Functional characterization of VTA afferents from pedunculopontine tegmental nucleus (PPTg)

我将光遗传刺激与自由活动小鼠的多视电极记录相结合，以研究腹侧被盖区(VTA)的奖赏联想学习和神经活动是如何被VTA传入调节的。VTA在奖励、动机和联想学习中起着至关重要的作用。中脑边缘多巴胺(DA)系统有助于在获得刺激-奖赏联系的过程中建立中性刺激的激励价值。多巴胺神经元在呈现奖赏或奖赏预测线索的过程中会激发相性猝发活动。据认为，DA神经元的爆发活动依赖于传入输入。解剖学和生理学证据使我研究了桥脑脚被盖核(PPTg)在VTA环路中的调节作用及其在调节行为中的作用。我使用光遗传学方法选择性地抑制PPTG谷氨酸或胆碱能传入VTA，以检验这些传入在巴甫洛夫食欲条件反射中的作用。此外，我在自由活动的小鼠身上进行了体内光电极记录，因为它们执行了巴甫洛夫任务，以检查PPTG谷氨酸或胆碱能传入对VTA回路的调节。结果表明，PPTG到VTA的兴奋性输入通过抑制线索辨别，在刺激-奖赏联系的获得中起着关键作用。令人惊讶的是，活体记录实验的结果表明，线索诱发的DA神经元的爆发活动不受PPTG到VTA兴奋输入的光抑制的影响。相反，我观察到光抑制显著影响线索诱导的非DA神经元的神经活动。这提出了一种可能性，即VTA非DA神经元可能在线索-奖赏联系的获得中发挥作用。为了检验这种可能性，在巴甫洛夫条件反射学习过程中，用光遗传抑制方法抑制VTA GABA能或谷氨酸能神经活动。结果表明，抑制VTA、GABA能或谷氨酸能神经活动抑制线索-奖赏联想学习。总之，我的研究揭示了PPTG到VTA通路在调节VTA非DA神经元的活动和线索-奖赏联想学习中发挥着前所未有的作用。 我未来的研究将以这些发现为基础，探索VTA非DA传出物质可能参与线索-奖赏联想学习的可能性。我们的目标是确定在辨别性学习中，哪些被VTA非DA神经元支配的假定靶点是关键的，长期使用滥用物质是否会抑制辨别性学习并影响选择性的VTA非DA传出，并开发一种光学干预技术来挽救学习缺陷。

I combine optogenetic stimulation with multi-optetrode recordings in freely moving mice to study how reward associative learning and neural activities in the ventral tegmental area (VTA) are modulated by VTA afferents. The VTA plays an essential role in reward, motivation and associative learning. The mesolimbic dopamine (DA) system helps establish incentive value for neutral stimulus in acquisition of stimulus-reward associations. Dopamine neurons fire phasic burst activity during presentation of reward or reward predictive cues. It is believed that DA neuron burst activity depends on afferent inputs. Anatomical and physiological evidence lead me to study the regulatory roles of the pedunculopontine tegmental nucleus (PPTg) in VTA circuits and its role in modulating behaviors. I employed optogenetic approach to selectively inhibit PPTg glutamatergic or cholinergic inputs to the VTA in order to examine the contribution of these inputs in Pavlovian appetitive conditioning. Furthermore, I performed in vivo optetrode recording in freely moving mice as they performed a Pavlovian task to examine the regulation of VTA circuits by PPTg glutamatergic or cholinergic afferents. The results show that PPTg-to-VTA excitatory inputs play a critical role in the acquisition of stimulus-reward associations by dampening cue discrimination. Surprisingly, the results from in vivo recording experiments show that cue-elicited burst activity of DA neurons is not affected by photoinhibition of PPTg-to-VTA excitatory inputs. Instead, I observe that photoinhibition significantly impacts cue-elicited neural activity in non-DA neurons. This raised a possibility that VTA non-DA neurons may play a role in acquisition of cue-reward association. To examine this possibility, VTA GABAergic or glutamatergic neural activity is inhibited with optogenetic inhibition approach during Pavlovian conditioning learning. The results show that inhibition of VTA GABAergic or glutamatergic neural activity dampens cue-reward associative learning. In conclusion, my study reveals an unprecedented role of PPTg-to-VTA pathways in modulating the activity of VTA non-DA neurons and cue-reward associative learning. My future research will build on these findings to explore possible involvement of VTA non-DA efferents in cue-reward associative learning. The goals are to determine which putative targets innervated by VTA non-DA neurons are critically required in discrimination learning, whether chronic use of substance of abuse will dampen discrimination learning and impact selective VTA non-DA efferents and develop an optical intervention technique to rescue learning deficits.