A two-compartment in vitro model for studies of modulation of nociceptive transmission.

Here we present a two-compartment in vitro model in which embryonic rat dorsal root ganglia (DRG) neurons are cultured separately from their target dorsal horn neurons. Although separated, synaptic contact can be established between the peripheral and central neurons since the system allows the DRG axons to project into the other compartment, which contains a network of dorsal horn neurons. The efficacy of the model was evaluated by immunocytochemical, calcium imaging and electrophysiological experiments. The results showed that a subpopulation of the DRG neurons had nociceptor characteristics and that these made synaptic contact with the dorsal horn network. Application of current pulses, according to the stimulus paradigm used, evoked action potentials in DRG axons selectively. This in turn gave rise to increased postsynaptic activity in the network of dorsal horn neurons. The model offers a high degree of efficiency since large numbers of DRG axons can be stimulated simultaneously, thus permitting recording of strong output responses from the dorsal horn neurons. This in vitro model provides a means for studying the mechanisms by which modulatory factors, such as immunoregulatory molecules, applied at either the PNS or the CNS level, can affect synaptic activity and nociceptive transmission in single neurons or network of neurons in the dorsal horn.