The roles of co-transmission in neural network modulation

Neuromodulation provides considerable flexibility to the output of neural n etworks. In spite of the extensive literature documenting the presence of m odulatory peptide co-transmitters in many neurons, considerably less is kno wn about the specific roles of co-transmission in circuit function. This re view describes some of the potential consequences of peptide cotransmission in functional circuits, using specific examples from recent work on the ac tions of identified peptidergic projection neurons acting on the multifunct ional neural network within the crustacean stomatogastric ganglion. This sy stem reveals that co-transmission provides projection neurons with a rich a ssortment of strategies for eliciting multiple outputs from a multifunction al network.