The microvasculature of python pit organs: morphology and blood flow microkinetics

Area of Science:

• Comparative anatomy
• Sensory biology
• Herpetology

Background:

• Boid and crotaline snakes have infrared sensing pits with functional similarities but morphological differences.
• Boid pits are simpler, more numerous, and located in labial scales, unlike the complex, paired facial pits of crotalines.

Purpose of the Study:

• To investigate the capillary bed morphology and blood flow microkinetics in the infrared pits of the ball python (Python regius).
• To compare these findings with the known conditions in crotaline snakes to understand infrared sensing mechanisms.

Main Methods:

• Utilized Doppler blood flow recorder and electrocardiograph to measure blood flow and heart rate.
• Employed resin casting, transmission electron microscopy, and laser confocal microscopy for capillary morphology analysis.
• Applied immunohistochemical staining to identify pericytes and smooth muscle actin.

Main Results:

• Infrared stimulus evoked nearly identical blood flow responses in both boid and crotaline snakes.
• The ball python's pit capillary bed features vertically oriented loops with domes contacting the receptor layer.
• Pericytes with smooth muscle alpha-actin labeled processes were observed constricting capillaries and domes.

Conclusions:

• The capillary network in boid snake pits responds rapidly (as fast as 1 ms) under local control.
• This system efficiently provides nutrition and cooling to heat-sensitive receptors.
• Mitochondria-rich receptors coupled with a swift cooling system represent an optimal biological solution for infrared imaging.