Effects of scopolamine on radial maze performance in rats

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.

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 scopolamine on performance of rats in a delayed-response radial maze task

The effects of the cholinergic blocker scopolamine on performance of rats in an 8-arm radial maze were studied. In Experiment 1, rats received injections of scopolamine-HBr (0.2 mg/kg, IP) or saline, 20 min before a trial. The drug impaired performance only when midtrial delays were introduced (10 sec, 5, 20, 60 or 120 min), during which the animals were removed from the apparatus, and to a similar extent at all delays. Injection of scopolamine directly after choice 4 in a 20 min delayed trial affected performance at a dose of 0.4 mg/kg, but not at 0.2 mg/kg. In Experiment 2, the rats were kept in the apparatus during the delay. There was a significant effect of scopolamine at 0.1 and at 0.2 mg/kg, initially irrespective of the length of the delay (10 sec, 2.5 or 5 min). After considerable training, administration of scopolamine (0.2 mg/kg) had no significant effect at the 10 sec delay but did impair performance after longer (5 or 10 min) midtrial intervals. These results suggest that scopolamine has differential effects, depending on dose and degree of training, and that an effect on memory storage may be one of them.

Potential interactions between GABAb and cholinergic systems: baclofen augments scopolamine-induced performance deficits in the eight-arm radial maze

Sixteen male Fischer-344N rats were trained on a eight-arm radial maze task for food reinforcement. The effects of various doses of baclofen (1.25 or 2.50 mg/kg) and scopolamine (0.188, 0.375, and 0.750 mg/kg) were determined alone and in combination. Relative to vehicle controls, baclofen alone did not affect performance in the radial arm maze (number correct in the first eight responses, total errors) or the time required to complete the maze. Scopolamine alone decreased the number of correct responses in the first eight arm choices, while increasing both the number of errors and the time necessary to complete the maze. When the two drugs were co-administered, baclofen had no effect on the number of errors or time required to complete the maze in the presence of scopolamine; however, in combination with the high dose of scopolamine, it significantly increased the number of errors made during the first eight choices. Baclofen thus can exacerbate some radial arm maze dificits produced by an anticholinergic drug. In a subsequent experiment to test the interaction between scopolamine and baclofen using a nonlearned behavior, baclofen (1.25 and 2.5 mg/kg) did not affect motor activity, whereas all doses of scopolamine (0.188-0.75 mg/kg) increased activity. The higher dose of baclofen attenuated scopolamine-induced hypermotility by 50%, but the lower dose of baclofen was not effective. These data demonstrate pharmacological interactions between baclofen, a drug used clinically for spaticity, and a drug having anticholinergic properties.

An evaluation of the mechanism of scopolamine-induced impairment in two passive avoidance protocols

The effects of several doses of the centrally-acting muscarinic antagonist, scopolamine, on subsequent learning and memory were examined using two versions of a standard light versus dark passive avoidance paradigm. The first protocol was employed primarily to examine the effects of scopolamine on the acquisition component of learning and memory as subject performance was measured during five successive (repeated) training trials. The second protocol employed a one-trial twenty-four hour retention task in which subjects were given one training trial followed by one testing trial twenty-four hours later. This latter test encompasses acquisition, retention, and recall components of learning and memory. Dose response studies indicated an effective dose range of 0.4-1.2 mg/kg with 0.8 mg/kg producing maximal performance decrement. Differential scopolamine treatment demonstrated that the drug's primary effect was on the acquisition component only under the present experimental protocols. Furthermore, scopolamine was not found to produce state-dependent learning. Animals administered scopolamine before training and testing failed to perform better than animals receiving pre-training administration only.

Effects of selection delays on radial maze performance: acquisition and effects of scopolamine

The effects of post-selection confinement (delays) on both the acquisition of performance and the response to the muscarinic blocker, scopolamine, were examined in an automated version of the eight arm radial maze. Long-Evans rats, exposed to post-selection delays of 0.5 sec (n = 4) or 100 sec (n = 4) during daily training trials did not differ in either the number of trials to acquire an accurate baseline of performance or in the amount of time required to obtain all eight food pellets. However, the pattern (delta-arm scores) of within-session arm selections demonstrated by the two groups of rats differed. Rats exposed to the 0.5-sec delay typically selected arms adjacent to arms from which they exited while rats exposed to the 100-sec delay were more likely to enter arms 2-removed from the exit arm. When scopolamine (0.03 to 1.0 mg/kg) was administered prior to testing, rats in the 100-sec delay group showed a greater reduction of accuracy and a larger increase in selection latency than rats in the 0.5-sec delay group. The differential effect of delay value on delta-arm scores was also eliminated in a dosage dependent manner with scopolamine. Scopolamine methylbromide (0.3 mg/kg) was found to have little effect on performance. In summary, the results indicate that the post-selection delay procedure is a sensitive and selective test for chemical-induced dysfunctioning of spatial memory in rats.

Differences in the acquisition process and the effect of scopolamine on radial maze performance in three strains of rats

The acquisition process and the effect of scopolamine (SCOP) on the radial maze task were studied in 3 strains of male rats, Fischer 344 (F344), Sprague-Dawley (SD) and Wistar. The pretraining level of locomotor activity was measured and performance was quantitatively and qualitatively evaluated. The highest pretraining locomotor activity was observed in Wistar rats. In this experiment, rats were allowed to select each arm successively. The changes in the number of correct choices during the first eight selections, error choice in a trial and the total duration of a trial differed with the strain in the first 5 training sessions. Acquisition curve for F344 rats gradually rose. Wistar rats made many error choices. However, during the final 5 sessions, only the total duration of a trial differed with the strain. Wistar rats took the shortest time to finish a trial, but the number of sessions taken to acquire this task was the fewest with F344 rats, and the most with Wistar rats. The effect of SCOP differed among strains in all the above 3 indexes. Generally, the Wistar rat was the most affected by the injection of SCOP. Moreover, the change of the choice accuracy and the spatial strategy by the administration of SCOP were investigated. SD and Wistar rats showed a dose-dependent decrease in choice accuracy in the earlier selection. The spatial strategy was changed in every strain by the injection of SCOP. These findings do not support the previous finding that a high level of locomotor activity yields fast acquisition of this task or that Wistar rats are better in learning than SD, but indicates that SCOP affects not only the working memory but also the motivational factor.

Chlordiazepoxide, an anxiolytic benzodiazepine, impairs place navigation in rats

There are separate proposals that the hippocampus is involved in 'spatial memory' and in the control of 'anxiety'. Despite a larger number of common effects of anxiolytic drugs and hippocampal lesions, no effect of anxiolytic drugs has yet been reported in those spatial tasks which are particularly sensitive to the effects of hippocampal lesions. The present study addresses this issue. Separate groups of rats were treated, i.p., with 5 mg/kg chlordiazepoxide (an anxiolytic benzodiazepine), 1 mg/kg scopolamine (a muscarinic antagonist which has previously been shown to impair spatial learning) and a saline placebo. They were then trained to find a platform which was hidden in a constant location just under the surface of opaque water in a swimming pool. Separate groups of rats were trained with 4 trials per day and with 1 trial per day. Number of trials per day did not significantly influence the effects of the drugs. Chlordiazepoxide and scopolamine produced similar degrees of impairment in spatial learning to each other--but less impairment than has previously been reported with hippocampal lesions. The effectiveness of the anxiolytic drug chlordiazepoxide in the swimming pool, a specifically spatial task, suggests that the opposing concepts of 'spatial memory' and 'anxiety' which have been used previously to describe hippocampal function may represent different aspects of a unitary concept.

Neurochemical and behavioral effects of N-ethyl-acetylcholine aziridinium chloride in mice

N-ethyl-choline aziridinium (ECA) and N-ethyl-acetylcholine aziridinium (EAA) were shown to be inhibitors of high affinity choline uptake in vitro (IC50 = 0.4 microM and 1.5 microM, respectively), and intraventricular administration showed that EAA was more selective in its inhibition of hippocampal choline uptake in vivo. EAA significantly reduced the activity of choline acetyltransferase in the hippocampus 3 to 28 days following intraventricular infusion, but not in the striatum or parahippocampal cortex. Neither muscarinic receptor binding nor glutamic acid decarboxylase activity were affected in any of the three brain regions. EAA (12 or 16 nanomoles, intraventricular) significantly impaired memory performance of mice in a radial arm maze when tested two weeks after treatment. A subgroup analysis implicated long-term reference memory as the mechanism disrupted.

Effects of age on antidepressant kinetics and memory in Fischer 344 rats

Experiments were conducted in young (3-4 months) and old (24-25 months) male Fischer 344 rats to assess the effects of amitriptyline, scopolamine, and zimelidine on short term memory using an eight arm radial maze paradigm. Kinetic analyses employing serial blood sampling were also conducted for amitriptyline and zimelidine in an attempt to determine if age-related deficits in performance could be related to changes in pharmacokinetics. In the maze, acquisition of performance was significantly decreased in old rats compared to young. Amitriptyline (5 mg/kg) produced a significant decrement in maze performance on day four of a five day testing period in both young and old rats, while scopolamine (1 mg/kg) produced an initial decrement on day one, followed by a return towards pre-treatment levels in these two age groups. Zimelidine (5 mg/kg) produced no performance decrement in either young or old rats. Kinetic analyses revealed an increased half-life, slower plasma clearance, and a larger volume of distribution of amitriptyline and zimelidine in old rats. Although the kinetic parameters in aged rats exhibited a change in the direction of a decreased ability to metabolize both drugs, this change was not of sufficient magnitude to produce an additive detrimental effect on maze performance.

The radial arm maze as a tool in behavioral pharmacology

This paper will review briefly the use of the radial arm maze as a tool to examine the neural systems that are involved in memory, and the influence of pharmacological compounds on memory. Of particular interest is the question of task validity, which is assessed by reference to four different criteria: operational, psychological, ethological, and neural (see also Walsh, this issue; [45, 53, 70, 75]). Each of these types of validity is reviewed below.

Scopolamine disrupts visual reversal without affecting the first discrimination

The effect of scopolamine (0.5 mg/kg) was determined in a brightness discrimination test (Y maze) motivated by electrical shocks (escape avoidance). Male adult Sprague Dawley rats were used. Results show that scopolamine impairs significantly the visual reversal without affecting the first brightness discrimination. The qualitative analysis reveals that the anticholinergic drug-induced deficit involves both perseveration, i.e. failure to suppress inappropriate response, and a tendency to adopt a position habit. A parallelism with hippocampal and frontal lobe damage symptoms is discussed and an interpretation in terms of disinhibition and incapacity to solve a more difficult problem is proposed.

Blockade of spatial learning by the M1 muscarinic antagonist pirenzepine

Two experiments were conducted to determine the effects of the M1 muscarinic receptor antagonist pirenzepine on place navigation in a water maze. In the first experiment rats were required to learn the location of a hidden platform following intracerebroventricular injections of equimolar doses of pirenzepine or scopolamine methylbromide. Both drugs dose-dependently impaired spatial learning according to both escape latency data and transfer test analysis. Pirenzepine was approximately 3 times less potent than scopolamine, a potency ratio which suggests M1 receptor mediation of the impairment. In the second experiment pirenzepine (1 approximately 92.3 micrograms/rat ICV) was injected prior to training on a simultaneous place discrimination task in the water maze. Impairments of choice accuracy were found with a dose of 20 micrograms/rat in the absence of any marked increases in either errors of omission or choice latency. These data suggest that M1 receptor blockade impairs processes which are involved in spatial learning.

Cholinergic function and memory: extensive inhibition of choline acetyltransferase fails to impair radial maze performance in rats

The present study investigated the effects of a potent inhibitor of choline acetyltransferase (ChAT), BW813U, on the choice accuracy of rats in the radial arm maze. BW813U (100 mg/kg, IP) produced a rapid (within 1 hour) and substantial decrease in ChAT activity throughout the brain, ranging from 66% (hippocampus) to 80% (caudate nucleus) that lasted up to 5 days. A single injection (50 mg/kg, IP) into rats with lesions (using ibotenic acid) in the nucleus basalis magnocellularis and medial septal area, decreased ChAT activity by 75% and 60% in the cortex and hippocampus, respectively. Lesioned and unlesioned rats were trained on the radial arm maze until they reached a criterion level of performance. Each rat then received an injection of BW813U (50 or 100 mg/kg, IP). Choice accuracy was not impaired at any time following the injection. The lack of effect on performance may be due to 2 possible factors: The radial maze retention paradigm chosen may not be sufficiently difficult, or the decrease in acetylcholine production was not sufficient to affect behavior. Compensation by non-cholinergic neural systems might account for the insensitivity of the rats to significant cholinergic depletion.

Scopolamine impairs learning performance of rats in a 14-unit T-maze

To assess involvement of muscarinic cholinergic systems in performance of a shock-motivated 14-unit T-maze task, 3-month old Fischer-344 rats were given an IP injection of scopolamine (0.1, 0.3, 1.0 or 3.0 mg/kg), methylscopolamine (1.0 mg/kg), or saline 30 min prior to maze training on 2 consecutive days. Scopolamine, but not methylscopolamine, impaired all components of acquisition performance. Measures of error performance, run time, shock duration, and number of shocks received were significantly increased but only at the 1.0 and 3.0 mg/kg scopolamine doses. The cognitive component of the task, measured by error performance, appeared most affected. Cognitive performance deficits observed following scopolamine administration in the present study resembled age-related impairments in rats and mice previously observed in this task. The cholinergic hypothesis of geriatric memory dysfunction appears to be implicated by these findings; however, the degree to which memory systems are involved remains unclear. Other performance variables such as discriminative control of stimuli or mechanisms of attention are implicated and discussed.

Effects of phencyclidine, N-allyl-N-normetazocine (SKF-10,047), and verapamil on performance in a radial maze

Two groups of eight rats were trained to obtain food pellets in an 8-arm radial maze. Stable performance was assumed to be present when a criterion of 89% efficiency, i.e., all arms entered within 9 arm entries, was reached in 5 consecutive sessions. The effects of phencyclidine (PCP) and N-allyl-N-normetazocine (SKF-10,047) were then evaluated in Group 1. The interaction between verapamil and PCP was examined in Group II. Both PCP (6 mg/kg, IP, 15 min before testing) and SKF-10,047 (30 mg/kg, IP, 30 min) decreased efficiency but only PCP caused a concurrent increase in rate of arm entry. Significant effects of PCP on rate and efficiency lasted for greater than 6 hours and less than 40 minutes, respectively. Verapamil (20 mg/kg, IP, 30 minutes) was found to selectively potentiate the effect of PCP on efficiency. This finding does not support the suggestion that verapamil may be useful in the treatment of PCP intoxication. It is concluded that the radial maze may provide an interesting method for the study of PCP and other psychoactive drugs.

Interactions between response stereotypy and memory strategies on the eight-arm radial maze

Three groups of water-deprived rats collected water from the ends of the 8-arm radial maze. Sighted subjects, and subjects blinded either with or without pre-enucleation experience on the radial maze, all retrieved the water efficiently. Most of the subjects exhibited the same response stereotypy, regularly choosing 8 adjacent arms of the maze, then stopping in the center of the maze. The strategies underlying this performance were analysed by interrupting trials and rotating the maze 180 degrees after the subject had made 3 choices. Sighted subjects depended on extramaze stimuli, naive-blind subjects depended on intramaze stimuli and experienced-blind subjects ignored their initial 3 choices after the trial was interrupted. Choice accuracy was equally good whether the subject was returned to the position from which it had been removed, or returned to the opposite side of the central platform. All 3 groups of subjects maintained their stereotyped adjacent-arm responding only as long as such responding was consistent with high choice accuracy. Response stereotypy was prevalent on the radial maze, but response strategies were secondary to memory strategies.

Spatial and temporal response patterns on the eight-arm radial maze

Six maze-experienced hooded rats were timed during five trials on which they collected water from all arms of an eight-arm radial maze, then made five more choices. All subjects frequently exhibited a "task-completion pause:" The subjects rarely spent more than 1 sec in the center of the maze between choices until they had entered all eight arms, then stopped in the center of the maze. In contrast, the time spent in each arm gradually increased until all of the water had been obtained, then decreased slightly. Four subjects began every trial by choosing eight consecutive adjacent arms. The task-completion pause indicates that these subjects recognized when all of the arms had been entered, without having to repeat one. Therefore, even extreme degrees of response stereotypy do not imply a fundamental dependence on response strategies.

Scopolamine-induced deficits in acquisition of a complex spatial learning

The role of scopolamine was studied in a complex spatial orientation task. The procedure involved an increasing difficulty of the task: at the pretraining stage a cue (box) was placed at the reinforcement spot and the animal could give a correct response by adopting either a cue-strategy or an orientation response (i.e., go to the arm on the right of a visual landmark). In the subsequent spatial training, the box was removed, so that the orientation response was the only correct one. Results show that scopolamine-injected animals are able to use a cue-strategy but are unable to acquire a spatial orientation strategy: this more complex task asks for more time and for more sustained attention. When the response is already partly acquired, scopolamine has less effect. The cholinergic system would thus be involved in the quality or even the complexity of the response rather than in the retention itself. Though a state-dependent effect may not be excluded, it by itself cannot explain the observed differences. Finally, an impairment of the maintenance of attention could be responsible for the deficits observed in the acquisition of the complex task.

Is cholinergic activity of the caudate nucleus involved in memory?

A review was made of experiments dealing with the involvement of cholinergic activity of the caudate nucleus in memory processes. Injections of acetylcholine-receptor blockers or of neurotoxins against cholinergic interneurons into the striatum produce marked impairments in acquisition and retention of instrumental tasks while injections of acetylcholine or choline into the caudate produce the opposite effect. However, after a period of overtraining cholinergic blockade or interference with neural activity of the caudate does not produce significant deficits in retention. It is concluded that striatal cholinergic activity is critically involved in memory of recent events and that long-term memory is mediated by different neurochemical systems outside the caudate nucleus.

Spatial learning and memory, maze running strategies and cholinergic mechanisms in two inbred strains of mice

The acquisition process of the radial maze task was studied in two inbred strains of mice, C57BL/6 and DBA/2. A quantitative and qualitative evaluation of performance was performed and the pretest level of activity was measured. The results showed a significant correlation between activity and performance since the highly active C57BL/6 mice exhibited better performance of the radial maze task than the less active DBA/2 mice. Moreover, for correct trials, strain-dependent maze-running strategies were observed: while both strains displayed about the same percentage of clockwise and spatial strategies, it was observed that among the spatial strategies C57BL/6 used a larger number of different correct solutions. Subsequently, the effect of scopolamine administration on working memory processes was assessed in sequential and discrete trials. A different reactivity of each strain to anti-cholinergic treatment was found in discrete trials since only DBA/2 mice were impaired. The effect of scopolamine is discussed in relation to the different models of information processing involved in learning and memorizing the experimental rule.

Early phenobarbital-induced alterations in hippocampal acetylcholinesterase activity and behavior

Early exposure to phenobarbital (PhB) causes marked destruction of large neurons which are then forming both in the hippocampus and in the cerebellum. Such exposure to PhB also reduces the achievements of mice in hippocampus-related behaviors such as radial 8-arm maze performance. Experimental evidence suggests that these behaviors are partially mediated by cholinergic transmission. We studied the performance of mice, exposed to PhB prenatally or neonatally, in radial 8-arm maze. Both treatments caused significant impairments in the animals' performance in the maze. Acetylcholinesterase (AChE) and pseudocholinesterase (pChE) activities were studied in the hippocampus and cerebellum of mice who were exposed to PhB prenatally or neonatally. These enzymes are involved both in cholinergic transmission and in neuronal development. A significant decrease (13-16%, P less than 0.01) in hippocampal AChE specific activity was found between days 15 and 22 in animals exposed to PhB neonatally. The total hippocampal activity of AChE was also greatly reduced (25-39%, P less than 0.01) during that period as a result of both the reduction in specific activity and a reduction in hippocampal weight of the treated animals. These alterations were transient and were not detected in adulthood. No changes in hippocampal AChE or pChE activities were found in animals treated prenatally. Cerebellar AChE and pChE activities were not altered after prenatal nor after neonatal exposure to PhB. It is possible that the short-term effect of neonatal treatment on AChE specific activity might mediate the long-term impairments in hippocampus-related behaviors.

Facilitation of spontaneous and learned spatial behaviours following 6-hydroxydopamine lesions of the lateral septum: a cholinergic hypothesis

Mice received injections of 6-hydroxydopamine (6-OHDA) in the lateral septum; they were tested for spontaneous alternation, acquisition and reversal of a spatial discrimination in a T-maze. In each of these tasks, performance of 6-OHDA lesioned mice was improved relative to controls. Neurochemical analysis revealed that 6-OHDA lesioned mice exhibited a significant increase in the rate of sodium-dependent high affinity choline uptake in the hippocampus. These results are discussed in relation to current theories concerning the role of the septo-hippocampal complex and cholinergic system in the control of behaviour.

Scopolamine degrades spatial working memory but spares spatial reference memory: dissimilarity of anticholinergic effect and restriction of distal visual cues

The influence of the centrally active anticholinergic, scopolamine hydrobromide, on working and reference memory was studied in rats tested in a 12-arm radial maze. Both 0.25 and 0.5 mg/kg doses of the drug increased the number of working memory (WM) errors but had no effect on reference memory (RM) errors. A lower dose (0.125 mg/kg) was ineffective, as was the peripherally active anticholinergic, scopolamine methylbromide (0.5 mg/kg). Some of the behavioral effects of anticholinergics on spatial memory are mimicked by blindness or eliminating distal visual cues. If distal visual cues were more important for maintaining accurate WM than for RM, the selective effect of scopolamine on WM could be easily explained. But surrounding the maze with a curtain to eliminate extramaze cues increased RM errors without significantly increasing WM errors. Thus, the selective effect of anticholinergies on spatial memory in the radial maze is qualitatively different from the effect of restricting distal visual cues and must arise from some other action of the drug.

Behavioral perturbations in the vitamin K-deficient rat

Anecdotal observations of the behavior of rats with a vitamin K-deficiency suggested that this deficiency was associated with hypoactivity, general malaise, and a lack of exploratory behavior. These observations were pursued by assessing locomotor activity in a circular photocell-monitored track, open-field activity, and radial-arm maze performance in rats rendered vitamin K-deficient by dietary depletion or by warfarin treatment. There was a significant reduction (approximately 25% at the median) in the locomotor activity of dietary vitamin K-deficient rats compared with rats fed a control diet. In the open-field, warfarin administration was associated with a significant shift from more exploratory behaviors to less exploratory behaviors. Consistent with these findings, radial-arm maze assessment showed a comparative reduction in locomotor activity in the dietary vitamin K-deficient rats with no alteration in performance, i.e., short-term memory. These animal behavioral studies suggest that sub-clinical and clinical vitamin K-deficiency may contribute to physical and psychiatric symptomatology.

Learning and memory deficits after lesions of the nucleus basalis magnocellularis: reversal by physostigmine

The role of the cholinergic nucleus basalis magnocellularis in spatial learning and memory was studied in the rat. Animals received bilateral injections of ibotenic acid (5 micrograms/microliters) into the region of the nucleus basalis magnocellularis. Six weeks postoperatively they were deprived of food and trained for 5 weeks in a 16-arm radial maze in which 9 of the arms were baited with food. The nucleus basalis magnocellularis-lesioned animals showed significant deficits in the acquisition of the task. Further analysis of the data indicated that this was due primarily to a deficit in reference (long-term) as opposed to working (short-term) memory. After the 5-week training period the nucleus basalis magnocellularis-lesioned animals received intraperitoneal injections of physostigmine sulphate (0.5 mg/kg) 30 min before each daily trial for 1 week. This treatment resulted in a significant improvement in the performance of the spatial memory task on all three measures. The ibotenate lesions reduced the activity of choline acetyltransferase by about 40% in the anterior cortex and by 15% in the posterior cortex. Hippocampal choline acetyltransferase activity was not affected, indicating that the septohippocampal cholinergic projection was spared by the lesions. The activity of glutamate decarboxylase was not affected in any of these regions. These results suggest that the cholinergic projections of the nucleus basalis magnocellularis play an important role in the acquisition of a spatial memory task.

Scopolamine impairs the response-to-change following observation of the environment but not after its exploration by the rat

The tendency to select the T-maze arm that has been changed in brightness between two successive trials (response-to-change) was investigated in rats injected with scopolamine (Sc) or saline (NaCl) 20 min before the test. In the "passive" version of the test, when in trial 1 rats could inspect the white-black arms through clear partitions blocking the entrance to the arms, a dose of when in trial 1 rats could inspect the white-black arms through clear partitions blocking the entrance to the arms, a dose of 1.0 mg/kg Sc decreased significantly the number of changed arm choices in trial 2, as compared to saline controls. A lower dose of Sc (0.5 mg/kg) was ineffective. In the "active" test version, when in trial 1 the rats were allowed to explore the white-black arms, doses of 1.0 and 2.0 mg/kg Sc did not affect the preference for the changed arm in trial 2. NaCl rats showed a significant preference for the changed arm choices in both tests. The scopolamine effects on response-to-change, i.e., impairment of performance in the passive but not in the active version, were essentially the same as those found by us previously in hippocampal rats.

Radial maze performance in young and aged mice: neurochemical correlates

Young (8 month) and aged (27-28 month) male C57BL/6J mice were trained in a spatial discrimination task requiring working memory. The mice were tested during three trials daily in an eight-arm radial maze for 36 test days. Correct choices were reinforced with isotonic saline. In contrast to past reports, young mice learned the task. Old mice also learned the task, and no significant age-related differences in performance were observed. Following maze training, the mice were killed, the brains removed, and the specific activities of choline acetyltransferase (E.C.2.3.1.6., ChAT) and L-glutamic acid decarboxylase (E.C.4.1.1.15., GAD) were assayed in the hippocampus, and in frontal, sensorimotor, and cingulate areas of the cerebral cortex. The activities of these neurotransmitter synthetic enzymes did not differ significantly between young and old mice. Correct responding in the radial maze was positively correlated to ChAT activity in the cingulate cortex and negatively correlated to ChAT activity in the sensorimotor cortex. There was a similar pattern of correlation between performance and regional GAD activity, although none of the correlations involving GAD reached statistical significance.

The effect of hypothermia on the rat's spatial memory in the water tank task

The effect of hypothermia on the retention of the water tank navigation task has been examined in 21 male hooded rats. After a 3-min swimming test on Day 1 the animals were trained on Days 2 and 3 (2 X 12 trials) to find a small submerged platform 1 cm below the surface of a large pool (120 cm in diameter) of opaque water. On Day 4, the rats were divided into three groups (n = 7) which were cooled to colonic temperatures of 22-24 degrees C (H1), 25-27 degrees C (H2), and 28-31 degrees C (H3), respectively, and given 12 retrieval trials in the water tank. Average escape latencies increased from 6 s in normothermic rats on Day 3 to 33, 19, and 12 s on Day 4 in the H1, H2, and H3 groups, respectively. Under the same testing conditions the performance of groups H1, H2, and H3 improved on Day 5 to 20, 8 and 6 s, respectively. It is concluded that spatial memory retrieval is resistant to mild hypothermia (30 degrees C), but that it is severely impaired at body temperatures below 25 degrees C. Reacquisition of the task is slowed down but not fully prevented in deep hypothermia.

Behavioral methods for measuring effects of drugs on learning and memory in animals

This review describes methods for measuring effects of drugs on learning and memory in animals, proceeding from relatively simple nonassociative learning (habituation) to classical and instrumental conditioning, and concluding with complex measures for measuring learning and memory repeatedly in the individual animal. Procedures for separating drug effects specific to learning and memory from non-specific effects on activity, motivation, sensory and motor capacity, etc., were emphasized. For each method, selected experimental examples were presented which described the action of drugs on learning and memory, elucidated the behavioral processes involved in the drug effects, or illustrated methodological points. The various procedures used to measure drug effects on learning and memory in animals have yielded a bewildering array of often-contradictory results. Quantitative differences in effectiveness of drugs in the different procedures are common. Drugs (for example, the nootropics) that alter learning or memory in a few procedures may be totally without activity in many others. How are these discrepancies to be interpreted? The apparent inconsistencies in the data can, for the most part, be understood in terms of the nature of learning and memory. "Learning" and "memory" are hypothetical processes presumed to underlie enduring changes in behavior resulting from the organism's interaction with environmental stimuli. Given such a broad definition, the prevalence of inconsistencies in the data is hardly surprising. It is unlikely that the same mechanisms should underlie all of the wide variety of behavioral changes included under the rubrics "learning" or "memory." (For a contrary view, based on consistencies among results obtained in the diverse procedures, see Zornetzer). How, then, should drug effects on learning and memory be identified or measured? The first step, of course, is to rule out those drug effects that do not conform to the definition of learning or memory. This review has described strategies and procedures by which this can be accomplished. However, even when this is done there is no single procedure that can detect drug effects on learning and memory in general, nor, in view of the heterogeneous behaviors involved, is it likely that such a universal procedure will ever be found. Thus, a multi-faceted strategy will be required. Some of the simpler procedures described in this review may be adequate for the initial identification of interesting effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects of scopolamine on working and reference memory of rats in the radial maze

Anticholinergics have often been found to impair choice accuracy in the radial maze. Some researchers have suggested that this indicates involvement of cholinergically innervated structures in cognitive mapping while others argue that these structures mediate working memory. However, most results are open to either interpretation since the baiting method did not allow a distinction between reference and working memory errors. To further test these hypotheses this study examined the effects of systemic scopolamine on radial maze performance, using a 4-out-of-8 baiting procedure. Food-deprived Wistar rats were pretrained until working memory choice accuracy stabilized to a criterion of 87% or better. Scopolamine (0.1, 0.4 and 0.8 mg/kg, IP, 30 min before a session) significantly increased the number of working memory errors (re-entries into baited arms) whereas reference memory errors (entries into never baited arms) did not change significantly. Observed deficits appeared not to be attributable to a drug-induced disruption of motivational systems. Results confirm the behavioural similarities between the memorial effects of hippocampectomy and anticholinergics, and implicate cholinergically innervated structures in working memory.

Effects of cholinergic and monoaminergic antagonists and tranquilizers upon spatial memory in rats

To explore the pharmacological mechanisms of the spatial memory, performance on the radial arm maze was tested in rats under the following drugs, using a within-subject design; scopolamine (0.25 and 0.5 mg/kg), methylscopolamine (0.5 and 1 mg/kg), phentolamine (5 and 10 mg/kg), propranolol (10 and 20 mg/kg), chlorpromazine (1 and 2 mg/kg), and chlordiazepoxide (5 and 10 mg/kg). The number of correct choices was significantly decreased by scopolamine, while the other drugs, including methylscopolamine, showed no effects on the correct choices. Almost all drugs affected the running time. These findings indicate that the brain cholinergic system is involved in the spatial memory.

The radial maze performance of mice: assessing the dimensional requirements for serial order memory in animals

Two versions of the eight-arm radial maze were used to test the working memory abilities of CD-1 mice. In an elevated open-arm radial maze, mice quickly and successfully learned the multiple-choice procedure. However, mice trained in an enclosed-arm radial maze mastered the task only by developing a kinesthetic strategy of response. When a delay was imposed between choices 4 and 5, mice in the open-arm radial maze retained high performance levels. Choice accuracy declined markedly for mice in the enclosed-arm radial maze under delay conditions. Transference of the two groups of mice between the two mazes resulted in a complete reversal of sampling strategies. Minor changes to the enclosed-arm maze and room illumination permitted mice to successfully perform in the non-egocentric manner which they exclusively employed in the open-arm maze. The results show that mice can demonstrate a working memory capacity when in an environmentally adequate radial maze, and provide evidence against the existence of nonspatial working memory ability. The discussion examines the procedural and environmental requirements for displays of working memory, and a set of hypotheses is presented which serve to integrate the working memory and cognitive mapping theories.

Radial arm maze performance of mice: acquisition and atropine effects

CD-1 mice were successfully trained in a six-arm radial maze in which half of the arms were baited, a procedure which had been used to differentiate between reference and working memory. Stable performance was achieved following eight daily training sessions, as measured by decreasing running time and number of errors. This finding strengthens the foraging hypothesis as a basis for the performance of rodents in the radial maze. Acute subcutaneous administration of the cholinergic antagonist atropine sulfate (1-6 mg/kg) to trained mice produced dose-related increases in running time and working memory errors, with a slight decrease in reference memory errors. This is in agreement with other studies on the role of the cholinergic system in memory processes. The peripheral cholinergic blocker, atropine methyl nitrate (4 mg/kg), somewhat increased running time without decreasing performance accuracy. In contrast to the prolonged pharmacological and physiological effects of atropine, behavioral decrements disappeared within 3 hr. It is concluded that mice trained in the radial arm maze may be used for screening of the effects of drugs on cognitive function.

Acute and chronic amphetamine treatment: differential modification of exploratory behavior in a radial maze

Mice permitted to explore an 8-arm radial maze displayed high levels of spontaneous alternation as measured by the frequency of visiting (a) the 4 least recently entered arms, (b) the 2 least recently visited arms, and (c) sequences of arms which are adjacent to one another. Acute treatment with low doses of amphetamine (1.0 mg/kg) eliminated the alternation tendency. Higher doses (5.0-7.0 mg/kg) also produced marked stimulus perseverance, such that mice tended to revisit the two arms that had been most recently entered. With repeated amphetamine treatment the perseverance tendency was attenuated. The abatement of perseverance in the radial maze did not appear to reflect simply the reduction in the potency of the drug. That is, the reduction of perseverance after chronic exposure to amphetamine was not accompanied by recovery of normal exploratory patterns. In fact, the alternation and adjacent alternation patterns typical of naive animals were absent in mice chronically treated with amphetamine even when tested in the nondrug state. It was suggested that the attenuation of amphetamine induced perseverance after chronic amphetamine administration may reflect a breakdown of normal behavior patterns rather than the development of a genuine tolerance.

Radial maze performance in three strains of mice: role of the fimbria/fornix

Three strains of mice were tested on an 8-arm radial maze, an index of hippocampus-dependent spatial memory. Levels of performance differed between strains with C57Br/cj greater than Balb/cj greater than C57Bl/6j. Lesions of the fimbria/fornix disrupted performance in the C57Br and Balb strains: the C57Bl mice never performed better than chance before or after surgery. Choline acetyltransferase activity in hippocampus was not correlated with radial maze performance. These findings suggest a possible genetic contribution towards radial maze behavior.

Medial septal lesions, radial arm maze performance, and sympathetic sprouting: a study of recovery of function

Long-Evans rats received septal lesions or sham operations and were tested for performance in a radial arm maze, level of activity and water intake in order to test whether recovery of function was mediated by sprouting of peripheral sympathetic fibers. Animals receiving septal lesions displayed an initial deficit in radial arm maze performance followed by recovery. No critical changes occurred in activity level and no recovery was seen in water intake. Subsequent superior cervical ganglionectomies had no effect on recovery of radial arm maze performance. There was a significant relationship between behavioral recovery and the degree of hippocampal AChE depletion. It is concluded that recovery of radial arm maze performance is not mediated by sympathetic sprouting following septal lesions but might be mediated by residual septohippocampal fibers.