Venue: Centre Broca
Language of presentation : English
IINS
Thesis supervisor : Mario Carta
Title
Two types of layer 5 pyramidal neurons in the gustatory cortex show differential plasticity during safe-taste learning
Abstract
The gustatory system is essential for survival, allowing organisms to evaluate the sensory properties, hedonic value, and safety of sampled substances and thereby guiding feeding behaviors. These behaviors are continuously shaped by experience and learning, leading to preferences for safe and nutritionally relevant foods while promoting the avoidance of potentially harmful substances. A well-studied example of this form of learning is the transition from taste neophobia, the initial reluctance to consume a novel food, to familiarization, characterized by increased consumption once the food is established as safe. Several brain structures are essential for this transition, among which the gustatory cortex (GC) is of particular relevance. Located within the insular cortex, the GC plays a key role in integrating and processing gustatory information and in behaviors associated with taste memories. Although numerous studies have established the involvement of the GC in these processes, the cellular and synaptic mechanisms underlying the formation of these taste memories remain incompletely understood. I hypothesized that GC layer 5 pyramidal neurons (L5PNs), given their capacity to integrate sensory and higher-order inputs across their dendritic arbors and their role as major cortical output neurons, are well positioned to contribute to these processes.
Using the mouse as a model system, I employed single-cell electrophysiology, optogenetic manipulation and behavioral assays combined with activity reporters to investigate the organization and experience-dependent plasticity of GC L5PNs. I identified two major L5PN types with distinct electrophysiological and morphological properties (thick-tufted and slender-tufted L5PNs) and developed an approach to reliably predict L5PN type based solely on morphology. I then characterized synaptic inputs from the gustatory thalamus and basolateral amygdala, two major afferent pathways that convey distinct information relevant to taste processing. These axonal projections were spatially segregated within the GC, and light-evoked responses differed depending on both L5PN type and input source. Finally, we investigated experience-dependent changes in the electrophysiological properties of GC L5PNs during the transition from a novel to a familiar taste. Novel taste exposure induced distinct, L5PN type-specific electrophysiological changes that were differentially modified as the taste became familiar.
Together, these findings reveal distinct spatial distributions of thalamic and amygdalar inputs within the gustatory cortex, along with L5PN type- and input-dependent differences in synaptic response properties. They further demonstrate differential experience-dependent plasticity across L5PN populations during novel taste exposure and familiarization. This work provides a cellular and circuit framework for understanding how gustatory experience reshapes cortical networks in the context of taste memory formation.
Keywords: sensory processing, gustatory cortex, synaptic circuits, safe taste memories, electrophysiology, activity reporters
Jury
- Dr. François Georges (president)
- Dr. Rebecca Ann Piskorowski (spokesperson)
- Dr. Belén Pardi (spokesperson)
- Dr. Elena Avignone (examinator)
- Dr. Desdemona Fricker (examinator)
- Dr. Mario Carta (Thesis supervisor)