NK₁ and NK₂ receptors contribute to C-fibre evoked slow potentials in the spinal cord

Abstract

SMALL diameter primary afferents produce slow synaptic potentials in spinal neurones. These can be recorded as prolonged ventral root potentials (VRPs) in the isolated neonatal rat spinal cord preparation. The VRP elicited by stimulating C-fibres consists of two phases: an early phase comprising a monosynaptic and a short polysynaptic response identical to that elicited by low threshold Aβ fibres and a late phase which has an initial component (0.1–1 s) which is sensitive to N-methyl-D-aspartic acid receptor antagonism and a very long lasting second component (1–20 s) which is resistant to these antagonists. We now demonstrate that the slowest component of the VRP is significantly reduced by both NK₁ and NK₂ tachykinin receptor antagonists and as a consequence, tachykinins have a particular contribution to the cumulative depolarization produced by low frequency (1 Hz) C-fibre stimulation.