Long-Range–Projecting GABAergic Neurons Modulate Inhibition in Hippocampus and Entorhinal Cortex

Inhibiting the Inhibitors Excitatory neurons in the hippocampus and entorhinal cortex are under control of local γ-aminobutyric acid–releasing (GABAergic) interneurons that are the major source of inhibition in the adult brain. In contrast to the wealth of knowledge regarding connectivity in the hippocampus, much less is known about the cross-talk between the hippocampus and other brain regions. Melzer et al. (p. 1506 ) investigated long-range GABAergic projections from the hippocampal formation to the medial entorhinal cortex and vice versa. These GABAergic neurons bidirectionally couple the hippocampus and medial entorhinal cortex and preferentially target local inhibitory neurons, forming disinhibitory loops that could help synchronize neuronal activity.