Amygdala Kindling Potentiates Seizure-Stimulated Immediate-Early Gene Expression in Rat Cerebral Cortex

Kindling induces long-term adaptations in neuronal function that lead to a decreased threshold for induction of seizures. In the present study, the influence of amygdala kindling on levels of mRNA for the immediate-early genes (IEGs) c-fos, c-jun, and NGF1-A were examined both before and after an acute electroconvulsive seizure (ECS). Although amygdala kindling did not significantly influence resting levels of c-fos mRNA in cerebral cortex, ECS-stimulated levels of c-fos mRNA (examined 45 min after ECS) were approximately twofold greater in the cerebral cortex of kindled rats relative to sham-treated controls. The influence of kindling on IEG expression was dependent on the time course of kindling, as ECS-stimulated levels of c-fos mRNA were not significantly increased in stage 2 kindled animals. ECS-stimulated levels of c-jun and NGF1-A mRNA were also significantly increased in cerebral cortex of kindled rats relative to sham-treated controls. The influence of kindling on IEG expression was long-lasting because an acute ECS stimulus significantly elevated levels of c-fos and c-jun mRNA in the cerebral cortex of animals that were kindled 5 months previously. In contrast to these effects in cerebral cortex, kindling did not influence ECS-stimulated levels of c-fos mRNA in hippocampus. Finally, immunohistochemical studies revealed lamina-specific changes in the cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of immediate early gene and neuropeptide gene response to prolonged immobilization stress: evidence against a critical role of the termination of exposure to the stressor

Stress-induced expression of immediate early genes (IEGs) appears to be transient even if the exposure to the stressor persists. However, there are some exceptions which suggest that particular characteristics of stressors can affect the dynamics of IEG expression. We studied in selected telencephalic, diencephalic and brainstem regions the mRNA levels of two clearly distinct IEGs (c-fos and arc) during prolonged exposure to a severe stressor such as immobilization (IMO) and after releasing the rats from the situation. Although regional differences were observed with the two IEGs, overall, c-fos mRNA levels progressively declined over the course of 4 h of continuous exposure to IMO, whereas arc mRNA levels were maintained at high levels in the brain regions that express this gene under stress (telencephalon). Levels of CRF hnRNA in the hypothalamus paraventricular nucleus only slightly declined during prolonged exposure to IMO. Surprisingly, termination of exposure to IMO did not modify CRF gene expression in the paraventricular nucleus or the pattern of IEGs expression, with the exception of c-fos in the lateral septum. Thus, putative signals associated to the termination of exposure to IMO were unable to modify either IEG expression in most brain areas or CRF gene expression in the paraventricular nucleus.     

Differential effects of rabies and borna disease viruses on immediate-early- and late-response gene expression in brain tissues.

In situ hybridization and Northern blot analysis were used to examine expression of the immediate-early-response genes (IEGs) egr-1, junB, and c-fos, and the late response gene encoding enkephalin in the brains of rats infected intranasally with Borna disease virus (BDV) or rabies virus. In both Borna disease and rabies virus infections, a dramatic and specific induction of IEGs was detected in particular regions of the hippocampus and the cortex. Increased IEG mRNA expression overlapped with the characteristic expression patterns of BDV RNA and rabies virus RNA, although relative expression levels of viral RNA and IEG mRNA differed, particularly in the hippocampal formation. Furthermore, the temporal relationship between viral RNA synthesis and activation of IEG mRNA expression in BDV infection differed markedly from that in rabies virus infection, suggesting that IEG expression is upregulated by different mechanisms. Expression of proenkephalin (pENK) mRNA was also significantly increased in BDV infection, whereas in rabies virus infection, pENK mRNA levels and also the levels of glyceraldehyde-3-phosphate dehydrogenase mRNA were reduced at terminal stages of the disease, probably reflecting a generalized suppression of cellular protein synthesis due to massive production of rabies virus mRNA. The correlation between activated IEG mRNA expression and the strong increase in viral RNA raises the possibility that IEG products induce some phenotypic changes in neurons that render them more susceptible to viral replication.     

Induction of immediate early genes in the mouse auditory cortex after auditory cued fear conditioning to complex sounds

Immediate early genes (IEGs) are widely used as markers to delineate neuronal circuits because they show fast and transient expression induced by various behavioral paradigms. In this study, we investigated the expression of the IEGs c-fos and Arc in the auditory cortex of the mouse after auditory cued fear conditioning using quantitative polymerase chain reaction and microarray analysis. To test for the specificity of the IEG induction, we included several control groups that allowed us to test for factors other than associative learning to sounds that could lead to an induction of IEGs. We found that both c-fos and Arc showed strong and robust induction after auditory fear conditioning. However, we also observed increased expression of both genes in any control paradigm that involved shocks, even when no sounds were presented. Using mRNA microarrays and comparing the effect of the various behavioral paradigms on mRNA expression levels, we did not find genes being selectively upregulated in the auditory fear conditioned group. In summary, our results indicate that the use of IEGs to identify neuronal circuits involved specifically in processing of sound cues in the fear conditioning paradigm can be limited by the effects of the aversive unconditional stimulus and that activity levels in a particular primary sensory cortical area can be strongly influenced by stimuli mediated by other modalities.     

Expression of c-fos, c-jun and HSP70 mRNA in rat brain following high acceleration stress

Rats exposed to high +Gz forces in a small animal centrifuge (SAC) exhibit loss of neuronal function (isoelectric EEG), termed G-induced loss of consciousness (G-LOC). This phenomenon is presumably due to a reduction in cerebral blood flow (CBF) or ischemia. Ischemia induces various metabolic and physiologic changes including expression of immediate early genes (IEGs) in the brain. Expression of IEGs have been suggested to be reliable markers for neuronal response to external stimuli or stress. In the present study expression of IEGs c-fos, c-jun and stress response gene HSP70 were measured in the brains of rats subjected to six 30 s exposures of +22.5Gz in a small animal centrifuge. The level of c-fos, HSP70 and beta-actin mRNA were measured by both Northern blot and RT-PCR. Expression of c-jun was measured only by RT-PCR. Expression of c-fos and c-jun was significantly stimulated at 0.5, 15, 30 and 60 min post-centrifugation. The level of HSP70 mRNA was significantly higher only at 60 and 180 min post-centrifugation. Measurement of metabolities showed a significant increase in lactate and a decrease in Cr-P level at 30 s and 15 min post-centrifugation, respectively. Lactate, but not Cr-P and ATP levels were restored to control levels by 60 min post-centrifugation. It is concluded that the transient expression of c-fos, c-jun and HSP70 mRNA is stimulated by repeated ischemic/reperfusion episodes induced by high acceleration stress.     

Ca2+ channel modulation and kinase-C activation in a pituitary cell line: induction of immediate early genes and inhibition of proliferation.

We have studied the interaction between dihydropyridine (DHP) Ca2+ modulators and the phorbol ester phorbol 12-myristate 13-acetate (PMA) on whole cell Ca2+ currents, 45Ca2+ uptake, immediate early gene (IEG) expression, and proliferation in the rat pituitary GH4C1 cell line. When short (3- to 5-msec) depolarizing voltage clamp steps were used to activate L-type Ca2+ channels, the DHP Ca2+ agonist (-)Bay K 8644 markedly enhanced Ca2+ entry by slowing channel closing upon repolarization. In contrast, the Ca2+ agonist induced only small and inconsistent increases in c-fos mRNA and did not measurably increase NGFI-A. Ca2+ channel activation by depolarization with 50 mM KCl in the presence of (-)Bay K 8644 induced large increases in 45Ca2+ uptake, but failed to markedly induce either of the IEGs. The phorbol ester PMA did not alter T- or L-type Ca2+ current or 45Ca2+ uptake by GH4C1 cells, but triggered large increases in both c-fos and NGFI-A mRNA. In combination, PMA and (-)Bay K 8644 acted synergistically to increase mRNAs for both IEGs. The effect of the DHPs was stereospecific; (+)Bay K 8644, a Ca2+ antagonist, inhibited PMA-induced increases in c-fos and NGFI-A mRNAs. Both PMA and (-)Bay K 8644 inhibited the proliferation of GH4C1 cells, measured by cell count or [3H]thymidine incorporation. The inhibition by the Ca2+ agonist was stereoselective and approximately additive to that of PMA. These results indicate that the expression of c-fos IEG and that of NGFI-A IEG are differentially regulated by separate second messenger pathways in GH4C1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Examination of the involvement of protein kinase A in D2 dopamine receptor antagonist-induced immediate early gene expression

Immediate early genes (IEGs) are induced by different signaling pathways. It has been proposed that D2 dopamine receptor blockade induces IEG expression through activation of protein kinase A (PKA), although few studies have examined this issue in vivo. We infused the PKA inhibitor H-89 into the striatum of male rats, followed 30 min later by systemic administration of eticlopride. Eticlopride-induced c-fos and zif268 mRNA expression in striatum was not blocked by H-89. In addition, eticlopride did not produce measurable levels of PKA activity in striatum, whereas the cAMP activator Sp-8-Br-cAMPs increased levels of activated PKA. Neither the adenosine A2a receptor agonist CGS 21680 nor the phosphodiesterase-4 inhibitor rolipram, each of which should increase PKA activation, potentiated eticlopride-induced IEG expression. To test whether other signaling pathways are involved in eticlopride-mediated gene induction, we also infused inhibitors of the mitogen-activated and calcium/calmodulin-dependent protein kinases into animals and then treated them with eticlopride. The data suggest that eticlopride-induced IEG expression is not solely dependent on these kinases either. These data suggest that PKA activation may not be necessary for induction of IEGs by D2 dopamine receptor antagonists and that other intracellular signaling pathways may be involved.