Development of 24 hour retention of escape learning in neonatal C3H mice

The development of 24-hr memory of an escape response in neonatal C3H mice was examined in 2 experiments. In experiment 1, separate groups of mice received 25 trials of escape training for 3 consecutive days (24 hour Inter-session-interval) beginning at 5, 7, and 9 days of age. Several different measures demonstrated witin-session improvement for all ages on all test days. However, between-session improvement which was not due to maturation did not occur until after 9 days of age. In experiment 2, separate groups of mice received 25 escape training trials at either 8 or 10 days of age, and were retested 24 hrs later. Comparisons of the retest scores with original training scores as well as with littermate controls without prior training experience, showed that 8-day old mice failed to show retention effects of prior training, whereas 10-day old mice performed better on the retention test than they had on original training, as well as better than controls without previous training. The results suggest that 24-hr memory of the escape task develops at 9–10 days of age in the C3H mouse.     

Learning and retention of a discriminated escape response in infant mice

Separate groups of mice received 25 training trials in a shock-escape T-maze at 7,9,11, or 13 days of age, followed by retention trials 24 hr later. During original training, all mice were trained to the goal opposite their 1st-trial choice-point turn. During the retraining sessions, half of the mice in each age group received an additional 25 trials to the same goal as original training, while the other half was trained to the goal opposite that of original training. All age groups demonstrated improved performance during training in reaching the choice point, although only mice 9 days of age and older indicated an increase in correct choice-point turns. During retraining, only the groups trained at 11 and 13 days of age showed significant effects of prior training.     

Development of learning and memory in mice genetically selected for differences in brain weight

Mice selected for high (H), medium (M), and low (L) brain weight were trained to the goal arm opposite their preference in a shock-escape T-maze at 7, 9, 11, or 13 days of age. Twenty-four hours later, half of the trained groups at each age received additional training to the original goal, whereas the other half was trained to the opposite goal. Maturational control groups without prior training were trained on the selected retest days for the previously trained groups. Improvement in correct choice-point turns during training was suggested for the H-line by 9 days of age and by 11 days of age for the M- and L-lines. During retraining, H-line mice demonstrated 24-hr retention effects by 10 days of age, whereas 24-hr memory was not indicated for M- and L-lines at any of the ages investigated. These results indicate that the onsets of learning and memory were influenced by genes affecting brain weight, in that H-line mice demonstrated more rapid brain growth as well as heavier brain weights at every age studied as compared with M- and L-line mice which showed similar brain growth functions.     

Acquisition and retention of a passive-avoidance task as a function of age in mice

In Experiment I groups of mice between 16 to 100 days of age were tested for retention of a passive-avoidance response between 1 min and 96 hr following a single training trial at 2 shock intensities. In general, although almost all age groups displayed reliable retention at all retest intervals, some retention losses were found among the youngest age groups at the longer retention intervals. Higher shock intensity resulted in longer retest latencies, primarily among the youngest mice. In Experiment II mice 16, 25, and 100 days of age were trained to criterion on the passive-avoidance task and retested on a single trial following retention intervals of 24, 96, 192, and 384 hr. Young mice exhibited severe retention losses relative to 100-day-old mice at the longer intervals, even though they did not show deficiencies in acquisition. Neurological maturity at the time of original training appears to account for the age-related memory differences.     

Hypothermia causes adult-like retention deficits of prior learning in infant mice

Nine-day-old S-W mice receiving deep body hypothermia or hyperthermia immediately after escape training were retested 1 or 24 hr later. Results indicated that hypothermia impaired 24-hr retention but had no effect upon 1-hr memory. Hyperthermia had no effect, with the mice demonstrating retention of the escape response at both retest intervals. In Experiment 2, administration of hypothermia or hyperthermia 23 hr after original training had no effect upon memory nor did either treatment produce motoric deficits upon retest 1 hr following thermal exposure. Experiment 3 indicated that hypothermia administered immediately after training produced retention deficits directly related to amount of body temperature reduction following hypothermia. These data are similar to those obtained with adult mice and suggest that memory processess occurring in 9-day-old mice may represent the onset of functioning of processes underlying adult long-term memory.     

Age effects in the acquisition and retention of active and passive avoidance learning by rats

Three groups of 8 male albino rats within each of the age ranges 24, 50, and 100 days were trained on an active avoidance task to a criterion of 10 successive avoidances. The number of trials to criterion was found to be a monotonic function of age. One group at each age was tested immediately thereafter for passive avoidance of the conditioning chamber, another group was tested for passive avoidance after 25 days, and the third was tested for retention of active avoidance after 25 days. Groups at 50, 75, and 125 days were used as controls for the active avoidance retention groups. All animals took significantly fewer trials to relearn the active avoidance after 25 days than did controls on the acquisition of the original learning task. On passive avoidance 24-day olds performed less efficiently than the older groups and failed to show any retention after 25 days.     

Developmental aspects of passive and active avoidance learning in rats

In Experiment 1, groups of rats 16, 19, 25, 32, and 90 to 120 days of age, were tested for retention of a passive avoidance response 2 min or 24 hr following a single training trial. Passive avoidance learning improved markedly with age, and retention over a 24-hr interval was complete for all age groups. In Experiment 2, rats 19, 25, 32, and 90 to 120 days of age were trained in a simple, active avoidance task. A trials-to-criterion measure indicated that learning was relatively independent of age, although 19-day rats were somewhat inferior to older rats. The occurrence of differences in passive avoidance learning through developmental ranges in age where simple active avoidance is little affected suggests that inhibition of responding may be selectively influenced by maturational variables.     

The effect of criterion level on the acquisition and retention of a 1-way avoidance response in young and old rats

Young (23–25 days old) and adult (80–84 days old (rats) n = 8, per group) were trained on an active-avoidance task to a criterion of 0, 5, or 15 consecutive correct trials and then tested for retention 30 days later. In original training, both age groups acquired the response in about the same number of trials when the criterion was set at 5/5 but young subjects required significantly more trials than older subjects to learn the response under the 15/15 criterion. In retraining, both age groups performed equally well when original training was to the 15/15 criterion although adults retained significantly better than weanlings when original training was to 5/5 correct responses.     

Novel experience prior to training attenuates the amnestic effects of posttraining ECS

In this article, mice were given a novel exploratory experience 1 hr prior to training on a one-trial inhibitory avoidance task or a Y-maze shock-motivated visual discrimination task. Half of the animals in each group received immediate posttraining electroconvulsive shock (ECS) delivered through implanted cortical screws. Retention was tested 24 hr later. In the inhibitory avoidance task, retention was assessed by the response latencies on Day 2. In the Y-maze, the discrimination was reversed on Day 2 and retention of the original discrimination was assessed by errors made on six reversal training trials. Comparable results were obtained in the two tasks: ECS impaired retention in controls not given the novel experience but did not affect retention in mice given the novel experience. These findings are interpreted in terms of previous evidence, which suggests that ECS-induced amnesia may be mediated by the release of brain beta-endorphin.     

Straight-alley escape behavior in infant mice: effect of shock intensity

Separate groups of Swiss-Webster mice between 5-15 days of age received 25 training trials in a straight-alley escape task at 1 of 4 shock intensities, ranging from .1-.8 mA. An increase in shock level led to better escape performance at all ages, although the amount of improvement varied directly as a function of age. The results supported earlier work suggesting that the competing response measure was the most useful index of improved escape behavior at the early ages. Running speeds did not indicate improved within-session escape performance at any age or shock level, although speeds clearly reflected maturational and motivational differences between groups.     

Experience-hormone interactions and maternal behavior in rats

Three studies were conducted to determine the effects of reproductive condition and hormonal background on the acquisition and retention of a prior maternal experience. In the first study five experience conditions were compared. All animals gave birth and received either no postpartum contact with pups or 1/2 hr, 1 hr, 2 hr or 24 hr of pup contact and were tested for maternal behavior 10 days later. Animals receiving pregnancy and parturitional experience, but minimal social experience with young, exhibited significantly longer maternal onset latencies than did groups receiving 2 or 24 hr of prior experience; also, comparisons of 10- and 30-day retention intervals indicated that animals tested 10 days after a 24-hr experience exhibited shorter latencies than those tested 30 days later. Thus, the duration of the postpartum experience and the interval since prior experience both affect the level of maternal responsiveness shown. In the second study six groups of females were tested. Four groups were permitted one day of interaction with pups either after parturition (primiparous animals) or following pup induction procedures (nulliparous animals) and were tested for their maternal responsiveness to foster pups 25-35 days later, either on day 19 of a subsequent pregnancy or following resumption of estrous cycling. For most measures of maternal behavior there were significant main experience and test effects; experienced and pregnant animals exhibited shorter latencies to retrieve, lick and crouch over pups than did inexperienced and cycling animals, respectively. Significant interactions were also found for genital licking latency as well as for retrieval and crouch frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Escape learning in infant mice as a function of drive level and drive shifts during acquisition

Separate groups of 9-day-old Swiss-Webster mice began straight-alley escape training at .1 or .4 mA. After 12 trials, half of the mice in each group were shifted to .4 or .1 mA, respectively, whereas the remaining half continued at their orginal level for an additional 12 trials. Twenty-four hours later, half of each of the 4 shock-level groups were retested at .1 mA, half at .4 mA. The result indicated that those groups which made a large number of competing responses during early trials and showed a gradual reduction over training trials (.1-.1 and .1-.4) emitted the fewest number during retest at either shock level. In contrast, those groups with either limited (.4-.1) or no (.4-.4) opportunity to decrease competing responses during training showed evidence of poor (.4-.1) and no (.4-.4) retention of learned inhibition of that response. Running speed was clearly a performance measure, as it only reflected existing shock levels during both training and retention trials.     

Effects of protein synthesis inhibition on memory for active avoidance training.

Inhibition of brain protein synthesis by anisomycin and acetoxycycloheximide was studied in mice for its biochemical and behavioral effects. By employing both drugs in low doses in a series of injections, we were able to maintain inhibition of protein synthesis of 80% or greater for up to 14 hr without causing detectable permanent physiological impairment. The drugs were employed as amnestic agents in mice trained to avoid footshock in a T-maze. As the duration of inhibition increased, the percentage of mice classed as amnesic increased. This amnesia could be reduced by increasing (a) the rate of acquisition, or (b) the number of training trials. Anisomycin was shown to cause a significant degree of amnesia for the escape component as well as the avoidance component of the learning. A single injection of anisomycin given 15 min prior to training did not cause significant changes in the acquisition or retention of avoidance conditioning, when comparison was made with saline-injected controls. Only additional injections given after training to prolong inhibition caused amnesia. Thus, those injections critical in obtaining amnesia were given at a time at which interference with acquisition could not have occurred, so the results bear clearly on memory processes.     

Influence of training strength on amnesia induced by pretraining injections of cycloheximide

Cycloheximide-treated mice and saline controls were given one-trial training in a black and white, step-through, passive avoidance box. The following parameters were shown to affect the degree of amnesia in cycloheximide-treated animals: (a) shock intensity; (b) shock duration; (c) original latency to enter the shock compartment; and, (d) retention interval (periods used were 24 hr and 1, 2, and 3 weeks). When those parameters are measured and controlled, highly consistent amnestic effects can be obtained. In the present experiment, certain groups showed over 80% amnesia while the controls showed less than 2% amnesia. Amnesia could best be obtained in passive avoidance when animals were trained to just under the asymptote of the acquisition curve. Measures of inhibition of protein synthesis by cycloheximide showed differences among 5 strains, but there were no significant individual differences within a strain.     

The effects of ECS and hypoxia on information retrieval

Seven groups of rats were trained in a passive avoidance task. All groups were tested 24 hr later to assure retention of the task. One group of animals was then administered an ECS treatment. Three groups were administered an ECS treatment under conditions which eliminate or reduce the production of hypoxia. Another group was exposed to a nitrogen atmosphere to induce hypoxia by a different method. All groups were then retested for retention of the passive avoidance task 3 and 24 hr later. The results indicate that ECS or nitrogen inhalation (both hypoxia producing treatments) produce an amnesia for the passive avoidance task at the 3 hr retest but not at the 24 hr retest. In contrast, minimizing or eliminating the hypoxic consequences of an ECS treatment does not result in a temporary amnesic effect.     

Increased training in an aversively motivated task attenuates the memory-impairing effects of posttraining N-methyl-D-aspartate-induced amygdala lesions.

This study was designed to examine the effect of variations in the amount of preoperative training on the retention deficit produced by posttraining lesions of the amygdaloid complex (AC). Rats received 1, 10, or 20 training trials in a footshock-motivated escape task 7 days before receiving N-methyl-D-aspartate lesions of the AC. Inhibitory avoidance retention performance, which was measured 4 days postoperatively, indicated that increased training improved retention in AC-lesioned animals as well as in control animals. The retention performance of AC-lesioned animals was impaired when compared with that of controls; however, the impairment was partially attenuated by increased preoperative training. The finding that AC-lesioned animals displayed greater locomotor activity on the retention test compared with nonlesioned controls suggests that the increased activity may have contributed to the impaired inhibitory avoidance retention performance. Two days after the retention test, some of the AC-lesioned animals were subsequently trained on a continuous multiple-trial inhibitory avoidance response in the same apparatus. AC lesions did not block acquisition or retention of the task. These findings suggest that the amygdala may not be a critical site for the permanent changes mediating stimulus-affect associations based on extensive training.     

Noncontingent footshock attenuation of retrograde amnesia: a generalization effect

Mice were either well trained and rendered amnesic with transcorneal electroconvulsive shock (ECS) or poorly trained on a one-trial inhibitory avoidance task and given a retention test 24 and 48 hr later. Noncontingent footshock administered either 1 hr after the training or 1 hr after the 24 hr test significantly increased retention latencies of groups which had received training and ECS, as well as those of groups which were poorly trained. These findings suggest that animals which are partially amnesic or poorly trained are able to generalize the effects of a subsequent NCFS experience to the inhibitory avoidance training task.     

Aging and water submersion in C57BL/6J mice: Initial performance and retest as a function of recovery and water temperature

A total of 300 C57BL/6J male mice of 5 age groups (350, 470, 615, 720, or 845 ± 30 days of age) ranging from 50 to 120% of their expected life span were tested in a water submersion task with water temperature maintained at 23.5°C. Mice were retested to evaluate recovery from this stressor at either 24 or 168 hr after initial test. The retest was conducted at 1 of 3 temperatures (12.5, 23.5, or 34.5°C). On the initial water submersion test at 23.5°C, significant effects of advanced age were evident, with the oldest group (845 days) having the shortest time to submersion. No significant difference was evident between the two younger age groups with the longest time to submersion found in the middle (615-day old) group. In the 2 oldest groups, submersion time scores decreased progressively and significantly. On the retest, significant effects were found for water temperature. The effects of water temperature were linear and consistent across ages and conditions with increasing temperature up to the maximum used in this experiment, resulting in longer time to submersion. The longer recovery time (168 hr.) to retest yielded inconsistent results with longer time to submersion scores found only in the 350 and 720-day old groups.     

Ontogeny of short- and long-term memory capacities for passive avoidance training in undernourished mice

To assess the effects of early postnatal undernutrition upon the developing abilities of infant and juvenile mice to acquire and retain a passive-avoidance response, we reared mice following birth in either “normally nourished” or “undernourished” conditions by maintaining litter sizes of 6 or 16, respectively. At ages ranging from 7 to 21 days of age, mice from each nutritional condition were trained to withhold stepping off from a small vibrating platform in order to avoid shock. Following training to a common criterion, separate groups of mice were retrained to the same criterion either 1 or 24 hr later. From the comparisons with yoked control groups at each age and retention interval, we conclude that although undernutrition results in some age-related differences in the ability to withhold responding, these are quite small during acquisition within each age group. In contrast, the retention data suggest that undernutrition delayed the development of both short- and long-term memory abilities on this task. In general, these results are similar to earlier data involving discriminated shock-escape wherein undernutrition had little apparent effect upon acquisition at the early ages but rather marked effects upon developing memory systems.     

Differing role of dendritic cells and macrophages in the induction of delayed-type hypersensitivity responses to PPD.

In order to study the antigen-presenting cell (APC) requirements for the priming of delayed-type hypersensitivity (DTH), murine spleen cells were fractionated on bovine serum albumin gradients, pulsed in vitro with tuberculin, and then injected subcutaneously into normal mice. The other footpad was challenged with tuberculin between 24 hr and 7 days later and swelling was measured 2 hr and 18-24 hr after challenge. Optimum priming for 2-hr and 24-hr responses at 7 days was achieved by an injection of 5 X 10(5) tuberculin-pulsed intermediate-density Fc + ve cells. Time-course studies revealed that the 2-hr component could be elicited as early as 24 hr after injection of pulsed APC, while the 24-hr component became significant at 3 days. Elimination of T cells or B cells did not affect the response. Injection of pulsed APC into allogeneic mice primed the 2-hr but not the 24-hr component. Neither pulsed high-density cells (mostly T cells) nor pulsed dendritic cells (DC) primed mice for these responses. Failure to elicit DTH after injection of tuberculin-pulsed DC was due to their failure to prime the 2-hr component, which other authors have shown to be a prerequisite for the appearance of the later components. That DC did prime the MHC-restricted 24-hr component was demonstrated by protocols involving the use of both macrophages and DC as APC.