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Beta-amyloid, a 39-43 amino acid peptide, may exert its biological effects via neuronal nicotinic acetylcholine receptors. Using the ratiometric dye, fura-2, we examined the effect of soluble beta-amyloid(1-42) on the concentration of intracellular Ca(2+) ([Ca(2+)](i)) in acutely dissociated rat basal forebrain neurons. Focal applications of nicotine (0.5-20 mM), evoked dose-dependent increases in intracellular [Ca(2+)](i) that were mediated by the entry of extracellular Ca(2+) via nicotinic acetylcholine receptors, and the release of intracellular Ca(2+) from stores. With repeated nicotine challenges, the nicotinic responses were potentiated by 98 +/- 12% (P < 0.05) while beta-amyloid(1-42)(100 nM) was present for approximately 5 min. This potentiation became larger during the subsequent washout of beta-amyloid(1-42), which was associated with a gradual rise in baseline [Ca(2+)](i). Application of beta-amyloid(1-42)by itself did not alter [Ca(2+)](i), and beta-amyloid(1-42)also had no significant effect on the response to repeated KCl challenges. Therefore, beta-amyloid(1-42) caused neither gross disturbance of cellular Ca(2+) homeostasis nor enhancement of voltage-gated Ca(2+) channels. Interestingly, beta-amyloid(1-42) transiently potentiated the response to repeated caffeine challenges, which was also associated with a transient rise in baseline [Ca(2+)](i). beta-amyloid(1-42) potentiation of nicotine-evoked rises in [Ca(2+)](i) was reversed by the SERCA pump inhibitor, thapsigargin, and the mitochondrial Na(+)/Ca(2+) exchanger inhibitor, CGP-37157. These results suggest that the dysregulation of [Ca(2+)](i) by beta-amyloid(1-42) during multiple challenges with nicotine or caffeine involved the sensitization or overfilling of intracellular stores that are maintained by SERCA pump and Ca(2+) efflux from the mitochondria.

Nociceptin/orphanin FQ (N/OFQ) is an endogenous opioid-like heptadecapeptide that plays an important role in a variety of physiological functions. N/OFQ and its receptor opioid receptor-like orphan receptor-1 are abundant in the diagonal band of Broca (DBB), a basal forebrain nucleus where the loss of cholinergic neurons is linked to memory and spatial learning deficits. In the whole animal, central injections of N/OFQ have been shown to disrupt spatial learning. In this study, we investigated the basis for these behavioral observations by examining the cellular effects of N/OFQ on chemically identified DBB neurons. Whole cell patch-clamp recordings were performed on enzymatically dissociated DBB neurons. Under voltage-clamp conditions, bath application of N/OFQ (10 pM-1 M) resulted in a dose-dependent depression of whole cell currents. Single cell reverse transcription-polymerase chain reaction analysis identified cholinergic and fewer GABAergic cells to be N/OFQresponsive.[Nphe 1 ]nociceptin-(1-13)-NH 2 and CompB (J-113397) antagonized the N/OFQ response, but both compounds also displayed partial agonist activity. Using a combination of channel blockers we determined that the effects of N/OFQ were mediated via a suite of Ca 2ϩ (N-and L-type) and Ca 2ϩ -dependent K ϩ (iberiotoxin-sensitive) conductances. In addition, biophysical analysis of voltage subtraction protocols revealed that N/OFQ reduces transient outward and the delayed rectifier K ϩ currents. Because N-type and L-type Ca 2ϩ channels are important in the context of neurotransmitter release, our observations indicate that N/OFQ inhibition of Ca 2ϩ -dependent conductances in cholinergic neurons would be expected to result in depression of acetylcholine release, which may explain the behavioral actions of N/OFQ in the brain.

Purpose Electrical impedance increases following test injections of non-conducting solutions around nerves; however, this increase should diminish rapidly with intravascular needle placement, wherein the systemic circulation will dissipate the solution. For this observational study, we hypothesized that the impedance increases significantly at the perineural space after an injection of 5% dextrose in water (D5W), but that it does not increase correspondingly at the intravascular location Methods After Ethics Research Board approval, electrical impedance was measured by a nerve stimulator displaying resistance, StimuplexÒ HNS 12, before and during (30 sec) an injection of D5W 3 mL: 1) during intravenous cannula placement using an insulated stimulating needle sheathed in its plastic cannula, MultiSet NanoLine with 18G needle; and 2) during needle placement (Pajunk 22G insulated) for an ultrasound-guided supraclavicular block in patients undergoing hand surgery. The impedance changes at each location were analyzed and compared. Results Data were collected from 16 patients. Baseline impedance was lower intravascularly (mean 16.5 ± standard deviation 7.2 kX) compared with perineurally (23.5 ± 8.3 kX) (P = 0.037). Peak impedance after intravascular D5W injection was 20.1 ± 6.8 kX, which was not a significant change (P = 0.15). In contrast, peak impedance after perineural D5W injection was 58.6 ± 29.1 kX, an increase of 35.1 ± 26.4 kX (155 ± 117%), and then it reached a plateau of 36.7 ± 19.6 kX. The increase in impedance was significantly greater at the perineural location (P \ 0.0001). Conclusion The absence of a significant increase in impedance upon injection of D5W prior to injection of local anesthetic may provide useful information to warn of intravascular injection. RésuméObjectif L'impe´dance e´lectrique augmente apre`s les injections de test de solutions non conductrices autour des nerfs; toutefois, cette augmentation devrait diminuer rapidement lors d'un positionnement intravasculaire de l'aiguille, situation dans laquelle la circulation syste´mique dissipera la solution. Pour re´aliser cette e´tude observationnelle, nous avons e´mis l'hypothe`se que l'impe´dance augmentait de façon significative dans l'espace pe´rineural apre`s une injection de dextrose a`5 % dilue´e dans de l'eau (D5W), mais qu'elle n'augmentait pas de la meˆme manie`re dans un site intravasculaire. Méthode Apre`s avoir reçu l'approbation du Comited 'e´thique de la recherche, l'impe´dance e´lectrique a e´teḿ esure´e à l'aide d'un stimulateur nerveux affichant la re´sistance, le StimuplexÒ HNS 12, avant et pendant (30 sec) une injection de 3 mL de D5W: 1) pendant le positionnement d'une canule intraveineuse a`l'aide d'une aiguille de stimulation isole´e prote´ge´e par sa canule de plastique, le MultiSet NanoLine avec une aiguille 18G; et 2) pendant le positionnement de l'aiguille (Pajunk 22G isole´e) pour un bloc supraclaviculaire par e´choguidage chez des patients subissant une chirurgie de la main. Les changements d'impe´dance a`c...

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