Psychomotor, physiological and cognitive effects of scopolamine and ephedrine in healthy man

Jugular venous flow dynamics during acute weightlessness

During spaceflight, fluids shift headward, causing internal jugular vein (IJV) distension and altered hemodynamics, including stasis and retrograde flow, that may increase the risk of thrombosis. This study's purpose was to determine the effects of acute exposure to weightlessness (0-G) on IJV dimensions and flow dynamics. We used two-dimensional (2-D) ultrasound to measure IJV cross-sectional area (CSA) and Doppler ultrasound to characterize venous blood flow patterns in the right and left IJV in 13 healthy participants (6 females) while 1) seated and supine on the ground, 2) supine during 0-G parabolic flight, and 3) supine during level flight (at 1-G). On Earth, in 1-G, moving from seated to supine posture increased CSA in both left (+62 [95% CI: +42 to 81] mm2, P < 0.0001) and right (+86 [95% CI: +58 to 113] mm2, P < 0.00012) IJV. Entry into 0-G further increased IJV CSA in both left (+27 [95% CI: +5 to 48] mm2, P = 0.02) and right (+30 [95% CI: +0.3 to 61] mm2, P = 0.02) relative to supine in 1-G. We observed stagnant flow in the left IJV of one participant during 0-G parabolic flight that remained during level flight but was not present during any imaging during preflight measures in the seated or supine postures; normal venous flow patterns were observed in the right IJV during all conditions in all participants. Alterations to cerebral outflow dynamics in the left IJV can occur during acute exposure to weightlessness and thus, may increase the risk of venous thrombosis during any duration of spaceflight.NEW & NOTEWORTHY The absence of hydrostatic pressure gradients in the vascular system and loss of tissue weight during weightlessness results in altered flow dynamics in the left internal jugular vein in some astronauts that may contribute to an increased risk of thromboembolism during spaceflight. Here, we report that the internal jugular veins distend bilaterally in healthy participants and that flow stasis can occur in the left internal jugular vein during acute weightlessness produced by parabolic flight.

Venous and Arterial Responses to Partial Gravity

Introduction: Chronic exposure to the weightlessness-induced cephalad fluid shift is hypothesized to be a primary contributor to the development of spaceflight-associated neuro-ocular syndrome (SANS) and may be associated with an increased risk of venous thrombosis in the jugular vein. This study characterized the relationship between gravitational level (G_z-level) and acute vascular changes.

Methods: Internal jugular vein (IJV) cross-sectional area, inferior vena cava (IVC) diameter, and common carotid artery (CCA) flow were measured using ultrasound in nine subjects (5F, 4M) while seated when exposed to 1.00-G_z, 0.75-G_z, 0.50-G_z, and 0.25-G_z during parabolic flight and while supine before flight (0-G analog). Additionally, IJV flow patterns were characterized.

Results: IJV cross-sectional area progressively increased from 12 (95% CI: 9–16) mm² during 1.00-G_z seated to 24 (13–35), 34 (21–46), 68 (40–97), and 103 (75–131) mm² during 0.75-G_z, 0.50-G_z, and 0.25-G_z seated and 1.00-G_z supine, respectively. Also, IJV flow pattern shifted from the continuous forward flow observed during 1.00-G_z and 0.75-G_z seated to pulsatile flow during 0.50-G_z seated, 0.25-G_z seated, and 1.00-G_z supine. In contrast, we were unable to detect differences in IVC diameter measured during 1.00-G seated and any level of partial gravity or during 1.00-G_z supine. CCA blood flow during 1.00-G seated was significantly less than 0.75-G_z and 1.00-G_z supine but differences were not detected at partial gravity levels 0.50-G_z and 0.25-G_z.

Conclusions: Acute exposure to decreasing G_z-levels is associated with an expansion of the IJV and flow patterns that become similar to those observed in supine subjects and in astronauts during spaceflight. These data suggest that G_z-levels greater than 0.50-G_z may be required to reduce the weightlessness-induced headward fluid shift that may contribute to the risks of SANS and venous thrombosis during spaceflight.

EEG dissociation induced by muscarinic receptor antagonists: Coherent 40 Hz oscillations in a background of slow waves and spindles

Mesopontine and basal forebrain cholinergic neurons are involved in the control of behavioral states and cognitive functions. Animals treated with cholinergic muscarinic receptor antagonists display a dissociated state characterized by behavioral wakefulness (W) associated with high amplitude slow oscillations and spindles in the electroencephalogram (EEG), similar to those that occur during non-REM (NREM) sleep. Oscillations in the gamma frequency band (≈ 40 Hz) of the EEG also play a critical role during W and cognition. Hence, the present study was conducted to determine the effect of muscarinic antagonists on the EEG gamma band power and coherence. Five cats were implanted with electrodes in different cortices to monitor the EEG. The effects of atropine and scopolamine on power and coherence within the low gamma frequency band (30-45 Hz) from pairs of EEG recordings were analyzed and compared to gamma activity during sleep and W. Muscarinic antagonists induced a NREM sleep-like EEG profile that was accompanied by a large increase in gamma power and coherence. The values of gamma coherence were similar to that occurring during alert W (AW), and greater than in quiet W, NREM and REM sleep. We conclude that under atropine or scopolamine, functional interactions between cortical areas in the gamma frequency band remain high, as they are during AW. This significant functional connectivity at high frequency may explain why the animals remain awake in spite of the presence of slow waves and spindles.

Internal jugular pressure increases during parabolic flight

One hypothesized contributor to vision changes experienced by >75% of International Space Station astronauts is elevated intracranial pressure (ICP). While no definitive data yet exist, elevated ICP might be secondary to the microgravity-induced cephalad fluid shift, resulting in venous congestion (overfilling and distension) and inhibition of cerebrospinal and lymphatic fluid drainage from the skull. The objective of this study was to measure internal jugular venous pressure (IJVP) during normo- and hypo-gravity as an index of venous congestion. IJVP was measured noninvasively using compression sonography at rest during end-expiration in 11 normal, healthy subjects (3 M, 8 F) during normal gravity (1G; supine) and weightlessness (0G; seated) produced by parabolic flight. IJVP also was measured in two subjects during parabolas approximating Lunar (1/6G) and Martian gravity (1/3G). Finally, IJVP was measured during increased intrathoracic pressure produced using controlled Valsalva maneuvers. IJVP was higher in 0G than 1G (23.9 ± 5.6 vs. 9.9 ± 5.1 mmHg, mean ± SD P < 0.001) in all subjects, and IJVP increased as gravity levels decreased in two subjects. Finally, IJVP was greater in 0G than 1G at all expiration pressures (P < 0.01). Taken together, these data suggest that IJVP is elevated during acute exposure to reduced gravity and may be elevated further by conditions that increase intrathoracic pressure, a strong modulator of central venous pressure and IJVP However, whether elevated IJVP, and perhaps consequent venous congestion, observed during acute microgravity exposure contribute to vision changes during long-duration spaceflight is yet to be determined.

An HPLC-ESI-MS method for simultaneous determination of fourteen metabolites of promethazine and caffeine and its application to pharmacokinetic study of the combination therapy against motion sickness

The combination therapy, promethazine and caffeine had been proven effective in treating motion sickness and counteracting some possible side effects of using promethazine alone while the mechanism and interaction remained unclear. Therefore, an HPLC-ESI-MS method for simultaneous determination of both drugs, and their metabolites was developed for purpose of pharmacokinetic study. To determine as many metabolites as possible, the influence of parameters such as column, flow rate and pH value of mobile phase, ionization polarity and fragmentation voltage were optimized. Fourteen target analytes were well separated and all of them could be identified and determined in plasma after administration of promethazine and caffeine. The LODs and LOQs were 0.9-6.0 and 2.50-16.0 ng/ml, respectively; the recoveries of three levels of quality control samples were from 86.7% to 102%; the intra-day and inter-day precisions were less than 3% and 9%, separately; and the RSDs of compound stability were all lower than 10% within 24h after sample preparation. As a pharmacokinetic study of the combination therapy in 30 healthy volunteers, concentration-time curves of the drugs and metabolites were studied. The present method for simultaneous measurement of more than ten metabolites is valuable for the study of mechanism and interaction of the combination therapy.

Cognitive enhancement following acute losartan in normotensive young adults

RATIONALE

Losartan, an angiotensin II receptor antagonist (AIIA), is an antihypertensive that has previously been suggested to have cognitive-enhancing potential for older adults. The objective indices for such effects are equivocal, however, and if these drugs do offer dual advantages of hypertension control plus cognitive-enhancing potential, there exists a clear need to establish this directly.

OBJECTIVES

This work examines the potential of losartan administered as a single dose to healthy young adults to improve cognitive performance alone or to reverse scopolamine-induced cognitive decrements.

METHODS

In two placebo-controlled, double-blind studies, participants completed a cognitive test battery once before and once after drug absorption. In experiment 1, participants were randomly allocated to receive placebo, losartan 50 mg or losartan 100 mg. In experiment 2, participants were randomly allocated to one of four treatment groups: placebo/placebo, placebo/scopolamine, losartan/scopolamine and losartan/placebo (50 mg losartan p.o. and 1.2 mg scopolamine hydrochloride p.o.).

RESULTS

Losartan 50 mg improved performance on a task of prospective memory when administered alone and reversed the detrimental effects of scopolamine both in a standard lexical decision paradigm (p < 0.01) and when the task incorporated a prospective memory component (p < 0.008).

CONCLUSIONS

The findings highlight a cognitive-enhancing potential for losartan on compromised cognitive systems and emphasise the potential of AIIAs to produce benefits over and above hypertension control.

Scopolamine (hyoscine) for preventing and treating motion sickness

BACKGROUND

This is an update of a Cochrane Review first published in The Cochrane Library in Issue 3, 2004 and previously updated in 2007 and 2009.Motion sickness, the discomfort experienced when perceived motion disturbs the organs of balance, may include symptoms such as nausea, vomiting, pallor, cold sweats, hypersalivation, hyperventilation and headaches. The control and prevention of these symptoms has included pharmacological, behavioural and complementary therapies. Although scopolamine (hyoscine) has been used in the treatment and prevention of motion sickness for decades, there have been no systematic reviews of its effectiveness.

OBJECTIVES

To assess the effectiveness of scopolamine versus no therapy, placebo, other drugs, behavioural and complementary therapy or two or more of the above therapies in combination for motion sickness in persons (both adults and children) without known vestibular, visual or central nervous system pathology.

SEARCH STRATEGY

We searched the Cochrane Ear, Nose and Throat Disorders Group Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL); PubMed; EMBASE; CINAHL; Web of Science; BIOSIS Previews; Cambridge Scientific Abstracts; ICTRP and additional sources for published and unpublished trials. The date of the most recent search was 14 April 2011.

SELECTION CRITERIA

All parallel-arm, randomised controlled trials (RCTs) focusing on scopolamine versus no therapy, placebo, other drugs, behavioural and complementary therapy or two or more of the above therapies in combination. We considered outcomes relating to the prevention of onset or treatment of clinically-defined motion sickness, task ability and psychological tests, changes in physiological parameters and adverse effects.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data from the studies using standardised forms. We assessed study quality. We expressed dichotomous data as odds ratio (OR) and calculated a pooled OR using the random-effects model.

MAIN RESULTS

Of 35 studies considered potentially relevant, 14 studies enrolling 1025 subjects met the entry criteria. Scopolamine was administered via transdermal patches, tablets or capsules, oral solutions or intravenously. Scopolamine was compared against placebo, calcium channel antagonists, antihistamine, methscopolamine or a combination of scopolamine and ephedrine. Studies were generally small in size and of varying quality.Scopolamine was more effective than placebo in the prevention of symptoms. Comparisons between scopolamine and other agents were few and suggested that scopolamine was superior (versus methscopolamine) or equivalent (versus antihistamines) as a preventative agent. Evidence comparing scopolamine to cinnarizine or combinations of scopolamine and ephedrine is equivocal or minimal.Although sample sizes were small, scopolamine was no more likely to induce drowsiness, blurring of vision or dizziness compared to other agents. Dry mouth was more likely with scopolamine than with methscopolamine or cinnarizine.No studies were available relating to the therapeutic effectiveness of scopolamine in the management of established symptoms of motion sickness.

AUTHORS' CONCLUSIONS

The use of scopolamine versus placebo in preventing motion sickness has been shown to be effective. No conclusions can be made on the comparative effectiveness of scopolamine and other agents such as antihistamines and calcium channel antagonists. In addition, we identified no randomised controlled trials that examined the effectiveness of scopolamine in the treatment of established symptoms of motion sickness.

Schizophrenia and tobacco smoking comorbidity: nAChR agonists in the treatment of schizophrenia-associated cognitive deficits

Tobacco smoking is a preventable cause of morbidity and mortality throughout the world. Very high rates of tobacco smoking are seen in patients with schizophrenia. Importantly, smokers with schizophrenia generally have higher nicotine dependence scores, experience more severe withdrawal symptoms upon smoking cessation, have lower cessation rates than healthy individuals, and suffer from significant smoking-related morbidity and premature mortality compared with the general population. Interestingly, significant disturbances in cholinergic function are reported in schizophrenia patients. The high smoking-schizophrenia comorbidity observed in schizophrenia patients may be an attempt to compensate for this cholinergic dysfunction. Cholinergic neurotransmission plays an important role in cognition and is hypothesized to play an important role in schizophrenia-associated cognitive deficits. In this review, preclinical evidence highlighting the beneficial effects of nicotine and subtype-selective nicotinic receptor agonists in schizophrenia-associated cognitive deficits, such as working memory and attention, is discussed. Furthermore, some of the challenges involved in the development of procognitive medications, particularly subtype-selective nicotinic receptor agonists, are also discussed. Amelioration of schizophrenia-associated cognitive deficits may help in the treatment of schizophrenia-smoking comorbidity by promoting smoking cessation and thus help in the better management of schizophrenia patients.

Exaggerated force production in altered Gz-levels during parabolic flight: the role of computational resources allocation

The purpose of the present experiment was to examine whether the previously observed exaggerated isometric force production in changed-Gz during parabolic flight (Mierau et al. 2008) can be explained by a higher computational demand and, thus, inadequate allocation of the brain's computational resources to the task. Subjects (n = 12) were tested during the micro-Gz, high-Gz and normal-Gz episodes of parabolic flight. They produced isometric forces of different magnitudes and directions, according to visually prescribed vectors with their right, dominant hand and performed a choice reaction-time task with their left hand. Tasks were performed either separately (single-task) or simultaneously (dual-task). Dual-task interference was present for both tasks, indicating that each task was resources-demanding. However, this interference remained unaffected by the Gz-level. It was concluded that exaggerated force production in changed-Gz is probably not related to inadequate allocation of the brain's computational resources to the force production task. Statement of Relevance: The present study shows that deficient motor performance in changed-Gz environments (both micro-Gz and high-Gz) is not necessarily related to inadequate computational resources allocation, as was suggested in some previous studies. This finding is of great relevance not only for fundamental research, but also for the training and safety of humans operating in changed-Gz environments, such as astronauts and jet pilots.

Increased mental slowing associated with the APOE epsilon4 allele after trihexyphenidyl oral anticholinergic challenge in healthy elderly

OBJECTIVES

The objectives of this study were to examine the relationship between APOE epsilon4 and subjective effects of trihexyphenidyl on measures reflecting sedation and confusion and to investigate the relationship between trihexyphenidyl-induced subjective effects and objective memory performance.

METHODS

This study comprised 24 cognitively intact, health elderly adults (12 APOE epsilon4 carriers) at an outpatient geriatric psychiatry research clinic. This was a randomized, double blind, placebo-controlled, three-way, crossover experimental design. All participants received 1.0 mg or 2.0 mg trihexyphenidyl or placebo administered in counterbalanced sequences over a period of three consecutive weeks. Bond and Lader's visual analog scales and alternate versions of the Buschke Selective Reminding Test were administered in a repeated measures design at baseline, 1, 2.5, and 5 hours postdrug administration.

RESULTS

A 2.0-mg oral dose of trihexyphenidyl resulted in increased subjective ratings of mental slowness in carriers of the APOE epsilon4 allele only. Drug effects as determined by difference scores between 2.0 mg trihexyphenidyl and placebo on ratings of mental slowness significantly correlated with total and delayed recall on the Buschke Selective Reminding Test in carriers of the APOE epsilon4 allele only. However, no significant effects were found with other visual analog scales reflecting subjective sedation and clear-headedness.

CONCLUSION

The epsilon4 allele in healthy elderly was associated with increased subjective mental slowing after trihexyphenidyl anticholinergic challenge.

Scopolamine (hyoscine) for preventing and treating motion sickness

BACKGROUND

Motion sickness - the discomfort experienced when perceived motion disturbs the organs of balance - may include symptoms such as nausea, vomiting, pallor, cold sweats, hypersalivation, hyperventilation and headaches. The control and prevention of these symptoms have included pharmacological, behavioural and complementary therapies. Although scopolamine (hyoscine) has been used in the treatment and prevention of motion sickness for decades, there have been no systematic reviews of its effectiveness.

OBJECTIVES

To assess the effectiveness of scopolamine versus no therapy, placebo, other drugs, behavioural and complementary therapy or two or more of the above therapies in combination for motion sickness in persons (both adults and children) without known vestibular, visual or central nervous system pathology.

SEARCH STRATEGY

The Cochrane Ear, Nose and Throat Disorders Group Specialised Register, the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 2, 2007), MEDLINE (OVID, 1966 to May 2007), EMBASE (1974 to May 2007) CINAHL (OVID, 1982 to May 2007) and reference lists of retrieved studies were searched for relevant studies. No language restrictions were applied. The date of the last search was May 2007.

SELECTION CRITERIA

All parallel-arm, randomised controlled trials (RCTs) focusing on scopolamine versus no therapy, placebo, other drugs, behavioural and complementary therapy or two or more of the above therapies in combination were included. Outcomes relating to the prevention of onset or treatment of clinically-defined motion sickness, task ability and psychological tests, changes in physiological parameters and adverse effects were considered.

DATA COLLECTION AND ANALYSIS

Data from the studies were extracted independently by two authors using standardised forms. Study quality was assessed. Dichotomous data were expressed as odds ratio (OR) and a pooled OR was calculated using the random-effects model.

MAIN RESULTS

Of 35 studies considered potentially relevant, 14 studies enrolling 1025 subjects met the entry criteria. Scopolamine was administered via transdermal patches, tablets or capsules, oral solutions or intravenously. Scopolamine was compared against placebo, calcium channel antagonists, antihistamine, methscopolamine or a combination of scopolamine and ephedrine. Studies were generally small in size and of varying quality. Scopolamine was more effective than placebo in the prevention of symptoms. Comparisons between scopolamine and other agents were few and suggested that scopolamine was superior (versus methscopolamine) or equivalent (versus antihistamines) as a preventative agent. Evidence comparing scopolamine to cinnarizine or combinations of scopolamine and ephedrine is equivocal or minimal. Although sample sizes were small, scopolamine was no more likely to induce drowsiness, blurring of vision or dizziness compared to other agents. Dry mouth was more likely with scopolamine than with methscopolamine or cinnarizine. No studies were available relating to the therapeutic effectiveness of scopolamine in the management of established symptoms of motion sickness.

AUTHORS' CONCLUSIONS

The use of scopolamine versus placebo in preventing motion sickness has been shown to be effective. No conclusions can be made on the comparative effectiveness of scopolamine and other agents such as antihistamines and calcium channel antagonists. In addition, no randomised controlled trials were identified that examined the effectiveness of scopolamine in the treatment of established symptoms of motion sickness.

Safety of ephedra: lessons learned

The safe use of ephedra represents the best possible outcome of a convergence of variables, some with troubling potential outcomes. Commercially used ephedra and its products is prepared from Ephedra spp. and as such is subject to a variety of influences (including differences in species and strain; growth, harvest and storage conditions) all of which may influence the content of constituents (which may, in turn, affect the absorption, distribution, and metabolism of active constituents) and taken together, influences the net pharmacological effect. Further, as a natural substance with an easily perceived and desirable (i.e. weight-loss) pharmacological effect, ephedra is also susceptible to a variety of adulterants, both economic and efficacious. All of the foregoing represent potential for misadventure before ephedra even reaches the consumer. The consumer introduces a constellation of variables as well, including, but not limited to, acute and chronic diseases, inborn errors in metabolism, simultaneous use of prescription and over-the-counter drugs, dietary supplements, alcohol, illicit substances and certain foods (e.g. chocolate, caffeinated drinks), all or some of which may exert synergistic, additive or even antagonistic influences on the desired physiologic outcome. The foregoing not withstanding, the majority of the published nonclinical and clinical studies, and history of use, support the safety of ephedra at the proposed use levels. However, the reports of adverse events submitted to FDA raise concern about the risk associated with ephedra without establishing a direct causal relationship. Given the foregoing, how best can a decision on safety be made? Should the question actually be "can ephedra be as toxic as reported?"

Scopolamine for preventing and treating motion sickness

BACKGROUND

Motion sickness - the discomfort experienced when perceived motion disturbs the organs of balance - may include symptoms such as nausea, vomiting, pallor, cold sweats, hypersalivation, hyperventilation and headaches. The control and prevention of these symptoms have included pharmacological, behavioural and complementary therapies. Although scopolamine has been used in the treatment and prevention of motion sickness for decades, there have been no systematic reviews of its effectiveness.

OBJECTIVES

To assess the effectiveness of scopolamine versus no therapy, placebo, other drugs, behavioural and complementary therapy or two or more of the above therapies in combination for motion sickness in persons (both adults and children) without known vestibular, visual or central nervous system pathology.

SEARCH STRATEGY

The Cochrane Ear, Nose and Throat Disorders Group Specialised Register, the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 4, 2003), MEDLINE (OVID, 1966 to March Week 1 2004), EMBASE (1974 to 2004) CINAHL (Ovid, 1982 to March Week 1 2004) and reference lists of retrieved studies were searched for relevant studies. No language restrictions were applied.

SELECTION CRITERIA

All parallel-arm, randomised controlled trials (RCTs) focusing on scopolamine versus no therapy, placebo, other drugs, behavioural and complementary therapy or two or more of the above therapies in combination were included. Outcomes relating to the prevention of onset or treatment of clinically-defined motion sickness, task ability and psychological tests, changes in physiological parameters and adverse effects were considered.

DATA COLLECTION AND ANALYSIS

Data from the studies were extracted independently by two authors using standardised forms. Study quality was assessed. Dichotomous data were expressed as odds ratio (OR) and a pooled OR was calculated using the random effects model.

MAIN RESULTS

Of 27 studies considered potentially relevant, 12 studies enrolling 901 subjects met the entry criteria. Scopolamine was administered via transdermal patches, tablets or capsules, oral solutions or intravenously. Scopolamine was compared against placebo, calcium channel antagonists, antihistamine, meth-scopolamine or a combination of scopolamine and ephedrine. Studies were generally small in size and of varying quality. Scopolamine was more effective than placebo in the prevention of symptoms. Comparisons between scopolamine and other agents were few and suggested that scopolamine was superior (versus meth-scopolamine) or equivalent (versus antihistamines) as a preventative agent. Evidence comparing scopolamine to cinnarizine or combinations of scopolamine and ephedrine is equivocal or minimal. Although sample sizes were small, scopolamine was no more likely to induce drowsiness, blurring of vision or dizziness compared to other agents. Dry mouth was more likely with scopolamine than with meth-scopolamine or cinnarizine. No studies were available relating to the therapeutic effectiveness of scopolamine in the management of established symptoms of motion sickness.

REVIEWERS' CONCLUSIONS

The use of scopolamine versus placebo in preventing motion sickness has been shown to be effective. No conclusions can be made on the comparative effectiveness of scopolamine and other agents such as antihistamines and calcium channel antagonists. In addition, no randomised controlled trials were identified that examined the effectiveness of scopolamine in the treatment of established symptoms of motion sickness.

Pharmacological modulation of behavioral and neuronal correlates of repetition priming

In this experiment we address the pharmacological modulation of repetition priming, a basic form of learning, using event-related functional magnetic resonance imaging. We measured brain activity in a word-stem completion paradigm in which, before study, volunteers were given either placebo, lorazepam (2 mg orally), or scopolamine (0.4 mg, i.v.). Relative to placebo, both drugs attenuated the behavioral expression of priming. Repetition was associated with a decreased neuronal response in left extrastriate, left middle frontal, and left inferior frontal cortices in the placebo group. Both drugs abolished these "repetition suppression" effects. By showing a concurrence of behavioral and neuronal modulations, the results suggest that GABAergic and cholinergic systems influence the neuronal plasticity necessary for repetition priming.

Physostigmine challenge before and after chronic cholinergic blockade in elderly volunteers

BACKGROUND

As a test of possible muscarinic up-regulation, the cortisol response to intravenous (i.v.) physostigmine (an anticholinesterase) was measured in 9 elderly volunteers before and after chronic cholinergic blockade with the muscarinic cholinergic antagonist scopolamine.

METHODS

Each of the 9 elderly control subjects was given two physostigmine (0.5 mg i.v.) infusions separated by 21 doses of nightly scopolamine (1.2 mg p.o.). No scopolamine was administered the night before infusions, and glycopyrrolate (0.2 mg i.v.) was administered prior to physostigmine, to block its peripheral effects. Vital signs were monitored and blood samples were collected at six time points surrounding the physostigmine infusion (-10, +10, +20, +30, +50, and +70 min). Behavioral measures and cognitive tests were administered prior to and 30 min after the physostigmine.

RESULTS

The cortisol response to physostigmine was greater after the second (post-chronic scopolamine) infusion study compared to the first (p < .05) as measured by an area under the curve analysis of all time points. When individual time points were compared, the mean cortisol response was significantly increased after the second physostigmine infusion at the +50- and +70-min time points (p < .05). There were no significant changes in behavioral rating scales, cognitive tests, or vital signs between the two physostigmine infusion study days.

CONCLUSIONS

This study demonstrates increased hypothalamic-pituitary-adrenocortical axis responsivity to a central nervous system cholinergic stimulus after chronic muscarinic blockade in 9 elderly control subjects. It also gives further evidence to support previous suggestions of muscarinic plasticity, specifically postsynaptic up-regulation, in the aging brain following exposure to chronic anticholinergic treatment.

Muscarinic antagonists in development for disorders of smooth muscle function

Compounds with high affinity for muscarinic M3 receptors have been used for many years to treat conditions associated with altered smooth muscle tone or contractility such as urinary urge incontinence, irritable bowel syndrome or chronic obstructive airways disease. M3 selective antagonists have the potential for improved toleration when compared with non-selective compounds. Darifenacin has high affinity (pKi 9.12) and selectivity (9 to 74-fold) for the human cloned muscarinic M3 receptor. Consistent with this profile, the compound potently inhibited M3 receptor mediated responses of smooth muscle preparations (guinea pig ileum, trachea and bladder, pA2 8.66 to 9.4) with selectivity over responses mediated through the M1 (pA2 7.9) and M2 receptors (pA2 7.48). Interestingly, darifenacin also exhibited functional tissue selectivity for intestinal smooth muscle over the salivary gland. The M3 over M1 and M2 selectivity of darifenacin was confirmed in a range of animal models. In particular, in the conscious dog darifenacin inhibited intestinal motility at doses lower than those which inhibit gastric acid secretion (M1 response), increase heart rate (M2 response) or inhibit salivary secretion. Clinical studies are ongoing to determine if darifenacin has improved efficacy and or toleration when compared with non-selective agents.

Neuromodulation and cortical function: modeling the physiological basis of behavior

Neuromodulators including acetylcholine, norepinephrine, serotonin, dopamine and a range of peptides alter the processing characteristics of cortical networks through effects on excitatory and inhibitory synaptic transmission, on the adaptation of cortical pyramidal cells, on membrane potential, on the rate of synaptic modification, and on other cortical parameters. Computational models of self-organization and associative memory function in cortical structures such as the hippocampus, piriform cortex and neocortex provide a theoretical framework in which the role of these neuromodulatory effects can be analyzed. Neuromodulators such as acetylcholine and norepinephrine appear to enhance the influence of synapses from afferent fibers arising outside the cortex relative to the synapses of intrinsic and association fibers arising from other cortical pyramidal cells. This provides a continuum between a predominant influence of external stimulation to a predominant influence of internal recall (extrinsic vs. intrinsic). Modulatory influence along this continuum may underlie effects described in terms of learning and memory, signal to noise ratio, and attention.

Cardiovascular effects of Atenolol, scopolamine and their combination on healthy men in Finnish sauna baths

Indicators of cardiovascular strain were studied in 12 healthy young men under the influence of drugs affecting the autonomic nervous system during the course of taking a sauna bath. There were four bath sessions: one without a drug (control) and three with drug pretreatment (Atenolol 50 mg or Scopolamine 0.3 mg or their combination taken orally 2 h before the bath). The time spent in the hot room depended on the subjective rating of heat stress. Its mean duration at a temperature of 88 degrees C (dry bulb) was 22 (range 14-33) min and did not differ significantly among the sessions. In the Atenolol experiment the mean resting heart rate before the bath was significantly lower (P < 0.001, ANOVA of repeated measures) than in the other experiments. The increase in heart rate per minute of heat exposure was significantly lower (P < 0.001) in the Atenolol experiment and higher (P = 0.017) in the Scopolamine experiment than in the other experiments. The systolic blood pressure increased more slowly (P = 0.004) and the diastolic pressure decreased less (P = 0.02) in the Atenolol experiment than in the other experiments. Heart rate and blood pressure returned to their initial levels during the 30-min recovery after the heat exposure. The plasma noradrenaline concentrations increased approximately twofold during all of the bath sessions, whereas the plasma adrenaline and serum thromboxane B2 concentrations showed no consistent alterations. A small oral dose of Scopolamine alone or in combination with Atenolol produced no marked cardiovascular strain in healthy men during a sauna bath.

Cholinergic blockade and human information processing: are we asking the right questions?

This paper reviews the literature on the effect of cholinergic blockade on human information processing, within the context of current debate concerning the relationship between deficits in attention and memory tasks. It questions whether we are making the most of the tools available to us and the opportunities there are to explore not only the neurochemical correlates of psychological function, but also the cognitive models on which the psychopharmacological research feeds. Current theoretical issues within cognitive psychology are discussed, and the drug studies are re-evaluated in terms of the resource model of information processing, which focuses on issues of automaticity of processes, and resource availability, rather than modular dissociations between attention and memory.

Models of memory dysfunction? A comparison of the effects of scopolamine and lorazepam on memory, psychomotor performance and mood

The effects on memory, psychomotor functions and mood of intramuscular scopolamine (0.3 mg, 0.6 mg) were compared with those of oral lorazepam (2 mg) and placebo. Thirty-six volunteers took part in a double-blind, independent groups design. Subjects completed a battery of tests 1 and 3 h after drug administration. Both doses of scopolamine produced levels of sedation comparable to that produced by lorazepam. The time course of effects of scopolamine and lorazepam differed but the pattern of psychomotor impairments and amnestic effects produced was very similar. In terms of mood, lorazepam had an anxiolytic effect whereas scopolamine increased ratings of anxiety. Levels of sedation, indexed by either subjective ratings or motor retardation (tapping speed), were related more to psychomotor performance than to performance on memory tasks. The results suggest that benzodiazepines and scopolamine have similar amnestic and sedative effects and as such may not offer distinct models of memory dysfunction.

Scopolamine effects on memory, language, visuospatial praxis and psychomotor speed

Scopolamine hydrobromide was administered by subcutaneous injection to 30 young subjects in a dose of 0.22 mg/70 kg, 0.43 mg/70 kg, or 0.65 mg/70 kg. Treatment effects were compared to placebo on an extensive cognitive assessment battery. Almost all tests in the battery had been previously administered to Alzheimer's disease patients and nondemented elderly subjects. Scopolamine produced deficits on tests of verbal recall, visuospatial recall, visual recognition memory, visuospatial praxis, visuoperceptual function, and psychomotor speed. Immediate memory, language function, object sorting, and frequency of intrusion errors were unaffected. The low dose of scopolamine produced some peripheral anticholinergic signs but did not affect the cognitive measures. The results support the conclusion reached in previous studies that the cognitive profile of scopolamine-injected young subjects is more similar to that of the nondemented elderly than to that of Alzheimer's disease patients.

Interaction of alcohol and transdermally administered scopolamine

In a placebo-controlled, randomized, double-blind cross-over study in 12 healthy volunteers the effect of acute alcohol intake during treatment with transdermally administered scopolamine (TTS-scopolamine) was investigated. One group of six subjects reached maximal blood alcohol concentrations (BAC) of 80 mg/dL and another group of six subjects a BAC of 130 mg/dL. There was no significant potentiation of alcohol effects on critical flicker fusion frequency by TTS-scopolamine. Sensorimotor function (choice reaction task) was also not significantly more influence by the combination. There was no effect of scopolamine on the elimination of alcohol. The urinary excretion of scopolamine was not influenced by oral intake of alcohol. TTS-scopolamine caused only minor side effects in a few volunteers, such as dry mouth (2 of 12) and blurred vision (1 of 12).

Assessment of the effects of drugs on memory

This survey is based on 70 controlled investigations of the effects of drugs on memory in healthy volunteers. Although detracting effects were predominant, enhancements were reported as well. The effects of 29 well-known drugs on 15 familiar tests are summarized in a way that permits comparisons of the effects of different drugs and of test sensitivities. There is a discussion of factors that could bias or obscure investigations of the effects of drugs on learning and remembering.

The cholinergic neurotransmitter system in human memory and dementia: a review

The present paper reviews three types of evidence implicating the role of acetylcholine in human memory and dementia: (1) neuropathological evidence that the cholinergic transmitter system is depleted in Alzheimer-type dementia; (2) psychopharmacological studies that have employed “cholinergic blockade” as a model of cholinergic depletion; and (3) clinical studies of cholinergic “replacement” therapy in Alzheimer-type dementia. The evidence that the cholinergic system is depleted in Alzheimer-type dementia has been complemented by the finding that cholinergic blockade in healthy subjects causes a substantial learning (or “acquisition”) deficit in episodic memory. The overall results of studies of replacement therapy have generally been disappointing, but a few have reported benefits in recall and recognition tests. The role of the cholinergic system in many aspects of memory remains to be elucidated; but it seems unlikely that cholinergic depletion accounts for all aspects of the memory disorder in Alzheimer-type dementia, and possibly the depletions of other neurotransmitters also contribute to the memory impairment.

Pharmacologic modelling of Alzheimer's disease

Evidence pointing to the central role of the cholinergic system in normal human memory function and disorders such as Alzheimer's disease has grown tremendously in recent years. Anticholinergic and non-cholinergic agents have been found to create transient memory impairments in young adults which mimic the changes associated with normal aging or amnesia. The rationale for using scopolamine, a centrally active anticholinergic agent, as a pharmacologic probe of memory function is reviewed using data from studies in animals and humans. The cognitive functioning of normal elderly controls given scopolamine is compared to the baseline functioning of patients with Alzheimer's disease, followed by a discussion of the use of scopolamine as a modelling agent for dementia.

Failure of amantadine and bromocriptine to counteract alcoholic inebriation in man

Oral amantadine 100 mg and bromocriptine 2.5 + 2.5 mg, alone and in combination with ethanol (1 g/kg), were investigated in two placebo-controlled, double-blind and cross-over trials. In the first trial the psychomotor effects of amantadine and bromocriptine were compared to those of placebo, and in the second trial ethanol was added to the treatment. Bromocriptine lowered serum prolactin levels, thus confirming its absorption. Amantadine and bromocriptine alone had no psychomotor effects but unpleasant sensations, nausea and dizziness were reported after bromocriptine. Ethanol impaired performance in terms of impaired coordinative and reactive skills, lowered tapping speed, prolonged critical flicker interval and reduced gaze nystagmus angle (P less than 0.05 to 0.001; two-way ANOVA). Subjectively, ethanol induced mental slowness, clumsiness and impairment of performance (P less than 0.05 to 0.001). Amantadine and bromocriptine failed to counteract any of these ethanol-induced changes. It is concluded that in man, an acute dopaminergic activation by amantadine or bromocriptine does not significantly modify the psychomotor effects of ethanol.

Naloxone-ethanol interaction in experimental and clinical situations

The effect of naloxone on ethanol-induced impairment of psychomotor performance was studied in a series of three placebo-controlled, double-blind trials. In all trials, two successive intravenous injections of naloxone (0.4 and 2.0 mg) were given at an interval of 0.5-1.5 hours. Cross-over trials with healthy volunteers (n = 17) were performed in laboratory. In these conditions, naloxone alone had no effect on performance. Ethanol alone (1.0 and 1.5 g/kg) dose-dependently induced nystagmus and impaired coordination, reactions, hand cooperation, body balance, flicker discrimination and extraocular muscle balance. When naloxone was given after ethanol, the first injection reduced slightly but significantly ethanol-induced (1.5 g/kg) nystagmus, while the second injection did not enhance this counteraction any more. Other alcohol effects were not significantly antagonized by naloxone. The clinical part of the study, consisting of parallel groups of either naloxone (n = 11) or saline (n = 7) -treated alcohol-intoxicated (mean blood alcohol concentration 2.9 mg/ml) out-patients, most of them alcoholics, showed that no counteraction of alcohol inebriation (measured by clinical inebriation tests) was associated with the treatment with naloxone in the clinical situation either. Our results suggest that naloxone has no clinical significance in antagonizing ethanol intoxication. The inebriating effects of ethanol are not importantly mediated via central opioid mechanisms.