Oscillations in the embryonic chick olfactory bulb: initial expression and development revealed by optical imaging with a voltage-sensitive dye

Abstract

In a previous study, we applied a multiple-site optical recording technique with a voltage-sensitive dye to the embryonic chick olfactory system and showed that functional synaptic transmission in the olfactory bulb was expressed at embryonic 6-7-day stages. It is known that oscillations, i.e. stereotyped sinusoidal neural activity, appear in the olfactory system of various species. The focus of the present study is to determine whether the oscillation is also generated in the embryonic chick olfactory bulb and, if this is the case, when the oscillation appears and how its profiles change during embryogenesis. At the early stages of development (embryonic 6- to 8-day stages), postsynaptic response-related optical signals evoked by olfactory nerve stimulation exhibited a simple monophasic waveform that lasted for a few seconds. At embryonic 9-day stage, the optical signal became multi-phasic, and the oscillatory event was detected in some preparations. The oscillation was restricted to the distal half of the olfactory bulb. As development proceeded, the incidence and duration of the oscillation gradually increased, and the waveform became complicated. In some cases at embryonic 12-day stage, the oscillation lasted for nearly a minute. The frequency of the oscillation increased slightly with development, but it remained in the range of theta oscillation during the 9- to 12-day stages. We discuss the ontogenetic dynamics of the oscillation and the significance of this activity in the developing olfactory bulb.

Functional development of olfactory nerve‐related neural circuits in the embryonic chick forebrain revealed by voltage‐sensitive dye imaging

“…Optical signals in these traces comprised the following components: a fast spike-like signal that was prominent at site 1 (OB) and a delayed long-lasting slow signal. Oscillatory activity, which we previously reported (Sato et al, 2016), was not detected in this recording.…”

“…The generation of glutamatergic synaptic connections between the N. I and OB was detected at the embryonic 6-7 day (E6-E7) stage. We then recorded oscillatory activity in the E9-E12 OB and detected developmental changes in its incidence, duration, and frequency (Sato et al, 2016). In the present study, we focussed on olfactory circuits in the forebrain and surveyed their functional development.…”