Vincenzo Cestari

Essential role for TrkB receptors in hippocampus-mediated learning.

Brain-derived neurotrophic factor (BDNF) and its receptor TrkB regulate both short-term synaptic functions and long-term potentiation (LTP) of brain synapses, raising the possibility that BDNF/TrkB may be involved in cognitive functions. We have generated conditionally gene targeted mice in which the knockout of the trkB gene is restricted to the forebrain and occurs only during postnatal development. Adult mutant mice show increasingly impaired learning behavior or inappropriate coping responses when facing complex and/or stressful learning paradigms but succeed in simple passive avoidance learning. Homozygous mutants show impaired LTP at CA1 hippocampal synapses. Interestingly, heterozygotes show a partial but substantial reduction of LTP but appear behaviorally normal. Thus, CA1 LTP may need to be reduced below a certain threshold before behavioral defects become apparent.

A role for the Ras signalling pathway in synaptic transmission and long-term memory.

Members of the Ras subfamily of small guanine-nucleotide-binding proteins are essential for controlling normal and malignant cell proliferation as well as cell differentiation. The neuronal-specific guanine-nucleotide-exchange factor, Ras-GRF/CDC25Mm (refs 2,3,4), induces Ras signalling in response to Ca2+ influx and activation of G-protein-coupled receptors in vitro, suggesting that it plays a role in neurotransmission and plasticity in vivo. Here we report that mice lacking Ras-GRF are impaired in the process of memory consolidation, as revealed by emotional conditioning tasks that require the function of the amygdala; learning and short-term memory are intact. Electrophysiological measurements in the basolateral amygdala reveal that long-term plasticity is abnormal in mutant mice. In contrast, Ras-GRF mutants do not reveal major deficits in spatial learning tasks such as the Morris water maze, a test that requires hippocampal function. Consistent with apparently normal hippocampal functions, Ras-GRF mutants show normal NMDA (N-methyl-D-aspartate) receptor-dependent long-term potentiation in this structure. These results implicate Ras-GRF signalling via the Ras/MAP kinase pathway in synaptic events leading to formation of long-term memories.

In vivo gene therapy of metachromatic leukodystrophy by lentiviral vectors: correction of neuropathology and protection against learning impairments in affected mice

Metachromatic leukodystrophy (MLD) is a lipidosis caused by deficiency of arylsulfatase A (ARSA). Although the genetics of MLD are known, its pathophysiology is not understood. The disease leads to progressive demyelination and early death and no effective treatment is available. We used lentiviral vectors to deliver a functional ARSA gene (human ARSA) into the brain of adult mice with germ-line inactivation of the mouse gene encoding ARSA, As2. We report sustained expression of active enzyme throughout a large portion of the brain, with long-term protection from development of neuropathology and hippocampal-related learning impairments. We show that selective degeneration of hippocampal neurons is a central step in disease pathogenesis, and provide evidence that in vivo transfer of ARSA by lentiviral vectors reverts the disease phenotype in all investigated areas. Therefore, in vivo gene therapy offers a unique option for MLD and other storage diseases affecting the central nervous system.

Memory for prices and the euro cash changeover: an analysis for cinema prices in Italy

The question addressed by this study is whether consumers remember past prices correctly. We test Italian citizensi?½ memory for cinema prices with questionnaires distributed to moviegoers. The analysis concentrates on the memory of pre-euro prices, but the recall for a more recent period is also investigated. The results show that only a small percentage of respondents recalled the correct price, and that the average prices recalled were much lower than the actual pre-euro prices and dated back to years before the changeover. Price recall is less accurate for the respondents who perceive higher and more persistent inflation; it is also worse for the older respondents and for the less frequent movie-goers.

The Timing of Differentiation of Adult Hippocampal Neurons Is Crucial for Spatial Memory

Adult neurogenesis in the dentate gyrus plays a critical role in hippocampus-dependent spatial learning. It remains unknown, however, how new neurons become functionally integrated into spatial circuits and contribute to hippocampus-mediated forms of learning and memory. To investigate these issues, we used a mouse model in which the differentiation of adult-generated dentate gyrus neurons can be anticipated by conditionally expressing the pro-differentiative gene PC3 (Tis21/BTG2) in nestin-positive progenitor cells. In contrast to previous studies that affected the number of newly generated neurons, this strategy selectively changes their timing of differentiation. New, adult-generated dentate gyrus progenitors, in which the PC3 transgene was expressed, showed accelerated differentiation and significantly reduced dendritic arborization and spine density. Functionally, this genetic manipulation specifically affected different hippocampus-dependent learning and memory tasks, including contextual fear conditioning, and selectively reduced synaptic plasticity in the dentate gyrus. Morphological and functional analyses of hippocampal neurons at different stages of differentiation, following transgene activation within defined time-windows, revealed that the new, adult-generated neurons up to 3–4 weeks of age are required not only to acquire new spatial information but also to use previously consolidated memories. Thus, the correct unwinding of these key memory functions, which can be an expression of the ability of adult-generated neurons to link subsequent events in memory circuits, is critically dependent on the correct timing of the initial stages of neuron maturation and connection to existing circuits.

D1 and D2 receptor antagonists differently affect cocaine-induced locomotor hyperactivity in the mouse

Pretreament with small, per se ineffective doses of the selective D1 antagonist SCH 23390 inhibited hyperactivity induced by cocaine. On the other hand, the classic neuroleptic haloperidol and the selective D2 antagonist metoclopramide prevented the stimulatory effects of cocaine on locomotion only at hypokinetic doses, while the atypical neuroleptic (−)-sulpiride, a selective D2 antagonist, did not produce significant effects when administered at the hypokinetic dose of 12 mg/kg. Finally, at low doses (−)-sulpiride dose-dependently potentiated the locomotor-stimulating effects of cocaine, an effect that is not shared either with haloperidol or with metoclopramide. These results are discussed in terms of different roles of DA receptor subtypes in the modulation of the stimulant effects of cocaine on locomotion.

Cannabinoids and memory: animal studies.

This review will consider studies concerning the effects of cannabinoid receptor agonists and antagonists on memory in laboratory animals. Two subtypes of cannabinoid receptors have been identified to date: the central CB1 subtype and the peripheral CB2 subtype. The receptor which specifically binds Delta9-tetrahydrocannabinol (Delta9-THC) and related compounds in rat and human brain has been discovered and cloned by a number of researchers. This cannabinoid receptor is localized with high concentrations in different brain areas, including hippocampus and amygdala, which play an important role in the modulation of memory. In recent years evidence has been obtained that cannabinoids influence memory processes. It has been shown, for example, that Delta9-THC impairs memory in rats, mice and monkeys tested in a variety of experimental conditions (radial maze, instrumental discrimination tasks, Morris water maze, etc.). In some of these researches the effect of Delta9-THC was antagonized by the CB1 receptor antagonist SR 141716A, showing the involvement of this subtype of cannabinoid receptor in its effect. Anandamide, arachidonylethanolamide, was recently discovered as the first endogenous ligand for the cannabinoid receptor. It has been reported to stimulate CB1 receptors and to mimic the pharmacological effects of cannabinoids. Experiments carried out by our group have shown that anandamide impairs memory consolidation in random bred mice (CD1), exerts genotype-dependent influences on memory in inbred strain of mice (C57 BL/6 and DBA/2), and that opioid and dopaminergic systems might be involved in its effects.

Post-training dopamine receptor agonists and antagonists affect memory storage in mice irrespective of their selectivity for D1 or D2 receptors

Post-training administration of the selective D1 and D2 agonists SKF 38393 and LY 171555 dose-dependently facilitated retention of an inhibitory avoidance response in mice, while the selective D1 or D2 antagonists SCH 23390 and (-)sulpiride produced an impairment of retention. These effects are not to be ascribed to a nonspecific action of the drugs on retention performance, as the latencies during the retention test of those mice that had not received a footshock during the training were not increased by the post-training drug administration. The effects on retention performance induced by DA agonists and antagonists seem to be due to an effect on memory consolidation, since they have been observed when drugs were given at short, but not at long, periods of time after training. These results showing a similar role of D1 and D2 receptor types on memory storage appear not to be consistent with a body of neuropharmacological, neurophysiological, and behavioral evidence pointing to a different functional role of these types of DA receptors. This discrepancy is discussed in terms of possible involvement of different brain systems, peripheral systems, or possible second messenger processes activated by the two receptor types and leading to similar effects on memory processes.

Impaired Terminal Differentiation of Hippocampal Granule Neurons and Defective Contextual Memory in PC3/Tis21 Knockout Mice

Neurogenesis in the dentate gyrus of the adult hippocampus has been implicated in neural plasticity and memory, but the molecular mechanisms controlling the proliferation and differentiation of newborn neurons and their integration into the synaptic circuitry are still largely unknown. To investigate this issue, we have analyzed the adult hippocampal neurogenesis in a PC3/Tis21-null mouse model. PC3/Tis21 is a transcriptional co-factor endowed with antiproliferative and prodifferentiative properties; indeed, its upregulation in neural progenitors has been shown to induce exit from cell cycle and differentiation. We demonstrate here that the deletion of PC3/Tis21 causes an increased proliferation of progenitor cells in the adult dentate gyrus and an arrest of their terminal differentiation. In fact, in the PC3/Tis21-null hippocampus postmitotic undifferentiated neurons accumulated, while the number of terminally differentiated neurons decreased of 40%. As a result, PC3/Tis21-null mice displayed a deficit of contextual memory. Notably, we observed that PC3/Tis21 can associate to the promoter of Id3, an inhibitor of proneural gene activity, and negatively regulates its expression, indicating that PC3/Tis21 acts upstream of Id3. Our results identify PC3/Tis21 as a gene required in the control of proliferation and terminal differentiation of newborn neurons during adult hippocampal neurogenesis and suggest its involvement in the formation of contextual memories.

Strain-dependent effects of post-training GABA receptor agonists and antagonists on memory storage in mice

Post-training administration of the GABA-A and GABA-B receptor agonists muscimol and baclofen dose-dependently impaired retention of an inhibitory avoidance response in C57 mice, while improving memory consolidation in the DBA strain. By contrast, picrotoxin (blocker of GABA-activated ionophores), bicuculline (GABA-A antagonist) and CGP 35348 (GABA-B antagonist) dose-dependently improved retention in C57 mice and impaired it in DBA mice. These effects cannot be ascribed to non-specific actions of the drugs on retention performance, as the latencies during the retention test of those mice that had not received footshock during the training were not lengthened by the post-training drug administration. The effects on retention performance induced by GABA agonists and antagonists are probably due to an effect on memory consolidation, since they are observed when the drugs are given at short, but not at long, intervals after training. These results are discussed in terms of possible interaction of GABA systems with endogenous opioid and dopamine systems, whose activation has been shown to produce strain-dependent effects on memory processes. The possible utilization of these results for a genetic behavioral approach with recombinant inbred (RI) mice is also considered.