Epithelial conduction in hydromedusae.

Area of Science:

• * Marine Biology
• * Neurobiology
• * Electrophysiology

Background:

• * Electrophysiological studies on hydromedusae (Sarsia, Euphysa) reveal nonnervous conducting epithelia.
• * These tissues exhibit properties similar to those previously observed in siphonophores.
• * Understanding epithelial conduction is crucial for comprehending primitive nervous system function.

Purpose of the Study:

• * To investigate the electrophysiological properties of nonnervous conducting epithelia in hydromedusae.
• * To characterize the nature of electrical signal propagation within these epithelial tissues.
• * To explore the interaction between nervous and nonnervous conduction systems.

Main Methods:

• * Electrophysiological recordings using suction electrodes.
• * Application of electrical stimuli to induce and measure epithelial responses.
• * Pharmacological manipulation (e.g., Mg(++) concentration) to differentiate nervous and nonnervous activity.

Main Results:

• * Nonmuscular epithelia exhibit all-or-none, nondecremental, unpolarized electrical signal propagation.
• * Conduction velocities range from 15-35 cm/sec with biphasic pulses (0.75-2.0 mv, 5-15 msec).
• * Myoepithelium shows composite events (2.0-4.0 mv, 150-300 msec) linked to muscle contraction.

Conclusions:

• * Nonnervous epithelia in hydromedusae function as independent conduction systems.
• * These systems can be excited by and can excite the nervous system, but spontaneous activity originates neurally.
• * Epithelial conduction is distinct from nervous conduction, as evidenced by differential responses to Mg(++).