A GABAergic axo-axonic cell in the fascia dentata controls the main excitatory hippocampal pathway.

Neuronal discharge is very efficiently blocked by inhibitory synapses on the axon initial segment. Here we describe a novel type of gamma-aminobutyric acid (GABA)-ergic inhibitory neurons in the rat fascia dentata that exclusively forms synaptic contacts with the axon initial segments of numerous dentate granule cells. This way the main excitatory pathway of the hippocampal formation which interconnects the fascia dentata with the hippocampus proper is controlled. We hypothesize that hypofunction of this inhibitory neuron causes overexcitation in the main excitatory pathway which could play a role in epilepsy.