Optical recording of oscillatory activity in the absence of external Ca2+ in the embryonic chick olfactory bulb.

• We optically detected oscillatory activity in the embryonic chick olfactory bulb. • Olfactory nerve stimulation induced the oscillation following the EPSP. • The short-term perfusion of a Ca2+-free solution blocked the EPSP and oscillation. • The long-term perfusion of a Ca2+-free solution newly induced oscillatory activity. • The patterns of the oscillatory activity are different between with and without Ca2+. We applied 464/1020-site optical recording systems with a voltage-sensitive dye (NK2761) to the embryonic chick olfactory system and detected oscillatory activity in the olfactory bulb (OB) in the absence of synaptic transmission. In embryonic day 8–10 (E8-E10) chick olfactory nerve (N.I)-OB-forebrain preparations, the removal of Ca2+ from the external solution completely blocked the glutamatergic excitatory postsynaptic potential (EPSP) from the N.I to the OB as well as oscillations following the EPSP. However, a novel type of oscillatory activity was detected in the OB with the long-term perfusion of a Ca2+-free solution. The characteristics of oscillatory activity in the Ca2+-free solution differed from those in normal physiological solution. The present results suggest the existence of a neural communication system in the absence of synaptic transmission at the early stage of embryonic development. [ABSTRACT FROM AUTHOR]