Epileptiform lesions in rat hippocampus and acquisition of two-way avoidance

Three experiments were conducted to examine the effects on the acquisition of two-way active avoidance of implantation into the hippocampus of rats of two substances (aluminum hydroxide, penicillin) known to produce epileptogenic electrical discharges. In Experiment 1 bilateral deposits of aluminum hydroxide (ALOH) were placed in the hippocampus and the effects of this manipulation were compared to the effects of bilateral hippocampal aspiration. Sufficient postoperative time (130 days) was allowed such that epileptogenic discharges developed in the ALOH-implanted rats. Both bilateral hippocampal-ALOH deposits and bilateral hippocampal aspiration resulted in facilitated acquisition of the two-way avoidance. The results of Experiment 2 replicated this observation, but also indicated that bilateral hippocampal deposits of penicillin did not cause detectable effects on acquisition of the avoidance. Epileptiform activity produced by the penicillin was observed to disappear by postoperative Day 4. In Experiment 3 unilateral hippocampal aspiration was combined with contralateral implants of either ALOH or penicillin and avoidance training was begun 13 days postoperatively. Epileptiform activity was not observed in the ALOH-implanted rats and disappeared by postoperative Day 4 in the penicillin implanted rats. No significant changes were observed in the rate of acquisition of two-way active avoidance as a result of the manipulations done in Experiment 3. It is concluded that epileptiform discharge initiated focally within the hippocampus produces effects on the acquisition of two-way active avoidance which are similar to the effects produced by bilateral ablation.     

Effects of paradoxical sleep deprivation on two-way avoidance acquisition

Immediately following 72 hrs of paradoxical sleep (PS) deprivation, Wistar rats were given a shuttle-box avoidance task consisting of 50 trials. At an interval of 6 days retention was assessed through a reacquisition session of 20 trials. In a first experiment, the pendulum technique was employed for PS deprivation and its effects were compared with those produced by the conventional watertank technique. The first technique consists of arousing animals from sleep before PS can arise, by swinging their cages in a way that produces postural imbalance at regular intervals. A moving pendulum just not causing imbalance in the animals served as control for this technique. As control for the watertank technique the large platform was chosen. Shuttle-box avoidance was greatly impaired during the second half of the acquisition session in both platform conditions as compared to both pendulum conditions. A relatively small deficit was found toward the end of the session in both PS deprivation conditions as compared to both control conditions. No differences in avoidance were established during retention testing, suggesting that performance rather than learning deficits occurred during acquisition. In a second experiment, the multiple platform was used for PS deprivation. This modified version of the watertank technique also disrupted performance during shuttle-box avoidance acquisition. However, this effect appeared to be less pronounced than the effect found in the classical platform condition of Experiment 1. It is concluded that the performance deficit induced by both the classical and the multiple platform condition was mainly due to nonspecific effects.     

Nucleus basalis magnocellularis lesions facilitate two-way active avoidance

Bilateral ibotenic acid lesions of the nucleus basalis magnocellularis (NBM), which resulted in 30% depletion of cortical choline acetyltransferase, facilitated acquisition of shuttlebox two-way active avoidance learning in rats. These results contrast with a report of impaired two-way active avoidance after bilateral electrolytic lesions of the NBM, but support findings of facilitation after ibotenic acid lesions. The data suggest that electrolytic lesions impair shuttlebox learning by damaging fibers of passage in the vicinity of the NBM.     

On the interactive role of central noradrenaline neurons and corticosterone in two-way active avoidance acquisition in the rat

The noradrenaline (NA) neurotoxin, DSP4, caused a marked impairment of two-way active avoidance acquisition. Pretreatment with desipramine, which inhibits the degeneration of NA neurons by DSP4, consistently blocked the avoidance deficit. Daily treatment with corticosterone (2 × 1 mg/kg, s.c.) also blocked the impaired acquisition of avoidance induced by DSP4 but failed to affect the increase in cortical β-noradrenergic receptors induced by DSP4. The present findings give further evidence for the important role interactions between the pituitary-adrenal axis and the locus coeruleus NA system play in aversive learning.     

Electrolytic and ibotenic acid lesions of the nucleus basalis magnocellularis interrupt long-term retention, but not acquisition of two-way active avoidance, in rats

Previous experiments on two-way active avoidance have shown conflicting results after nucleus basalis magnocellularis lesion: disrupting effects with electrolytic lesions and facilitative effects with excitotoxic lesions. To resolve this issue, in this experiment, Wistar rats received pre-training bilateral electrolytic or ibotenic acid lesions and were trained in a massed two-way active avoidance conditioning. In order to test the long-term retention of the learned response, one additional session was conducted 10 days after the acquisition. Results showed that whereas electrolytic lesions did not affect the acquisition, ibotenic acid lesions enhanced it. Retention of active avoidance response was impaired by both electrolytic and ibotenic lesions of the NBM. These results suggest a role of the NBM in the memory consolidation and/or retrieval of two-way active avoidance. Electronic Publication     

Ontogeny of two-way avoidance in male and female rats

In Experiment I, 17-, 21-, 36-, 51-, 90-, and 200-day-old male and female rats were given a single session of 100 two-way avoidance (TWA) trials. In the 2nd experiment, males and females of these ages and 15 and 28 days of age that were obtained from a different source, weaned at a later age, and housed differently received TWA training. Results of both studies showed that avoidance of 15-, 17-, and 21-day-old rats is low, but avoidance increases from 21 to 51 days of age. Avoidance of 95- and 200-day-old animals was generally lower than 51-day-old rats. No significant gender differences appeared until 90 days of age; at this age avoidance of males was lower than females. In Experiment III, CS intensity was varied and the US intensity was lower than that used in Experiment I and II. Avoidance of 21- and 90-day-old rats was higher with a more intense CS, but 21-day-olds were still lower than adults. Avoidance of 17-day-old rats was not affected by CS intensity.     

Differential gene expression between inbred Roman high- (RHA-I) and low- (RLA-I) avoidance rats

Microarray technology was used to explore differences in brain gene expression under basal conditions in two strains of psychogenetically selected rats which differ in anxiety/stress responses, the inbred Roman High-(RHA-I) and Roman Low-(RLA-I) Avoidance rats. Microarray analysis detected 14 up-regulated and 24 down-regulated genes in RLA-I vs. RHA-I rats functionally related to neurobiological processes. The differentially expressed genes CAMKK2, CRHBP, EPHX2, HOMER3, NDN, PRL and RPL6 were selected for microarray validation using qRT-PCR. EPHX2, CAMKK2 (both up-regulated in RLA-I vs. RHA-I rats) and HOMER3 (down-regulated in RLA-I vs. RHA-I rats) showed a similar tendency and fold-change both in microarray and RT-PCR analyses; PRL (up-regulated in RLA-I vs. RHA-I rats), CRHBP and RPL6 (both down-regulated in RLA-I vs. RHA-I animals) showed a similar tendency but a different order of magnitude of change among experiments; finally, NDN was validated neither in tendency nor in magnitude of change.     

One-way avoidance learning in female inbred Roman high- and low-avoidance rats: Effects of bilateral electrolytic central amygdala lesions

Female inbred Roman high- (RHA-I) and low- (RLA-I) avoidance rats show differences in one-way avoidance learning only when the task implies a highly aversive situation (1 s in the “non-shock”-associated safe compartment, as opposed to 30 s). These between-strain differences seem to depend on strain differences in emotionality, given that: (i) they are abolished by IP administration of the GABAergic anxiolytic diazepam (Torres et al. [32]) and (ii) avoidance responding appears to correlate with cellular density in the basolateral amygdala (Gómez et al. [9]). In the present study we further analyzed whether the implication of the amygdala in one-way avoidance depends on the experimental situation aversiveness (30 s vs. 1 s in safety). After bilateral electrolytic lesions (1 mA; 20 s) of the central amygdala (CeA), RHA-I and RLA-I rats were exposed to a danger compartment (where they received a warning signal – 88 dB tone – followed by a 1 mA electric foot-shock), and a safe compartment, where these stimuli were not presented. The number of trials needed to reach 5 consecutive avoidance responses was used as dependent variable. Sham lesioned RLA-I rats showed poorer performance than sham lesioned RHA-I rats only under the 1 s condition. The CeA lesion disrupted the avoidance response only in 1 s groups, abolishing the between-strain performance differences observed under this condition. These results indicate the implication of CeA in one-way avoidance performance, and suggest a reciprocal modulation of fear and reinforcement (i.e. fear relief) in this form of aversive learning.     

Posttraining presentation of a flashing light alters retrieval of a two-way active avoidance task in rats.

Rats were trained and tested in a two-way active avoidance task (30 trials, 0.4-mA footshock, 24-h training-test interval). Exposure to an open field with flashing light (60-W lamp, 30 Hz, for 7 min, OFL) 2 h after training caused a retrieval impairment for the avoidance task, a phenomenon called retroactive interference. Animals familiarized with the OFL 24 h before training showed no retrieval impairment when exposed to the OFL 2 h after training. Both adrenal medullectomy (performed 7 to 14 days before training) and dexamethasone treatment (2 mg/kg, injected IP 24 h and 12 h before training) prevented the OFL interfering effect. Time-course experiments revealed that OFL presented either 1 or 4 h after training caused no retrieval deficit, and that animals exposed to the OFL 2 h after training and receiving another OFL presentation 1 or 2 h, but not 4 h, prior to testing had normal retrieval performance. These results suggest: 1) that the retroactive interference caused by presentation of OFL 2 h after training is due to failure of retrieval of the avoidance task since it is counteracted by the pretest presentation to the OFL, 2) that the OFL-induced retrieval interfering effect partly depends on the novelty of the OFL situation, and on the functional integrity of pituitary ACTH and adrenomedullar-dependent mechanisms and 3) that there are different mechanisms involved in posttraining and pretest OFL effects since they present distinct time-courses.     

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.     

One-way avoidance acquisition and cellular density in the basolateral amygdala: Strain differences in Roman high- and low-avoidance rats

The goal of the present experiment was to study the performance of inbred Roman high- (RHA-I) and low- (RLA-I) avoidance rats in one-way avoidance learning and to relate the behaviour of the animals to cellular density in the basolateral amygdala (BLA), a brain region related to fear and anxiety. Thus, females from both strains were exposed either to 30 s or 1 s in the safe place as a function of experimental condition, until they reached five consecutive avoidance responses. Thereafter, the rats were perfused, and their brains sectioned in 40 μm coronal sections, stained with cresyl violet. The area (percentage of field) corresponding to the BLA structures was quantified by computerized-assisted image analysis. The results indicated that RLA-I showed a significantly poorer acquisition of the one-way avoidance task than did RHA-I rats, but only when safe time was the shortest (1 s). In addition, the number of trials needed to reach the behavioural acquisition criterion was negatively correlated with BLA cellular density in RLA-I rats. These data suggest the possibility of relating behavioural and neuro-anatomical indexes, enabling exploration of the biological basis of fear/anxiety behaviours.     

Effects of posttraining damage to the pedunculopontine tegmental nucleus on conditioned stimulus transfer in two-way active avoidance in rats

The effects of posttraining excitotoxic lesions of the pedunculopontine tegmental nucleus (PPTg) on two-way active avoidance after changing the conditioned stimulus (CS) used during prelesion training were examined. Prelesion training was carried out with either a tone or a light as the CS, and this CS was changed during postlesion training. Replacing the tone with a light reduced the performance of control and lesioned rats, but the degree of reduction was higher in the latter. Replacing the light with a tone had slight detrimental effects in lesioned rats but not in controls. Thus, posttraining PPTg lesions slowed down the reacquisition of shuttle-box avoidance under conditions of CS transfer, an effect that may be attributable to disruption of attention and/or gating of sensory stimuli.     

Differences in one-way active avoidance learning in mice of three inbred strains

DBA/2J, C57BL/6J, and C3H/HeJ mice were given 10 one-way avoidance training trials per day, using an unconditioned stimulus intensity that provided equivalent motivation for learning to mice of all three strains, and were found to differ in their abilities to learn and retain the response. DBA/2J mice acquired the response in fewer days than did the mice of the other two strains, although C57BL/6J mice eventually reached a level of performance similar to that of DBA/2J mice. Both the rate of acquisition and the level at which avoidance performance stabilized were significantly lower in C3H/HeJ, than in DBA/2J or C57BL/6J, mice. In addition, DBA/2J mice showed a significantly greater task retention from one testing day to the next than did C57BL/6J or C3H/HeJ mice.This work was supported by National Institute on Drug Abuse Grants DA04195 and DA06192 to J.L.M. and Mental Health Grant MH-47680 to G.F.K.     

Effects of muscarinic receptor antagonism in the basolateral amygdala on two-way active avoidance

The aim of the present study was to investigate whether the blockade of muscarinic receptors (mRs) in the basolateral amygdala (BLA), which receives important cholinergic inputs related to avoidance learning, affects the consolidation of two-way active avoidance (TWAA). In Experiment 1, adult male Wistar rats were bilaterally infused with scopolamine (SCOP, 20 μg/site) or PBS (VEH) in the BLA immediately after a single 30-trial acquisition session. Twenty-four hours later, avoidance retention was tested in an identical session. Results indicated that scopolamine in the BLA did not affect TWAA performance measured by the number of avoidance responses. Experiment 2 was conducted to test whether such a negative outcome might be due to the occurrence of overtraining during acquisition, which may indeed have a protective effect against scopolamine-induced memory deficits. In this experiment, rats were infused with scopolamine in the BLA immediately after a brief 10-trial acquisition session and tested 24 h later in a 30-trial retention session. The SCOP group showed significantly more avoidances and inter-trial crossings in the retention session than the VEH rats. Together, these results reveal that mRs blockade in the BLA does not disrupt TWAA consolidation and may even enhance avoidance performance when infused after a low number of acquisition trials. Performance factors, such as locomotor activity in the shuttle-box, may account, at least in part, for the facilitative effects of muscarinic antagonism in the BLA.     

Successive negative contrast in one-way avoidance learning in female Roman rats

The inbred RLA (Roman Low-Avoidance) and RHA (Roman High-avoidance) rat strains have been psychogenetically selected for rapid (RHA) vs. extremely poor acquisition (RLA) of two-way active avoidance. As a consequence of this selective breeding, RLA animals exhibit a higher level of emotionality that can be observed in many anxiety models. The present study was conducted in order to analyze the performance of female RLA, RHA and Wistar rats in a behavioral test of anxiety that involves the reduction of the magnitude of an expected reward: the negative contrast effect that is obtained in one-way avoidance learning by reducing the time spent in the safe compartment. To this aim, three groups of animals (30-1/RLA, 30-1/RHA and 30-1/W) were trained to avoid an electric foot-shock administered in a "danger" compartment, by running from this compartment to a "safe" compartment. We observed an impairment of the avoidance response when time spent in the safe compartment was reduced from 30 to 1 s, when 30-1/RLA and 30-1/W groups were compared with control groups that were trained with a constant safe time (1-1/RLA and 1-1/W, respectively). We also obtained significant differences between 30-1/RLA and 30-1/RHA groups in the postshift phase. These results indicate that RLA rats respond more negatively to the frustration triggered by the reduction in time spent in the safe compartment, suggesting that animal models based on negative contrast effects can be useful tools for studying the genetic basis of anxiety.     

Effects of infant and adult amygdaloid lesions upon acquisition of two-way active avoidance by the adult rat: Influence of rearing conditions

When performed in the adult rat, bilateral and complete amygdalectomy resulted in a clear deficit in the acquisition of a 2-way active avoidance in a shuttle-box. When performed in the 7 day old rat pup, the same complete lesion resulted in no disruption of acquisition of the 2-way AA task by the rats when adult, irrespective of the environmental conditions in which they were reared from weaning. However, isolation-reared rats showed shorter response latencies than did group-reared rats. When the amygdaloid lesion was restricted to the centromedial area of the amygdala, operations carried out at 7 days resulted in a reliable impairment of the 2-way active avoidance in the initial phase of the acquisition, but only when the rats had been group-reared from weaning. The same lesion resulted in a reliable improvement in acquisition when the rats had been reared in isolation. In short, the degree of recovery of function with respect to 2-way AA acquisition following a bilateral amygdaloid lesion depends on the age at which the lesion is carried out (at infant or adult age), on the extent of the lesion (complete or restricted to the CM area) and on the rearing conditions (in groups or in isolation).     

Successive positive contrast in one-way avoidance behavior with Roman low-avoidance rats

The inbred Roman High- (RHA-I) and Roman Low-Avoidance (RLA-I) rats, psychogenetically selected for rapid (RHA-I) vs. extremely poor (RLA-I) acquisition of two-way active avoidance, exhibit a lower or a higher level of fearfulness, respectively, that can be observed in many laboratory anxiety models. The present study analyzed the performance of female RLA-I and RHA-I rats in a successive positive contrast situation induced during one-way avoidance learning. Three groups of RLA-I and three of RHA-I rats (1–30, 30–30 and 1–1 groups, the numbers stand for the time spent in the safe compartment during the first and second phase of training) were trained to avoid an electric foot-shock administered in a “danger” compartment, by running from this compartment to a “safe” one. Only RLA-I rats showed a significant positive contrast effect, in such a way that the reinforcement increase from the lower (1 s spent in safety) to the higher reward (30 s) led to a response enhancement, surpassing the performance of rats trained with the low (1–1 s) or the high (30–30 s) reward from the beginning of training. The results are discussed in the context of an opponent process theory based upon the interaction between the motivational strength of fear and the incentive value of relief taking place during one-way avoidance learning.     

The effect of partial reinforcement on instrumental successive negative contrast in inbred Roman High- (RHA-I) and Low- (RLA-I) Avoidance rats

Frustration is an emotional response that can be induced by the sudden devaluation of a reinforcer in the presence of greater reinforcement expectancies (e.g. instrumental successive negative contrast, iSNC). This emotional response seems to be similar to anxiety and can be attenuated by previous experiences of reward loss (e.g. partial reinforcement, PR, as opposed to continuous reinforcement, CR). In this study we used iSNC and PR procedures in order to compare the performance of two strains of rats psychogenetically selected on the basis of their emotional reactivity: the inbred Roman High- (RHA-I, low anxiety) and Low- (RLA-I, high anxiety) Avoidance rats. Animals were exposed to a straight alley, where they were changed from 12 pellets in the preshift phase (presented in 100% of trials-CR vs. 50% of trials-PR) to 2 pellets in the postshift phase, or exposed to 2 pellets throughout the training. The results indicated that the iSNC only appeared in RLA-I rats exposed to CR, as opposed to RLA-I animals exposed to PR and to RHA-I rats exposed to PR or CR. These data seem to support the implication of emotional responses in both iSNC and PR situations, and indicate that the behavioral reactivity to reward loss experiences is modulated by genetic variables.     

The effect of home cage stimuli on acquisition and retention of an active avoidance response in previsual rats

The effect of home cage environmental stimuli on learning and the effects on retention of the presence or absence of these familiar contextual training stimuli during the retention test (Experiment 1) or during the retention interval (Experiment 2) were examined using 10-day-old rats, a multidirectional active avoidance task, and a 30-min retention interval. Home cage environmental stimuli were found to improve learning. A change in stimuli immediately after training, during the 30-min retention interval, was found to have a greater impact on retention performance than stimulus change introduced at the time of the retention test. The implications of these findings are discussed in relation to ontogenetic differences in retention performance and theories of forgetting.