Neurokinin-1 receptor expression in dorsal root ganglion neurons of young rats

The expression of neurokinin-1 receptors was studied in the fourth lumbar d orsal root ganglia of young rats using immunohistochemical and electrophysi ological techniques. Use of a specific immunoserum raised against the C-ter minal fragment of rat neurokinin-1 receptor revealed immunoreactivity in 32 +/- 1.5% of dorsal root ganglion neurons. The diameter of the majority of the neurokinin-1 receptor immunostained neurons was smaller than 30 mu m Do uble immunohistochemical labelling using neurokinin-1 receptor and substanc e P antibodies revealed that about 1/3 of the neurokinin-1 receptor express ing neuron contains substance P. Likewise, about 1/3 of the substance P pro ducing DRG cells expressed the neurokinin-1 receptor. Superfusion of substa nce P (1 mu M) to an in vitro preparation of the fourth lumbar dorsal root ganglion induced a reversible long-lasting depolarization as measured by ex tracellular suction electrodes attached to the dorsal roots. This response to substance P was only partially antagonized by the selective neurokinin-1 receptor antagonist RP 67580 (1 mu M). Intracellular recordings distinguis hed between A alpha/beta-, A delta- and C-sub-types of ganglion neurons. Su perfusion of substance P (1 mu M) evoked excitatory responses in A delta- a nd C-type neurons. These results demonstrate the expression of functional n eurokinin-1 receptors on a subpopulation of A delta- and C-type sensory gan glion neurons. Our data suggest the possible physiological importance of pe ripheral neurokinin-1 receptors located on dorsal root ganglion neurons.