Some synapses contain and can release more than one neurotransmitter, and a well-studied example is the autonomic, sympathetic synapse in the vas deferens.
This synapse uses ATP, noradrenaline and NPY as transmitters.
ATP produces a rapid depolarisation by opening an ion channel that allows calcium entry and a rapid contraction of the smooth muscle.
Noradrenaline (NA) interacts with alpha adrenoceptors which utilise a second messenger that also results i an increase in intracellular calcium concentration, and results i a slower contraction
NPY is also released at this synapse and interacts with the ATP and NA release and binding with the receptors.
Co-transmission can also occur in parasympathetic, enteric and sensory pathways, and the table shows some of the transmitters involved
Also shown is a list of sites in the CNS where ATP is invovled in co-transmission.
In the CNS one example is the nociceptive nerve endings in the dorsal horn that release glutamate and Substance P.
The latter can sensitize post-synaptic neurones, but not initiate EPSPs themselves; Substance P is an example of a neuromodulator - a transmitter that can alter the sensitivity of a neurone to other transmitters.