Anne Pereira de Vasconcelos

Spatial memory consolidation is associated with induction of several lysine-acetyltransferase (histone acetyltransferase) expression levels and H2B/H4 acetylation-dependent transcriptional events in the rat hippocampus.

Numerous genetic studies have shown that the CREB-binding protein (CBP) is an essential component of long-term memory formation, through its histone acetyltransferase (HAT) function. E1A-binding protein p300 and p300/CBP-associated factor (PCAF) have also recently been involved in memory formation. By contrast, only a few studies have reported on acetylation modifications during memory formation, and it remains unclear as to how the system is regulated during this dynamic phase. We investigated acetylation-dependent events and the expression profiles of these HATs during a hippocampus-dependent task taxing spatial reference memory in the Morris water maze. We found a specific increase in H2B and H4 acetylation in the rat dorsal hippocampus, while spatial memory was being consolidated. This increase correlated with the degree of specific acetylated histones enrichment on some memory/plasticity-related gene promoters. Overall, a global increase in HAT activity was measured during this memory consolidation phase, together with a global increase of CBP, p300, and PCAF expression. Interestingly, these regulations were altered in a model of hippocampal denervation disrupting spatial memory consolidation, making it impossible for the hippocampus to recruit the CBP pathway (CBP regulation and acetylated-H2B-dependent transcription). CBP has long been thought to be present in limited concentrations in the cells. These results show, for the first time, that CBP, p300, and PCAF are dynamically modulated during the establishment of a spatial memory and are likely to contribute to the induction of a specific epigenetic tagging of the genome for hippocampus-dependent (spatial) memory consolidation. These findings suggest the use of HAT-activating molecules in new therapeutic strategies of pathological aging, Alzheimers disease, and other neurodegenerative disorders.

Postnatal changes in local cerebral blood flow measured by the quantitative autoradiographic [14C]iodoantipyrine technique in freely moving rats

The postnatal changes in local cerebral blood flow in freely moving rats were measured by means of the quantitative autoradiographic [14C]iodoantipyrine method. The animals were studied at 10, 14, 17, 21, and 35 days and at the adult stage. At 10 days after birth, rates of blood flow were very low and quite homogeneous in most cerebral structures except in a few posterior areas. From these relatively uniform levels, values of local cerebral blood flow rose notably to reach a peak at 17 days in all brain regions studied. Rates of blood flow decreased between 17 and 21 days after birth and then increased from weaning time to reach the known characteristic distribution of the adult rat. The postnatal evolution of local cerebral blood flow in the rat is in good agreement with previous studies in other species such as dog and humans that also show higher rates of cerebral blood flow and glucose utilization at immature stages. However, in the rat, local cerebral blood flow and local cerebral glucose utilization are not coupled over the whole postnatal period studied, since blood flow rates reach peak values at 17 days whereas glucose utilization remains still quite low at that stage. The high rate of cerebral blood flow in the 17-day-old rat may reflect the energetic and biosynthetic needs of the actively developing brain that are completed by the summation of glucose and ketone body utilization.

The reuniens and rhomboid nuclei: neuroanatomy, electrophysiological characteristics and behavioral implications

The reuniens and rhomboid nuclei, located in the ventral midline of the thalamus, have long been regarded as having non-specific effects on the cortex, while other evidence suggests that they influence behavior related to the photoperiod, hunger, stress or anxiety. We summarise the recent anatomical, electrophysiological and behavioral evidence that these nuclei also influence cognitive processes. The first part of this review describes the reciprocal connections of the reuniens and rhomboid nuclei with the medial prefrontal cortex and the hippocampus. The connectivity pattern among these structures is consistent with the idea that these ventral midline nuclei represent a nodal hub to influence prefrontal-hippocampal interactions. The second part describes the effects of a stimulation or blockade of the ventral midline thalamus on cortical and hippocampal electrophysiological activity. The final part summarizes recent literature supporting the emerging view that the reuniens and rhomboid nuclei may contribute to learning, memory consolidation and behavioral flexibility, in addition to general behavior and aspects of metabolism.

The Ventral Midline Thalamus (Reuniens and Rhomboid Nuclei) Contributes to the Persistence of Spatial Memory in Rats

The formation of enduring declarative-like memories engages a dialog between the hippocampus and the prefrontal cortex (PFC). Electrophysiological and neuroanatomical evidence for reciprocal connections with both of these structures makes the reuniens and rhomboid nuclei (ReRh) of the thalamus a major functional link between the PFC and hippocampus. Using immediate early gene imaging (c-Fos), fiber-sparing excitotoxic lesion, and reversible inactivation in rats, we provide evidence demonstrating a contribution of the ReRh to the persistence of a spatial memory. Intact rats trained in a Morris water maze showed increased c-Fos expression (vs home cage and visible platform groups: >500%) in the ReRh when tested in a probe trial at a 25 d delay, against no change at a 5 d delay; behavioral performance was comparable at both delays. In rats subjected to excitotoxic fiber-sparing NMDA lesions circumscribed to the ReRh, we found normal acquisition of the water-maze task (vs sham-operated controls) and normal probe trial performance at the 5 d delay, but there was no evidence for memory retrieval at the 25 d delay. In rats having learned the water-maze task, lidocaine-induced inactivation of the ReRh right before the probe trial did not alter memory retrieval tested at the 5 d or 25 d delay. Together, these data suggest an implication of the ReRh in the long-term consolidation of a spatial memory at the system level. These nuclei could then be a key structure contributing to the transformation of a new hippocampal-dependent spatial memory into a remote one also depending on cortical networks.

The model of pentylenetetrazol-induced status epilepticus in the immature rat: short- and long-term effects

In order to assess acute, short and long-term effects of seizures in the immature rat brain, we studied the metabolic, circulatory and histopathological changes induced by pentylenetetrazol (PTZ) given at postnatal day 10 (P10) or 21 (P21). Seizures were induced by repetitive subconvulsive injections of PTZ given as a first dose of 40 mg/kg followed 10 min later by 20 mg/kg. Thereafter, rats received every 10 min additional injections of PTZ 10 mg/kg until the onset of status epilepticus. Local cerebral metabolic rates for glucose (LCMRglc) were measured both during the seizures in P10 and P21 rats and in the young adult animal at P60 by means of the quantitative 2-deoxyglucose technique. Rates of local cerebral blood flow (LCBF) were determined during the seizures by the iodoantipyrine technique. Short-term histological changes were assessed by acid fuchsin and hematoxylin-eosin staining and by HSP72 immunohistochemistry. At P10, LCMRglcs uniformly increased (38-400%) over control values during seizures. At P21, metabolic increases (39-181%) occurred only in 20% of the structures while LCMRglcs decreased in most cortical, hippocampal and sensory areas as well as in mammillary body, discrete thalamic nuclei and white matter areas. At P10, LCBF rose (32-184%) in all brain structures whereas, at P21, LCBF decreased in cortical, hippocampal and sensory regions and increased in most other areas. At P60, in animals having seized at either age, significant long-term decreases in LCMRglcs were recorded in hippocampus, auditory and piriform cortex, medial geniculate body and mammillary body. In P60 animals exposed to PTZ at P10, LCMRglcs were also decreased in 3 other sensory areas. In P60 animals exposed to seizures at P21, LCMRglcs were additionally decreased in sensory regions, cortices, thalamic and hypothalamic regions. Neuronal cells were transiently stained with acid fuchsin, with a peak occurring at 24 h after the seizures. The stain was visible in all regions of cerebral cortex and hippocampus and in some thalamic and hypothalamic nuclei. This transient staining was not accompanied by cell degeneration as assessed by hematoxylin-eosin histology. No HSP72 expression could be detected 24 h after the seizures, neither at P10 nor at P21. The present study shows that the immature rat neurons undergo altered metabolic rates and local circulatory decreases in the acute phase, a change in the affinity of acid fuchsin as a short-term effect and long-term metabolic decreases. All these changes are located in the same regions, i.e., cerebral cortex, hippocampus, sensory regions as well as scattered thalamic and hypothalamic nuclei. Thus, short- and long-term metabolic changes induced by seizures can be used as an index of cell stress in the immature rat brain. Since all these changes occur in the absence of visible neuronal death, they might be related to changes in the final arborization and synaptic organization of the developing brain.

Hippocampal-dependent spatial memory functions might be lateralized in rats: An approach combining gene expression profiling and reversible inactivation.

The hippocampus is involved in spatial memory processes, as established in a variety of species such as birds and mammals including humans. In humans, some hippocampal‐dependent memory functions may be lateralized, the right hippocampus being predominantly involved in spatial navigation. In rodents, the question of possible lateralization remains open. Therefore, we first microdissected the CA1 subregion of the left and right dorsal hippocampi for analysis of mRNA expression using microarrays in rats having learnt a reference memory task in the Morris water‐maze. Relative to untrained controls, 623 genes were differentially expressed in the right hippocampus, against only 74 in the left hippocampus, in the rats that had learnt the hidden platform location. Thus, in the right hippocampus, 299 genes were induced, 324 were repressed, and about half of them participate in signaling and transport, metabolism, and nervous system functions. In addition, most differentially expressed genes associated with spatial learning have been previously related to synaptic plasticity and memory. We then subjected rats to unilateral (left or right) or bilateral reversible functional inactivations in the dorsal hippocampus; lidocaine was infused either before each acquisition session or before retrieval of a reference spatial memory in the Morris water maze. We found that after drug‐free acquisition, right or bilateral lidocaine inactivation (vs. left, or bilateral phosphate buffered saline (PBS) infusions) of the dorsal hippocampus just before a delayed (24 h) probe trial impaired performance. Conversely, left or bilateral hippocampus inactivation (vs. right, or bilateral PBS infusions) before each acquisition session weakened performance during a delayed, drug‐free probe trial. Our data confirm a functional association between transcriptional activity within the dorsal hippocampus and spatial memory in the rat. Further, they suggest that there could be a leftward bias of hippocampal functions in engram formation or information transfer, and a rightward bias in spatial memory storage/retrieval processes.

The Ventral Midline Thalamus Contributes to Strategy Shifting in a Memory Task Requiring Both Prefrontal Cortical and Hippocampal Functions

Electrophysiological and neuroanatomical evidence for reciprocal connections with the medial prefrontal cortex (mPFC) and the hippocampus make the reuniens and rhomboid (ReRh) thalamic nuclei a putatively major functional link for regulations of cortico-hippocampal interactions. In a first experiment using a new water escape device for rodents, the double-H maze, we demonstrated in rats that a bilateral muscimol (MSCI) inactivation (0.70 vs 0.26 and 0 nmol) of the mPFC or dorsal hippocampus (dHip) induces major deficits in a strategy shifting/spatial memory retrieval task. By way of comparison, only dHip inactivation impaired recall in a classical spatial memory task in the Morris water maze. In the second experiment, we showed that ReRh inactivation using 0.70 nmol of MSCI, which reduced performance without obliterating memory retrieval in the water maze, produces an as large strategy shifting/memory retrieval deficit as mPFC or dHip inactivation in the double-H maze. Thus, behavioral adaptations to task contingency modifications requiring a shift toward the use of a memory for place might operate in a distributed circuit encompassing the mPFC (as the potential set-shifting structure), the hippocampus (as the spatial memory substrate), and the ventral midline thalamus, and therein the ReRh (as the coordinator of this processing). The results of the current experiments provide a significant extension of our understanding of the involvement of ventral midline thalamic nuclei in cognitive processes: they point to a role of the ReRh in strategy shifting in a memory task requiring cortical and hippocampal functions and further elucidate the functional system underlying behavioral flexibility.

Local cerebral blood flow during lithium-pilocarpine seizures in the developing and adult rat: role of coupling between blood flow and metabolism in the genesis of neuronal damage.

Coupling between local cerebral blood flow and local cerebral metabolic rate for glucose is involved in the pathogenesis of epilepsy-related neuronal damage in the adult brain; however, its role in the immature brain is unknown. Lithium–pilocarpine–induced status epilepticus is associated with extended damage in adult rats, mostly in the forebrain limbic areas and thalamus, whereas damage was moderate in 21-day-old rats (P21) or absent in P10 rats. The quantitative autoradiographic [14C]iodoantipyrine technique was applied to measure the consequences of lithium-pilocarpine status epilepticus on local cerebral blood flow. In adult and P21 rats, local cerebral blood flow rates increased by 50% to 400%; the highest increases were recorded in regions showing damage in adults. At P10, local cerebral blood flow rates decreased by 40% to 60% in most areas, except in some forebrain regions showing no change during status epilepticus. In areas injured when status epilepticus was induced in adults, a strong hypermetabolism (Fernandes et al., 1999) not matched by comparable local cerebral blood flow increases was present in rats of all ages, whereas in damage-resistant areas, local cerebral metabolic rate for glucose and local cerebral blood flow remained coupled in the three age groups. Thus, the level of coupling between blood flow supply and metabolism is not involved in seizure-related brain damage in the developing brain, which appears to be resistant to the consequences of such a mismatch.

MDMA: Interactions with other psychoactive drugs

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is one of the most widely abused illegal drugs. Some users self-report euphoria and an increased perception and feeling of closeness to others. When taken in warm environments, MDMA users may develop acute complications with potential fatal consequences. In rodents, MDMA increases locomotor activity and, depending on ambient temperature, may produce a dose-dependent, potentially lethal hyperthermia. Like most other recreational drugs, MDMA is frequently taken in combination with other substances including tobacco, EtOH, marijuana, amphetamines, cocaine and, caffeine. Although polydrug use is very common, the understanding of the effects of this multiple substance use, as well as the analysis of consequences of different drug-drug associations, received rather little attention. The purpose of this review is to summarize our current knowledge about the changes on MDMA-related behavior, pharmacology, and neurotoxicity associated with co-consumption of other drugs of abuse and psychoactive agents.

Context-dependent modulation of hippocampal and cortical recruitment during remote spatial memory retrieval.

According to systems consolidation, as hippocampal‐dependent memories mature over time, they become additionally (or exclusively) dependent on extra‐hippocampal structures. We assessed the recruitment of hippocampal and cortical structures on remote memory retrieval in a performance‐degradation resistant (PDR; no performance degradation with time) versus performance‐degradation prone (PDP; performance degraded with time) context. Using a water‐maze task in two contexts with a hidden platform and three control conditions (home cage, visible platform with or without access to distal cues), we compared neuronal activation (c‐Fos imaging) patterns in the dorsal hippocampus and the medial prefrontal cortex (mPFC) after the retrieval of recent (5 days) versus remote (25 days) spatial memory. In the PDR context, the hippocampus exhibited greater c‐Fos protein expression on remote than recent memory retrieval, be it in the visible or hidden platform group. In the PDP context, hippocampal activation increased at the remote time point and only in the hidden platform group. In the anterior cingulate cortex, c‐Fos expression was greater for remote than for recent memory retrieval and only in the PDR context. The necessity of the mPFC for remote memory retrieval in the PDR context was confirmed using region‐specific lidocaine inactivation, which had no impact on recent memory. Conversely, inactivation of the dorsal hippocampus impaired both recent and remote memory in the PDR context, and only recent memory in the PDP context, in which remote memory performance was degraded. While confirming that neuronal circuits supporting spatial memory consolidation are reorganized in a time‐dependent manner, our findings further indicate that mPFC and hippocampus recruitment (i) depends on the content and perhaps the strength of the memory and (ii) may be influenced by the environmental conditions (e.g., cue saliency, complexity) in which memories are initially formed and subsequently recalled.