Characterization of the cognitive effects of combined muscarinic and nicotinic blockade

Choice accuracy performance in the radial-arm maze is dependent upon the integrity of both the nicotinic and muscarinic cholinergic receptors. Pharmacological blockade of either of these subtypes of cholinergic receptors with mecamylamine or scopolamine impairs choice accuracy in the radial-arm maze. We have previously demonstrated that the performance deficit caused by muscarinic blockade is exacerbated in at least an additive fashion by coadministration of the nicotinic antagonist, mecamylamine. In the present study, it was found that mecamylamine and scopolamine act together in a greater than additive fashion in disrupting radial-arm maze choice accuracy. When doses of these drugs which do not by themselves cause significant impairments in choice accuracy are given together, they induce a pronounced impairment. Previous results have shown that the adverse effects of nicotinic blockade could be reversed by the dopaminergic D2 agonist LY 171555. In this study, this drug was found to attenuate the cognitive impairment caused by combined nicotinic and muscarinic blockade. On the other hand, the dopaminergic D1 antagonist SCH 23390 which has previously been shown to reverse the adverse effects of muscarinic blockade was not found in this study to attenuate the impairment of combined nicotinic and muscarinic blockade. Since combined nicotinic and muscarinic blockade approximates generalized cholinergic underactivation, treatments like LY 171555, which attenuate the adverse effects of this combined blockade, may be useful in treating syndromes like Alzheimer's disease, which are characterized by generalized cholinergic loss.     

Effects of combined muscarinic and nicotinic blockade on choice accuracy in the radial-arm maze

Acetylcholine (ACh) systems have been found to be crucial for the maintenance of accurate cognitive performance. A great variety of studies have shown that the muscarinic ACh receptor blocker scopolamine impairs choice accuracy in the radial-arm maze. Recently, it has been found that the nicotinic ACh receptor blocker mecamylamine also impairs radial-arm maze choice accuracy. In the present study, we investigated the effects of combined administration of these two ACh blockers. Scopolamine (0.15 mg/kg) and mecamylamine (10 mg/kg) each moderately impaired choice accuracy. Combined treatment with scopolamine and mecamylamine significantly decreased choice accuracy relative to either drug alone. This combination treatment lowered choice accuracy to chance levels. These data show that nicotinic and muscarinic blockade have at least additive effects in producing an anterograde memory deficit. Concurrent blockade of these two components of ACh systems may provide a better animal model of cognitive impairments due to the loss of cholinergic neurons, such as Alzheimer's disease.     

Scopolamine interactions with D1 and D2 antagonists on radial-arm maze performance in rats

Recent evidence indicates that acetylcholine and dopamine play complementary roles in cognitive as well as motor functions. In our previous study, the dopamine receptor blocker, haloperidol, was found to attenuate the radial-arm maze choice accuracy deficit caused by the muscarinic acetylcholine receptor blocker, scopolamine. Haloperidol has activity in blocking both D1 and D2 dopamine receptor subtypes. The current study was conducted to determine whether this dopamine-acetylcholine interaction specifically involved D1 or D2 dopamine receptors. The D1 antagonist, SCH 23390, and the D2 antagonist, raclopride, were administered with a dose of scopolamine which caused choice accuracy deficits in the radial-arm maze. The scopolamine-induced deficit was reversed by SCH 23390, the D1 antagonist, indicating that D1 blockade alone is sufficient to reverse the amnestic effects of muscarinic blockade. There was no indication in this study that the D2 blocker, raclopride, had a similar effect. However, this does not mean that such an effect may not be present at other doses of raclopride or with other D2 antagonists. The present finding that D1 blockade counteracts scopolamine-induced cognitive dysfunction not only furthers the understanding of dopamine-acetylcholine relationships in cognitive function, it also suggests a promising direction for the development of treatments for cognitive dysfunction due to cholinergic loss.     

Nicotinic-dopaminergic relationships and radial-arm maze performance in rats

Accurate performance on the radial-arm maze is dependent upon the integrity of nicotinic-cholinergic, muscarinic-cholinergic, and dopaminergic systems. Pharmacological blockade of these systems with mecamylamine, scopolamine, or haloperidol impairs choice accuracy in the maze. We have previously demonstrated that the performance deficit caused by muscarinic blockade is enhanced by coadministration of the nicotinic antagonist, mecamylamine, and is diminished by coadministration of the dopamine antagonist, haloperidol. In the present study, it was found that the choice accuracy deficit produced by nicotinic blockade is enhanced, not antagonized, by coadministration of haloperidol. Thus, although both nicotinic and muscarinic cholinergic systems are involved in radial-arm maze performance and antagonists of these receptors are additive in the deficits they cause, nicotinic and muscarinic interactions with dopaminergic systems are opposite in nature.     

Effects of the nicotinic receptor blocker mecamylamine on radial-arm maze performance in rats

Lesions of cholinergic neurons have been found by many investigators to impair choice accuracy in the radial arm maze. Because muscarinic receptor blockers, such as scopolamine, have also repeatedly been found to impair choice accuracy in the radial-arm maze, it has generally been thought that the critical effect of cholinergic lesions is the deafferentation of muscarinic receptors. The possible involvement of nicotinic receptors in the cholinergic bases of cognitive performance in the radial-arm maze has not been as well investigated. The present study examined the effects of the blockade of nicotinic receptors on performance of female Sprague-Dawley rats in the radial-arm maze. Acute administration of the the nicotinic receptor blocker, mecamylamine (10 mg/kg) was found to significantly impair radial-arm maze choice accuracy. This dose also caused a significant increase in response latency in the maze. The effect on choice behavior but not locomotor speed seemed to be due to the central effects of mecamylamine, because administration of the peripheral nicotine receptor blocker, hexamethonium (20 mg/kg), did not impair choice accuracy, even though it did increase response latency to a similar degree as the 10-mg/kg dose of mecamylamine. Lower doses of mecamylamine (2.5 and 5 mg/kg) did not impair choice accuracy. These results indicate that central nicotinic as well as muscarinic cholinergic receptors are involved with cognitive functioning.     

Cholinergic-dopaminergic interactions in radial-arm maze performance

Although acetylcholine and dopamine are believed to play complementary roles in motor function, a comparable neurochemical interaction has not been established for cognitive function. The muscarinic receptor blocker scopolamine and the dopaminergic antagonist haloperidol have been found to impair choice accuracy of rats in the radial-arm maze. In the present study, low doses of these two drugs were administered intraperitoneally either alone or in combination to rats trained on a working memory task (food reward) in an eight-arm radial maze. Scopolamine, 0.125 mg/kg, produced a significant decrease in choice accuracy (i.e., arm entries until an error). Haloperidol, 0.0625 mg/kg, did not cause a significant decrease in accuracy, but there was a trend in that direction. The combination of haloperidol with scopolamine attenuated significantly the amnestic effect of scopolamine. These results suggest that, like motor behavior, cognitive function may be influenced by the balance between acetylcholine and dopamine.     

Strain-dependent effects of post-training dopamine receptor agonists and antagonists on memory storage in mice.

Post-training administration of the selective D1 or D2 agonists SKF 38393 and LY 171555 dose dependently impairs retention of an inhibitory avoidance response in DBA/2 mice. In agreement, the selective D1 or D2 antagonists SCH 23390 and (-)-sulpiride improve retention. These effects are opposite to those observed in the C57BL/6 strain, as previously reported. Moreover, B6D2F1 hybrids present a response to SKF 38393, LY 171555, SCH 23390, and (-)-sulpiride that parallels that of the C57BL/6 strain, thus suggesting that the neural mechanisms underlying the effects of DA agonists or antagonists on memory processes may be inherited through a dominant mode of inheritance.     

Pharmacological evidence for a role of D2 dopamine receptors in the defensive behavior of the mouse

In this study the role of the DA system in the expression of defensive behavior of the mouse was investigated. C57BL/6 mice subjected to three daily defeat experiences (24 h apart) exhibited an increase of defensive behaviors (upright and sideways postures and escape) as well as a decrease of activity and a decrease of social investigation compared with undefeated mice (controls) when confronted with nonaggressive Swiss mice 24 h after the last aggressive confrontation. The selective D2 DA receptor antagonist (-)-sulpiride administered before confrontation with nonaggressive opponents (fourth day) dramatically decreased defensive behaviors and produced an increase of social investigation. The selective D1 DA receptor antagonist SCH 23390 did not affect either defence or social investigation. In further experiments the behavioral effects of the selective D1 agonist SKF 38393 and of the selective D2 agonist LY171555 on naive C57BL/6 mice interacting with nonaggressive opponents of the same strain were assessed. SKF 38393 in doses up to 30 mg/kg did not produce any significant behavioral changes while LY171555 produced a clear-cut dose-dependent increase of defensive behavior as well as a decrease of social investigation and activity and an increase of immobility. The behavioral profile produced by the D2 agonist did not differ from that produced by defeat experiences. These results indicate that D2 receptors play a major role in the expression of defensive behavior in the mouse. The hypothesis that alteration in D2 receptor functioning may produce hyperdefensiveness possibly due to altered perceptive processes is discussed.     

Does a cognitive map guide choices in the radial-arm maze?

Fifteen rats performed in a standard radial-arm maze task (Experiment 1) and in a modified task with a set of forced choices and a 15-min retention interval prior to completion of the maze (Experiment 2). In addition to the standard measure of choice in the radial-arm maze, orientation toward arms was measured and considered to constitute go-no-go "microchoice" decisions. Rats investigated but rejected many arms. A model of choice was developed in which it was assumed that choice decisions about arms were made independently and that microchoices were not selectively guided toward baited arms. The model performed nearly as well as the rats. These results place important limitations on the theory that choice behavior in the radial-arm maze is guided by a cognitive map.     

Low-dose mecamylamine improves learning of rats in the radial-arm maze repeated acquisition procedure

The nicotinic antagonist mecamylamine has been widely shown to cause cognitive impairment. However, these effects are mainly seen with high doses. There have been scattered findings that low doses of mecamylamine can have the opposite effect. This may be due to opposite effects of low doses of mecamylamine. In the current study, an extensive dose-effect function of mecamylamine was characterized in the low-dose range. Adult female Sprague-Dawley rats were trained on a repeated acquisition procedure on an automated 8-arm radial maze. Three of the eight arms were designated as correct for any particular session. Five trials per session were run. The number of errors per trial to find the three correct arms was determined. The rats were trained on the repeated acquisition procedure for at least 18 sessions at which time they showed reliable learning each session. Then, the effect of low doses of mecamylamine between 0 and 1 mg/kg were assessed in a repeated measures counterbalanced design. This dose range of mecamylamine did not affect performance on the first trial when the rats were na?ve to the array to be learned. On trials 2-5 a significant (p<.025) quadratic dose-effect function was seen over this dose range. The most substantial effect was seen with 0.125 mg/kg of mecamylamine, which caused a significant (p<.05) improvement relative to the saline control condition. The effect diminished with increasing mecamylamine doses and with the 1 mg/kg dose choice accuracy was back to control levels. This study showed that low doses of mecamylamine can effectively improve learning. A U-shaped dose-effect curve was documented. This suggests possible low-dose nicotinic antagonist lines of treatment for cognitive impairment.     

Cholinergic modulation of the hippocampus during encoding and retrieval

The present experiments were aimed at determining whether acetylcholine (ACh) plays a role in encoding and retrieval of spatial information using a modified Hebb-Williams maze. In addition, the present experiments tested two computational models of hippocampal function during encoding and retrieval using a maze sensitive to hippocampal disruption. Thirty male, Long-Evans rats served as subjects. Chronic cannulae were implanted bilaterally into the CA3 (n=26) and CA1 (n=5) subregions of the hippocampus. Rats were tested using a modified Hebb-Williams maze. In the first experiment, rats were injected with either saline or scopolamine hydrobromide 10 min before testing for each day. The number of errors made per day per group was used as the measure of learning. Encoding was assessed by the average number of errors made on the first five trials of Day 1 compared to the last five trials of Day 1, whereas the average number of errors made on the first five trials of Day 2 compared to the last five trials of Day I was used to assess retrieval. No deficit was found for the saline group. The scopolamine group showed a deficit in encoding, but not retrieval. In the second experiment, rats were injected with either saline or physostigmine 10 min before testing each day. In contrast to the scopolamine groups, the physostigmine group showed a deficit in retrieval, but not encoding. To test whether the retrieval deficit was due to a disruption in storage or gaining access to the information two groups of rats received either saline on Day 1 and physostigmine on Day 2 or physostigmine on Day 1 and saline on Day 2. In addition, one group received physostigmine immediately after testing on Day 1. Data indicate that physostigmine causes a disruption of retrieval by means of a disruption in consolidation process. In conclusion, the cholinergic antagonist, scopolamine, disrupts encoding in both CA3 and CA1 subregions of the hippocampus. Furthermore, the cholinesterase inhibitor, physostigmine, boosts ACh action during a time when cholinergic levels need to decline for proper consolidation.     

Roles of dopamine D1 and D2 receptors in the acquisition and expression of fat-conditioned flavor preferences in rats

Sugars and fats elicit innate and learned flavor preferences with the latter mediated by flavor-flavor (orosensory) and flavor-nutrient (post-ingestive) processes. Systemic dopamine (DA) D1 (SCH23390: SCH) and D2 (raclopride: RAC), but not opioid antagonists blocked the acquisition and expression of flavor-flavor preferences conditioned by sugars. In addition, systemic D1, but not D2 or opioid antagonists blocked the acquisition of flavor-nutrient preferences conditioned by intragastric (IG) sugar infusions. Given that DA antagonists reduce fat intake, the present study examined whether systemic D1 or D2 antagonists altered the acquisition and/or expression of conditioned flavor preferences (CFP) produced by pairing one novel flavor (CS+, e.g., cherry) with a 3.5% corn oil (CO: fat) solution relative to another flavor (CS-, e.g., grape) paired with a 0.9% CO solution. In an expression study, food-restricted rats were trained to drink either flavored 3.5% or 0.9% CO solutions on alternate days. Subsequent two-bottle tests with the CS+ and CS- flavors mixed in 0.9% CO solutions occurred 0.5h after systemic administration of vehicle (VEH), SCH (50-800 nmol/kg) or RAC (50-800 nmol/kg). The rats displayed a robust CS+ preference following VEH treatment (87-88%) the expression of which was attenuated by treatment with moderate doses of RAC, and to a lesser degree, SCH. In an acquisition study, six groups of rats received VEH, SCH (25, 50, 200 nmol/kg) or RAC (50, 200 nmol/kg) 0.5 h prior to 1-bottle training trials with CS+ flavored 3.5% and CS- flavored 0.9% (CS-) CO solutions. A seventh Limited VEH group was trained with its training intakes limited to that of the SCH and RAC groups. Subsequent two-bottle tests were conducted with the CS+ and CS- flavors presented in 0.9% CO without injections. Significant and persistent CS+ preferences were observed in VEH (75-82%), Limited VEH (70-88%), SCH25 (75-84%), SCH50 (64-87%), SCH200 (78-91%) and RAC200 (74-91%) groups. In contrast, the group trained with RAC50 displayed a significant initial CS+ preference (76%) which declined over testing to 61%. These data indicate limited DA D1 and D2 receptor signaling involvement in the expression and acquisition of a fat-CFP relative to previous robust effects for sugar-CFP.     

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)     

Spontaneous and learned turning behaviour in food- or water-restricted hooded rats

Some laboratory studies have suggested that whereas food restriction in animals leads to response alternation (behavioural flexibility), water restriction induces perseverative, stereotyped responding. Hooded rats, restricted to 1 hour per day access to either food or water, were tested on a radial-arm maze (using a procedure that eliminates algorithmic response strategies), for alternation in a 3-arm maze (both when the maze was familar and unfamilar, and with or without differential reward) and a 2-choice maze in which some animals were taught to alternate direction of turn, and others to perseverate. Both groups performed the radial-arm maze task competently and spontaneously alternated at a high rate. In the learned task, food-restricted rats were slower than water-restricted to reverse a consistent direction of turn; in the alternation condition, water-restricted rats developed a temporary, but strong, directional bias when making their first choice each day. Water-restricted subjects took water more readily than food-restricted took food when initially introduced to the apparatuses, but there was no consistent difference in motivation in the two conditions. The results provide little support for the notion that distinct cognitive-motivational states or behavioural strategies are induced by food- and water-restriction.     

Effects of scopolamine on repeated acquisition of radial-arm maze performance by rats.

Rats repeatedly acquired the performance of selecting only the four baited arms in an automated eight-arm radial maze, with the arms containing food pellets randomly assigned prior to each session. During each 14-trial (trial: obtain all four pellets) daily session, the number of errors (selecting nonbaited arms or repeating arm selections) showed a within-session decline, and choice accuracy for the first four arm selections showed a positive acceleration across trials for all rats. An index-of-curvature statistic, calculated for total errors, was used to quantify both the within- and between-session improvement of performance. Scopolamine (0.03 to 0.3 mg/kg, ip), but not methylscopolamine (0.3 mg/kg), reduced the accuracy of the first four selections of each trial and increased total within-session errors for all rats. Session times also were increased by scopolamine. An examination of within-session accuracy showed only slight signs of improvement at the higher dosages of scopolamine. The results indicate that behavior in transition states maintained by reinforcement contingencies in the radial maze is similar to that maintained by extended chained schedules, despite the fact that some of the stimuli controlling behavior in the maze are absent at the moment behavior is emitted.     

Effects of anandamide and morphine combinations on memory consolidation in cd1 mice: involvement of dopaminergic mechanisms

In the present research the interaction between the endogenous ligand for the cannabinoid CB1 receptor anandamide (arachidonylethanolamide) and morphine in memory consolidation was investigated. Four sets of experiments were carried out with CD1 mice tested in a one-trial inhibitory avoidance task. The drugs were administered intraperitoneally after training of the animals in the apparatus. In the first set of experiments morphine (0.3 or 0.5, but not 0.15mg/kg) or anandamide (3 or 6 but not 1.5mg/kg) dose-dependently impaired memory consolidation. In the second set of experiments the administration of an otherwise ineffective dose of anandamide (1.5mg/kg) enhanced the memory impairment exerted by morphine (0.3 and 0.5mg/kg) when the drugs were injected immediately after training. In the third set of experiments the combined treatments of anandamide (1.5mg/kg) and morphine (0.5mg/kg) 2h after training were ineffective showing that the effects observed on performance following immediate posttraining administration of anandamide and morphine combinations were reflecting direct influences on memory consolidation. In the fourth set of experiments otherwise ineffective doses of the D1 DA receptor agonist SKF 38393 or the D2 DA receptor agonist LY 171555 antagonized the memory impairment produced by anandamide and morphine in combination, suggesting a possible involvement of dopaminergic mechanisms.     

Spatial learning in the 5-HT1B receptor knockout mouse: selective facilitation/impairment depending on the cognitive demand

Age-related memory decline is associated with a combined dysfunction of the cholinergic and serotonergic systems in the hippocampus and frontal cortex, in particular. The 5-HT1B receptor occupies strategic cellular and subcellular locations in these structures, where it plays a role in the modulation of ACh release. In an attempt to characterize the contribution of this receptor to memory functions, 5-HT1B receptor knockout (KO) mice were submitted to various behavioral paradigms carried out in the same experimental context (water maze), which were aimed at exposing mice to various levels of memory demand. 5-HT1BKO mice exhibited a facilitation in the acquisition of a hippocampal-dependent spatial reference memory task in the Morris water maze. This facilitation was selective of task difficulty, showing thus that the genetic inactivation of the 5-HT1B receptor is associated with facilitation when the complexity of the task is increased, and reveals a protective effect on age-related hippocampal-dependent memory decline. Young-adult and aged KO and wild-type (WT) mice were equally able to learn a delayed spatial matching-to-sample working memory task in a radial-arm water maze with short (0 or 5 min) delays. However, 5-HT1BKO mice, only, exhibited a selective memory impairment at intermediate and long (15, 30, and 60 min) delays. Treatment by scopolamine induced the same pattern of performance in wild type as did the mutation for short (5 min, no impairment) and long (60 min, impairment) delays. Taken together, these studies revealed a beneficial effect of the mutation on the acquisition of a spatial reference memory task, but a deleterious effect on a working memory task for long delays. This 5-HT1BKO mouse story highlights the problem of the potential existence of "global memory enhancers."     

Fetal Alcohol-Exposed Rats Exhibit Differential Response to Cholinergic Drugs on a Delay-Dependent Memory Task

Fetal alcohol exposure in human and rodents produces a number of cognitive deficits including impairments in learning and memory. Recent evidence in our laboratory has shown that fetal alcohol-exposed (FAE) rats respond differently to systemic administration of cholinergic drugs when tested for vigilance and locomotor activity. The present study examined the effects of muscarinic and nicotinic agonists and antagonists on memory performance in a delayed alternation task. Subjects were male offspring of Sprague-Dawley rats fed a 35% ethanol-derived caloric diet, pair-fed with sucrose, or chow-fed with lab chow during the last 2 weeks of gestation. Rats (3 months old) were food-deprived prior to training in the T-maze. Rats were first trained in the alternation task at no delay for five sessions. Rats were then trained at longer delays (20, 60, 180 s) until all groups showed similar performance for two consecutive sessions. Each animal was then tested following systemic injections of the cholinergic antagonists scopolamine and mecamylamine (60-s delay) and the cholinergic agonists pilocarpine and nicotine (180-s delay). Rats received saline injections on alternate days of testing. The results revealed that FAE rats exhibited no impairments in alternation performance at the no delay and 20-s delay, but showed impairments on both the 60- and 180-s delays during the initial sessions. However, with additional training, FAE rats showed performance similar to that of control groups at these delays. Following both pilocarpine and nicotine injections, control groups, but not the FAE group, showed significant memory enhancement in the alternation task. Following scopolamine injections, the FAE rats showed a significant impairment, while control groups showed a nonsignificant decrease in performance. All three groups showed impairments in the alternation task following administration of mecamylamine compared to saline treatment. These findings suggest that alterations in the cholinergic system in FAE rats may underlie some of the cognitive deficits observed with prenatal alcohol exposure.     

Exposure to Spatial Cues Facilitates Visual Discrimination but Not Spatial Guidance

The performance in a radial-arm maze of two groups of rats with restricted access to extra-maze visual cues was studied. One group received extensive exposure to the visual environment of the maze, whereas the second group was never exposed to the environment, aside from their experience in the maze itself. Spatial exposure resulted in a slightly improved ability to discriminate between previously visited and unvisited spatial locations, which can be explained on the basis of general perceptual learning processes. However, there was no evidence that spatial exposure resulted in control of choices by the spatial relations among the maze locations. These results are discussed in terms of theories of spatial learning which appeal to perceptual learning and cognitive mapping.     

Participation of hippocampal cholinergic system in memory persistence for inhibitory avoidance in rats

Memory persistence needs a new event of consolidation 12h after the acquisition. We investigated the role of the cholinergic activity on the persistence of memory. For this purpose, we performed the treatments 9 or 12h after acquisition and the memory tested 2 or 7 days after inhibitory avoidance (IA) training. Here we report that activity of medial septum, by transitorily inactivating this structure with lidocaine 12h after IA training, is essential for memory persistence at the 7th day, but not for the formation at the 2nd day. We also report that muscarinic and nicotinic cholinergic receptors of CA1 area are engaged on memory persistence. Since scopolamine (mAChRs antagonist) and mecamylamine (nAChRs blocker) infusions, 12h post-training, demonstrated impairment on long term memory (LTM), persistence on the 7th day but no effect on LTM formation was found on the 2nd day in the IA test. The same effects were found with pirenzepine, an M1 antagonist. No effects on the formation and persistence of memory on the 2nd and 7th days were demonstrated after DHβE infusions (nAChRs subtype antagonist α4β2, α3β2). These findings suggest that mAChR and nAChR at the CA1 area, and also MS activation, are required for the persistence of memory.