Putative roles for local axon collaterals of projection neurons in spinal dorsal horn networks
The main axon of projection neurons (PNs) in the superficial spinal dorsal horn (SDH) – involved among other tasks in pain transmission – gives rise to distinct types of local axon collaterals before leaving the spinal grey matter (Szucs et al., 2010). The course and distribution of the collaterals suggest that they establish local and propriospinal synaptic connections. However, the target neuronal elements and the functional role of these synaptic contacts remain to be elucidated. Our research group combines classical and viral retrograde tracing methods to identify and selectively manipulate PNs in the SDH. Combining optogenetics and patch-clamp electrophysiology in an intact spinal cord preparation we found that axon terminals of PNs contact local interneurons as well as primary afferent terminals modulating synaptic transmission from primary afferent to secondary sensory neurons. Our findings support our earlier hypothesis that PNs are not simple output elements of the SDH circuitry but active participants of local information processing.