Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260.
Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260
eNeuro. 2023 Sep 7;10(9). doi: 10.1523/ENEURO.0196-23.2023. Print 2023 Sep.
When a Pavlovian cue is presented separately from its associated reward, some animals will acquire a sign tracking (ST) response - approach and/or interaction with the cue - while others will acquire a goal tracking response - approach to the site of reward. We have previously shown that cue-evoked excitations in the nucleus accumbens (NAc) encode the vigor of both behaviors; in contrast, reward-related responses diverge over the course of training, possibly reflecting neurochemical differences between sign tracker and goal tracker individuals. However, a substantial subset of neurons in the NAc exhibit inhibitory, rather than excitatory, cue-evoked responses, and the evolution of their signaling during Pavlovian conditioning remains unknown. Using single-neuron recordings in behaving rats, we show that NAc neurons with cue-evoked inhibitions have distinct coding properties from neurons with cue-evoked excitations. Cue-evoked inhibitions become more numerous over the course of training and, like excitations, may encode the vigor of sign tracking and goal tracking behavior. However, the responses of cue-inhibited neurons do not evolve differently between sign tracker and goal tracker individuals. Moreover, cue-evoked inhibitions, unlike excitations, are insensitive to extinction of the cue-reward relationship. Finally, we show that cue-evoked excitations are greatly diminished by reward devaluation, while inhibitory cue responses are virtually unaffected. Overall, these findings converge with existing evidence that cue-excited neurons in NAc, but not cue-inhibited neurons, are profoundly sensitive to the same behavior variations that are often associated with changes in dopamine release.
当条件刺激与奖赏分离呈现时,一些动物会习得一种标记追踪(ST)反应——接近和/或与刺激物互动,而另一些动物则会习得一种目标追踪反应——接近奖赏的位置。我们之前曾表明,伏隔核(NAc)中由线索引发的兴奋反应编码了这两种行为的活力;相比之下,在训练过程中,与奖赏相关的反应会出现分歧,这可能反映了标记追踪者和目标追踪者个体之间的神经化学差异。然而,NAc 中的大量神经元表现出抑制性而非兴奋性的线索诱发反应,其在条件反射过程中的信号演变尚不清楚。通过对行为大鼠进行单神经元记录,我们发现,NAc 中具有线索诱发抑制的神经元与具有线索诱发兴奋的神经元具有不同的编码特性。在训练过程中,线索诱发的抑制反应会变得更加频繁,并且与兴奋反应一样,可能编码标记追踪和目标追踪行为的活力。然而,线索抑制神经元的反应在标记追踪者和目标追踪者个体之间并没有不同的演变。此外,与兴奋反应不同,线索诱发的抑制反应对线索-奖赏关系的消退不敏感。最后,我们发现,与奖赏贬值相比,线索诱发的兴奋反应大大减弱,而抑制性线索反应几乎不受影响。总的来说,这些发现与现有证据一致,即 NAc 中的线索兴奋神经元而非线索抑制神经元对与多巴胺释放变化相关的相同行为变化非常敏感。
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