Taste Bud Connectome: Implications for Taste Information Processing

Area of Science:

• Neuroscience
• Sensory Biology
• Cell Biology

Background:

• Taste buds are complex sensory organs containing distinct cell types responsible for transducing specific taste qualities (sweet, bitter, umami, sour).
• Understanding the intricate connectivity between these taste receptor cells and afferent nerve fibers is crucial for deciphering taste perception mechanisms.

Purpose of the Study:

• To investigate the degree of interaction between different taste cell types (Type II and Type III) within taste buds.
• To determine the specificity of connectivity between taste receptor cells and afferent nerve fibers (NFs).

Main Methods:

• Utilized serial blockface scanning electron microscopy (sbfSEM) to image five circumvallate mouse taste buds in high resolution.
• Analyzed synaptic contacts between taste receptor cells and 127 identified afferent nerve fibers within the sampled volume.

Main Results:

• Rare direct synaptic contacts were observed between Type II and Type III taste cells.
• Approximately 70% of NFs innervated a single taste cell, while others innervated multiple cells of the same type.
• A small subset of NFs (∼3%) synapsed with both Type II and Type III cells, indicating multimodal innervation.

Conclusions:

• Direct synaptic interaction between taste cell types is minimal, suggesting indirect communication pathways.
• The presence of nerve fibers connecting to multiple taste cell types challenges a strict "labeled-line" model for taste coding.
• Variations in synaptic connections and nerve fiber innervation suggest complex encoding of taste quality and concentration.