Avoidance Learning Test Research Articles

Preparation of cerebral ischemia-induced amnesic model in mice and ameliorative effect of several compounds on the model

A simple and reliable method for the preparation of an ischemia-induced amnesic model was developed in mice and the model animals were employed for screening of the anti-amnesic effect of drugs. Under light thiopental anesthesia the bilateral carotid arteries were exfoliated from the surrounding tissues. Each artery was threaded through a small polyethylene tube, and the incision was sutured, leaving the tip of the tube and both ends of the thread out of the skin. To prevent the tube from falling off, both ends of the thread was ligated at the tip of the tube. Cerebral ischemia was attained by pulling the artery into the tube, and the occlusion was rapidly released by cutting the ligation in the thread and taking off the tube. Twenty-four hours after the surgery, the animals were used for the one trial passive avoidance learning test. In ddY strain mice, the amnesic state was obtained by 5 to 30 min cerebral ischemia, which was applied immediately after the acquisition trial. Mice of the ICR strain were more sensitive to the ischemic treatment and 2 min occlusion of the carotid arteries resulted in a high degree of amnesia. A potent prolyl endopeptidase inhibitor, Z-thiopro-thiazolidine, and 2 novel pyrrolidone derivatives, p-chlorobenzyl-2-pyrrolidone-5-carboxylate and N-(2-pyridylmethyl)-2-pyrrolidone-5-carboxamide, improved the acquisition of the passive avoidance response in the ischemia-induced amnesic models.

Developmental Toxicity of Aspirin Prenatally Given to Rats: Assessment in Slc: Wistar‐KY Rats

ABSTRACT Slc:Wistar‐KY rats were administered orally with 62.5, 125, 187.5 or 250mg/kg aspirin suspended with 0.5 % CMC‐Na on days 9–11 of gestation (plug += day 0). Suppression of maternal weight gain and food consumption during treatment was observed at and over 187.5 mg/kg. At term, the fetal mortality increased at and over 187.5 mg/kg and the fetal weight was lowered at and over 125 mg/kg. Among 15 live fetuses at 250 mg/kg, 4 had external malformations. In the skeletal examination (double staining), skeletal anomalies increased at and over 187.5 mg/kg. The skeletal variations such as vertebral anomalies, fused costal cartilages and increased presacral vertebrae were often encountered and delayed ossification was also found at and over 125 mg/kg. The internal anomalies tended to increase at and over 187.5 mg/kg. The live birth rate was significantly lower at 187.5 mg/kg than that in controls, and all pups, except for 3 from a dam, died before weaning. At 125 mg/kg, the pivoting locomotion on day 7 post partum was poorer as compared with controls. The physical and functional development at 62.5 mg/kg was not changed. There were no significant effects on male offspring in the open‐field, rotarod, under‐water T‐maze and avoidance learning tests. However, in the Biel T‐maze test (9–10 weeks of age), the aspirin‐treated groups showed more errors and the increased elapsed time on the 1st trial day than controls. These results indicate that aspirin may induce a slight learning defect on rat offspring even at the non‐teratogenic dose and the Biel T‐maze test is more sensitive than any other learning tests given in this study.

Effects of intracerebroventricularly administered somatostatin on passive avoidance, shuttle-box behaviour and open-field activity in rats

Behavioural effects of somatostatin after intracerebroventricular (icv) administration have been investigated in male rats. In a passive avoidance learning test, somatostatin (1 μg), given 30 min before the learning session, increased the avoidance latency at 24 h, but not at 48 h, after the injection, when compared to a 10 μg treated group. However, compared to a saline treated group, somatostatin (0.01, 0.1, 1, or 10 μg) did not significantly influence the avoidance latency. In a shuttle box experiment somatostatin (1 μg) facilitated the learning process. In an open-field behaviour test, immediately after the 24 h passive avoidance test, 10 μg of the peptide decreased the rearing activity without influencing other open field behaviours, like locomotion, grooming and defecation. In a second open-field experiment somatostatin (1 μg), given 30 min prior to the test, similarly as in the shuttle box learning experiment, increased the locomotion of the animals. These data suggest that somatostatin influences both the passive avoidance and shuttle box behaviours. The peptide-induced motor performance of the animals may play an important role in influencing the responses observed in these behavioural tests.

Developmental Toxicity of Aspirin Prenatally Given to Rats: Assessment in Sic: Wistar‐KY Rats

Abstract Slc:Wistar‐KY rats were administered orally with 62.5, 125, 187.5 or 250 mg/kg aspirin suspended with 0.5 % CMC‐Na on days 9–11 of gestation (plug += day 0). Suppression of maternal weight gain and food consumption during treatment was observed at and over 187.5 mg/kg. At term, the fetal mortality increased at and over 187.5 mg/kg and the fetal weight was lowered at and over 125 mg/kg. Among 15 live fetuses at 250 mg/kg, 4 had external malformations. In the skeletal examination (double staining), skeletal anomalies increased at and over 187.5 mg/kg. The skeletal variations such as vertebral anomalies, fused costal cartilages and increased presacral vertebrae were often encountered and delayed ossification was also found at and over 125 mg/kg. The internal anomalies tended to increase at and over 187.5 mg/kg. The live birth rate was significantly lower at 187.5 mg/kg than that in controls, and all pups, except for 3 from a dam, died before weaning. At 125 mg/kg, the pivoting locomotion on day 7 post partum was poorer as compared with controls. The physical and functional development at 62.5 mg/kg was not changed. There were no significant effects on male offspring in the open‐field, rotarod, under‐water T‐maze and avoidance learning tests. However, in the Biel T‐maze test (9–10 weeks of age), the aspirin‐treated groups showed more errors and the increased elapsed time on the 1st trial day than controls. These results indicate that aspirin may induce a slight learning defect on rat offspring even at the non‐teratogenic dose and the Biel T‐maze test is more sensitive than any other learning tests given in this study.

Specific inhibitors for prolyl endopeptidase and their anti-amnesic effect.

Several peptides and peptide derivatives were tested for their inhibitory effect on prolyl endopeptidase and possible properties as anti-amnesic agents. Among the compounds tested, Z-Gly-Pro-CH2Cl, Z-Val-prolinal, Boc-Pro-prolinal, Z-Pro-prolinal, aniracetam and pramiracetam inhibited the enzyme activities at Ki values in the order of nM to microM, and the effect of the prolinal-containing peptide derivatives was specific for prolyl endopeptidase. Z-Pro-prolinal was the most effective inhibitor in vitro (Ki = 5 nM) and in vivo (50 to 70% inhibition in various organs of rat at a dose of 1 mumol/animal i.p.). Regional differences were observed in the effect of inhibitors on the brain enzyme activities: most active in mesencephalon, followed by striatum, cerebellum, hippocampus, hypothalamus; and inactive in cerebral cortex and medulla oblongata. In the passive avoidance learning test using rats, pretreatment with Z-Pro-prolinal prevented the induction of amnesia by scopolamine at the dose of 1 mumol/animal, i.p. Z-Val-prolinal, Z-Pyr-prolinal and Z-Gly-Pro-CH2Cl were also effective in the retention test at 24 and 48 h after the training trial. The antiamnesic effect of these compounds was approximately parallel to the in vitro inhibitory activities on prolyl endopeptidase. These results suggest the possibility that the inhibitors exhibit their anti-amnesic effect through the regulation of the enzyme activity in the brain.

Behavioral changes in the rat after low doses of cholinesterase inhibitors

In rats the acute effects of low doses of five cholinesterase (ChE) inhibitors were investigated in six behavioral tests. Considerable differences were found between the inhibitors studied. TEPP and sarin at doses up to 30% LD50 were without effects. In contrast, soman, physostigmine, and pyridostigmine caused effects at dose levels which did not produce overt symptoms and did not affect running speed and simple coordinated locomotion. Soman (≤3% LD50), physostigmine (≤4.5% LD50), and pyridostigmine (≤10% LD50) interfered with two-way shuttlebox avoidance learning, open field behavior, and complex coordinated movements (hurdle-stepping task). Tests of retention in a passive avoidance learning test appeared less sensitive. It is concluded that paradigms that involve higher CNS structures and require motor activity are sensitive to some ChE inhibitors at doses far below those that cause overt symptoms. The individual characteristics of ChE inhibitors play an important role. In contrast to TEPP and sarin, soman has a predominantly central effect. Further, the finding that pyridostigmine was also effective at unexpectedly low dose levels suggests that this compound may have more central actions than hitherto accepted.

Effects of experimental suppression of active (REM) sleep during early development upon adult brain and behavior in the rat

In order to test the hypothesis that active sleep (AS) is important for the normal development of the central nervous system. 3 different deprivation methods were applied to male Wistar rat pups during the first month of life. Daily injection of clomipramine from 8 to 21 days of age reduced the high level of AS to less than the adult value throughout most of the experimental period. Administration of clonidine from 8 to 21 days of life induced an almost total suppression of AS. Instrumental deprivation, using the ‘pendulum’ method, led to a significant (but less severe) AS reduction during 2–4 weeks of postnatal age. Open-field behavior testing in adulthood revealed a higher than normal level of ambulation in all 3 experimental groups. Masculine sexual responses were deficient, due to a low level of both mounts and ejaculations, in both clomipramine- and clonidine-treated animals. Neither passive avoidance learning nor dark preference tests revealed any differences between the experimental and control rats. Sleep observations showed that there was an abnormally high incidence of large myoclonic jerks during AS in both clomipramine- and clonidine-treated rats. Subsequent measurement of regional brain weights showed a significant reduction in the cerebral cortex and medulla oblongata, as compared with the respective control groups, in both the clomipramine- and the clonidine-treated rats. In addition, DNA and protein determination in the affected brain areas showed a proportional reduction in the cortex and in the medulla. These results demonstrate that interference with normal functioning either of AS per se or of specific monoaminergic transmitter systems during early development can produce long-lasting behavioral as well as brain morphological and biochemical abnormalities in later life.

Avoidance behavior in folate--deficient rats.

The effects of folate deficiency in post-weanling male rats in an active avoidance learning test were studied. Ingestion of a folate-free diet for 3 weeks markedly decreased serum and erythrocyte folate concentrations but had only a slight effect on growth rate. The decrease in blood folates was correlated with an increase in the number of trials necessary to reach criterion in the learning test. There was no motor impairment since the mean escape latency was the same in control and folate-deficient animals. These results suggest that folic acid deficiency started at weaning could be responsible for learning impairment.