1,720,966 research outputs found
Regulation and function of the tonic component of cortical acetylcholine release
No full textRegulation and function of the tonic component of cortical acetylcholine release
Multiple modes of cholinergic neurotransmission - Multiple functions
No full textStimulation of nAChRs has been widely suggested as a new approach to treat the cognitive symptoms of a range of disorders. Our current model postulates two separate modes of cholinergic neurotransmission. First, a tonic component (changes over minutes; measured by microdialysis) of cholinergic activity modulates the gain of thalamic input processing, via stimulation of α4β2* nAChRs expressed by thalamic afferents. Second, cue-evoked glutamate release from thalamic afferents generates transient (seconds) increases in acetylcholine (ACh) release (measured by amperometry and enzyme-coated microelectrodes). Glutamatergic and cholinergic transients interact to enhance the probability and efficacy of cue detection. The tonic component of cholinergic activity is hypothesized to modulate the general readiness for cortical input processing (or “arousal”), by modulating the “neuronal salience” of the cue. The present experiments were designed to specify the regulation and role of the tonic component of cholinergic neurotransmission. To this end, we studied the behavioral/cognitive and cholinergic effects of the selective α7 nAChR agonist ABT-107, known to evoke lasting increases in tonic cholinergic activity in naïve animals, and the selective α4β2* nAChR agonist ABT-089, known to augment cholinergic transients in animals detecting cues. In animals conditioned to a simple arousing stimulus (darkness+palatable food), administration of ABT-107, but not ABT-089 increased basal and augmented stimulus-evoked increases in ACh release and increased exploratory activity. ABT-107 did not affect sustained attention performance, (SAT)-associated increases in ACh release and mildly impaired performance. ABT-089 enhanced SAT performance in non-tethered animals while lowering performance-associated increases in ACh release. These results suggest that the “arousal”-enhancing effects of increases in tonic cholinergic activity are restricted to situations devoid of behavioral/cognitive constraints. Tonic cholinergic activity supports both spontaneous and cognitive performance; however, tonic cholinergic activity is tightly regulated in cognitive contexts. In cognitive contexts, tonic activity levels are protected against pharmacological manipulation, as indicated by the absence of effects of ABT-107 in SAT performing animals and by reducing cholinergic tone in the presence of an α4β2* nAChR agonist. Finally, the two component of cholinergic activity do not necessarily co-vary, and that drug effects on cholinergic activity in naïve animals do not predict effects on cognitive performance-mediating cholinergic neurotransmission
Multiple time scales and variable spaces: synaptic neurotransmission in vivo
No full textRegulation and function of the tonic component of cortical acetylcholine release
Regulation and function of the tonic component of cortical acetylcholine release.
No full textStudies aiming at corroborating the regulation and function of the cortical cholinergic input system that postulates two separate modes of cholinergic neurotransmission. First a tonic component of cholinergic activity (changes on the scale of minutes) modulates the gain of thalamic input processing via stimulation of alfa4beta2 receptors expressed by thalamic afferents. Second , cue evoked glutamatergic release from thalamic afferents generates phasic or transient (scale of seconds) increases in acetylcholine release via stimulation of ionotropic glutamatergic receptors
Multiple time scales and variable spaces: synaptic neurotransmission in vivo
No full textMonitoring of cholinergic transmission on different time-scal
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effects of the selective alpha 7 nAChR agonist ABT-107 on prefrontal glutamatergic and cholinergic activity and attentional performance
No full textStimulation of alpha 7 nAChRs has been widely suggested as a new approach to treat the cognitive symptoms of a range of disorders, including schizophrenia. The present experiments focused on the effects of ABT-107 on cholinergic activity and attentional performance. Our prior research demonstrated that transient increases in prefrontal cholinergic activity mediate the detection of stimuli in attention-demanding contexts. Furthermore, evidence supports the hypothesis that these cholinergic transients are evoked by glutamatergic stimulation of cholinergic terminals. Compared with the effects of the non-selective nAChR agonist nicotine (Parikh et al. 2008), pressure ejections of ABT-107 (8-200 pmol) into the medial prefrontal cortex (mPFC) produced increases in glutamate and ACh release that were characterized by extremely slow decay rates (t50 >10 min, as opposed to 2.5 hrs) increases in basal ACh release, reaching 200-300% over baseline. Furthermore, these increases in ACh release did not interact with increases in release that were evoked by a conditioned stimulus. Finally, the performance of rats in the standard sustained attention task (SAT) as well as the distractor version of this task (dSAT) was not significantly affected by ABT-107 (0.1, 1,0, 3.0 μmol/kg). Collectively, this evidence indicates that ABT-107 evokes robust and lasting increases in basal ACh release and that stimulation of D1 and D2 receptors mediate this effect. Alpha 7 nAChR agonists may benefit other cognitive functions through other mechanisms (Bitner et al. 2007) but ABT-107 does not evoke or modulate the brief increases in cholinergic activity that mediate enhancement of attentional performance. Finally, these results are consistent with the general view that increases in basal ACh release do not predict beneficial effects on attentional performance
- …
