2025 Theses Doctoral

Investigating the evolution and function of telencephalic neural circuits in the salamander brain

Jaeger, Eliza Catharine Beach

The transition of vertebrates from water to land provided access to novel sensory environments, likely shaping the central neural circuits for processing and integrating diverse inputs. The outcome of this evolutionary process in mammals is exemplified by the expansion and specialization of cortical circuits within the telencephalon, which are crucial for sensory information processing and integration. Whether components of cortical circuit function existed in tetrapod ancestors is not well understood.

Amphibians, as the closest living relatives of amniotes, provide a crucial perspective to the evolution of telencephalic neural circuits. In this dissertation, I use the salamander Pleurodeles waltl to investigate amphibian telencephalic structure and function through molecular profiling, behavioral, and functional experiments. A single-cell atlas of the salamander forebrain places its neuron types in an evolutionary framework, revealing affinities to reptilian DVR and mammalian cortical regions, but no direct counterparts of neocortical excitatory neurons. Behavioral and brain-wide activity mapping show that salamanders exhibit innate responses to predator odor and bright light, recruiting pallial as well as subpallial and hypothalamic circuits.

By generating the first GCaMP salamander transgenic line, I performed Ca2+ imaging to investigate pallial responses to neutral and predator odors. Neurons within lateral (LP) and dorsal (DP) were differentially responsive, with LP more robustly encoding odor identity and DP enriched for context- and valence-sensitive neurons. Finally, I introduce new genetic tools for amphibian neuroscience, including adeno-associated viral (AAV) vectors.

Together, these findings establish Pleurodeles as a model for systems neuroscience and illuminate the evolution and function of neural circuits in the tetrapod forebrain.