Coordinated Synchronization in the Electrically Coupled Network of Terminal Nerve Gonadotropin-Releasing Hormone Neurons as Demonstrated by Double Patch-Clamp Study

The peptidergic neurons play important roles such as neuromodulatory and neuroendocrine functions in the central nervous system. However, our knowledge about the organization and the function of the peptidergic neuromodulator systems is still very poor. The terminal nerve GnRH peptidergic neurons of a teleost, the dwarf gourami (Colisa lalia), serve as an excellent model system for such study. The cell bodies are large and make up a tight cell cluster, and the easy access to the cell bodies on the ventral surface of the brain makes the electrophysiological measurements in a precisely controlled manner. Here we show direct evidence to demonstrate the electrical coupling and the synchronization of the neural firing activity among the terminal nerve GnRH neurons by using the double patch-clamp recording technique. The electrical coupling coefficient was strong enough (ranged from 0.083 to 0.370) to synchronize spontaneous firings of GnRH neurons in the cluster. A model, in which the firings in the cluster occur within a small time window (dozens of milliseconds), was verified by using the serial loose-seal extracellular patch-clamp recordings and the cross-correlogram analysis. The present findings provide several insights for understanding the physiological mechanisms and functional significance of synchronized activities in the peptidergic and/or aminergic neuromodulator system as well as in the peptidergic neuroendocrine cells.