Stretch receptors in urodele limb muscles

Area of Science:

• Neuroscience
• Comparative Anatomy
• Muscle Physiology

Background:

• Non-encapsulated, beaded nerve endings have been observed in amphibian limb muscles.
• The exact function and location of these nerve endings require further investigation.

Purpose of the Study:

• To histologically and physiologically characterize novel nerve endings found on amphibian muscle fibers.
• To determine the type of muscle fibers innervated by these sensory endings.
• To compare the physiological responses of these endings to known sensory receptors.

Main Methods:

• Histological examination of newt and axolotl limb muscles.
• Histochemical and ultrastructural characterization of innervated muscle fibers.
• In vivo electrophysiological recordings of afferent nerve activity in axolotls during muscle stretch.

Main Results:

• Non-encapsulated, beaded nerve endings were found on superficial muscle fibers (Type 1 and Type 2) in newts and axolotls.
• Innervated muscle fibers exhibited distinct histochemical and ultrastructural properties.
• Electrophysiological recordings revealed afferent responses analogous to those of muscle spindles.

Conclusions:

• The identified nerve endings are likely sensory in nature, potentially functioning as proprioceptors.
• These sensory endings innervate specific muscle fiber types in amphibians.
• The findings contribute to understanding proprioception in lower vertebrates.