Vasoactive intestinal polypeptide produces depolarization and facilitation of C-fibre evoked synaptic responses in superficial dorsal horn neurones (laminae I-IV) of the rat lumbar spinal cord in vitro

The actions of vasoactive intestinal polypeptide (VIP) were investigated on superficial dorsal horn (LI-IV) neurones in longitudinal slices of the rat lumbar spinal cord in vitro. Bath application of VIP (1-2 mM) cause depolarizations which were accompanied by a lowering of the threshold for excitation of the neu rone by current injection in the majority of cells studied. In some cases these depolarizations were very large and caused depolarization block and prolonged desensitization. An increase in spontaneous excitatory postsynaptic potential (EPSP) frequency and amplitude was also produced by VIP. Synaptic responses evoked by peripheral nerve stimuli at intensities which recruited C-fibres were also facilitated by VIP. The principle action was on the later components of these responses which are dependent on C-fibre activation. EPSP summation evoked by trains of peripheral nerve stimulation (wind-up) was also facilitated by VIP and the duration of these responses was clearly increased. These observations are discussed briefly in the context of the possible role of VIP in neuropathic pain. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.