Neuropeptidergic modulation on valence assignment (Postdoc)

During associative learning, distinct of basolateral amygdala (BLA) neurons are assigned with positive and negative valence. However, the specific mechanism underlying the assignment of valence to the appropriate BLA neurons remains unclear.

My postdoctoral project has uncovered a neurotensin (NT) role in mediating valance assignment in the BLA (Li et al., 2022, Nature). Specifically, I found that NT released from the paraventricular nucleus of the thalamus (PVT) mediates BLA ensemble formation of both positive and negative valences and bi-directionally modulates reward and punishment learning in a dose-dependent manner. One challenge was to isolate NT from co-released glutamate, as we had identified that NT inputs to the BLA co-release glutamate. Typical approaches such as optogenetics would inevitably affect glutamate along with neuropeptides and could potentially confound the interpretation of the results. To overcome this, I collaborated with Drs. Feng Zhang and Yulong Li’s labs on adapting CRISPR-mediated Nt gene knockout and validating a genetically-encoded NT sensor. As both approaches showed high specificity to NT, I found that the Nt gene knockout in the PVT^NT-BLA projection promotes punishment learning, while PVT^NT-BLA optogenetic activation promotes reward learning. Consistently, both calcium dynamics in PVT^NT axon terminals and NT sensor dynamics in the BLA are enhanced after reward learning and diminished after punishment learning.

Using functional clustering, and computational analysis, I found that Nt gene knockout in the PVT-BLA blunts BLA encoding of learned valences at both the single-unit and population levels. Furthermore, CRISPR and control groups showed a variety of different behavioral patterns in response to Sucrose and Shock CSs. To identify and quantify potentially different behavioral states, I performed an unsupervised trial-by-trial clustering of behavioral responses to CSs based on automatic pose estimation, and found that Nt knockout reduces the number of trials where mice showed active behavioral responses to CSs.

Taken together, these findings indicate a neuropeptide that signals valence in the BLA, and show that NT is a critical modulator for assigning positive and negative valence in amygdala neurons during associative learning.

Neural circuits encoding negative valence and punished reward seeking (Ph.D.)

‍Dopamine (DA) is one of the major neuromodulators that signal reward and motivation. Studies have shown that DA firing exhibits aphasic pause in response to aversive stimuli, which is thought to mediate behavioral avoidance and punishment learning. However, it was unclear how aversive stimuli could cause DA inhibition, largely because the underlying neural circuits were unknown.

In graduate school, I utilized multiple techniques including optogenetics, in vivo electrophysiology, and endoscopic calcium imaging, to illustrate the role of the rostromedial tegmental nucleus (RMTg), a major inhibitory input to DA neurons, in driving DA inhibition (Li et al., 2019a, Elife) and mediating punished reward-seeking behavior (Li et al., 2019, Neuron). By combining mono-synaptic rabies tracing with cFos immunostaining and in vivo electrophysiology, I identified that a di-synaptic input from the rostral entopeduncular nucleus to the RMTg via the lateral habenula encodes negative valence (Li et al., 2019b, Elife) and cocaine avoidance (Li et al., 2021, J Neurosci).

In collaboration with other lab members, we discovered that the individual differences in cocaine avoidance are correlated with their RMTg activity (Parrilla-Carrero et al., 2022, J Neurosci) and are highly heritable (Eid et al., 2019, BioRxiv).