Involvement of H1 receptors in the central antinociceptive effect of histamine: Pharmacological dissection by electrophysiological analysis

Intracerebroventricular (i.c.v.) administration of histamine (HA, 0.025–0.1 M/rat) to arthritic rats induces a dose-related inhibition of the neuronal thalamic firing evoked by peripheral noxious stimuli. To characterize the type(s) of HA receptors involved in this depressing activity of the amine we used electrophysiological techniques to examine the effects of i.c.v. administration of H₁ and H₂ agonists and antagonists on the spontaneous and evoked nociceptive firing of the thalamic neurons in rats rendered arthritic by Freund's adjuvant. The H₁ agonist 2-pyridylethylamine (0.4–1.0 M/rat, i.c.v) displayed a dose-dependent antinociceptive effect very similar to that of HA, while the H₂ agonist dimaprit (0.05–0.2 M/rat, i.c.v.) did not modify thalamic firing. Neither mepyramine (H₁ antagonist, 0.1 M/rat, i.c.v.) nor zolantidine (H₂ antagonist, 0.01 M/rat, i.c.v.) modified the evoked firing of rat thalamic neurons. When administered before HA (0.1 M/rat, i.c.v.) mepyramine but not zolantidine was able to inhibit the antinociceptive effect of HA. On the basis of the present electrophysiological results, we suggest that a specific interaction of histamine with H₁ receptors may be important for its antinociceptive effect on afferent peripheral inputs to the thalamus.     

Complete photonic bandgaps in 12-fold symmetric quasicrystals

Photonic crystals are attracting current interest for a variety of reasons, such as their ability to inhibit the spontaneous emission of light. This and related properties arise from the formation of photonic bandgaps, whereby multiple scattering of photons by lattices of periodically varying refractive indices acts to prevent the propagation of electromagnetic waves having certain wavelengths. One route to forming photonic crystals is to etch two-dimensional periodic lattices of vertical air holes into dielectric slab waveguides. Such structures can show complete photonic bandgaps, but only for large-diameter air holes in materials of high refractive index (such as gallium arsenide, n = 3.69), which unfortunately leads to significantly reduced optical transmission when combined with optical fibres of low refractive index. It has been suggested that quasicrystalline (rather than periodic) lattices can also possess photonic bandgaps. Here we demonstrate this concept experimentally and show that it enables complete photonic bandgaps--non-directional and for any polarization--to be realized with small air holes in silicon nitride (n = 2.02), and even glass (n = 1.45). These properties make photonic quasicrystals promising for application in a range of optical devices.