Differential improvement in memory-related task performance with nicotine by aged male and female rhesus monkeys.

Central nicotinc acetylcholine receptors have been targeted for the development of novel treatments for memory deficits in Alzheimer's disease (AD) and other neurodegenerative disorders. Nicotine itself has been shown to improve memory-related task performance in aged animals and in AD patients. Administration of nicotinic receptor agonists to laboratory animals, and the effects of cigarette smoking in humans attributed to nicotine, have in many instances been shown to exert sexually dimorphic actions. Low doses (2.5-20 microg/kg, intramuscularly) of nicotine have been shown to improve the performance of an automated delayed matching-to-sample (DMTS) task in aged rhesus monkeys. The purpose of this study was to determine whether aged females receive the same level of benefit to the positive mnemonic action of nicotine as do males. In this study six male (21.7+/-1.2 years) and seven female (22.5+/-0.9 years) rhesus monkeys each received an ascending series of four doses of nicotine over 5 weeks. Most control parameters were similar between the two sexes, although task latencies were longer and more variable in the female subjects. The males maintained a significant improvement in task performance over the entire nicotine dose range. This level of improvement extended to 24 h after nicotine administration. Task accuracy by females appeared to improve only after they received the two higher doses of nicotine, and their responses exhibited considerable variability over the entire dose range. However, in calculating an individualized 'Best Dose', males and females exhibited a similar level of task improvement (15-30% above baseline). Therefore, aged female subjects may require a greater level of individualized treatment and perhaps higher doses of nicotinic agonists to achieve the maximal mnemonic benefit.

Central nicotinic receptor agonists ABT-418, ABT-089, and (-)-nicotine reduce distractibility in adult monkeys.

Increased distractibility is associated with both Alzheimer's disease and attention deficit disorder. The present study examined the effects of (-)-nicotine and the novel central nicotinic receptor (nAChR) agonists ABT-418 [(S)-3-methyl-2-pyrrolidinyl)isoxazole] and ABT-089 [2-methyl-3-(2-(S)-pyrrolindinylmethoxy)pyridine dihydrochloride] on the delayed recall accuracy of adult monkeys exposed to distracting stimuli. Unpredictable exposure to a random visual array produced marked decrements in recall accuracy on trials with the shortest delay intervals, reducing the accuracy on these trials by 23.4%. Intramuscular (i.m.) administration of (-)-nicotine, in doses of 5.4-43.3 nmol/kg, attenuated the effect of the distractor, but did not completely prevent it. Both ABT-418 (2.0-16.2 nmol/kg, i.m.) and ABT-089 (16.4-32.8 nmol/kg, i.m.) prevented distractibility, producing increases of 7.5-25.0% in accuracy on trials disrupted by distractor exposure. Further, both compounds also improved accuracy on trials during which distractors were not presented, an effect which was not observed after (-)-nicotine administration. Nicotinic-mediated side effects were not observed following administration of any compound. Thus, nAChR stimulation reduces distractibility in adult monkeys and may, therefore, represent a target for the pharmacologic treatment of disorders associated with susceptibility to distraction. ABT-418 and ABT-089 appear to be particularly useful in this regard, a likely result of their selective agonist activity at nAChRs expressed in the brain.

ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine dihydrochloride]: II. A novel cholinergic channel modulator with effects on cognitive performance in rats and monkeys.

ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine dihydrochloride], a novel ligand at neuronal nicotinic acetylcholine receptors with reduced adverse effects and improved oral bioavailability relative to (-)-nicotine, was tested in a variety of cognitive tests in rats and monkeys. Administered acutely, ABT-089 only marginally improved the spatial discrimination water maze performance of septal-lesioned rats. However, more robust improvement (45% error reduction on the last training day) was observed when ABT-089 was administered continuously via subcutaneous osmotic pumps (minimum effective dose: 1.3 micromol/kg/day). Continuous infusion of (-)-nicotine produced comparable improvement in the spatial discrimination water maze performance of septal-lesioned rats, but a 40-fold higher dose of (-)-nicotine was required (62 micromol/kg/day). Continuous infusion of ABT-089 to aged rats enhanced spatial learning in a standard Morris water maze, as indexed by spatial bias exhibited during a probe trial conducted after 4 days of training, but not when they were subsequently trained in a two-platform spatial discrimination water maze. The compound induced a small impairment in young rats on the standard water maze, but not on the two-platform task. A probe trial conducted after additional training in the standard water maze revealed no age or drug effects. ABT-089 did not affect performance of either the aged or young rats during inhibitory (passive) avoidance training. Also, continuous infusion of ABT-089 did not affect responses to acoustic startle or prepulse inhibition of acoustic startle in young, aged or septal-lesioned rats and did not affect locomotor activity in either sham-lesioned or septal-lesioned rats. In monkeys, acute administration of ABT-089 modestly improved the delayed matching-to-sample performance of mature, adult monkeys and more robustly improved performance in aged monkeys. Improved performance in the aged monkeys was restricted to the longest delay intervals and was not accompanied by changes in response latencies.

Effects of stimulation or blockade of central nicotinic-cholinergic receptors on performance of a novel version of the rat stimulus discrimination task.

This study evaluated the effects of two central nicotinic-cholinergic receptor agonists and an antagonist on performance accuracy of a rat, delayed stimulus discrimination task (DSDT). Rats were trained to discriminate between an auditory and visual stimulus by pressing a right or left lever. To diminish the rat's ability to use mediating spatial strategies to solve the task, computer automated, retractable doors separated the animal from the levers during delay intervals, thus reducing positioning at the lever. After stable baselines were achieved, rats were grouped and administered placebo (saline) and nicotine, lobeline or mecamylamine in a randomized dose series. Each group received two complete series of the selected compound on different occasions. Mecamylamine impaired DSDT accuracy in a dose-dependent manner while optimal doses of nicotine and lobeline significantly improved accuracy. Nicotine differed from lobeline in regard to its interaction with a dose of mecamylamine (1.0 mg/kg) that had not impaired DSDT accuracy. Combined administration of lobeline and mecamylamine was followed by a significantly increased level of DSDT accuracy that was similar to the improvement following administration of lobeline alone. In contrast, combined administration of nicotine and mecamylamine did not result in increased DSDT accuracy. Furthermore, lobeline administration similarly improved accuracy of trials associated with both the light and the tone, while nicotine improved accuracy of trials associated with the light to a much greater degree. These data suggest that the increases in DSDT accuracy associated with lobeline may be expressed through non-nicotinic mechanisms or a nicotinic receptor which is not blocked by mecamylamine.

Improvement in performance of a delayed matching-to-sample task by monkeys following ABT-418: a novel cholinergic channel activator for memory enhancement.

ABT-418, a newly characterized centrally acting cholinergic channel activator (ChCA), was evaluated for its ability to improve performance in a delayed matching-to-sample (DMTS) task by mature macaques well trained in the task. Previous studies in rodents have indicated that ABT-418 shares the memory/cognitive enhancing actions of nicotine, but without many of nicotine's dose-limiting side effects. As DMTS provides a measure both of general cognitive function (the matching concept) and of recent memory, it was hypothesized that some doses of ABT-418 would enhance the monkeys' ability to correctly perform the DMTS task. Intramuscular administration of ABT-418 significantly enhanced DMTS performance at low (2-32.4 nmol/kg) doses. In fact, the drug was slightly more potent that nicotine in this regard, and all eight animals tested in this study exhibited enhanced performance at one or more doses. ABT-418 produced the greatest improvement in DMTS performance at the longest delay interval. In animals repeatedly tested with their individualized "Best Dose", DMTS performance increased on average by 10.1 +/- 3.5 percentage points correct, which was equivalent to an increase of 16.2% over baseline performance. ABT-418 did not significantly affect response times, i.e., latencies to make a choice between stimuli, or latencies to initiate new trials. Whereas nicotine enhanced DMTS performance both on the day of administration and on the following day (in the absence of drug), ABT-418-induced enhanced performance was detected only on the day of administration. Finally, single daily administration of the individualized best dose in three monkeys over a period of 8 days generally maintained enhancement of DMTS performance. Thus, the data were not consistent with the development of significant tolerance to the drug's mnemonic actions. In contrast to nicotine, no overt toxicity or side effects to acute or repeated administration of the drug were noted. Thus, ABT-418 represents a prototype of a new class of nicotinic agonists designed for the potential treatment of human dementias having a low profile of toxicity.

Electrical studies as a prognostic factor in the surgical treatment of carpal tunnel syndrome.

We attempted to determine if a prognostic value could be associated with preoperative electrodiagnostic testing in patients with carpal tunnel syndrome. Three groups of patients were included in the study of 151 workers whose symptoms were thought to be causally related to their jobs. A clinical diagnosis was made without electrical testing in 26 of the 151 patients. Normal electrical test values were present in 50 of the 125 patients tested, and abnormal values were noted in 75 patients. Pinch, power, and static grasp function were recorded monthly. Similar recovery patterns after operation were seen between the groups and within each group. Return to work time correlated well with measured functional recovery to preoperative levels, but some workers returned to their jobs before they had regained full function. Electrodiagnostic test results did not provide significant data for prediction of functional recovery or re-employment after carpal tunnel release.

Scopolamine reversal of nicotine enhanced delayed matching-to-sample performance in monkeys.

The basis for the memory enhancing action of nicotine was evaluated in five adult monkeys (Macaca fascicularis) well trained in the performance of a delayed matching-to-sample (DMTS) paradigm. Nicotine (1.25-20 micrograms/kg, IM) produced a dose-dependent improvement in performance of the task. The optimal dose of nicotine for each monkey also improved performance when the animals were tested 24 h later in the no-drug situation. In the same animals, low doses of scopolamine produced a dose-dependent decrement in DMTS performance. A subthreshold dose (defined by DMTS performance decrement) of scopolamine was administered 20 min prior to the optimal dose of nicotine. Scopolamine pretreatment completely blocked the enhanced performance observed earlier with nicotine. The results of this study are consistent with the hypothesis that the enhanced cognitive performance associated with nicotine is due to central acetylcholine release and subsequent muscarinic receptor stimulation.

Beneficial effects of nicotine administered prior to a delayed matching-to-sample task in young and aged monkeys.

Our earlier studies have demonstrated that administration of low micrograms/kg doses of nicotine to young adult monkeys prior to a delayed matching-to-sample (DMTS) task resulted in a centrally mediated improvement in performance of the task, particularly when delay intervals which most greatly challenged the animal's capabilities were involved. The present study confirmed these findings using a completely computer driven and automated procedure. In addition, performance on the DMTS was observed to be enhanced when animals were again tested 24 h after the dose of nicotine. Further analysis of the data indicated that the majority of enhancement to nicotine could be accounted for by a greatly increased performance at the least preferred stimulus color. Position preference (left vs. right stimulus) was not a factor in nicotine-induced enhancement. Two aged monkeys (34 years old Macaca mulatta) were significantly more difficult to train in the DMTS task and their longest delay capabilities were significantly shorter than the young animals (Macaca fascicularis). Nevertheless, the aged animals were essentially similar in most respects in their responses to nicotine administration. These data are consistent with a role for central nicotinic systems in memory performance and with the ability of nicotine to produce enhancement of selective features of mnemonic strategy in young and old monkeys. Furthermore, it is possible that either model, the aged animal, or the young animal stressed to his mnemonic capability may provide a good model for learning and memory disorders in humans.

Nicotine enhances delayed matching-to-sample performance by primates.

The non-human primate provides an excellent model for studies of learning and memory, and one particular test, the delayed matching-to-sample task, is performed in a similar manner by both humans and non-human primates. Five young adult macaques were employed in this study, displaying variable capacities for retention in the task. Baseline performance was very consistent and three levels of performance difficulties (95-100%, 80-85% and 65-75% correct choices) were employed by including several delay intervals (0-60 sec) in each session. A reproducible enhancement in performance by nicotine in macaques performing a delayed matching-to-sample task was demonstrated. Nicotine enhanced performance with an average increase of 10% at the longest retention delay interval. This beneficial effect of nicotine was abolished in animals pretreated with a low dose (0.5 mg/kg) of mecamylamine to block central nicotinic receptors. Selective blockade of peripheral nicotinic receptors with hexamethonium was without effect on the nicotine response. A high dose (2 mg/kg) of mecamylamine itself induced a marked inhibition of performance, while an equivalent dose of hexamethonium was without effect. These experiments point to the possibility that central nicotinic receptors may be exploited pharmacologically to enhance memory performance. In this respect it is interesting that nicotine was most effective at enhancing performance when recall was more difficult, that is, on the longer retention interval delays. This could signify that nicotine might be particularly effective in the most impaired individuals. Lastly, it is encouraging that the mecamylamine induced decrease in cognitive performance might provide a new model of memory impairment from which to study the pathogenesis and develop new pharmacological strategies for the dementias.

The structure of the mer operon.

The DNA sequence has been determined for a 3.8-kb region which encodes the mercury-resistance (mer) operon of the IncFII plasmid NR1. The sequence reveals 4 open reading frames which could encode proteins of 12,522, 9,429, 14,965, and 58,912 d corresponding to the 4 previously described Hg-inducible proteins detected in minicells carrying mer+ plasmids. The Hg(II) reductase protein sequence is about 90% homologous to that of Tn501, but the DNA sequence shows a homology of 60-70% to that of Tn501 except for short regions of very high homology. The entire mer region is 63.4% G-C overall. The region encoding the merR (positive regulatory) function has 3 possible open reading frames, 2 of which overlap in one direction and the third of which reads in the opposite direction. Attempts to visualize the polypeptide(s) encoded by the merR cistron were unsuccessful.

Biochemical characterization of HgCl2-inducible polypeptides encoded by the mer operon of plasmid R100.

Minicells carrying the subcloned mer operon from plasmid R100 were pulse-labeled with [35S]methionine, and the labeled polypeptides were analyzed at various subsequent times by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The Hg(II) reductase monomer encoded by plasmid R100 occurred as two proteins of 69 and 66 kilodaltons (kd). The minor 66-kd protein is a modified form of the 69-kd protein. This modification occurs in vivo. Both of these mer proteins are found in the soluble fraction of the cell; however, the 66-kd protein appears to have a slight affinity for the cellular envelope. Both the 69- and 66-kd mer proteins have pI values greater (pI = 5.8) than that reported (pI = 5.3) for the analogous monomer encoded by plasmid R831. The 15.1- and 14-kd mer proteins are localized in the inner membrane and are probably elements of the mer-determined Hg(II) uptake system. These two mer membrane proteins, which are antigenically unrelated to the Hg(II) reductase monomer, are quite basic (pI values greater than 7.8). The 12-kd mer protein is also a basic polypeptide that is present in the soluble fraction of the cell. Unlike the two membrane-bound mer proteins, the 12-kd mer protein is processed from a 13-kd precursor.

Polypeptides encoded by the mer operon.

HgCl2-induced polypeptides synthesized by Escherichia coli minicells containing recombinant or natural HgR plasmids were labeled with [35S]methionine and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. All plasmids examined encoded two heavily labeled, HgCl2-inducible polypeptides of 69,000 and 12,000 daltons. Most plasmids also encoded two additional HgCl2-inducible proteins in the 14,000- to 17,000-dalton range. Antiserum prepared against a purified mercuric ion reductase reacts with the 69,000-dalton polypeptide and a minor 66,000-dalton protein seen in several different HgR minicells. Recombinant plasmids constructed from portions of mer DNA from the IncFII plasmid NR1 were also analyzed in the minicell system. Five HgCl2-inducible polypeptides (69,000, 66,000, 15,100, 14,000, and 12,000 daltons) were synthesized in minicells carrying pRR130, a recombinant derivative containing the EcoRI-H and EcoRI-I restriction fragments of NR1. The EcoRI-H fragment of NR1 encodes the three small mer proteins of 15,100, 14,000, and 12,000 daltons and the amino-terminal 40,000 daltons of the mercuric ion reductase monomer.