Flexible Value Encoding by Ventral Tegmental Area Dopamine Neurons

The ability to flexibly encode the value of environmental stimuli is crucial for survival. Dopamine’s role in reward has been well-established, but its role in the encoding of aversion remains controversial. Currently, there are discrepancies in the methodological approaches used to study aversion. Aversive stimuli can oftentimes be avoided by animals making it difficult to measure responses accurately and consistently. To circumvent this issue, we used intra-oral catheters and in vivo fiber photometry in the ventral tegmental area (VTA) to measure dopamine activity following unavoidable, intra-oral delivery of taste stimuli. Infusions of a rewarding solution (0.3 M sucrose) briefly elevated, while infusions of an aversive solution (0.001 M quinine) briefly suppressed VTA dopamine activity. Next, to address whether value encoding changes as a function of experience, a conditioned taste aversion (CTA) paradigm was used where one group (Paired; n = 8) of animals received one visceral malaise inducing injection of lithium chloride (LiCl) while another group (Unpaired; n = 7) received a saline injection. As in the first experiment, VTA dopamine activity was measured in vivo in response to intra-oral sucrose on Conditioning Day and five successive extinction days. In addition, animals were subjected to a two-bottle sucrose preference test (SPT) following each extinction session to assay avoidance behavior. Our results demonstrate that VTA dopamine signaling in Paired animals was significantly suppressed relative to Unpaired on extinctions days 1 and 2. Moreover, CTA and SPT data revealed that Paired animals consumed less sucrose on extinction days 1 and 2, relative to Unpaired. Taken together, we show that VTA dopamine neurons can flexibly encode the value of taste stimuli as a function of experience.