Differential role of entorhinal and hippocampal nerve growth factor in short- and long-term memory modulation

We studied the effects of infusion of nerve growth factor (NGF) into the hippocampus and entorhinal cortex of male Wistar rats (250-300 g, N = 11-13 per group) on inhibitory avoidance retention. In order to evaluate the modulation of entorhinal and hippocampal NGF in short- and long-term memory, animals were implanted with cannulae in the CA1 area of the dorsal hippocampus or entorhinal cortex and trained in one-trial step-down inhibitory avoidance (foot shock, 0.4 mA). Retention tests were carried out 1.5 h or 24 h after training to measure short- and long-term memory, respectively. Immediately after training, rats received 5 æl NGF (0.05, 0.5 or 5.0 ng) or saline per side into the CA1 area and entorhinal cortex. The correct position of the cannulae was confirmed by histological analysis. The highest dose of NGF (5.0 ng) into the hippocampus blocked short-term memory (P < 0.05), whereas the doses of 0.5 (P < 0.05) and 5.0 ng (P < 0.01) NGF enhanced long-term memory. NGF administration into the entorhinal cortex improved long-term memory at the dose of 5.0 ng (P < 0.05) and did not alter short-term memory. Taken as a whole, our results suggest a differential modulation by entorhinal and hippocampal NGF of short- and long-term memory.

Pharmacological differences between memory consolidation of habituation to an open field and inhibitory avoidance learning

Rats implanted bilaterally with cannulae in the CA1 region of the dorsal hippocampus or the entorhinal cortex were submitted to either a one-trial inhibitory avoidance task, or to 5 min of habituation to an open field. Immediately after training, they received intrahippocampal or intraentorhinal 0.5-æl infusions of saline, of a vehicle (2 percent dimethylsulfoxide in saline), of the glutamatergic N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphono pentanoic acid (AP5), of the protein kinase A inhibitor Rp-cAMPs (0.5 æg/side), of the calcium-calmodulin protein kinase II inhibitor KN-62, of the dopaminergic D1 antagonist SCH23390, or of the mitogen-activated protein kinase kinase inhibitor PD098059. Animals were tested in each task 24 h after training. Intrahippocampal KN-62 was amnestic for habituation; none of the other treatments had any effect on the retention of this task. In contrast, all of them strongly affected memory of the avoidance task. Intrahippocampal Rp-cAMPs, KN-62 and AP5, and intraentorhinal Rp-cAMPs, KN-62, PD098059 and SCH23390 caused retrograde amnesia. In view of the known actions of the treatments used, the present findings point to important biochemical differences in memory consolidation processes of the two tasks

The brain decade in debate: I. Neurobiology of learning and memory

This article is a transcription of an electronic symposium in which some active researchers were invited by the Brazilian Society for Neuroscience and Behavior (SBNeC) to discuss the last decade's advances in neurobiology of learning and memory. The way different parts of the brain are recruited during the storage of different kinds of memory (e.g., short-term vs long-term memory, declarative vs procedural memory) and even the property of these divisions were discussed. It was pointed out that the brain does not really store memories, but stores traces of information that are later used to create memories, not always expressing a completely veridical picture of the past experienced reality. To perform this process different parts of the brain act as important nodes of the neural network that encode, store and retrieve the information that will be used to create memories. Some of the brain regions are recognizably active during the activation of short-term working memory (e.g., prefrontal cortex), or the storage of information retrieved as long-term explicit memories (e.g., hippocampus and related cortical areas) or the modulation of the storage of memories related to emotional events (e.g., amygdala). This does not mean that there is a separate neural structure completely supporting the storage of each kind of memory but means that these memories critically depend on the functioning of these neural structures. The current view is that there is no sense in talking about hippocampus-based or amygdala-based memory since this implies that there is a one-to-one correspondence. The present question to be solved is how systems interact in memory. The pertinence of attributing a critical role to cellular processes like synaptic tagging and protein kinase A activation to explain the memory storage processes at the cellular level was also discussed

Effect of inhibitory avoidance training on [3H]-glutamate binding in the hippocampus and parietal cortex of rats

Glutamate receptors have been implicated in memory formation. The aim of the present study was to determine the effect of inhibitory avoidance training on specific [3H]-glutamate binding to membranes obtained from the hippocampus or parietal cortex of rats. Adult male Wistar rats were trained (0.5-mA footshock) in a step-down inhibitory avoidance task and were sacrificed 0, 5, 15 or 60 min after training. Hippocampus and parietal cortex were dissected and membranes were prepared and incubated with 350 nM [3H]-glutamate (N = 4-6 per group). Inhibitory avoidance training induced a 29 percent increase in glutamate binding in hippocampal membranes obtained from rats sacrificed at 5 min (P<0.01), but not at 0, 15, or 60 min after training, and did not affect glutamate binding in membranes obtained from the parietal cortex. These results are consistent with previous evidence for the involvement of glutamatergic synaptic modification in the hippocampus in the early steps of memory formation

Involvement of hippocampal AMPA glutamate receptor changes and the cAMP/protein kinase A/CREB-P signaling pathway in memory consolidation of an avoidance task in rats

Training in step-down inhibitory avoidance (0.3-mA footshock) is followed by biochemical changes in rat hippocampus that strongly suggest an involvement of quantitative changes in glutamate AMPA receptors, followed by changes in the dopamine D1 receptor/cAMP/protein kinase A (PKA)/CREB-P signalling pathway in memory consolidation. AMPA binding to its receptor and levels of the AMPA receptor-specific subunit GluR1 increase in the hippocampus within the first 3 h after training (20-70 per cent). Binding of the specific D1 receptor ligand, SCH23390, and cAMP levels increase within 3 or 6 h after training (30-100 per cent). PKA activity and CREB-P levels show two peaks: a 35-40 per cent increase 0 h after training, and a second increase 3-6 h later (35-60 per cent). The results correlate with pharmacological findings showing an early post-training involvement of AMPA receptors, and a late involvement of the D1/cAMP/PKA/CREB-P pathway in memory consolidation of this task.

Agents that affect cAMP levels or protein kinase A activity modulate memory consolidation when injected into rat hippocampus but not amygdala

Male Wistar rats were trained in one-trial step-down inhibitory avoidance using a 0.4-mA footshock. At various times after training (0, 1.5, 3,6 and 9 h for the animals implanted into the CA1 region of the hippocampus; 0 and 3 h for those implanted into the amygdala), these animals received microinfusions of SKF38393 (7.5 mug/side), SCH23390 (0.5 mug/side), norepinephrine (0.3 mug/side), timolol (0.3 mug/side), 8-OH-DPAT (2.5 mug/side), NAN-190 (2.5 mug/side), forskolin (0.5 mug/side), KT5720 (0.5 mug/side) or 8-Br-cAMP (1.25 mug/side). Rats were tested for retention 24 h after training. When given into the hippocampus 0 h post-training, norepinephrine enhanced memory whereas KT5720 was amnestic. When given 1.5 h after training, all treatments were ineffective. When given 3 or 6 h post-training, 8-Br-cAMP, forskolin, SKF38393, norepinephrine and NAN-190 caused memory facilitation, while KT5720, SCH23390, timolol and 8-OH-DPAT caused retrograde amnesia. Again, at 9 h after training, all treatments were inffective. When given into the amygdala, norepinephrine caused retrograde facilitation at 0 h after training. The other drugs infused into the amygdala did not cause any significant effect. These data suggest that in the hippocampus, but not in the amygdala, a cAMP/protein kinase A pathway is involved in memory cosolidation at 3 and 6 h after training, which is regulated by D1, Beta, and 5HT1A receptors. This correlates with data on increased post-training cAMP levels and a dual peak of protein kinase A activity and CREB-P levels (at 0 and 3-6 h) in rat hippocampus after training in this task. These results suggest that the hippocampus, but not the amygdala, is involved in long-term storage of step-down inhibitory avoidance in the rat.

Effects of entorhinal cortex lesions on memory in different tasks

Lesions of the entorhinal cortex produce retrograde memory impairment in both animals and humans. Here we report the effects of bilateral entorhinal cortex lesions caused by the stereotaxic infusion of N-methyl-D-aspartate (NMDA) in rats at two different moments, before or after the training session, on memory of different tasks: two-way shuttle avoidance, inhibitory avoidance and habituation to an open field. Pre-or post-training entorhinal cortex lesions caused an impairment of performance in the shuttle avoidance task, which agrees with the previously described role of this area in the processing of memories acquired in sucessive sessions. In the inhibitory avoidance task, only the post-training lesions had an effect (amnesia). No effect was observed on the open field task. The findings suggest that the role of the entorhinal cortex in memory processing is task-dependent, perhaps related to the complexity of each task.

Involviment of the hippocampus, amygdala, entorhinal cortex and posterior parietal cortex in memory consolidation

A total of 182 young adult male Wistar rats were bilaterally implanted with cannulae into the CA1 region of the dorsal hippocampus and into the amygdaloid nucleus, the entorhinal cortex, and the posterior parietal cortex. After recovery, the animals were trained in a stepdown inhibitory avoidance task. At various times after training (0, 30, 60 or 90 min) the animals received a 0.5-mul microinfusion of vehicle (saline) or O.5 mug of muscimol dissolved in the vehicle. A retention test was carried out 24 h after training. Retention test performance was hindered by muscimol administered into both the hippocampus and amygdala at 0 but not at 30 min posttraining. The drug was amnestic when given into the entorhinal cortex 30, 60 or 90 min after training, or into the parietal cortex 60 or 90 min after training, but not before. These findings suggest a sequential entry in operation, during the posttraining period, of the hippocampus and amygdala, the entorhinal cortex, and the posterior parietal cortex in memory processing.

Encefalopatia hepática e o sistema GABAérgico: o papel dos benzodiazepínicos endógenos / Hepatic encephalopathy and GABA system: the role of endogenous benzodiazepinic agents

A Encefalopatia Hepática (EH) é uma síndrome neuropsiquiátrica decorrente da insuficiência hepática seja esta aguda ou crônica. Embora vários aspectos envolvidos na sua patofisiologia ainda näo estejam completamente esclarecidos, há um consenso de que esta seja multifatorial. Acredita-se que a falência hepática leve ao acúmulo de substâncias neuroativas e/ou potencialmente tóxicas responsáveis pelas alteraçöes no funcionamento cerebral. Desde o início da década de 80 o sistema GABAérgico vem sendo considerado potencialmente envolvido na patogênese da EH. Achados experimentais recentes, tanto em modelos animais quanto em humanos, confirmaram tal hipótese e levantam novas perspectivas na compreensäo e tratamento desta síndrome. Esta revisäo objetiva apresentar as bases teórico-experimentais que correlacionam o sistema GABAérgico e seus moduladores endógenos bem como a aplicabilidade de tais achados.

Role of the amygdala, hippocampus and entorhinal cortex in memory consolidation and expression

1. Experiments using localized microinfusions of specific agonists and antagonists of neurotransmitter receptors have shown that the amygdala, hippocampus, medial septum and entorhinal cortex are involved in memory consolidation, storage and expression. The data are consistent with observations derived from lesion studies suggesting a role for these structures in memory processes, but permit many additional conclusions concerning the mechanisms involved and their timing. 2. Memories are initially processed by glutamatergic N-methyl-D-aspartate (NMDA) receptors in amygdala, hippocampus and medial septum, which are sensitive to amino-phosphono valerate (AP5). Memory of inhibitory avoidance is processed by the three structures; memory of habituation to a novel environment is processed only by the hippocampus. At the time of consolidation, immediately after training, gamma-aminobutyrate type A (GABA-A) receptors, modulated by endogenous benzodiazepines, play an inhibitory role, and cholinergic muscarinic and beta-noradrenergic transmission play a modulatory role. 3. From 90 to 180 min after training, memories are blocked by cyano-nitro-quinoxalinedione (CNQX) given into the amygdala, septum and hippocampus. CNQX blocks non-NMDA glutamatergic receptors. Also between 90 and 180 min after training, memory of the habituation and inhibitory avoidance tasks is blocked by the infusion of AP5 or of the GABA-A agonist, muscimol, into the entorhinal cortex. This late post-training intervention of the entorhinal cortex is essential for the integration of successively acquired memories, and occurs in response to the simultaneous activation of CNQX-sensitive synapses in amygdala and hippocampus. 4. The expression of memory is blocked by the infusion of CNQX, at the time of testing, into the amygdala and hippocampus (inhibitory avoidance), into the hippocampus but not the amygdala (habituation), or into the entorhinal cortex (for the two tasks). Since consolidation is blocked by AP5 infused into these structures (see above), the data agree with the hypothesis that memories are mediated by (or actually consist of) long-term potentiation (LTP) in these areas of the brain. LTP induction is blocked by AP5 and LTP expression is blocked by CNQX. It is possible that, at the time of memory expression, the entorhinal cortex is an output of the amygdala and hippocampus

Memory consolidation of a habituation task: role of n-methyl-D-aspartate, cholinergic muscarinic and gaba-a receptors in different brain regions

The immediate post-training microinjection of the N-methyl-D-aspartate receptor antagonist amino-5-phosphonopenmtaanoic acid (5 ug) or of scopolamine, the cholinergic muscarinic antagonist (2 ug), into the dorsal hippocampus of rats caused retrograde amnesia for habituation to a novel environment, as measured by the number of rearings and crossings performed in a test session. In contrast, picrotoxin (0.08 ug), the indirect GABA-A antagonist, caused retrograde memory facilitation. Receptor agonist administered into the hippocampus had effects opposite to those of the respective antagonists: glutamate (5 ug) and oxotremorine (2 ug) enhanced memory and muscimol (0.03 ug) was amnestic. Aminophosphonopentanoic acid, scopolamine and picrotoxin had no effect when injected into the amygdala mor medial septum. Our result contrasted with the recent report of an inhibitory avoidance task in which these drugs, at the doses used here, were effective when injected post-training into any of the three structures. These findings suggest that similar neurotransmitter mechanisms operate in different brain regions in order to regulate memory consolidation processes; however, there is a specialization of these brain regions in relation to different types or components of memory

Memory modulation by brain benzodiazepines

1. Recent evidence indicates that post-training memory processes are down-regulated by benzodiazepine/GABA-A systems inthe amygdala, septum and hippocampus. Havituation and avoidance learning are accompanied by a decrease of benzodiazepine-like immunoreactivity in the three structures, explainable by a release of benzodiazepines. Immediate post-training microinjection of the benzodiazepine antagonist flumazenil into the hippocampus enhances retention of habituation. The post-training administration of glumazenil into any of the three structures enhances relation of avoidance learning. 2. The mode of operation of these systems was studied in detail in the amygdala using avoidance paradigms. The release of endogenous benzodiazepines during and particularly after training enhances sensitivity of local GABA-A receptors to muscimol, activation of the GABA-A receptors opens chloride channels that can be selectively blocked by picrotoxin and by Ro-4864. Training enhances, and fluazenil reduces, sensitivity of the amygdala to the amnestic effect of locally injected muscimol by a factor of 100. Post-training intra-amygdala administration of picrotoxin or Ro5-4864 enhances retention. 3. These findings suggest that the endogenous benzoidiazepine/GABA-A mechanisms that down-regulate memory int he amygdala, septum and hippocampus are activated in response to the anxiety and/or stress associated with each task. Memory lability which occurs in the psot-training period and characterizes consolidation would thus be a consequence of the brain's response to anxiety or stress

Effect of post-training injections of flumazenil into the amygdala, hippocampus and septum on retention of habituation and of inhibitory avoidance in rats

Adult rats were submitted to two different behavioral tasks using the same apparantus: the habituation of exploration of the apparatus considered as a novel environment as measured by the decrease in number of reaings and of ambulation between training and testing, and step-down inhibitory avoidance as measured by the increase in the latency to step down from a start platform into an electrified grid between the training and the test session.The training-test interval for both tasks was 20 h.The immediate post-training injection of the benzodiazepine receptor antagonist flumazenil (10 nmol) bilateral into the hippocampus enhanced retention of the two tasks.Application of the same drug, at the same dose to the septum or amygdala had no effect on habituation but enhanced retention of the avoidance task. The data are consistent with previous findings showing that both tasks are accompanied by the release of benzodiazepine like immunoreactivity in the three structures and that this release is greater after the avoidance task. The present findings suggest a differential regional involvement of endogenous benzodiazepine-mediated mechanisms in memory modulation, according to the task undertaken

Biochemical and behavioral effects of intraseptal microinjection of fasciculin, an irreversible acetylcholinesterase inhibitor

We examined the effect, in rats, of an intraseptal microinjection of fasciculin (FAS), an irreversible peptide acetylcholinesterase (AChE) inhibitor, on a)AChE activity measured in septum and hippocampus, b)3H-quinuclidiny benzylate (3H-QNB) and 3H-oxotremorine (3H-OXO) binding to hippocampal cholinergic muscarinic receptors, c) 3H-flunitrazepan (3H-FNZ) binding to hippocampal benzodiazepine receptors as a control for QNB and OXO binding, d) acquisition and retention in three different behavioral paradigms, i. e., water-finding (in which there is concomitant habituation to be apparatus), step-down inhibitory avoidance, and shuttle avoidance. AChE activity in septum decreased 2 days (-66%) and 5 days (-48%) after FAS microinjection; a slight reduction (-35%) occurred in the dorsal hippocampus on day 2 (P<0.05; N=6 per group); no changes in AChE activity were observed in ventral hippocampus ion day 2 or day 5. No changes in 3H-QNB, 3H-OXO, or 3H-FNZ binding constants were demonstrable in the hippocampus either 2 or 5 days after intraseptal FAS adminstration. No changes in training or test session performance in any of the three behavioral situations were observed 2-3 days after the intraseptal microinjection of FAS. The persistent inhibition of septal AChE caused by FAS microinjection into the septum is not sufficient to induce major changes either in hippocampal cholinergic muscarinic receptors, or in the learning or retention of behaviors regulated by the septum and/or hippocampus

Effect of acute administration of 2,5-hexanedione on nociception in rats

Hexacarbon compounds are neurotxic to man and animals. These substance also inhibit various enzymes in vitro, including acetylcholinesterase. Since some cholinesterase inhibitor alter nociceptor we determined the effect of acute ip administration of 2,5-hexanedione on nociception in female Wistar rats (75-90 days old, 170-200g; 15-17 rats in each group) using a tail-flick apparatus. The rats were injected ip with vehicle solution (120mMNaCl containing 10 mM potassium phosphate buffer, pH 7.2) and 200, 400 or 800 mg/Kg of 2,5-hexanedione in a volume of 1 ml/Kg body weight. Tail-flick latencies were obtained 10, 30, 60 and 90 min after drug administration. All doses of 2,5-hexanedione caused antinociception (p<0.001) but the appearance and duration of the analgesia varied according to the dose of the drug. The highest dose tested (800 mg/Kg) caused analgesia from 10 to 60 min, 400 mg/Kg caused anal00 mg/Kg caused analgesia at 30 and 60 min, and 200 mg/Kg produced antinociception only at 60 min after drug injection (P < 0.05 for all the above comparisons). These results suggest that 2,5-hexanedione induces antinociception in rats. Whether this effect is mediated by a cholinergic mechanism is under inverstigation

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 (BSD) receptor antagonist, or of n-butyl-B-carboline-carboxylate (BCCB), an inverse agonist, enhanced retention of inhibitory avoidance learning. Flumazenil vlocked 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 effects. The peripheral BZD receptor agonist/chloride channel blocker Ro5-4864 had no effect on the inhibitory avoidance task when given ip prior to training, buth 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 ther 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 acoidance training or mere exposure to the training apparatus.

Diazepam inhibits retroactive interference of memory in humans: pretreatment with naltrexone does not alter this effect

1. In a double-blind of the effects of diazepam and naltrexone on retroactive memory interference, 88 health human volunteers were asked to study a text on the 1954 world Soccer Cup and were submitted to a written questionnaire on the material 48 h later. Three hours reading the text, 58 of the subjects were exposed to a non-factual, derogatory comment on the worls Cup. 2. All subjects were given either placebo or naltrexone (50 mg) before reading the text, and either placebo or diazepam (5 mg), per os, 2h after reading the text (1 h prior to the comment), Subjects were assigned to the different treatment groups by a double-blind design. 3. Exposure to the derogatory comment caused retroactive memory interference with the retention of material from the text. Diazepam blocked the retroactive interference and had no effect of its own on retention of the text. Pretreatment with naltrexone did not influence retention, retrograde interference, or the effect of diazepam on these variables. 4. The results obtained here extend to health adult humans observations made on rats and mice in which diazepam blocked retroactive interference

Effects of ACTH, epinephrine and met-enkephalin on brain B-endorphin-like immunoreactivity, and of ACTH, epinephrine, met-enkephalin and naloxone on retention, in normal and in protein- malnourished rats

Rats raised and maintained on a normal-protein diet (25% protein) responded to the ip adminsitration of ACTH-(1-24), epinephrine or Met-enkephalin with a decrease in hypothalamic Beta-endorphin-like immunoreactivity, which is attributable to a release of this substance. This effect was not seen in rats raised an maintained on a low-protein diet (8% protein). In the normal animals, the pre-test administration of ACTH, epinephrine or Met-enkephalin and the post-training adminsitration of naloxone enhanced retention-test performance of a step-down inhibitory avoidance task. These behavioral effects were absent in the protein-malnourished rats. Previous studies have shown that the behavioral effect of post-training naloxone is secondary to the release of brain Beta-endorphin during training, and that the pre-test it is not likely that the differences were caused by hyperreactivity to the aversive stimuli employed, the suggested interpretation is that protein-malnourished rats present a dysfunction in the brain Beta-endorphin system which renders it unresponsive not only to novel training experiences, but also to the pre-test retrieval enchancing effects of ACTH, epinephrine and Met-enkephalin

The use of a new non-verbal test in the evaluation of recent memory

A test for recent memory was developed using non-verbal material. The present report describes a series of experiments conducted to evaluate its reproducibility and the influences of changes in the interval between acquisition and tetrieval, and age and level of instruction, and its sensitivity to the integrity of memory function. A total of 114 subjects participated in 5 experiments. The test of recent memory is reproducible over a period of at least 5 months and can be used with training-testing intervals of 24 to 48h. The performance of the test is affected by age and level of instruction. Moreover, thre memory test is sensitive to differences in the integrity of memory function. Thus, the memory test developed in this study may be used to evaluate the effects of behavioral and/or pharmacological manipulations on recent memory in homogeneous groups of subjects