Biomedical subjects

R Gerlai

Publications and source records attributed to R Gerlai.

At least 37 records · Page 2Linked to original sources

PubMed1999

Evidence for a protective role of metallothionein-1 in focal cerebral ischemia.

Metallothioneins (MTs) are a family of metal binding proteins that have been proposed to participate in a cellular defense against zinc toxicity and free radicals. In the present study, we investigated whether increased expression of MT in MT-1 isoform-overexpressing transgenic mice (MT-TG) affords protection against mild focal cerebral ischemia and reperfusion. Transient focal ischemia was induced in control (wild type) and MT-TG mice by occluding the right middle cerebral artery for 45 min. Upon reperfusion, cerebral edema slowly developed and peaked at 24 hr as shown by T2-weighted MRI. The volume of affected tissue was on the average 42% smaller in MT-TG mice compared with control mice at 6, 9, 24, and 72 hr and 14 days postreperfusion (P < 0.01). In addition, functional studies showed that 3 weeks after reperfusion MT-TG mice showed a significantly better motor performance compared with control mice (P = 0.011). Although cortical baseline levels of MT-1 mRNA were similar in control and MT-TG mice, there was an increase in MT-1 mRNA levels in the ischemic cortex of MT-TG mice to 7.5 times baseline levels compared with an increase to 2.3 times baseline levels in control mice 24 hr after reperfusion. In addition, MT-TG mice showed an increased MT immunoreactivity in astrocytes, vascular endothelial cells, and neurons 24 hr after reperfusion whereas in control mice MT immunoreactivity was restricted mainly to astrocytes and decreased in the infarcted tissue. These results provide evidence that increased expression of MT-1 protects against focal cerebral ischemia and reperfusion.

Animals↗

PubMed1999

Analysing hippocampal function in transgenic mice: an ethological perspective.

Advances in molecular genetics and technology have led to the dawn of a new era for neuroscience: manipulation of single genes now makes it possible to dissect the complexities of neurobiological phenotypes and to understand many of the intricacies of brain and behaviour, even in mammals. The phenotypical analysis of these mutant animals is complicated because the potential outcome of gene manipulation is difficult to predict. While behavioural analysis should form an integral part of any multidisciplinary research programme investigating the phenotypical effects of single genes on hippocampal function, it is crucial that the behavioural tests are designed and conducted appropriately. Approaches that take species-specific behavioural characteristics into account and use ethological methods could be the most useful for interpreting these behavioural findings and understanding the biological mechanisms of brain function.

Animals↗

PubMed1999

Reply.

Explore the source record for details and available documents.

Journal Article↗

PubMed1999

VEGF antagonism reduces edema formation and tissue damage after ischemia/reperfusion injury in the mouse brain.

VEGF is mitogenic, angiogenic, and a potent mediator of vascular permeability. VEGF causes extravasation of plasma protein in skin bioassays and increases hydraulic conductivity in isolated perfused microvessels. Reduced tissue oxygen tension triggers VEGF expression, and increased protein and mRNA levels for VEGF and its receptors (Flt-1, Flk-1/KDR) occur in the ischemic rat brain. Brain edema, provoked in part by enhanced cerebrovascular permeability, is a major complication in central nervous system pathologies, including head trauma and stroke. The role of VEGF in this pathology has remained elusive because of the lack of a suitable experimental antagonist. We used a novel fusion protein, mFlt(1-3)-IgG, which sequesters murine VEGF, to treat mice exposed to transient cortical ischemia followed by reperfusion. Using high-resolution magnetic resonance imaging, we found a significant reduction in volume of the edematous tissue 1 day after onset of ischemia in mice that received mFlt(1-3)-IgG. 8-12 weeks after treatment, measurements of the resultant infarct size revealed a significant sparing of cortical tissue. Regional cerebral blood flow was unaffected by the administration of mFlt(1-3)-IgG. These results demonstrate that antagonism of VEGF reduces ischemia/reperfusion-related brain edema and injury, implicating VEGF in the pathogenesis of stroke and related disorders.

Animals↗

PubMed1998

Protein targeting in the analysis of learning and memory: a potential alternative to gene targeting.

Gene targeting using homologous recombination in embryonic stem (ES) cells offers unprecedented precision with which one may manipulate single genes and investigate the in vivo effects of defined mutations in the mouse. Geneticists argue that this technique abrogates the lack of highly specific pharmacological tools in the study of brain function and behavior. However, by now it has become clear that gene targeting has some limitations too. One problem is spatial and temporal specificity of the generated mutation, which may appear in multiple brain regions or even in other organs and may also be present throughout development, giving rise to complex, secondary phenotypical alterations. This may be a disadvantage in the functional analysis of a number of genes associated with learning and memory processes. For example, several proteins, including neurotrophins--cell-adhesion molecules--and protein kinases, that play a significant developmental role have recently been suggested to be also involved in neural and behavioral plasticity. Knocking out genes of such proteins may lead to developmental alterations or even embryonic lethality in the mouse, making it difficult to study their function in neural plasticity, learning, and memory. Therefore, alternative strategies to gene targeting may be needed. Here, we suggest a potentially useful in vivo strategy based on systemic application of immunoadhesins, genetically engineered fusion proteins possessing the Fc portion of the human IgG molecule and, for example, a binding domain of a receptor of interest. These proteins are stable in vivo and exhibit high binding specificity and affinity for the endogenous ligand of the receptor, but lack the ability to signal. Thus, if delivered to the brain, immunoadhesins may specifically block signalling of the receptor of interest. Using osmotic minipumps, the protein can be infused in a localized region of the brain for a specified period of time (days or weeks). Thus, the location and timing of delivery are controlled. Here, we present methodological details of this novel approach and argue that infusion of immunoadhesins will be useful for studying the role particular receptors play in behavioral and neural plasticity.

Animals↗

PubMed1998

Contextual learning and cue association in fear conditioning in mice: a strain comparison and a lesion study.

Fear conditioning with electric shock (unconditioned stimulus, US) paired with tone cue (conditioned stimulus, CS) has been extensively applied in recent molecular neurobiological analysis of hippocampal dysfunction in mice because the context-dependent test phase of this learning paradigm is claimed to detect hippocampal impairment in a specific manner, whereas the cue-dependent test serves as a control situation independent of hippocampal function. These claims are based on hippocampal lesion studies performed with rats and have not been conclusively confirmed with mice with specific hippocampal lesion. Therefore, I investigated how hippocampal ibotenic acid lesion affects conditioned fear in mice. I confirm that extensive lesions localized to the hippocampus impair context-dependent learning but also show that, unlike in the original rat studies, the behavioral impairment is only partial. Furthermore, studying two inbred strains of mice (C57BL/6 and DBA/2) with highly different hippocampal function, I show that the presence or absence of CS during training may influence the mouse's ability to learn complex multiple contextual stimuli in a genotype-dependent manner. I conclude that performance at the 'context' test may be based on complex configural (hippocampal) learning but it can also be based on a more simple elemental (non-hippocampal) learning thus leading to potentially false-negative findings in the analysis of hippocampal dysfunction.

Acoustic Stimulation↗

PubMed1998

A new continuous alternation task in T-maze detects hippocampal dysfunction in mice. A strain comparison and lesion study.

The mammalian hippocampus has been the focus of several neurobiology studies because of its important behavioral function and because long-term potentiation (LTP) is a prominent feature of this brain region. Converging evidence suggests that hippocampal function is associated with learning multiple relationships of environmental cues. In this paper a novel behavioral test procedure is introduced, a modified T-maze continuous alternation task (T-CAT), that may serve as a simple, automatable, and quick test of hippocampal function in addition to the frequently applied water maze and fear conditioning paradigms. A comparison is made between mice (strain C57BL/6) with ibotenic acid lesioned or vehicle injected hippocampus, two transgenic strains (on CD1 background) overexpressing a calcium binding protein, S100beta, and inbred (C57BL/6, DBA/2, 129/SV and 129/SVEV) and outbred (CD1) strains of mice. This study shows that hippocampal lesioning led to a significant impairment in T-CAT. Furthermore, overexpression of S100beta, which impairs hippocampal LTP, also led to an impairment demonstrating that T-CAT is sensitive to detect hippocampal dysfunction. Analysis of the mouse strains revealed that C57BL/6 and CD1 mice performed well in T-CAT, whereas 129/SV, 129/SVEV and DBA/2 were significantly impaired, a finding that underscores the importance of strain differences in pharmacological or single gene manipulation studies of hippocampal function in mice.

Animals↗

PubMed1998

Multiple behavioral anomalies in GluR2 mutant mice exhibiting enhanced LTP.

We have previously disrupted the ionotropic glutamate receptor type 2 gene (GluR2) using gene targeting in embryonic stem cells and generated mice which lacked the GluR2 gene product. Neurophysiological analyses of these mice showed a markedly enhanced long-term potentiation (LTP) and a 9-fold increase in kainate induced Ca2+ permeability in the hippocampus. Here, we analyze the behavioral and neuroanatomical consequences of GluR2 deficiency in homozygous null mutant and age-matched littermate control mice. We show that despite unaltered gross brain morphology, several aspects of behavior were abnormal in the mutants. Object exploration, rearing, grooming and locomotion were altered in the novel arena. Eye-closure reflex, motor performance on the rotating rod and spatial and non-spatial learning performance in the water maze were also abnormal in the mutants. These abnormalities together with the widespread expression pattern of GluR2 in most excitatory CNS pathways suggest that the absence of GluR2 leads to neurological phenotypes associated with not only the hippocampus but several other brain regions potentially including the cortex and cerebellum. We speculate that GluR2 mutant mice suffer from an overall non-specifically increased excitability that may alter cognitive functions ranging from stimulus processing to motivation and learning.

Animals↗

PubMed1998

Altered spatial learning and memory in mice lacking the mGluR4 subtype of metabotropic glutamate receptor.

The glutamate analog, L-2-amino-4-phosphonobutyric acid (L-AP4) is a selective agonist for several members of the metabotropic glutamate receptor (mGluR) family. Activation of presynaptic mGluRs by L-AP4 causes a suppression of synaptic transmission in the central nervous system. In this study, the role of 1 subtype of mGluR in the nervous system was investigated by analyzing mutant mice lacking the L-AP4-sensitive receptor, mGluR4. Experiments designed to probe hippocampal function showed no impairments in acquisition of spatial learning in the water maze task. However, in a spatial reversal learning task, the mutant mice exhibited significantly accelerated learning performance. Furthermore, in a probe trial administered 6 weeks posttraining, these mice showed impaired spatial accuracy. The results suggest that the mutant mice differed in their ability to learn and integrate new spatial information into previously formed memory traces and that their use of stored spatial information also was altered. Thus, the presynaptically expressed mGluR4 plays a role in the processing of spatial information.

Analysis of Variance↗

PubMed1997

Transgenic mice overexpressing the neurotrophic factor S-100 beta show neuronal cytoskeletal and behavioral signs of altered aging processes: implications for Alzheimer's disease and Down's syndrome.

S-100 beta is a neurotrophic factor released by astroglial cells and localized to chromosome 21, within the region which is considered obligate for Down's syndrome (DS). S-100 beta is increased in the postmortem brains of both DS and Alzheimer's disease. Transgenic mice, produced by insertion of the human gene for S-100 beta, were examined for dendritic development at two ages, using an antibody against microtubule associated protein-2 (MAP-2). At the earliest stages, the density of dendrites within the hippocampus of transgenic animals exceeded that of controls. Also, MAP-2 immunostaining was evident in the region of the cell body. By 1 year of age, the transgenic animals had significant loss of dendrites compared to controls and the number of cells showing cell body staining was further increased. These pathological changes could be indicative of the presence of neurofibrillary tangles and cytoskeletal collapse. Behaviorally, younger transgenic animals could not perform in a learning task as well as controls. Together, these findings suggest that increased S-100 beta in brain may lead to accelerated development, followed by increased aging. The pathological changes may prove useful as an animal model of Down's syndrome and Alzheimer's disease.

Aging↗

PubMed1997

Mice lacking metabotropic glutamate receptor 5 show impaired learning and reduced CA1 long-term potentiation (LTP) but normal CA3 LTP.

Class I metabotropic glutamate receptors (mGluRs) have been postulated to play a role in synaptic plasticity. To test the involvement of one member of this class, we have recently generated mutant mice that express no mGluR5 but normal levels of other glutamate receptors. The CNS revealed normal development of gross anatomical features. To examine synaptic functions we measured evoked field EPSPs in the hippocampal slice. Measures of presynaptic function, such as paired pulse facilitation in mutant CA1 neurons, were normal. The response of mutant CA1 neurons to low concentrations of (1S,3R)-1-amino-cyclopentane-1,3-dicarboxylic acid (ACPD) was missing, which suggests that mGluR5 may be the primary high affinity ACPD receptor in these neurons. Long-term potentiation (LTP) in mGluR5 mutants was significantly reduced in the NMDA receptor (NMDAR)-dependent pathways such as the CA1 region and dentate gyrus of the hippocampus, whereas LTP remained intact in the mossy fiber synapses on the CA3 region, an NMDAR-independent pathway. Some of the difference in CA1 LTP could lie at the level of expression, because the reduction of LTP in the mutants was no longer observed 20 min after tetanus in the presence of 2-amino-5-phosphonopentanoate. We propose that mGluR5 plays a key regulatory role in NMDAR-dependent LTP. These mutant mice were also impaired in the acquisition and use of spatial information in both the Morris water maze and contextual information in the fear-conditioning test. This is consistent with the hypothesis that LTP in the CA1 region may underlie spatial learning and memory.

Animals↗

PubMed1997

Antipredator behavior in paradise fish (Macropodus opercularis) larvae: the role of genetic factors and paternal influence.

The paradise fish, a small insectivore, coinhabits marshes of Southeast Asia with several predator fish species. Its ability to recognize and avoid harmful fish may depend upon both genetic factors and experience. Here we demonstrate genetic variability between the 20-day-old larvae of two inbred strains of paradise fish (P and S) in predator exploration and avoidance, using predator models. We show that, in comparison to S larvae, P larvae exhibited an elevated frequency of leaping and backing and an increased approach latency when faced with a predator model with eyespots. Analysis of a classical cross system between the two strains revealed significant departure from an additive-dominance genetic model and suggested the involvement of both epistatic effects of several genes and paternal effects. The effect of the paternal influence during the 5-day postspawning period was found to be strain dependent: later predator avoidance behaviors were influenced by the presence of the father in P larvae but not in S larvae. On the basis of these and previous results, we speculate that the 5 postspawning days may represent a developmentally sensitive period during which specific environmental stimulation, e.g., stimuli associated with the father, is critical for later development of appropriate antipredatory responses. We conclude that developmental aspects of antipredatory behavior in paradise fish are influenced by a complex interplay between genetic and environmental factors.

Animals↗

PubMed1996

Impaired cerebellar synaptic plasticity and motor performance in mice lacking the mGluR4 subtype of metabotropic glutamate receptor.

The application of the glutamate analog L-2-amino-4-phosphonobutyric acid (L-AP4) to neurons produces a suppression of synaptic transmission. Although L-AP4 is a selective ligand at a subset of metabotropic glutamate receptors (mGluRs), the precise physiological role of the L-AP4-activated mGluRs remains primarily unknown. To provide a better understanding of the function of L-AP4 receptors, we have generated and studied knockout (KO) mice lacking the mGluR4 subtype of mGluR that displays high affinity for L-AP4. The mGluR4 mutant mice displayed normal spontaneous motor activity and were unimpaired on the bar cross test, indicating that disruption of the mGluR4 gene did not cause gross motor abnormalities, impairments of novelty-induced exploratory behaviors, or alterations in fine motor coordination. However, the mutant mice were deficient on the rotating rod motor-learning test, suggesting that mGluR4 KO mice may have an impaired ability to learn complex motor tasks. Patch-clamp and extracellular field recordings from Purkinje cells in cerebellar slices demonstrated that L-AP4 had no effect on synaptic responses in the mutant mice, whereas in the wild-type mice 100 microM L-AP4 produced a 23% depression of synaptic responses with an EC50 of 2.5 microM. An analysis of presynaptic short-term synaptic plasticity at the parallel fiber-->Purkinje cell synapse demonstrated that paired-pulse facilitation and post-tetanic potentiation were impaired in the mutant mice. In contrast, long-term depression (LTD) was not impaired. These results indicate that an important function of mGluR4 is to provide a presynaptic mechanism for maintaining synaptic efficacy during repetitive activation. The data also suggest that the presence of mGluR4 at the parallel fiber-->Purkinje cell synapse is required for maintaining normal motor function.

Animals↗

PubMed1996

Spatial and nonspatial learning in mice: effects of S100 beta overexpression and age.

S100 beta, a Ca2+ binding astrocytic brain protein implicated in brain development and neurophysiology, has elevated levels in progressive neurodegenerative diseases, Down's Syndrome, and Alzheimer Disease. Transgenic mice carrying multiple S100 beta gene copies exhibited abnormal exploratory behaviors and synaptic processes suggesting hippocampal dysfunction. Here we analyze learning in a hippocampal-dependent (spatial) as well as a non-hippocampal-dependent (nonspatial) version of the Morris water maze and compare CD1 control and CD1-derived S100 beta transgenic mice. We also investigate possible progressive age-dependent effects of S100 beta overexpression by comparing two age groups of the above mice: 3- and 16-month-old. We show that 3-month-old S100 beta transgenic mice have a spatial task-specific impairment confirming a hippocampal dysfunction. However, we found the 16-month-old transgenic mice statistically indistinguishable from their normal counterparts, a result that does not confirm progressive S100 beta transgene effects. We also show that age, independently of the transgene, impairs spatial learning, spares nonspatial learning and reference memory, but leads to behavioral rigidity.

Age Factors↗

PubMed1996

Conspecific exploration in the T-maze: abnormalities in S100 beta transgenic mice.

S100 beta, a calcium binding brain protein expressed by astrocytes, has been shown to be involved in higher neural processes, including hippocampal-dependent behavioral traits and hippocampal neuronal long-term potentiation (LTP) and depression (LTD), neurophysiological phenomena that may be involved in exploring, learning and remembering novel stimuli. In the present study, the exploratory behavior of previously generated transgenic mice overexpressing the protein are compared to that of normal control mice of identical genetic background and age in a T-maze. The test mice encountered a normal control and an S100 beta transgenic mouse (the choice mice) in the goal arms of the T-maze. We show that no test mice exhibited any preference for either genotype of choice mouse. However, there was a significant difference in the spatial and temporal exploratory pattern between control and S100 beta test mice, demonstrating that S100 beta overexpression significantly altered the behavior of the transgenic mice. We suggest that one probable factor underlying the abnormalities observed is impaired short-term memory.

Animals↗

PubMed1996

Memory and the effect of cold shock in the water maze in S100 beta transgenic mice.

S100 beta, a calcium binding astrocytic brain protein, influences hippocampal long-term potentiation (LTP) and depression (LTD), synaptic processes suggested to play role in spatial (contextual) learning and memory. In the present study we trained S100 beta transgenic and wild-type control mice in a nonspatial version of the Morris water maze, the visible platform task, and analyzed retention of memory over periods of 18 h, several days, and weeks. The results show that acquisition and retention were not altered in the S100 beta transgenic mice compared to control. However, a single alteration of an environmental stimulus, water temperature, significantly worsened the performance of transgenic mice. This impairment lasted for two consecutive trials separated by a 2-week intertrial interval, suggesting a temporary disturbance associated with memory processes. We discuss the possibility that these results are compatible with normal cortical but abnormal hippocampal functioning in the S100 beta transgenic mice.

Animals↗

PubMed1996

Gene-targeting studies of mammalian behavior: is it the mutation or the background genotype?

Gene targeting to create null mutations in mice is a powerful new tool in biology which will allow the molecular dissection of complex phenotypes such as mammalian brain function, and learning and memory. However, the attempt to interpret the phenotypical changes which arise in null-mutant mice is subject to several caveats. For example, the ability to disrupt a single gene in a targeted manner might lead one to overlook the effects of other genes. Ignoring the genetic background might lead to misinterpretation of results: the present article will demonstrate that the phenotypical abnormalities attributed to the null mutation in several molecular neurobiological studies could simply result from the effects of background genes.

Animals↗

PubMed1996

Enhanced LTP in mice deficient in the AMPA receptor GluR2.

AMPA receptors (AMPARs) are not thought to be involved in the induction of long-term potentiation (LTP), but may be involved in its expression via second messenger pathways. However, one subunit of the AMPARs, GluR2, is also known to control Ca2+ influx. To test whether GluR2 plays any role in the induction of LTP, we generated mice that lacked this subunit. In GluR2 mutants, LTP in the CA1 region of hippocampal slices was markedly enhanced (2-fold) and nonsaturating, whereas neuronal excitability and paired-pulse facilitation were normal. The 9-fold increase in Ca2+ permeability, in response to kainate application, suggests one possible mechanism for enhanced LTP. Mutant mice exhibited increased mortality, and those surviving showed reduced exploration and impaired motor coordination. These results suggest an important role for GluR2 in regulating synaptic plasticity and behavior.

Animals↗