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 ϫ 1 sec at 100 Hz) of peptidergic cutaneous afferents (27% above baseline, undiminished for Ͼ3 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 m diameter) in skin adjacent to the HFS-LFS conditioning skin site revealed a marked twofold to threefold increase in pain sensitivity (secondary hyperalgesia, undiminished for Ͼ3 hr) after HFS but also a moderate secondary hyperalgesia (30% above baseline) after strong LFS. Additionally, HFS but not LFS caused pain to light tactile stimuli in adjacent skin (allodynia). In summary, HFS and LFS stimulus protocols that induce LTP or LTD in spinal nociceptive pathways in animal experiments led to similar LTP-and LTD-like changes in human pain perception (long-term hyperalgesia or hypoalgesia) mediated by the conditioned pathway. Additionally, secondary hyperalgesia and allodynia in adjacent skin induced by the HFS protocol and, to a minor extent, also by the LFS protocol, suggested that these perceptual changes encompassed an LTP-like heterosynaptic facilitation of adjacent nociceptive pathways by a hitherto unknown mechanism.

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Due to the cyclophane structure the energies of the lowest triplet state, phosphorescence lifetimes and phosphorescence/fluorescence quantum yield ratios of [2,2](l,4)naphthalenoparacyclophane (2) and [2,2](1.4)chrysenoparacyclophane (4) differ markedly from the data of 1,4-dimethyl naphthalene and chrysene respectively. By ground state complexation of 2 and 4 with silver Perchlorate the transannular interaction in the cyclophanes is reduced. In contrast to naphthalene. 2 does not effectively quench the benzophenone phosphorescence in benzophenone/ 2 mixed crystals at 77 K. It is shown, however, that this cannot be regarded as a specific property of 2 but rather as an example of the more general phenomenon that steric or stereoelectronic factors can play a considerable role in intermolecular triplet-triplet energy transfer.

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ChemInform Abstract Compounds (I) are reduced with alkali metals (Li, K) in THF-d8 at -78 rc C to give tetraanions (I)4-which are stable at room temp. in the absence of air (1H, 13C NMR; cyclic voltammetry; quenching experiments). Some of these anions exist as conformational isomers what is dependent in same cases on the counterion; e.g., conformational isomers are observed for (Ia)44-K+ but not for the Li-salt.