Identification of in vitro phosphorylation sites in the growth cone protein SCG10. Effect Of phosphorylation site mutants on microtubule-destabilizing activity

SCG10 is a neuron-specific, membrane-associated protein that is highly concentrated in growth cones of developing neurons. Previous studies have suggested that it is a regulator of microtubule dynamics and that it may influence microtubule polymerization in growth cones. Here, we demonstrate that in vivo, SCG10 exists in both phosphorylated and unphosphorylated forms. By two-dimensional gel electrophoresis, two phosphoisoforms were detected in neonatal rat brain. Using in vitro phosphorylated recombinant protein, four phosphorylation sites were identified in the SCG10 sequence. Ser-50 and Ser-97 were the target sites for protein kinase A, Ser-62 and Ser-73 for mitogen-activated protein kinase and Ser-73 for cyclin-dependent kinase. We also show that overexpression of SCG10 induces a disruption of the microtubule network in COS-7 cells. By expressing different phosphorylation site mutants, we have dissected the roles of the individual phosphorylation sites in regulating its microtubule-destabilizing activity. We show that nonphosphorylatable mutants have increased activity, whereas mutants in which phosphorylation is mimicked by serine-to-aspartate substitutions have decreased activity. These data suggest that the microtubule-destabilizing activity of SCG10 is regulated by phosphorylation, and that SCG10 may link signal transduction of growth or guidance cues involving serine/threonine protein kinases to alterations of microtubule dynamics in the growth cone.     

Nicotine withdrawal in chippers and regular smokers: Subjective and cognitive effects.

From previous studies, chippers (very light, long-time cigarette smokers) seem not to be nicotine dependent, despite decades of smoking. The effect of tobacco deprivation on chippers' withdrawal reactions was examined. Matched groups of 26 chippers and 25 regular smokers were studied while abstaining or smoking for 2-day blocks, with assessments administered 5 times daily by palm-top computers. As hypothesized, chippers showed no changes as a result of nicotine deprivation. In contrast, regular smokers demonstrated distinct changes in craving, mood, arousal, and sleep disturbance. The computers also tested participants' cognitive performance. Unlike chippers, regular smokers' performance on complex tasks was slower under deprivation; the effect could not be explained by changes in motor performance or simple reaction time. Results suggest performance may have been improved by nicotine rather than worsened by withdrawal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differentiation of hydroxyproline isomers and isobars in peptides by tandem mass spectrometry

The isomeric 3- and 4-hydroxyprolines are isobaric with the isomers leucine and isoleucine, and all four have, therefore, the same "residue mass" of 113. Secondary fragmentation processes were found that differentiate the hydroxyproline isomers from each other and from the leucines. Variants of synthetic bradykinin containing one or two hydroxyproline moieties were prepared by using manual Edman degradation and/or enzymatic methods. The tandem mass spectra of these peptides were recorded. The C-terminal wn fragment ions allow the differentiation of 4-hydroxyproline from the 3-isomer and isoleucine, while the N-terminal an ions containing 4-hydroxyproline undergo H2O elimination to differentiate this amino acid from the 3-isomer and leucine. Lys-C digestion of a mussel adhesive protein produced a set of decapeptides varying in the degree of hydroxylation of proline and tyrosine. Heterogeneity with respect to 3-hydroxyproline and 4-hydroxyproline at a certain position in these peptides was assessed by tandem mass spectrometry based on the wn ion series in the CID spectra of these Lys-C peptides. Some N-terminal ions further allow for the differentiation of these two isomeric species.     

The effect of nicotine and attention allocation on physiological and self-report measures of induced anxiety in PTSD: A double-blind placebo-controlled trial.

Rates of smoking among populations with psychiatric disorders are more than twice as high as among the general population, yet there are few controlled studies of the mechanisms of this relationship. This trial examined the effect of nicotine by way of cigarette smoking on both self-report and autonomic parameters of anxiety among individuals with PTSD who were also heavy smokers. Half of the participants were randomized to an anxiety-eliciting condition, whereas the other half were assigned to a condition of neutral emotional content. Within each of these conditions, participants were randomized into a nicotine condition (high-yield nicotine cigarette) or a placebo condition (denicotinized cigarette). The final layer of randomization involved assigning participants to either an attention-demanding task or a no task condition. We examined the interactive effects of nicotine and attentional demand on parameters of anxious responding. Nicotine exerted an anxiolytic effect relative to placebo on self-report measures; however, nicotine did not interact with attentional demand in producing this effect. In contrast to the findings on the self-report measures of distress, nicotine enhanced autonomic reactivity to trauma cues, thereby suggesting a decoupling of self-reported anxiety and autonomic arousal associated with responding to trauma-relevant cues. The implications for understanding smoking and psychiatric comorbidity are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Smoking and stress: Correlation, causation, and context.

Comments on the article by A. C. Parrott (see record 1999-11644-002) regarding the link between cigarette smoking and stress. Parrott was correct in claiming that nicotine provides relief from the subjective distress evoked by withdrawal, as ample evidence supports this contention. However, his assertions that (1) smoking has no direct effect on affective distress and (2) smoking actually causes stress must be questioned. Identifying the contexts in which smoking exerts its effects on behavior, cognition, and emotion is crucial to furthering the understanding of why nicotine is so reinforcing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Smoking and attention: a review and reformulation of the stimulus-filter hypothesis

An accumulation of evidence suggests that smoking may be reinforcing, in part, due to nicotine's capacity to enhance attentional processing. Correspondingly, the stimulus-filter model of nicotine reinforcement asserts that nicotine facilitates cognitive performance by acting as a stimulus-barrier, thereby screening irrelevant and annoying stimuli from the smoker's awareness. A review of the available data suggests that while nicotine does appear to reliably enhance sustained, divided, and focused attention, the stimulus-filter model falls short of adequately explaining the findings. An alternative, attention, allocation model of nicotine reinforcement is reviewed, the tenets of which suggest that nicotine differentially augments attentional processing via its propensity to: (a) induce attentional narrowing, and (b) increase perceptual processing capacity. The motivational implications of the model, including smokers' use of nicotine to dampen stress, are discussed.     

A day at a time: Predicting smoking lapse from daily urge.

Smokers who recently quit (N?=?214) monitored smoking urges for up to 26 days after quitting. Computers administered 4–5 assessments daily at random times; participants rated urges on waking and when they experienced temptation episodes. Urge intensity after cessation did not generally exceed urges reported during baseline ad lib smoking. Urge intensity and temptation frequency consistently declined over the quit period. Controlling for urge intensity at baseline, all daily urge intensity measures predicted lapse the following day in proportional hazards survival analyses. Average duration of temptation episodes also predicted lapses; frequency of temptation did not. To isolate the effect of day-to-day variations in urges, participants' nicotine dependence and urge intensity on quit day were controlled for. Only urge intensity at waking still predicted lapse risk; this was not because of this measure being closer in time to the day's lapses. Among lapsers, urge intensity at waking and in temptations rose preceding a lapse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Caffeine expectancy: Instrument development in the Rasch measurement framework.

Although caffeine is the most widely consumed psychoactive drug in the world, the mechanisms associated with consumption are not well understood. Nonetheless, outcome expectancies for caffeine use are thought to underlie caffeine’s reinforcing properties. To date, however, there is no available, sufficient measure by which to assess caffeine expectancy. Therefore, the current study sought to develop such a measure employing Rasch measurement models. Unlike traditional measurement development techniques, Rasch analyses afford dynamic and interactive control of the analysis process and generate helpful information to guide instrument construction. A 5-stage developmental process is described, ultimately yielding a 37-item Caffeine Expectancy Questionnaire (CEQ) comprised of 4 factors representing “withdrawal symptoms,” “positive effects,” “acute negative effects,” and “mood effects.” Initial evaluation of the CEQ yielded sufficient evidence for various aspects of validity. Although additional research with more heterogeneous samples is required to further assess the measure’s reliability and validity, the CEQ demonstrates potential with regard to its utility in experimental laboratory research and clinical application. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does smoking abstinence self-efficacy vary across situations? Identifying context-specificity within the Relapse Situation Efficacy Questionnaire.

According to self-efficacy and relapse theories, abstinence self-efficacy (ASE) ratings should be context-specific; they should vary across situations. This variability may be important, as it could signal high-risk for relapse situations. In this study, confirmatory factor analysis was used to identify situational variability in a novel ASE assessment (Relapse Situation Efficacy Questionnaire, or RSEQ). Results supported a hierarchical structure, where both context-specific and unidimensional measures of ASE exist within the assessment. Context-specific factors included Negative Affect, Positive Affect, Restrictive Situations (to smoking), Idle Time, Social–Food Situations, Low Arousal, and Craving. Multiple context-specific factors and the aggregate factor predicted cessation outcome, even after controlling for concurrent smoking rate. However, the context rated with the least confidence proved to be the best outcome predictor, suggesting the existence of "Achilles' heel" situations. These data indicate the internal and predictive validity of the RSEQ. (PsycINFO Database Record (c) 2010 APA, all rights reserved)