Heartbeat control in leeches. II. Fictive motor pattern

Area of Science:

• Neuroscience
• Comparative Physiology
• Biophysics

Background:

• The medicinal leech's heartbeat is controlled by segmental heart motor neurons.
• These neurons receive rhythmic inhibitory input from a heart interneuron network, forming the heartbeat central pattern generator (CPG).
• Previous work identified two distinct heart coordination modes (peristaltic and synchronous) and their switching in intact leeches.

Purpose of the Study:

• To analyze the intersegmental and side-to-side coordination of the fictive motor pattern for heartbeat in denervated nerve cords.
• To determine if sensory feedback is necessary for intersegmental coordination.
• To investigate the central mechanisms underlying coordination mode switching.

Main Methods:

• Analysis of the fictive motor pattern for heartbeat in denervated leech nerve cords.
• Electrophysiological recordings of segmental heart motor neuron activity.
• Comparison of fictive motor patterns with previously observed constriction patterns in intact animals.

Main Results:

• Intersegmental phase relations among heart motor neurons were independent of the heartbeat period in both coordination modes.
• The fictive motor pattern's intersegmental and side-to-side coordination closely matched that of intact leeches.
• The fictive motor pattern exhibited regular switches in coordination mode, mirroring those in intact animals.

Conclusions:

• Sensory feedback is not essential for the proper intersegmental coordination of leech heartbeat.
• The observed coordination modes and their switching likely originate from a central neural mechanism within the CPG.
• This study provides insights into the neural basis of rhythmic motor control and coordination in invertebrates.