Biomedical subjects

Jelena Radulovic

Publications and source records attributed to Jelena Radulovic.

14 recordsLinked to original sources

PubMed2006

Hippocampal Mek/Erk signaling mediates extinction of contextual freezing behavior.

Fear memories elicit multiple behavioral responses, encompassing avoidance, or behavioral inhibition in response to threatening contexts. Context-specific freezing, reflecting fear-induced behavioral inhibition, has been proposed as one of the main risks factors for the development of anxiety disorders. We attempted to define the key hippocampal mediators of extinction in a mouse model of context-dependent freezing. Nine-week-old male C57BL/6J mice were trained and tested for contextual fear conditioning and extinction. Freezing behavior scored by unbiased sampling, was used as an index of fear. Proteomic, immunoblot, and immunohistochemical approaches were employed to identify, verify, and analyze the alterations of the hippocampal extracellular signal-regulated kinases 1 and 2 (Erk-1/2). Targeted pharmacological inhibition of the Erk-1/2 activating kinase, the mitogen activated and extracellular signal-regulated kinase (Mek), served to establish the role of Mek/Erk signaling in extinction. When compared to acquisition, extinction of contextual freezing triggered a rapid activation of Erk-1/2 showing a distinctive time-course, nuclear localization, and subcellular isoform distribution. These differences suggested that the upstream regulation and downstream effects of this pathway might be specific for each process. Dorsohippocampal injections of the Mek inhibitors U0126 (0.5 microg/site) and PD98059 (1.5 microg/site) immediately after the nonreinforced trials prevented Erk-1/2 activation and significantly impaired extinction. This effect was dissociable from potential actions on memory retrieval or reconsolidation. On the basis of these findings, we propose that hippocampal Mek/Erk signaling might serve as one of the key mediators of contextual fear extinction.

Analysis of Variance↗

PubMed2006

Extinction: [corrected] does it or doesn't it? The requirement of altered gene activity and new protein synthesis.

Many accounts of memory suggest that an initial learning experience initiates a cascade of cellular and molecular events that are required for the consolidation of memory from a labile into a more permanent state. Studies of memory in many species have routinely found that altered gene activity and new protein synthesis are the critical components of this memory consolidation process. During extinction, when organisms learn that previously established relations between stimuli have been severed, new memories are formed and consolidated. However, the nature of the learning that underlies extinction remains unclear and there are many processes that may contribute to the weakening of behavior that occurs during extinction. In this review, we suggest that the molecular mechanisms that underlie extinction may differ depending on the learning process that is engaged by extinction. We review evidence that extinction, like initial learning, requires transcription and translation, as well as evidence that extinction occurs when protein synthesis is inhibited. We suggest that extinction occurs through the interaction of multiple behavioral and molecular mechanisms.

Animals↗

PubMed2006

Mapping of the habenulo-interpeduncular pathway in living mice using manganese-enhanced 3D MRI.

This magnetic resonance imaging (MRI) study describes mapping of the habenulo-interpeduncular pathway in living mice based on manganese-induced contrast. Six hours after intracerebroventricular microinjection of MnCl2, T1-weighted 3D MRI (2.35 T) at 117 mum isotropic resolution revealed a continuous pattern of anterograde labeling from the habenula via the fasciculus retroflexus to the interpeduncular nucleus. Alternatively, the less invasive systemic administration of MnCl2 allowed for monitoring of the dynamic uptake pattern of respective neural components with even higher reproducibility across animals. Time courses covered the range from 42 min to 24 h after injection. In conclusion, manganese-enhanced MRI may open new ways for functional assessments of the habenulo-interpeduncular system in animal models with cognitive impairment.

Animals↗

PubMed2005

Corticotropin-releasing factor binding protein--a ligand trap?

The actions of the neuropeptide corticotropin-releasing factor (CRF) are modulated by a CRF binding protein (CRFBP). In view of the memory-enhancing effects of CRF, the release of endogenous CRF from CRFBP by CRFBP inhibitors has been suggested as a therapeutical strategy for the treatment of cognitive deficits. This mini-review will summarize recent advances in the field with a focus on the pharmaceutical potential of CRFBP inhibitors.

Amino Acid Sequence↗

PubMed2004

Distinct roles of hippocampal de novo protein synthesis and actin rearrangement in extinction of contextual fear.

It is believed that de novo protein synthesis is fundamentally linked to synaptic changes in neuronal circuits involved in acquisition and extinction of conditioned responses. Recent studies show that neuronal plasticity may be also altered by cytoskeletal rearrangement independently of protein synthesis. We investigated the role of these processes in the hippocampus during acquisition and extinction of context-dependent conditioned fear in mice. Intrahippocampal injections of the protein synthesis inhibitors anisomycin and puromycin, or of the actin rearrangement inhibitors cytochalasin D and latrunculin A, prevented the acquisition of context-dependent fear. Unexpectedly, anisomycin and puromycin enhanced extinction without erasing the fear memory. In contrast, cytochalasin D and latrunculin A prevented extinction of context-dependent freezing. On the basis of these findings, it is suggested that certain hippocampal mechanisms mediating extinction of conditioned contextual fear are inhibited by protein synthesis and involve actin rearrangement. Such mechanisms might predominantly elicit modifications of hippocampal circuits that store the conditioning memory.

Acoustic Stimulation↗

PubMed2004

The role of hippocampal signaling cascades in consolidation of fear memory.

We investigated the involvement of hippocampal protein kinase A (PKA), protein kinase C (PKC), calcium/calmodulin-dependent protein kinases (CaMK II), and mitogen-activated extracellular signal-regulated kinases 1 and 2 (Mek-1/2) in the phosphorylation of their downstream targets extracellular signal-regulated kinases 1 and 2 (Erk-1/2), cAMP-response element-binding protein (CREB), Elk-1, and p90 ribosomal S6 kinase 1 (p90Rsk-1). The role of these processes in memory consolidation of conditioned fear was determined. C57BL/6N mice were injected into the dorsal hippocampus with inhibitors of PKA, PKC, CaMK II, Mek-1/2, or vehicle before training consisting of a single exposure to a context, tone, and footshock. Freezing behavior of mice reflecting fear memory was scored after their re-exposure to the conditioned stimuli. Inhibition of PKA impaired context- and tone-dependent fear conditioning and significantly reduced the phosphorylation of Elk-1, p90Rsk-1, Erk-1/2, and CREB. PKC inhibition also impaired context- and tone-dependent fear conditioning and prevented the phosphorylation of Erk-1/2, Elk-1, and CREB, without affecting p90Rsk-1. Inhibition of CaMK II did not affect fear conditioning and reduced the phosphorylation of Erk-1/2, Elk-1, CREB, and p90Rsk-1 only transiently, whereas Mek-1/2 inhibition was ineffective in all experiments. It was concluded that hippocampal PKA and PKC play crucial roles in one-trial fear conditioning. Erk-1/2, Elk-1, and CREB were identified as common targets of PKA, PKC, and CaMK II during memory consolidation, however, the time window and sequence of their phosphorylation was specific for the individual kinase.

Animals↗

PubMed2004

In vivo 3D MRI staining of the mouse hippocampal system using intracerebral injection of MnCl2.

The morphology and function of the hippocampal system of C57BL/6J mice (n = 8) was studied in vivo using T1-weighted 3D magnetic resonance imaging (MRI) (117 microm isotropic resolution) after bilateral injection of MnCl(2) (0.25 microl, 5 or 200 mM) into the posterior hippocampal formation. The neuronal uptake of the T1-shortening Mn(2+) ions resulted in a pronounced MRI signal enhancement within the CA3 subfield and dentate gyrus with milder increases in CA1 and subiculum. This finding is in line with differences in the excitability of hippocampal neurons previously reported using electrophysiologic recordings. The subsequent axonal transport of Mn(2+) highlighted the principal extrinsic projections from the posterior hippocampal formation via the fimbria and the precommissural fornix to the dorsal part of the lateral septal nucleus. A strong MRI signal enhancement was also observed in the ventral hippocampal commissure. A time-course analysis revealed unsaturated conditions of Mn(2+) accumulation at about 2 h after injection and optimal contrast-to-noise ratios at about 6 h after injection. The present results using Mn(2+)-enhanced 3D MRI open new ways for studying the role of the hippocampal system in specific aspects of learning and memory in normal and mutant mice.

Animals↗

PubMed2003

Mitogen-activated protein kinase signaling in the hippocampus and its modulation by corticotropin-releasing factor receptor 2: a possible link between stress and fear memory.

A coordinated activation of multiple interlinked signaling pathways involving cAMP-dependent protein kinase (PKA) and mitogen-activated extracellular signal-regulated kinases (Mek-1/2) regulates gene expression and neuronal changes underlying memory consolidation. In the present study we investigated whether these molecular cascades might mediate the effects of stress on memory formation. We also investigated the role of hippocampal corticotropin-releasing factor receptor 2 (CRF2) in stress-enhanced learning and molecular signaling mediated by PKA, Mek-1/2, and their downstream targets extracellularly regulated kinases 1 and 2 (Erk-1/2) and p90-ribosomal-s-kinase-1 (p90Rsk-1). Acute 1 hr immobilization was used as a stressful stimulus, and one-trial context-dependent fear conditioning was used as a model for associative learning. Training of BALB/c mice 3 hr after the end of immobilization resulted in an enhancement of conditioned fear, as indicated by significantly increased freezing behavior of stressed when compared with nonstressed mice. Interestingly, Erk-1/2 phosphorylation after conditioning of nonstressed and stressed mice depended on PKA and Mek-1/2, respectively. Intrahippocampal injection of the selective Mek-1/2 inhibitor U0126 or CRF2 antagonist antisauvagine-30 (aSvg-30) prevented stress-enhanced fear conditioning and Mek-1/2-dependent activation of Erk-1/2 and p90Rsk-1. aSvg-30 did not affect the phosphorylation of the PKA regulatory subunit II of stressed mice. The molecular and behavioral effects of CRF2 coincided with stress-induced upregulation of CRF2 mRNA. These results suggest that modulation of Mek-1/2-dependent signaling by hippocampal CRF2 can be selectively involved in the delayed effects of stress on memory consolidation.

Animals↗

PubMed2003

Regulation of contextual fear conditioning by baseline and inducible septo-hippocampal cyclin-dependent kinase 5.

In this work, we confirm the novel role of cyclin-dependent kinase (Cdk) 5 in associative learning by demonstrating that injection of the Cdk5 inhibitor butyrolactone I into the lateral septum or hippocampus profoundly impaired context-dependent fear conditioning of C57BL/6J mice. However, unlike the inducible up-regulation of Cdk5 and its regulator p35 observed in Balb/c mice, high baseline levels, which were not affected by fear conditioning, were found in C57BL/6J mice. Surprisingly, microinjections of butyrolactone I into the lateral septum or hippocampus significantly decreased baseline Cdk5 activity within the entire septo-hippocampal circuitry, suggesting a functional link between septal and hippocampal Cdk5 activity. Significantly higher levels of the transcription factor Sp4 in the septo-hippocampal system of C57BL/6J mice may account for the high baseline Cdk5/p35 production. On the other hand, the stronger cFos production observed in the lateral septum of fear conditioned Balb/c mice may be responsible, at least in part, for the inducible up-regulation of Cdk5 in this strain. These results suggest that the role of Cdk5 in memory consolidation is strain independent and functionally related to the septo-hippocampal circuitry. However, the molecular regulation of baseline and inducible Cdk5 protein might be different among individual mouse strains and possibly other species.

4-Butyrolactone↗

PubMed2003

Small-conductance, Ca2+-activated K+ channel SK3 generates age-related memory and LTP deficits.

Cognitive deficits are among the most devastating changes associated with the aging process. Age-related decrement in performance on learning tasks is correlated with substantial changes in neuronal signal processing in the hippocampus. Here we show that elevated expression of small-conductance Ca2+-activated K+ channels (SK channels) of the SK3 type in hippocampi of aged mice contributes to reduced long-term potentiation (LTP) and impaired trace fear conditioning, a hippocampus-dependent learning task.

Aging↗

PubMed2003

Cdk5 in the adult non-demented brain.

Cyclin-dependent kinase 5 (Cdk5), a Ser/Thr kinase, regulates the phosphorylation of neuronal proteins and thereby influences neuronal morphology, migration and axon growth. Tightly coordinated interactions between Cdk5 and its activator proteins p35 and p39 are critical for the developmental processes of post-mitotic neurons as well as functioning of the adult CNS. Excessive up-regulation of Cdk5 activity leading to hyperphosphorylation of cytoskeletal proteins has been linked to neurodegenerative disorders, such as Alzheimer's disease (AD). On this basis it was proposed that Cdk5 might be a promising drug target. The physiologic role of Cdk5 in the adult CNS has been addressed recently. It was demonstrated that Cdk5 is involved in striatal and hippocampal neuronal plasticity and long-term behavioral changes associated with these processes. On the basis of the newly identified role of Cdk5 in synaptic plasticity, learning and memory the view that Cdk5 represents a good drug target in AD accompanied by cognitive dysfunctions may have to be revisited. Alternatively, targeting the mechanisms up-stream of Cdk5 leading to deregulation of Cdk5 activity, such as proteolytic cleavage of its activating subunits may prove to be more beneficial as a therapeutical approach.

Animals↗

PubMed2002

Cyclin-dependent kinase 5 is required for associative learning.

Transient stressful experiences may persistently facilitate associative and nonassociative learning, possibly through alterations of gene expression. Here we identify, by subtractive hybridization, differential expression of the Cdk5 gene in response to stress. The Cdk5 protein is selectively induced in the fibers of septohippocampal cholinergic neurons but not in other regions of prominent Cdk5 production. This upregulation is accompanied by increased Cdk5 kinase activity, which is blocked completely by the Cdk5 inhibitor butyrolactone I. Microinjection of butyrolactone I into the lateral septum and hippocampus prevents the acquisition of conditioned context-dependent fear as well as its stress-induced facilitation. By demonstrating that a transient increase of Cdk5 activity within the septohippocampal system is required for associative learning, an important novel role of Cdk5 has been identified.

4-Butyrolactone↗

PubMed2002

Phosphorylation of hippocampal Erk-1/2, Elk-1, and p90-Rsk-1 during contextual fear conditioning: interactions between Erk-1/2 and Elk-1.

The phosphorylation of proteins involved in the MAP kinase signal transduction pathway was investigated during associative learning of C57BL/6J mice. Context-dependent fear conditioning, consisting of a single exposure of mice to a context followed by foot shock, was employed as a learning paradigm. Control groups consisted of mice exposed to context only or an immediate shock in the context. Coincident up-regulation of phosphorylated Erk-1/2 and Elk-1 was observed in the CA3 hippocampal subfield and dentate gyrus 30 min after fear conditioning but not after the control paradigms. Phosphorylated Erk-1/2 and Elk-1 were associated and predominantly colocalized in the mossy fibers. In vitro kinase assays showed that hippocampal Erk-1/2 phosphorylates Elk-1. Notably, Elk-1 in turn enhances the phosphorylation of Erk-1/2 and its downstream target p90Rsk-1. Increased phosphorylation and nuclear translocation of p90Rsk-1 was also demonstrated in the CA3 hippocampal area in vivo during contextual fear conditioning. The observed interactions between hippocampal Elk-1 and Erk-1/2 proteins may affect the consolidation of contextual memories through activation of the downstream nuclear targets of Erk-1/2, such as p90Rsk-1, without requiring nuclear translocation of Elk-1 and Erk-1/2.

Active Transport, Cell Nucleus↗

PubMedDate not supplied

Cdk5: a novel role in learning and memory.

Learning and memory are processes by which organisms acquire, retain and retrieve information. They result in modifications of behavior in response to new or previously encountered stimuli thereby enabling adaptation to a permanently changing environment. Protein phosphorylation has long been known to play a key role in triggering synaptic changes underlying learning and memory. Although intracellular phosphorylation and dephosphorylation is orchestrated by a complex network of interactions between a number of protein kinases and phosphatases, significant advances in the understanding of neuronal mechanisms underlying learning and memory have been achieved by investigating the actions of individual molecules under defined experimental conditions, brain areas, neuronal cells and their subcellular compartments. On the basis of these approaches, the cyclic AMP protein kinase (PKA), protein kinase C (PKC) and extracellularly regulated protein kinases 1 and 2 (Erk-1/2) have been identified as the core signaling pathways in memory consolidation. Here we review recent findings demonstrating an important novel role for Cdk5 in learning and memory. We suggest that some of the well-characterized roles of Cdk5 during neurodevelopmental processes, such as interactions with distinct cytoplasmic and synaptic target molecules, may be also involved in synaptic plasticity underlying memory consolidation within the adult central nervous system.

Animals↗