A network of electrically coupled interneurons drives synchronized inhibition in neocortex

The neocortex has at least two different networks of electrically coupled i nhibitory interneurons: fast-spiking (FS) and low-threshold-spiking (LTS) c ells. Agonists of metabotropic glutamate or acetylcholine receptors induced synchronized spiking and membrane fluctuations, with irregular or rhythmic patterns, in networks of LTS cells. LTS activity was closely correlated wi th inhibitory postsynaptic potentials in neighboring FS interneurons and ex citatory neurons. Synchronized LTS activity required electrical synapses, b ut not fast chemical synapses. Tetanic stimulation of local circuitry induc ed effects similar to those of metabotropic agonists. We conclude that an e lectrically coupled network of LTS interneurons can mediate synchronized in hibition when activated by modulatory neurotransmitters.