The effects of nicotine on attention, information processing, and short-term memory in patients with dementia of the Alzheimer type

Nicotinic receptor agonists facilitate retention of avoidance training: participation of dopaminergic mechanisms

The effect of nicotinic receptor agonists on retention of the inhibitory avoidance (IA) response were investigated in mice. Animals received intraperitoneal drug injections before training, and retention was evaluated 24 h later. Nicotine and cytisine, but not lobeline, significantly increased retention of the IA training. Cotinine, the main metabolite of nicotine, was inactive in the same test. Retention was not affected by the injection of the D1-D2 receptor antagonist cis-flupentixol, but the preadministration of cis-flupentixol significantly blocked the facilitatory effect of nicotine and cytisine on memory. These results demonstrate that the nicotinic receptor agonists nicotine and cytisine facilitate the retention of avoidance responses and suggest that this effect is mediated through central dopaminergic pathways.

A physiologically based pharmacokinetic model for nicotine disposition in the Sprague-Dawley rat

A physiologically based pharmacokinetic (PBPK) model was developed to describe the disposition of nicotine in the Sprague-Dawley (SD) rat. Parameters for the model were either obtained from the literature (blood flows, organ volumes) or determined experimentally (partition coefficients). Nicotine metabolism was defined in the liver compartment by the first-order rate constants KNC and KNP which control the rate of nicotine metabolism to cotinine and "polar metabolites" (PM), respectively. These rate constants were estimated by optimizing the model fit to pharmacokinetic data obtained by administering an intraarterial (S)-[5-3H]nicotine bolus of 0.1 mg/kg to 6 rats. Model simulations that optimized for the appearance of cotinine in plasma estimated KNC and KNP to be 75.8 and 24.3 hr-1, respectively. Use of these constants in the model allowed us to accurately predict nicotine plasma kinetics and the fraction of the dose eliminated by renal (8.5%) and metabolic (91.5%) clearance. To validate the model's ability to predict tissue kinetics of nicotine, 21 male SD rats were administered 0.1 mg/kg (S)-[5-3H]nicotine intraarterially. At seven time points following treatment, 3 rats were euthanized and tissues were removed and analyzed for nicotine. Model-predicted nicotine tissue kinetics were in agreement with those determined experimentally in muscle, liver, skin, fat, and kidney. The brain, heart, and lung exhibited nonlinear nicotine elimination, suggesting that saturable nicotinic binding sites may be important in nicotine disposition in these organs. Inclusion of saturable receptor binding expressions in the mathematical description of these compartments resulted in better agreement with the experimental data. The Bmax and KD estimated by model simulations for these tissues were brain, 0.009 and 0.12; lung, 0.039 and 2.0; and heart, 0.039 nmol/tissue and 0.12 nM, respectively. This PBPK model can successfully describe the tissue and plasma kinetics of nicotine in the SD rat and will be a useful tool for pharmacologic studies in humans and experimental animals that require insight into the plasma or tissue concentration-effect relationship.

Persistence of chronic nicotine-induced cognitive facilitation

Nicotine has been found in a variety of species and behavioral paradigms to improve memory performance. The beneficial effect of nicotine has been seen after both acute and chronic administration. Interestingly, improved performance has been seen 24 h after acute injection and for at least 2 weeks after chronic administration. However, it is not clear from previous studies whether the persistence of the improved performance represents a true carryover of the drug effect or is due to the behavioral experience while under nicotine's effect. The current study was conducted to determine whether the facilitating effect of nicotine on learning and memory performance could be seen after withdrawal even if there was no behavioral training during the period of chronic nicotine administration. Rats were administered nicotine chronically for 3 weeks but were not tested during that time. Starting 1 week after withdrawal they were trained on a working memory paradigm in an eight-arm radial maze. The nicotine-treated rats started out at control-like levels of performance, but showed significantly faster learning as detected by three different measures of choice accuracy. By the final phase of testing the control subjects had caught up with the nicotine-treated rats. After the acquisition phase, acute challenges with the nicotinic and muscarinic antagonists, mecamylamine and scopolamine, did not elicit any differential effects in the nicotine-treated and control groups. The current study demonstrated that nicotine-induced cognitive facilitation persists for at least 4 weeks after withdrawal and does not depend upon behavioral test experience under the influence of the drug. The mechanism for this persisting effect is not currently understood.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic distribution of [3H]nicotine binding in human cortex: relative abundance in subicular complex

Distinct patterns of [3H]nicotine (3 nM) binding were apparent in various regions of adult human neo- and archicortex. Receptor binding was greatest in the subicular complex--particularly presubiculum--and entorhinal cortex, where it was prominent in the characteristic parvo- and magnocellular islands of these regions and in middle layers of entorhinal cortex. In somatosensory cortex (Brodmann areas 3, 1 and 2) and occipital (area 17) cortex binding was highest in the upper and lower layers, and relatively sparse in the sensory input, layer IV. In primary motor (area 4) and temporal (area 21) cortex, binding in the outer half of the cortical ribbon was denser than that in the inner half and a distinct band was apparent in temporal and cingulate (area 32) in the lower portion of layer III. In prefrontal association cortex the pattern of binding was less distinct although slightly higher in the lower architectonic layers. There was generally little binding in the hippocampus (areas CA1-4) and dentate gyrus with the exception of the stratum lacunosum moleculare in CA2-3 and, to a lesser extent, supra- and subgranule zones of the dentate. These patterns of reactivity, which are distinct from that of the major cortical cholinergic innervation, suggest that the nicotinic receptor, detected using nanomolar concentrations of [3H]nicotine, may primarily be associated with intracortical circuitry in the neocortex. The relatively high density in entorhinal and subicular regions may be related to the extensive phylogenetic development of these regions which has occurred in conjunction with the development of multimodal association circuitry in the human cortex.

Cholinergic activity and constraints on information processing

In humans, close relationships are found between cholinergic activity and constraints placed on information processing operations. This is true for all operations where the effects of cholinergic activity have been studied. Studies of vigilance, memory, problem solving, stimulus processing and response processing are cited as illustrations. These studies suggest the hypothesis that cholinergic activity controls constraints in all information processing operations. Alternative hypotheses are proposed and experimental tests are suggested.

Nicotine as a cognitive enhancer

1. Nicotine improves attention in a wide variety of tasks in healthy volunteers. 2. Nicotine improves immediate and longer term memory in healthy volunteers. 3. Nicotine improves attention in patients with probable Alzheimer's Disease. 4. While some of the memory effects of nicotine may be due to enhanced attention, others seem to be the result of improved consolidation as shown by post-trial dosing.

Effects of acute subcutaneous nicotine on attention, information processing and short-term memory in Alzheimer's disease

This single-blind, placebo controlled study reports on the effects of administering three acute doses of nicotine (0.4, 0.6 and 0.8 mg) subcutaneously to a group of Alzheimer's disease (DAT) patients (n = 22), young adult controls (n = 24), and normal aged controls (n = 24). The study extends our previous findings obtained using smaller groups of subjects. Drug effects were examined on three computerised tests: the first measuring rapid visual information processing, sustained visual attention and reaction time (RVIP task); a delayed response matching to location-order task measuring sustained visual attention and visual short-term memory (DRMLO task); and a finger tapping test measuring simple reaction time (FT task). The critical flicker fusion test (CFF) was used as a measure of perception and the WAIS digit span forwards (DS), of auditory short-term memory. Tests were graded in difficulty, titrated to avoid floor and ceiling effects so that meaningful, direct comparisons between groups could be made. Nicotine significantly improved sustained visual attention (in both RVIP and DRMLO tasks), reaction time (in both FT and RVIP tasks), and perception (CFF task--both ascending and descending thresholds). Nicotine administration did not improve auditory and visual short-term memory. There were no consistent, overall patterns of difference in performance between smokers and non-smokers in the control groups, or between males and females in any group. Despite the absence of change in memory functioning, these results demonstrate that DAT patients have significant perceptual and visual attentional deficits which are improved by nicotine administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotinic systems and cognitive function

Nicotinic acetylcholine receptors have been found to be important for maintaining optimal performance on a variety of cognitive tasks. In humans, nicotine-induced improvement of rapid information processing is particularly well documented. In experimental animals nicotine has been found to improve learning and memory on a variety of tasks, while the nicotinic antagonist mecamylamine has been found to impair memory performance. Nicotine has been found to be effective in attenuating memory deficits resulting from lesions of the septohippocampal pathway or aging in experimental animals. Nicotinic receptors are decreased in the cortex of patients with Alzheimer's disease. Preliminary studies have found that some aspects of the cognitive deficit in Alzheimer's disease can be attenuated by nicotine. Nicotine may prove to be useful therapeutic treatment for this and other types of dementia.

Memory modulation with peripherally acting cholinergic drugs

Physostigmine (PHYSO), in doses as low as 0.003 mg/kg IP, antagonized scopolamine (SCOP, 3 mg/kg) induced amnesia of step-through passive avoidance in mice. The peripherally acting acetylcholinesterase (AChE) inhibitor neostigmine (NEO) was also found to reliably, though less strongly, antagonize the SCOP induced amnesia at a dose of 0.03 mg/kg. The NEO antagonism of the SCOP amnesia could be reversed with SCOP (0.3, 1, and 3 mg/kg) and mecamylamine (MECA, 1, 3, and 10 mg/kg), muscarinic and nicotinic antagonists, respectively, which are active both peripherally and centrally, as well as with M-SCOP (0.3 and 1 mg/kg) and hexamethonium (HEX, 1 and 3 mg/kg), muscarinic and nicotinic antagonists, respectively, which are active only in the periphery. In contrast to the ability of these four compounds to attenuate the SCOP amnesia, only the centrally acting compounds SCOP (3 mg/kg) and MECA (10 mg/kg) induced an amnesia when administered alone. These findings suggest that the induction of amnesia of passive avoidance involves central cholinergic systems, whereas the NEO, and possibly PHYSO, reversal of the SCOP induced amnesia is mediated peripherally by both muscarinic and nicotinic receptors. It is hypothesized that the release of adrenal catecholamines, the influence of which on memory processes is well known, and secondarily glucose, may be responsible for the NEO antagonism of the SCOP amnesia.

Psychomotor performance in smokers following single and repeated doses of nicotine gum

The psychomotor effects of single and repeated doses of 2 mg nicotine gum were investigated in 13 regular smokers who had abstained from tobacco overnight. In comparison to baseline, a first dose of nicotine led to significantly raised critical flicker fusion thresholds, faster motor reaction times, improved compensatory tracking performance, and faster short-term memory reaction times. Performance after a second and third dose of nicotine remained significantly improved on all measures in comparison to baseline, and absolutely improved when comparing first and third nicotine doses on measures of sensorimotor performance. Throughout, comparisons with a placebo gum condition confirmed that these effects were genuine and not subject to the development of acute nicotine tolerance, suggesting that the enhancement of psychomotor performance experienced by smokers after a first cigarette may be maintained by repeated smoking.

Behavioral screening for cognition enhancers: from indiscriminate to valid testing: Part I

Preclinical efforts to detect and characterize potential cognition enhancers appear to have been dominated by a strategy of demonstrating a wide variety of apparently beneficial behavioral effects with little attention given to the specific psychological mechanisms underlying behavioral enhancement. In particular, the question of whether or not behavioral facilitation is based on relevant mnemonic mechanisms and is independent of the stimulus properties and/or the motivational and attentional components of a task is not often considered. As a result, an overwhelming number of compounds have failed to produce the clinical effects predicted for them on the basis of preclinical research. The available data suggest that a more successful approach requires deductive research strategies rather than the indiscriminate accumulation of apparently beneficial effects in a variety of behavioral tasks and animal models. The first step towards such an approach is a systematic and rigorous evaluation of the different aspects of validity for the models most frequently used in preclinical research. It is concluded that a combination of good construct validity and good face validity represents a necessary condition for screening tests with predictive validity, and that the most popular paradigms fail to fulfil these criteria. Future screening programs for cognition enhancers will probably be characterized by a depreciation of "fast and dirty tests" in favor of approaches focussing on the validity of the effects of potential cognition enhancers.

Effects of physostigmine on stimulus encoding in a memory-scanning task

Previous studies of the effects of physostigmine on memory have involved other drugs, a memory that has already been impaired, or both, often with contradictory results. Also, traditional memory tests do not differentiate memory from other task components such as perception and response, and drug effects on these could be mistaken for effects on memory. The present study was designed to investigate the effects of physostigmine alone on normal memory using Sternberg's additive-factor, memory-scanning task, with additional variables to isolate effects on stimulus encoding and response stages. Sixteen volunteers participated, the design was between-groups, and physostigmine or normal saline was given, double-blind, by intravenous infusion for 70 min. The drug had no effect on the memory component of the task, but significantly improved stimulus encoding (P < 0.001). Thus, it is possible that physostigmine improves performance on memory tests by improving perception as well as, or instead of, memory.

A comparison of the attentional and consolidation hypotheses for the facilitation of memory by nicotine

Studies examining facilitation of human memory by the administration of nicotine have given equivocal results and it has been argued that the positive findings on memory may have resulted indirectly from an effect on attention, rather than from a direct effect on memory storage. This study compared the "attentional" and the "mnemonic" hypotheses directly, by using both immediate and delayed recall tasks in a verbal free recall study, in which volunteers smoked on a fixed regime during presentation of a 32 word list (namely, one puff after each of eight 4-word blocks). The serial position curve for immediate recall demonstrated a significant improvement on the later blocks of the list (an attentional effect) when volunteers smoked a nicotine-containing cigarette. However, improved performance was found for items at the beginning of the list on the delayed recall measure and this improvement was significant on the first block of 4 words. Since nicotine input had been taken after presentation of this information, the results demonstrate post-learning facilitation of memory by nicotine.

Acute nicotinic blockade produces cognitive impairment in normal humans

Single oral doses of the central and peripheral nicotinic antagonist mecamylamine were administered to healthy young normal males in doses of 5, 10, and 20 mg in a placebo-controlled, double-blind study. The 20 mg dose caused a significant increase in errors in the learning condition of the Repeated Acquisition task, producing a slower acquisition curve. The lower doses produced less errors, but more than in the placebo condition. There was no effect of drug on the performance component (retrieval of previously learned information). On the recognition memory task, dose-related increases in false-alarms during the delay period were seen, with little effect on misses or hits. Reaction time measures suggested a dose-related slowing of RT on several tasks. Behavioral effects were minimal and physiologic measures were consistent with dose-related ganglionic blockade. We interpret these results to indicate that acute blockade of nicotinic receptor function can produce measurable and significant cognitive impairment, even in non-smoking normals.

Dementia: the neurochemical basis of putative transmitter orientated therapy

The neurotransmitter deficits of dementias, including Alzheimer's dementia, Lewy body dementia and Parkinson's disease are discussed in relation to cognitive and behavioural impairments together with neuropathological changes and available data on the status of receptor transmembrane signalling. Potential therapeutic strategies for dementia are outlined based on the following systems: excitatory amino acids, gamma-amino butyric acid, acetylcholine (muscarinic and nicotinic), noradrenaline, serotonin and peptides. These include the attenuation of transmitter deficits by agonists and agents inhibiting transmitter breakdown and support for surviving neurons by suppression of inhibitory inputs, trophic factors and neural implantation.

Taking stock of cognition enhancers

An increasing number of structurally heterogeneous compounds, which may act via very different categories of neuronal mechanisms, have been proposed to facilitate attentional abilities and acquisition, storage and retrieval of information, and/or to attenuate the impairments of such cognitive functions associated with age or dementia. In this article, Martin Sarter briefly reviews the data on putative cognition enhancers and examines the possible bases for the discrepancy between preclinical predictions of efficacy and the fact that unequivocal demonstration of drug-induced cognition enhancement in humans has only rarely been reported. Previous preclinical research strategies appear to have focused on the demonstration of drug effects in a wide variety of tests of uncertain validity, rather than on determination of the specific psychological and neurobiological processes affected by putative cognition enhancers. Some criteria are proposed for evaluating the validity of preclinical tests for cognition enhancers.

Memory and attention in patients with senile dementia of the Alzheimer type and in normal elderly subjects

Previous studies have shown that cholinergic blockade in normal subjects induces impairment of vigilance as well as memory deficits. In the present investigation we have examined the validity of this pharmacological model of dementia by administering a battery of cognitive tasks to patients with mild and moderate senile dementia of the Alzheimer type and to age-matched controls. In contrast to volunteers receiving scopolamine all the mildly demented patients, and half of those moderately affected, performed normally on tests of vigilance whilst exhibiting the expected memory deficits. These data suggest that the mechanism of memory loss in Alzheimer's disease may differ from that found in scopolamine-induced amnesia.

Cholinergic neuropharmacology: an update

The current status of the pharmacology of central cholinergic transmission is reviewed. Particular attention is paid to the compounds that have been or are potential candidates as therapeutic agents for the treatment of mental disorders, particularly senile dementia. Compounds affecting acetylcholine synthesis, storage and release, affecting the enzyme acetylcholinesterase, acting on nicotinic cholinergic receptors, as well as compounds acting on muscarinic cholinergic receptors are reviewed. It is concluded that the most promising approaches for the development of new therapeutic agents might be specific acetylcholinesterase inhibitors and compounds with specific action at only one of the muscarinic cholinergic receptor subtypes.

Cholinergic grafts, memory and ageing

Neural grafts rich in cholinergic neurones can survive transplantation to the neocortex or hippocampus in rats. Such grafts have the capacity to ameliorate a variety of functional deficits associated both with explicit lesions that deafferent the neocortex or hippocampus and with natural ageing. The transplantation technique enhances our understanding of the involvement of forebrain cholinergic systems in normal cognitive functions (including memory) and of the role of cholinergic degeneration in the dysfunctions associated with ageing. It is unlikely, however, that these observations will extend to a therapeutic strategy for dementia using neural transplantation, because the human diseases (at least in the case of Alzheimer's disease and multi-infarct dementia) involve widespread degeneration of other populations of cortical neurones that are not so amenable to functional transplantation as the diffuse forebrain cholinergic systems.

Studies on choline transport enhancement into fibroblasts from normals and Alzheimer's donors

Human dental fibroblasts transport choline actively. This transport is inhibitable by hemicholinium-3. In this paper, choline transport into fibroblasts of normal donors (four cell lines) and into those of Alzheimer victims (four cell lines, age and sex matched to the normals) is accelerated by methylated xanthines, nicotine, and dexamethasone. At a caffeine concentration of 10 microM the stimulation of choline transport into normal cells averages 128% and into Alzheimer donor cells, 45%. 1 microM Dexamethasone stimulates choline influx by 86% in normal cells and 36% in Alzheimer cells. Nicotine enhances choline transport by 35% in normal cells and by 16% in Alzheimer cells. The implication is that if Alzheimer's disease is a cholinergic disorder, it may be amenable to transport-directed chemotherapies.

Relation between nicotine intake and Alzheimer's disease

OBJECTIVE

To study the association between Alzheimer's disease and nicotine intake through smoking.

DESIGN

Population based case-control study.

SETTING

City of Rotterdam and four northern provinces of The Netherlands.

SUBJECTS

198 patients with early onset Alzheimer's disease, 198 controls matched for age and sex, and families of 17 patients in whom Alzheimer's disease was apparently inherited as an autosomal dominant disorder.

MAIN OUTCOME MEASURES

Age of onset of dementia, relative risk of Alzheimer's disease.

RESULTS

89 of 193 patients with Alzheimer's disease had a history of smoking compared with 102 of 195 controls. Among the patients and controls with a family history of dementia, smoking was significantly less common in those with dementia (40/95 with dementia v 55/96 controls; relative risk 0.35; 95% confidence interval 0.16 to 0.78). The risk of Alzheimer's disease decreased with increasing daily number of cigarettes smoked before onset of disease (relative risk 0.3 in those smoking greater than 21/day v 1 in non-smokers). In six families in which the disease was apparently inherited as an autosomal dominant disorder, the mean age of onset was 4.17 years later in smoking patients than in non-smoking patients from the same family (p = 0.03).

CONCLUSIONS

These findings suggest an inverse association between smoking and Alzheimer's disease, although smoking cannot be advocated for other health reasons. We speculate that nicotine may have a role in the aetiology of both Alzheimer's disease and Parkinson's disease.

The role of nicotine and nicotinic mechanisms in neuropsychiatric disease

Cigarette smoking, and by implication nicotine, may be involved as a negative or positive risk factor in some neuropsychiatric disorders and possibly as a treatment in others. Nicotine exposure may be a negative risk factor for the development of Parkinson's disease, but a positive risk factor for the development of tardive dyskinesia. For Alzheimer's disease and Tourette's syndrome, the role of nicotine exposure is equivocal, however, the role of nicotine as a possible therapeutic agent, alone or in combination, remains an intriguing question. For functional psychiatric disorders, the data are suggestive of a link between tobacco use and at least exacerbation of some disorders. While nicotine exposure is unlikely to be critical in the genesis of these disorders, it may complicate the pharmacological therapeutics and long-term prognosis. Further research is needed to examine the actual importance of tobacco use in behavioural disturbances. The relative importance of central nicotinic mechanisms in normal and disordered human cognition and movement is now beginning to be fully explored.

Beneficial effects of nicotine

Nicotine in tobacco brings illness and death to millions of people. Yet nicotine in its pure form has the potential to be a valuable pharmaceutical agent. Nicotine fairly specifically binds to the cholinergic nicotinic gating site on cationic ion channels in receptors throughout the body. This action stimulates the release of a variety of neurotransmitters including especially catecholamines and serotonin. When chronically taken, nicotine may result in: (1) positive reinforcement, (2) negative reinforcement, (3) reduction of body weight, (4) enhancement of performance, and protection against; (5) Parkinson's disease (6) Tourette's disease (7) Alzheimers disease, (8) ulcerative colitis and (9) sleep apnea. The reliability of these effects varies greatly but justifies the search for more therapeutic applications for this interesting compound.

The effects of cholinergic drugs and cholinergic-rich foetal neural transplants on alcohol-induced deficits in radial maze performance in rats

Chronic alcohol (20% v/v in drinking water for 28 weeks) impaired acquisition of radial maze spatial and associative tasks by increasing both within-trial working and long-term reference memory errors; animals with high (above the median of 100 mg/100 ml) blood alcohol concentrations (BACs) during treatment were significantly more impaired than those with BACs below the median. Alcohol-treated rats showed improvements in radial maze performance after treatment with cholinergic agonists (arecoline and nicotine) and disruption with antagonists (scopolamine and mecamylamine) at low doses which did not affect controls. These effects were more pronounced for working than reference memory, and not manifest with the peripherally acting antagonists hexamethonium and N-methylscopolamine. Transplants into cortex and hippocampus of cholinergic-rich basal forebrain (BF) and ventral mesencephalon (VM) foetal neural tissue improved radial maze performance of alcohol-treated rats to control level over a period of 9-12 weeks after grafting. Cholinergic-poor foetal hippocampal (HC) grafts were without effect. BF and VM, but not HC, grafts showed dense acetylcholinesterase (AChE) staining, tyrosine-hydroxylase staining was most pronounced in VM sections and dopamine-beta-hydroxylase staining was minimal in all grafts. Choline acetyltransferase (ChAT) activity was significantly reduced in cortex and hippocampus of alcohol-treated rats, except those given cholinergic-rich transplants. Alcohol treatment also significantly reduced AChE-positive cell counts in the nucleus basalis, medial septal and diagonal band brain areas, at the sources of the forebrain cholinergic projection system (FCPS). Cortical levels of noradrenaline were significantly reduced in all alcohol-treated rats, regardless of transplant, whereas cortical dopamine content was significantly elevated in all rats receiving transplants, regardless of behavioural effect, but not in alcohol-treated controls. Forebrain serotonin levels were not significantly altered by grafting or alcohol treatment. These results suggest that damage to the FCPS, as shown by reduced ChAT activity in target areas, and reduced AChE cell counts in projection areas, played an important part in the radial maze deficits displayed by alcohol-treated rats, since these animals were sensitive to cholinergic drug challenge, and cholinergic-rich transplants from two different sites in foetal brain elevated ChAT activity and restored cognitive function. In contrast alcohol- or graft-induced alterations in other transmitter systems did not correlate with the pattern of behavioural deficit and recovery.

Effects of cholinergic-rich neural grafts on radial maze performance of rats after excitotoxic lesions of the forebrain cholinergic projection system--II. Cholinergic drugs as probes to investigate lesion-induced deficits and transplant-induced functional recovery

The effects of two doses of muscarinic (arecoline and scopolamine) and nicotinic (nicotine and mecamylamine) cholinergic receptor agonists and antagonists on the radial maze errors of rats, performing poorly after ibotenate lesions to the nucleus basalis and medial septal brain regions, were assessed before and after transplantation of cholinergic-rich and -poor fetal grafts, using tasks which measured short- (working) and long-term (reference) spatial and associative memory. Lesioned rats showed improvement with the agonists, and impairment with the antagonists, at low doses which did not affect the performance of controls; these effects were more marked for working than reference memory, especially in the spatial task. The peripherally acting antagonists N-methylscopolamine and hexamethonium did not affect the performance of control or lesioned rats. Effects of the cholinergic probes were re-examined 16 weeks after grafting, in groups with cholinergic-rich grafts to cortex and/or hippocampus which showed functional recovery, and groups with cholinergic-rich grafts to basal forebrain, or cholinergic-poor grafts to basal forebrain, cortex, and hippocampus, which showed no improvement. All lesioned rats, regardless of site, type, or efficacy of transplant, continued to show marked impairment with the antagonists. Poorly performing grafted animals also showed improvement with the agonists. In rats with behaviourally effective cholinergic-rich grafts, arecoline had no effect, but nicotine substantially increased working and reference memory errors, particularly spatial working memory errors. Rats with grafts in both cortex and hippocampus showed the largest increases in errors after nicotine. These results show that lesioned rats were more sensitive to the bi-directional effects of cholinergic receptor ligands than controls, consistent with a role for acetylcholine in the lesion-induced deficits. The predominant effect of drugs on working memory may also be consistent with disruption of acquisition rather than of storage or retrieval processes in memory, and may be related to impairment of attention. The results further show that, despite behavioural recovery, supersensitive responses to cholinergic drugs were not normalized in rats with cholinergic-rich grafts, and that an additive interaction between graft and host may have occurred in response to nicotine.

Separate and combined effects of the social drugs on psychomotor performance

Ten female subjects (five smokers and five non-smokers) performed a choice reaction time task (CRT), a compensatory tracking task (CTT), a short-term memory task (STM) and were tested for their critical flicker fusion threshold (CFF) at set points over 4 h after the administration of each possible combination of nicotine (2 mg gum or placebo), caffeine (250 mg capsule or placebo) and alcohol (30 g or placebo). Memory and motor function were shown to be facilitated by nicotine or caffeine, and the debilitating effects of alcohol were frequently antagonised by either drug. In spite of the differences in their neuropharmacological actions, combinations of nicotine, caffeine and alcohol may be compared through their effects on common information processing mechanisms involved in psychomotor performance.

Effects of cholinergic-rich neural grafts on radial maze performance of rats after excitotoxic lesions of the forebrain cholinergic projection system--I. Amelioration of cognitive deficits by transplants into cortex and hippocampus but not into basal forebrain

After ibotenate (10.0 mg/ml) lesions to the nucleus basalis and medial septal regions, at the source of the cortical and hippocampal branches of the forebrain cholinergic projection system, rats displayed long-lasting stable impairment in reference and working memory in both spatial (place) and associative (cue) radial maze tasks. Cell suspension transplants of cholinergic-rich fetal basal forebrain tissue dissected at embryonic day 15 substantially improved all aspects of radial maze performance to a comparable degree whether sited in cortex, hippocampus, or both regions of the host brain. No additive effects were obtained with grafts in both terminal regions, but total graft volume, assessed stereologically, showed a significant negative correlation with error scores. Rats with behaviourally effective grafts, like controls, were disrupted in the place task when tested in dim light which obscured extra-maze spatial cues. Lesioned rats were not affected by change in lighting. Grafts of cholinergic-poor fetal hippocampal tissue did not improve radial maze performance; neither did grafts of cholinergic-rich tissue placed within the host basal forebrain lesion sites. In rats with cholinergic-rich terminal grafts, cortical and hippocampal choline acetyltransferase activity was restored to control level, commensurate with site of transplant, whereas it was significantly reduced in lesioned animals and those with functionally ineffective grafts. The indiscriminate error pattern and insensitivity to changes in lighting shown by lesioned rats suggested that lesioning primarily disrupted attention rather than short- or long-term spatial or associative memory processes. Since rats with cholinergic-rich grafts showed both reduced errors and recovery of stimulus control, the data indicated that grafts affected information processing, rather than changes in motor or motivational processes. Changes in choline acetyltransferase activity and the behavioural efficacy of cholinergic-rich grafts are consistent with the involvement of acetylcholine in the behavioural deficits and recovery displayed by lesioned and grafted groups, but do not rule out contributions from other factors. The equipotency of grafts within each terminal region suggests also that there may be a considerable degree of functional cooperation between the two branches of the forebrain cholinergic projection system. Functional recovery may involve local, nonspecific synaptic or paracrine mechanisms within the target regions, since grafts were efficacious only when placed in the terminal areas, but not when sited homotopically in the basal forebrain, indicating that they did not achieve any functionally significant structural repair to the host brain at that site.

Distinguishing between attentional and amnestic effects in information processing: the separate and combined effects of scopolamine and nicotine on verbal free recall

An important issue in our understanding of cholinergic modulation of information processing is the extent to which drug-induced changes affect memory processes per se or simply the attentional processes required for effective acquisition of information. In this study, we examined the separate and combined effects of scopolamine and nicotine on verbal free recall. A single dose of nicotine improved recall performance on supraspan lists (30 words), but not on short lists (10 words). The same dose of nicotine had no effect on the scopolamine-induced recall deficits observed for both 30 and 10 word lists. The results are discussed in terms of the independence of attention and memory processes and the specificity of action of these two cholinergic compounds.

Effect of nicotine and tacrine on acetylcholine release from rat cerebral cortical slices

The effect of nicotine (1-10 microM) and tacrine (9-amino-1,2,3,4-tetrahydroacridine; THA) on stimulation evoked release of [3H]acetylcholine from the rat brain slice preparation preincubated with [3H]choline was investigated. In these preparations, nicotine enhanced while tacrine inhibited evoked [3H]acetylcholine release. These effects were blocked by (+)tubocurarine (1 microM) and atropine (0.1 microM) respectively. In the presence of idazoxan (0.3 microM) plus atropine (0.1 microM), nicotine (3 microM) continued to enhance evoked [3H]acetylcholine release while the inhibitory effect of tacrine (1 microM) on evoked [3H]acetylcholine release was reversed to an enhancement. Under these circumstances the effects of both nicotine and tacrine were blocked by (+)tubocurarine (1 microM). These findings demonstrate that tacrine can both inhibit or enhance [3H]acetylcholine release, most likely through its activity as a cholinesterase inhibitor. Under normal circumstances following tacrine the predominant effect of the elevated levels of acetylcholine will be activation of inhibitory presynaptic muscarine receptors on cholinergic nerves and an inhibition of evoked [3H]acetylcholine release. Under conditions where both presynaptic inhibitory muscarine and alpha 2-adrenoceptors are blocked, the elevated levels of acetylcholine produced by tacrine will lead to the activation of facilitatory presynaptic nicotine cholinoceptors on cholinergic nerves and an enhancement of evoked [3H]acetylcholine release.

Low dose tetrahydroaminoacridine (THA) improves cognitive function but does not affect brain acetylcholine in rats

Eight days of treatment with two low doses of tetrahydroaminoacridine (THA), given once daily, substantially improved radial maze performance in two groups of rats which showed persistent deficits either after ibotenic acid lesions at the source of forebrain cholinergic projections, or after 28 weeks treatment with alcohol (20% v/v) in drinking water. However, in immature, aged or aged and alcohol-treated rats, acetylcholine content was not significantly affected in any of the brain areas measured, even though the treatment regime had proved behaviourally effective. Inhibition of brain acetylcholinesterase activity was only marginally increased by this treatment regime. Thus, if THA influences behaviour by enhancing cholinergic transmission, its effects do not appear to be related to its activity as a cholinesterase inhibitor, and alternative mechanisms of action should be investigated.

Sparing of attentional relative to mnemonic function in a subgroup of patients with dementia of the Alzheimer type

Patients with dementia of the Alzheimer type (DAT) received two tests of visual selective attention, together with tests of spatial and visual recognition memory and visuospatial conditional learning previously used to show deficits early in the course of DAT. One set of attentional tests compared visual discrimination learning along intra- and extra-dimensional shifts, using a "total change" design. In the 12 DAT patients capable of attempting the extra-dimensional shift (subgroup 1), performance was equivalent to that of controls. This subgroup was also unimpaired at simple and compound discrimination learning and reversal and an intra-dimensional shift. They were as accurate as controls on a visual search task requiring matching of stimuli on two dimensions with variable numbers of alternatives, but were significantly impaired in the tests of recognition memory and learning. By contrast, the other 13 patients showed marked impairments in the attentional tasks. This subgroup was also significantly worse than subgroup 1 in performance on the visual recognition and conditional learning tasks, and showed greater severity on most of the clinical ratings of dementia. The sparing of attentional shifting in patients early in the course of DAT is contrasted with the impairments previously described in patients with Parkinson's disease with only mild or absent memory loss. The implications of this double dissociation of deficits for understanding the neural bases of the cognitive deficits in these two neurodegenerative diseases are discussed and their significance for the staging of DAT is considered.

Effects of nicotine, oxotremorine and 9-amino 1,2,3,4- tetrahydroacridine (tacrine) on matching and non matching to position in rats: no evidence for mnemonic enhancement

Groups of rats were trained on one of two variants of an operant memory task which allows strength of memory (accuracy), bias and response rates to be measured directly. In matching to position (MTP), one of two retractable response levers appeared at random as the sample. A response caused the lever to retract and this was followed by a delay (0-64 s) interval, during which the rat had to approach, and respond at, the magazine tray. Both levers were then presented and the rat had to respond to the lever which had most recently appeared as the sample, for food reward. A second group of rats learned non-matching to position (NMTP). In this task, rats had to respond to the lever which had not appeared as the sample.The subjects were then divided into subgroups and injected, peripherally and prior to test, with one of three cholinergic drugs. These were nicotine (NIC: 0-0.3 mg/kg), oxotremorine (OXO: 0-0.3 mg/kg) and 9-amino 1,2,3,4-tetrahydroacridine (tacrine, THA: 0-3.0 mg/kg). NIC had a delay-independent disruptive effect on accuracy, but only in the non-matching version, and it did not affect rate of responding. OXO and THA had no effect on accuracy, but adversely affected response latencies and rates.The results suggest that these drugs do not affect memory mechanisms; instead, and at the doses used, certain types of bias may be induced (NIC) and general responsiveness altered (OXO and THA).

Activating the damaged basal forebrain cholinergic system: tonic stimulation versus signal amplification

The hypothesis that the cognitive decline in senile dementia is related to the loss of cortical cholinergic afferent projections predicts that pharmacological manipulations of the remaining cholinergic neurons will have therapeutic effects. However, treatment with cholinesterase inhibitors or muscarinic agonists has been, for the most part, largely unproductive. These drugs seem to disrupt the normal patterning of cholinergic transmission and thus may block proper signal processing. An alternative pharmacological strategy which focuses on the amplification of presynaptic activity without disrupting the normal patterning of cholinergic transmission appears to be more promising. Such a strategy may make use of the normal GABAergic innervation of basal forebrain cholinergic neurons in general, and in particular of the inhibitory hyperinnervation of remaining cholinergic neurons which may develop under pathological conditions. Disinhibition of the GABAergic control of cholinergic activity is assumed to intensify presynaptic cortical cholinergic activity and to enhance cognitive processing. Although the extent to which compounds such as the benzodiazepine receptor antagonist beta-carboline ZK 93,426 act via the basal forebrain GABA-cholinergic link is not yet clear, the available data suggest that the beneficial behavioral effects of this compound established in animals and humans are based on indirect cholinomimetic mechanisms. It is proposed that an activation of residual basal forebrain cholinergic neurons can be achieved most physiologically via inhibitory modulation of afferent GABAergic transmission. This modulation may have a therapeutic value in treating behavioral syndromes associated with cortical cholinergic denervation.

Non-smokers show acute tolerance to subcutaneous nicotine

Plasma nicotine concentrations following subcutaneous (SC) injection were measured in six subjects who included three life-long nonsmokers. On average, a peak plasma level of 8.5 ng/ml (SD = 3.1) was reached 15 min after the mean dose of 13.25 micrograms/kg nicotine base. Subjective effects were reported by five subjects. The peak heart rate response (mean boost 11 beats per min at 10 min) preceded and was already declining by the time plasma nicotine concentrations peaked. Hysteresis plots showed clear evidence of acute nicotine tolerance in subjects who had never smoked, indicating that acute tolerance is not an acquired phenomenon. The acquisition by smokers of chronic tolerance to nicotine has not yet been systematically demonstrated. Reliable dose-response studies in smokers and nonsmokers are needed, and use of the SC route for this purpose is discussed.