Free operant avoidance in rats under increased nitrogen pressures.

Rats performed on a free operant avoidance schedule with a response-shock interval of 20 sec. and a shock-shock interval of 2 sec. Avoidance response rates increased and shock frequency decreased when the rats were exposed to elevated pressures of both air and a nitrogen-oxygen mixture in a hyperbaric chamber. Increases in response rates were related to raised partial pressures of nitrogen at 89.0 psi and 111.3 psi. Conditional probabilities of interresponse times indicated that increases in response rates were not due to disruption of temporal discrimination. Increased avoidance rates under pressure suggested direct excitatory effects of high pressures of nitrogen.     

The effects of cocaine on behavior maintained by timeout from avoidance.

Rats were trained on concurrent schedules under which responses on one lever postponed shock (avoidance) and responses on the other lever produced brief (2-min) periods of signaled timeout from avoidance. For 6 rats, timeout from avoidance was programmed on a variable-interval 45-s schedule that generally resulted in rates that were lower than those on the avoidance lever. For another 6 rats, timeout was arranged on a variable-ratio 15 schedule that produced higher baseline rates. Cocaine (3 to 40 mg/kg) produced large, dose-dependent increases in behavior maintained by timeout in both groups of rats. Avoidance responding was also generally increased by cocaine, but the increases were of lesser magnitude. Increases in response rates were seen across a broad range of doses on behavior maintained by either interval or ratio schedules, an outcome that was unexpected on the basis of most studies of cocaine on food-maintained behavior. These results were similar to those of previous studies of the effects of amphetamine on behavior maintained by timeout from avoidance and suggest that stimulant drugs affect behavior maintained under a shock-postponement schedule differently than they affect behavior maintained by timeout from avoidance.     

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.     

Open-field and avoidance behavior after neostriatal lesions in male and female rats.

The behavioral effects of lesions of the anterodorsal or posteroventral parts of the caudate-putamen were studied in adult male and femle rats that were gonadectomized or left untreated prior to brain surgery. Anterodorsal (ADC) lesions consistently impaired acquistion of one-way avoidance behavior and tended to interfere with the development of a two-way avoidance response; comparable effects were observed in gonadectomized and intact animals of both sexes. By contrast, ADC lesions increased activity in the open field only in intact females and increased rearing only in ovariectomized females. Posteroventral caudate (PVC) lesions caused transient aphagia and adipsia in both sexes but did not consistently affect open-field activity or the acquistion of one-way avoidance responses by either sex. These lesions profoundly impaired acquistion of shuttle box avoidance responses by intact males. By contrast, castrated males and intact and ovariectomized females with PVC lesions avoided normally in the shuttle box. The present results suggest that localization of behavioral functions within the striatum differs with the sex of the subject, in part because of activational effects of gonadal hormones.     

Acquisition and retention of active avoidance behavior in previsual rats

The ability of previsual rats to acquire and retain an active avoidance response at intervals ranging from 0 min to 48 hr was examined in five experiments. Experiments 1 and 2 demonstrated that improvement in avoidance responding over trials was a training effect. Experiments 3 and 4 demonstrated that there was no evidence of retention of the avoidance response over retention intervals ranging from 15 min to 48 hr. Testing at intervals of 0-30 min in Experiment 5 indicated that 10-day-old rats could retain the response over intervals ranging from 0-15 min, but not over a 30-min interval. However, even at the very short intervals (5-15 min), there was evidence of a retention deficit. In general, the results suggest that previsual rats have sufficient memory capabilities to acquire an active avoidance response and to retain it over a 15-min interval. However, without intervention, e.g., reactivation, a retention deficit appears almost immediately, and retention loss seems complete within 30 min. This procedure and phenomenon may prove useful in allowing an immediate assessment of variables believed to alleviate retention loss and in eliminating the influence of many extraneous variables that could alter the retention performance of developing animals.     

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.     

Role of pituitary-adrenocortical system in mediating avoidance behavior of rats with septal lesions.

Three experiments examined the hypothesis that the effects of septal lesions and systemic injections of scopolamine on avoidance acquisition could be attributed to the effects of either of these treatments on adrenocorticotropic hormone (ACTH) secretion. Septal lesions and scopolamine facilitated 2-way conditioned avoidance response acquisition, and the lesions retarded passive avoidance acquisition. However, neither the injections of dexamethasone, a synthetic glucocorticoid which inhibited ACTH secretion as did septal lesions, nor injections of ACTH which mimicked the facilitatory effects of scopolamine on basal ACTH secretion, affected avoidance in these paradigms. Thus, the main hypothesis was not supported. The finding that scopolamine did not affect passive avoidance indicates that a cholinergic system may not be involved in mediating the suppressive effects of punishment.     

Effects of naloxone on acquisition and extinction of jump-up avoidance behavior in rats

Two experiments were carried out to assess the effects of the opioid antagonist, naloxone, on the acquisition and extinction of shock avoidance by rats in the jump-up apparatus. In Experiment 1 naloxone pretreatment facilitated acquisition but had no effect on extinction of avoidance behavior. In the second experiment the effect of naloxone on acquisition was replicated and in addition, it was shown that naloxone enhanced freezing when a response prevention or flooding procedure was introduced. Again naloxone failed to alter the course of extinction, nor did it interact with the effects of flooding which, by itself, facilitated extinction. The results suggest that naloxone's effects are limited to increasing the functional intensity of the US, and provide further support for the dissociation between extinction of avoidance behavior and other indices of fear.     

Passive avoidance behavior in rats after electroconvulsive shock: facilitative effect of response retardation.

Rats were trained in a one-trial passive avoidance task and then were submitted to electroconvulsive shock (ECS) or to sham ECS. Twenty-four hours later they were tested for retention, with the door opened either immediately or 30 sec after the beginning of the test. Rats initially forced to avoid for 30 sec continued to avoid for the entire test, but the others had the usual low step-through latencies seen with ECS-treated animals. Activity measures for those animals stepping through differentiated groups having received footshock from those not having footshock and ECS. A retest 5--10 min later showed "recovery" in the amnestic animals and continued avoidance behavior for those that avoided on the first test. Results are taken as evidence that ECS effects are not on memory storage but on the capacity of the animal to organize information effectively and quickly in order to produce an adaptive response.     

Locomotor, avoidance,and maze behavior in rats with selective disruption of hippocampal output.

Behavioral correlates of selective disruption of hippocampal output were investigated in a series of five experiments. In two experiments an attempt was made through behavioral investigation to determine whether the CA1 neurons project to the fimbria or to the subiculum. The results supported recent views that the subiculum is the recipient of CA1 axons. Disruption of the CA1 output in the dorsal hippocampus of rats produced increased open-field activity, whereas passive avoidance and spontaneous alternation behaviors remained unchanged. No differentiation was obtained between CA1 damage and neocortical lesions in maze learning. Blocking of the fimbrial CA3 output from the dorsal hippocampus improved passive avoidance performance and impaired active avoidance performance, whereas open-field and spontaneous alternation behaviors were unaffected. Interruption of the CA3 output from the ventral hippocampus improved active avoidance performance and reduced spontaneous alternation behavior. Open-field behavior and passive avoidance performance remained unchanged. Total fimbrial sections increased open-field activity, improved passive and active avoidance, and reduced spontaneous alternation. The results are discussed in terms of functional differentiation between the CA1 and CA3 of the dorsal hippocampus and in terms of functional differences in the fimbrial CA3 output from the dorsal and ventral hippocampus.     

Intracerebroventricular effects of angiotensin II on a step-through passive avoidance task in rats

A wealth of evidence indicates that angiotensin II (Ang II) is involved in learning and memory. However, the precise role of this peptide in these cognitive processes is still controversial, with data indicating either an inhibitory or an enhancing action. The present study was designed to further investigate the effects of intracerebroventricular injections of Ang II (0.5, 1 or 3nmol/5microl) on a step-through passive avoidance task in male adult Wistar rats. When administered pretraining, Ang II did not affect the acquisition of passive avoidance, but markedly improved avoidance performance when given before the retrieval test. The latter effect was observed in retest sessions performed up to 72h after training. Administration of the peptide five minutes after training impaired retention of inhibitory avoidance. Therefore, Ang II may exert opposite effects on passive avoidance memory according to its interference with brain mechanisms leading to the storage or retrieval of this aversively motivated task.     

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.     

Active avoidance behavior following archistriatal lesions in pigeons.

Experiment 1 examined the performance of 10 pigeons, 5 with bilateral medial archistriatal lesions and 5 sham-operated controls, in the acquisition and maintnenance of a discrete-press avoidance response. The archistriatal subjects had longer response latencies and never attained the level of performance achieved by the controls. In Experiment 2 eight pigeons learned a treadle-press response to avoid or escape shock on a signaled free-operant schedule. After 17 daily sessions four subjects received bilateral lesions in the medial archistriatum, and four received control lesions in the neostriatum. After recovery from surgery, all subjects were returned to the experimental procedure. Avoidance of those subjects with archistriatal lesions was impaired relative to the postoperative level while that of the control group was unchanged. These results are interpreted in the light of earlier experiments showing reduced escape and avoidance behavior both in order avian species and in mammals with lesions in the amygdala, to which the archistriatum is considered homologous.