The escape response and rhythmic swimming in zebrafish are distinct behaviors mediated by two functionally distinct motoneuron (Mn) types. The primary (1°Mn) type depresses and has a large quantal content (Qc) and a high release probability (Pr). Conversely, the secondary (2°Mn) type facilitates and has low and variable Qc and Pr. This functional duality matches well the distinct associated behaviors, with the 1°Mn providing the strong, singular C bend initiating escape and the 2°Mn conferring weaker, rhythmic contractions. Contributing to these functional distinctions is our identification of P/Q-type calcium channels mediating transmitter release in 1°Mns and N-type channels in 2°Mns. Remarkably, despite these functional and behavioral distinctions, all ∼15 individual synapses on each muscle cell are shared by a 1°Mn bouton and at least one 2°Mn bouton. This blueprint of synaptic sharing provides an efficient way of controlling two different behaviors at the level of a single postsynaptic cell.

The escape response and rhythmic swimming in zebrafish are distinct behaviors mediated by two functionally distinct motoneuron (Mn) types. The primary (1˚Mn) type depresses, has a large quantal content (Qc), and a high release probability (Pr). Conversely, the secondary (2˚Mn) type facilitates and has low and variable Qc and Pr. This functional duality matches well the distinct associated behaviors, with the 1˚Mn providing the strong, singular C-bend initiating escape and the 2˚Mn confers weaker, rhythmic contractions. Contributing to these functional distinctions is our identification of P/Q type calcium channels mediating transmitter release in 1˚Mns and N type channels in 2˚Mns. Remarkably, despite these functional and behavioral distinctions, all ~15 individual synapses on each muscle cell are shared by a 1˚Mn bouton and at least one 2˚Mn bouton. This novel blueprint of synaptic sharing provides an efficient way of controlling two different behaviors at the level of a single postsynaptic cell.