Expression of neurokinin-1 receptors on cultured dorsal root ganglion neurons from the adult rat

Abstract

The expression of neurokinin-1 receptors in isolated dorsal root ganglion neurons of adult rats was investigated using substance P covalently bound to a 1.4-nm gold particle. Binding of substance P–gold was determined in neurons after 0.8, 1.8 or 3.8 days under culture conditions. Substance P–gold binding sites were identified in 9.5±1.8% of the neurons that were cultured for 0.8 days. The proportion of neurons with substance P–gold binding sites increased to 21.5±3.6% after 1.8 days in culture and returned to the initial values (9.2±2.1%) after 3.8 days in culture. Binding of substance P–gold was suppressed by co-administration of [Sar 9, Met(O 2) 11] substance P, a specific agonist at the neurokinin-1 receptor, but not by co-administration of [ β-Ala 8] Neurokinin A (4–10), an agonist at the neurokinin-2 receptor, and senktide, an agonist at the neurokinin-3 receptor. This indicates that substance P–gold was bound specifically to neurokinin-1 receptors. Double-labelling with RT97, an antibody that selectively labels somata of A-fibres revealed that substance P binding sites were present in small neurons with myelinated and unmyelinated axons. These data show that a proportion of dorsal root ganglion neurons of adult rat in culture exhibit neurokinin-1 receptors. A transient increase in the proportion of neurons expressing neurokinin-1 receptors after 1.8 days in culture suggests that the expression of neurokinin-1 receptors is subjected to regulation.