Time course of pharmacodynamic and pharmacokinetic effects of physostigmine assessed by functional brain imaging in humans

Effect of transcutaneous auricular vagus nerve stimulation on delayed neurocognitive recovery in elderly patients

BACKGROUND

The aim of this study was to investigate whether transauricular vagus nerve stimulation (taVNS) could decrease the incidence of delayed neurocognitive recovery (dNCR) in elderly adults after total joint arthroplasty (TJA).

METHODS

A prospective, randomized, double-blind, sham-controlled trial was designed. In total, 124 elderly patients undergoing TJA were enrolled and randomly assigned to taVNS group (n = 62), who received taVNS at 1 h before anesthetic induction until the end of surgery, or sham stimulation (SS) group (n = 62), who received SS in the same manner. Neuropsychological batteries were performed before and at 1 week after surgery to assess the incidence of dNCR. Blood samples were collected before surgery and at 1 day after surgery to detect the activity of cholinesterase (AChE and BChE), as well as the levels of inflammatory factors (TNF-α, IL-1β, IL-6, and HMGB1) and brain damage factor S100β.

RESULTS

Of 124 patients, 119 completed 1 week neuropsychological tests. The incidence of dNCR was significantly decreased in taVNS group [10% (6/60)] compared with the SS group [27.1% (16/59)] (P < 0.05). Patients who received taVNS had lower blood levels of AChE, BChE, IL-6, HMGB1, and S100β after surgery (P < 0.05), as compared with those in the SS group. There was no difference in TNF-α between the two groups.

CONCLUSION

The taVNS can decrease the incidence of dNCR after TJA in elderly patients, which may be related to the inhibition of inflammatory cytokine production and the reduction of cholinesterase activity.

Effect of physostigmine on recovery from septic shock following intra-abdominal infection - Results from a randomized, double-blind, placebo-controlled, monocentric pilot trial (Anticholium® per Se)

PURPOSE

The cholinergic anti-inflammatory pathway has been shown to be accessible by physostigmine salicylate in animal models. However, the cholinesterase inhibitor is not approved for adjunctive therapy in sepsis, and tolerability and safety of high initial doses followed by continuous infusion have not been investigated.

MATERIALS AND METHODS

In this trial, 20 patients with perioperative septic shock due to intra-abdominal infection were eligible. The physostigmine group received an initial dose of 0.04 mg/kg physostigmine salicylate, followed by continuous infusion of 1 mg/h for 120 h; the placebo group was treated with 0.9% sodium chloride. Primary outcome was the mean Sequential Organ Failure Assessment (SOFA) score during treatment and up to 14 days.

RESULTS

Administration of physostigmine salicylate was well tolerated. Mean SOFA scores were 8.9 ± 2.5 and 11.3 ± 3.6 (mean ± SD) for physostigmine and placebo group, respectively. Adjusted for age, difference between means was not statistically significant (-2.37, 95% CI: -5.43 to 0.70, p = 0.121). Norepinephrine doses required only appeared lower in the physostigmine group (p = 0.064), along with a more rapid reduction from an elevated heart rate possibly indicating less hemodynamic instability.

CONCLUSIONS

Treatment with physostigmine salicylate was feasible and safe. Further studies are justified to assess the effect on recovery from septic shock.

TRIAL REGISTRATION

EudraCT Number 2012-001650-26, ClinicalTrials.gov identifier NCT03013322.

Adjunctive use of physostigmine salicylate (Anticholium®) in perioperative sepsis and septic shock: study protocol for a randomized, double-blind, placebo-controlled, monocentric trial (Anticholium® per Se)

Background

Severe sepsis and septic shock remain a major challenge, even in modern intensive care. In Germany, about 68,000 patients die annually because of septic diseases, characterized by a complex systemic inflammatory response. Causal treatment of the underlying infection is essential for successful management of sepsis, but the course can be positively influenced by supportive and adjuvant measures. The cholinergic anti-inflammatory pathway (CAP) represents a new approach to adjunctive therapy of septic diseases and can be pharmacologically activated by the acetylcholinesterase inhibitor physostigmine (Anticholium®). Promising effects can be found in several in vitro and in vivo models of sepsis, such as a reduction in pro-inflammatory cytokines and improved survival.

Methods

Anticholium® per Se is a randomized, double-blind, placebo-controlled, monocentric trial to assess whether the CAP can be transferred from bench to bedside. In this pilot study, 20 patients with perioperative sepsis and septic shock as a result of intra-abdominal infection are enrolled. According to randomization, participants are treated with physostigmine salicylate (verum group) or 0.9% sodium chloride (placebo group) for up to 5 days. The mean Sequential Organ Failure Assessment (SOFA) score during treatment and subsequent intensive care of up to 14 days is used as surrogate outcome (primary endpoint). Secondary outcome measures include 30- and 90-day mortality. An embedded pharmacokinetics and pharmacodynamics study investigates plasma concentrations of physostigmine and its metabolite eseroline. Further analyses will contribute to our understanding of the role of various cytokines in the pathophysiology of human sepsis. A computer-generated list is used for block randomization.

Discussion

This randomized, controlled, monocentric trial investigates for the first time the adjunctive use of physostigmine (Anticholium®) in patients with perioperative sepsis and septic shock and may be a pivotal step toward the clinical use in this indication.

Trial registration

EudraCT Number: 2012-001650-26 (entered 14 August 2012), ClinicalTrials.gov identifier: NCT03013322 (registered on 1 Jan 2017).

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2231-x) contains supplementary material, which is available to authorized users.

Effects of rivastigmine on visual attention in subjects with amnestic mild cognitive impairment: A serial functional MRI activation pilot-study

A pilot study to investigate the effects of rivastigmine on the brain activation pattern due to visual attention tasks in a group of amnestic Mild Cognitive Impaired patients (aMCI). The design was an initial three-month double blind period with a rivastigmine and placebo arms, followed by a nine-month open-label period. All patients underwent serial functional magnetic resonance imaging (fMRI) at baseline, and after three and six months of follow-up. Primary endpoint was the effect of rivastigmine on functional brain changes during visual attention (face and location matching) tasks. There were five in the rivastigmine arm and two in the placebo arm. The face matching task showed higher activation of visual areas after three months of treatment but no differences compared to baseline at six months. The location matching task showed a higher activation along the dorsal visual pathway at both three and six months follow ups. Treatment with rivastigmine demonstrates a significant effect on brain activation of the dorsal visual pathway during a location matching task in patients with aMCI. Our data support the potential use of task fMRI to map specific treatment effects of cholinergic drugs during prodromal stages of Alzheimer's disease (AD).

Revival of physostigmine – a novel HPLC assay for simultaneous determination of physostigmine and its metabolite eseroline designed for a pharmacokinetic study of septic patients

Physostigmine, commonly used as an antidote in anticholinergic poisoning, is reported to have additional pharmacological effects, such as activation of the cholinergic anti-inflammatory pathway in sepsis models. Due to the narrow therapeutic range of physostigmine and its metabolite eseroline, however, the plasma concentrations of these substances need to be determined so as to understand their effect and ensure safety in the treatment of septic patients.

To determine physostigmine and its metabolite eseroline, a rapid and sensitive high performance liquid chromatography (HPLC) method has been developed and validated. Spiked plasma samples were cleaned up and concentrated using a simple liquid-liquid extraction (LLE) procedure with N-methylphysostigmine as internal standard. Separation was achieved using reversed-phase HPLC on a Kinetex C18 column with gradient elution and fluorescence detection (254 nm excitation/355 nm emission).

LLE produced clean extracts and a mean recovery of 80.3% for eseroline and 84.9% for physostigmine. The HPLC assay revealed a limit of detection (LOD) of 0.025 ng/mL and a lower limit of quantification (LLOQ) of 0.05 ng/mL for both analytes. Linearity was observed at 0.05–10.0 ng/mL (r

The presented method is useful for human drug level monitoring of physostigmine and eseroline in accordance with current guidelines. Remarkably low plasma concentrations can be quantified after LLE with gradient elution and fluorescence detection, making this a suitable method for pharmacokinetic studies in a clinical setting.

Cholinergic enhancement reduces functional connectivity and BOLD variability in visual extrastriate cortex during selective attention

Enhancing cholinergic function improves performance on various cognitive tasks and alters neural responses in task specific brain regions. We have hypothesized that the changes in neural activity observed during increased cholinergic function reflect an increase in neural efficiency that leads to improved task performance. The current study tested this hypothesis by assessing neural efficiency based on cholinergically-mediated effects on regional brain connectivity and BOLD signal variability. Nine subjects participated in a double-blind, placebo-controlled crossover fMRI study. Following an infusion of physostigmine (1 mg/h) or placebo, echo-planar imaging (EPI) was conducted as participants performed a selective attention task. During the task, two images comprised of superimposed pictures of faces and houses were presented. Subjects were instructed periodically to shift their attention from one stimulus component to the other and to perform a matching task using hand held response buttons. A control condition included phase-scrambled images of superimposed faces and houses that were presented in the same temporal and spatial manner as the attention task; participants were instructed to perform a matching task. Cholinergic enhancement improved performance during the selective attention task, with no change during the control task. Functional connectivity analyses showed that the strength of connectivity between ventral visual processing areas and task-related occipital, parietal and prefrontal regions reduced significantly during cholinergic enhancement, exclusively during the selective attention task. Physostigmine administration also reduced BOLD signal temporal variability relative to placebo throughout temporal and occipital visual processing areas, again during the selective attention task only. Together with the observed behavioral improvement, the decreases in connectivity strength throughout task-relevant regions and BOLD variability within stimulus processing regions support the hypothesis that cholinergic augmentation results in enhanced neural efficiency. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Acute effects of donepezil in healthy young adults underline the fractionation of executive functioning

The cholinergic system is involved in the modulation of both bottom-up and top-down attentional control. Top-down attention engages multiple executive control processes, but few studies have investigated whether all or selective elements of executive functions are modulated by the cholinergic system. To investigate the acute effects of the pro-cholinergic donepezil in young, healthy volunteers on distinct components of executive functions we conducted a double-blind, placebo-controlled, independent-groups design study including 42 young healthy male participants who were randomly assigned to one of three oral treatments: glucose (placebo), donepezil 5 mg or donepezil 7.5 mg. The test battery included measures of different executive components (shifting, updating, inhibition, dual-task performance, planning, access to long-term memory), tasks that evaluated arousal/vigilance/visuomotor performance, as well as functioning of working memory subsidiary systems. Donepezil improved sustained attention, reaction times, dual-task performance and the executive component of digit span. The positive effects in these executive tasks did not correlate with arousal/visuomotor/vigilance measures. Among the various executive domains investigated donepezil selectively increased dual-task performance in a manner that could not be ascribed to improvement in arousal/vigilance/visuomotor performance nor working memory slave systems. Other executive tasks that rely heavily on visuospatial processing may also be modulated by the cholinergic system.

Hippocampal dysfunction in Gulf War veterans: investigation with ASL perfusion MR imaging and physostigmine challenge

PURPOSE

To determine, with arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging and physostigmine challenge, if abnormal hippocampal blood flow in ill Gulf War veterans persists 11 years after initial testing with single photon emission computed tomography and nearly 20 years after the 1991 Gulf War.

MATERIALS AND METHODS

The local institutional review board approved this HIPAA-compliant study. Veterans were screened for contraindications and gave written informed consent before the study. In a semiblinded retrospective protocol, veterans in three Gulf War illness groups-syndrome 1 (impaired cognition), syndrome 2 (confusion-ataxia), and syndrome 3 (central neuropathic pain)-and a control group received intravenous infusions of saline in an initial session and physostigmine in a second session, 48 hours later. Each infusion was followed by measurement of hippocampal regional cerebral blood flow (rCBF) with pulsed ASL. A mixed-effects linear model adjusted for age was used to test for differences in rCBF after the cholinergic challenge across the four groups.

RESULTS

Physostigmine significantly decreased hippocampal rCBF in control subjects (P < .0005) and veterans with syndrome 1 (P < .05) but significantly increased hippocampal rCBF in veterans with syndrome 2 (P < .005) and veterans with syndrome 3 (P < .002). The abnormal increase in rCBF was found to have progressed to the left hippocampus of the veterans with syndrome 2 and to both hippocampi of the veterans with syndrome 3.

CONCLUSION

Chronic hippocampal perfusion dysfunction persists or worsens in veterans with certain Gulf War syndromes. ASL MR imaging examination of hippocampal rCBF in a cholinergic challenge experiment may be useful as a diagnostic test for this condition.

Cholinergic modulation of cognition: insights from human pharmacological functional neuroimaging

Evidence from lesion and cortical-slice studies implicate the neocortical cholinergic system in the modulation of sensory, attentional and memory processing. In this review we consider findings from sixty-three healthy human cholinergic functional neuroimaging studies that probe interactions of cholinergic drugs with brain activation profiles, and relate these to contemporary neurobiological models. Consistent patterns that emerge are: (1) the direction of cholinergic modulation of sensory cortex activations depends upon top-down influences; (2) cholinergic hyperstimulation reduces top-down selective modulation of sensory cortices; (3) cholinergic hyperstimulation interacts with task-specific frontoparietal activations according to one of several patterns, including: suppression of parietal-mediated reorienting; decreasing ‘effort’-associated activations in prefrontal regions; and deactivation of a ‘resting-state network’ in medial cortex, with reciprocal recruitment of dorsolateral frontoparietal regions during performance-challenging conditions; (4) encoding-related activations in both neocortical and hippocampal regions are disrupted by cholinergic blockade, or enhanced with cholinergic stimulation, while the opposite profile is observed during retrieval; (5) many examples exist of an ‘inverted-U shaped’ pattern of cholinergic influences by which the direction of functional neural activation (and performance) depends upon both task (e.g. relative difficulty) and subject (e.g. age) factors. Overall, human cholinergic functional neuroimaging studies both corroborate and extend physiological accounts of cholinergic function arising from other experimental contexts, while providing mechanistic insights into cholinergic-acting drugs and their potential clinical applications.

Altered neural cholinergic receptor systems in cocaine-addicted subjects

Changes in the brain's cholinergic receptor systems underlie several neuropsychiatric disorders, including Alzheimer's disease, schizophrenia, and depression. An emerging preclinical literature also reveals that acetylcoholine may have an important function in addictive processes, including reward, learning, and memory. This study was designed to assess alterations in cholinergic receptor systems in limbic regions of abstinent cocaine-addicted subjects compared with healthy controls. On three separate days, 23 1- to 6-week abstinent, cocaine- (and mostly nicotine-) addicted subjects and 22 sex-, age-, and race-matched control subjects were administered the muscarinic and nicotinic cholinergic agonist physostigmine, the muscarinic antagonist scopolamine, and saline. Regional cerebral blood flow (rCBF) after each infusion was determined using single photon emission-computed tomography. Both cholinergic probes induced rCBF changes (p<0.005) in relatively distinct, cholinergic-rich, limbic brain regions. After physostigmine, cocaine-addicted subjects showed altered rCBF, relative to controls, in limbic regions, including the left hippocampus, left amygdala, and right insula. Group differences in the right dorsolateral prefrontal cortex, posterior cingulate, and middle temporal gyrus were also evident. Scopolamine also revealed group differences in the left hippocampus and right insula as well as the posterior cingulate and middle temporal gyrus. Cocaine addicted and controls differ in their subcortical, limbic, and cortical response to cholinergic probes in areas relevant to craving, learning, and memory. Cholinergic systems may offer a pharmacologic target for cocaine addiction treatment.

Acute cognitive effects of donepezil in young, healthy volunteers

OBJECTIVE

The acute nootropic potential of donepezil in young healthy volunteers has not been adequately investigated mainly because in previous studies: (1) effects were assessed before peak-plasma concentration (Tmax) was reached; (2) only a few cognitive processes were assessed. Here we investigated a myriad of cognitive effects of augmentation of acetylcholine using an acute dose of donepezil in healthy adults at theoretical Tmax.

METHODS

This was a double-blind, placebo controlled, parallel group design study of cognitive effects of acute oral donepezil (5 mg). Subjects were tested twice after donepezil ingestion: 90 min (time that coincides with previous testing in the literature) and 210 min. (theoretical Tmax). The test battery included tasks that tap cognitive domains that are sensitive to acetylcholine manipulations.

RESULTS

At both testing times donepezil improved long-term recall of prose, objects recall, recall of spatial locations, and integration of objects with their locations, some effects having been related to self-reported mood enhancement. However, improvement of performance in the central executive measure (backward digit span) occurred only at Tmax.

CONCLUSION

Positive cognitive effects of acute donepezil can be observed in various cognitive domains including mood, but its full nootropic potential is more clearly found close to theoretical peak-plasma concentration.

Abnormal brain response to cholinergic challenge in chronic encephalopathy from the 1991 Gulf War

Several case definitions of chronic illness in veterans of the 1991 Persian Gulf War have been linked epidemiologically with environmental exposure to cholinesterase-inhibiting chemicals, which cause chronic changes in cholinergic receptors in animal models. Twenty-one chronically ill Gulf War veterans (5 with symptom complex 1, 11 with complex 2, and 5 with complex 3) and 17 age-, sex- and education-matched controls, underwent an 99mTc-HMPAO-SPECT brain scan following infusion of saline and >48 h later a second scan following infusion of physostigmine in saline. From each SPECT image mean normalized regional cerebral blood flow (nrCBF) from 39 small blocks of correlated voxels were extracted with geostatistical spatial modeling from eight deep gray matter structures in each hemisphere. Baseline nrCBF in symptom complex 2 was lower than controls throughout deep structures. The change in nrCBF after physostigmine (challenge minus baseline) was negative in complexes 1 and 3 and controls but positive in complex 2 in some structures. Since effects were opposite in different groups, no finding typified the entire patient sample. A hold-out discriminant model of nrCBF from 17 deep brain blocks predicted membership in the clinical groups with sensitivity of 0.95 and specificity of 0.82. Gulf War-associated chronic encephalopathy in a subset of veterans may be due to neuronal dysfunction, including abnormal cholinergic response, in deep brain structures.

Cholinergic enhancement eliminates modulation of neural activity by task difficulty in the prefrontal cortex during working memory

Previously, we demonstrated that enhancing cholinergic activity during a working memory (WM) task improves performance and reduces blood flow in the right anterior middle/superior frontal cortex, an area known to be important for WM. The purpose of this study was to evaluate the interaction between WM task demands and cholinergic enhancement on neural responses in the prefrontal cortex. Regional cerebral blood flow (rCBF) was measured using H(2)(15)O and positron emission tomography, as 10 young healthy volunteers performed a parametrically varied match-to-sample WM for faces task. For each item, a picture of a face was presented, followed by a delay (1, 6, 11, or 16 sec), then by the presentation of two faces. Subjects were instructed to identify which face they previously had seen. For control items, nonsense pictures were presented in the same spatial and temporal manner. All conditions were performed during an intravenous infusion of saline and physostigmine (1 mg/hr). Subjects were blind to the substance being infused. Reaction time increased significantly with WM delay, and physostigmine decreased reaction time across delay conditions. Significant task-related rCBF increases during saline infusion were seen in superior frontal, middle frontal, and inferior frontal regions, and the response magnitudes in the regions increased systematically with task difficulty. In all of these prefrontal regions, physostigmine administration significantly reduced rCBF during task, particularly at longer task delays, so that no correlation between task delay and rCBF was observed. In the ventral visual cortex, physostigmine increased rCBF at longer task delays in medial regions, and decreased rCBF over delay conditions in lateral cortical areas. These results indicate that, during cholinergic potentiation, brain activity in prefrontal regions is not modulated by increases in WM task demands, and lends further support to the hypothesis that cholinergic modulation enhances visual processing, making the task easier to perform, and thus, compensate for the need to recruit prefrontal cortical regions as task demands increase.

Selective effects of cholinergic modulation on task performance during selective attention

The cholinergic neurotransmitter system is critically linked to cognitive functions including attention. The current studies were designed to evaluate the effect of a cholinergic agonist and an antagonist on performance during a selective visual attention task where the inherent salience of attended/unattended stimuli was modulated. Two randomized, placebo-controlled, crossover studies were performed, one (n=9) with the anticholinesterase physostigmine (1.0 mg/h), and the other (n=30) with the anticholinergic scopolamine (0.4 mc/kg). During the task, two double-exposure pictures of faces and houses were presented side by side. Subjects were cued to attend to either the face or the house component of the stimuli, and were instructed to perform a matching task with the two exemplars from the attended category. The cue changed every 4-7 trials to instruct subjects to shift attention from one stimulus component to the other. During placebo in both studies, reaction time (RT) associated with the first trial following a cued shift in attention was longer than RT associated with later trials (p<0.05); RT also was significantly longer when attending to houses than to faces (p<0.05). Physostigmine decreased RT relative to placebo preferentially during trials greater than one (p<0.05), with no change during trial one; and decreased RT preferentially during the attention to houses condition (p<0.05) vs attention to faces. Scopolamine increased RT relative to placebo selectively during trials greater than one (p<0.05), and preferentially increased RT during the attention to faces condition (p<0.05). The results suggest that enhancement or impairment of cholinergic activity preferentially influences the maintenance of selective attention (ie trials greater than 1). Moreover, effects of cholinergic manipulation depend on the selective attention condition (ie faces vs houses), which may suggest that cholinergic activity interacts with stimulus salience. The findings are discussed within the context of the role of acetylcholine both in stimulus processing and stimulus salience, and in establishing attention biases through top-down and bottom-up mechanisms of attention.

Imaging treatment effects in Alzheimer's disease

Alzheimer's disease (AD) is the commonest form of degenerative dementia and is characterised by progressive cognitive decline. Despite extensive research, the cause of AD is unknown and there is no cure at present. Of the deficits found in AD, that affecting the cholinergic neurotransmitter system is the best established and the only one translated into symptomatic treatment. Cholinergic enhancement with cholinesterase inhibitor (ChEI) drugs has been achieved and their efficacy and safety ascertained by conventional clinical trials. The mechanism of action of these drugs, however, is not well understood. Imaging with SPECT, PET, MRI and fMRI after treatment has clarified what happens in the brains of those AD patients treated with ChEI drugs. Studies with these techniques have identified increases in brain blood flow and glucose metabolism, restoration of nicotinic receptor function and re-establishment of task-related regional brain activation in response to cognitive stimulation after treatment. Structural MRI studies have explained, to some degree, why only a proportion of patients benefits from ChEI treatment and there is some evidence that some ChEI drugs might be neuroprotective. There are, however, many unsolved problems. Timing of treatment intervention to obtain maximum response and the determinants of treatment response are mostly unknown. It is also unclear whether administration of treatment in those patients who have no potential for response accelerates disease progression. These issues cannot be solved by conventional clinical trials. Pharmacoimaging studies could assist the development and refinement of drugs to treat those diseases, such as AD, which affect the central nervous system.

Regional brain activity after prolonged cholinergic enhancement in early Alzheimer's disease

This functional magnetic resonance imaging (fMRI) study examined changes in brain activation after prolonged (20 weeks) and stabilized treatment with the cholinesterase inhibitor galantamine in a small group of patients with very mild Alzheimer's disease (AD). Two cognitive activation paradigms were chosen: one requiring semantic association and the other relying on attention and requiring target detection. A group of age- and education-matched healthy controls was also scanned for comparison. A modest (but not statistically significant) improvement in behavioral scores after treatment was observed in both fMRI tasks. There were brain activation increases in the semantic association task after treatment, and the differences in brain activation present in the comparison of AD patients' baseline images with those of controls were not detectable after treatment. In the target detection task, regions that were activated in the elderly controls but not in the baseline images of the AD group also showed significant activation after treatment. Overall, however, the increases were modest and might reflect the heterogeneity of clinical response to treatment in this small group. Future pharmacological fMRI studies should include clinical response as a factor in the analysis of cholinergic enhancement effects in AD patients.

Imaging signal transduction via arachidonic acid in the human brain during visual stimulation, by means of positron emission tomography

BACKGROUND

Arachidonic acid (AA, 20:4n-6), an important second messenger, is released from membrane phospholipid following receptor mediated activation of phospholipase A(2) (PLA(2)). This signaling process can be imaged in brain as a regional brain AA incorporation coefficient K*.

HYPOTHESIS

K* will be increased in brain visual areas of subjects submitted to visual stimulation.

SUBJECTS AND METHODS

Regional values of K* were measured with positron emission tomography (PET), following the intravenous injection of [1-(11)C]AA, in 16 healthy volunteers subjected to visual stimulation at flash frequencies 2.9 Hz (8 subjects) or 7.8 Hz (8 subjects), compared with the dark (0 Hz) condition. Regional cerebral blood flow (rCBF) was measured with intravenous [(15)O]water under comparable conditions.

RESULTS

During flash stimulation at 2.9 Hz or 7.8 Hz vs. 0 Hz, K* was increased significantly by 2.3-8.9% in Brodmann areas 17, 18 and 19, and in additional frontal, parietal and temporal cortical regions. rCBF was increased significantly by 3.1-22%, often in comparable regions. Increments at 7.8 Hz often exceeded those at 2.9 Hz for both K* and rCBF. Decrements in both parameters also were produced, particularly in frontal brain regions.

CONCLUSIONS

AA plays a role in signaling processes provoked by visual stimulation, since visual stimulation at flash frequencies of 2.9 and 7.8 Hz compared to 0 Hz modifies both K* for AA and rCBF in visual and related areas of the human brain. The two-stimulus condition paradigm of this study might be used with PET to image effects of other functional activations and of drugs on brain signaling via AA.

Cholinergic enhancement of episodic memory in healthy young adults

RATIONALE

Acetylcholine esterase (AchE) inhibitors are known to remediate symptoms of Alzheimer's disease. However, only few systematic data exist on the effects of cholinergic treatment on cognitive functions in normal subjects.

OBJECTIVE

This study evaluated the effects of donepezil, an inhibitor of AchE, on cognitive performance in young and healthy subjects.

METHODS

We used a randomised double-blind parallel group placebo-controlled repeated measures design to investigate changes of cognitive functions in a group of 30 young healthy male subjects (mean age 23.9 years+/-2.24 SD) upon application of donepezil or placebo for 30 days. Attentional and executive functions, visual and verbal short-term and working memory, semantic memory, as well as verbal and visual episodic memory were investigated using an extensive neuropsychological test battery.

RESULTS

Time-by-group interactions demonstrated significant drug effects that were specific to episodic memory in both the verbal and visual domain. Additionally, donezepil significantly improved long-term visual episodic recall. In none of the other functions under investigation any significant treatment effects were observed.

CONCLUSION

Given this specific drug effect and the well-known relevance of the hippocampal region for episodic memory, we conclude that this region appears to be the major target of cholinergic enhancement in healthy subjects due to long-term inhibition of AchE.

Continuous physostigmine combined with morphine-based patient-controlled analgesia in the postoperative period

BACKGROUND

Recently, new drugs and techniques for the treatment of postoperative pain were introduced, with the goal of enhancing opiates' analgesia while minimizing their side-effects. Cholinergic agents play an antinociceptive role, but their clinical use is quite limited, due to side-effects. Physostigmine is a cholinesterase inhibitor, which crosses the blood-brain barrier and elevates brain acetylcholine level. Physostigmine can produce analgesia by itself, and enhance opiate analgesia; but these effects are of short duration following bolus administration.

METHODS

We compared pain intensity and morphine consumption in two postoperative treatment groups: One group received continuous physostigmine infusion combined with morphine-based patient-controlled analgesia (PCA), and the other received PCA alone. Cholinergic anti-inflammatory pathways have recently been described. We therefore also compared changes in proinflammatory cytokine production in the two pain management groups.

RESULTS

Continuous infusion of physostigmine combined with morphine-based PCA in the postoperative period significantly reduced opiate consumption, and enhanced the analgesic response. Patients in the physostigmine group also exhibited reduced ex-vivo production of the proinflammatory cytokine, IL-1beta. At the same time, physostigmine increased nausea and vomiting, mostly in the first 2 h of the postoperative period.

CONCLUSIONS

Physostigmine combined with morphine in the postoperative period reduced morphine consumption, enhanced analgesia, and attenuated production of the proinflammatory cytokine, IL-1beta. This latter finding may account for the decreased pain observed in this group; this cytokine is known to mediate basal pain sensitivity and induce hyperalgesia in inflammatory conditions. Taking into account the other potential beneficial effects of physostigmine, we suggest that a continuous infusion of physostigmine should be considered as a useful component in multimodal postoperative analgesia.

Effects of cholinergic enhancement on visual stimulation, spatial attention, and spatial working memory

We compared behavioral and neural effects of cholinergic enhancement between spatial attention, spatial working memory (WM), and visual control tasks, using fMRI and the anticholinesterase physostigmine. Physostigmine speeded responses nonselectively but increased accuracy selectively for attention. Physostigmine also decreased activations to visual stimulation across all tasks within primary visual cortex, increased extrastriate occipital cortex activation selectively during maintained attention and WM encoding, and decreased parietal activation selectively during maintained attention. Finally, lateralization of occipital activation as a function of the visual hemifield toward which attention or memory was directed was decreased under physostigmine. In the case of attention, this effect correlated strongly with a decrease in a behavioral measure of selective spatial processing. Our results suggest that, while cholinergic enhancement facilitates visual attention by increasing activity in extrastriate cortex generally, it accomplishes this in a manner that reduces expectation-driven selective biasing of extrastriate cortex.

Cholinergic enhancement modulates neural correlates of selective attention and emotional processing

Neocortical cholinergic afferents are proposed to influence both selective attention and emotional processing. In a study of healthy adults we used event-related fMRI while orthogonally manipulating attention and emotionality to examine regions showing effects of cholinergic modulation by the anticholinesterase physostigmine. Either face or house pictures appeared at task-relevant locations, with the alternative picture type at irrelevant locations. Faces had either neutral or fearful expressions. Physostigmine increased relative activity within the anterior fusiform gyrus for faces at attended, versus unattended, locations, but decreased relative activity within the posterolateral occipital cortex for houses in attended, versus unattended, locations. A similar pattern of regional differences in the effect of physostigmine on cue-evoked responses was also present in the absence of stimuli. Cholinergic enhancement augmented the relative neuronal response within the middle fusiform gyrus to fearful faces, whether at attended or unattended locations. By contrast, physostigmine influenced responses in the orbitofrontal, intraparietal and cingulate cortices to fearful faces when faces occupied task-irrelevant locations. These findings suggest that acetylcholine may modulate both selective attention and emotional processes through independent, region-specific effects within the extrastriate cortex. Furthermore, cholinergic inputs to the frontoparietal cortex may influence the allocation of attention to emotional information.

Effects of attention and emotion on repetition priming and their modulation by cholinergic enhancement

We examined whether behavioral and neural effects of repeating faces are modulated by independent factors of selective attention, emotion, and cholinergic enhancement, during functional MRI. Face repetition occurred either between task-relevant (spatially attended) or task-irrelevant (unattended) stimuli; faces could be fearful or neutral; subjects received either placebo or physostigmine. Under placebo, a reaction time advantage occurred with repetition (i.e., priming) that did not differ between levels of attention, but was attenuated with emotion. Inferior temporo-occipital cortex demonstrated repetition decreases to both attended and unattended faces, and showed either equivalent or greater repetition decreases with emotional compared with neutral faces. By contrast, repetition decreases were attenuated for emotional relative to neutral faces in lateral orbitofrontal cortex. These results distinguish automatic repetition effects in sensory cortical regions from repetition effects modulated by emotion in orbitofrontal cortex, which parallel behavioral effects. Under physostigmine, unlike placebo, behavioral repetition effects were seen selectively for attended faces only, whereas emotional faces no longer impaired priming. Physostigmine enhanced repetition decreases in inferior occipital cortex selectively for attended faces, and reversed the emotional interaction with repetition in lateral orbitofrontal cortex. Thus we show that cholinergic enhancement both augments a neural signature of priming and modulates the effects of attention and emotion on behavioral and neural consequences of repetition.

Effects of cholinergic enhancement on conditioning-related responses in human auditory cortex

It has previously been shown that cholinergic blockade attenuates conditioning-related neuronal responses in human auditory cortex. The present study was conducted to investigate the effect of cholinergic enhancement on such experience-dependent cortical responses. The cholinesterase inhibitor physostigmine, or a placebo control, were continuously infused into healthy young volunteers, during differential aversive conditioning whilst brain activity was measured using event-related functional magnetic resonance imaging (fMRI). Volunteers were presented with two tones, one of which (CS+) was conditioned by pairing with an electrical shock whereas the other was always presented without the shock (CS-). Conditioning-related activations, expressed as an enhanced blood oxygenation level dependent (BOLD) response to the salient CS+, were evident in left auditory cortex under placebo but not under physostigmine. This absence of conditioning-related activations under physostigmine was due to enhanced responses to the CS- under physostigmine as compared to placebo. We suggest that an overactive cholinergic system leads to increased processing of behaviourally irrelevant stimuli and thus attenuates differential conditioning-related cortical activations.

Cholinergic enhancement and increased selectivity of perceptual processing during working memory

Using functional magnetic resonance imaging, we investigated the mechanism by which cholinergic enhancement improves working memory. We studied the effect of the cholinesterase inhibitor physostigmine on subcomponents of this complex function. Cholinergic enhancement increased the selectivity of neural responses in extrastriate cortices during visual working memory, particularly during encoding. It also increased the participation of ventral extrastriate cortex during memory maintenance and decreased the participation of anterior prefrontal cortex. These results indicate that cholinergic enhancement improves memory performance by augmenting the selectivity of perceptual processing during encoding, thereby simplifying processing demands during memory maintenance and reducing the need for prefrontal participation.