The effects and after effects of the α2-adrenoceptor antagonist idazoxan on mood, memory and attention in normal volunteers

EEG Frequency Correlates with α2-Receptor Density in Parkinson's Disease

INTRODUCTION

Increased theta and delta power and decreased alpha and beta power, measured with quantitative electroencephalography (EEG), have been demonstrated to have utility for predicting the development of dementia in patients with Parkinson's disease (PD). Noradrenaline modulates cortical activity and optimizes cognitive processes. We claim that the loss of noradrenaline may explain cognitive impairment and the pathological slowing of EEG waves. Here, we test the relationship between the number of noradrenergic α2 adrenoceptors and changes in the spectral EEG ratio in patients with PD.

METHODS

We included nineteen patients with PD and thirteen healthy control (HC) subjects in the study. We used positron emission tomography (PET) with [11C]yohimbine to quantify α2 adrenoceptor density. We used EEG power in the delta (δ, 1.5-3.9 Hz), theta (θ, 4-7.9 Hz), alpha (α, 8-12.9 Hz) and beta (β, 13-30 Hz) bands in regression analyses to test the relationships between α2 adrenoceptor density and EEG band power.

RESULTS

PD patients had higher power in the theta and delta bands compared to the HC volunteers. Patients' theta band power was inversely correlated with α2 adrenoceptor density in the frontal cortex. In the HC subjects, age was correlated with, and occipital background rhythm frequency (BRF) was inversely correlated with, α2 adrenoceptor density in the frontal cortex, while occipital BRF was inversely correlated with α2 adrenoceptor density in the thalamus.

CONCLUSIONS

The findings support the claim that the loss or dysfunction of noradrenergic neurotransmission may relate to the parallel processes of cognitive decline and EEG slowing.

Association between dopamine beta-hydroxylase polymorphism and attention function in suicide attempters with chronic schizophrenia

BACKGROUND

Patients with schizophrenia are at a higher risk for suicide compared with the general population. Dopamine beta-hydroxylase (DβH) plays a key role in the conversion of dopamine to norepinephrine, which is related to suicidal behavior and cognitive regulation.

OBJECTIVE

To examine whether there is the effect of DβH 5'-insertion/deletion (Ins/Del) polymorphism on cognitive performance in suicide attempters with chronic schizophrenia.

METHODS

This polymorphism was detected in 114 suicide attempters and 617 non-suicide attempters with chronic schizophrenia. Cognitive performance was assessed by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS).

RESULTS

The allelic and genotypic frequencies of this polymorphism between two groups did not differ after controlling for covariates (both, p > .05). There were no differences in RBANS scores between two groups after adjusting for covariates (all, p > .05). However, based on the genotype grouping in suicide attempters and non-attempters, the attention score significantly differed after adjusting for covariates (both, p < .05). Further analysis indicated that this polymorphism was associated with attention score in suicide attempters (p < .05), but not in non-suicide attempters (p > .05).

CONCLUSIONS

DβH 5'-Ins/Del polymorphism was not a risk locus of suicide attempters, but it was implicated in attention regulation in suicide attempters with chronic schizophrenia.

Role of cortical alpha-2 adrenoceptors in alcohol withdrawal-induced depression and tricyclic antidepressants

INTRODUCTION

Although a role for alpha-2 adrenoceptors (alpha-2 ARs) in alcohol use disorder (AUD) and depression is suggested, very little information on a direct interaction between alcohol and these receptors is available.

METHODS

In this study adult female Wistar and Wistar-Kyoto (WKY) rats, a putative animal model of depression, were exposed to alcohol vapor 3h daily for 10days (blood alcohol concentration ∼150mg%) followed by daily injection of 10mg/kg of imipramine (IMP, a selective norepinephrine NE/serotonin reuptake inhibitor) or nomifensine (NOMI, a selective NE/dopamine reuptake inhibitor). On day 11 animals were tested for open field locomotor activity (OFLA) and forced swim test (FST) and were sacrificed 2h later for measurement of alpha-2 ARs densities in the frontal cortex and hippocampus using [3H]RX 821002 as the specific ligand.

RESULTS

Chronic alcohol treatment increased the immobility in the FST, without affecting OFLA in both Wistar and WKY rats, suggesting induction of depressive-like behavior in Wistar rats and an exacerbation of this behavior in WKY rats. Alcohol treatment also resulted in an increase in cortical but not hippocampal alpha-2 ARs densities in both Wistar and WKY rats. The behavioral effects of alcohol were completely blocked by IMP and NOMI and the neurochemical effects (increases in alpha-2 ARs) were significantly attenuated by both drugs in both strains.

CONCLUSIONS

The results suggest a role for cortical alpha-2 ARs in alcohol withdrawal-induced depression and that selective subtype antagonists of these receptors may be of adjunct therapeutic potential in AUD-depression co-morbidity.

Pharmacological Fingerprints of Contextual Uncertainty

Successful interaction with the environment requires flexible updating of our beliefs about the world. By estimating the likelihood of future events, it is possible to prepare appropriate actions in advance and execute fast, accurate motor responses. According to theoretical proposals, agents track the variability arising from changing environments by computing various forms of uncertainty. Several neuromodulators have been linked to uncertainty signalling, but comprehensive empirical characterisation of their relative contributions to perceptual belief updating, and to the selection of motor responses, is lacking. Here we assess the roles of noradrenaline, acetylcholine, and dopamine within a single, unified computational framework of uncertainty. Using pharmacological interventions in a sample of 128 healthy human volunteers and a hierarchical Bayesian learning model, we characterise the influences of noradrenergic, cholinergic, and dopaminergic receptor antagonism on individual computations of uncertainty during a probabilistic serial reaction time task. We propose that noradrenaline influences learning of uncertain events arising from unexpected changes in the environment. In contrast, acetylcholine balances attribution of uncertainty to chance fluctuations within an environmental context, defined by a stable set of probabilistic associations, or to gross environmental violations following a contextual switch. Dopamine supports the use of uncertainty representations to engender fast, adaptive responses.

Pharmacological interventions and hierarchical Bayesian modelling pinpoint the roles of noradrenaline, acetylcholine, and dopamine in computing different forms of uncertainty and in sensitizing actions to our beliefs about uncertainty.

Interacting with dynamic and ever-changing environments requires frequent updating of our beliefs about the world. By learning the relationships that link events in the current environmental context, it is possible to prepare and execute fast, accurate responses to those events that are predictable. However, the world’s complex dynamics give rise to uncertainty about the relationships that exist between events and uncertainty about how these relationships might change over time. Several neuromodulators have been proposed to signal these different forms of uncertainty, but their relative contributions to updating beliefs and modulating responses have remained elusive. Here we combine a probabilistic reaction time task, pharmacological interventions, and a hierarchical Bayesian learning model to identify the roles of noradrenaline, acetylcholine, and dopamine in individual computations of uncertainty. We propose that noradrenaline modulates learning about the instability of the relationships that link environmental events. Acetylcholine balances the attribution of uncertainty to unexpected events occurring within an environmental context or to gross violations of our expectations following a context change. In contrast, dopamine sensitises our actions to our beliefs about uncertainty.

An Investigation of the Acute Effects of Oligofructose-Enriched Inulin on Subjective Wellbeing, Mood and Cognitive Performance

Inulin is a natural food component found in many plants that are part of the human diet (e.g., leeks, onions, wheat, garlic, chicory and artichokes). It is added to many foods and is used to increase dietary fibre, replace fats or carbohydrates, and as a prebiotic (a stimulant of beneficial bacteria in the colon). Oligofructose, which is also present in these foods, produces similar effects and most research has used a combination of these products. A previous study (Smith, 2005) investigated the effects of regular consumption of oligofructose-enriched inulin on wellbeing, mood, and cognitive performance in humans. The results showed that oligofructose-enriched inulin had no negative effects but that it did not improve wellbeing, mood, or performance. The aim of the present study was to examine the acute effects of oligofructose-enriched inulin (5 g) over a 4 h period during which the participants remained in the laboratory. A double blind placebo (maltodextrin) controlled study (N = 47) was carried out with the order of conditions being counterbalanced and the two sessions a week apart. On each test day mood and cognitive performance were assessed at baseline (at 8:00) and then following inulin or placebo (at 11:00). Prior to the second test session (at 10:30) participants completed a questionnaire assessing their physical symptoms and mental health during the test morning. The inulin and placebo were provided in powder form in 5 g sachets. Volunteers consumed one sachet in decaffeinated tea or decaffeinated coffee with breakfast (9:00). Questionnaire results showed that on the day that the inulin was consumed, participants felt happier, had less indigestion and were less hungry than when they consumed the placebo. As for performance and mood tasks, the most consistent effects were on the episodic memory tasks where consumption of inulin was associated with greater accuracy on a recognition memory task, and improved recall performance (immediate and delayed). Further research is required to identify the mechanisms that underlie this effect with glucose metabolism being one candidate.

α2-Adrenoceptors in the treatment of major neuropsychiatric disorders

Presynaptic autoreceptors mediate a retrograde transfer of information by a negative feedback mechanism mediated by the transmitter of the neuron, and fulfill an autoregulatory function in neurotransmission in the peripheral and central nervous system (CNS). Starting with norepinephrine (NE), it was later reported that an autoreceptor-mediated negative feedback mechanism exists for other neurotransmitters, including dopamine (DA), serotonin, acetylcholine, histamine, GABA, and glutamate. This feedback mechanism regulates calcium-dependent transmitter release and synthesis through terminal presynaptic autoreceptors, while the firing rate of the neuron is regulated through somatodendritic autoreceptors.

Effects of upper respiratory tract illnesses, ibuprofen and caffeine on reaction time and alertness

RATIONALE

Compared with healthy individuals, those with upper respiratory tract illnesses (URTIs) report reduced alertness and have slower reaction times. It is important to evaluate medication that can remove this behavioural malaise.

OBJECTIVES

The aim of this study was to compare the effects of a combination of ibuprofen plus caffeine with ibuprofen and caffeine alone, and placebo on malaise associated with URTIs, as measured by psychomotor performance and mood testing.

METHODS

Volunteers were randomly assigned to one of four medication conditions as follows: 200 mg ibuprofen and 100 mg caffeine; 200 mg ibuprofen; 100 mg caffeine; placebo. A single oral dose was given and testing followed for 3 h. Efficacy variables were based on the volunteers' performance, measured by psychomotor performance and mood.

RESULTS

The pre-drug results confirmed that those with an URTI had a more negative mood and impaired performance. Results from the simple reaction time task, at both 55- and 110-min post-dosing, showed that a single-dose of caffeinated products (I200/C100 and CAF100) led to significantly faster reaction times than IBU200 and placebo. These effects were generally confirmed with the other performance tasks. Subjective measures showed that the combination of ibuprofen and caffeine was superior to the other conditions. There were no serious adverse events reported, and study medication was well tolerated.

CONCLUSIONS

The results from the post-drug assessments suggest that a combination of ibuprofen and caffeine was the optimum treatment for malaise associated with URTIs in that it had significant effects on objective performance and subjective measures.

Remembering under stress: different roles of autonomic arousal and glucocorticoids in memory retrieval

It is commonly assumed that stress impairs memory retrieval. Glucocorticoids, released with a delay of several minutes in response to stressful experiences, are thought to play a key role in the stress-induced retrieval impairment. Accordingly, most studies on the impact of stress on retrieval tested memory a considerable time after stressor exposure, when glucocorticoid levels were elevated. Here, we asked how stress affects memory when retrieval takes place under stress, that is, when stress is part of the retrieval situation and glucocorticoids are not yet increased at the time of testing. To contrast stress effects on ongoing and delayed memory retrieval, 72 participants learned first neutral and emotional material. Twenty-four hours later, half of the learned material was tested either in a stressful, oral examination-like testing situation or in a standard, non-stressful free recall test. Memory for the other half of the learned material was assessed 25 min after the first, stressful or non-stressful retention test. Significant increases in blood pressure and salivary cortisol confirmed the stress induction by the first, examination-like testing situation. Retrieval performance under stress was positively correlated with the blood pressure response to the stressor but unaffected by cortisol. Conversely, retrieval performance 25 min post stress was negatively correlated with the cortisol response to the stressor, particularly for emotional items. These results suggest that the same stressor may have opposite effects on ongoing and delayed memory retrieval, depending on the presence of autonomic arousal and glucocorticoids.

Noradrenergic modulation of cognition: therapeutic implications

The noradrenaline (norepinephrine) system exerts profound influences on cognition via ascending projections to the forebrain, mostly originating from the locus coeruleus. This paper provides an overview of available infrahuman and healthy human studies, exploring the effects of specific noradrenergic manipulations on dissociable cognitive functions, including attention, working memory, cognitive flexibility, response inhibition and emotional memory. Remarkable parallels across species have been reported which may account for the mechanisms by which noradrenergic medications exert their beneficial effects in disorders such as depression and attention-deficit hyperactivity disorder (ADHD). The literature is discussed in relation to prevailing models of noradrenergic influences over cognition and novel therapeutic directions, including in relation to investigating the effects of noradrenergic manipulations on other disorders characterized by impulsivity, and dementias. Unanswered questions are also highlighted, along with key avenues for future research, both proof-of-concept and clinical.

Rigid analogues of the α2-adrenergic blocker atipamezole: small changes, big consequences

We report the discovery of a new family of α(2) adrenergic receptor antagonists derived from atipamezole. Affinities of the compounds at human α(2) and α(1b) receptors as well as their functional activities at hα(2A) receptors were determined in competition binding and G-protein activation assays, respectively. Central α(2) antagonist activities were confirmed in mice after oral administration. Further studies on a selected example: (+)-4-(1a,6-dihydro-1H-cyclopropa[a]inden-6a-yl)-1H-imidazole, (+)-1 (F 14805), were undertaken to probe the potential of the series. On the one hand, (+)-1 increased the release of noradrenaline in mouse frontal cortex following acute systemic administration, the magnitude of this effect being much larger than that obtained with reference agents. On the other, (+)-1 produced minimal cardiovascular effects in intact, anesthetized rat, a surprising outcome that might be explained by its differential action at peripheral and central α(2) receptors. A strategy for improving the therapeutic window of α(2) antagonists is put forward.

Noradrenergic genotype predicts lapses in sustained attention

Sustained attention is modulated by the neurotransmitter noradrenaline. The balance of dopamine and noradrenaline in the cortex is controlled by the DBH gene. The principal variant in this gene is a C/T change at position -1021, and the T allele at this locus is hypothesised to result in a slower rate of dopamine to noradrenaline conversion than the C allele. Two hundred participants who were genotyped for the DBH C-1021T marker performed the Sustained Attention to Response Task (SART). DBH genotype was found to significantly predict performance; participants with more copies of the T allele made more errors of commission, indicative of lapses in sustained attention. A significant negative correlation was also observed for all participants between errors of commission and mean reaction time. The decrease in noradrenaline occasioned by the T allele may impair sustained attention by reducing participants' ability to remain alert throughout the task and by increasing their susceptibility to distractors.

Noradrenergic mechanisms in neurodegenerative diseases: a theory

A deficiency in the noradrenergic system of the brain, originating largely from cells in the locus coeruleus (LC), is theorized to play a critical role in the progression of a family of neurodegenerative disorders that includes Parkinson's disease (PD) and Alzheimer's disease (AD). Consideration is given here to evidence that several neurodegenerative diseases and syndromes share common elements, including profound LC cell loss, and may in fact be different manifestations of a common pathophysiological process. Findings in animal models of PD indicate that the modification of LC-noradrenergic activity alters electrophysiological, neurochemical and behavioral indices of neurotransmission in the nigrostriatal dopaminergic system, and influences the response of this system to experimental lesions. In models related to AD, noradrenergic mechanisms appear to play important roles in modulating the activity of the basalocortical cholinergic system and its response to injury, and to modify cognitive functions including memory and attention. Mechanisms by which noradrenaline may protect or promote recovery from neural damage are reviewed, including effects on neuroplasticity, neurotrophic factors, neurogenesis, inflammation, cellular energy metabolism and excitotoxicity, and oxidative stress. Based on evidence for facilitatory effects on transmitter release, motor function, memory, neuroprotection and recovery of function after brain injury, a rationale for the potential of noradrenergic-based approaches, specifically alpha2-adrenoceptor antagonists, in the treatment of central neurodegenerative diseases is presented.

Estimation of endogenous noradrenaline release in rat brain in vivo using [3H]RX 821002

Noradrenaline plays an important role in many normal brain functions, e.g., attention, memory, and emotion. Dysfunction in the noradrenergic system is thought to lead to a number of abnormal brain conditions. The lack of suitable in vivo tracers to monitor noradrenaline release, levels, and regulation has hampered our fully understanding the roles that it plays in the brain. Presented here are data showing that the in vivo binding of the alpha2-adrenoceptor antagonist [3H]RX 821002 is sensitive to endogenous noradrenaline. Elevation of extracellular noradrenaline, using three different pharmacological challenges in rat, led to a reduction in the binding potential (BP) of [3H]RX 821002 when compared with vehicle controls. The challenges used were i.p. administration of D-amphetamine, the imidazoline2 binding site-selective ligand BU224, and L-deprenyl. Of the cortical regions measured, the reduction in BP reached significance in the anterior cingulate cortex for all of these pharmacological challenges. These initial observations in rat indicate that labelling of the alpha2-adrenoceptors with RX 821002 can be used to estimate changes in extracellular noradrenaline concentration in the cortex. This has the potential to enable the investigation of the role that noradrenaline plays both in the normal and abnormal brain and, if the ligand can be radiolabelled with a suitable positron-emitting isotope at high specific radioactivity, it could be an invaluable PET tracer.

Alpha2C-adrenoceptor overexpression disrupts execution of spatial and non-spatial search patterns

We investigated the role of alpha2C-adrenoceptors in the modulation of spatial and non-spatial navigation behaviour. Alpha2C-adrenoceptor overexpressing mice developed an ineffective thigmotaxic search pattern characterized by swimming close to the pool walls during both spatial and non-spatial water maze training. A subtype-non-selective alpha2-adrenoceptor antagonist, atipamezole (1000 microg/kg, s.c.), fully reversed this impairment in their search strategy. Withdrawal of atipamezole at the end of spatial training resulted in an immediate disruption of the search pattern in alpha2C-adrenoceptor overexpressing mice. The swimming pattern of alpha2C-adrenoceptor overexpressing mice during a five day free swimming period was normal, when no cognitive component was required. Diazepam (0.3 and 1.0 mg/kg, i.p.), neither improved the accuracy in finding the platform nor decreased thigmotaxis. These results suggest that alpha2C-adrenoceptors may modulate the execution of complex navigation patterns.

Noradrenergically mediated plasticity in a human attentional neuronal network

Noradrenaline is implicated in the modulation of attention and arousal, but the neuroanatomical basis of this effect in humans is unknown. A previous functional neuroimaging study failed to find clear effects of clonidine (alpha2 adrenoceptor agonist) on activity of brain regions implicated in attention. Therefore, we now investigate whether clonidine affects the functional integration of a neuroanatomical attentional network, by modulating connectivity between brain regions rather than activity within discrete regions. Following infusion of either clonidine or placebo, positron emission tomography measurements of brain activity were collected in 13 normal subjects while they were either resting or performing an attentional task. Effective connectivity analysis showed that during rest, clonidine decreased the functional strength of connections both from frontal cortex to thalamus and in pathways to and from visual cortex. Conversely, during the attentional task, functional integration generally increased, with changes being centered on parietal cortex (increased connectivity from locus coeruleus to parietal cortex and from parietal cortex to thalamus and frontal cortex). A drug-induced increase in the modulatory effects of frontal cortex on projections from locus coeruleus to parietal cortex was also observed. Collectively, these results highlight cognitively dissociable effects of clonidine on interactions among functionally integrated brain regions and implicate the noradrenergic system in mediating the functional integration of attentional brain systems. The context-sensitive nature of the changes are consistent with observations that noradrenergic drugs have differential effects on brain processes depending on subjects' underlying arousal levels. More generally, the results illustrate the dynamic plasticity of cognitive brain systems following neurochemical challenge.

Alpha 2-adrenoceptor antagonists potentiate acetylcholinesterase inhibitor effects on passive avoidance learning in the rat

The cholinergic hypothesis of Alzheimer's disease (AD) has strongly influenced research on learning and memory over the last decade. However, there has been limited success treating AD dementia with cholinomimetics. Furthermore, there are indications that other neurotransmitter systems affected by this disease may be involved in cognitive processes. Animal studies have suggested that norepinephrine and acetylcholine may interact in learning and memory. The current experiments investigate this interaction in a step-down passive avoidance paradigm after coadministration of acetylcholinesterase inhibitors and alpha 2-adrenoceptor antagonists. Administration of acetylcholinesterase inhibitors heptylphysostigmine (0.625-5.0 mg/kg, IP), tacrine (2.5-10.0 mg/kg, PO), velnacrine (0.312-2.5 mg/kg, SC), and galanthamine (0.312-2.5 mg/kg IP) each enhanced retention of a passive avoidance response at selected moderate doses administered 30-60 min prior to training. The alpha 2-adrenoceptor antagonists idazoxan (0.312-2.5 mg/kg, IP), yohimbine (0.078-0.312 mg/kg, IP) and P86 7480 (0.156-0.625 mg/kg, IP) alone failed to enhance learning in this paradigm. Coadministration of a subthreshold dose of heptylphysostigmine (0.625 mg/kg, IP) with doses of idazoxan, yohimbine or P86 7480 enhanced passive avoidance learning. This synergistic interaction may represent effects of antagonism of presynaptic alpha 2-adrenoceptor since coadministration of heptylphysostigmine and the selective postsynaptic alpha 2-adrenoceptor antagonist SKF 104856 did not result in enhanced learning. Taken together these data suggest noradrenergic activation through pre-synaptic alpha 2-adrenoceptor blockade may potentiate cholinergic activity in the formation of a long-term memory trace. These observations may have implications for the treatment of AD with cholinergic and adrenergic agents.

The alpha(2) antagonist idazoxan remediates certain attentional and executive dysfunction in patients with dementia of frontal type

Abstract The mixed alpha(1)/alpha(2) adrenoceptor agonist clonidine has been shown by us previously to impair certain attentional and executive functions in healthy volunteers. The present investigation examines the effects of the alpha(2) adrenoceptor antagonist idazoxan (IDZ) on cognitive function in patients with dementia of frontal type (DFT). Using a placebo-controlled ABBA design, three DFT patients were given two doses of IDZ and tested on a range of computerised tests of attention, memory and executive function. Idazoxan was found to produce dose-dependent improvements in performance, particularly on tests of planning, sustained attention, verbal fluency and episodic memory. In contrast, IDZ produced deficits in performance on a test of spatial working memory. These results suggest that IDZ may be useful as a putative cognitive enhancer, particularly in patients showing a specific pattern of frontal lobe dysfunction.

Clonidine and diazepam have differential effects on tests of attention and learning

The noradrenergic system has repeatedly been implicated in the mediation of attentional processes. Using a double-blind, placebo-controlled design, the present investigation examines the effects of two doses (1.5 micrograms/kg and 2.5 micrograms/kg) of the alpha 2 adrenoceptor agonist clonidine (CLO) on performance of various computerised tests of attention and learning in healthy, young volunteers. These are compared to the effects produced by two doses (5 mg and 10 mg) of diazepam (DZP) on largely the same set of neuropsychological tests in a comparable set of subjects. Both doses of CLO were found to impair performance of the RVIP test of sustained attention, while the higher dose alone improved visuo-spatial learning. Conversely, the higher dose of DZP produced profound deficits on visuo-spatial learning, and impaired attentional set-shifting. This study suggests a role for the alpha 2 adrenoceptor in selective attention, and for the benzodiazepine receptor in specific cognitive processes mediated by discrete cortical regions.

A comparison of the acute effects of a low dose of alcohol on mood and performance of healthy volunteers and subjects with upper respiratory tract illnesses

An experiment was carried out to determine whether a low dose of alcohol produced different behavioural effects in healthy volunteers to those suffering from an upper respiratory tract illness. Ninety-nine subjects were tested, with 48 subjects being assigned to the alcohol condition and 51 to the juice only condition. A dose of 1.5 ml of vodka per kg body weight was used and the alcohol manipulation was double-blind. Approximately half of the subjects in each condition were healthy and the others had upper respiratory tract illnesses, probably colds. Subjects with colds reported an increase in negative affect and were slower at performing psychomotor tasks. Few main effects of alcohol were obtained. Of major interest were the interactions between health status and alcohol conditions. The alcohol improved the mood of healthy subjects but produced greater negative moods in subjects with colds. Similarly, performance of selective and sustained attention tasks showed different effects of alcohol in healthy and ill subjects.

Pharmacological manipulations of the alpha 2-noradrenergic system. Effects on cognition

Electrophysiological and neurosurgical lesion studies with experimental animals have implicated the ascending dorsal noradrenergic bundle of the locus coeruleus system in cognitive process such as memory, learning and selective attention. However, it has also been suggested that noradrenaline (norepinephrine) is crucial in certain cognitive functions associated with the frontal lobes, particularly the prevention of distractibility by irrelevant stimuli. The alpha 2-receptors of the prefrontal cortex appear to be of particular importance in this respect. Studies with humans and experimental primates provide substantial support for this view. The aged primate brain is prone to degeneration of the locus coeruleus, as well as profound catecholamine depletion in the prefrontal cortex, and so is ideal for psychopharmacological investigation of the role of noradrenaline in frontal lobe function. Elderly monkeys show deficits in performance of the delayed response task, which can be reversed directly by both the mixed alpha 1/alpha 2-agonist clonidine, the more specific alpha 2-agonist guanfacine and also, indirectly, by the alpha 2-antagonist yohimbine. It is suggested that these results can be explained by an attenuation of the distracting properties of irrelevant stimuli following stimulation of noradrenergic activity. Conversely, distractibility is magnified whenever noradrenergic activity is reduced. This is supported by similar findings in psychopharmacological studies of healthy humans. The exception to this is when the locus coeruleus is likely to be firing, e.g. in times of stress or when novel stimuli are encountered. Clonidine attenuates locus coeruleus firing on such occasions, and so counteracts any beneficial (or deleterious) effects of stress on task performance. alpha 2-Adrenoceptor agents have little therapeutic value in patients with dementia of the Alzheimer's type. However, they may have some clinical use in patients who have a cognitive symptomatology similar to that of patients who have received neurosurgical excisions to the frontal lobes, e.g. deficits in working memory, executive function or focused attention, with relative sparing of episodic short term memory. Patients with Korsakoff's disease, attention deficit disorder or schizophrenia may benefit from treatment with alpha 2-agents. In particular, idazoxan has putative therapeutic effects in patients with a neurodegenerative disorder, namely dementia of frontal type.

The effects of caffeine and evening meals on sleep and performance, mood and cardiovascular functioning the following day

An experiment was carried out to examine the effects of caffeine and evening meals on sleep and performance, mood and cardiovascular functioning in the early morning of the next day. Forty-eight subjects were assigned to one of the four conditions formed by combining caffeine and meal conditions. Subjects in the caffeine condition were given 3 mg/kg caffeine in de-caffeinated coffee. The caffeine manipulation was double blind. Subjects in the meal condition were given a 3-course meal (∼ 1300 calories). Sleep was assessed by subjective ratings and these showed that both caffeine and consumption of the meal influenced sleep, but that there were no interactions between caffeine and meal conditions. Although caffeine disrupted sleep there was no evidence of performance or mood being impaired the next day. However, blood pressure was still higher the next day in subjects given caffeine the previous evening.