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

Nicotine patches in Alzheimer's disease: pilot study on learning, memory, and safety

In view of the cholinergic deficits present in patients with Alzheimer's disease (AD), a widely investigated treatment strategy for the cognitive deficits in AD is cholinergic stimulation. Although nicotinic cholinergic receptor binding has been demonstrated to be deficient in the AD brain, the predominant theoretical and therapeutic focus to date has been on muscarinic cholinergic receptors and systems. The purpose of the present study was to evaluate the effects of sustained nicotine administration on behavior, cognition, and physiology. A double-blind placebo-controlled trial was conducted in which six patients with probable AD were exposed to 7, 8, and 7 days of placebo, nicotine, and washout, respectively. Daily sessions evaluating learning, memory, and behavior were conducted. Global cognitive functioning, rest and activity levels, cardiac activity, and blood levels were also measured. Findings included improved learning during the nicotine condition, which persisted throughout washout. Memory, behavior, and global cognition were not significantly affected. Sustained administration of nicotine appeared to be safe, although sleep showed a significant decrease.

Increases in hippocampal and frontal cortical acetylcholine release associated with presentation of sensory stimuli

In vivo microdialysis was employed to monitor acetylcholine release in the hippocampus and frontal cortex of freely behaving rats. Four stimuli were presented on separate occasions in the course of a dialysis session to rats with microdialysis probes implanted in the hippocampus or frontal cortex. Visual, auditory, olfactory and tactile stimuli elicited a number of different responses such as exploratory and consummatory behaviours. Presentation of two of the stimuli (auditory and tactile) also produced periods of alert immobility (freezing). All of the stimuli increased acetylcholine release in both the hippocampus and cortex: in the hippocampus, this increase was statistically significant with all except the olfactory stimulus, whereas in the cortex all but the visual stimulus resulted in significant increases. In the hippocampus, there were no significant differences between the increases in acetylcholine release produced by the four stimuli. In contrast, in the cortex, there was significant variation between the magnitude of acetylcholine release produced by the different stimuli: acetylcholine release elicited by tactile stimulation was greater than that produced by the other stimuli. There was no significant variation in the duration of increases in acetylcholine release produced by the stimuli in either the hippocampus or cortex. These results provide evidence that acetylcholine release is associated with a variety of behavioural responses to stimuli designed to produce arousal, and point to a role for cortical and hippocampal cholinergic mechanisms in arousal or attention. Further, the results suggest that under some circumstances cortical and hippocampal acetylcholine release may be regulated differentially.

Nicotinic and muscarinic receptors in the rat prefrontal cortex: differential roles in working memory, response selection and effortful processing

The aim of the present study was to evaluate the effects of cholinergic receptor blockade in the rat prefrontal cortex on cognitive processes. The nicotinic antagonists neuronal bungarotoxin and dihydro-beta-erythroidine and the muscarinic antagonist scopolamine were injected into the prelimbic area of the prefrontal cortex. Their behavioural effects were assessed in a T-maze to test reference memory (visual discrimination task) and working memory in delayed matching (MTS) and non-matching to sample (NMTS) tasks. Neuronal bungarotoxin produced a significant decrease in working memory performance in the MTS task but not in the NMTS task. In contrast, scopolamine impaired working memory in both MTS and NMTS tasks. Reference memory was not altered by any of the cholinergic antagonists. These results demonstrate a differential role of nicotinic and muscarinic receptors in the rat prefrontal cortex. Nicotinic transmission appears to be important in delayed response tasks requiring effortful processing for response selection, while the muscarinic system is involved in general working memory processes.

Minor alkaloids of tobacco release [3H]dopamine from superfused rat striatal slices

In addition to S(-)-nicotine, several minor tobacco alkaloids ((+/-)-nornicotine, anabaseine, S(-)-anabasine, and S(-)-N-methylanabasine) are present in tobacco smoke. This study demonstrates that these alkaloids increase fractional 3H release in a concentration-dependent manner from rat striatal slices preloaded with [3H]dopamine, with desensitization of this response. The rank order of EC50 values was S(-)-nicotine (3.0 +/- 2.2 microM) > (+/-)-nornicotine (6.7 +/- 2.1 microM) > anabaseine (15.4 +/- 6.1 microM) = S(-)-N-methylanabasine (16.3 +/- 4.7 microM) = S(-)-anabasine (19.3 +/- 3.2 microM). The alkaloids did not modulate fractional 3H release evoked by electrical-field depolarization. Thus, minor tobacco alkaloids may contribute to the apparent neuroprotective effects of smoking in neurodegenerative diseases.

Improved learning and memory in aged rats with chronic administration of the nicotinic receptor agonist GTS-21

The ability of two synthetic nicotine receptor ligands, TGS-21 and DMAB, to chronically enhance the cognitive function of aged rats was evaluated in three diverse tasks and compared to the cognition-enhancing effects of nicotine administration. 15 min prior to daily behavioral testing, aged 22-24 month old rats received an i.p. injection of nicotine (.02 mg/kg), GTS-21 (1 mg/kg), DMAB (2mg/kg), or saline vehicle and were tested in either one-way active avoidance pole jumping, Lashley III maze, or a 17-arm radial maze. GTS-21 pretreatment was as effective as nicotine for enhancing the acquisition of aged rats in both one-way active avoidance and Lashley III maze training. In 17-arm radial maze testing, GTS-21 improved both general learning and reference (long-term) memory to the same extent as nicotine. Although DMAB pretreatment enhanced reference memory in 17-arm radial maze testing to the same as nicotine, it did not affect general learning in this complex task and did not exert any cognition-enhancing effects in Lashley III maze training. These results indicate that GTS-21 has cognition-enhancing abilities in aged rats that are comparable to those of nicotine in a variety of behavioral tasks. Since GTS-21 acts preferentially on brain nicotinic receptors and is less toxic than nicotine, thses results further indicate that GTS-21 may have substantive therapeutic value in the treatment of age-associated memory impairment (AAMI) and/or Alzheimer's disease.

Effects of nicotinic acetylcholine receptor ligands on behavioral vigilance in rats

The effects of nicotinic receptor ligands on performance in a task measuring sustained attention, or vigilance, were tested. This task required the animals to discriminate between signal and non-signal events. The sequence of signal (central panel light illumination for 500, 50 or 25 ms) and non-signal presentations was randomized over three blocks of 54 trials each (27 signal trials, 9 per length, and 27 non-signal trials). A left lever press following a signal was counted as a hit, and a right lever press following a non-signal event was counted as a correct rejection. Hits and correct rejections were rewarded, whereas misses and false alarms (defined as incorrect right and left lever presses, respectively) were not. Baseline performance was characterized by a signal length dependent ability of the animals to discriminate between signal and non-signal events. Administration of nicotine (0.19, 0.62, 1.9 mumol) or of two novel nicotinic receptor agonists, ABT-418 and A-82695, did not produce main effects on vigilance performance. Lobeline (1.9, 6.2, 19 mumol), a nicotinic receptor ligand with mixed agonist/antagonist activities, impaired the animals' ability to discriminate between signal and non-signal events. The antagonist mecamylamine (5, 15, 50 mumol) potently impaired performance while increasing the number of errors of omission. The lack of effect of nicotine largely corresponds with the findings from previous studies on the acute effects of nicotine in intact subjects and non-smoking humans. While the detrimental effects of lobeline may have been related to the antagonist effects of this compound, the reasons for the differences between the effects of nicotine and lobeline still remain unsettled. These data support the hypothesis that nicotine receptor mechanisms are maximally activated in intact animals performing this task, and suggest that effects of acute nicotinic agonist treatment would not produce further cognitive benefit for these animals.

Reversal of visual attentional dysfunction following lesions of the cholinergic basal forebrain by physostigmine and nicotine but not by the 5-HT3 receptor antagonist, ondansetron

To investigate further the cholinergic specificity of the effects of basal forebrain lesion-induced disruption of attentional performance, the present study examined the efficacy of various pharmacological agents in improving performance of a five-choice serial reaction time task in rats that had received lesions of the cholinergic basal forebrain. Specifically, the effects of the novel 5-HT3 receptor antagonist, ondansetron (0.3, 1, 10 ng/kg), and of nicotine (0.03, 0.06, 0.1, 0.3 mg/kg) and the anticholinesterase, physostigmine (0.05, 0.1 mg/kg), on attentional function were examined in animals which had received AMPA-induced lesions of the nucleus basalis magnocellularis (nbM). The behavioural impairments observed immediately following the lesion were a reduction were choice accuracy and an increase in correct response latency. Although these impairments showed recovery over the course of the following weeks, the deficit in choice accuracy could be reinstated by reducing the duration of the visual stimulus and thus increasing the attentional load placed on the animals. This reduction in choice accuracy could be dose dependently improved by systemic administration of either physostigmine or nicotine, suggesting that this impairment in attentional function may be attributed to disruption of cholinergic function. The pharmacological specificity of these improvements was supported by the inability of d-amphetamine to improve task performance (0.2, 0.4, 0.8 mg/kg). Ondansetron was also unable to improve accuracy of performance in lesioned animals, but was effective in reducing the anticipatory or premature responding observed in both control and lesioned animals, even when elevated (in the case of controls) by treatment with systemic d-amphetamine. The results of the present study therefore suggest that cholinergic dysfunction can lead to attentional impairments which can be ameliorated by cholinergic treatments such as physostigmine and nicotine, but that ondansetron, despite its proposed ability to release cortical acetylcholine, was unable to restore choice accuracy at the doses employed. The results further suggest a double dissociation of effects on accuracy and the disinhibition of responding.

The selective 5-HT3 receptor antagonist, WAY100289, enhances spatial memory in rats with ibotenate lesions of the forebrain cholinergic projection system

The effects of three doses (0.003, 0.03 and 1.0 mg/kg sc) of the 5-HT3 receptor antagonist, WAY 100289, on spatial learning and memory in the water maze were examined in rats before and after ibotenate lesions to the nucleus basalis and medial septal brain regions at the source of cholinergic projections to cortex and hippocampus. The representative cholinergic nicotinic and muscarinic receptor agonists nicotine (0.1 mg/kg) and arecoline (1.0 mg/kg) were also tested for comparison. Both arecoline and nicotine improved initial acquisition in rats before lesioning, in terms of latency to find a hidden platform and accuracy of search strategy. WAY100289 did not affect the performance of normal rats significantly, apart from some non-significant trends towards improvement with the highest dose. However, in animals showing transient navigational deficits in retention and relearning after lesioning, WAY100289 improved performance at all three doses, though ameliorative effects of nicotine and arecoline were more marked also in lesioned rats. These results show that WAY100289 improved spatial learning in animals impaired after lesions to cholinergic projection nuclei, which may reflect an interaction with cholinergic transmission to enhance cognitive function. However, in the present study, WAY100289 appeared to be less effective than direct cholinergic agonists.

Diversity of neuronal nicotinic acetylcholine receptors: lessons from behavior and implications for CNS therapeutics

Although the molecular biology of neuronal nicotinic acetylcholine receptors (nAChRs) provides evidence for multiple receptor subtypes, few selective pharmacological tools exist to identify these subtypes in vivo. However, the diversity of behavioral effects of available nAChR agonists and antagonists reviewed in this paper suggests that neuronal nAChR subtypes may play distinct roles in a variety of behavioral outcomes. Further characterization of the behavioral effects of the activation of discrete nAChR subtypes may eventually provide information useful in designing selective nAChR ligands targeting a variety of CNS disorders.

Alteration in nicotine binding sites in Parkinson's disease, Lewy body dementia and Alzheimer's disease: possible index of early neuropathology

High-affinity nicotine binding, considered to primarily reflect the presence of CNS alpha 4 beta 2 nicotinic receptor subunits, was examined autoradiographically in brain regions most severely affected by Alzheimer and Parkinson types of pathology. In the midbrain, the high density of binding associated with the pars compacta of the substantia nigra was extensively reduced (65-75%, particularly in the lateral portion) in both Lewy body dementia and Parkinson's disease. Since loss of dopaminergic neurons in Lewy body dementia was only moderate (40%), loss or down-regulation of the nicotinic receptor may precede degeneration of dopaminergic neurons in this region. In the dorsolateral tegmentum, where diffuse cholinergic perikarya are located, nicotine binding was highly significantly decreased in both Lewy body dementia and Parkinson's disease with almost no overlap between the normal and disease groups, indicative of a major pathological involvement in or around the pedunculopontine cholinergic neurons. In the hippocampus, binding was decreased around the granular layer in Lewy body dementia and Alzheimer's disease, although unchanged in the stratum lacunosum moleculare, where binding was relatively higher. Dense bands of receptor binding in the presubiculum and parahippocampal gyrus--areas of highest binding in human cortex--were diminished in Alzheimer's disease but not Lewy body dementia. In temporal neocortex there were reductions in Alzheimer's disease throughout the cortical layers but in Lewy body dementia only in lower layers, in which Lewy bodies are concentrated. Abnormalities of the nicotinic receptor in the diseases examined appear to be closely associated with primary histopathological changes: dopaminergic cell loss in Parkinson's disease and Lewy body dementia, amyloid plaques and tangles in subicular and entorhinal areas in Alzheimer's disease. Loss or down-regulation of the receptor may precede neurodegeneration.

Nucleus basalis of Meynert cell responses in awake monkeys

Extracellular cell activity was recorded in the intermediate and posterior subdivisions of the nucleus basalis of Meynert (NBM) of awake monkeys to determine cell characteristics and the motor and sensory participation. Animals were trained to move a lever by elbow flexion-extensions to receive a reward. Cell activity was recorded when the animal was at rest and executing the task. The electromyogram of the upper limb, contralateral to the recording site, was recorded simultaneously with NBM neuron activity. The effect of visual, auditory, and tactile stimuli were also studied after performance of the learned task. A moderate number of cells responded to the reward (16%), while a higher percentage of them was associated with unexpected, unspecific stimuli (22%). Firing rates correlated positively with limb movement (30%). Visual (34%) and auditory (15%) responses were also found. No NBM cell responded to tactile stimulation. Considering these findings and the anatomical projections over the cortex, the NBM role ion complex integrative processes in discussed.

Nicotine improves cognitive disturbance in senescence-accelerated mice

Senescence-accelerated mice (SAM), a murine model of age-related deterioration in learning ability, were studied as to the acetylcholine (ACh) contents in the brain tissues and the effect of nicotine administration. We found that the ACh content of SAM-P/8 (accelerated senescence-prone) mice was lower than that of SAM-R/1 (accelerated senescence-resistant) mice in the midbrain thalamus and the hypothalamus. In addition, an IP administration of nicotine was found to improve learning ability of SAM-P/8 as shown by performance of a passive avoidance task. Nicotine may potentiate cognitive function in SAM-P/8.

Are the cognitive-enhancing effects of nicotine in the rat with lesions to the forebrain cholinergic projection system mediated by an interaction with the noradrenergic system?

Experiments were conducted to test the hypothesis that the enhancing effect of nicotine on water maze performance in rats with lesions of the forebrain cholinergic projection systems (FCPS) is mediated by an interaction with the noradrenergic system, in particular the ascending dorsal noradrenergic bundle (DNAB) and its projection areas. Three groups of rats received lesions of either: i) the nucleus basalis (NBM) and medial septal area/diagonal band (MSA/DB) by infusion of alpha-amino-3-hydroxy-4-izoxazole propionic acid (AMPA) (FCPS group), ii) DNAB, by infusion of 6-hydroxydopamine (6-OHDA) (NOR group), or iii) both FCPS plus DNAB (COMB group). Control animals received vehicle. Choline acetyltransferase activity was reduced in the cortex and hippocampus of the FCPS and COMB groups and in the hippocampus of the NOR group. NA level was reduced in the cortex and hippocampus of the FCPS and COMB groups, but not the FCPS group. In a reference memory task, the performance of both the NOR and COMB groups, but not the NOR group, was significantly worse than that of controls; there was no effect of nicotine administration (0.1 mg/kg) on escape latency or other measures in this task. In a working memory task, FCPS and COMB rats took longer to find the submerged platform on the second and following trials, and there was a significant enhancement of performance by nicotine in both groups, but not in controls. These results indicate that the enhancing effects of nicotine in rats with FCPS lesions are not mediated by an interaction with the DNAB.

Effects of smoking on memory for prose passages

The present study examined the effects of smoking on memory for prose passages. Habitual male smokers were matched on verbal ability, impulsivity level, and habitual smoking level and were instructed to smoke either a 0.1 mg (control), a 0.7 mg, or a 1.5 mg nicotine cigarette in a controlled fashion. Immediate recall after reading expository passages was obtained. The results indicated that the subjects who smoked the 0.7 mg nicotine cigarette recalled a greater proportion of the idea units than the control group, with no difference between the 1.5 mg group and the control. In addition, blood pressure and heart rate significantly increased in all groups immediately after smoking, with heart rate increases greater in the 0.7 mg and 1.5 mg groups than the control. Interpretive hypotheses for the results include arousal theory, with optimal arousal levels being obtained in the 0.7 mg nicotine group for the prose recall task, and nicotine specific effects, including nicotine's influence on the cholinergic system.

Enhanced acetylcholine release in hippocampus and cortex during the anticipation and consumption of a palatable meal

In rats trained for 14 days to consume a palatable liquid chocolate meal (Sustacal), in vivo brain microdialysis was used to measure release of acetylcholine in the frontal cortex and hippocampus during anticipation and consumption of the meal. Rats were trained in an experimental chamber in which they were separated from the Sustacal by a screen for 20 min (trained, rewarded group). The screen was then removed and the rats were allowed 20 min of access to the meal. Two control groups were run concurrently: these groups consisted of rats (i) that were trained over 14 days but only had access to water in the experimental chamber (trained, non-rewarded), or (ii) that were introduced into the experimental chamber for the first time on the final test (i.e. dialysis) session, and presented with Sustacal (naive). Different results were obtained in the hippocampus and frontal cortex. In the hippocampus there were no group differences with respect to acetylcholine release. Thus, in all three groups acetylcholine release increased to about 220% of basal values when animals were placed in the experimental chamber. In the frontal cortex, acetylcholine release also increased significantly in all three groups. However, the extent of this increase was significantly greater in the trained, rewarded group, reaching approximately 300% of basal values during the anticipatory and consummatory components of the task. The significant increases in acetylcholine release which occurred in both the hippocampus and frontal cortex of each of the three groups are consistent with an involvement of cholinergic basal forebrain neurons in the regulation of arousal or attention. In addition, however, acetylcholine release in the frontal cortex can be further selectively enhanced by the animal's past training experience, perhaps being associated with the anticipation of reward.

Nootropic effect of nicotine on carbon monoxide (CO)-induced delayed amnesia in mice

The effects of nicotine on carbon monoxide (CO)-induced amnesia in mice were investigated using a step-down type passive avoidance task. Mice were exposed to CO 3 times at 1-h intervals, 7 days before the first training and retention test and 24 h after the first training session. Memory deficiency occurred in mice when training commenced more than 3 days after CO exposure (delayed amnesia): the median step-down latency in the retention test of the CO-exposed group was significantly shorter than that of the control group. Administration of (-)-nicotine (15.6 and 31.3 nmol/kg, IP) 15 min before the first training session prolonged the step-down latency in the CO-exposed group, but (+)-nicotine did not. To determine whether this effect of (-)-nicotine was mediated via nicotinic cholinergic receptors, we attempted to block its action using a nicotinic acetylcholine receptor antagonist (mecamylamine). Mecamylamine (1.25 mumol/kg) blocked the effect of (-)-nicotine (31.3 nmol/kg) on delayed amnesia. Administration of (-)-nicotine (15.6-62.5 nmol/kg) immediately after the first training session failed to ameliorate learning ability in the CO-exposed group. These results suggest that (-)-nicotine potentiates the nicotinic cholinergic neuronal system and may potentiate acquisition of memory.

Effects of disrupting the cholinergic system on short-term spatial memory in rats

The effects of disrupting the muscarinic or nicotinic systems on short-term spatial memory were investigated using a delayed matching to position (DMTP) procedure. Rats were trained on the DMTP until stability and then divided into two groups: one group was implanted with an indwelling cannula aimed at the lateral ventricle. The cannulated group received injections of selective muscarinic antagonists (pirenzepine, M1; AFDX 116, M2; UH-AH 37, M1/M3) or hemicholinium-3 (a choline uptake inhibitor). The remaining animals were treated with conventional muscarinic antagonists (scopolamine, methyl scopolamine) or nicotinic channel blockers (mecamylamine, hexamethonium). Scopolamine, methyl scopolamine and UH-AH 37 disrupted all performance parameters in a non-specific but dose related manner. Pirenzepine disrupted accuracy in a delay, but not dose dependent manner, and exerted no other negative effects on performance. Hemicholinium-3-induced performance deficits showed some elements of effects seen following pirenzepine and scopolamine (delay dependent effects on accuracy, some negative effects on other motoric aspects of performance). AFDX 116 and hexamethonium had no significant effects on performance with respect to control. Mecamylamine reduced accuracy and increased response latencies at the highest dose tested. These data indicate that muscarinic antagonists are more effective at disrupting mnemonic performance than nicotinic blockers, and moreover, that distinct muscarinic receptors may have differential effects on cognitive performance.

A nicotinic agonist (GTS-21), eyeblink classical conditioning, and nicotinic receptor binding in rabbit brain

The septo-hippocampal cholinergic system is of demonstrated involvement in eyeblink classical conditioning (EBCC). To determine if a nicotinic cholinergic agonist, GTS-21, would facilitate acquisition of EBCC in older rabbits, three doses (0.1, 0.5, 1.0 mg/kg) in sterile saline vehicle and vehicle alone were administered to older rabbits (n = 48; mean age = 29.8 months). A control group of vehicle-treated young rabbits (n = 12; mean age = 3.5 months) was included. Rabbits were conditioned for fifteen 90-trial sessions in the 750 ms delay paradigm with a tone conditioned stimulus and corneal airpuff unconditioned stimulus. Dependent measures of trials to learning criterion, percentage of conditioned responses (CRs) and CR amplitude consistently showed significant improvement in older rabbits treated with 0.5 and 1.0 mg/kg of GTS-21. Acquisition was similar in vehicle-treated young and GTS-treated older rabbits. Vehicle-treated older rabbits conditioned more poorly than vehicle-treated young rabbits. No non-associative learning effects were observed in GTS-21 treated animals. Nicotinic receptor binding was similar in all groups of older rabbits, indicating that GTS-21 administration over a 15-day period did not affect nicotinic receptors. Alzheimer's disease (AD) has been associated with significant loss of nicotinic cholinergic receptors, and patients diagnosed with probable AD are seriously impaired on EBCC. These results demonstrating that the nicotinic agonist, GTS-21, facilitated EBCC in older rabbits suggest that the compound should receive additional investigation for its potential to affect cognition in AD.

Tryptophan depletion in normal volunteers produces selective impairments in learning and memory

The amino-acid L-tryptophan is essential in the synthesis of brain serotonin, and its depletion can lead to a widespread reduction in central serotonergic activity. A placebo-controlled cross-over within-subjects design (n = 12) examined the effects of tryptophan depletion on human cognitive performance. A low-tryptophan (low-TRP) drink successfully reduced the levels of plasma and total free tryptophan. Computerized tests of memory, learning and executive function revealed selective and non-sedative impairments on cognitive performance following the active drink. Specifically, low-TRP impaired learning as seen in tests of visual discrimination and paired associates. Furthermore, low-TRP lengthened thinking times during the Tower of London planning task, but only in subjects already familiar with the task, suggesting a retrieval deficit. No evidence was found for an effect of the low-TRP drink on measures sensitive to frontal lobe dysfunction, supporting instead a specific role for the serotonergic system in the processes of memory and learning not directly implicated in frontal lobe function.

Determination of enantiomeric purity of nicotine in pharmaceutical preparations by 13C-NMR in the presence of a chiral lanthanide shift reagent

A method for the determination of enantiomeric composition of nicotine samples, based on 13C-NMR spectroscopy in the presence of the chiral lanthanide shift reagent, tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]ytte rbium [Yb(tfc)3], was developed. Observation at 100.6 MHz of the C2' resonance of nicotine in the presence of 0.15-0.20 mol of the ytterbium complex, either in ordinary 13C[1H]-NMR spectra or in carbon spectra enhanced by polarization transfer (refocused INEPT), allowed precise determination of the ratios of (S)- to (R)-nicotine. At least 1% of (R)-nicotine could be determined in samples of (S)-nicotine, milligram amounts being required for the analysis. Use of the 13C-NMR spectra is more advantageous than use of 1H-NMR spectra. Thus, Yb(tfc)3 induced separation of the proton resonances of the enantiomers of nicotine, and the shifted resonances of nicotine enantiomers could be assigned by use of 1H-13C heteronuclear chemical shift correlation, but the proton resonances were broad, their chemical shifts were sensitive to small variations of the ratio between Yb(tfc)3 and nicotine, and signals of the enantiomer present in small amounts were easily obscured by impurities. Therefore, although 13C-NMR is more time consuming, this method is more suitable for routine analysis. The method was applied for the determination of enantiomeric purity of (S)-nicotine in pharmaceutical formulations, including chewing gums, skin absorption patches, inhalators, and nasal sprays.

A novel nicotinic agonist facilitates induction of long-term potentiation in the rat hippocampus

Long-term potentiation (LTP) can be modulated by a number of neurotransmitter receptors including muscarinic and GABAergic receptor types. We have found that a novel nicotinic agonist, 2,4-dimethoxybenzylidene anabaseine (DMXB), facilitated the induction of LTP in the hippocampus in a dose-dependent and mecamylamine-sensitive manner. DMXB displaced high affinity nicotinic [125I]alpha-bungarotoxin and [3H]acetylcholine binding in rat brain. Xenopus oocyte studies demonstrated that DMXB has agonist activity at alpha 7 but not alpha 4/beta 2 nicotinic receptor subtypes. These results indicated that DMXB is a novel nicotinic agonist with apparent specificity for the alpha 7/alpha-bungarotoxin nicotinic receptor subtype and indicate that nicotinic receptor activation is capable of modulating the induction of long-term potentiation.

Advances in the pharmacotherapy of Alzheimer's disease

The authors reviewed the literature on the agents proposed for the treatment of Alzheimer's disease (AD). Different classes of drugs have been tested for this indication including psychostimulants, anticoagulants, vasodilators, hyperbaric oxygen, hormones, nootropics, cholinomimetics, monoaminergics and neuropeptides without conclusive evidence of being beneficial for the treatment of this condition. Among the cholinomimetics recent research data seems to indicate that they might produce modest benefits in mild-to-moderate AD patients. Recently, other drugs have also been proposed including neurotrophic factors, phosphatidylserine, angiotension [corrected] converting enzyme (ACE) inhibitors, calcium channel blockers, acetyl-L-carnitine, xanthine derivatives, anti-inflammatory agents, aluminum chelate agents, and D-cycloserine. Of these new strategies few hold promise of more substantial benefits for AD, with the possibility of altering the course of the disease, but these drugs await confirmatory trials.

Interaction between genetic and environmental risk factors for Alzheimer's disease: a reanalysis of case-control studies

To study the interaction among genetic and environmental risk factors, a reanalysis of case-control studies of Alzheimer's disease (AD) was conducted based on the original data of all studies carried out to January 1, 1990. Seven studies were included in the present analysis, comprising a total of 814 AD patients and 894 control subjects. When comparing those with a positive and negative family history of dementia, similar odds ratio were found for late maternal age [1.7; 95% confidence interval (0.6-4.8) vs. 2.0 (1.1-3.5)], head trauma [1.7 (0.7-4.2) vs. 1.9 (1.1-3.2)], and history of depression [2.0 (0.2-19.8) vs. 2.1 (0.8-1.7)]. This suggests a model in which these risk factors increase the risk for AD independent of family history of dementia. Among those with a positive family history of dementia, the odds ratios for family history of Down's syndrome [4.2 (0.9-20.0)] and of Parkinson's disease [3.3 (0.4-28.2)] tended to be higher than among those with a negative family history of dementia [2.6 (0.8-8.5) and 2.4 (0.8-7.0), respectively]. However, for both disorders the difference in odds ratio was not statistically significant. For history of cigarette smoking, there was no association to AD for those with no first degree relatives with dementia and an inverse relation with AD for those with a positive family history. Although in all analyses, family history of dementia remained significantly associated with AD in the absence of other factors, the odds ratio associated with family history of dementia tended to be lower for those with a positive smoking history, particularly for those with two or more affected relatives. These findings suggest that smoking may interact specifically with a genetically determined process.

Chronic nicotine reverses working memory deficits caused by lesions of the fimbria or medial basalocortical projection

Nicotine has been found in a variety of studies to improve performance in memory tasks. This study was conducted to determine if chronic nicotine administration is useful in counteracting the working memory deficits seen after lesions of the fimbria or the medial basalocortical projection. Rats were trained to asymptotic performance on a working memory version of the radial-arm maze. Then, they were given knife cut lesions of the fimbria or the medial basalocortical projection or underwent sham surgeries. At the time of surgery, rats in each treatment group were implanted with either nicotine-containing or placebo glass and Silastic pellets. Rats with fimbria or basalocortical lesions showed a significant decline in working memory performance. Chronic nicotine significantly improved choice accuracy in both lesioned and unlesioned rats. Nicotine treatment restored performance of the lesioned rats to control levels. These data show that in addition to improving memory performance in normal rats, nicotine can counteract lesion-induced memory impairments. Nicotine also may be useful for treatment of disease-related memory impairments such as seen in Alzheimer's disease.

Nicotinic and muscarinic modulations of excitatory synaptic transmission in the rat prefrontal cortex in vitro

The importance of the cholinergic innervation of the neocortex in cognitive functions has been shown in a number of clinical and animal studies. Until recently, attempts to study the mode of action of acetylcholine in the neocortex have concentrated on muscarinic effects, whereas cholinergic actions mediated by nicotinic receptors have been difficult to demonstrate. The present work was undertaken to study the mechanism of action of nicotinic agents on cortical neurons and compare it to muscarinic effects by means of intracellular recordings in a slice preparation. The study was performed in the prelimbic area of the rat prefrontal cortex, a cortical region particularly involved in cognitive processes. Recordings were made from pyramidal cells located in layers II/III and synaptic potentials were evoked by stimulation of superficial cortical layers. Iontophoretic applications of nicotinic agonists (nicotine, dimethylphenylpiperazinium, cytisine) increased the amplitude of the monosynaptic excitatory postsynaptic potential mediated by non-N-methyl-D-aspartate glutamate receptors in 14% (22/159) of cells. This effect was abolished by the selective nicotinic blocker, neuronal bungarotoxin (IC50 = 0.6-0.7 microM) and by dihydro-beta-erythroidine (IC50 = 20-30 microM), whereas hexamethonium, mecamylamine, curare and alpha-bungarotoxin were ineffective. The nicotinic agonists did not change resting membrane potential, input resistance or current-voltage relationship. They also did not affect the depolarizations produced by glutamate applied by iontophoresis in the somatic or dendritic area. In contrast, the muscarinic agonists (muscarine, acetyl-beta-methylcholine) decreased the amplitude of the excitatory postsynaptic potential in 100% of the neurons tested. Atropine was more effective (IC50 = 0.08 microM) than pirenzepine (IC50 = 2 microM) to antagonize the muscarinic action. These effects were observed in the absence of any direct postsynaptic change in membrane potential or input resistance, provided that the site of the iontophoretic application was more than 100 microM distant from the soma. The muscarinic agonists did not influence the actions of iontophoretically applied glutamate. These results suggest that nicotinic and muscarinic agonists modulate excitatory synaptic transmission mediated at dendritic sites by non-N-methyl-D-aspartate glutamate receptors, possibly through a presynaptic action. Thus ascending cholinergic systems may take part in information processing in the prefrontal cortex through the control of ongoing excitation to pyramidal cells.

Effects of central nicotinic cholinergic receptor blockade produced by chlorisondamine on learning and memory performance in rats

The effects of chronic nicotinic receptor blockade on the performance of learning and memory tasks were determined using chlorisondamine, a compound which produces central nicotinic cholinergic receptor blockade that lasts for several weeks after a single icv administration. Chlorisondamine treatment did not affect the acquisition of spatial information in the Morris water maze or in the radial arm maze, tasks in which performance is reportedly disrupted by acute administration of the nicotinic antagonist, mecamylamine. Chlorisondamine also did not affect performance in the inhibitory avoidance task and did not alter the memory enhancement found in this task after post-training administration of nicotine. Mecamylamine, however, completely blocked the memory-enhancing effects of nicotine. In contrast to the differential ability to chlorisondamine and mecamylamine to block nicotine's memory-enhancing effects, these antagonists produced comparable blockade of nicotine's effects on open field behavior. It is unlikely that the different effects of systemically administered mecamylamine and centrally administered chlorisondamine on nicotine-induced memory enhancement are due to mecamylamine's peripheral effects, since hexamethonium, a peripherally active nicotinic antagonist, did not block nicotine-induced memory enhancement. The different pattern of effects of mecamylamine and chlorisondamine may be related to compensatory mechanisms being selectively induced by chronic blockade produced by chlorisondamine and not by acute blockade produced by mecamylamine. Alternatively, different effects of these two nicotinic cholinergic antagonists on the performance of learning and memory tasks might be related to selective actions of these compounds at nicotinic receptor subtypes or at nonnicotinic receptors.

Differential effects of scopolamine and mecamylamine on working and reference memory in the rat

The effects of the muscarinic antagonist scopolamine (0.1-0.6 mg/kg, IP) and the nicotinic antagonist mecamylamine (1-10 mg/kg) were compared in T-maze alternation and discrimination tasks in the rat. Scopolamine dose dependently disrupted performance on the alternation task and potentiated the increase in errors made in controls when the delay between forced and choice runs was increased from 0 to 30 s. Mecamylamine disrupted performance at the 10-mg/kg dose only and dose dependently inhibited the increase in errors made in controls when the delay between forced and choice runs was increased to 30 s. In simple T-maze discrimination, only the 0.6-mg/kg dose of scopolamine disrupted performance of the task, while mecamylamine at both 5 and 10 mg/kg disrupted task performance. These results confirm that working memory tasks are more sensitive to central muscarinic blockade than reference memory tasks. They also demonstrate that in delay conditions working memory performance is enhanced following central nicotinic blockade while reference memory performance is disrupted. This suggests that centrally active muscarinic and nicotinic antagonists have dissociable effects on memory processes in the rat.

Increased responsiveness of hippocampal pyramidal neurons to nicotine in aged, learning-impaired rats

The effect of aging upon the responsiveness of hippocampal CA1 pyramidal neurons to nicotine was investigated using electrophysiological techniques in male Fischer 344 rats. Prior to electrophysiological recording, animals were behaviorally tested using the Morris water maze. All 3-6 and 18-21 month rats displayed rapid place learning in this task, while none of the 27-30 month animals learned within the 5-day test period. By contrast, rats of all age groups were able to learn a cue version of the water maze task. Following behavioral testing, the animals were anesthetized with sodium pentobarbital for acute recording. Nicotine was locally applied to electrophysiologically identified CA1 pyramidal neurons using pressure microejection from two-barreled glass microelectrodes. For each neuron, a dose of nicotine was found which elicited a 300-400% increase in basal firing rate. These data were used to construct cumulative dose response curves for populations of neurons tested in 3-6-, 18-21-, and 27-30-month-old animals. An age-related increase in the responsiveness of CA1 pyramidal neurons to locally applied nicotine was observed. The results of this study suggest that an increase in hippocampal CA1 pyramidal cell responsiveness to nicotine could be related to the impaired place learning ability seen with aging.

A clinical pharmacological study of subcutaneous nicotine

The stable isotope-labeled compound 3',-3'-dideuteronicotine (nicotine-d2) was used to investigate the disposition kinetics and effects of nicotine administered subcutaneously to 6 smokers. Plasma nicotine-d2 concentrations were measured for 8 h after subcutaneous injection of 4 doses (0.4, 0.8, 1.2, and 2.4 mg). Peak plasma nicotine concentration correlated well with the dose, averaging 2.8 to 14.8 ng/ml, 19 to 25 min after injection of the 0.4 mg and 2.4 mg doses, respectively. The plasma clearance over bioavailability ratio (CL/f) averaged 12 to 13 ml.min-1.kg-1, similar to the clearance reported previously for intravenously administered nicotine. Thus, bioavailability appears to be approximately 100%. The heart rate response was more sensitive to the nicotine dose than the blood pressure response. Subjective effects showed large interindividual variability. The results reported herein may be useful in planning future studies. Administration of nicotine by the subcutaneous route appears to be a practical and safe method for studying the human pharmacology of nicotine.

Further analysis of the cognitive effects of tetrahydroaminoacridine (THA) in Alzheimer's disease: assessment of attentional and mnemonic function using CANTAB

Results of a placebo controlled cross-over trial (N = 89) of the anticholinesterase drug THA as a treatment for dementia of the Alzheimer's type (DAT) are reported, with reference to previous trials of the drug and the cholinergic hypothesis of aging and dementia. Using computerised tests sensitive to specific aspects of memory and attention, evidence is found for improvements in attentional function rather than memory, in patients with mild to moderate DAT. Although these improvements were significant, they were small and restricted to certain tests of attentional function. Nevertheless, they add to the growing body of evidence that the cholinergic system is involved in the control of attentional processes. The results will be relevant to future investigations into the therapeutic effects of enhancement of the cholinergic system in DAT sufferers.

Chronic treatments with cholinoceptor drugs influence spatial learning in rats

Nicotine, scopolamine, oxotremorine, diisopropyl-fluorophosphate (DFP) and tetrahydroaminoacridine (THA) were administered chronically to different groups of rats in doses reported to alter central muscarinic and/or nicotinic receptor numbers. Beginning 24 h after final drug injection, the groups were compared to a vehicle control group on acquisition of a hidden platform position in the Morris water maze over 20 trials with a 30-min inter-trial interval. Chronic treatment with either nicotine or scopolamine significantly improved the rate of learning, but oxotremorine and DFP retarded learning and THA had no effect on learning. The chronic drug effects on behaviour were consistent with known effects of the injected drugs on muscarinic and nicotinic binding in the forebrain and on the sensitivity of frontal cortex neurones to iontophoretically applied cholinoceptor agonists. However, alternative explanations for the observed changes cannot be ruled out, since the drugs used are known to have a wide range of effects on other neurotransmitters.

Caffeine and nicotine improve visual tracking by rats: a comparison with amphetamine, cocaine and apomorphine

Psychomotor stimulant drugs such as caffeine, nicotine, amphetamine and cocaine, have been shown to improve vigilance in man under conditions of fatigue. Nicotine has also been shown to improve performance in some cognitive tests in patients with Alzheimer's disease. In rodents these drugs increase activity which may confound "performance enhancing effects" in rodent models. However, improvements have been found in a number of tests that do not seem to be directly dependent upon an enhancement of locomotor activation. In one example, Evenden and Robbins (1985) reported consistent improvements in a visual tracking test following amphetamine. The present study was undertaken to determine whether these performance enhancing effects of amphetamine could also be obtained with cocaine and apomorphine, which both have psychomotor stimulant effects through their actions as, respectively, indirect and direct dopamine agonists, and by caffeine and nicotine, which do not have a direct dopaminergic mechanism of action. The results of the study indicate that all five drugs improved tracking performance at one or more doses. The most consistent effects were obtained with amphetamine which, like cocaine and nicotine, improved tracking at a dose which did not produce other changes in behaviour. Taking into account previous studies (Evenden and Robbins 1983, 1985), these results were interpreted as indicating that psychomotor stimulant drugs produce a general activation of behaviour. At all but the highest doses of such drugs, the form of behaviour that is observed depends upon the environment.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulant drugs and vigilance performance: a review

The literature on the effects of some stimulant drugs (amphetamine, methylphenidate, caffeine, and nicotine) on vigilance performance is reviewed. Improvement of overall level of performance (both accuracy and speed) after the intake of amphetamine, caffeine, and nicotine has often been reported, and the decrement in performance with time has been shown to be prevented especially with amphetamine and nicotine. Effects on false alarms are negligible. In studies where a test battery was employed, vigilance tasks appeared to be the most sensitive performance tests in detecting the effects of stimulants; however, different vigilance tasks may measure different aspects of mental functions. There is no support for earlier conclusions that improvements are noticed only in fatigued subjects in protracted sessions. Evidence from several studies does not support the hypothesis that improvements are only a recovery of withdrawal-induced impairment. Because positive effects have been obtained with drugs possessing different mechanisms of action, there is as yet no clear support for a noradrenergic, dopaminergic, or cholinergic theory of sustained attention. Simple neurotransmitter theories of attention and information processing may be untenable.