Chantelle Kinzel will present her work during the poster presentation of the Mary Gates Undergraduate Research Symposium. Chantelle's abstract is reprinted below.
· Chantelle Kinzel, Senior, Psychology
· Sheri Mizumori, Psychology
Ventral tegmental area (VTA) dopaminergic cell firing encodes reward information and has been implicated in reinforcement learning, spatial memory and decision-making. However the mechanisms which modulate VTA dopaminergic burst firing are not well known. A division of the mesonpontine tegmentum, the laterodorsal tegmental nucleus (LDTg) provides inputs into the VTA. Inactivation of the LDTg greatly reduces VTA dopaminergic burst firing, implicating the LDTg’s role in permitting VTA activity. In the current study we sought to determine the nature of the information coded by LDTg neurons in order to better understand the type of information that regulates dopamine cell activity. We assessed this by neurophysiological single unit recordings of LDTg cell activity in freely behaving rats. Rats were trained on an 8-arm radial maze, which required spatial and working memory in order to, without errors, forage for large and small rewards located at the end of arms. Experimental manipulations consisted of omitting expected rewards, switching the location of rewards of different magnitudes and imposing darkness during the maze trials. We recorded a total of 83 different cells, which were histologically confirmed to be located in the LDTg. We found a large number of reward-related cells (9.6% became excited when rats encountered reward, 8.4% showed excitation in anticipation of reward, 4.8% showed excitatory, then inhibitory and then excitatory responses around the time of reward) and movement related cells (76% were correlated with the rat’s velocity). The large proportion of velocity-correlated cells supports the LDTg’s role in motor behavior. Context and reward manipulations did not consistently affect the firing rate of LDTg cellular activity. However, the current study demonstrates that with 25% of LDTg cells exhibiting reward-related responses, the LDTg has a role in reward encoding by a permissive affect on VTA dopaminergic burst firing.