Properties of Quantum Release of Glutamate and Glycine in Synapses between Co-Cultured Primary Afferent and Spinal Dorsal Horn Neurons

Using the patch-clamp technique, we recorded transmembrane currents and potentials in pairs of synaptically connected co-cultured rat primary afferent neurons (dorsal root ganglion, DRG, cells) and spinal dorsal horn (DH) units; the peculiarities of release of glutamate and glycine in the corresponding synapses were determined. By analyzing distributions of the amplitudes of postsynaptic currents recorded in DH neurons, we estimated the quantum parameters of release of these neurotransmitters. We found that the release of neurotransmitter quanta due to the entry of a presynaptic action potential into glutamate- and glycinergic DRG–DH synapses is realized independently. The probability of transmitter release can be described by binomial statistics. There are reasons to believe that, under co-culturing conditions, a pre-synaptic DRG neuron forms a few synaptic connections with a post-synaptic DH cell. As is concluded, presynaptic terminals in such synapses can have more than one release zone for the transmitter; the possibility of multiquantum release of glycine or glutamate in several zones of release during neurotransmission cannot be ruled out.