Gabriela Izowit - Brain state dependent responses of midbrain dopaminergic neurons

ViDA 2021 - Thur June 24th 2021
Gabriela Izowit
Jagiellonian University
Brain state dependent responses of midbrain dopaminergic neurons’ to the aversive stimulus

​For a long time, it has been assumed that dopaminergic (DA) neurons of the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) respond to reward and aversive stimuli homogenously across the entire population with either increase or decrease of their activity respectively – coding in this manner information about the value of perceived stimuli. This notion was questioned after the identification of midbrain DA neurons that are excited by both rewarding and aversive stimuli. This resulted in division of midbrain DA neurons into two functionally distinct subpopulations: one encoding the value and the other encoding the salience of the stimuli. Additionally, it has been shown that the general state of the brain modulates the electrical activity of midbrain DA neurons, but it remains unknown whether this factor may also influence signalling of value and salience. Our experiments were aimed at answering this question. For this purpose, we recorded responses of VTA and SNc DA neurons to electrical footshocks across alternating brain states of urethane anaesthetized rats. We identified DA neurons based on electrophysiological criteria combined with the use of either juxtacellular recording-labelling technique or optotagging. Besides the previously described populations of value- and salience-coding neurons, we also observed unidentified so far subpopulation of VTA and SNc DA neurons, that changes its type of response to an aversive stimulus depending on the ongoing brain state. Majority of these neurons were inhibited by footshocks during a REM-like brain state, but with the appearance of nREM-like brain state, they changed their type of response to excitation. Based on our observations, it can be hypothesised that there is a subpopulation of DA neurons that are involved in ‘dual-coding’ of both the value and the salience of the stimulus depending on the general state of the brain.