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

Utility of an elevated plus-maze for the evaluation of memory in mice: effects of nootropics, scopolamine and electroconvulsive shock

An elevated plus-maze consisting of two open and two enclosed arms was employed for an evaluation of memory in mice. Mice in the plus-maze escaped from the open arm to the enclosed arm because mice apparently dislike open and high spaces. The time it took for the mice to move from the open arm to the enclosed arm (transfer latency) was recorded. The transfer latency after the 2nd day was significantly shorter than that on the 1st day when it was recorded at a rate of one trial a day for 5 days. The transfer latency on the 2nd day was significantly prolonged in the mice administered electroconvulsive shock (300 V, 1 s) or scopolamine (20 micrograms, ICV) immediately after the first trial compared to the transfer latency in the control group. The prolongation of transfer latency in the mice administered an electroconvulsive shock was reversed by pretreatment with aniracetam (20 mg/kg, PO), but not tacrine and physostigmine. The prolongation of transfer latency in the mice administered scopolamine was reversed by pretreatment with aniracetam (10 and 20 mg/kg, PO) tacrine (1 and 3 mg/kg, PO), or physostigmine (0.025-0.2 mg/kg, IP). These results suggest that transfer latency may be one of the parameters of learning and memory.

Minaprine improves impairment of working memory induced by scopolamine and cerebral ischemia in rats

Using a repeated acquisition procedure in a three-panel runway apparatus, the effects of minaprine on the impairment of working memory produced by scopolamine, ethylcholine aziridinium ion (AF64A) or cerebral ischemia were investigated in rats. Minaprine (3.2-32 mg/kg IP) as well as idebenone (10-100 mg/kg IP) and physostigmine (0.1-0.32 mg/kg IP) dose-dependently reduced the increase of errors (pushes made on the two incorrect panels located at each choice point) induced by 0.56 mg/kg IP scopolamine. Cerebral ischemia for 5 min caused a significant increase of errors in the runway task. Minaprine at 3.2 and 10 mg/kg administered IP immediately after blood recirculation and again 30 min before the runway test conducted 24 h after ischemia, significantly reduced increases in errors expected to occur after 5 min of ischemia. Physostigmine 0.1 mg/kg similarly attenuated the increase in errors in ischemic rats. However, minaprine at doses up to 32 mg/kg IP failed to reduce the increase of errors induced by AF64A 2.5 nmol injected into the dorsal hippocampus. These findings suggest that minaprine exerts an ameliorating effect on amnesia produced by scopolamine and cerebral ischemia, probably through mediation of its stimulant action on central cholinergic systems.

Parietal cortex lesions do not impair retention performance of rats in a 14-unit T-maze unless hippocampal damage is present

Young male F-344 rats, pretrained in a straight runway to avoid shock, were then trained in a shock-motivated 14-unit T-maze. One day after maze acquisition, extensive parietal cortex lesions (PC) or sham operations (CON) were performed to assess possible involvement of parietal cortex in the age-related impairment previously observed in this task. Twelve days after surgery, a first 10-trial retention session in the 14-unit T-maze was conducted. One day later the vibrissae of half the rats in each group were clipped to examine involvement of the damaged barrel cortex field in maze performance of rats with PC lesions. The following day a second 10-trial retention session occurred. Finally, retention of the straight runway avoidance response was tested. Histological verification revealed a group with consistent parietal damage but also a subgroup with relatively small lesions to dorsal or lateral hippocampus in addition to parietal damage (PC + HIP). Behavioral results revealed virtually perfect maze retention for CON and PC rats. In contrast, PC + HIP rats were severely impaired in maze retention performance. Retention of the straight runway avoidance response was perfect in CON and PC rats but was impaired in PC + HIP rats. Vibrissae clipping did not affect error performance in the maze but led to a transitory increase in runtime. Overall, the results indicate that parietal lobe damage shortly after acquisition does not impair retention performance of young rats in the 14-unit T-maze, unless hippocampal damage is also evident. Thus, parietal lobe dysfunction alone would not appear to be involved in the age-related retention impairment previously observed in this task.

Comparison of retention performance between young rats with fimbria-fornix lesions and aged rats in a 14-unit T-maze

Young (3-months) and aged (24-months) male F-344 rats were pretrained in one-way active avoidance in a straight runway for 3 days. Then two 10-trial daily sessions were given in a 14-unit T-maze in which the response requirement was to negotiate each of 5 maze segments within 10 s to avoid footshock. One day or one week after acquisition, bilateral electrolytic lesions were made in the fimbria-fornix of young rats (1-day lesion or 1-week lesion). Corresponding sham operations were made for remaining young rats (1-day sham or 1-week sham). Aged animals did not receive any surgical treatment. One week after surgery, a 10-trial retention test was conducted to assess the lesion effects on retention and to manipulate the interval between acquisition and lesions. Aged animals were tested in the maze 1 week after acquisition. Results revealed that rats with fimbria-fornix lesions exhibited significant impairment compared to sham-operated groups on all retention performance measures including errors, runtime, number of shocks, duration of shock, and alternation errors. The number of errors and alternation errors of lesioned animals were still higher than those of sham-operated animals at the second half of the retention test, whereas other non-cognitive measures for lesioned animals recovered to control levels. The interval between acquisition training and lesions had no influence on retention performance. Although performance of aged rats during acquisition and retention trials was significantly worse than that of young controls and lesioned animals, a similar recovery pattern during retention testing was found for young rats with fimbria-fornix lesions and aged rats, i.e. both groups showed significant declines in non-cognitive measures with less decline in cognitive measures. These results suggest that the fimbria-fornix is partially involved in retention of 14-unit T-maze performance and that the age-related retention deficit observed in this task may be related to impaired transmission through this pathway.

Scopolamine impairs response-to-change based on distal cues in the rat

The effect of a scopolamine injection (1 mg/kg, IP) on response-to-change behavior was investigated in two experiments. After exploration of a T-maze with one arm black and the other white (Trial 1), rats were tested with both arms either black or white (Trial 2). Experiment 1 revealed that the opportunity to make body turns into the arms did not help scopolamine-injected rats to locate the changed arm after visual exploration of the arms during Trial 1. Saline-injected animals chose the changed arm. In Experiment 2, rats were allowed to move freely into the arms during Trial 1. During Trial 2, they were tested either from the same start as that used during Trial 1 or from a different start 180 degrees from the original start. While scopolamine-injected animals reacted appropriately to the change when tested from the same start, they were impaired when tested from the opposite start. In both conditions, saline-injected animals chose the changed arm. These results, together with others, support the notion that the cholinergic system plays a crucial role in the processing of distal information.

Effect of S-adenosyl-L-methionine on impairment of working memory induced in rats by cerebral ischemia and scopolamine

A repeated acquisition procedure in a 3-panel runway apparatus was used to investigate the effects to S-adenosyl-L-methionine (SAM) on impairment of working memory produced either by cerebral ischemia or by scopolamine in rats. Cerebral ischemia (2-10 min) produced duration-dependent increases in the number of errors (pushes made on the two incorrect panels located at each choice point) and increased latency (time before the rat reached the goal box). The increase in errors induced by a 5 or 10 min period of ischemia decreased gradually in subsequent training sessions, returning to the control levels in 6 days. The increases in both errors and latency induced by 5 min of ischemia were significantly reduced by 100 and 180 mg/kg SAM administered i.p. immediately after blood recirculation and 1 h before a test conducted 24 h after ischemia. SAM at doses up to 180 mg/kg nevertheless failed to reduce the increases in errors and latency if they were induced by 0.56 mg/kg of scopolamine. These results suggest that SAM has a beneficial effect on memory that has been impaired by cerebral ischemia.

Age-related impairment in complex maze learning in rats: relationship to neophobia and cholinergic antagonism

Scopolamine was utilized to assess cholinergic muscarinic blockade on the performance of young (3 months) and aged (23 months) male F-344 rats in a 14-unit T-maze task. Prior to training, a portion of each age group received a gustatory neophobia test (percent consumption of a novel sucrose solution) to assess involvement of norepinephrine systems implicated in age-related impairments of rats in other memory tasks. All rats were pretrained in one-way active avoidance (1.0 mA) on 3 consecutive days. Rats meeting criterion (8/10 avoidances on last day) began maze training the next day consisting of 10 trials on 2 consecutive days. The task required the rat to negotiate each of 5 maze segments within 10 sec to avoid scrambled footshock (1.0 mA). Rats received an intraperitoneal injection of either scopolamine hydrochloride (0.5 mg/kg or 0.75 mg/kg) or saline vehicle 30 min prior to maze testing. Consistent with past reports, aged rats were more neophobic (i.e., consumed less sucrose) than were young rats, but the degree of neophobia was not significantly correlated with maze error performance in either age group. Also consistent with previous studies, aged rats were significantly impaired, compared to young counterparts, in all maze performance measures including errors, alternation errors, runtime, and shock frequency and duration. Significant scopolamine-induced deficits were observed in both age groups, but only in errors and alternation strategy. No age by drug interaction was manifested in any performance measure indicating that scopolamine impaired learning of young and aged rats equivalently.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex maze learning in rodents as a model of age-related memory impairment

Research is reviewed concerning the age-related learning deficit observed in a 14-unit T-maze (Stone maze). Rats and mice of several strains representing different adult age groups are first trained to criterion in one-way active avoidance in a straight runway. Then training in the Stone maze is conducted which involves negotiation of five maze segments to avoid footshock. Results indicate a robust age-related impairment in acquisition observed in males and females, and in outbred, inbred, and hybrid strains. Pharmacological studies using the muscarinic antagonist, scopolamine, in young and aged rats indicate cholinergic involvement for accurate encoding during acquisition of this task. Retention aspects of storage and retrieval do not appear to be affected by scopolamine treatment. Bilateral electrolytic lesions to the fimbria-fornix of young rats also produce an acquisition deficit to implicate involvement of the septo-hippocampal cholinergic system in Stone maze learning. A salient feature of Stone maze performance is the tendency to demonstrate an alternation strategy in solving the maze. This strategy is exacerbated by impairment of cholinergic neurotransmission with either scopolamine treatment or fimbria-fornix lesions. Various models of hippocampal function are applied toward the psychological characterization of the Stone maze task without complete success. Future research is outlined to provide more thorough psychological characterization of maze performance, to analyze the specificity of cholinergic involvement in the task, and to test possible therapeutic interventions for alleviating the age-related impairments observed.

Scopolamine in rats impairs acquisition but not retention in a 14-unit T-maze

To follow up a previous report noting that scopolamine impaired acquisition performance of young rats in a shock-motivated 14-unit T-maze, the present study assessed the effects of muscarinic antagonism on retention aspects of the same task. The broader objective was to further the investigation of possible defects in cholinergic neurotransmission that might underlie the age-related impairments previously observed in this task. Young (3-month) male F-344 rats were given preliminary training to criterion in one-way active avoidance in a straight runway. Then on the first day of complex maze training, each rat received 5 acquisition (AQ) trials followed by a second 10-trial retention (RET) session conducted the following day. Subjects were assigned to one of eight groups receiving an intraperitoneal injection of either scopolamine hydrochloride (1.0 mg/kg) or saline as follows: (a) 30 min prior to training on the first day (PRE-AQ); (b) 30 min prior to training on both the first and second day (PRE-AQ-RET); (c) immediately after completing the trial on the first day (POST-AQ); (d) 30 min prior to testing on the second day (PRE-RET). Dependent measures included errors, alternation errors, run time, number of shocks, and total shock received. On the first day of maze training, all performance measures except for alternation errors were significantly higher for the two acquisition groups (PRE-AQ and PRE-AQ-RET) compared to all other groups which did not differ significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in working and reference memory performance and locomotor activity in the Wistar rat

Wistar rats of three age groups were tested in an automated tunnel-maze system of variable geometry to investigate whether changes in spontaneous locomotor activity and in learning and memory develop differentially or in a correlated fashion as a function of age. Senescent (30 months) as well as mature-adult (17 months) rats showed an age-correlated decline of locomotor activity as compared to the mature-young (5 months) group. Both working-memory (measured as within-trial arm discrimination performance) and reference-memory (measured as avoidance of "blind alley" visits) were severely affected in the senescent group, whereas the middle-aged animals suffered only from a working-memory deficit. The findings provide evidence that locomotor deficits do not necessarily interfere in the assessment of age-related changes in cognitive performance. Furthermore the results support the hypothesis that working and reference memory have different underlying physiological correlates and that these neuronal systems are differentially affected by the aging process.

Co-dergocrine, cerebral glucose utilization and maze performance in middle-aged rats

The objective of this study was to determine the effect of co-dergocrine in rats on local cerebral glucose utilization and performance in a complex T-maze. Middle-aged (12-16 months) male Fischer-344 rats were given injections of co-dergocrine (3 or 10 mg/kg, IP) 35 min before behavioral testing or the administration of 2-deoxy-D-[1-14C]glucose ([14C]DG), a radiotracer for local cerebral glucose utilization (LCGU). Both doses stimulated LCGU in the locus ceruleus and median raphe nucleus and in subcortical structures associated with learning and memory (hippocampus and subiculum). The higher dose also stimulated LCGU in motor areas (caudate-putamen, globus pallidus, internal capsule). In contrast, co-dergocrine decreased LCGU in the frontal cortex. Poorer performance in a complex maze (increased shocks, errors and run time) was observed in middle-aged as compared with younger animals (3 months). Acute co-dergocrine treatment did not improve performance of middle-aged rats in this task. Thus, in the present experimental paradigm employing single dose administration, co-dergocrine's stimulation of LCGU was not associated with an alteration of maze performance in age-matched animals.