Regional distribution of nicotinic receptors during prenatal development of human brain and spinal cord.

The development of nicotinic acetylcholine receptors (nAChRs) in brains from human fetuses of 4-12 weeks gestational age was studied. The expression of nAChR subunit mRNAs was analyzed using reverse transcriptase-polymerase chain reaction. Expression of alpha 3, alpha 4, alpha 5, alpha 7, beta 2, beta 3 and beta 4 mRNA were all detected in the prenatal spinal cord, medulla oblongata, pons, cerebellum, mesencephalon, subcortical forebrain and cortex during first trimester development. Relative quantification of mRNA showed that the highest levels for alpha 3, alpha 4 and alpha 7 were expressed in the spinal cord, alpha 5 was most abundant in the cortex and beta 3 was highest in the cerebellum. beta 4 seemed to be equally distributed in all regions whereas beta 2 was high in the cortex and cerebellum. A comparison of expression of nAChR subunit mRNAs in the cortex and cerebellum of prenatal and aged (54-81 years) brain showed that mRNA levels for alpha 4, alpha 5, alpha 7, beta 2 and beta 4 were significantly higher in the prenatal cortex and cerebellum than in aged brain, whereas the level of alpha 3 transcript was similar, and beta 3 significantly higher in aged cortex. Specific binding of [3H]-epibatidine to prenatal brain membranes was detected as early as 4-5 weeks of gestation in the spinal cord, medulla oblongata, pons and subcortical forebrain. A positive correlation between gestational age and [3H]-epibatidine and [3H]-cytisine binding was found in several brain regions. The highest specific binding of [3H]-epibatidine and [3H]-cytisine was detected in the spinal cord, pons and medulla oblongata and the lowest in the cortex. Saturation analysis of [3H]-cytisine binding in both prenatal and aged brain were best fit by a model for a single site, whereas binding data for [3H]-epibatidine revealed two classes of binding sites. The early presence of nAChR proteins and gene transcripts shown in the present study suggests an important role for nAChRs in modulating dendritic outgrowth, establishment of neuronal connections and synaptogenesis during development.

Chronic ethanol treatment decreases [3H]epibatidine and [3H]nicotine binding and differentially regulates mRNA levels of nicotinic acetylcholine receptor subunits expressed in M10 and SH-SY5Y neuroblastoma cells.

For a study of the underlying mechanisms of a possible interaction between ethanol and nicotinic receptors during ethanol dependence, the aim of this work was to investigate the effect of chronic ethanol exposure on nicotinic receptor subtypes in a transfected fibroblast cell line (M10 cells) stably expressing alpha4beta2 nicotinic receptor subtype and an SH-SY5Y neuroblastoma cell line expressing alpha3, alpha5, alpha7, beta2, and beta4 nicotinic acetylcholine receptor (nAChR) subunits. A significant dose-related decrease (-30-80%) in number of [3H]nicotine binding sites was observed in ethanol-treated (25-240 mM) compared with untreated M10 cells. Similarly, 4-day treatment with ethanol in concentrations relevant to chronic alcoholism (100 mM) decreased the number of nicotinic receptor binding sites in the SH-SY5Y cells when measured using [3H]epibatidine. When M10 cells were chronically treated with nicotine, ethanol partly inhibited the up-regulation of nicotinic receptors when present in the cells together with nicotine. Chronic treatment for 4 days with 100 mM ethanol significantly decreased the mRNA level for the alpha3 nAChR subunit (-39%), while the mRNA levels for the alpha7 (+30%) and alpha4 (+22%) subunits were significantly increased. Chronic ethanol treatment did not affect the mRNA levels for the beta2 nAChR subunit. Changes in the levels of nAChR protein and mRNA may have adaptive significance and be involved in the development of dependence, tolerance, and addiction to chronic ethanol and nicotine exposure. They also may be targets for therapeutic strategies in the treatment of ethanol and nicotine dependence.

Optical frequency shifters based on cascaded second-order nonlinear processes.

We propose a novel scheme for an optical frequency shifter that exploits cascaded second-order nonlinearity in a semiconductor material. The cascade comprises a sum-frequency interaction followed by a differencefrequency conversion in a coupled waveguide-to-vertical-cavity structure. For a 50-microm-long planar waveguide, efficient conversion is supported over an effective -3-dB bandwidth of 39 nm at a pump power density of 3.3 W/microm. A longitudinal in-plane cavity can reduce the required pump power density so that effective conversion occurs over a bandwidth of 20 nm at a pump power density of 6 mW/microm.