Biomedical subjects

Joachim Spiess

Publications and source records attributed to Joachim Spiess.

At least 19 recordsLinked to original sources

PubMed2005

Urocortin II enhances contractility in rabbit ventricular myocytes via CRF(2) receptor-mediated stimulation of protein kinase A.

OBJECTIVE: Urocortin II (UcnII), a peptide of the corticotropin-releasing factor (CRF) family, exerts profound actions on the cardiovascular system. Direct effects of UcnII on adult cardiomyocytes have not been evaluated before. Our aim was to characterize functional effects of UcnII on cardiomyocytes and to elucidate the underlying signaling pathway(s) and cellular mechanisms. METHODS: Rabbit ventricular cardiomyocytes were stimulated at 0.5 Hz (22-25 degrees C). Unloaded cell shortening (FS, edge detection), [Ca(2+)](i) transients (Fluo-4), and L-type Ca(2+) currents (I(Ca), whole-cell patch clamping) were measured. Sarcoplasmic reticulum (SR) Ca(2+) load was assessed by rapid application of caffeine (20 mmol/L). RESULTS: UcnII increased cell shortening and accelerated relaxation in a time- and concentration-dependent manner (EC(50): 10.7 nmol/L). The inotropic effect of UcnII was maximal at 100 nmol/L (35%+/-11% increase in FS, n=8, P<0.05). The inotropic and lusitropic actions of UcnII were largely eliminated by inhibition of CRF(2) receptors (10 nmol/L antisauvagine-30, n=5) or protein kinase A (PKA, 500 nmol/L H-89, n=5). UcnII increased [Ca(2+)](i) transient amplitude (by 63%+/-35%, n=7, P<0.05) and decreased the time constant for decay (from 800+/-63 to 218+/-27 ms, n=7, P<0.001). UcnII also increased SR Ca(2+) load (by 19%+/-7%, n=7, P<0.05) and fractional Ca(2+) release (from 57%+/-7% to 98%+/-2%, n=7, P<0.01). I(Ca) was augmented by 32.7%+/-10.0% (n=9, P<0.05) and the I(Ca)-V relationship was shifted by -15 mV during UcnII treatment. CONCLUSION: UcnII exerts positive inotropic and lusitropic effects in cardiomyocytes via CRF(2) receptor-mediated stimulation of PKA which augments I(Ca) and SR Ca(2+) load to increase SR Ca(2+) release and [Ca(2+)](i) transients.

Animals↗

PubMed2005

Cholecystokinin-2 (CCK2) receptor-mediated anxiety-like behaviors in rats.

Cholecystokinin (CCK) is a neurotransmitter in the brain closely related to anxiety. Of the two CCK receptor subtypes, CCK(2) receptors are most implicated in the control of anxiety-related behavior. CCK(2) receptor activation causes anxiogenic effects while the blockade of this receptor has anxiolytic effects. This review focuses on the molecular mechanisms of CCK(2) receptors underlying anxiety-related behaviors of PVG hooded and Spraque-Dawley (SD) rats in two anxiety models (elevated plus-maze [EPM] and cat exposure test). PVG hooded rats showed prolonged freezing behavior in the cat exposure test while SD rats showed very low levels of freezing. A CCK(2) receptor antagonist (LY225910) attenuated freezing behavior in PVG hooded rats while a CCK(2) receptor agonist (CCK-4) increased freezing behavior in SD rats. In contrast, the two strains behaved similarly on the EPM. CCK-4 caused a pronounced anxiogenic effect in PVG hooded rats but only a slight effect in SD rats. CCK(2) antagonists also showed more pronounced anxiolytic effects in PVG hooded rats than in SD rats. CCK(2) receptor expression was greater in PVG hooded than in SD rats in the cortex and hippocampus. Genetic studies also demonstrated four differences in the DNA sequence of the CCK(2) receptor gene between the two rat strains.

Animals↗

PubMed2005

Urocortin 1 and Urocortin 2 induce macrophage apoptosis via CRFR2.

Macrophages undergo apoptosis as a mechanism of regulating their activation and the inflammatory reaction. Macrophages express the Corticotropin-Releasing Factor Receptor-2 (CRFR2) the endogenous agonists of which, the urocortins, are also present at the site of inflammation. We have found that urocortins induced macrophage apoptosis in a dose- and time-dependent manner via CRFR2. In contrast to lipopolysaccharide (LPS)-induced apoptosis, the pro-apoptosis pathway activated by urocortins involved the pro-apoptotic Bax and Bad proteins and not nitric oxide, JNK and p38MAPK characteristic of LPS. In conclusion, our data suggest that endogenous CRFR2 ligands exert an anti-inflammatory effect via induction of macrophage apoptosis.

Animals↗

PubMed2005

The role of CRF receptors in anxiety and depression: implications of the novel CRF1 agonist cortagine.

Corticotropin-releasing factor (CRF), a 41 amino acid peptide exhibits its actions through two pharmacologically distinct CRF receptor subtypes CRF(1) and CRF(2). Regulation of the relative contribution of the two CRF receptors to central CRF activity may be essential in coordinating physiological responses to stress. To facilitate the analysis of their differential involvement, we recently developed a CRF(1)-selective agonist cortagine by synthesis of chimeric peptides derived from human/rat CRF, ovine CRF, and sauvagine. Cortagine was analyzed in behavioral experiments using male wild type and CRF(2)-deficient C57BL/6J mice for its action on anxiety- and depression-like behaviors. In contrast to the current hypothesis that increased CRF(1) activity facilitates the expression of anxiety- and depression-like behavior, cortagine combines anxiogenic properties with antidepressant effects. In this article, we show that antidepressant effects are partially mediated by CRF(1) of the dorsal hippocampus. Possible pathways responsible for the paradoxical antidepressant effects observed after CRF(1) activation are discussed.

Animals↗

PubMed2005

Time-dependent involvement of the dorsal hippocampus in trace fear conditioning in mice.

Hippocampal and amygdaloid neuroplasticity are important substrates for Pavlovian fear conditioning. The hippocampus has been implicated in trace fear conditioning. However, a systematic investigation of the significance of the trace interval has not yet been performed. Therefore, this study analyzed the time-dependent involvement of N-methyl-D-aspartate (NMDA) receptors in the dorsal hippocampus in one-trial auditory trace fear conditioning in C57BL/6J mice. The NMDA receptor antagonist APV was injected bilaterally into the dorsal hippocampus 15 min before training. Mice were exposed to tone (conditioned stimulus [CS]) and footshock (unconditioned stimulus [US]) in the conditioning context without delay (0 s) or with CS-US (trace) intervals of 1-45 s. Conditioned auditory fear was determined 24 h after training by the assessment of freezing and computerized evaluation of inactivity in a new context; 2 h later, context-dependent memory was tested in the conditioning context. NMDA receptor blockade by APV markedly impaired conditioned auditory fear at trace intervals of 15 s and 30 s, but not at shorter trace intervals. A 45-s trace interval prevented the formation of conditioned tone-dependent fear. Context-dependent memory was always impaired by APV treatment independent of the trace interval. The results indicate that the dorsal hippocampus and its NMDA receptors play an important role in auditory trace fear conditioning at trace intervals of 15-30-s length. In contrast, NMDA receptors in the dorsal hippocampus are unequivocally involved in contextual fear conditioning independent of the trace interval. The results point at a time-dependent role of the dorsal hippocampus in encoding of noncontingent explicit stimuli. Preprocessing of long CS-US contingencies in the hippocampus appears to be important for the final information processing and execution of fear memories through amygdala circuits.

2-Amino-5-phosphonovalerate↗

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

Corticotropin-releasing factor receptor 1 and central heart rate regulation in mice during expression of conditioned fear.

The present study was performed to 1) determine heart rate (HR) effects mediated through central corticotropin-releasing factor receptor subtypes 1 (CRF(1)) investigate and 2 (CRF(2)) and 2) to the contribution of endogenous CRF to baseline HR and its fear-induced adjustment in freely moving mice. CRF ligands were injected into both lateral ventricles (i.c.v.) 15 min before the presentation of a conditioned auditory fear stimulus (CS). Initial behavioral results suggest an ovine CRF (oCRF)-mediated enhanced baseline fear and mildly enhanced conditioned auditory fear. In contrast, i.c.v. injection of oCRF (35-210 ng/mouse) dose-dependently decreased baseline HR, increased HR variability, and attenuated the CS-induced tachycardia. This effect is suggested to depend on a combined activation of sympathetic and parasympathetic activity referred to as enhanced sympathovagal antagonism. An extreme bradycardia was elicited by oCRF injection into the lower brainstem. All HR effects were probably mediated by CRF(1) because injection of the CRF(2)-selective agonist mouse urocortin II was ineffective, and the baseline bradycardia by i.c.v. CRF was preserved in CRF(2)-deficient mice. Injection of various CRF receptor antagonists including the CRF(2)-selective antisauvagine-30 did not affect the conditioned HR response. This finding suggests that endogenous CRF does not contribute to the fear-mediated tachycardia. Thus, the hypothesis of an involvement of CRF in HR responses of mice to acute aversive stimulation is rejected. Pharmacological evidence points at the involvement of CRF(1) in enhanced sympathovagal antagonism, a pathological state contributing to elevated cardiac risk, whereas the physiological role of the brain CRF system in cardiovascular regulation remains to be determined.

Animals↗

PubMed2004

Central NPY receptor-mediated alteration of heart rate dynamics in mice during expression of fear conditioned to an auditory cue.

Neuropeptide Y (NPY) is involved in the regulation of emotionality including fear and anxiety, which modulate autonomic control of cardiovascular function. We therefore investigated the central effects of porcine NPY, selective Y1, Y2 and Y5 receptor agonists and a Y1 receptor antagonist on heart rate (HR) and HR variability in freely moving mice using auditory fear conditioning. Intracerebroventricular (i.c.v.) injections were applied 15 min before the tone-dependent memory test. NPY dose-dependently induced bradycardia associated with decreased HR variability, and blunted the stress-induced tachycardic response. The selective Y1 receptor antagonist BIBO 3304 blocked the NPY- and Y1-receptor agonist-induced suppression of conditioned tachycardia without affecting basal HR. The tachycardia elicited by both conditioned and unconditioned stressor was effectively attenuated by the Y1 receptor agonist. These results suggest a specific contribution of Y1, but not Y2 and Y5 receptors, to modulation of emotional responses most likely unrelated to impairment or modulation of memory. The NPY-induced bradycardia is attributed to not yet characterized NPY receptor subtypes other than Y1, Y2 and Y5, or a complex receptor interaction. In conclusion, NPY mediates central inhibition of sympathetic outflow, potentially coupled with attenuation of parasympathetic tone, i.e., mechanisms that may be associated with the reported anxiolytic action.

Animals↗

PubMed2004

Calmodulin and Munc13 form a Ca2+ sensor/effector complex that controls short-term synaptic plasticity.

The efficacy of synaptic transmission between neurons can be altered transiently during neuronal network activity. This phenomenon of short-term plasticity is a key determinant of network properties; is involved in many physiological processes such as motor control, sound localization, or sensory adaptation; and is critically dependent on cytosolic [Ca2+]. However, the underlying molecular mechanisms and the identity of the Ca2+ sensor/effector complexes involved are unclear. We now identify a conserved calmodulin binding site in UNC-13/Munc13s, which are essential regulators of synaptic vesicle priming and synaptic efficacy. Ca2+ sensor/effector complexes consisting of calmodulin and Munc13s regulate synaptic vesicle priming and synaptic efficacy in response to a residual [Ca2+] signal and thus shape short-term plasticity characteristics during periods of sustained synaptic activity.

Animals↗

PubMed2004

Cortagine, a specific agonist of corticotropin-releasing factor receptor subtype 1, is anxiogenic and antidepressive in the mouse model.

Two subtypes of the corticotropin-releasing factor (CRF) receptor, CRF(1) and CRF(2), differentially modulate brain functions such as anxiety and memory. To facilitate the analysis of their differential involvement, we developed a CRF(1)-specific peptidic agonist by synthesis of chimeric peptides derived from human/rat CRF, ovine CRF (oCRF), and sauvagine (Svg). High affinity to the CRF-binding protein was prevented by introduction of glutamic acid in the binding site of the ligand. The resulting chimeric peptide, [Glu(21),Ala(40)][Svg(1-12)]x[human/rat CRF(14-30)]x[Svg(30-40)], named cortagine, was analyzed pharmacologically in cell culture by using human embryonic kidney-293 cells transfected with cDNA coding for CRF(1) or CRF(2), in autoradiographic experiments, and in behavior experiments using male C57BL/6J mice for its modulatory action on anxiety- and depression-like behaviors with the elevated plus-maze test and the forced swim test (FST), respectively. We observed that cortagine was more selective than oCRF, frequently used as CRF(1)-specific agonist, in stimulating the transfected cells to release cAMP. Cortagine's specificity was demonstrated in autoradiographic experiments by its selective binding to CRF(1) of brain sections of the mouse. After injection into the brain ventricles, it enhanced anxiety-like behavior on the elevated plus-maze at a lower dose than oCRF. Whereas at high doses, oCRF injected into the lateral intermediate septum containing predominantly CRF(2) increased anxiety-like behavior as CRF(2)-specific agonists do, cortagine did not. In contrast to its anxiogenic actions, cortagine reduced significantly the immobility time in the FST as described for antidepressive drugs. Thus, cortagine combines anxiogenic properties with antidepressive effects in the FST.

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↗

PubMed2004

Three-amino acid motifs of urocortin II and III determine their CRF receptor subtype selectivity.

Corticotropin-releasing factor (CRF) and the CRF-like peptide urocortin I (UcnI) exert their activity through two different CRF receptors, CRF1 and CRF2. Recently, UcnII and UcnIII have been discovered as potential endogenous agonists selective for CRF2 known to be involved in brain functions such as learning and anxiety, as well as in cardiovascular functions. A structure-affinity relationship study using chimeric peptides was designed to characterize mouse UcnII (mUcnII) and mUcnIII further and to investigate the structural basis of their receptor subtype selectivity. In the framework of this study, mUcnII (IC50 = 4.4 nM) but not mUcnIII was identified as high-affinity ligand for the rat CRF binding protein. Such affinity had previously not been observed for the human version of this protein. On the basis of secondary structure predictions, it was hypothesized that the amino acid motifs Pro-Ile-Gly of mUcnII and Pro-Thr-Asn of mUcnIII decrease alpha-helicity and thereby impair binding to CRF1. In support of this hypothesis, binding affinity to CRF1 of the chimeric peptides [Pro11Ile12Gly13]h/rCRF, [Pro11Thr12Asn13]h/rCRF, and the corresponding rUcnI analogs was found to be decreased by three orders of magnitude, whereas binding affinity to CRF2 was much less affected. The dramatic decrease in binding affinity to CRF1 correlated with a decrease in alpha-helicity as indicated by the data of circular dichroism spectroscopy.

Amino Acid Sequence↗

PubMed2004

Molecular determinants mediating effects of acute stress on hippocampus-dependent synaptic plasticity and learning.

The understanding of the molecular events underlying the neuroendocrine and behavioral sequelae of the response to stress has advanced rapidly over recent years. The hippocampus is a target of stress hormones, and we are beginning to dissect the molecular players in the modulation of synaptic plasticity and learning and memory involving this region of the brain. Given the wealth of data obtained from electrophysiological and behavioral experiments and in view of the importance to use identical experimental protocols in order to correlate the results obtained under both experimental conditions, this review focuses primarily on those contributions, which combine both approaches. From these studies it is evident that a single stressful event elicits responses in the hippocampus with different time-spans ranging from rapid changes in glutamatergic neurotransmission (i.e., N-methyl-d-aspartate receptor signaling), activation of second messenger cascades by corticotropin-releasing factor to long-lasting transcriptional changes of acetylcholinesterase. The relative contribution of these molecular targets to the stress response, the relation to hippocampal synaptic plasticity and memory formation, and the possible interaction of the underlying processes are discussed.

Acute Disease↗

PubMed2004

Small conductance Ca2+-activated K+ channels as targets of CNS drug development.

In most central neurons, small conductance Ca(2+)-activated K(+) channels (SK channels) contribute to afterhyperpolarizations (AHPs), which control neuronal excitability. The medium AHP has pharmacological properties similar to recombinant SK channels, consistent with the hypothesis that SK channels generate this afterhyperpolarization component. It is still unclear how recombinant SK channels are functionally related to the slow AHP component. Cloned SK channels are heteromeric complexes of SK channel subunits and calmodulin. The channels are activated by Ca(2+) binding to calmodulin that induces conformational changes resulting in channel opening. Channel deactivation is the reverse process brought about by dissociation of Ca(2+) from calmodulin. In the mammalian brain, the three SK channel subunits (SK1-3) display partially overlapping distributions. Most of the higher brain regions such as the neocortex and hippocampus show expression of both genes encoding SK1 and SK2 channels, whereas phylogenetically older brain regions such as the thalamus, basal ganglia, cerebellum, and brainstem show high levels of SK3 gene expression. At present, it is still unclear whether native SK channels are generated as heteromeric or homomeric channels. Peptide toxins such as apamin and scyllatoxin, as well as organic compounds such as quaternary salts of bicuculline, dequalinium, UCL 1684 and UCL 1848 serve as non-specific SK channel blockers. The only known exceptions so far are the scorpion toxin tamapin and the peptide inhibitor Lei-Dab(7), which bind preferentially to SK2. Electrophysiological and behavioral studies indicate that blockade of SK channels by apamin increases excitability, lowers the threshold for the induction of synaptic plasticity, and facilitates hippocampus-dependent memory. The potential value of pharmacological SK channel modulation in various pathological states such as increased epileptiform activity, cognitive impairment, pain, mood disorders and schizophrenia will be discussed.

Animals↗

PubMed2003

Characterization of peptide-protein interactions using photoaffinity labeling and LC/MS.

The combination of photoaffinity labeling (PAL) with modern mass spectrometric techniques is a powerful approach for the characterization of peptide-protein interactions. Depending on the analytical strategy applied, a PAL experiment can provide different levels of information ranging from the identification of interaction partners to the structural characterization of ligand-binding sites. On the basis of LC/MS data generated in the framework of the identification of the binding site of the neuropeptide corticotropin-releasing factor (CRF) on its binding protein (CRFBP), the key role of LC/MS in the characterization of photoadducts on different structural levels was demonstrated. Covalent photoadducts of rat CRFBP (rCRFBP) were obtained by PAL with different mono- and bifunctional benzophenone photoprobes designed on the basis of the sequence of the synthetic CRF fragment human/rat CRF(6-33) which binds to CRFBP with high affinity. In view of the stoichiometry, LC/MS analysis revealed that the photoadducts consisted of one molecule of photoprobe and one molecule of rCRFBP. For a further characterization of the photoadducts on the oligopeptide level, enzymatic digests of unlabeled rCRFBP and of the respective photoadduct were compared by peptide mapping monitored with LC/MS. Thereby, it was found that the photoprobe that contained the photophore at its N-terminus labeled the amino acid sequence rCRFBP(34-38), whereas the photoprobe that contained the photophore at its C-terminus labeled rCRFBP(12-26). On the basis of the characterization of the photoadduct formed by rCRFBP and the bifunctional photoprobe that contained photophores on both termini, semiquantitative comparison of different enzymatic digests was accomplished by application of the mass-selective multiple ion chromatogram strategy.

Amino Acid Sequence↗

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↗