Methylphenidate, amygdalectomy, and active avoidance performance in the rat

Amygdalectomized and control rats were given 400 active avoidance training trials in a shuttle box. Control animals received 0, 4, 8, or 16 mg/kg of methylphenidate throughout acquisition. Amygdalectomized animals were given the first 200 trials without drug, followed by 200 trials with drug. The administration of methylphenidate produced an abrupt and large improvement in performance in the amygdalectomized animals. One month after acquisition under the drug, retraining without drug revealed a significant retention effect for the three amygdaloid-drug groups relative to the nondrug-amygdaloid group. These results indicate that although amygdalectomy impairs the performance of avoidance responses, it does not prevent the learning or retention of such responses. Since methylphenidate appears to act primarily on dopaminergic mechanisms, the possible influence of amygdalectomy on such mechanisms is discussed.     

The High Relief Finger Maze for Human Learning

Albino rats in independent studies were administered varying dosages of diazepam and methylphenidate prior to a daily shock traumatization experience in infancy. All animals were tested on avoidance conditioning in adulthood. Both drugs were found to be effective in modifying the typically obtained shock deficit. The results failed to substantiate that increased dosage level resulted in more effective modification of trauma effects. Delayed consequences of methylphenidate administration included modification of central nervous system reactivity as manifested in quicker reaction times and growth depression as manifested in lessened body weights in this group in comparison to the diazepam group. An additional feature of the study was the finding that male and female animals responded differently to the drug and shock experiences.     

Some effects of methylphenidate on stimulus control of ratio avoidance behavior in the rat

After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response-shock interval, delaying shock, and the second component differed only in that four bar-presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. At a dosage of 2 mg/kg, methylphenidate given intraperitoneally decreased shock frequency during FR 4 periods while FR 1 behavior was not affected; at 4 mg/kg, stimulus control of avoidance responding was impaired during both components. Results at 4 mg/kg were partially confirmed by two animals exposed to an FR 4 avoidance schedule which included a warning signal but with different parameters. Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio-avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non-drug) periods.     

Avoidance of heat by rats: Effects of thermal context on rapidity of extinction

Rats were trained to avoid radiant heat in a one-way, jump-up apparatus. The animals that could avoid heat responded more frequently and more rapidly than did yoked controls that received heat, but for whom no avoidance contingency was deliberately arranged. Control animals trained with light, rather than heat, did not learn to avoid. Using this jump-up avoidance, rats were trained to avoid heat in a room maintained at 27°C. They were then given a series of extinction trials, with no heat presentations, with the temperature maintained at either 27 or 7°C. Placing the rats in a cold environment facilitated extinction of heat avoidance behavior, but only in animals that had previously experienced heat while they were in the cold. Prior heat experience administered in a warm, rather than cold, context was not sufficient to potentiate the effect of ambient temperature on avoidance extinction. Implications of these results for theories of avoidance learning are discussed.     

Chronic oral methylphenidate induces post-treatment impairment in recognition and spatial memory in adult rats

Recent pre-clinical research has indicated that chronic treatment with methylphenidate (Ritalin^®) in young animals can result in lasting and potentially detrimental alterations in brain function that can persist into adulthood. Chronic methylphenidate-induced neuronal alterations may result in behavior and cognitive deficits that include increases in behavioral responses and impairment in recognition memory. This study compared the cognitive consequences following chronic treatment with two doses (5 and 10 mg/kg) of methylphenidate on recognition and spatial memory in adult male Long-Evans rats using an established oral dosing procedure. The animals were then tested in the Object Recognition test at 14 days post treatment and the Object Placement test at 21 days post treatment. The results indicate that repeated exposure to oral methylphenidate impaired the performance of rats in these tests. The current findings add to recent research demonstrating negative consequences in rats pre-treated with methylphenidate, and extend previous findings to include deficits in spatial recognition memory.     

What is both necessary and sufficient to maintain avoidance responding in the shuttle box?

To learn what maintains the frequency of shuttle box avoidance responses, male rats from the Berkeley S₁ strain, after 200 trials of standard discriminative avoidance training, were given 100 additional trials under one of four different conditions. Responding at the maximum rate was maintained when animals performed under the training conditions or when responses continued to terminate the warning signal immediately, even though shock was never given for failing to respond. In contrast, avoidance responding was reduced markedly if, and only if, trials were given in which the signal ceased to terminate immediately (i.e. it shut off either well before or well after a response). This decrement occurred even though avoidance responses continued to avert shock. Thus, under the conditions of this experiment prompt signal offset was both necessary and sufficient to maintain the occurrence of well-established shuttle box avoidance responses.     

Facilitation of a Distributed Shuttle-Box Conditioning with Posttraining Intracranial Self-Stimulation in Old Rats

Old Wistar rats (16–17 months) were trained in a two-way active avoidance task for 5 consecutive days (10 trials/day). Immediately after each training session a lateral hypothalamic intracranial self-stimulation session (ICSS group) or a sham-treatment session (Control group) was given to the animals. Long-term retention was tested 7 days after the last acquisition session. ICSS treatment led to a significant improvement in acquisition. In the long-term retention session the level of avoidance in both groups was similar to that achieved in the last acquisition session, although differences among groups failed to reach statistical significance. These results are compared with those obtained in previous experiments with young adult rats. While ICSS facilitated the process of acquisition in both young and old rats (however, it was much more powerful in young animals), further experiments are needed to elucidate whether this effect is long-lasting in old rats, as occurs in young adult subjects.     

The effects of overtraining on flooding of jump-up and shuttlebox avoidance responses

Two experiments are reported which test the effects of overtraining (2, 4 or 6 days) on the efficacy of flooding (response-prevention) in hastening the extinction of jump-up and two-way shuttlebox avoidance responses. In the jump-up box, overtraining reduces the effectiveness of flooding in two ways: Rats trained for 6 days and given a flooding treatment are more resistant to extinction than rats trained for only 2 or 4 days and given a flooding treatment. By contrast, rats trained for 6 days and given a control treatment are less resistant to extinction than control rats trained for 2 or 4 days. In the shuttlebox, overtraining neither reduces the effectiveness of flooding in hastening avoidance response extinction, nor reduces the resistance to extinction of control animals. Implications of these different effects of overtraining on jump-up and two-way shuttlebox responses are discussed.     

Paradoxical Sleep Deprivation and Sleep Recording Following Training in a Brightness Discrimination Avoidance Task in Sprague–Dawley Rats: Paradoxical Effects

Previously, we reported that posttraining paradoxical sleep deprivation (PSD) resulted in an enhancement of the subsequent avoidance performance for rats trained for 15 trials in a Y-maze brightness avoidance discrimination task. A series of experiments were conducted to try to further understand the reasons for results which were contrary to those of the bulk of the sleep-learning literature. Experiment 1 investigated the effectiveness of the PSD technique. Rats (N= 4) were sleep recorded while residing on a “swimming pool” apparatus for 24 h. Compared to their baseline values, all animals showed a very large reduction in paradoxical sleep and spent significantly more time awake. Slow-wave sleep was unchanged. In Experiment 2, proactive motor effects were tested. Rats were deprived of PS for 24 h and then tested in a hole board motor activity task. There was a slight effect of PS deprivation on the day following the PSD and no effect when the rats were retested 1 week later. Experiment 3 investigated possible proactive effects of PSD on avoidance performance. Rats exposed to PSD in the 24 h before training in the Y-maze task did not demonstrate any facilitative effect on the subsequent avoidance performance. Experiment 4 investigated the possibility that the PSD facilitative effect could be due to partial training. Rats were given 75 acquisition trials in the brightness discrimination Y-maze avoidance before being subjected to 24 h of PSD. PS-deprived animals showed superior avoidance scores compared to non-PSD controls when retested 24 h later. In Experiment 5, the same strain of rats (N= 11) were sleep recorded after exposure to a partial acquisition in a Y-maze brightness avoidance discrimination task. They were then continuously monitored for 4 consecutive days. The percent PS for the Trained rats was significantly lower than that for the Control animals. This drop in percent PS was not confined to any particular time period in the 24-h day. None of the other sleep parameters reached significance. Analyses of the present results suggest that PSD exerts its facilitative effects on posttraining consolidation processes. We present arguments suggesting that PSD can have effects opposite to those generally reported, in animals demonstrating poor avoidance abilities, in an avoidance task.     

Preconditioning of reinforcing properties to an exteroceptive feedback stimulus

Three groups of rats were given Pavlovian preconditioning by means of a yoking procedure and subsequently trained to avoid. One group received a light stimulus during preconditioning at the same times as the master avoiding animals received an exteroceptive feedback stimulus. During the subsequent avoidance training, this group was then given the same light stimulus as a feedback stimulus on successful avoidance trials. The group learned two-way avoidance in about the same number of trials as one-way avoidance is typically learned and substantially faster than two other control groups. These data indicate that feedback stimuli develop reinforcing properties by a Pavlovian mechanism. The data of the control groups indicate that feedback stimuli do not provide “information” about responding in the present situation.     

Classical Avoidance without a warning stimulus

White rats were scheduled to be shocked every 15 sec; but they were given a limited time interval between shocks when they could prevent the next scheduled shock from occurring if they pressed a lever. The duration of this limited avoidance period was varied, as was its location within the interval between scheduled shocks. Response rate, shock frequency, and the temporal distribution of lever presses were examined. Conditions were generated in which the formation of a temporal discrimination prevented the animals from maintaining successful avoidance behavior.     

Immobility as an avoidance response, and its disruption by drugs

Much of the available literature on avoidance behavior is based on responses which require the animal to run, lever-press, or to make some active response to avoid noxious stimulation. The purpose of Experiment I reported in this paper was to determine whether animals can learn to sit or stand motionless in order to escape or avoid electric shock. Five experimental rats were given escape-avoidance training, while five yoked control animals received electric shocks without any response-related contingency. It was shown that an immobility avoidance response, as distinct from the unconditioned “freezing” response to shock, can be trained. The results of Experiment II (30 rats) revealed that this response is more readily acquired at higher shock intensities than at lower ones, provided escape by jumping is prevented at the high shock intensities. The effects of six doses of each of three drugs on the immobility avoidance response were studied in Experiment III (13 rats). Methylphenidate, chlorpromazine, and imipramine all produced a decrement in the immobility response, but the pattern and amount of the effects of the three drugs were quite different, one from the other. The implications of these findings for a general theory of avoidance behavior and for drug screening are discussed.     

CGS 5649 B, a new compound, reverses age-related cognitive dysfunctions in rats.

CGS 5649 B improves the learning performance of aged rats in a one-way active-avoidance situation. If, under reversed conditions, treated aged rats are also tested for passive avoidance, they show "place learning," which our findings have demonstrated to be typical of young rats. The effects of the substance are not confined to these experimental models nor are they species specific: it also facilitates passive avoidance in mice and social learning in rats. The compound is effective if administered before or immediately after the learning trial.     

Shock-induced aggression as a function of prior experience with avoidance, fighting, or unavoidable shock

Rats were trained in shock-induced aggression, free operant avoidance, or were presented with unavoidable shocks. Fighting in response to shock was subsequently measured by intermatching individual animals that had received the three training procedures. The fighting probabilities of animals with histories of avoidance and dominant animals with histories of fighting were higher than the fighting probabilities of non-dominant fighting rats or rats with a history of unavoidable shocks. Animals with higher fighting probabilities disrupted avoidance baselines more than animals with lower fighting probabilities. Control experiments suggested that fighting decrements produced by administration of prior grid-shock were due to the acquisition of behaviors incompatible with aggression.     

MODIFICATION OF SHUTTLE BOX TO IMPROVE RATE OF AVOIDANCE LEARNING IN RATS

W allgren , H. & S avolainen , S. Modification of shuttle-box to improve rate of avoidance learning in rats. Scand. J. Psychol ., 1962, 3 , 78–80.—Acquisition by rats of a conditioned avoidance response seems to be retarded in an ordinary shuttle-box by the necessity to re-enter the compartment where shocks have previously been received. To avoid this, a four-compartment box was introduced in which the animals can proceed in one direction. Rats were given either continuous trials until nine avoidance responses were made during 10 consecutive trials, or 30 trials per day until 27 correct responses were made during one session. With both methods of training, the rate of learning was approximately 40 per cent more rapid in the four-compartment box than in the ordinary shuttle-box.     

Nimodipine accelerates recovery from the hyperemotionality produced by septal lesions

Rats with large electrolytic lesions of the septal area were given the calcium channel antagonist nimodipine (70 micrograms/kg, ip) or its vehicle on the day of surgery and for 3 subsequent days. They were tested for emotionality and compared to control rats for 10 days beginning on the third day after surgery. Forty days after surgery all animals were trained in a two-way active avoidance task for 120 trials. Nimodipine reduced the hyperemotionality found after septal lesions as early as the first test day, and increased the rate of recovery toward control levels on subsequent days. Both septal-lesion groups exhibited more avoidance responses than controls, even though the intertrial crossings were enhanced only in rats with septal lesions that did not receive nimodipine.     

The fearless avoiders: Comparison of various strains of rats in an active avoidance task

The effect of exploratory activity and emotional reactivity on the acquisition of active avoidance learning was assessed in rats. Four strains of rats selectively bred for a high or low degree of either of the two traits (Maudsley emotionally reactive animals, Maudsley emotionally non-reactive animals, high rearers, and low rearers) and a control strain (randombred animals) took part in the experiment. Significant differences were found between strains in the number of animals showing active avoidance behaviour. Emotional reactivity was shown to facilitate active avoidance behaviour and so did, unexpectedly, a low degree of exploratory activity. An attempt was made to explain the latter result in terms of differences in channel capacity between high and low exploring animals and the ensuing differences in attention focus on the relevant stimulus for the test situation.     

Hormonal dissociation of limbic lesion effects on shuttle box avoidance in rats.

Rats with septal or hippocampal lesions, relative to normal rats, showed facilitated acquisition of a shuttle box avoidance response. The rats with septal lesions were also highly resistant to extinction compared with normal rats. When the same lesion effects were examined in hypophysectiomized rats, the animals with septal lesions continued to show facilitated performance, and those rats with hippocampal lesions performed no differently than nonoperated control animals. These findings are consistent with the hypothesis that the facilitated avoidance performance found in rats with hippocampal lesions is attributable to lesion-induced changes in hypophyseal activity, but similar changes induced by septal lesions are not.     

The Effects of Estradiol on Avoidance Learning in Ovariectomized Adult Rats

The present study examined the effects of ovariectomy and subsequent estradiol replacement on learning in young adult rats using a set of instrumental avoidance paradigms differing in the nature and extent of prior experience in the learning context. Thus, one group of animals was placed directly into avoidance learning (AV). A second group was trained on an appetitive task first, and then transferred into the aversive context (AP-AV). The third group was exposed to the training context without any specific appetitive response requirement, and then required to learn an active avoidance response (Context-AV). We found that estradiol (OVX+E) impaired avoidance acquisition in all cases relative ovariectomized controls (OVX). In contrast, while avoidance learning is improved following appetitive training or context exposure in both OVX+E and OVX animals, the OVX+E animals profit to a greater extent from the appetitive or context experience than do the OVX controls. We suggest that this difference may be due to enhanced attentional processes or improved hippocampal processing of contextual factors. Thus, estradiol negatively influences simple associative avoidance learning in ovariectomized rats, but appears to promote positive transfer.     

The effects of estradiol on avoidance learning in ovariectomized adult rats

The present study examined the effects of ovariectomy and subsequent estradiol replacement on learning in young adult rats using a set of instrumental avoidance paradigms differing in the nature and extent of prior experience in the learning context. Thus, one group of animals was placed directly into avoidance learning (AV). A second group was trained on an appetitive task first, and then transferred into the aversive context (AP-AV). The third group was exposed to the training context without any specific appetitive response requirement, and then required to learn an active avoidance response (Context-AV). We found that estradiol (OVX+E) impaired avoidance acquisition in all cases relative ovariectomized controls (OVX). In contrast, while avoidance learning is improved following appetitive training or context exposure in both OVX+E and OVX animals, the OVX+E animals profit to a greater extent from the appetitive or context experience than do the OVX controls. We suggest that this difference may be due to enhanced attentional processes or improved hippocampal processing of contextual factors. Thus, estradiol negatively influences simple associative avoidance learning in ovariectomized rats, but appears to promote positive transfer.