The infrared trigemino-tectal pathway in the rattlesnake and in the python

Area of Science:

• Neuroscience
• Comparative Anatomy
• Sensory Biology

Background:

• The trigemino-tectal pathway processes sensory information in vertebrates.
• Infrared sensing is crucial for predatory behaviors in certain snake species.

Purpose of the Study:

• To elucidate the neural circuitry of infrared detection in rattlesnakes (Crotalus viridis) and pythons (P. reticulatus).
• To compare the infrared sensory pathways between these two snake species.

Main Methods:

• Utilized horseradish peroxidase (HRP) injections to trace neural projections in both species.
• Employed cobalt chloride injections to map the pit organ's primary projection in rattlesnakes.
• Performed electrophysiological recordings to identify infrared-responsive neurons in the rattlesnake's nucleus reticularis caloris (RC).

Main Results:

• In rattlesnakes, the infrared pathway involves the pit organ projecting to the nucleus of the lateral descending trigeminal tract (LTTD), then to the nucleus reticularis caloris (RC), and finally to the contralateral optic tectum.
• In pythons, a direct projection from the LTTD to the optic tectum was identified.
• Neurons in the rattlesnake RC and larger LTTD cells in pythons showed similar acetylcholinesterase activity and morphology, suggesting a potential common evolutionary origin.

Conclusions:

• The study reveals distinct but related infrared sensory pathways in rattlesnakes and pythons.
• The findings suggest a conserved evolutionary basis for tectal-projecting neurons involved in sensory processing in snakes.