Neural Cotransmission in Spinal Circuits Governing Locomotion

Many neuronal circuits contain, or are influenced by, colocalized neurotransmitters, which are suggested to fine-tune circuit function. Much of our knowledge about cotransmission derives from studies in non-mammalian model systems, although a growing number of studies have provided insights into the physiological role of cotransmission in more complex mammalian circuits, including the spinal cord. Here we discuss the current picture of colocalized neurotransmitters in spinal circuits of non-mammalian and mammalian systems, as well as the progression towards understanding of their functional roles. We delineate both evolutionarily conserved and divergent aspects of spinal cotransmission and highlight open questions in the area.