Pacemaker activity in hydra is modulated by glycine receptor ligands

Area of Science:

• Neurobiology
• Evolutionary Biology
• Developmental Biology

Background:

• Glycine is a neurotransmitter in the mammalian central nervous system, acting on inhibitory strychnine-sensitive glycine receptors (GlyR) and excitatory NMDA receptors.
• Hydra possess two primary pacemaker systems: the endodermal rhythmic potential (RP) system for elongation and the ectodermal contraction burst (CB) system for contraction.

Purpose of the Study:

• To investigate the effects of glycine and its modulators on the RP and CB pacemaker systems in hydra.
• To explore the potential presence and function of vertebrate-like glycine receptors in a simple invertebrate model.

Main Methods:

• Electrophysiological recordings were used to measure the activity of the RP and CB systems.
• Pharmacological agents including glycine, taurine, strychnine, and indole-2-carboxylic acid (I2CA) were applied to hydra.

Main Results:

• Glycine decreased the activity of the CB system (rate of contraction bursts, pulses per burst, and burst duration).
• Glycine, when combined with I2CA (a blocker of the strychnine-insensitive glycine site), decreased RP activity but not CB activity, an effect mimicked by taurine.
• Strychnine increased RP duration and decreased CB duration, counteracting the effects of glycine with I2CA.

Conclusions:

• The results suggest that a vertebrate-like strychnine-sensitive glycine receptor (GlyR) may modulate the endodermal RP system in hydra.
• A glycine site on an NMDA receptor-like system may be involved in regulating the ectodermal CB system in hydra.