Effects of the NMDA-receptor antagonist ketamine on perceptual correlates of long-term potentiation within the nociceptive system
We recently reported perceptual correlates of long-term potentiation (LTP) of synaptic strength within the nociceptive system demonstrating the functional relevance of LTP for human pain sensation. LTP is generally classified as NMDA-receptor dependent or independent. Here we show that low doses of the NMDA-receptor antagonist ketamine (0.25 mg/kg) prevented the long-term increase in perceived pain to electrical test stimuli, which was induced by high-frequency electrical stimulation (HFS) of nociceptive afferents. Whereas in a control experiment HFS led to a stable increase in perceived pain by 51% for the entire observation period of 1 h HFS given 4 min after i.v. ketamine was ineffective…
Perceptual correlates of nociceptive long-term potentiation and long-term depression in humans.
Long-term potentiation (LTP) and long-term depression (LTD) of synaptic strength are ubiquitous mechanisms of synaptic plasticity, but their functional relevance in humans remains obscure. Here we report that a long-term increase in perceived pain to electrical test stimuli was induced by high-frequency electrical stimulation (HFS) (5 × 1 sec at 100 Hz) of peptidergic cutaneous afferents (27% above baseline, undiminished for >3 hr). In contrast, a long-term decrease in perceived pain (27% below baseline, undiminished for 1 hr) was induced by low-frequency stimulation (LFS) (17 min at 1 Hz). Pain testing with punctate mechanical probes (200 μm diameter) in skin adjacent to the HFS–LFS con…