THE SUPRAMAMMILLARY NUCLEUS IN MOTIVATED BEHAVIORS
Kesner, Andrew J
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Motivated behaviors ultimately manifest through reward and aversion processes – where animals must appropriately approach positive ‘rewarding’ stimuli and avoid negative ‘aversive’ stimuli in order to survive. The neural mechanisms mediating these basic processes are not yet fully understood. The supramammillary nucleus (SuM) is a small posterior hypothalamic nucleus that has connections throughout the cerebrum. It is known that stimulation of SuM neurons is rewarding, however, little else is known about the neuronal mechanism that mediate this reward or the role this region plays in motivated behaviors. In this dissertation I describe my research using both classical and modern system neuroscience techniques to elucidate the role of the SuM in motivated behaviors. In experiments described in chapter 2, I used optogenetics to stimulate specific populations of SuM neurons and found that stimulation of distinct subpopulations of SuM neurons and their downstream targets induces either reward or aversion. Next, the experiments described in chapter 3 tested correlation and causation of SuM activity in reward seeking behaviors. The neurons in the SuM showed single-unit activity patterns that correlate to various aspects of reward-seeking behaviors and inhibition of this brain region disrupted reward-seeking but not reward-consuming behaviors. Lastly, in chapter 4, I provide evidence that dopamine is involved in the perceived reward from stimulation of SuM neurons, and compare brain activation from optogenetic stimulation of a canonical reward pathway and the novel reward pathway described in this dissertation. These data identify the SuM as a potential locus for future research into neural mechanisms of approach and avoidance, and psychiatric disorders such as addiction, depression, and anxiety, that result from maladaptations in these basic behaviors.