Divergent excitatory and inhibitory signaling in a head direction circuit
Neural cell types are often clustered into inhibitory, excitatory, or neuromodulatory populations. However, the signaling mechanism between two neurons ultimately depends on their neurotransmitter-receptor pairings. Here, we demonstrate an example of a glutamatergic population of neurons that appears to either excite or inhibit their downstream partners depending on the type of glutamate receptor expressed in the downstream cell type. The upstream population encodes a sinusoidal head direction signal. The downstream partners that are excited by glutamate encode the same signal while the downstream partners that are inhibited by glutamate encode a 180{degrees} phase-shifted copy. The upstream population therefore appears to pass on two different phases of the same signal by making either excitatory or inhibitory connections to different downstream partners.