Taste helps establish food preference and the neural processing of taste aspect of food reward starts from the gustatory system. The gustatory information via cranial nerves reaches the brain first in the nucleus of the solitatory tract (NST). Parabrachial nucleus (PBN) receives the excitatory glutamatergic input from the NST and has been shown to control feeding. In addition, PBN is also necessary to convey hedonic information of taste stimuli. Given that PBN sends substantial projections to midbrain dopamine neurons, it raises the possibility that taste stimuli may engage dopamine neurons in the ventral tegmental area (VTA) via PBN to modulate food intake. Thus, in the present study, we set out to study the functional connection between PBN and VTA in food consumption. We first carried out in situ hybridization to verify the neuronal types in PBN. In the past, locally electrical stimulation or pharmacological manipulation has the limitation to characterize defined connections. Thus, we would employ optogenetic approach by selectively express channelrhodopsin (ChR2) in specific Cre transgenic mouse line to target specific subtype of PBN neurons. Littermates of the same mouse line were injected with cre-dependent virus encoding EYFP alone into PBN to serve as control group to rule out confounding variables such as surgery procedures. We specifically tweaked PBN-to-VTA afferent input by delivering 473 nm blue light to the VTA via fiber optics while mice were performing behavioral task. The preliminary results showed that VTA receives functional inputs from the PBN and photostimulation of PBN-to-VTA input affects food consumption. In addition to my own project, I also contribute to another research with Dr. Dong Wang and Dr. Ikemoto Satoshi. We focused on studying modulation of neuronal oscillation in conditioned fear paradigm. By combining optogenetics and in vivo simultaneous electrophysiology recordings in freely-moving mice, our study exhibited that optical stimulation of subcortical median raphe nucleus to hippocampal ripple oscillation during sleep impairs hippocampus-dependent fear memory. This work was published in Nature Neuroscience in 2015.

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National Institute on Drug Abuse
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