[Neural circuit analysis using isolated whole brain preparation]

Abstract

Many electrophysiological studies have been conducted on the 'limbic system', which is known to play a crucial role in mnemonic, emotional, and olfactory functions. Because of the difficulty in accessing such deep brain structures under in vivo conditions, in vitro brain slice preparations are often used. Recertly, an isolated whole brain preparation in which multi-synaptic circuits and the intracellular activity they generate are well preserved has also become available. In this paper, we described about the studies of the olfactory circuits by using this unique preparation. This experimental approach combines the advantages of the in vivo experimental condition with those of in vitro slice preparations, i.e. an intact synaptic network, excellent mechanical stability, and control over the ionic and biochemical extracellular environment. In particular, it provides easy access to the limbic system and preserves the neuronal network of the entorhinal-hippocampal loop. We used this preparation in combination with optical imaging performed using voltage-sensitive dyes in order to investigate how olfactory information is transferred from the olfactory bulb to the piriform, entorhinal and amygdaloid cortices. We visualized the propagation pattern of the neural activity after olfactory nerve stimulation and found that piriform and entorhinal activities converge in the amygdaloid cortex. This convergence may allow the amygdaloid cortex to integrate olfactory sensation with the information retained or processed in the entorhinal cortex.