Pharmacogenetic and whole-brain activity analyses uncover integration of distinct molecular and circuit programs that drive learning

Abstract

Habituation is a foundational learning process critical for animals to adapt their behavior to changes in their sensory environment. Although habituation is considered a simple form of learning, the identification of a multitude of molecular pathways including several neurotransmitter systems that regulate this process suggests an unexpected level of complexity. How the vertebrate brain integrates these various pathways to accomplish habituation learning, whether they act independently or intersect with one another, and whether they act via divergent or overlapping neural circuits has remained unclear. To address these questions, we combined pharmacogenetic pathway analysis with unbiased whole-brain activity mapping using the larval zebrafish. This approach revealed five distinct molecular and circuit modules that regulate habituation learning and identified a set of molecularly defined brain regions associated with four of the five modules. Moreover, we find that in module 1 the palmitoyltransferase Hip14 cooperates with dopamine and NMDA signaling to drive plasticity, while in module 3 the adaptor protein complex subunit Ap2s1 drives habituation by antagonizing dopamine signaling, revealing two distinct and opposing roles for dopaminergic neuromodulation in the regulation of learning. Combined, our results define a core set of distinct modules that act in concert to regulate learning-associated plasticity, and provide compelling evidence that even seemingly simple learning behaviors in a compact vertebrate brain are regulated by a complex and overlapping set of molecular and circuit mechanisms.

Larval Zebrafish as a Model for Mechanistic Discovery in Mental Health

“…Multiple mechanisms of C-start habituation have also been discovered (Wolman et al, 2011;Corradi and Filosa, 2021;Nelson et al, 2022). For example, the persistent form of habituation response in zebrafish that lasts 25 min to 1 h could be inhibited by N-methyl-D-aspartate receptors (NMDAR) antagonists (Roberts et al, 2011).…”

Functional and pharmacological analyses of visual habituation learning in larval zebrafish

“…Recently, we found that long-term habituation of the response of larval zebrafish to sudden pulses of whole-field darkness, or dark flashes (DFs), involves multiple molecularly independent plasticity processes that act to suppress different components of the behavioural response (Randlett et al, 2019). Similar behavioural, pharmacological, and genetic experiments have led to comparable conclusions in acoustic short-term habituation (Nelson et al, 2022), and habituation in C. elegans (McDiarmid et al, 2019a,b), indicating that habituation generally acts via multiple modular plasticity processes. These modules act to mute or shift behavioural responses to repeated stimuli.…”