Differential expression of immediate early genes in the hippocampus and spinal cord

Patterns of expression of the immediate-early gene egr-1 in the accessory olfactory bulb of female mice exposed to pheromonal constituents of male urine

Male mice excrete large quantities of major urinary proteins that have been proposed to have an important pheromonal role either alone or by way of their bound ligands. We have found that these major urinary proteins are not only likely to mediate the pregnancy blocking effects of male urine, but that they also convey the strain recognition signal of the male pheromone. Recent molecular biological investigations have characterized two classes of pheromonal receptor in the vomeronasal organ that appear to project separately to anterior and posterior regions of the accessory olfactory bulb. However, it is not known whether these separate pathways handle fundamentally different types of pheromonal information. We have attempted to investigate this question using the expression of the immediate-early gene egr-1 as a marker for activity of neurons in the accessory olfactory bulb of female mice in response to putative pheromonal constituents. Exposure to 2,3 dihydro-exo-brevicomin and 2-sec-butyl-4,5-dihydro-thiazole, the main ligands bound to the major urinary proteins, elicited expression of egr-1 in clusters of presumed mitral neurons at the medial and lateral margins of the posterior accessory olfactory bulb. Whole male urine and a preparation of major urinary proteins that had been stripped of their ligands induced egr-1 expression in mitral cells of the anterior half of the accessory olfactory bulb in addition to the posterior clusters. This would suggest that the anterior and posterior halves of the accessory olfactory bulb are processing different aspects of the male pheromone signal with the anterior region, which responds preferentially to major urinary proteins, being principally concerned with the strain recognition component.

Calcium influx through NMDA receptors, chronic receptor inhibition by ethanol and 2-amino-5-phosponopentanoic acid, and receptor protein expression

Chronic treatment of neurons with either ethanol or competitive and noncompetitive antagonists of NMDA receptors leads to enhanced expression of NMDA receptor density and function in neurons. The signal transduction pathways for such receptor up-regulation are not known. The focus of the present study was on the role of Ca2+ entry into neurons, either through receptor or voltage-gated channels, in the expression of the NMDA receptor subunit NR1 and the 71-kDa glutamate-binding protein (GBP) of a glutamate/NMDA receptor-like complex. Chronic inhibition of NMDA receptors in cortical neurons in primary cultures by either 100 mM ethanol or 100 microM 2-amino-5-phosphonopentanoic acid (2-AP5) increased the expression of NR1 and GBP. The effect of 2-AP5 on the expression of the two proteins was not additive with that of ethanol when neuronal cultures were treated with both agents at the same time. However, the effects of ethanol on NR1 and GBP expression were blocked by the simultaneous treatment with NMDA (50 microM). Activation or inhibition of other glutamate ionotropic receptors had no effect on the expression of NR1 and GBP. The inhibition of L- or N-type voltage-sensitive Ca2+ channels and voltage-gated Na+ channels also had little effect on the expression of either protein; neither did exposure of neurons to elevated extracellular Ca2+ concentrations (3 or 5 mM). On the other hand, treatment of neurons for 48 h with the intracellular Ca2+ chelator BAPTA-AM as well as partial chelation of extracellular Ca2+ with EGTA caused an up-regulation in NR1 and GBP expression. The enhanced expression of NR1 in neurons treated for 48 h with either ethanol or EGTA was correlated with increases in the activity of NMDA receptors demonstrated as a doubling of the NMDA-stimulated rise in intracellular free Ca2+ concentration. The effects of chronic administration of EGTA on both NR1 expression as well as NMDA receptor function were probably related to an acute inhibition by EGTA of NMDA-induced Ca2+ influx into neurons. It appears that the expression of both the NR1 subunit of NMDA receptors and the GBP of a receptor-like complex is regulated by intracellular Ca2+, especially that entering through NMDA receptor ion channels.

The EGR family of transcription-regulatory factors: progress at the interface of molecular and systems neuroscience

The EGR family of transcription regulatory factors, which is implicated in orchestrating the changes in gene expression that underlie neuronal plasticity, has attracted the attention of both molecular and systems neuroscientists. In this article, the advances made in both these fields of research are reviewed. Recent systems-based studies underscore the remarkable sensitivity and specificity of the induction of the expression of genes encoding EGR-family members in naturally occurring plasticity paradigms. However, they also challenge conventional views of the role of this family in plasticity. Recent molecular studies have identified the gonadotropin subunit, luteinizing hormone beta, as an EGR1-regulated gene in vivo and uncovered an essential role for EGR3 in muscle-spindle development. In addition, the discovery of novel proteins that are capable of suppressing EGR-mediated transcription cast doubt over the prevalent assumption that changes in EGR mRNA or protein levels provide an accurate measure of EGR-driven transcriptional activity.

Effect of pre-emptive NMDA antagonist treatment on long-term Fos expression and hyperalgesia in a model of chronic neuropathic pain

The unilateral sciatic nerve chronic constriction injury (CCI) model of Bennett and Xie [G.J. Bennett, Y.-K. Xie, A peripheral neuropathy in rat that produces disorders of pain sensation like those seen in man, Pain, 33 (1988) 87-108] shows features of a neuropathic pain state. We examined mechanical hyperalgesia and Fos protein staining in the lumbar spinal cord 1, 7, 14 and 28 days after unilateral CCI to the sciatic nerve or sham operation. In addition, we examined the effect of the NMDA antagonist MK-801 (0.3 mg/kg s.c. administered 30 min prior to and 6 h following operation) on Fos expression and hyperalgesia at 28 days. CCI animals were hyperalgesic compared to the sham operated animals at 14 and 28 days post injury. MK-801 reduced hyperalgesia by 68% in CCI animals on day 28 (p=0.0001). In the spinal cord, Fos positive cells were present bilaterally in deeper laminae in both sham and CCI animals at all time points examined. Relatively few Fos positive cells were present in laminae 1-2 at any time point examined. At days 1 and 7, there were increased numbers of Fos positive cells ipsilaterally in the deeper laminae of the spinal cord in CCI animals compared to sham animals, but by 14 and 28 days Fos counts were similar in sham and CCI despite the obvious behavioural differences between the two groups. Fos counts ipsilateral to the injury in laminae 3-10 correlated with hyperalgesia scores in the CCI but not sham animals. Analysis at the 28-day time point showed that MK-801 differentially affected Fos expression: MK-801 significantly reduced the Fos count bilaterally in laminae 3-10 in the CCI but not in the sham group animals. These results indicate that Fos expression is initiated by different peripheral and central mechanisms following nerve injury or sham operation.

Vasopressin in the mammalian brain: the neurobiology of a mnemonic peptide

We have sought to understand the mechanisms by which VP can enhance memory function and in the process determine whether VP fulfills the requirements for neurotransmitter status. The latter goal of proving the neurotransmitter status of VP has been achieved through our findings and the results of many of the scientists contributing to this volume. With respect to elucidating the mechanisms by which VP can enhance memory function, results of our work have shown that VP and its receptors are present in brain regions known to be involved in memory function, that release of VP is inhibited by a factor that inhibits memory function, that VP can significantly enhance the morphological complexity and outgrowth of neurons involved in memory function, that second messenger systems held to be involved in learning and memory, cyclic AMP and calcium signaling pathways, are potentiated and activated by VP, that electrophysiological models of memory function are induced by VP, and that when animals remember a learned association VP content in brain increases over time during the active phase of remembering. Collectively, these studies have taught us a great deal about the sites and mechanisms of VP action and have led us to pursue avenues of investigation that we would not have imagined 15 years ago when we began this work. We stand on the threshold of a new era in our research as we begin our studies of the role VP and its receptors play in the cerebral cortex. Thus far, results of these studies are quite exciting and promise to yield fascinating insights into the complexities of VP action in the most highly developed region of the mammalian brain, the cerebral cortex, the site of abstract reasoning, judgment, complex analysis and the repository of those memories that last a life-time.

Delayed induction of JunB precedes CA1 neuronal death after global ischemia in the gerbil

The immediate early genes (IEGs), c-jun, junB and c-fos are expressed after global ischemia in the gerbil. The role of these genes remains unclear. Whilst moderate ischemia (7 min) causes delayed CA1 neuronal death, pre-conditioning with mild ischemia (2 min) neuroprotects the CA1 subfield. This differential response allows the specific expression patterns of IEGs to be associated with either delayed neuronal death, or cell survival, depending upon the insult severity. Using a graded insult strategy we have shown that (1) early IEG expression is prominent in the neuronal layers of the CA3, hilar and dentate regions, and (2) a delayed, secondary wave of JunB expression is localized to the selectively vulnerable CA1 neuronal layer after moderate ischemia. This expression precedes the histological and histochemical features of neuronal death. Delayed JunB expression was not observed in animals subject to 2 min ischemia. The glial fibrillary acidic protein (GFAP) promotor possesses an AP-1 binding site, the target for IEG dimers. To examine the possible link between IEG expression and astrocyte activation the transcriptional activation of GFAP was assessed. GFAP mRNA was evident within 8 h of ischemia after both insults. The extent of the astrocytic reaction was dependent upon the severity of the ischemia. The temporospatial distribution of IEG and GFAP expression differed, indicating that glial activation is unlikely to be regulated by the hippocampal expression of IEGs. We conclude that early IEG expression is involved in signalling mechanisms that invoke neuroprotective effects in the dentate and CA3 regions, and that delayed JunB expression in the CA1 subfield is associated with neuronal death, and may be involved in the commitment or execution phases of cell death. Early astrocytic responses may play a role in the mechanism of ischaemic tolerance.

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.

Differential decreases in c-fos and aldolase C mRNA expression in the rat cerebellum after repeated administration of methamphetamine

The effects of repeated methamphetamine administration on c-fos mRNA and aldolase C (Zebrin) mRNA expression in the rat cerebellum were investigated. A single dose of methamphetamine induced c-fos mRNA expression in granule and Purkinje cells of both anterior and posterior lobes. In the posterior lobe, in particular, c-fos mRNA signals were distributed in a parasagittal organization, like Zebrin bands. Repeated methamphetamine injections reduced methamphetamine-induced c-fos mRNA signals in the anterior hemisphere and in part of the posterior vermis (lobule VII) and posterior hemisphere. Aldolase C mRNA signals in Purkinje cells decreased only in lobules where methamphetamine-induced c-fos signals were not reduced (lobules VI and IX). Therefore, differential decreases in c-fos mRNA and aldolase C mRNA expression after repeated methamphetamine administration depend upon the localization of Purkinje cells in the cerebellum. Since c-fos mRNA and aldolase C mRNA expressions are markers of excitability and the metabolic state of Purkinje cells, respectively, hypofunction of inhibitory Purkinje cells could be induced if methamphetamine is repeatedly injected. Since repeated methamphetamine administration in this experimental paradigm increased horizontal movement and the rearing activity of rats, the hemisphere of the cerebellum may be involved in development of methamphetamine-induced motor behavioral sensitization in addition to the striatum and the nucleus accumbens.

The induction of pain: an integrative review

The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.

Fetal spinal cord transplants and exogenous neurotrophic support enhance c-Jun expression in mature axotomized neurons after spinal cord injury

The responses of the central (CNS) and peripheral (PNS) nervous system to axotomy differ in a number of ways; these differences can be observed in both the cell body responses to injury and in the extent of regeneration that occurs in each system. The cell body responses to injury in the PNS involves the upregulation of genes that are not upregulated following comparable injuries to CNS neurons. The expression of particular genes following injury may be essential for regeneration to occur. In the present study, we have evaluated the hypothesis that expression of the inducible transcription factor c-Jun is associated with regrowth of axotomized CNS neurons. In these experiments, we compared c-Jun expression in axotomized brainstem neurons after thoracic spinal cord hemisection alone (a condition in which no regrowth occurs) and in groups of animals where hemisections were combined with treatments such as transplants of fetal spinal cord tissue and/or application of neurotrophic factors to the lesion site. The latter conditions enhance the capacity of the CNS for regrowth. We have demonstrated that hemisections alone do not upregulate expression of c-Jun, indicating that this particular cell body response is not a direct result of axotomy. However, c-Jun expression is upregulated in animals that received application of transplants and neurotrophins. Because these interventions also promote sprouting and regrowth of CNS axons after spinal cord lesions, we suggest that transplants and exogenous neurotrophic factor application activate a cell body response consistent with a role for c-Jun in axonal growth.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

NMDA receptor subunit NR1-immunoreactivity in the rat pons and brainstem and colocalization with Fos induced by nasal stimulation

In the present study, we examined the distribution of neurons in the parabrachial nucleus (PB), the Kölliker-Fuse nucleus (KF), the spinal trigeminal nucleus caudalis (Sp5C), the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM), which are activated by evoking the nasotrigeminal reflex and which exhibit immunoreactivity for the N-methyl-D-aspartate (NMDA) receptor subunit NR1. By stimulating the nasal mucosa with saline, we induced the expression of the immediate early gene c-fos and combined the immunocytochemical detection of the Fos protein with the detection of the NR1 subunit. Cell counts revealed that nasal stimulation, compared to anesthesia controls, resulted in highly significant increases (p < or = 0.001) of Fos-immunoreactive (-ir) neurons in the midlevel KF, the external lateral PB, and the Sp5C. In the central lateral PB, the rostral ventrolateral medulla including the Bötzinger/pre-Bötzinger complex, and in the ventrolateral and commissural NTS the increases were only moderately significant (p < or = 0.05). With respect to the numbers of NR1-/Fos-ir double-labeled neurons, significant increases were only observed in a subset of these pontomedullary nuclei. Increases were highly significant in the Sp5C (p < or = 0.001) and the midlevel KF (p < or = 0.01) and moderately significant (p < or = 0.05) in the external lateral PB, Bötzinger/pre-Bötzinger complex, and ventrolateral NTS. The present study revealed that nasotrigeminally activated neurons in mandatory and potential relay sites of the nasotrigeminal reflex circuit express the NR1 subunit. This finding strongly suggests that NMDA-type glutamate receptors are involved in the mediation of the nasotrigeminally evoked cardiovascular and respiratory responses.

Occurrence of a transcription factor, cAMP response element-binding protein (CREB), in the postsynaptic sites of the brain

The postsynaptic density (PSD) fraction prepared from the rat forebrain contained a transcription factor, cAMP response element-binding protein (CREB). The occurrence of CREB in the PSD was confirmed by immunoelectron microscopic examination. CREB in the PSD fraction was phosphorylated both by protein kinase A and Ca2+/calmodulin-dependent protein kinase II (CaMKII) endogenous to the fraction, and dissociated from the PSD after phosphorylation, especially under CaMKII-activated conditions. The fraction containing CREB that was released from PSD after phosphorylation possessed cAMP response element (CRE)-binding activity. Thus, PSD anchors functionally active CREB. These results suggest that CREB anchored to the PSD is liberated by phosphorylation upon specific synaptic stimulation, translocates into the nucleus, and then triggers synaptic activity-dependent changes in gene expression.

Effects of prolactin on expression of the mRNAs encoding the immediate early genes zif/268 (NGF1-A), nur/77 (NGF1-B), c-fos and c-jun in the hypothalamus

Prolactin (PRL) exerts a short-loop negative feedback effect on hypothalamic neurons which control its secretion from the anterior pituitary gland. The purpose of this study was to identify the location of hypothalamic neurons which respond to acute PRL exposure. Increasing evidence indicates that excitation of neurons often results in the rapid transcription of immediate early genes (IEGs). In the present study, quantitative in situ hybridization histochemistry (ISHH) was used to visualize the induction of mRNAs for four different IEGs: zif/268 (NGF1-A), nur/77 (NGF1-B), c-fos and c-jun. Three groups of male rats were compared: unmanipulated controls, rats injected s.c. with 2.4 mg ovine PRL (oPRL) suspended in polyvinylpyrrolidone (PVP), and PVP-injected controls. Animals were decapitated 0, 0.5, 1, 2, 3 or 4 h following injection. In all rats, the four probes labeled cells within the cortex, particularly the cingulate and piriform cortices, the hippocampus and the striatum. In the arcuate nucleus, there was a modest increase in the average number of cells/animal which expressed zif/268 mRNA following the injection of PVP and oPRL at all times studied. The average area of grains/cell representing zif/268 message also increased following the injection stimulus. The number of neurons expressing nur/77 mRNA was greater in PRL-treated rats compared with PVP-treated controls 0.5 and 1 h following injection. Nur/77-labeled neurons were co-extensive with the tuberoinfundibular dopaminergic (TIDA) neurons. The data suggest that cells located within the arcuate nucleus are involved in mediating PRL autofeedback on the brain.

Increase in Syntaxin 1B mRNA in Hippocampal and Cortical Circuits During Spatial Learning Reflects a Mechanism of Trans-synaptic Plasticity Involved in Establishing a Memory Trace

It has long been proposed that the cellular and molecular mechanisms responsible for LTP may well involve the mechanisms that lead to the type of synaptic modification that occurs during learning. However, it is also known that a single memory trace is encoded in spatially distributed networks; implying that alterations of synaptic strength occur at multiple sites along circuits of connected cells. Recent evidence suggests that regulation of the gene encoding syntaxin 1B, a presynaptic protein involved in exocytosis, plays an important role in the mediation of trans-synaptic LTP, a candidate mechanism for the propagation of plasticity in neural circuits during learning. Using in situ hybridization to measure the mRNA levels at different time points after learning a spatial working or reference memory task, we show that expression of the gene encoding this protein in the hippocampal and corticoprefrontal circuits increases linearly with performance at a critical window of learning when rats are reaching between 75% and 100% of their maximal performance. No changes were observed during the early phases of learning or when rats where overtrained. The correlational analysis indicates that coordinated increases in syntaxin 1B expression occurs in hippocampal circuits during working memory and in more widespread hippocampocortical circuits during reference memory. These results suggest that a form of trans-synaptic plasticity mediated in part by regulation of the expression of syntaxin 1B may play an active role in configuring specific spatially distributed circuits during the laying down of memories.

Macromolecular synthesis contributes to nociceptive response to subcutaneous formalin injection in mice

Subcutaneous formalin injection into the hindpaw produces two phases of nociceptive response: phase 1 and phase 2. Activation of N-methyl-D-aspartate (NMDA) receptors in the spinal cord during phase 1 is important for phase 2. We report here that phase 2 but not phase 1 requires new RNA and protein synthesis in the spinal cord.

Dissociation between genes activated in long-term potentiation and in spatial learning in the rat

We have compared changes in mRNA of three genes, zif268, raf B, and syntaxin 1 B, following the unilateral induction of long-term potentiation (LTP) in rats previously trained in a water maze, and in behaviourally naive animals. mRNA of all three genes was enhanced in the potentiated dentate gyrus of naive animals 3 h after the induction of LTP. Training did not affect expression of mRNA for zif268 or for syntaxin 1 B. Expression of raf B was enhanced by training, and in trained animals the LTP-associated increase in expression of raf B was occluded. These results suggest that LTP and spatial training engage a common pathway utilizing an increase in mRNA for raf B, and demonstrate a dissociation between LTP and spatial learning with respect to expression of zif268 and syntaxin 1B.

Increased jun immunoreactivity in an in vitro model of mammalian spinal neuron physical injury

Dendrites were transected from murine spinal neurons. Unlesioned neurons showed dark nucleolar and patchy cytoplasmic jun immunostaining. By 0.5 and 2 h, most lesioned neurons stained intensely throughout the soma. However, at 24 h only dead neurons displayed intense somal staining, and 100% of the surviving cells stained like unlesioned controls. Correlation of immunostaining patterns with viability, injury, and death suggests jun gene expression may influence the survival of neurons after physical injury.

Immediate-early gene expression in the amygdala following footshock stress and contextual fear conditioning

This study investigated the increase in expression in the amygdala of 2 immediate-early genes, c-fos and NGFI-A, following contextual fear conditioning. The immediate-shock freezing deficit paradigm was used to compare rats that received footshock after exploring a context to rats that received footshock immediately after placement in the chamber. The former procedure produces contextual fear conditioning while the latter does not. Rats were either handled (handled group), placed in a test chamber without receiving footshock (context-no-footshock group), received footshock immediately upon being placed in the chamber (immediate-footshock group), or received footshock after a 1 min delay (delayed-footshock group). Only the delayed-footshock group displayed a fear response (freezing behavior). Rats were sacrificed either 15 min after the experience or after a retention test 24 h later. The c-fos mRNA was increased in the medial nucleus of the amygdala in all of the groups that were placed in the test chamber. However, rats that received footshock (immediate- and delayed-footshock groups) had greater levels of c-fos mRNA expression than rats of the context-no-footshock group. The c-fos mRNA expression in the immediate- and delayed-footshock groups did not differ. However, after the retention test, the expression of c-fos mRNA in the medial nucleus of the amygdala did not differ between groups. In contrast to c-fos, NGFI-A mRNA expression in the lateral nucleus of the amygdala was greater in the delayed-footshock group than the handled and context-no-footshock groups 15 min after the footshock. This elevation in NGFI-A mRNA was not seen in the immediate-footshock group. This suggests that NGFI-A mRNA in the lateral nucleus of the amygdala may play a role in contextual fear conditioning.

Induction of immediate-early genes c-fos and zif268 in the subnucleus oralis by noxious tooth pulp stimulation

c-fos and zif268 expression were assessed by immunocytochemistry for c-Fos and Zif268 proteins in the sensory trigeminal nuclear complex following noxious mechanical stimulation of the mandibular incisor pulp of rats. Marked up-regulation of both immediate early genes was observed in the subnucleus oralis ipsilateral to the stimulation. Cavity preparation of the dentine without reaching the pulp did not cause significant up-regulation detectable by immunocytochemistry. These results provide evidence that noxious dental signals reach the ipsilateral subnucleus oralis and up-regulate the transcription of immediate early genes c-fos and zif268.

Vasopressin-induction of the immediate early gene, NGFI-A, in cultured hippocampal glial cells

Our earlier autoradiographic work had documented a wide distribution of vasopressin receptors in the hippocampus [R.E. Brinton, K.W. Gee, J.K. Wamsley, T.P. Davis, H.I. Yamamura, Regional distribution of putative vasopressin receptors in rat brain and pituitary by quantitative autoradiography, in: Proc. Natl. Acad. Sci. USA, 81 (1984) pp. 7248-7252; C. Chen, R.D. Brinton, T.J. Shors, R.F. Thompson, [Arg 8]-Vasopressin-induction of long lasting potentiation of synaptic transmission in the dentate gyrus, Hippocampus 3 (1993) 193-203.] which suggested the possibility that receptors for vasopressin were present in both neurons and glia. In the periphery, vasopressin is a potent mitogen in select proliferative cell types [E. Rozengurt, A. Legg, P. Pettican, Vasopressin stimulation of mouse 3T3 cell growth, Proc. Natl. Acad. Sci. USA, 76 (1979) pp. 1284-1287.] which also suggested a possible association between vasopressin receptor activation and the proliferative capacity of astrocytes. We therefore investigated whether vasopressin would induce the expression of the immediate early response gene, NGFI-A (also known as zif/268, ZENK, egr-1, krox 24), which is associated with initiation of mitogenesis [M. Sheng, M.E. Greenberg, The regulation and function of c-fos and other immediate early genes in the nervous system, Neuron, 4 (1990) pp. 477-485.]. Cultured hippocampal glial cells were exposed to vasopressin or a selective V1 vasopressin receptor agonist and in situ hybridization for NGFI-A mRNA was conducted. Results of these experiments demonstrated that vasopressin induced a highly significant dose-dependent increase in the number of cells expressing NGFI-A. Studies to determine the receptor subtype mediating vasopressin induction of NGFI-A were conducted utilizing the specific V1 agonist, [Phe2, Ile3, Orn8]-vasopressin. The V1 receptor agonist induced a highly significant dose dependent increase in the number of grains per NGFI-A positive cell. Time course analysis demonstrated that V1 agonist induction of NGFI-A occurred within 5 min, was maximally induced at 15 min of exposure and exhibited a gradual decline within 30 min of exposure which continued to decline over the 60 min time course. Glial cell responsivity was selective in that vasopressin and V1 agonist induction of NGFI-A occurred in a subpopulation of glial cells. Within a sea of glial cells, vasopressin and V1 agonist would induce islands of NGFI-A positive cells. Results of combined immunocytochemical labeling for the astrocyte specific marker, GFAP, and in situ hybridization for NGFI-A demonstrated that V1 agonist-induced NGFI-A expression occurred in GFAP positive cells. We observed no evidence for V1 agonist induction of NGFI-A in neurons. Collectively, these data document that vasopressin, acting via V1 vasopressin receptors, induces a highly significant increase in NGFI-A expression in select GFAP positive hippocampal astrocytes. To our knowledge, these data are the first report of a vasopressin mediated response in hippocampal glial cells. The potential functional significance of these findings is discussed.

Fos expression in rat brain during depletion-induced thirst and salt appetite

The expression of Fos protein (Fos immunoreactivity, Fos-ir) was mapped in the brain of rats subjected to an angiotensin-dependent model of thirst and salt appetite. The physiological state associated with water and sodium ingestion was produced by the concurrent subcutaneous administration of the diuretic furosemide (10 mg/kg) and a low dose of the angiotensin-converting enzyme (ACE) inhibitor captopril (5 mg/kg; Furo/Cap treatment). The animals were killed 2 h posttreatment, and the brains were processed for Fos-ir to assess neural activation. Furo/Cap treatment significantly increased Fos-ir density above baseline levels both in structures of the lamina terminalis and hypothalamus known to mediate the actions of ANG II and in hindbrain regions associated with blood volume and pressure regulation. Furo/Cap treatment also typically increased Fos-ir density in these structures above levels observed after administration of furosemide or captopril separately. Fos-ir was reduced to a greater extent in forebrain than in hindbrain areas by a dose of captopril (100 mg/kg sc) known to block the actions of ACE in the brain. The present work provides further evidence that areas of lamina terminalis subserve angiotensin-dependent thirst and salt appetite.

Ischemia-induced CA1 neuronal death is preceded by elevated FosB and Jun expression and reduced NGFI-A and JunB levels

Alterations in levels of the immediate-early gene (IEG) proteins Fos, FosB, DeltaFosB, Jun, JunB, JunD, and NGFI-A were investigated in rat hippocampus by immunohistochemistry 2, 12, 24, and 48 h after forebrain ischemia. Transient global ischemia of 20 min, produced by four vessel occlusion (4-VO), elicited different patterns of IEG expression in vulnerable CA1 and more resilient CA3 neurons. Cell counts revealed that except for JunD and NGFI-A, immunoreactivity for all examined IEGs was initially elevated by forebrain ischemia in both CA1 and CA3 hippocampal subfields. However, distinct patterns of IEG expression became evident in these regions at later time points. The pivotal difference was the persistence of ischemia-induced elevations of FosB and Jun expression in the CA1 region of the hippocampus. Unlike CA3 neurons, where IEG immunoreactivity had subsided to basal levels by 24-48 h, CA1 neurons continued to display increased FosB- and Jun-like immunoreactivity 48 h post-ischemia. Western blot analysis revealed that elevated expression of both FosB and DeltaFosB-like proteins were responsible for the immunohistochemical detection of enhanced FosB-like immunoreactivity in CA1 neurons at 48 h. These findings are consistent with recent in vitro studies that implicate FosB and Jun in gene signalling pathways responsible for programmed cell death. In contrast to FosB and Jun, JunB expression declined significantly below basal levels in CA1 neurons at 48 h, yet remained unaltered in CA3 neurons. Given that JunB can inhibit the transactivating properties of Jun, decreased JunB levels may contribute to the apoptotic death of CA1 neurons by enhancing the transcriptional regulating activity of Jun. Also notable at 48 h was the complete loss of constitutive NGFI-A expression from CA1 neurons of ischemic animals. These findings suggest that persistent elevations in FosB and Jun expression, concurrent with reductions in JunB and NGFI-A levels, contribute to the apoptotic death of CA1 neurons after forebrain ischemia.

ZENK protein regulation by song in the brain of songbirds

When songbirds hear the song of another individual of the same species or when they sing, the mRNA levels of the ZENK gene increase rapidly in forebrain areas involved in vocal communication. This gene induction is thought to be related to long-term neuronal change and possibly the formation of song-related memories. We used immunocytochemistry to study the levels and distribution of ZENK protein in the brain of zebra finches and canaries after presentation of song playbacks. Birds that heard the playbacks and did not sing in response showed increased ZENK protein levels in auditory brain areas, including the caudomedial neostriatum and hyperstriatum ventrale, fields L1 and L3, the shelf adjacent to the high vocal center (HVC), the cup adjacent to the nucleus robustus archistriatalis (RA), and the nucleus mesencephalicus lateralis pars dorsalis (MLd). No ZENK expression was seen in song nuclei in these birds. Males that sang in response to the playbacks showed, in addition to auditory areas, increased ZENK protein in several song control nuclei, most prominently in HVC, RA, area X, and the dorsomedial nucleus (DN) of the intercollicular complex. The rise in ZENK protein followed that described previously for ZENK mRNA by a short lag, and the distribution of ZENK-labeled cells was in agreement with previous analysis of mRNA distribution. Thus, ZENK protein regulation can be used to assess activation of brain areas involved in perceptual and motor aspects of song. Possible implications of ZENK induction in these areas are discussed.

Acute administration of cocaine, but not amphetamine, increases the level of synaptotagmin IV mRNA in the dorsal striatum of rat

Synaptotagmin IV (Syt IV) is an inducible member of a multi-gene family of synaptic vesicle proteins that participate in Ca2+-dependent and Ca2+-independent interactions during membrane trafficking. We have examined the pattern of expression of Syt IV mRNA following the administration of cocaine and amphetamine. A single acute dose of cocaine, but not amphetamine, resulted in a transient increase, as determined by in situ hybridization, in the steady-state level of Syt IV mRNA in the dorsal striatum of rats 1 h after the administration of the drug. No change in the hybridization pattern of the Syt IV-specific probe to other regions of the rat brain were observed following cocaine or amphetamine administration at the time points examined (1, 3, 6, 12 and 24 h). The pattern of synaptotagmin I-(Syt I) specific hybridization remained constant, relative to controls, for both the cocaine- and amphetamine-treated animals. Northern hybridization analysis of mRNA isolated from striatal tissue using oligonucleotide probes specific to Syt I and Syt IV demonstrated that the probes hybridized exclusively to transcripts of the sizes previously reported for these two synaptotagmins and confirmed that the relative level of Syt IV to Syt I mRNA increased following the administration of cocaine but not amphetamine. These results indicate that these drugs have different effects on altering the levels of Syt IV mRNA. This work, in conjunction with earlier work that demonstrated that cocaine and amphetamine have different effects on the expression of immediate early genes such as c-Fos, supports the hypothesis that these psychotropic agents evoke different patterns of gene expression which may lead to alteration in synaptic efficacy.

Molecular biology of glutamate receptors in the central nervous system and their role in excitotoxicity, oxidative stress and aging

Forty years of research into the function of L-glutamic acid as a neurotransmitter in the vertebrate central nervous system (CNS) have uncovered a tremendous complexity in the actions of this excitatory neurotransmitter and an equally great complexity in the molecular structures of the receptors activated by L-glutamate. L-Glutamate is the most widespread excitatory transmitter system in the vertebrate CNS and in addition to its actions as a synaptic transmitter it produces long-lasting changes in neuronal excitability, synaptic structure and function, neuronal migration during development, and neuronal viability. These effects are produced through the activation of two general classes of receptors, those that form ion channels or "ionotropic" and those that are linked to G-proteins or "metabotropic". The pharmacological and physiological characterization of these various forms over the past two decades has led to the definition of three forms of ionotropic receptors, the kainate (KA), AMPA, and NMDA receptors, and three groups of metabotropic receptors. Twenty-seven genes are now identified for specific subunits of these receptors and another five proteins are likely to function as receptor subunits or receptor associated proteins. The regulation of expression of these protein subunits, their localization in neuronal and glial membranes, and their role in determining the physiological properties of glutamate receptors is a fertile field of current investigations into the cell and molecular biology of these receptors. Both ionotropic and metabotropic receptors are linked to multiple intracellular messengers, such as Ca2+, cyclic AMP, reactive oxygen species, and initiate multiple signaling cascades that determine neuronal growth, differentiation and survival. These cascades of complex molecular events are presented in this review.

Long-term effects of axotomy on excitability and growth of isolated Aplysia sensory neurons in cell culture: potential role of cAMP

Crushing nerves, which contain the axons of central sensory neurons, in Aplysia causes the neurons to become hyperexcitable and to sprout new processes. Previous experiments that examined the effects of axonal injury on Aplysia sensory neurons have been performed in the intact animal or in the semi-intact CNS of Aplysia. It therefore has been unclear to what extent the long-term neuronal consequences of injury are due to intrinsic or extrinsic cellular signals. To determine whether injury-induced changes in Aplysia sensory neurons are due to intrinsic or extrinsic signals, we have developed an in vitro model of axonal injury. Isolated central sensory neurons grown for 2 days in cell culture were axotomized. Approximately 24 h after axotomy, sensory neurons exhibited a greater excitability-reflected, in part, as a significant reduction in spike accommodation-and greater neuritic outgrowth than did control (unaxotomized) neurons. Rp diastereoisomer of the cyclic adenosine 3',5'-monophosphorothiate (Rp-cAMPS), an inhibitor of protein kinase A, blocked both the reduction in accommodation and increased neuritic outgrowth induced by axotomy. Rp-cAMPS also blocked similar, albeit smaller, alterations observed in control sensory neurons during the 24-h period of our experiments. These results indicate that axonal injury elevates cAMP levels within Aplysia sensory neurons, and that this elevation is directly responsible, in part, for the previously described long-term electrophysiological and morphological changes induced in Aplysia sensory neurons by nerve crush. In addition, the results indicate that control sensory neurons in culture are also undergoing injury-related electrophysiological and structural changes, probably due to cellular processes triggered when the neurons are axotomized during cell culturing. Finally, the results provide support for the idea that the cellular processes activated within Aplysia sensory neurons by injury, and those activated during long-term behavioral sensitization, overlap significantly.

Kindling and associated mossy fibre sprouting are not affected in mice deficient of NGFI-A/NGFI-B genes

Kindling is an animal model of epileptogenesis, whereby repeated administration of an initially subconvulsive electrical stimulation eventually leads to the development of generalized motor seizures. Once established, the kindling effect is permanent. Although the molecular basis of kindling remains incompletely understood, emerging lines of evidence suggest that the induction of immediate-early genes could represent a link between periodic short-term stimuli and the long-lasting functional and structural alterations in the brain associated with the development of seizures. A recent study showed that null mutation of the immediate-early gene c-fos impairs the structural and functional plasticities in kindling. In the present study, we examined whether two other seizure-inducible immediate-early genes--NGFI-A (also termed EGR-1, zifl268, and Krox-24) and NGFI-B (also termed Nur77)--play requisite roles in kindling. We found that neither the rate of kindling nor seizure-induced granule cell axonal sprouting was affected in mice carrying a null mutation of NGFI-A. Furthermore, double knock-out of NGFI-A and NGFI-B genes does not result in detectable changes in kindling development and associated mossy fibre sprouting. Taken together, our observations indicate that neither constitutive nor seizure-induced expression of NGFI-A or NGFI-B is uniquely required for the establishment of kindling. These findings underscore the specificity of the immediate-early genes whose transcriptional activation contributes to kindling epileptogenesis.

A molecular biological approach to synaptic plasticity and learning

Until the more recent advances made in molecular biology, attempts to link synaptic plasticity and learning have focused on using LTP as a marker of learning-induced synaptic plasticity, where one has expected to observe the same magnitude of change in synaptic strength as that observed with artificial stimulation. To a large extent this approach has been frustrated by the fact that it is generally assumed that the representation of the memory traces is distributed throughout widespread networks of cells. By implication it is more likely that one would observe small distributed changes within a network; a formidable task to measure. In this review we describe how the advances in molecular biology give us both the tools to investigate the mechanisms of synaptic plasticity and to apply these to investigations of the underlying mechanisms in learning and the formation of memories that have until now remained out of our grasp.

Central renin injections: effects on drinking and expression of immediate early genes

This study investigated the drinking response and the expression of Fos- and Egr-1-immunoreactivity (Fos-ir; Egr-1-ir) in the brain induced by endogenous angiotensin generated by intracerebroventricular (i.c.v.) injection of renin. Renin induced Fos-ir in the subfornical organ (SFO), median preoptic (MnPO), supraoptic and paraventricular nuclei (SON and PVN), area postrema (AP), nuclei of the solitary tract (NTS) and lateral parabrachial nuclei (LPBN). Renin-induced Egr-1-ir exhibited a similar pattern of distribution as that observed for Fos-ir. The dose of i.c.v. renin that induced expression of immediate early gene (IEG) product immunoreactivity also produced vigorous drinking. When renin-injected rats were pretreated with captopril, an angiotensin converting enzyme inhibitor, drinking was blocked. With the same captopril pretreatment, both Fos- and Egr-1-ir in the SFO, MnPO, SON, PVN, AP and LPBN were also significantly reduced.

Identification of c-fos related genes and their induction by neural activation in rainbow trout brain

A number of studies have shown that the induction of c-fos gene is an indicator of the responses of cells and tissues to the environmental stimuli. In the present study, using RT-PCR-based strategy, we isolated, from the brain of the rainbow trout, two partial cDNA clones (RT-fos1 and RT-fos2) that code proteins homologous to c-Fos proteins of higher vertebrates. Sequence analysis of the two clones indicated that the two rainbow trout clones are very similar to each other over the entire cloned region (88% amino acid identity) and showed moderate similarity to c-Fos proteins of higher vertebrates (40% amino acid identity with human c-Fos). Two functionally important domains (i.e. the leucine zipper and zinc finger) are highly conserved among all the vertebrate species analyzed, although the region between the two domains was highly variable between different species. Intraperitoneal administration of kainic acid, a stable agonist of glutamate receptors, transiently induced the mRNAs for both RT-fos1 and RT-fos2 in the rainbow trout brain. These results indicate that the expression pattern of the two clones can be utilized as a suitable anatomical marker for the increased neural activities in salmonid fish brain to investigate the higher order behavior such as the learning and imprinting of odors of the home river.

Organization and transmitter specificity of medullary neurons activated by sustained hypertension: implications for understanding baroreceptor reflex circuitry

In situ expression of c-fos observed in response to phenylephrine (PE)-induced hypertension provided a basis for characterizing the organization and neurotransmitter specificity of neurons at nodal points of medullary baroreflex circuitry. Sustained hypertension induced by a moderate dose of PE provoked patterns of c-fos mRNA and protein expression that conformed in the nucleus of the solitary tract (NTS) to the termination patterns of primary baroreceptor afferents and in the caudal ventrolateral medulla (CVLM) to a physiologically defined depressor region. A majority of barosensitive CVLM neurons concurrently displayed markers for the GABAergic phenotype; few were glycinergic. Phenylephrine-sensitive GABAergic neurons that were retrogradely labeled after tracer deposits in pressor sites of the rostral ventrolateral medulla (RVLM) occupied a zone extending approximately 1.4 mm rostrally from the level of the calamus scriptorius, intermingled partly with catecholaminergic neurons of the A1 and C1 cell groups. By contrast, barosensitive neurons of the NTS were found to be phenotypically complex, with very few projecting directly to the RVLM. Extensive colocalization of PE-induced Fos-IR and markers for the nitric oxide phenotype were seen in a circumscribed, rostral, portion of the baroreceptor afferent zone of the NTS, whereas only a small proportion of PE-sensitive neurons in the NTS were found to be GABAergic. PE treatment parameters have been identified that provide a basis for defining and characterizing populations of neurons at the first station in the central processing of primary baroreceptor input and at a key inhibitory relay in the CVLM.

Zif268 and Fos-like immunoreactivity in tetanus toxin-induced epilepsy: reciprocal changes in the epileptic focus and the surround

Altered gene expression for a number of molecules has been suggested as one of the underlying mechanisms of epileptogenesis. Changes in expression of the immediate early genes, zif268 and c-fos, were investigated in chronic focal epilepsy induced by tetanus toxin (TT, 20-35 ng) injected in the rat motor cortex. Most rats injected with TT and perfused on postoperative day 5, 7 or 14 had recurrent focal seizures after a latent period of 4-13 days, and showed enhanced Zif268 immunoreactivity in a cluster of neurons at the injection site, as well as reduced Zif268 immunoreactivity in a distinct cortical zone around this cluster. C-fos or Fos-related immunoreactivity was decreased over widespread areas of frontoparietal and piriform cortex in epileptic rats, except for a focus at the injection site which, in most cases, showed increases in Fos-like immunoreactivity. Some epileptic rats showed increased Zif268 immunoreactivity in neurons of the ipsilateral ventral lateral and central lateral thalamic nuclei and increased Zif268 and Fos-like immunoreactivity in the pontine nuclei. Rats perfused before onset of seizures, showed no overt changes other than a slight decrease in Zif268 and Fos-like immunoreactivity at the injection site. The reciprocal changes in Zif268 immunoreactive neurons in the epileptic focus and the immediate surround parallel changes in gene expression for a number of molecules important in epileptogenesis and suggest a state of functional disconnection of the epileptic focus from other cortical areas that may contribute to the development and maintenance of focal epilepsy.

Temporal variability of jun family transcription factor levels in peripherally or centrally transected adult rat dorsal root ganglia

Enhanced chemiluminescent (ECL) immunoblotting was used to quantitatively assess the initial changes in jun family transcription factor protein levels in adult rat lumbar dorsal root ganglia (DRG) after peripheral axotomy and dorsal root transection, and to study the effects of neurotrophic factor administration on these changes. Transection of central (dorsal root) or peripheral (spinal nerve) branches of DRG neurons resulted in rapid elevation of c-jun protein levels, which was transient after dorsal root transection but sustained, though slightly attenuated, after spinal nerve transection. These results suggest that injury-induced c-jun elevation is biphasic, consisting of an early, transient, injury-initiated phase and a more prolonged secondary phase specific to peripheral target disconnection. c-jun protein changes were not modulated by administration of NGF or BDNF. Immunohistochemistry was used to localize c-jun protein induction to DRG neurons. Using ECL immunoblotting, we also observed temporally regulated increases in junD protein levels after both injuries. A transient up-regulation of junB was detected by immunoblotting 5 days after peripheral axotomy, coincident with a slight decrease in c-jun protein levels.

Peripheral noxious stimulation induces CREM expression in dorsal horn: involvement of glutamate

Peripheral noxious stimulation is known to trigger signalling cascades in neurons of the spinal cord. The response to pain and stress at the level of gene expression involves transcriptional activation of several cyclic AMP responsive genes. Here, we show induction of the CREM (cyclic-AMP responsive element modulator) gene in distinct subpopulations of spinal cord neurons upon thermal noxious stimulation. The addition of forskolin or glutamate to cultured spinal cord neurons results in the induction of the CREM isoform, ICER (Inducible cyclic-AMP Early Repressor), a powerful repressor of cAMP-induced transcription. Overexpression of ICER in cultured spinal cord neurons results in the repression of the c-fos and c-jun promoters induced by forskolin and glutamate. On this basis, we postulate that early activation of ICER in spinal cord participates in the attenuation of early gene induction following noxious stimulation.

Effect of global system for mobile communication microwave exposure on the genomic response of the rat brain

The acute effect of global system for mobile communication (GSM) microwave exposure on the genomic response of the central nervous system was studied in rats by measuring changes in the messenger RNAs of hsp70, the transcription factor genes c-fos and c-jun and the glial structural gene GFAP using in situ hybridization histochemistry. Protein products of transcription factors, stress proteins and marker proteins of astroglial and microglial activation were assessed by immunocytochemistry. Cell proliferation was evaluated by bromodeoxyuridine incorporation. A special GSM radiofrequency test set, connected to a commercial cellular phone operating in the discontinuous transmission mode, was used to simulate GSM exposure. The study was conducted at time averaged and brain averaged specific absorption rates of 0.3 W/kg (GSM exposure), 1.5 W/kg (GSM exposure) and 7.5 W/kg (continuous wave exposure), respectively. Immediately after exposure, in situ hybridization revealed slight induction of hsp70 messenger RNA in the cerebellum and hippocampus after 7.5 W/kg exposure, but not at lower intensities. A slightly increased expression of c-fos messenger RNA was observed in the cerebellum, neocortex and piriform cortex of all groups subjected to immobilization, but no differences were found amongst different exposure conditions. C-jun and GFAP messenger RNAs did not increase in any of the experimental groups. 24 h after exposure, immunocytochemical analysis of FOS and JUN proteins (c-FOS, FOS B, c-JUN JUN B, JUN D), of HSP70 or of KROX-20 and -24 did not reveal any alterations. Seven days after exposure, neither increased cell proliferation nor altered expression of astroglial and microglial marker proteins were observed. In conclusion, acute high intensity microwave exposure of immobilized rats may induce some minor stress response but does not result in lasting adaptive or reactive changes of the brain.

Layer-specific differential regulation of transcription factors Zif268 and Jun-D in visual cortex V1 and V2 of macaque monkeys

To investigate intracellular mechanisms of cortical layer-specific gene regulation, we quantitatively examined the expression of two transcription factors, Zif268 and JunD, and compared their expression levels in each layer of the primary visual cortex (VI) and visual area 2 (V2) of macaque monkeys (Macaca fuscata). The brain sections were immunohistochemically stained for determination of the percentage of Zif268- or JunD-expressing neurons in the total neuronal population. We found area- and layer-specific expression of these transcription factors; Zif268 tended to be expressed at high levels in layers on the parvocellular pathway in V1, whereas JunD did not show such an expression pattern. In V1, many Zif268-immunopositive neurons were observed in layers II/III, IVC beta and VI. The percentage of Zif268-immunopositive neurons was highest in layer IVC beta and lowest in layer IVC alpha. JunD-immunopositive neurons were fewest in layer IVC beta and most abundant in layer VI. In V2, the level of expression of Zif268 was almost the same as that of JunD in layer II/II. However, layer IV of V2 tended to contain more Zif268-immunopositive neurons than JunD-immunopositive neurons, whereas layer VI contained more JunD-immunopositive neurons than Zif268-immunopositive neurons. Although it has been reported that the same extracellular signals induce both Zif268 and JunD, the present results indicate that the expression of these transcription factors is differentially controlled in each layer of the primate visual cortical areas. Furthermore, the present results suggest that these transcription factors contribute to area- and layer-specific gene regulation by mediating transmission of extracellular signals to the nucleus via different intracellular signalling pathways.

Increased expression of NGFI-A mRNA in the rat striatum following burst stimulation of the medial forebrain bundle

Using in situ hybridization, we examined the mRNA expression for several immediate early genes in dopamine-innervated brain areas following electrical burst vs. regular stimulation of the medial forebrain bundle in anaesthetized rats. Two hours after 5 Hz burst stimulation, the expression of the nerve growth factor-inducible clone A (NGFI-A) mRNA was increased in the medial part of the striatum. This increase was prevented by pretreatment with the dopamine-D1 receptor antagonist, SCH23390 (0.1 mg/kg i.p.). After 8 Hz burst stimulation, NGFI-A mRNA expression was increased in the medial, central and lateral parts of the striatum. Induction occurred predominantly in cells expressing mRNAs for the dopamine-D1 receptor, substance P and dopamine and cAMP-regulated phosphoprotein (DARP-32). Regular stimulation had no effect on NGFI-A mRNA expression. The induction of NGFI-A was related to the levels of dopamine released by burst or regular stimulation as demonstrated with in vivo amperometry. Two hours after stimulation, the expression of none of the other genes studied was altered. One hour after 8 Hz burst stimulation, the expression of NGFI-A, NGFI-B and jun-B mRNAs was increased in the striatum and that of NGFI-A, NGFI-B, c-fos, fos-B and jun-B mRNAs was variably increased in the nucleus accumbens and lateral septum. These results provide additional support for the physiological importance of burst firing activity in midbrain dopamine neurons for the activation of their target cells. They demonstrate a spatial and temporal specificity as regards the brain region, the gene activated, the receptor involved and the phenotype of the cells affected.

Comparison of the expression of c-fos, nur77 and egr1 mRNAs in rat hypothalamic magnocellular neurons and their putative afferent projection neurons: cell- and stimulus-specific induction

Hypothalamic magnocellular neurons and their afferent inputs provide a model system in which to study the regulation of inducible transcription factors in the brain in vivo. Osmotic stimulation of rats produced by graded infusions of saline at different tonicities was found to lead to the induction of c-fos, nur77 and egr1 mRNAs in magnocellular neurons, as well as in putative afferent neurons, including those in structures of the forebrain (subfornical organ, median preoptic nucleus and organum vasculosum of the lamina terminalis). The results presented suggest that stronger levels of osmotic stimulation recruit additional afferents from the forebrain and brainstem that can act on magnocellular neurons via alternative receptors. A single systemic injection of the peptide cholecystokinin produced robust induction of c-fos and nur77 mRNAs in afferent neurons of the brainstem nucleus tractus solitarii and in magnocellular neurons. Despite the fact that these two neuronal populations are clearly electrically active, egr1 was not induced by this stimulus, providing examples of cell- and stimulus-specificity of its expression. This study re-emphasizes that the induction of transcription factors is largely dependent on the nature of the afferent input and does not correlate necessarily to the electrical activity of the neuron.

Expression of activating transcription factor-2, serum response factor and cAMP/Ca response element binding protein in the adult rat brain following generalized seizures, nerve fibre lesion and ultraviolet irradiation

The expression of the constitutive transcription factors activating transcription factor-2 (ATF-2), serum response factor (SRF) and cAMP/Ca response element binding factor (CREB), and the phosphorylation of SRF and CREB were studied in the untreated adult rat nervous system and following seizure activities and neurodegenerative stimuli. In the untreated rat, intense nuclear SRF immunoreactivity was present in the vast majority of neurons in the forebrain, cortex, striatum, amygdala and hippocampus, and in some scattered neurons in the medulla and spinal cord. In contrast, SRF immunoreactivity was absent in the midline areas of the forebrain, e.g., the globus pallidum and septum, and in the hypothalamus, thalamus, mesencephalon and motoneurons. Nuclear ATF-2 was expressed at high levels in apparently all neurons, but not glial cells, throughout the neuraxis except for those neuronal populations which exhibit a high basal level of c-Jun, i.e. dentate gyrus and the motoneurons of cranial and somatosensory neurons. CREB immunoreactivity was present at a rather uniform intensity in all neuronal and glial cells throughout the neuraxis. Two hours, but not 5 h or 24 h, following systemic application of kainic acid, an increase in SRF was detectable by western blot analysis in hippocampal and cortical homogenates whereas the expression of ATF-2 and CREB did not change. Phosphorylation of CREB at serine 133 and of SRF at serine 103 were studied with specific antisera. In untreated rats, intense phosphoCREB and phosphoSRF immunoreactivities labelled many glial cells and/or neurons with the highest levels in the dentate gyrus, the entorhinal cortex and the retrosplenial cortex. Following kainate-induced seizures, phosphoSRF-IR but not phosphoCREB-IR transiently increased between 0.5 h and 2 h. Following transection of peripheral or central nerve fibres such as optic nerve, medial forebrain bundle, vagal and facial nerve fibres, ATF-2 rapidly decreased in the axotomized neurons during that period when c-Jun was rapidly expressed. SRF remained unchanged and CREB disappeared in some axotomized subpopulations. Similar to axotomy, c-Jun increased and ATF-2 decreased in cultured adult dorsal root ganglion neurons following ultraviolet irradiation. The distribution of SRF and ATF-2 suggests that their putative target genes c-fos, junB, krox-24 and c-jun can be independently regulated from SRF and ATF-2. The suppression of ATF-2 and the expression of c-Jun following axotomy and ultraviolet irradiation might be part of a novel neuronal stress response in the brain that strongly resembles the stress response characterized in non-neuronal cells.

Basal expression, subcellular distribution, and up-regulation of the proto-oncogene c-JUN in the rat dentate gyrus after unilateral entorhinal cortex lesion

The expression of the transcription factor c-JUN was investigated in the rat fascia dentata under normal conditions and after entorhinal cortex lesion. As shown by immunocytochemistry and in situ hybridization histochemistry c-JUN and its messenger RNA are present in the principal cell layers of the dentate gyrus and Ammon's horn (except hippocampal region CA2). Pre-embedding immunogold electron microscopy revealed an almost exclusive nuclear localization of c-JUN, where it is associated with chromatin. In addition, double immunolabelling for c-JUN and parvalbumin demonstrated that c-JUN immunoreactivity is primarily found in principal neurons since GABAergic parvalbumin-positive interneurons did not express c-JUN. After unilateral electrolytic lesion of the entorhinal cortex c-JUN was strongly up-regulated in the ipsilateral dentate gyrus within 2 h postlesion. This up-regulation was also present in the contralateral fascia dentata 12 h after entorhinal cortex lesion and returned to control levels on both sides 24 h postlesion. The cellular distribution of c-JUN did not change after entorhinal cortex lesion: parvalbumin-positive interneurons never contained c-JUN. These results point to a specific role of c-JUN in the granule cells of the fascia dentata in the normal animal and in rats with entorhinal cortex lesions. The selective induction of c-JUN after entorhinal lesion could be one of the first molecular steps that regulate transneuronal changes within granule cells after their denervation. A different mechanism has to be assumed for GABAergic interneurons known to receive an entorhinal innervation as well.

Long-term potentiation activates the GAP-43 promoter: selective participation of hippocampal mossy cells

Perforant path long-term potentiation (LTP) in intact mouse hippocampal dentate gyrus increased the neuron-specific, growth-associated protein GAP-43 mRNA in hilar cells 3 days after tetanus, but surprisingly not in granule cells, the perforant path target. This increase was positively correlated with level of enhancement and restricted to central hilar cells on the side of stimulation. Blockade of LTP by puffing DL-aminophosphonovalerate (APV), an N-methyl-D-aspartate (NMDA) receptor blocker into the molecular layer, eliminated LTP-induced GAP-43 mRNA elevation in hilar cells. To determine whether the mRNA elevation was mediated by transcription, LTP was studied in transgenic mice bearing a GAP-43 promoter-lacZ reporter gene. Promoter activity as indexed by Transgene expression (PATE) increased as indicated by blue staining of the lacZ gene product, beta-galactosidase. Potentiation induced a blue band bilaterally in the inner molecular layer of the dentate gyrus along the entire septotemporal axis. Because mossy cells are the only neurons in the central hilar zone that project to the inner molecular layer bilaterally along the entire septotemporal axis and LTP-induced activation of PATE in this zone was confined to the side of stimulation, we concluded that mossy cells were unilaterally activated, increasing synthesis of beta-galactosidase, which was transported bilaterally. Neither granule cells nor pyramidal cells demonstrated increased PATE or increased GAP-43 mRNA levels. These results and recent evidence indicating the necessity of hilar neurons for LTP point to previously unheralded mossy cells as potentially critical for perforant path LTP and the GAP-43 in these cells as important for LTP persistence lasting days.

Region-specific immediate-early gene expression following the administration of corticotropin-releasing hormone in virgin and lactating rats

Central administration of corticotropin-releasing hormone (CRH) induces immediate-early gene (IEG) expression (c-fos and NGFI-B) in forebrain structures in a pattern similar to that observed following restraint stress. Lactating rats display modified neuroendocrine and behavioural responses to stress which have been hypothesized to be at least partially mediated through changes within the circuitry converging on the PVN, including CRH activated pathways. Quantitative measures of regional expression of c-fos and NGFI-B mRNA representative of two classical intracellular pathways, were used to define modification of the circuitry involved in the altered response to central CRH in the lactating female. Compared to saline controls, virgin female rats injected with 5 micrograms CRH i.c.v. displayed significantly increased immediate-early gene expression in the hypothalamic paraventricular nucleus (PVN), arcuate nucleus, lateral septum, bed nucleus of the stria terminalis, central, medial and cortical nuclei of the amygdala, and all subfields of the hippocampal formation. In lactating rats treated with CRH there was a significant increase in c-fos gene expression in the CeA and in the hippocampal subfields CA1, CA4 and dentate gyrus but not in the other areas examined. The i.c.v. administration of CRH significantly increased NGFI-B expression in the PVN, arcuate nucleus, medial amygdala and all hippocampal subfields of virgin rats. Lactating rats treated with CRH failed to show a significant increase in NGFI-B expression in the PVN, median eminence, arcuate nucleus, medial amygdala, CA2 and CA3 subfields of the hippocampus. These results further suggest that changes in specific neural circuits might at least partially underlie the modified responses to CRH and perhaps to stress in the lactating female.

Egr transcription factors in the nervous system

The Egr proteins, Egr-1, Egr-2, Egr-3 and Egr-4, are closely related members of a subclass of immediate early gene-encoded, inducible transcription factors. They share a highly homologous DNA-binding domain which recognises an identical DNA response element. In addition, they have several less-well conserved structural features in common. As immediate early proteins, the Egr transcription factors are rapidly induced by diverse extracellular stimuli within the nervous system in a discretely controlled manner. The basal expression of the Egr proteins in the developing and adult rat brain and the induction of Egr proteins by neurotransmitter analogue stimulation, physiological mimetic and brain injury paradigms is reviewed. We review evidence indicating that Egr proteins are subject to tight differential control through diverse mechanisms at several levels of regulation. These include transcriptional, translational and post-translational (including glycosylation, phosphorylation and redox) mechanisms and protein-protein interaction. Ultimately the differentially co-ordinated Egr response may lead to discrete effects on target gene expression. Some of the known target genes of Egr proteins and functions of the Egr proteins in different cell types are also highlighted. Future directions for research into the control and function of the different Egr proteins are also explored.

Chronic glucocorticoid administration as well as repeated stress affects the subsequent acute immobilization stress-induced expression of immediate early genes but not that of NGFI-A

We reported that repeated immobilization for six days attenuates the subsequent acute immobilization stress-induced expression of the immediate early genes c-fos, fos B, jun B and nerve growth factor-induced gene-B (NGFI-B), but not of NGFI-A, in the rat paraventricular hypothalamic nucleus. In this study, we confirmed these findings by means of a time-course study, and further investigated whether the elevated plasma basal glucocorticoid level induced by repeated stress underlies the attenuated response of immediate early genes and the preserved reactivity of NGFI-A. Rats implanted with 100, 200 or 400 mg corticosterone or placebo pellets (control), were immobilized for 1 h and decapitated seven days later. In control rats acute immobilization induced c-fos, fos B, jun B, NGFI-A and NGFI-B messenger RNA in the paraventricular hypothalamic nucleus, whereas all of them except NGFI-A, were significantly reduced in rats given 200 and 400 mg corticosterone implants. The similarity of the results from the two procedures suggests that glucocorticoid is involved in regulating immediate early genes in the paraventricular hypothalamic nucleus under repeated stress and that the NGFI-A gene is not regulated by this mechanism. However, the plasma basal corticosterone level in repeatedly stressed rats was lower than that of rats implanted with 100 mg corticosterone, suggesting that a repetitive stress-induced corticosterone surge also contributes to this mechanism.

Differential expression of alpha-bungarotoxin-sensitive neuronal nicotinic receptors in adrenergic chromaffin cells: a role for transcription factor Egr-1

Adrenomedullary chromaffin cells express at least two subtypes of acetylcholine nicotinic receptors, which differ in their sensitivity to the snake toxin alpha-bungarotoxin. One subtype is involved in the activation step of the catecholamine secretion process and is not blocked by the toxin. The other is alpha-bungarotoxin-sensitive, and its functional role has not yet been defined. The alpha7 subunit is a component of this subtype. Autoradiography of bovine adrenal gland slices with alpha-bungarotoxin indicates that these receptors are restricted to medullary areas adjacent to the adrenal cortex and colocalize with the enzyme phenylethanolamine N-methyl transferase (PNMT), which confers the adrenergic phenotype to chromaffin cells. Transcripts corresponding to the alpha7 subunit also are localized exclusively to adrenergic cells. To identify possible transcriptional regulatory elements of the alpha7 subunit gene involved in the restricted expression of nicotinic receptors, we isolated and characterized its 5' flanking region, revealing putative binding sites for the immediate early gene transcription factor Egr-1, which is known to activate PNMT expression. In reporter gene transfection experiments, Egr-1 increased alpha7 promoter activity by up to sevenfold. Activation was abolished when the most promoter-proximal of the Egr-1 sites was mutated, whereas modification of a close upstream site produced a partial decrease of the Egr-1 response. Because Egr-1 was found to be expressed exclusively in adrenergic cells, we suggest that this transcription factor may be part of a common mechanism involved in the induction of the adrenergic phenotype and the differential expression of alpha-bungarotoxin-sensitive nicotinic receptors in the adrenal gland.

Putative roles for the inducible transcription factor c-fos in the central nervous system: studies with antisense oligonucleotides

Although immediate-early genes such as c-fos are widely believed to play an important role in neuroplasticity, there is limited evidence to support involvement in the initiation of molecular events leading to medium- and long-term changes in brain function following a stimulus. Results using techniques such as transgenic knockout of the gene are often difficult to interpret. Antisense oligonucleotide technology offers an alternative. Infusion of antisense oligonucleotide to modify the expression of c-fos in the brain results in dramatic changes in rotation behaviour in animals challenged with psychostimulant drugs such as amphetamine. Similarly, the knockdown of c-fos expression using antisense oligonucleotides can also alter the rate of amygdala kindling in response to electrical stimulation of the brain. While studies using antisense oligonucleotides to knockdown c-fos expression provide evidence that the expression of c-fos plays an important role in regulating neuronal function, the use of antisense nucleotides has limitations and experiments must be very carefully controlled. Many details of antisense oligonucleotide actions remain unknown.

Calcium controls gene expression via three distinct pathways that can function independently of the Ras/mitogen-activated protein kinases (ERKs) signaling cascade

Calcium ions are the principal second messenger in the control of gene expression by electrical activation of neurons. However, the full complexity of calcium-signaling pathways leading to transcriptional activation and the cellular machinery involved are not known. Using the c-fos gene as a model system, we show here that the activity of its complex promoter is controlled by three independently operating signaling mechanisms and that their functional significance is cell type-dependent. The serum response element (SRE), which is composed of a ternary complex factor (TCF) and a serum response factor (SRF) binding site, integrates two calcium-signaling pathways. In PC12 cells, calcium-regulated transcription mediated by the SRE requires the TCF site and is not inhibited by expression of the dominant-negative Ras mutant, RasN17, nor by the MAP kinase kinase 1 inhibitor PD 98059. In contrast, TCF-dependent transcriptional regulation by nerve growth factor or epidermal growth factor is mediated by a Ras/MAP kinases (ERKs) pathway targeting the TCF Elk-1. In AtT20 cells and hippocampal neurons, calcium signals can stimulate transcription via a TCF-independent mechanism that requires the SRF binding site. The cyclic AMP response element (CRE), which cooperates with the TCF site in growth factor-regulated transcription, is a target of a third calcium-regulated pathway that is little affected by the expression of RasN17 or by PD 98059. Thus, calcium can stimulate gene expression via a TCF-, SRF-, and CRE-linked pathway that can operate independently of the Ras/MAP kinases (ERKs) signaling cascade in a cell type-dependent manner.