in the inhibitory feedback networks within the medial amygdala. / A Dissertation submitted to the Department of Biological Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2017. / January 30, 2017. / accessory olfactory system, chemosensory processing, electrophysiology, hamster, intercalated nucleus, medial amygdala / Includes bibliographical references. / Michael Meredith, Professor Directing Dissertation; Colleen Kelley, University Representative; Emily DuVal, Committee Member; Elaine Hull, Committee Member; Paul Trombley, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_507628 |
| Contributors | Biggs, Lindsey Marie (authoraut), Meredith, Michael (professor directing dissertation), Kelley, Colleen M. (university representative), DuVal, Emily H. (committee member), Hull, Elaine M. (committee member), Trombley, Paul Q. (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Biological Science (degree granting departmentdgg) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (200 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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