The sea lamprey has a primordial accessory olfactory system

Area of Science:

• Olfactory system evolution
• Comparative neuroanatomy
• Vertebrate sensory systems

Background:

• Dual olfactory systems are known in tetrapods, with lungfish possessing the earliest known example.
• Lampreys exhibit a single nasal capsule with two distinct olfactory epithelia: main (MOE) and accessory (AOE).
• The vomeronasal system (VNO) is a key component of dual olfactory systems in tetrapods.

Purpose of the Study:

• To investigate the neural circuits and molecular characteristics of the accessory olfactory epithelium (AOE) in sea lampreys.
• To determine if lamprey AOE serves as a precursor to the tetrapod vomeronasal system.
• To understand the evolutionary origins of dual olfactory systems.

Main Methods:

• Neural tract-tracing techniques were employed to map connections.
• High-throughput sequencing was used for molecular profiling.
• Real-time quantitative PCR (qPCR) confirmed gene expression.

Main Results:

• Neural tract-tracing revealed direct, reciprocal connections between lamprey AOE and the dorsomedial telencephalic neuropil (DTN).
• The DTN showed projections to the dorsal pallium and rostral hypothalamus.
• High-throughput sequencing indicated nearly identical gene expression profiles between MOE and AOE.
• qPCR confirmed the expression of all three known sea lamprey chemoreceptor gene families in the AOE.

Conclusions:

• Sea lampreys possess a primordial accessory olfactory system.
• Anatomical and molecular data suggest a potential chemosensory function for the lamprey AOE.
• This system may represent an early evolutionary stage of the tetrapod vomeronasal system.