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Memory expression is independent of memory labilization/reconsolidation

There is growing evidence that certain reactivation conditions restrict the onset of both the destabilization phase and the restabilization process or reconsolidation. However, it is not yet clear how changes in memory expression during the retrieval experience can influence the emergence of the labilization/reconsolidation process. To address this issue, we used the context-signal memory model of Chasmagnathus. In this paradigm a short reminder that does not include reinforcement allows us to evaluate memory labilization and reconsolidation, whereas a short but reinforced reminder restricts the onset of such a process. The current study investigated the effects of the glutamate antagonists, APV (0.6 or 1.5 μg/g) and CNQX (1 μg/g), prior to the reminder session on both behavioral expression and the reconsolidation process. Under conditions where the reminder does not initiate the labilization/reconsolidation process, APV prevented memory expression without affecting long-term memory retention. In contrast, APV induced amnesic effects in the long-term when administered before a reminder session that triggers reconsolidation. Under the present parametric conditions, the administration of CNQX prior to the reminder that allows memory to enter reconsolidation impairs this process without disrupting memory expression. Overall, the present findings suggest that memory reactivation--but not memory expression--is necessary for labilization and reconsolidation. Retrieval and memory expression therefore appear not to be interchangeable concepts.

Dissociation between memory reactivation and its behavioral expression: scopolamine interferes with memory expression without disrupting long-term storage.

The reconsolidation hypothesis has challenged the traditional view of fixed memories after consolidation. Reconsolidation studies have disclosed that the mechanisms mediating memory retrieval and the mechanisms that underlie the behavioral expression of memory can be dissociated, offering a new prospect for understanding the nature of experimental amnesia. The muscarinic antagonist scopolamine has been used for decades to induce experimental amnesias The goal of the present study is to determine whether the amnesic effects of scopolamine are due to storage (or retrieval) deficits or, alternatively, to a decrease in the long-term memory expression of a consolidated long-term memory. In the crab Chasmagnathus memory model, we found that scopolamine-induced amnesia can be reverted by facilitation after reminder presentation. This recovery of memory expression was reconsolidation specific since a reminder that does not triggers reconsolidation process did not allow the recovery. A higher dose (5 μg/g) of scopolamine induced an amnesic effect that could not be reverted through reconsolidation, and thus it can be explained as an interference with memory storage and/or retrieval mechanisms. These results, showing that an effective amnesic dose of scopolamine (100 ng/g) negatively modulates long-term memory expression but not memory storage in the crab Chasmagnathus, are consistent with the concept that dissociable processes underlie the mechanisms mediating memory reactivation and the behavioral expression of memory.

Updating contextual information during consolidation as result of a new memory trace.

Reconsolidation studies have led to the hypothesis that memory, when labile, would be modified in order to incorporate new information. This view has reinstated original propositions suggesting that short-term memory provides the organism with an opportunity to evaluate and rearrange information before storing it, since it is concurrent with the labile state of consolidation. The Chasmagnathus associative memory model is used here to test whether during consolidation it is possible to change some attribute of recently acquired memories. In addition, it is tested whether these changes in behavioral memory features can be explained as modifications on the consolidating memory trace or as a consequence of a new memory trace. We show that short-term memory is, unlike long-term memory, not context specific. During this short period after learning, behavioral memory can be updated in order to incorporate new contextual information. We found that, during this period, the cycloheximide retrograde amnesic effect can be reverted by a single trial in a new context. Finally, by means of memory sensitivity to cycloheximide during consolidation and reconsolidation, we show that the learning of a new context (CS) during this short-term memory period builds up a new memory trace that sustains the behavioral memory update.

Pre-Excitation syndrome and hypertrophic cardiomyopathy

Among one hundred and five consecutive patients with pre-excitation (PE) syndrome studied during a 10-year period, eight had an associated hypertrophic cardiomyopathy (HC) (7.62 per cent), eight had a coronary heart disease (7.62 per cent) and nine had a hypertensive heart disease (8.57 per cent). Of the eight patients with HC, four had an asymmetrical form (three of them with an obstructive component), and four a symmetrical form. Seven of these patients had a Wolff-Parkinson-White (WPW) type of PE and the remainder a Lown-Ganong-Levine type of PE. The incidence of paroxysmal tachycardias in the total group was 56.2% (61/105) and in the patients with associated HC was 62.5% (5/8). One of these latter patients had a concomitant brady-tachy syndrome and a severe obstructive form of HC. He was surgically treated (septal myomectomy and section of accessory atrioventricular pathway). The ECGs and VCGs of the seven patients with the HC-WPW type of PE association showed the coexistence of incomplete left bundle branch block of left ventricular hypertrophy patterns. The eight patients with associated HC were closely followed up from two to seven years (total follow-up period 435 patient/months). One of them died suddenly during the 40th month of follow-up. This study suggests that: 1) HC-PE association is not infrequent; 2) the incidence of paroxysmal tachycardias in the subgroup is quite similar to that presented in isolated PE; and 3) the electrocardiographic and vectorcardiographic changes in the HC-WPW type of PE association are highly specific.

Swallowing-dependent atrial tachyarrhythmias. Their mechanism

We describe here the case of one patient who exhibited several types of atrial tachyarrhythmias induced by swallowing. There was no evidence of other cardiac or gastroesophagic abnormalities. The electrophysiologic study demonstrated a second degree A-V block due to block within the atria. Our findings suggest that the mechanism operative may be an intra-atrial micro-reentry induced by an increased vagovagal reflex triggered by the normal esophageal peristalsis.

Angiotensin modulates long-term memory expression but not long-term memory storage in the crab Chasmagnathus

Memory reconsolidation is a dynamic process in which a previously consolidated memory becomes labile following reactivation by a reminder. In a previous study in the crab Chasmagnathus memory model, we showed that a water-shortage episode, via angiotensin modulation during reconsolidation, could reveal a memory that otherwise remains unexpressed: weakly trained animals cannot reveal long-term memory (LTM) except when an episode of noticeable ethological meaning, water deprivation, is contingent upon reconsolidation. However, these results are at variance with two of our previous interpretations: weak training protocols do not build LTM and angiotensin II modulates the strength of the information storing process. A parsimonious hypothesis is that in Chasmagnathus angiotensins regulate LTM expression, but not LTM storage. Here, we tested three predictions of this hypothesis. First, the well-known retrograde amnesic effect of the angiotensin II antagonist saralasin is not due to interference on memory storage, but to modulation of memory expression. Second, the recovery of the LTM memory expression of the apparently amnesic retrograde effect produced by saralasin, through the water-shortage episode contingent upon reconsolidation, must be reconsolidation specific. Consequently, summation-like effects and retrieval deficits cannot explain these results because of the parametric conditions of reconsolidation. Third, weak training protocols build an unexpressed LTM that requires mRNA transcription and translation, a diagnostic characteristic of LTM. Results show that angiotensin modulates LTM expression but not LTM memory storage in the crab Chasmagnathus. The results lead us to suggest that, in Chasmagnathus, LTM expression - the process of gaining appreciable control over behavior of the reactivated trace in the retrieval session - may be considered a distinct attribute of its long-term storage. This strategy, a positive modulation during reconsolidation, is proposed to distinguish between memories that can be reactivated, labilized and are not expressed, and memories that are not stored long term, obliterated or altered in other retrieval mechanisms.

Memory beyond expression.

The idea that memories are not invariable after the consolidation process has led to new perspectives about several mnemonic processes. In this framework, we review our studies on the modulation of memory expression during reconsolidation. We propose that during both memory consolidation and reconsolidation, neuromodulators can determine the probability of the memory trace to guide behavior, i.e. they can either increase or decrease its behavioral expressibility without affecting the potential of persistent memories to be activated and become labile. Our hypothesis is based on the findings that positive modulation of memory expression during reconsolidation occurs even if memories are behaviorally unexpressed. This review discusses the original approach taken in the studies of the crab Neohelice (Chasmagnathus) granulata, which was then successfully applied to test the hypothesis in rodent fear memory. Data presented offers a new way of thinking about both weak trainings and experimental amnesia: memory retrieval can be dissociated from memory expression. Furthermore, the strategy presented here allowed us to show in human declarative memory that the periods in which long-term memory can be activated and become labile during reconsolidation exceeds the periods in which that memory is expressed, providing direct evidence that conscious access to memory is not needed for reconsolidation. Specific controls based on the constraints of reminders to trigger reconsolidation allow us to distinguish between obliterated and unexpressed but activated long-term memories after amnesic treatments, weak trainings and forgetting. In the hypothesis discussed, memory expressibility--the outcome of experience-dependent changes in the potential to behave--is considered as a flexible and modulable attribute of long-term memories. Expression seems to be just one of the possible fates of re-activated memories.

Dissimilar atrial rhythms. A patient with triple right atrial rhythm.

A patient with complete A-V block and atrial fibrillation was analyzed by multiple intra-atrial electrograms. Three areas were recorded in the right atrium, each of them with different electrophysiological properties: (1) persistent atrial standstill, (2) irregular atrial activity with a rate of 50/minute, and (3) fibrilloflutter waves with a rate of 450/minute. The latter were also registered in the left atrium. This case illustrates another form of dissimilar atrial rhythms, and provides additional evidence of the importance of recording multiple electrograms from each atrium in the evaluation of the atrial events in atypical atrial arrhythmias.

Enhancement of long-term memory expression by a single trial during consolidation.

Before the memory trace is stored long term, it must undergo a phase of consolidation during which it remains susceptible to modifications. It has previously been proposed that during consolidation, memories are kept from being stored long term, and can therefore be modified with additional information resulting from ongoing behavior. The Chasmagnathus associative memory model is used here to test whether it is possible during consolidation to modify the long-term expression of a memory generated by a weak training procedure. In this memory model, long-term memory expression is achieved after strong training protocols, a 15-spaced trial procedure. After a weak training protocol (WTP, six spaced trials), crabs do not show memory retention when tested in the long term. Nevertheless, the WTP builds a long-term memory that it is indeed consolidated, but remains unexpressed. Here we show that memory can be modified by experience during this short period after learning: memory expression can be enhanced by a Single Trial Session, on the condition that this session takes place contingent upon the consolidation period. We also found that during this time, the memory built by the WTP is behaviorally expressed, in contrast with what occurs at long term. Our results support the idea that during consolidation memories can be evaluated in the background of concurrent experiences. In particular, we propose that during the consolidation period it is possible for crabs to assess which experiences, among those stored long term, will be expressed long term.

Captopril versus hydralazine in primary pulmonary hypertension.

Abstract: Captopril was tested as the treatment for a patient with primary pulmonary hypertension (PPH) and its effects were compared with those of hydralazine. Captopril induced a rise in pulmonary pressures and in intrapulmonary shunt; hydralazine lowered pulmonary resistances and increased paO2 and blood O2 transport. Prospective studies in PPH treated with captopril are recommended and evaluation of all drugs not only by hemodynamic but also respiratory and O2 transport measurements.