Influence of hippocampectomy on habituation, exploratory behavior, and spatial memory in rats

Biological significance and pathophysiological role of Matrix Metalloproteinases in the Central Nervous System

Matrix Metalloproteinases (MMPs), which are endopeptidase reliant on zinc, are low in embryonic tissues but increases in response to a variety of physiological stimulus and pathological stresses. Neuro-glial cells, endothelial cells, fibroblasts, and leucocytes secrete MMPs, which cleave extracellular matrix proteins in a time-dependent manner. MMPs affect synaptic plasticity and the development of short-term memory by controlling the size, shape, and excitatory synapses' function through the lateral diffusion of receptors. In addition, MMPs influence the Extracellular Matrix proteins in the Peri-Neuronal Net at the Neuro-glial interface, which aids in the establishment of long-term memory. Through modulating neuronal, and glial cells migration, differentiation, Neurogenesis, and survival, MMPs impact brain development in mammals. In adult brains, MMPs play a beneficial role in physiological plasticity, which includes learning, memory consolidation, social interaction, and complex behaviors, by proteolytically altering a wide variety of factors, including growth factors, cytokines, receptors, DNA repair enzymes, and matrix proteins. Additionally, stress, depression, addiction, hepatic encephalopathy, and stroke may all have negative effects on MMPs. In addition to their role in glioblastoma development, MMPs influence neurological diseases such as epilepsy, schizophrenia, autism spectrum disorder, brain damage, pain, neurodegeneration, and Alzheimer's and Parkinson's. To help shed light on the potential of MMPs as a therapeutic target for neurodegenerative diseases, this review summarizes their regulation, mode of action, and participation in brain physiological plasticity and pathological damage. Finally, by employing different MMP-based nanotools and inhibitors, MMPs may also be utilized to map the anatomical and functional connectome of the brain, analyze its secretome, and treat neurodegenerative illnesses.

Exploring the Role of MMP-9 and MMP-9/TIMP-1 Ratio in Subacute Stroke Recovery: A Prospective Observational Study

Despite the significant changes that unfold during the subacute phase of stroke, few studies have examined recovery abilities during this critical period. As neuroinflammation subsides and tissue degradation diminishes, the processes of neuroplasticity and angiogenesis intensify. An important factor in brain physiology and pathology, particularly neuroplasticity, is matrix metalloproteinase 9 (MMP-9). Its activity is modulated by tissue inhibitors of metalloproteinases (TIMPs), which impede substrate binding and activity by binding to its active sites. Notably, TIMP-1 specifically targets MMP-9 among other matrix metalloproteinases (MMPs). Our present study examines whether MMP-9 may play a beneficial role in psychological functions, particularly in alleviating depressive symptoms and enhancing specific cognitive domains, such as calculation. It appears that improvements in depressive symptoms during rehabilitation were notably linked with baseline MMP-9 plasma levels (r = -0.36, p = 0.025), and particularly so with the ratio of MMP-9 to TIMP-1, indicative of active MMP-9 (r = -0.42, p = 0.008). Furthermore, our findings support previous research demonstrating an inverse relationship between pre-rehabilitation MMP-9 serum levels and post-rehabilitation motor function. Crucially, our study emphasizes a positive correlation between cognition and motor function, highlighting the necessity of integrating both aspects into rehabilitation planning. These findings demonstrate the potential utility of MMP-9 as a prognostic biomarker for delineating recovery trajectories and guiding personalized treatment strategies for stroke patients during the subacute phase.

Propofol-Induced Developmental Neurotoxicity: From Mechanisms to Therapeutic Strategies

Propofol is the most commonly used intravenous general anesthetic in clinical anesthesia, and it is also widely used in general anesthesia for pregnant women and infants. Some clinical and preclinical studies have found that propofol causes damage to the immature nervous system, which may lead to neurodevelopmental disorders and cognitive dysfunction in infants and children. However, its potential molecular mechanism has not been fully elucidated. Recent in vivo and in vitro studies have found that some exogenous drugs and interventions can effectively alleviate propofol-induced neurotoxicity. In this review, we focus on the relevant preclinical studies and summarize the latest findings on the potential mechanisms and therapeutic strategies of propofol-induced developmental neurotoxicity.

Perfluorinated chemicals (PFOA) can, by interacting with highly brominated diphenyl ethers (PBDE 209) during a defined period of neonatal brain development, exacerbate neurobehavioural defects

Perfluorinated compounds (PFCs) and polybrominated diphenyl ethers (PBDEs) are ubiquitous persistent environmental compounds, present in humans and at higher levels in infants/children than in adults. This study shows that co-exposure to pentadecafluorooctanoic acid (PFOA) and 2,2',3,3',4,4',5,5',6,6'-decaBDE (PBDE 209) can significantly exacerbate developmental neurobehavioural defects. Neonatal male NMRI mice, 3 and 10 days old, were exposed perorally to PBDE 209 (1.4 or 8.0 μmol/kg bw), PFOA (1.4 or 14 μmol/kg bw), co-exposed to PBDE 209 and PFOA (at the given doses), or a vehicle (20% fat emulsion) and observed for spontaneous behaviour in a novel home environment when 2 and 4 months old. The behavioural defects observed included hyperactivity and reduced habituation indicating cognitive defects. This interaction appears most likely dependent on the presence of PBDE 209 and/or its metabolites together with PFOA, during a defined critical period of neonatal brain development, corresponding to the perinatal and newborn period in humans.

Extracellular matrix metalloproteinase-9 (MMP-9) is required in female mice for 17β-estradiol enhancement of hippocampal memory consolidation

Hippocampal plasticity and memory are modulated by the potent estrogen 17β-estradiol (E₂). Research on the molecular mechanisms of hippocampal E₂ signaling has uncovered multiple intracellular pathways that contribute to these effects, but few have questioned the role that extracellular signaling processes may play in E₂ action. Modification of the extracellular matrix (ECM) by proteases like matrix metalloproteinase-9 (MMP-9) is critical for activity-dependent remodeling of synapses, and MMP-9 activity is required for hippocampal learning and memory. Yet little is known about the extent to which E₂ regulates MMP-9 in the hippocampus, and the influence this interaction may have on hippocampal memory. Here, we examined the effects of hippocampal MMP-9 activity on E₂-induced enhancement of spatial and object recognition memory consolidation. Post-training bilateral infusion of an MMP-9 inhibitor into the dorsal hippocampus of ovariectomized female mice blocked the enhancing effects of E₂ on object placement and object recognition memory, supporting a role for MMP-9 in estrogenic regulation of memory consolidation. E₂ also rapidly increased the activity of dorsal hippocampal MMP-9 without influencing its protein expression, providing further insight into hippocampal E₂/MMP-9 interactions. Together, these results provide the first evidence that E₂ regulates MMP-9 to modulate hippocampal memory and highlight the need to further study estrogenic regulation of extracellular modification.

Paracetamol (Acetaminophen) and its Effect on the Developing Mouse Brain

Paracetamol, or acetaminophen (AAP), is the most commonly used analgesic during pregnancy and early life. While therapeutic doses of AAP are considered harmless during these periods, recent findings in both humans and rodents suggest a link between developmental exposure to AAP and behavioral consequences later in life. The aim of this study is to evaluate the impact of neonatal exposure to clinically relevant doses of AAP on adult spontaneous behavior, habituation, memory, learning, and cognitive flexibility later in life using a mouse model. Markers of oxidative stress, axon outgrowth, and glutamatergic transmission were also investigated in the hippocampus during the first 24 h after exposure. In addition, potential long-term effects on synaptic density in the hippocampus have been investigated. In a home cage setting, mice neonatally exposed to AAP (30 + 30 mg/kg, 4 h apart) on postnatal day 10 displayed altered spontaneous behavior and changed habituation patterns later in life compared to controls. These mice also displayed reduced memory, learning and cognitive flexibility compared to control animals in the Morris water maze. An increase of markers for oxidative stress was observed in the hippocampus 6 h after AAP exposure. As AAP is the first choice treatment for pain and/or fever during pregnancy and early life, these results may be of great importance for risk assessment. Here we show that AAP can have persistent negative effects on brain development and suggest that AAP, despite the relatively low doses, is capable to induce acute oxidative stress in the hippocampus.

Ubisol-Q10, a Nanomicellar and Water-Dispersible Formulation of Coenzyme-Q10 as a Potential Treatment for Alzheimer's and Parkinson's Disease

The world continues a desperate search for therapies that could bring hope and relief to millions suffering from progressive neurodegenerative diseases such as Alzheimer’s (AD) and Parkinson’s (PD). With oxidative stress thought to be a core stressor, interests have long been focused on applying redox therapies including coenzyme-Q₁₀. Therapeutic use has failed to show efficacy in human clinical trials due to poor bioavailability of this lipophilic compound. A nanomicellar, water-dispersible formulation of coenzyme-Q₁₀, Ubisol-Q₁₀, has been developed by combining coenzyme-Q₁₀ with an amphiphilic, self-emulsifying molecule of polyoxyethanyl α-tocopheryl sebacate (derivatized vitamin E). This discovery made possible, for the first time, a proper assessment of the true therapeutic value of coenzyme-Q₁₀. Micromolar concentrations of Ubisol-Q₁₀ show unprecedented neuroprotection against neurotoxin exposure in in vitro and in vivo models of neurodegeneration and was extremely effective when delivered either prior to, at the time of, and most significantly, post-neurotoxin exposure. These findings indicate a possible way forward for clinical development due to effective doses well within Federal Drug Administration guidelines. Ubisol-Q₁₀ is a potent mobilizer of astroglia, antioxidant, senescence preventer, autophagy activator, anti-inflammatory, and mitochondrial stabilizer. Here we summarize the work with oil-soluble coenzyme-Q₁₀, its limitations, and focus mainly on efficacy of water-soluble coenzyme-Q₁₀ in neurodegeneration.

Hypermethylation of EFEMP1 in the Hippocampus May Be Related to the Deficit in Spatial Memory of Rat Neonates Triggered by Repeated Administration of Propofol

It has been confirmed that repeated application of propofol, as an intravenous and short-fast-acting anesthetic, in neonatal animals or humans may produce long-term deficits in cognitive functions. With the aim of explaining the neurotoxic effects of repeated administration of propofol on neonatal rat pups from P7 to P9 especially from an epigenetic perspective, the present study used the Morris water maze to detect cognitive deficits in spatial learning and memory, Sequenom methylation on the CpG island located in the promoter region of epidermal growth factor-containing fibulin-like extracellular matrix protein 1 (EFEMP1) to assess the methylation level of this region, and Western blot to measure the expression of EFEMP1, TIMP-3, and MMP-9. As the results have shown, repeated propofol administration on neonatal rats caused significant systemic growth retardation, impairment of spatial learning and memory, and hypermethylation of the CpG sites in the promoter region of EFEMP1 accompanied by lower expression of EFEMP1 and TIMP-3 and enhanced expression of MMP-9. These data suggest that repeated propofol administration in neonatal rats may generate hypermethylation in the promoter region of EFEMP1 which results in downregulation of the expression of EFEMP1 and tissue inhibitor of metalloproteinase-3 (TIMP-3) but upregulation of the expression of matrix metalloproteinase-9 (MMP-9), which together may affect the stability of ECM to hamper the development of the central nervous system and therefore lead to deficits in cognitive functions.

MMP-9 in translation: from molecule to brain physiology, pathology, and therapy

Matrix metalloproteinase-9 (MMP-9) is a member of the metzincin family of mostly extracellularly operating proteases. Despite the fact that all of these enzymes might be target promiscuous, with largely overlapping catalogs of potential substrates, MMP-9 has recently emerged as a major and apparently unique player in brain physiology and pathology. The specificity of MMP-9 may arise from its very local and time-restricted actions, even when released in the brain from cells of various types, including neurons, glia, and leukocytes. In fact, the quantity of MMP-9 is very low in the naive brain, but it is markedly activated at the levels of enzymatic activity, protein abundance, and gene expression following various physiological stimuli and pathological insults. Neuronal MMP-9 participates in synaptic plasticity by controlling the shape of dendritic spines and function of excitatory synapses, thus playing a pivotal role in learning, memory, and cortical plasticity. When improperly unleashed, MMP-9 contributes to a large variety of brain disorders, including epilepsy, schizophrenia, autism spectrum disorder, brain injury, stroke, neurodegeneration, pain, brain tumors, etc. The foremost mechanism of action of MMP-9 in brain disorders appears to be its involvement in immune/inflammation responses that are related to the enzyme's ability to process and activate various cytokines and chemokines, as well as its contribution to blood-brain barrier disruption, facilitating the extravasation of leukocytes into brain parenchyma. However, another emerging possibility (i.e., the control of MMP-9 over synaptic plasticity) should not be neglected. The translational potential of MMP-9 has already been recognized in both the diagnosis and treatment domains. The most striking translational aspect may be the discovery of MMP-9 up-regulation in a mouse model of Fragile X syndrome, quickly followed by human studies and promising clinical trials that have sought to inhibit MMP-9. With regard to diagnosis, suggestions have been made to use MMP-9 alone or combined with tissue inhibitor of matrix metalloproteinase-1 or brain-derived neurotrophic factor as disease biomarkers. MMP-9, through cleavage of specific target proteins, plays a major role in synaptic plasticity and neuroinflammation, and by those virtues contributes to brain physiology and a host of neurological and psychiatric disorders. This article is part of the 60th Anniversary special issue.

Neonatal exposure to whole body ionizing radiation induces adult neurobehavioural defects: Critical period, dose--response effects and strain and sex comparison

Development of the brain includes periods which can be critical for its normal maturation. The present study investigates specifically vulnerable peri-/postnatal periods in mice which are essential for understanding the etiology behind radiation induced neurotoxicity and functional defects, including evaluation of neurotoxicity between sexes or commonly used laboratory mouse strains following low/moderate doses of ionizing radiation (IR). Male Naval Medical Research Institute (NMRI) mice, whole body irradiated to a single 500 mGy IR dose, on postnatal day (PND) 3 or PND 10 showed an altered adult spontaneous behaviour and impaired habituation capacity, whereas irradiation on PND 19 did not have any impact on the studied variables. Both NMRI and C57bl/6 male and female mice showed an altered adult spontaneous behaviour and impaired habituation following a single whole body irradiation of 500 or 1000 mGy, but not after 20 or 100 mGy, on PND 10. The present study shows that exposure to low/moderate doses of IR during critical life stages might be involved in the induction of neurological/neurodegenerative disorder/disease. A specifically vulnerable period for radiation induced neurotoxicity seems to be around PND 3-10 in mice. Further studies are needed to investigate mechanisms involved in induction of developmental neurotoxicity following low-dose irradiation.

Matrix Metalloproteinase-9 as a Novel Player in Synaptic Plasticity and Schizophrenia

Recent findings implicate alterations in glutamate signaling, leading to aberrant synaptic plasticity, in schizophrenia. Matrix metalloproteinase-9 (MMP-9) has been shown to regulate glutamate receptors, be regulated by glutamate at excitatory synapses, and modulate physiological and morphological synaptic plasticity. By means of functional gene polymorphism, gene responsiveness to antipsychotics and blood plasma levels MMP-9 has recently been implicated in schizophrenia. This commentary critically reviews these findings based on the hypothesis that MMP-9 contributes to pathological synaptic plasticity in schizophrenia.

Hippocampal Cortactin Levels are Reduced Following Spatial Working Memory Formation, an Effect Blocked by Chronic Calpain Inhibition

The mechanism by which the hippocampus facilitates declarative memory formation appears to involve, among other things, restructuring of the actin cytoskeleton within neuronal dendrites. One protein involved in this process is cortactin, which is an important link between extracellular signaling and cytoskeletal reorganization. In this paper, we demonstrate that total hippocampal cortactin, as well as Y421-phosphorylated cortactin are transiently reduced following spatial working memory formation in the radial arm maze (RAM). Because cortactin is a substrate of the cysteine protease calpain, we also assessed the effect of chronic calpain inhibition on RAM performance and cortactin expression. Calpain inhibition impaired spatial working memory and blocked the reduction in hippocampal cortactin levels following RAM training. These findings add to a growing body of research implicating cortactin and calpain in hippocampus-dependent memory formation.

The cognitive defects of neonatally irradiated mice are accompanied by changed synaptic plasticity, adult neurogenesis and neuroinflammation

Background/purpose of the study

Epidemiological evidence suggests that low doses of ionising radiation (≤1.0 Gy) produce persistent alterations in cognition if the exposure occurs at a young age. The mechanisms underlying such alterations are unknown. We investigated the long-term effects of low doses of total body gamma radiation on neonatally exposed NMRI mice on the molecular and cellular level to elucidate neurodegeneration.

Results

Significant alterations in spontaneous behaviour were observed at 2 and 4 months following a single 0.5 or 1.0 Gy exposure. Alterations in the brain proteome, transcriptome, and several miRNAs were analysed 6–7 months post-irradiation in the hippocampus, dentate gyrus (DG) and cortex. Signalling pathways related to synaptic actin remodelling such as the Rac1-Cofilin pathway were altered in the cortex and hippocampus. Further, synaptic proteins MAP-2 and PSD-95 were increased in the DG and hippocampus (1.0 Gy). The expression of synaptic plasticity genes Arc, c-Fos and CREB was persistently reduced at 1.0 Gy in the hippocampus and cortex. These changes were coupled to epigenetic modulation via increased levels of microRNAs (miR-132/miR-212, miR-134). Astrogliosis, activation of insulin-growth factor/insulin signalling and increased level of microglial cytokine TNFα indicated radiation-induced neuroinflammation. In addition, adult neurogenesis within the DG was persistently negatively affected after irradiation, particularly at 1.0 Gy.

Conclusion

These data suggest that neurocognitive disorders may be induced in adults when exposed at a young age to low and moderate cranial doses of radiation. This raises concerns about radiation safety standards and regulatory practices.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-57) contains supplementary material, which is available to authorized users.

Developmental exposure to the polybrominated diphenyl ether PBDE 209: Neurobehavioural and neuroprotein analysis in adult male and female mice

Polybrominated diphenyl ethers (PBDEs), used as flame retardants in polymer products, are reported to cause developmental neurotoxic effects in mammals. The present study have investigated neurotoxic effects arising from neonatal exposure to PBDE 209, including alterations in sex differences, spontaneous behaviour, learning and memory, neuroproteins and altered susceptibility of the cholinergic system in adults. Three-day-old NMRI mice, of both sexes, were exposed to PBDE 209 (2,2',3,3',4,4',5,5',6,6'-decaBDE at 0, 1.4, 6.0 and 14.0μmol/kg b.w.). At adult age (2-7 months) a similar developmental neurotoxic effects in both male and female mice were seen, including lack of or reduced habituation to a novel home environment, learning and memory defects, modified response to the cholinergic agent's paraoxon (males) and nicotine (females) indicating increased susceptibility of the cholinergic system. The behavioural defects were dose-response related and persistent. In mice of both sexes and showing behavioural defects, neuroprotein tau was increased.

Ontogenetic analysis of behavior in the tail suspension test: temporal differences in the emergence of within- and between-session habituation in Swiss mice

Habituation is an important tool in the investigation of learning/memory throughout life. Despite that, few studies describe habituation from an ontogenetic perspective. Considering that, as soon as they are born, rodents can twist their bodies when lifted by their tails in an attempt to escape, this behavior should be well suited to study habituation behavior from birth to adulthood. Here, we implement a tail suspension test to study the ontogenetic development of habituation in Swiss mice. Our data indicate that a continuous within-session decrease in trunk movements can be observed from postnatal day (P) 10 onwards and that between-sessions habituation (from one day to another) can be observed from P16 onwards. Furthermore, we show that the adult pattern of within- and between-sessions reductions in activity is already present by the beginning of adolescence, at P28. Our results indicate that between-sessions habituation involves a more complex mechanism of memory and learning than within-session habituation, requiring a longer period of brain maturation before it can be displayed.

The endocannabinoid 2-arachidonoylglycerol negatively regulates habituation by suppressing excitatory recurrent network activity and reducing long-term potentiation in the dentate gyrus

Endocannabinoids are known to mediate retrograde suppression of synaptic transmission, modulate synaptic plasticity, and influence learning and memory. The 2-arachidonoylglycerol (2-AG) produced by diacylglycerol lipase α (DGLα) is regarded as the major endocannabinoid that causes retrograde synaptic suppression. To determine how 2-AG signaling influences learning and memory, we subjected DGLα knock-out mice to two learning tasks. We tested the mice using habituation and odor-guided transverse patterning tasks that are known to involve the dentate gyrus and the CA1, respectively, of the hippocampus. We found that DGLα knock-out mice showed significantly faster habituation to an odor and a new environment than wild-type littermates with normal performance in the transverse patterning task. In freely moving animals, long-term potentiation (LTP) induced by theta burst stimulation was significantly larger at perforant path-granule cell synapses in the dentate gyrus of DGLα knock-out mice. Importantly, prior induction of synaptic potentiation at this synapse caused a significant retardation of habituation in DGLα knock-out but not in wild-type littermates. The excitability of granule cells became higher in DGLα knock-out mice after they generated action potentials. Since no differences were found in intrinsic membrane properties and responses to odor stimuli in granule cells, the elevated excitability is considered to result from enhanced activity of an excitatory recurrent network composed of granule cells and mossy cells. These results suggest that retrograde 2-AG signaling negatively regulates habituation by suppressing excitatory recurrent network activity and reducing LTP in the dentate gyrus.

Contributions of matrix metalloproteinases to neural plasticity, habituation, associative learning and drug addiction

The premise of this paper is that increased expression of matrix metalloproteinases (MMPs) permits the reconfiguration of synaptic connections (i.e., neural plasticity) by degrading cell adhesion molecules (CAMs) designed to provide stability to those extracellular matrix (ECM) proteins that form scaffolding supporting neurons and glia. It is presumed that while these ECM proteins are weakened, and/or detached, synaptic connections can form resulting in new neural pathways. Tissue inhibitors of metalloproteinases (TIMPs) are designed to deactivate MMPs permitting the reestablishment of CAMs, thus returning the system to a reasonably fixed state. This review considers available findings concerning the roles of MMPs and TIMPs in reorganizing ECM proteins thus facilitating the neural plasticity underlying long-term potentiation (LTP), habituation, and associative learning. We conclude with a consideration of the influence of these phenomena on drug addiction, given that these same processes may be instrumental in the formation of addiction and subsequent relapse. However, our knowledge concerning the precise spatial and temporal relationships among the mechanisms of neural plasticity, habituation, associative learning, and memory consolidation is far from complete and the possibility that these phenomena mediate drug addiction is a new direction of research.

Influence of dorsal hippocampal lesions and MMP inhibitors on spontaneous recovery following a habituation/classical conditioning head-shake task

The present investigation combined a classical conditioning paradigm with a head-shake response (HSR) habituation task in order to evaluate the importance of dorsal hippocampal neural plasticity to spontaneous recovery. In the first experiment animals exhibited rapid HSR habituation (air stimulus to the ear) and an 85% level of spontaneous recovery following a 24 h inter-session interval. The addition of a brief tone prior to the air stimulus produced a similar pattern of habituation during the first session, but the level of spontaneous recovery was reduced (44%) during Session II. In a second experiment dorsal hippocampal lesioned rats placed on this tone/HSR paradigm responded with an 87% level of spontaneous recovery during Session II; while neocortex lesioned control rats indicated significantly reduced levels of spontaneous recovery (55%). In a third experiment bilateral injections of a general MMP inhibitor, FN-439, into the dorsal hippocampus resulted in high levels of spontaneous recovery (81%); while control rats injected with artificial cerebrospinal fluid displayed a significant attenuation of spontaneous recovery (45%). Finally, animals bilaterally injected with a specific MMP-3 inhibitor into the dorsal hippocampus indicated very similar results to those obtained following FN-439 injection. These findings indicate that animals prepared with dorsal hippocampal lesions, or injections with an MMP inhibitor, revealed an impaired association between the tone and air stimulus thus maximum spontaneous recovery was present 24 h later. Thus, it appears that the dorsal hippocampus influences habituation by conserving responses and reducing spontaneous recovery when a temporally contingent signaling cue is present.

Habituation-induced neural plasticity in the hippocampus and prefrontal cortex mediated by MMP-3

Head-shake response (HSR) habituation was presently used to investigate the phenomena of spontaneous recovery and neural plasticity. Independent groups of rats were presented with five consecutive habituation sessions separated by inter-session intervals (ISIs) of 2, 24 or 72 h. At the conclusion of testing hippocampus and prefrontal cortex tissue samples were collected for determination of matrix metalloproteinase-3 (MMP-3:stromelysin-1) expression as a marker of neural plasticity. The results indicated that by the fifth session the 2 h ISI group showed no spontaneous recovery, the 72 h ISI group revealed nearly complete spontaneous recovery; while the 24 h ISI group showed intermediate recovery. MMP-3 expression in the hippocampus and prefrontal cortex was elevated in the 2 and 72 h ISI groups, but not in the 24 h group. A second experiment utilized 7-day osmotic pumps to intracerebroventricularly infuse an MMP-3 inhibitor for 6 days. The animals were then tested on the seventh day using the 2 h ISI protocol. Delivery of the MMP-3 inhibitor facilitated spontaneous recovery, thus compromising the animal's ability to appropriately habituate. This effect was accompanied by a significant inhibition of hippocampus and prefrontal cortex MMP-3 expression. These results suggest that elevations in hippocampus and prefrontal cortex MMP-3 expression contribute to this simplest form of learning and may be a mechanism underlying spontaneous recovery.

Inhibition of matrix metalloproteinase activity disrupts reconsolidation but not consolidation of a fear memory

The reconsolidation hypothesis posits that memories that have been reactivated can be either enhanced or disrupted by pharmacological manipulation. Synaptic plasticity is presumed to underlie the reconsolidation process. Matrix metalloproteinases are proteins that regulate the extracellular matrix involved in plasticity events, and these proteins have recently been shown to influence learning and memory. However, all studies on the role of matrix metalloproteinases in learning and memory have employed tasks that rely on contextual cues. The goal of this study was to determine the extent to which FN-439 would disrupt the consolidation and/or reconsolidation of a fear memory associated with a conditioned stimulus that signaled tone-shock pairings and that was independent of contextual cues. Male Sprague-Dawley rats were given infusions of FN-439 (35 microg intracerebroventricular) 30 min prior to conditioning (tone-shock paired association) or 30 min prior to a single reactivation session given 24h after conditioning. Administration of FN-439 did not disrupt consolidation of the freezing response when the tone (conditioned stimulus) was presented. In contrast, FN-439 infusion disrupted reconsolidation of the fear memory in a reactivation-dependent manner. The reduced freezing behavior was not due to a decrease in general anxiety levels, since FN-439 had no effect on the percent of open-arm time or open-arm entries in an elevated-plus maze task. Thus, we demonstrated for the first time that matrix metalloproteinase inhibition in the brain is capable of disrupting the reconsolidation of a tone-shock association memory that does not depend on contextual cues. The finding that a fear response to a previously paired conditioned stimulus can be disrupted by treatment with an MMP inhibitor during a single reactivation session suggests that this class of compounds may have therapeutic potential for posttraumatic stress disorder and/or simple phobias.

Delay-dependent involvement of the rat entorhinal cortex in habituation to a novel environment

Evidence has accumulated that the entorhinal cortex (EC) is involved in memory operations underlying formation of a long-term memory. Because entorhinal-lesioned rats are impaired for long delays in delayed matching and non-matching to sample tasks, it has been proposed that EC contributes to the maintenance of information in short-term memory. In the present study, we asked whether such a time-limited role applies also when learning complex spatial information in a novel environment. We therefore examined the effects of EC lesions on habituation in an object exploration task in which a delay of either 4min or 10min is imposed between successive sessions. EC-lesioned rats exhibited a deficit in habituation at 10min but not 4min delays. Following habituation, reactions to spatial change (object configuration) and non-spatial change (novel object) were also examined. EC-lesioned rats were impaired in detecting the spatial change but were able to detect a non-spatial change, irrespective of the delay. Overall, the results suggest that EC is involved in maintaining a large amount of novel, multidimensional information in short-term memory therefore enabling formation of long-term memory. Switching to a novelty detection mode would then allow the animal to rapidly adapt to environmental changes. In this mode, EC would preferentially process spatial information rather than non-spatial information.

Intermittent hypoxia and sleep restriction: motor, cognitive and neurochemical alterations in rats

The present study evaluated the effects of intermittent hypoxia (IH) and sleep restriction (SR) upon motor and cognitive function in rats. Also evaluated were catecholamine concentrations and tyrosine hydroxylase (TH) protein expression in different regions of the forebrain. Wistar Hannover rats were submitted to IH for 4 days or 21 days (2 min room air to 2 min 10% O(2) for 10:00-16:00 h), followed by SR for 18 h (16:00-10:00 h). Rats were randomly assigned into four experimental groups: (1) control (2) IH (3) SR and (4) IH-SR. In the inhibitory avoidance task, an additional group of rats was submitted to paradoxical sleep deprivation (PSD) for 96 consecutive hours. Results showed that SR induced an increase in motor activity without modifying catecholaminergic turnover in the frontal cortex and striatum. The increase in exploratory activity in SR rats could be the result of impaired habituation. Neither SR periods induced cognitive deficits in the inhibitory avoidance task after 5 or 21 days. However, 96 h of PSD impaired acquisition/retention in rats. Exposure to IH did not affect motor and cognitive function but IH was associated with SR in increased motor activity. After 21 days, IH and IH-SR reduced striatal norepinephrine concentration although neither SR nor IH affected TH protein expression. The results presented here suggest that hypoxia and sleep loss exert distinct deleterious effects upon the central nervous system.

Inhibition of hippocampal matrix metalloproteinase-3 and -9 disrupts spatial memory

Memory consolidation requires synaptic reconfiguration dependent upon extracellular matrix (ECM) molecules interacting with cell adhesion molecules. Matrix metalloproteinase (MMP) activity is responsible for transient alterations in the ECM that may be prerequisite to hippocampal-dependent learning. In support of this hypothesis we have measured increases in MMP-3 and MMP-9 levels within the hippocampus and prefrontal cortex during Morris water maze training. The present investigation extends these findings by determining that infusion of an MMP inhibitor (FN-439) into the dorsal hippocampus disrupted acquisition of this task. In vitro fluorescence enzyme assays to determine the specificity of FN-439 against the catalytic domains of MMP-3 and MMP-9 indicated mean ± SEM IC₅₀s of 16.2 ± 7.8 and 210.5 ± 37.8 μM, respectively, while in situ zymography using hippocampal sections treated with FN-439 indicated significant reductions in MMP gelatinase activity. These results suggest that compromising the ability of the dorsal hippocampus to reconfigure ECM molecules by inhibiting MMP activity interferes with appropriate spatial memory acquisition, and support a role for hippocampal MMPs in the phenomena of spatial memory acquisition and storage.

Multivariate neurocognitive and emotional profile of a mannosidosis murine model for therapy assessment

alpha-Mannosidosis is a lysosomal storage disorder caused by lysosomal alpha-mannosidase (LAMAN) deficiency that leads to neurocognitive dysfunctions, psychotic symptoms and emotional changes in human patients. A murine mannosidosis model, LAMAN-deficient mice, was examined on a behavioral task battery that included test for neuromotor, exploratory and neurocognitive (spatial learning and memory) abilities, and multivariate statistical analyses were used to identify behavioral and neurocognitive domains that are most heavily affected by LAMAN deficiency. In addition, we further investigated synaptic plasticity recordings on hippocampal slices that may relate to these behavioral alterations. Correlation analysis revealed significant intra- and intertask correlations and factor analysis that included all 21 behavioral variables identified three main factors (exploration/emotionality, locomotion and learning/memory abilities). Significant correlations were observed between genotype, and factor 1 (exploration/emotionality) and factor 3 (learning/memory abilities). Discriminant function analysis showed that "path length in the open field test" and "time spent in the target quadrant during the water maze probe trial" were the most decisive variables to distinguish between the genotypes. We therefore suggest that these variables would be especially important in forthcoming therapy assessment experiments using this murine mannosidosis model. LAMAN-deficient mice displayed severe changes in synaptic plasticity, which may have contributed to the neurocognitive impairments observed. The present report further shows that targeted deletion of the LAMAN gene in mice mimics many aspects of human alpha-mannosidosis, and these data provide a basis for future therapeutic experiments.

Impaired spatial reference memory and increased exploratory behavior in P301L tau transgenic mice

The neuropathological hallmark shared between Alzheimer's disease (AD) and familial frontotemporal dementia (FTDP-17) are neurofibrillary tangles (NFT) which are composed of filamentous aggregates of the microtubule-associated protein tau. Their formation has been reproduced in transgenic mice, which express the FTDP-17-associated mutation P301L of tau. In these mice, tau aggregates are found in many brain areas including the hippocampus and the amygdala, both of which are characterized by NFT formation in AD. Previous studies using an amygdala-specific test battery revealed an increase in exploratory behavior and an accelerated extinction of conditioned taste aversion in these mice. Here, we assessed P301L mice in behavioral tests known to depend on an intact hippocampus. Morris water maze and Y-maze revealed intact spatial working memory but impairment in spatial reference memory at 6 and 11 months of age. In addition, a modest disinhibition of exploratory behavior at 6 months of age was confirmed in the open field and the elevated O-maze and was more pronounced during aging.

Systemic lupus erythematosus and the brain: what mice are telling us

Neuropsychiatric symptoms occur in systemic lupus erythematosus (SLE), a complex, autoimmune disease of unknown origin. Although several pathogenic mechanisms have been suggested to play a significant role in the etiology of the disease, the exact underlying mechanisms still remain elusive. Several inbred strains of mice are used as models to study SLE, which exhibit a diversity of central nervous system (CNS) manifestations similar to that observed in patients. This review will attempt to give a brief overview of the CNS alterations observed in these models, including biochemical, structural and behavioral changes.

Double dissociation between hippocampal and prefrontal lesions on an operant delayed matching task and a water maze reference memory task

The hippocampus and prefrontal cortex have both been implicated in various aspects of the acquisition, retention and performance of delayed matching to position (DMTP) tasks in the rat, although their precise respective contributions remain unclear. In the present study, rats were trained preoperatively on DMTP before receiving excitotoxic bilateral lesions of either the entire hippocampus or the medial prefrontal cortex. Rats with lesions of the prefrontal cortex exhibited a significant delay-dependent impairment on retention of the DMTP task, whereas hippocampal lesions were without effect. Rats were also exposed to a switch in the contingencies to a 'non-matching' rule, as an analogue of switching between decision rules in the human Wisconsin Card Sorting Test, in which human patients with prefrontal damage are impaired. Both lesion groups acquired the new contingency at control levels, providing no evidence towards a role for either of these areas in this type of rule-switching. The same rats were also assessed in a spatial reference memory task in the water maze, which revealed an impairment in escape latencies and path length that was specific to the hippocampal lesions. The results corroborate previous evidence that the hippocampus is not necessary for at least some aspects of working memory performance in the DMTP task, whereas the delay-dependent deficit in the prefrontal lesion group support this task as a potentially powerful tool for assessing the cognitive changes associated with frontal damage and repair.

Neurocognitive and psychotiform behavioral alterations and enhanced hippocampal long-term potentiation in transgenic mice displaying neuropathological features of human alpha-mannosidosis

Mice with alpha-mannosidase gene inactivation provide an experimental model for alpha-mannosidosis, a lysosomal storage disease with severe neuropsychological and psychopathological complications. Neurohistological alterations in these mice were similar to those in patients and included vacuolations and axonal spheroids in the CNS and peripheral nervous system. Vacuolation was most prominent and evenly distributed in neuronal perikarya of the hippocampal CA2 and CA3 regions, whereas CA1 and dentate gyrus were weakly or not affected. Field potential recordings from CA1 region in hippocampal slices showed enhanced theta burst-induced long-term potentiation (LTP) in alpha-mannosidase-deficient mice. Longitudinal assessment in age-matched alpha-mannosidase-deficient and wild-type littermates, using an extended test battery, demonstrated a neurocognitive and psychotiform profile that may relate to the psychopathological alterations in clinical alpha-mannosidosis. Brainstem auditory-evoked potentials and basic neuromotor abilities were not impaired and did not deteriorate with age. Exploratory and conflict tests revealed consistent decreases in exploratory activity and emotional blunting in the knock-out group. alpha-Mannosidosis mice were also impaired in aversively motivated learning and acquisition of signal-shock associations. Acquisition and reversal learning in the water maze task, passive avoidance learning in the step-through procedure, as well as emotional response conditioning in an operant procedure were all impaired. Acquisition or shaping of an appetitive instrumental conditioning task was unchanged. Appetitive odor discrimination learning was only marginally impaired during shaping, whereas both the discrimination and reversal subtasks were normal. We propose that prominent storage and enhanced LTP in hippocampus have contributed to these specific behavioral alterations in alpha-mannosidase-deficient mice.

Effects of extracellular matrix-degrading proteases matrix metalloproteinases 3 and 9 on spatial learning and synaptic plasticity

Rats learning the Morris water maze exhibit hippocampal changes in synaptic morphology and physiology that manifest as altered synaptic efficacy. Learning requires structural changes in the synapse, and multiple cell adhesion molecules appear to participate. The activity of these cell adhesion molecules is, in large part, dependent on their interaction with the extracellular matrix (ECM). Given that matrix metalloproteinases (MMPs) are responsible for transient alterations in the ECM, we predicted that MMP function is critical for hippocampal-dependent learning. In support of this, it was observed that hippocampal MMP-3 and -9 increased transiently during water maze acquisition as assessed by western blotting and mRNA analysis. The ability of the NMDA receptor channel blocker MK801 to attenuate these changes indicated that the transient MMP changes were in large part dependent upon NMDA receptor activation. Furthermore, inhibition of MMP activity with MMP-3 and -9 antisense oligonucleotides and/or MMP inhibitor FN-439 altered long-term potentiation and prevented acquisition in the Morris water maze. The learning-dependent MMP alterations were shown to modify the stability of the actin-binding protein cortactin, which plays an essential role in regulating the dendritic cytoskeleton and synaptic efficiency. Together these results indicate that changes in MMP function are critical to synaptic plasticity and hippocampal-dependent learning.

Role of mitogen-activated protein kinases during recovery from head-shake response habituation in rats

Habituation is defined as a decrease in responsiveness to a repeatedly presented stimulus. The head-shake response (HSR) consists of a rapid twisting of the head about the front-to-rear axis elicited by a stream of air to the ear. This response demonstrates several fundamental properties of habituation including sensitivity to the frequency and intensity of stimulation, and spontaneous recovery. Despite an abundance of behavioral data on the HSR, relatively little is known about its physiological mechanism(s). To address this issue, changes in mitogen-activated protein kinases (MAPK) were assessed 5 min and 2, 6, and 24 h following the habituation of the HSR. Three cascades of MAPK activity were measured in the cerebellum and hippocampal, prefrontal, and piriform cortices, including extracellular-response kinase (ERK), p-38 kinase (p-38), and stress-activated protein kinase (SAPK). Significant activation of p-38 and SAPK was observed in all four brain structures, accompanied by modest changes in ERK activity. Recovery of the HSR was characterized by decreasing MAPK activation with control levels re-established 24 h after habituation. The present results suggest that MAPK activation mediates recovery from habituation; however, these findings may also support alternative interpretations such that MAPK activation reflects the encoding of spatial cues associated with the testing environment and/or are due to stress induced by the habituation protocol.

Effects of systemic lupus erythematosus on spatial cognition and cerebral regional metabolic reactivity in BxSB lupus-prone mice

Brain-reactive auto-antibodies appear as key elements in the progressive CNS disturbances associated with systemic lupus erythematosus. The BxSB lupus prone mice are a model of this pathology, in which a gene located on the Y chromosome provokes a sex specific morbidity in males. This study was aimed to establish and characterize the relationships between behavioral disorders, neurological deficiencies and the aged-related immunological perturbations in this murine model. For this purpose, spatial and motor abilities were evaluated in male and female mice at six and 26 weeks of age. The results showed that the older males were greatly altered in their spatial abilities while the young ones and the females, whatever their age, were not. None of the animals had motor skill and motor learning disabilities. These spatial alterations were associated with modifications of basal neuronal activity measured by the cytochrome oxidase histochemical method in several areas directly or indirectly involved in spatial behavior, such as the hippocampus, the amygdala, the parietal and perirhinal cortex. Immunological study allowed us to correlate the behavioral abnormalities to the appearance of antibodies reactivities against cellular and nuclear components.

Ontogenesis of within-session locomotor habituation in the open field

Habituation signifies a decreased response to a constant or repeated stimulus or environment. Although habituation is a fundamental form of nonassociative learning, little is known about its ontogenesis. Here, locomotor activity of postnatal ferrets within individual open field sessions was quantitatively analysed. The patterns of activity revealed a gradual shift across developmental time between relative increment and decrement of activity within sessions. The increment-to-decrement turning point was around postnatal day 48. These novel findings indicate that systematic changes in the interplay between mechanisms that drive exploratory behaviour and those that inhibit it shape the ontogenesis of open field habituation. The remarkable robustness of the data underscores the suitability of the ferret as an experimental animal for investigating ontogenesis of habituation.