Astrocyte Intermediaries of Septal Cholinergic Modulation in the Hippocampus

The neurotransmitter acetylcholine, derived from the medial septum/diagonal band of Broca complex, has been accorded an important role in hippocampal learning and memory processes. However, the precise mechanisms whereby acetylcholine released from septohippocampal cholinergic neurons acts to modulate hippocampal microcircuits remain unknown. Here, we show that acetylcholine release from cholinergic septohippocampal projections causes a long-lasting GABAergic inhibition of hippocampal dentate granule cells in vivo and in vitro. This inhibition is caused by cholinergic activation of hilar astrocytes, which provide glutamatergic excitation of hilar inhibitory interneurons. These results demonstrate that acetylcholine release can cause slow inhibition of principal neuronal activity via astrocyte intermediaries.