Endogenous glutamatergic synaptic activity elicits acetylcholine release from rat cultured septal cells

Continuous depolarization induces choline acetyltransferase activity in septal and hippocampal co-cultured embryonic rat neurons

We tested the influence of continuous high-K+ treatment on acetylcholine (ACh) release and choline acetyltransferase (ChAT) activity on septal cell culture, and septal and hippocampal cell co-culture obtained from rat embryos. Continuous 9 mM K+ treatment did not affect ACh release and ChAT activity in septal culture, but increased ACh release in co-culture without affecting ChAT activity. A slight increase in extracellular K+ concentration, therefore, induced neuronal excitation. Continuous 55 mM K+ treatment increased ACh release in septal culture. This effect was due to direct excitation of septal neurons. In co-culture, 55 mM K+ treatment increased both ACh release and ChAT activity. These results indicate that hippocampal neurons are indispensable for the depolarization-induced increase in ChAT activity in the early stage of developing septal cholinergic neurons.

Picrotoxin increased acetylcholine release from rat cultured embryonic septal neurons

GABA is a major inhibitory neurotransmitter in the mature mammalian brain. In the early stages of brain development, it has been reported that GABA(A) receptor stimulation and the associated increase in Cl(-) conductance lead to membrane depolarization. In this study, we tested the effects of picrotoxin, a GABA(A) receptor Cl(-) channel blocker, on spontaneously released acetylcholine (ACh) from cultured rat embryonic septal cells. Picrotoxin increased spontaneously released ACh. These results indicate that blockade of GABA-activated Cl(-) channel increases neuronal excitability even in an early stage of the development.