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Our work assesses the effects of µ opioid receptor activation on high-threshold Ca2+/Ba2+ currents in freshly dispersed pyramidal neurons of the medial prefrontal cortex in rats. Application of the specific µ receptor agonist (D-Ala2, N-Me-Phe4, Gly5-ol)-enkephalin (DAMGO) at 1 µM decreased Ca2+ current amplitudes from 0.72 to 0.49 nA. The effect was abolished by naloxone and ω-Conotoxin GVIA. Inhibition was not abolished by strong depolarisation of the cell membrane. In addition, a macroscopic Ba2+ current recorded in cell-attached configuration was inhibited when DAMGO was applied outside the patch pipette. An adenylyl cyclase inhibitor (SQ 22536) and a protein kinase A inhibitor (H-89) decreased Ca2+ current amplitude. Moreover, the inhibitory effect of µ opioid receptors on Ca2+ currents required the activation of protein kinase A. We conclude that activation of µ opioid receptors in medial prefrontal cortex pyramidal neurons inhibits N type Ca2+ channel currents, and that protein kinase A is involved in this transduction pathway.
Flower buds, cotyledons and hypocotyls of Pharbitis nil were used as plant material. Flower buds (1-2 mm long) were excised from 3-week-old plants, grown in soil. Cotyledons of 7-day-old sterile seedlings were cut into 25 mm2 squares cotyledons whereas hypocotyls were cut to 1 mm long fragments. Explants were transferred into Petri dishes containing the Murashige and Skoog medium (MS), supplemented with either BA (11 μM·U⁻¹) alone or BA (22 μM·U⁻¹) and NAA (0.55 μM·U⁻¹), and different sugars: sucrose, fructose, glucose, mannose or sorbitol (autoclaved or filter-sterilized). Addition of glucose instead of sucrose to the medium stimulated the induclion of callus on flower buds and cotyledoniry explants, but inhibited its growth on fragments of hypocotyls. The medium supplemented with fructose (especially filter-sterilized) stimulated the development of flower elements. Organogenesis of shoots and roots on explants was also observed. Flower buds and hypocotyls were able to regenerate both organs. Addition of fructose or glucose to the medium stimul ated the organogenesis of shoots, whereas root organogenesis was inhibited on all explants used. Sorbitol strongly inhibited both induction of callus and organogenesis on all explants used.
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