The acute and chronic effects of capsaicin on slow excitatory transmission in rat dorsal horn

The acute and chronic effects of capsaicin on rat spinal dorsal horn neurons and the excitatory transmission in the dorsal horn were investigated by means of intracellular recording techniques in the spinal cord slice preparation. Bath application of capsaicin (1–2 × 10⁻⁵M) produced in a majority of cells a prolonged depolarization associated with an increase in synaptic activity and intense neuronal discharges. During and immediately following the capsaicin depolarization, repetitive stimulation of a dorsal root failed to elicit the slow depolarization.

After neonatal capsaicin treatment the proportion of dorsal horn neurons exhibiting the slow excitatory transmission was markedly reduced, however, the fast excitatory postsynaptic potentials were present in all examined cells. In addition, the proportion and sensitivity of the cells responding with a slow depolarization to substance P increased.