Hippocampectomized Rats Research Articles

Effects of atropine sulphate on repeated extinction performance in hippocampectomized rats.

Hippocampectomized and partially neodecorticated rats were trained on repeated extinction until similar baselines were obtained. Identical doses of atropine sulphate were administered to each group and the dose-response curves compared. The partially neodecorticated rats showed a marked increase in responding during the extinction periods and the magnitude of the effect increased with dose as in intact animals. The hippocampectomized animals showed little change in responding with any dose. The attenuation of the dose-response effect, in conjunction with other evidence, was consistent with the hypothesis of a second system which mediates response control in the hippocampectomised animals and is not cholinosensitive.

Faster acquisition of discriminated lever-press avoidance by hippocampectomized rats.

Faster acquisition of discriminated lever-press avoidance by hippocampectomized rats.

Plasma corticosterone levels during extinction of a lever-press response in hippocampectomized rats.

Abstract Male Long-Evans rats with bilateral lesions of the hippocampus or of the cortex overlying the hippocampus and unoperated rats were trained to lever press for water reinforcement on a continuous reinforcement schedule, and then extinguished. The hippocampectomized animals responded at higher rates than controls during early acquisition sessions, the difference decreasing over training and increasing again during extinction. Plasma levels of corticosterone were determined in the resting (non-stressed) state on ad lib and deprivation watering schedules, and following ether anesthesia, exposure to a novel environment, a reinforced operant session and the first extinction operant session. The results indicated that hippocampal lesions produced by aspiration cause no essential deficit in pituitary-adrenal function. However, the hippocampectomized rats failed to exhibit the normal elevation of plasma corticosterone during the first extinction session. This finding contradicts proposals that hippocampectomy increases the frustrative-emotional response to unmet reward expectancies. It is supportive of attentional process theories of hippocampal function.

The effects of hippocampectomy on alternation behavior and response to novelty

Rats with hippocampal lesions, cortical lesions and unoperated rats were tested for maze activity, spontaneous alternation, food-reinforced alternation, perseveration of the alternation response, and response to a novel alley before and after training. The animals with hippocampal lesions were more active in the maze and deficient on spontaneous and food-reinforced alternation, compared with the animals with cortical lesions and normal animals. Further, the hippocampectomized rats did not perseverate the alternation response and failed to enter a relatively novel alley when tested after maze training. Animals in both control groups (cortical and normal) entered the novel alley with equal frequency on tests given both before and after maze training.

General behavioral activity and its component patterns in hippocampectomized rats

General behavioral activity and its component patterns in hippocampectomized rats

The effect of hippocampectomy and prior experience in exploratory activity in the albino rat

Exposure to a novel alley (E-alley) did not affect exploration of this alley during straight running for reinforcement in later trials for hippocampectomized (HIP) rats. Unoperated (NORM) and neocortical-lesioned (CORT) Ss explored E-alley more than did HIP Ss. Side of final presentation of E-alley affected only NORM Ss, the E-alley presented on the same side as during the initial exposure eliciting more entries. The lack of perseverative entries to the same-sided E-alley in HIP Ss is contrary to predictions based on Douglas’s (1967) model of hippocampal functioning.

Extinction of active avoidance as a measure of passive avoidance in hippocampectomized rats

Rats with large, aspiration lesions of the hippocampus, neocortical lesions, or normal controls were first trained to actively avoid (AA) shock in a one-way shockbox, and later to passively avoid (PA) the previously safe compartment following one forced extinction trial Both hippocampectomized and cortically lesioned Ss displayed deficits in AA. Although no statistical differences were found across groups during PA testing, the possibility of a PA deficit was considered.

Effects of atropine sulfate on single alternation in hippocampectomized rats

Abstract Hippocampectomized and partially neodecorticated rats were trained on single alternation until similar baselines were obtained. The same doses of atropine sulfate were administered to each group and a comparison made of the dose-response curves. The partially neodecorticate, like normal animals, showed an increase in alternation errors with increasing doses of atropine sulfate. In contrast, the hippocampectomized animals showed little increase in errors with any dose. This flattening of the dose-response curve, in conjunction with other evidence, was consistent with the hypothesis that an alternative, noncholinergic system mediated response inhibition in hippocampectomized animals.

An examination of the task and trial parameters in passive avoidance learning by hippocampectomized rats

Abstract The performance of 10 rats with bilateral hippocampal damage, 10 rats with bilateral neocortical lesions, and 10 normal rats was compared on 3 different passive avoidance problems. The results indicated that the hippocampectomized rats were only deficient in the ability to inhibit a trained response as opposed to a spontaneous response, regardless of the number of training trials or motivational level.

Brightness discrimination and reversal in hippocampally-lesioned rats

Abstract Eleven albino rats with large bilateral hippocampal lesions, nine rats with bilateral lesions of the cortex overlying the hippocampus and 10 unoperated controls were trained on a brightness discrimination and tested on the reversal of the discrimination. The three groups did not differ in learning the discrimination, but the hippocampectomized rats were severely impaired in the reversal of the discrimination. Persistent positional responding during reversal characterized the behavior of the hippocampectomized rats. It is proposed that these results are best understood by postulating that hippocampal lesions produce a deficit in attentional processes.

Hippocampal lesions and active avoidance

Abstract Rats with lesions of the hippocampus were impaired relative to normal rats in the acquisition and retention of a one-way active avoidance task, but were superior to normal and partially neodecorticate rats in the acquisition of a two-way active avoidance task. The deficit of rats with hippocampal damage in the one-way task was accentuated when “no shock trials” (CS only) preceded acquisition or reacquisition training. Neocortically lesioned animals showed a slight deficit on both response and latency measures of performance. It is suggested that hippocampectomized rats are deficient in the ability to associate noxious events with cues indicating spatial location.

Retention of a successive discrimination problem by hippocampectomized and neodecorticate rats.

An experiment and its replication are reported in which the postoperative retention of a successive discrimination problem was studied following destruction of the hippocampus and overlying cortex or of the neocortical areas only. Animals with lesions of the posterolateral neocortex showed severe deficits in performance of the problem. Hippocampectomized Ss were also impaired but their deficit was marked by consistent responding to one arm of the maze, i.e., response fixation.

Response perseveration interpretation of passive avoidance deficits in hippocampectomized rats.

Response perseveration interpretation of passive avoidance deficits in hippocampectomized rats.

The maze behavior of hippocampectomized rats under massed and distributed trials

Twenty-four rats with bilateral hippocampal lesions and 24 intact controls were trained for 12 trials in a Lashley III maze. Half of each group had a 10 sec. intertriai interval and the other half a 10 min. intertrial interval. Results indicated a highly significant lesion effect and a tendency for the hippocampectomized Ss to perform better under the more distributed condition.

Effects of hippocampal lesions on maze learning and retention in rats

Clinical observations suggest that bilateral damage of the hippocampal region and fornix may result in severe disturbances of recent memory. Experiments were undertaken to determine whether hippocampal and fornical lesions in rats have deleterious effects on maze learning and retention. A fourteen-choice mutiple-T alley maze was employed. The effect on postoperative initial learning was studied in fifty-two rats. One group of animals sustained bilateral and another group unilateral hippocampal or fornical lesions. A third group served as operated controls and received lesions in the same neocortical areas as the hippocampectomized animals. A fourth group of one hundred four rats were used as nonoperated normal controls. The animals with hippocampal or fornical lesions showed a significantly defective maze learning compared with the operated and nonoperated controls in terms of total errors and time required to run the maze. Deficit in maze performance also followed removal of the mamillary bodies. Thirty-eight rats were used in retention experiments and sustained either bilateral or unilateral hippocampal lesions, or removals of the neocortex overlying the hippocampus. All animals in this series were incompletely trained preoperatively and retrained postoperatively. The hippocampectomized rats suffered significant impairment in maze retention and relearning compared with the operated controls. It was concluded that lesions of the hippocampus, fornix, and mamillary bodies seem to interfere with maze learning and retention, when incompletely trained preoperatively. The data obtained do not allow any conclusions as to how these structures are involved in learning and retention, neither as to their relative importance compared with other brain structures like neocortex or thalamus, both of which are previously known to influence learning and retention.