Dopamine neurons projecting to distinct brain regions have unique biophysical properties, which is thought to reflect functional specialization. One defining feature is the duration of hyperpolarization-induced firing pauses, or rebound delays, which are longer in atypical dopamine neurons targeting ventromedial striatal areas like the nucleus accumbens core. Differences in rebound delay are determined by Kv4 channel-mediated A-type currents, but the mechanisms underlying these differences and their functional implications are not well understood. We hypothesized that KChIP4a, a unique Kv4 β-subunit splice variant, determines rebound delay duration in atypical dopamine neurons. To test this, we generated a transgenic mouse line with dopamine neuron-selective removal of KChIP4a. We found that KChIP4a deletion shortened rebound delays in core-projecting, atypical dopamine neurons by changing A-type current kinetics, without affecting conventional dopamine neurons. This indicates that KChIP4a acts as a selective biophysical amplifier of hyperpolarizing inhibition in core-projecting dopamine neurons, and computational modelling suggests that this effect is robust across a wide range of in vivo-like conditions of excitation/inhibition balance. Since firing pauses in core-projecting dopamine neurons are thought to drive learning from reward omission, or negative prediction errors, we tested the effect of KChIP4a deletion on different types of behavior in male and female mice. We found that removal of KChIP4a from dopamine neurons selectively accelerated learning from negative prediction errors, without affecting learning from positive prediction errors or other behavioral variables. Together, our results suggest that KChIP4a fine-tunes subthreshold excitability in projection-defined dopamine neuron populations to regulate specific types of learning. Significance statement Dopamine neurons that project to different brain areas have distinct cellular properties that are thought to support their specialized roles in behavior. Uncovering the genetic and molecular underpinnings of this functional diversity is critical for understanding how the dopamine system shapes learning and other behaviors in health and disease. We discovered that KChIP4a, a splice variant of a Kv4 potassium channel modulatory subunit, amplifies inhibition in a population of atypical dopamine neurons by changing the kinetics of Kv4 potassium channels. Moreover, removing KChIP4a from dopamine neurons selectively accelerated learning from reward omission, without affecting other behavioral variables. Our findings reveal a novel cell type-specific, alternative splicing-dependent, biophysical mechanism for fine-tuning distinct components of learning.
Costa et al. (Tue,) studied this question.