Browsing by Subject "dopamine"

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    Distribution and diversity of intrinsically photosensitive retinal ganglion cells in tree shrew.
    (The Journal of comparative neurology, 2017-12-14) Johnson, Elizabeth N; Westbrook, Teleza; Shayesteh, Rod; Chen, Emily L; Schumacher, Joseph W; Fitzpatrick, David; Field, Greg D
    Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate the pupillary light reflex, circadian entrainment, and may contribute to luminance and color perception. The diversity of ipRGCs varies from rodents to primates, suggesting differences in their contributions to retinal output. To further understand the variability in their organization and diversity across species, we used immunohistochemical methods to examine ipRGCs in tree shrew (Tupaia belangeri). Tree shrews share membership in the same clade, or evolutionary branch, as rodents and primates. They are highly visual, diurnal animals with a cone-dominated retina and a geniculo-cortical organization resembling that of primates. We identified cells with morphological similarities to M1 and M2 cells described previously in rodents and primates. M1-like cells typically had somas in the ganglion cell layer, with 23% displaced to the inner nuclear layer (INL). However, unlike M1 cells, they had bistratified dendritic fields ramifying in S1 and S5 that collectively tiled space. M2-like cells had dendritic fields restricted to S5 that were smaller and more densely branching. A novel third type of melanopsin immunopositive cell was identified. These cells had somata exclusively in the INL and monostratified dendritic fields restricted to S1 that tiled space. Surprisingly, these cells immunolabeled for tyrosine hydroxylase, a key component in dopamine synthesis. These cells immunolabeled for an RGC marker, not amacrine cell markers, suggesting that they are dopaminergic ipRGCs. We found no evidence for M4 or M5 ipRGCs, described previously in rodents. These results identify some organizational features of the ipRGC system that are canonical versus species-specific.
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    Dopamine Dynamics Drive Birdsong Learning
    (2024) Qi, Jiaxuan

    While learning in response to extrinsic reinforcement is theorized to be driven by dopamine signals that encode the difference between expected and experienced rewards, skills that enable verbal or musical expression can be learned without extrinsic reinforcement. Instead, spontaneous execution of these skills is thought to be intrinsically reinforcing. Whether dopamine signals similarly guide learning of these intrinsically reinforced behaviors is unknown. Juvenile zebra finches are distinguished by their ability to copy the song of an adult tutor, a spontaneous, intrinsically reinforced process. Here, I use the zebra finch as a model system to study the neural mechanisms that operate within a song-specialized region of the basal ganglia (sBG) to enable this remarkable form of motor learning. Using in vivo microdialysis and computational methods to quantify juvenile song development, I first determined that dopamine (DA) signaling in the sBG is necessary for song learning. Using genetically encoded DA sensors and fiber photometry, I showed that DA dynamics in the sBG faithfully track the learned quality of juvenile song performance on a rendition-by-rendition basis. Consequently, my experiments provide compelling evidence that DA functions in the sBG as a reward prediction error-like signal to drive song learning, a process that evolves spontaneously and does not depend on extrinsic reward or punishment. Furthermore, I found that DA release in the sBG is driven not only by inputs from midbrain DA neurons classically associated with reinforcement learning but also by song premotor “cortical” inputs, which act via local cholinergic signaling in the sBG to elevate DA during singing. While I was able to show that both cholinergic and dopaminergic signaling in the sBG are necessary for song learning, I further found that only DA tracks the learned quality of song performance. Therefore, dopamine dynamics in the basal ganglia encode performance quality to drive self-directed and long-term learning of natural behaviors.