Effects of dorsal-striatum lesions and fimbria-fornix lesions on the problem-solving strategies of rats in a shallow water maze

In solving a spatial problem, animals can use a place, cue, or response strategy. The present research was designed to evaluate the role of dorsal striatum (DS) in spatial problem solving and to compare it with that of fimbria fornix (FF). Rats were trained with a place + cue task in a shallow pool, then were divided into three groups (DS, FF, control), and lesions were made in the corresponding areas. After retraining, four probe tests were given: Test 1 (start position moved), Test 2 (goal and start positions moved), Test 3 (invisible goal), and Test 4 (curtain test). The test results suggest that the DS and Control groups performed the original task by using the place strategy, whereas the FF group used the cue strategy, which strongly implies that the DS group was impaired in the use of the cue strategy. This research also provides evidence supporting the usefulness of a shallow pool in evaluating animal behavior.     

Effects of glucose on scopolamine-induced learning deficits in rats performing the Morris water maze task

In order to assess the effects of glucose on drug-induced spatial learning deficits, three experiments were conducted using the Morris water maze. Scopolamine and glucose were injected ip at various stages of training. Rats of Wistar strain served as subjects. In Experiment 1, scopolamine (0.4 mg/kg) and 10, 100, or 500 mg/kg of glucose were administered every day from the start of training, and the effect on acquisition was evaluated. In Experiment 2, scopolamine and 100 or 500 mg/kg of glucose were administered after 6 days of training, and the effect on performance was assessed. In Experiment 3, scopolamine and 500 mg/kg of glucose were injected after 2 days of training, and the effect on the following trial was tested. In all experiments, scopolamine impaired acquisition/performance of the task. Glucose at 500 mg/kg showed a significant enhancing effect on acquisition regardless of scopolamine injection only when injected daily from the start of training (Experiment 1). Glucose injected after the performance has reached asymptote (Experiment 2) did not affect performance, and glucose in the middle of training showed a slight but insignificant enhancing effect (Experiment 3). These results may suggest that the effect of glucose changes as a function of the degree of learning of the spatial learning task. The possibility of task specificity of the glucose effect was also discussed in relation to the cholinergic systems and local cerebral glucose utilization.     

The effect of cul length and hippocampal lesions on maze learning in the rat

Integrative Psychological and Behavioral Science - Twenty-four tats, 8 with bilateral hippocampal lesions, 8 with cortical lesions and 8 unoperated rats, were tested on one of 2 mazes. Half of each...     

Sex-dependent effects of neonatally administered morphiceptin and D-ala-D-leu-enkephalin on maze learning in rats

Newborn rats were injected (ip) with morphiceptin [72.7 micrograms/kg (a mu-type opioid receptor agonist)], D-alanine2-D-leucine5-enkephalin [79.4 micrograms/kg (a delta-receptor agonist)], or saline for 7 days after birth. Testing on a complex maze on Day 25 revealed a significant sex-dependent facilitation of performance by the opioid peptides. Peptide-treated females performed better than the males on the first day of training as measured by errors. Opioid treatment increased mortality, as three times as many peptide-treated animals died in comparison to the saline control group. Peptide treatment did not affect locomotor activity measured in an open field. Weight at Day 24 was also affected by the peptide treatment, females and males injected with the opioids being lighter and heavier, respectively, than the control group.     

Effects of anterior or dorsomedial thalamic ibotenic lesions on learning and memory in rats

Sprague-Dawley rats were used to study the effects of ibotenic acid lesions of the anterior (A.Th.) and the dorsomedial (MD) thalamic nuclei on learning and memory. Memory was assessed by employing a temporal alternation task in a straight alley with varying intertrial intervals. In addition, spatial orientation and response flexibility were evaluated on a radial maze and on a spatial reversal task (SSDR). The results indicated that MD rats required more trials to learn the temporal alternation task and exhibited impaired performance compared to A.Th. and control groups at the shortest delay (15 s). In contrast, compared to the control group, A.Th. subjects which required less trials to master the task and exhibited normal performance at the 15-s delay were impaired when the intertrial interval was increased to 45 s. Whatever the lesion, no impairments were found in the SSDR or the radial maze while only MD lesions were found to result in a night hyperactivity associated with greater food and water consumptions. These findings indicate that A.Th. and MD are differentially involved in learning and memory processes. It is suggested that the MD is mostly involved in registering new information while the A.Th. plays a role in the maintenance of information over time.