Inhibitory Avoidance Learning Research Articles

A dissociation between the proactive ECS effects on inhibitory avoidance learning and on classical fear conditioning

This study investigated if the nature of the task is a determinant factor of whether or not a series of electroconvulsive shock (ECS) will proactively affect learning in animals. Rats were administered one daily ECS for 7 days. A day after the last administration they were concomitantly trained on an inhibitory avoidance task and on classical conditioning of fear response to a brief tone. Twenty-four hours later they were exposed for 8 min to an open-field arena and the freezing reaction was measured both before and after tone presentation (classical fear conditioning test). On the subsequent day the step-through latency (without presentation of the tone) was measured on the avoidance apparatus (inhibitory avoidance test). Impairment of inhibitory avoidance was seen in ECS-administered animals in comparison to controls, but the freezing reaction to the tone was equally high in both groups. Additional groups of rats were trained in order to control for ECS alone-induced freezing and pseudoconditioning. Also, it was demonstrated that the differential ECS effects on the two tasks were not due to the order of testing since similar dissociation was obtained when inhibitory avoidance test was conducted before the open-field test.

Enhanced learning produced by injection of neurokinin substance P into the region of the nucleus basalis magnocellularis: Mediation by the N-terminal sequence

The effect of unilateral injection of the neurokinin substance P (SP) and of certain N- or C-terminal SP-fragments into the region of the nucleus basalis magnocellularis (NBM) on inhibitory avoidance learning was investigated. Rats with chronically implanted cannulae were tested on a one-trial uphill avoidance task. Immediately after the training trial, rats were injected with 0.74 pmol SP or equimolar dosed SP(1–7), DIME-C7, or SP(7–11). Control groups included vehicle-injected rats and a group given an injection of SP(1–7) 5-h after the trial. When tested 24 h later, rats treated with SP or SP(1–7), but not with DIME-C7 or SP(7–11), exhibited longer step-up latencies than vehicle-treated controls. The retention latencies for rats in the SP(1–7) 5-h delay group did not differ from those of vehicle-injected animals, ruling out proactive effects of SP(1–7) on performance. The results show that SP facilitates retention of an inhibitory avoidance response when injected into the NBM. Furthermore, the amino acid sequence that encodes this effect may be located in the N-terminal part of the SP-molecule.

Effect of PAF antagonists in retinal diseases

Long-term potentiation (LTP), a model of activity-dependent synaptic plasticity and of certain forms of memory, comprises the persistent enhancement of excitatory neurotransmission that results from high-frequency activation. A presynaptic component of LTP is thought to be modulated by a retrograde messenger generated by the postsynaptic neuron. Arachidonic acid, nitrix oxide, carbon monoxide and PAF have each been proposed as retrograde messengers in LTP, but arachidonic acid, unlike PAF, requires NMDA receptor activation. A PAF antagonist (BN 52021) that provides neuroprotection in ischemia-reperfusion displaces [3H] PAF bound to presynaptic membranes, blocks PAF-induced glutamate exocytosis and inhibits LTP. An antagonist selective for the intracellular PAF binding site (BN 50730) did not affect LTP, nor did BN 52021 modify NMDA currents. LTP was induced with weak synaptic stimulation coupled with postsynaptically administered enzyme resistant mcPAF. Theta-burst stimulation (10 min) after bath applications of mcPAF (1 μM) induced APV-independent LTP that was blocked by 5 μM BN 52021. When this antagonist was infused into the hippocampus before or immediately after training, it impaired memory of inhibitory avoidance training in the rat. Memory was not altered if the antagonist is infused 30 or 60 min after training. Moreover, mcPAF enhances memory on retention test performance of step-down inhibitory avoidance habituation and learning in rats. Also, memory was studied using a caudate nucleus-dependent cued water maze task. Rats received an 8 trial (30 s intertrial interval) training session in which a visible cued escape platform was located in a different quadrant of the maze of each trial. Following trial 8, the rats received a unilateral post-training intra-caudate injection of mcPAF (1 μg/0.5 μl), BN 52021 (0.5 μg/0.5 μl) or vehicle. On a retention test session 24 h later, latency to mount the escape platform was used as a measure of memory. The retention test escape latencies of rats given mcPAF were significantly lower than those of the vehicle-injected controls, indicating a memory enhancing effect of mcPAF. Injection of mcPAF did not affect retention when administered 2 h post-training indicating a time-dependent effect of mcPAF on memory. The latencies for animals injected with BN 52021 were significantly higher than those of the controls, indicating that antagonism of endogenous PAF impairs memory. The findings show that PAF plays a role in memory formation in a caudate-mediated cued discrimination task. Administration of BN 52021 2 h post-training had no effect on retention, indicating a time-dependent effect of endogenous PAF on memory formation. PAF, the most potent bioactive lipid known, modulates excitatory synaptic transmission, neuronal plasticity and memory. When PAF production is overstimulated as in seizures or ischemia, it becomes neurotoxic.

Effects of intraseptal infusion of muscimol on inhibitory avoidance and spatial learning: Differential effects of pretraining and posttraining administration

Previous research in our laboratory showed that the pretraining administration of the GABAergic agonist muscimol into the medial septal area (MSA) of rats impaired place learning in a water-maze task. To determine whether this treatment impaired memory by acting at the time of training or after training, the first experiment examined the effects of posttraining intraseptal infusion of muscimol on retention in the place-learning task. The posttraining muscimol treatment facilitated learning on the second day of training (1 and 5 nmol) and produced an impairment on only one of the three retention measures on the free-swim trial (5 nmol). In additional experiments using an inhibitory avoidance task, pretraining, but not posttraining, administration of muscimol (5 nmol) into the MSA impaired retention. The findings of these experiments suggest that intraseptal administration of muscimol impairs memory formation primarily by affecting processes occurring at the time of training.

Halothane anesthesia causes state-dependent retrieval failure in mice

Effects of exposure to halothane on memory processing was studied using single-trial inhibitory avoidance learning to measure retention. Mice were anesthetized with halothane either before training, immediately after training, or both before training and before testing. Results showed that memory was not impaired by posttraining halothane exposure, indicating that the anesthetic does not cause retrograde amnesia. Mice trained after recovery from halothane showed a robust memory loss 24 h later. This deficit could be alleviated by reexposure to the anesthetic before the retention test. Mice given multiple training trials following recovery from the anesthetic showed a normal rate of learning when compared with controls, but deficient retention. This indicates that the performance deficit was the result of impaired retention (anterograde amnesia) rather than disrupted acquisition. Anterograde amnesia occurred when training was delayed up to 2 h after recovery from anesthesia. These findings indicate that the memory impairment following halothane anesthesia is the result of a state-dependent retrieval failure.

Comparative effects of carbamazepine, phenytoin, diazepam and clonazepam on inhibitory avoidance learning in mice

Four antiepileptic drugs were investigated in an inhibitory avoidance task in mice. Following IP administration 30 min prior to training, carbamazepine (32 mg/kg), phenytoin (30-60 mg/kg), diazepam (2-8 mg/kg) and clonazepam (0.125-0.5 mg/kg) impaired retention. When administered 30 min prior to the retention test none of the drugs under investigation affected retention. The drugs did not affect latencies in the hot plate test. This indicates that in the case of pretraining drug administration effects on retention cannot attributed to elevated pain thresholds. Carbamazepine and phenytoin impaired avoidance learning at doses above those which prevent electroshock induced tonic hindlimb convulsions. Diazepam and clonazepam were effective at lower than anticonvulsant doses. The results of the study are relevant to the evaluation of CNS side effects of anti-epileptic drugs in mice.

Multitrial inhibitory avoidance learning in the crab chasmagnathus

Chasmagnathus crabs placed in the dark compartment (DC) of a double-chamber device and given electrical shocks whenever they entered or remained in the light compartment (LC), showed an LC-avoidance behavior when tested 24 h after a training session of three 30-min periods with 60-min intervals. The avoidance behavior depended neither on the shock number nor on the distribution at training but only on exposure to the LC-shock contingency, thus suggesting that crabs learn to associate the LC with an aversive situation. The learning outcome disclosed a higher degree of refraining from entering the LC rather than a faster escaping to the DC. Distributed practice proved more effective on crab avoidance learning than massive practice. Retention of the learned behavior occurred after a 24-h rest interval in an environment different from that of the training apparatus. Experimental devices previously used in avoidance learning studies with crabs were improved here by automating both the computation of latency values and the event recording.

Fluoxetine and 8-OH-DPAT in the lateral septum enhances and impairs retention of an inhibitory avoidance response in rats

The present study investigated the role of lateral septal serotonin (5HT) in memory consolidation and the subtype of 5HT receptors involved in this process. Rats with cannulae implanted bilaterally into the lateral septum were trained in an inhibitory avoidance task. Immediately after training, the septal serotonergic function was manipulated by pharmacological agents selectively blocking 5HT reuptake (fluoxetine and zimelidine), antagonizing 5HT 2 receptors (ketanserin and ritanserin), or activating 5HT 1A receptors, respectively. Results indicated that direct fluoxetine infusions into the lateral septum at a dose of 6 μg/0.5 μl and zimelidine at a dose of 5 μg/0.5 μl both markedly enhanced memory. Intralateral septal injections of ketanserin (0.3 μg/0.5 μl and 0.5 μg/0.5 μl) and ritanserin (0.3 μg/0.5 μl and 0.6 μg/0.5 μl) did not have a significant effect by themselves on memory, and neither did they attenuate the memory-facilitating effect of fluoxetine in the same area. Intralateral septal infusions of 8-hydroxy-2-(di- n-propylamino)tetralin at 5 μg/0.5 μl significantly impaired memory retention. These findings altogether support the notion that the lateral septal nuclei of rats are involved in the memory processes of inhibitory avoidance learning. Furthermore, postsynaptic 5HT receptor activation (not the 5HT 2 receptor subtype) probably exerts a facilitatory effect while presynaptic 5HT 1A receptor activation exerts an impairing effect on the memory consolidation process, probably due to autoreceptor inhibition of 5HT release.

Insular Cortical Grafts: Factors Affecting the Recovery of Learning

tractus solitarius (the first-order relay for visceral information). The IC also has connections with limbic structures, including the amygdala and medial prefrontal cortex. Lesions of the IC region in adult rats impair the acquisition and retention of conditioned taste aversion (CTA). Recent findings showing that N-methylD-aspartate lesions of the IC disrupt the acquisition of inhibitory (passive) avoidance tasks, indicate that the IC is also involved in exteronociceptive-based learning. Our research has focused on the recovery of the acquisition of conditioned taste aversion and inhibitory avoidance learning task, by fetal brain grafts in IC-lesioned animals. In a first series of experiments, we have shown that cortical brain grafts produced a significant recovery in the ability to learn in IC-lesioned animals. The recovery induced by fetal brain grafts was related to the origin of the graft tissue used. That is, animals that received homotopic (IC), but not occipital cortical tissue recovered the capability

Comparison of the effects of acute and chronic ibotenic and quisqualic acid nucleus basalis lesioning

The present study examines the effects of acute (1 month recovery) and chronic (8 month recovery) bilateral quisqualic (quis) and ibotenic (ibo) acid nucleus basalis (NB) lesioning on the activity of cholinergic neurons and on passive avoidance (PA) and water-maze (WM) performance. Our data demonstrate that A: The activity of choline acetyltransferase (ChAT) in cortical tissue and the number of ChAT positive neurons in the NB were decreased 1 and 8 months after quis or ibo NB lesioning. B: Ibo NB lesioning produced a greater nonspecific subcortical cell loss than quis NB lesioning. C: PA retention was impaired by acute and chronic quis and ibo NB lesioning. D: Acute ibo NB lesioning impaired acquisition and reversal learning in WM performance whereas chronic ibo NB lesioning impaired only reversal WM learning. Acute and chronic quis NB lesioning impaired reversal WM learning. The present results suggest that NB cholinergic neurons do not recover spontaneously from excitotoxin-induced damage and that they may be importantly involved in inhibitory avoidance and spatial reversal learning performance.

Reversible inactivation of the insular cortex by tetrodotoxin produces retrograde and anterograde amnesia for inhibitory avoidance and spatial learning.

Tetrodotoxin (TTX; a voltage-sensitive sodium channel blocker) was microinjected bilaterally into the insular (IC), frontal (FC), or parietal (PC) cortex or the ventral caudate nucleus of rats either before or after they were trained in an inhibitory avoidance task. When administered either before or after training, injections of TTX into the IC impaired performance on a 48-hr retention test. Injections of TTX into the PC also impaired retention when administered before training. One week later, rats with cannulae in the IC, FC, and PC received microinjections of TTX either before or after training in a water maze (Morris) spatial learning task and retention was tested 24 hr later. TTX impaired retention when administered to the IC either before or after training. These findings indicate that a functionally intact IC during and after training in these tasks appears to be essential for the storage of long-term memory.

Insular cortex and amygdala lesions differentially affect acquisition on inhibitory avoidance and conditioned taste aversion

These experiments examined the effects of NMDA-induced lesions of the amygdala and insular (gustatory) cortex (IC) on inhibitory avoidance learning and conditioned taste aversion (CTA) in rats. IC lesions, but not amygdala lesions, disrupted CTA. In contrast, lesions of either brain region disrupted inhibitory avoidance learning. These findings support the view that the IC is strongly involved in the acquisition of external as well as visceral aversively motivated behavior. Despite extensive functional interconnections, these 2 brain regions appear to have different roles in mediating different forms of aversively based learning.

Benzodiazepine receptor ligand influences on learning: an endogenous modulatory mechanism mediated by benzodiazepines possibly of alimentary origin.

In rats, pre- but not post-training ip administration of either flumazenil, a central benzodiazepine (BZD) receptor antagonist, or of n-butyl-B-carboline-carboxylate (BCCB), an inverse agonist, enhanced retention of inhibitory avoidance learning. Flumazenil blocked the enhancing effect of BCCB, and the inhibitory effect of the BZD agonists clonazepam and diazepam also given pre-training. Post-training administration of these drugs had no effect. The peripheral BZD receptor agonist/chloride channel blocker Ro5-4864 had no effect on the inhibitory avoidance task when given ip prior to training, but it caused enhancement when given immediately post-training either ip or icv. This effect was blocked by PK11195, a competitive antagonist of Ro5-4864. These results suggest that there is an endogenous mechanism mediated by BZD agonists, which is sensitive to inverse agonists and that normally down-regulates the formation of memories through a mechanism involving GABA-A receptors and the corresponding chloride channels. The most likely agonists for the endogenous mechanism suggested are the diazepam-like BZDs found in brain whose origin is possibly alimentary. Levels of these BZDs in the cortex were found to sharply decrease after inhibitory avoidance training or mere exposure to the training apparatus.

Substance P enhancement of inhibitory avoidance learning: Mediation by the N-terminal sequence

Experiments were performed to investigate the effects of intraperitoneally administered undecapeptide substance P (SP), its N-terminal fragment SP(1–7) (SPN) and the C-terminal analog [pGlu 6]-SP(6–11) (SPC) on inhibitory avoidance learning, using a one-trial up-hill avoidance task. In Experiment 1 rats were injected with either SP (50 μg/kg), SPN (3.3, 33, 167, 333 μg/kg) or SPC (2.7, 27, 134, 268 μg/kg) immediately after the training trial. Controls received the diluent vehicles. When tested 24 hr later, rats injected with 50 μg/kg SP (37 nmol/kg) and 167 μg/kg SPN (185 nmol/kg) exhibited longer step-up latencies than vehicle-treated controls. None of the other doses of SPN nor of the C-terminal fragment influenced performance. In Experiment 2, 167 μg/kg SPN or vehicle was injected posttrial either immediately or 5 hr after the training trial. Retention latencies 24 hr later were longer for rats treated with 167 μg/kg SPN immediately after the training trial. Performance of the SPN 5-hr delay group did not differ from that of the vehicle-injected controls, ruling out proactive effects of SPN on recall.

Neonatal 6-hydroxydopa, but not DSP-4, elevates brainstem monoamines and impairs inhibitory avoidance learning in developing rats

The involvement of brain monoamines in learning and memory in developing rats was studied by comparing the effects of 3 different noradrenergic neurotoxin treatments. Two experimental groups of male Sprague-Dawley rat pups were injected systemically with 50 μg/g of N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine (DSP-4) either on the day of birth or on postnatal days 17–18. Rats in the third experimental group were injected systemically with 60 μg/g of 6-hydroxydopa (6-OHDOPA) on postnatal days 0 and 2. Control littermates received vehicle. The animals were trained on an inhibitory avoidance task on postnatal days 27–29 and tested for retention 24 h later. The drug treatments produced comparable depletion of norepinephrine in the hippocampus and frontal cortex. 6-OHDOPA, but neither DSP-4 treatment, significantly elevated brainstem concentrations of norepinephrine and serotonin. In addition, 6-OHDOPA, but not DSP-4, significantly impaired retention of the inhibitory avoidance task. The impairment did not reflect insensitivity to the footshock used in training: both neonatal drug treatments tended to lower, not raise, footshock thresholds, as measured by a flinh test. High affinity choline uptake was not affected by either neonatal drug treatment in any of the brain areas examined. Thus, the 6-OHDOPA-induced behavioral deficit did not involve altered acetylcholine function. The results implicate brainstem monoamines in the modulation of learning and memory during development.

Intra-amygdala injections of corticotropin releasing factor facilitate inhibitory avoidance learning and reduce exploratory behavior in rats.

The effects of intra-amygdala injections of corticotropin-releasing factor (CRF) on memory and exploratory behavior in rats were examined in the present study. Rats with chronically implanted cannulae received intra-amygdala injections of vehicle or CRF at a dose of 0.01, 0.1 or 1.0 micrograms, either immediately after the inhibitory avoidance training or prior to the open field activity test. Results indicated that while CRF at low (0.01 microgram) and high (1.0 micrograms) doses produced no significant effect on retention or exploration, immediate post-training intra-amygdala injections of CRF at the medium dose (0.1 microgram) significantly improved retention of the inhibitory avoidance response. The same dose of CRF, given shortly prior to the open field activity test, decreased locomotor activity, rearing and hole-poke responses in rats. These results suggest that the amygdala is one of the anatomical loci involved in CRF modulation of memory processing and exploration in rats. The implication of CRF in mediating the influences of stress on behavior is discussed.

Enhanced inhibitory avoidance learning produced by post-trial injections of substance P into the basal forebrain

The effects of injections of the neuropeptide substance P or the GABA agonist muscimol on performance of a step-down inhibitory avoidance task were examined. Immediately after the training trial, rats with chronically implanted cannulas were injected with 100 or 10 ng of substance P or 500 or 50 ng of muscimol into the region of the nucleus basalis magnocellularis. Control groups included vehicle-injected rats, a sham-operated group, a substance P 5-h delay group, and a substance P no-footshock group. Rats injected with 100 ng of substance P exhibited longer step-down latencies when tested 24 h later than did vehicle-injected rats. The retention latencies for rats in the substance P 5-h delay group did not differ from those of vehicle-injected animals, indicating that proactive effects on performance were not responsible for the effect. In contrast to injections of SP, injections of 500 or 50 ng of muscimol disrupted performance. However, in the absence of a delayed-injection control group, proactive effects cannot be ruled out.

Subtelencephalic locale of reinforcement and learning: Looking for the minimal necessary structures

This report summarizes 4 experiments which deal with the effects of surgical removal of the rat's telencephalic forebrain structures on performance of an inhibitory avoidance response, which was acquired either before or after the lesion was made. Two experiments provide evidence that inhibitory avoidance learning (using the single-trial up-hill avoidance task) is still possible after removal of all of the forebrain structures except for the hypothalamus. A third study using this preparation dealt with the question of whether this conditioned avoidance response can be eliminated as a consequence of it being punished. In a further experiment the conditioned avoidance response was established prior to ablation of the telencephalon plus thalamus. Recall of the conditioned response survived the lesion, suggesting that the avoidance response is also stored at a subtelencephalic level in the brain-intact animal.

Survival of a conditioned inhibitory avoidance response after decerebration

There is evidence that inhibitory avoidance learning is still possible after removal of the telencephalic forebrain. However, it is not known whether subtelencephalic storage of such a conditioned response takes place when the brain is intact. To investigate this possibility, rats received one training trial in the “up-hill avoidance” task, and 8 h later the entire forebrain except the hypothalamus was bilaterally ablated. When tested 24 h later, the decerebrate rats still exhibited the learned response, demonstrating a transfer of the conditioned response from the intact to the postlesion state. This result indicates that memory-storage for this avoidance task takes place, at least in part, subtelencephalically.

Retrograde memory enhancement by diazepam: its relation to anterograde amnesia, and some clinical implications.

The effect of diazepam on retention of an inhibitory avoidance task was investigated in mice. In Experiment 1, animals were trained in this task, and tested for retention 24 h later. The mice received, 20 min after training, an IP injection of either diazepam (2 mg/kg) or saline; half of the mice in each treatment group were exposed, 40 min after avoidance training (and 20 min after the injections) to a Y maze. Exposure to the Y maze disrupted retention of the avoidance task in the saline-treated animals, and enhanced it in the diazepam-treated mice. Retention of habituation to the Y maze was impaired in the diazepam group. The effect can be explained by an interaction of the drug with the Y maze, by which exposure to the Y maze became facilitatory, instead of deleterious, to retention of the avoidance task. This may or may not be related to anterograde amnesia for the Y maze; and may be related to effects of diazepam seen in clinical practice. In Experiment 2, diazepam was given prior to, instead of after, inhibitory avoidance training; it caused anterograde amnesia for this task, which was not reversed by pre-test diazepam, and was therefore not due to state dependency. In conclusion, the effect of diazepam on inhibitory avoidance learning depends on the time at which the drug is given. A pretraining injection causes amnesia, whereas a post-training injection, while ineffective per se, may facilitate retention of the task when it is followed by exposure to a habituation procedure.