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

Long-term induction of c-jun mRNA and Jun protein in rabbit retinal ganglion cells following axotomy or colchicine treatment

The expression of the c-jun, c-fos, and NGFI-A genes was studied in the rabbit retina after optic nerve crush (ONC) or an intravitreal injection of colchicine. By Northern blotting, the basal expression of c-fos and NGFI-A mRNAs were undetectable, whereas c-jun mRNA showed a low basal expression in sham-operated control retinas. Very few or no Jun- or Fos-immunoreactive nuclei were seen in control retinas. From 1 to 95 days after ONC a marked induction of JUN- but not FOS-immunoreactive neurons was seen in the ganglion cell layer peaking at 3 and 7 days. Jun-positive neurons also accumulated immunoreactive phosphorylated neurofilaments, indicating that they were ganglion cells. Northern blots demonstrated that retinal levels of c-jun mRNA, but not of c-fos or NGFI-A mRNAs, were increased 3 and 7 days after ONC. An intravitreal injection of colchicine also induced Jun-immunoreactivity within 24 hr in most of the neurons in the ganglion cell layer, but not in the inner nuclear and outer nuclear layers. The results indicate that axonal damage induces a specific pattern of IEG expression including a long-term induction of the c-jun gene in CNS neurons.

Temporal and spatial preferences of c-fos mRNA expression in the rat brain following cortical lesion

The expression of the proto-oncogene c-fos is increased in neuronal cells by a number of stimuli and the usefulness of this gene as a marker of neuronal activity has been demonstrated. The temporal and spatial expression of c-fos mRNA following the induction of a unilateral cortical lesion have been investigated in the rat brain by Northern blot analysis and in situ hybridization histochemistry. It was observed that the lesion evoked a rapid increase (20-fold) in the content of c-fos mRNA in the ipsilateral cortex, whereas in the contralateral cortex c-fos mRNA expression was more modest (7-fold). In the whole hippocampus a large and very rapid increase (17-fold) of c-fos mRNA expression was detected. The effect of a cortical lesion on Ca2+ uptake and membrane potential was also investigated. Using synaptosomes as a model system, we have provided evidence that Ca2+ entry via membrane depolarization increases in coordination with c-fos gene expression in neuronal cells. The principal conclusions from this study are that cortical lesions induce transient expression of the c-fos gene in specific neuronal cells of the rat brain.

A synaptic model of memory: long-term potentiation in the hippocampus

Long-term potentiation of synaptic transmission in the hippocampus is the primary experimental model for investigating the synaptic basis of learning and memory in vertebrates. The best understood form of long-term potentiation is induced by the activation of the N-methyl-D-aspartate receptor complex. This subtype of glutamate receptor endows long-term potentiation with Hebbian characteristics, and allows electrical events at the postsynaptic membrane to be transduced into chemical signals which, in turn, are thought to activate both pre- and postsynaptic mechanisms to generate a persistent increase in synaptic strength.

Biochemical correlates of long-term potentiation in hippocampal synapses

Figure 2 summarizes biochemical events which are currently known or hypothesized to participate in LTP induction/maintenance. Current evidence strongly suggests that postsynaptic Ca2+, both entered from the outside of cells and released from intracellular stores, is the initial key substance for the induction of LTP. A rise of [Ca2+]i triggers a variety of enzymatic reactions and initiates the enhancement of synaptic transmission. This first step may be achieved by direct/indirect phosphorylations of protein molecules in postsynaptic receptors/ion channels. This would result in an increase in receptor sensitivity. An immediate increase in the number of available postsynaptic receptors by modifications of spine morphology is another candidate. Such modifications may be accomplished by cytoskeleton rearrangements or changes in extracellular environments. A change in spine structure may also cause an increase in spine neck conductance. Although it is unknown to what extent the increase in [Ca2+]i affects cellular chemistry, Ca2+ probably also directly/indirectly stimulates cascades which exert effects more slowly. A delayed increase in metabotropic receptor sensitivity may occur. New synthesis of protein molecules may be involved in late periods of LTP by replacing turnovered molecules and/or by supplying new materials. Some of these chains of biochemical events may also apply to presynaptic terminals, although the existence of retrograde messenger substances must still be confirmed. In addition, interactions between different protein kinases and second messengers appear to occur to bring about final effects.

Induction of c-FOS immunoreactivity in the hippocampus following potassium stimulation

In microdialysis procedures high potassium ion concentrations are generally used to induce neurotransmitter release. However, the widespread effects, if any, of such a treatment have not been described. In order to establish a possible link between c-fos expression and stimulating conditions for neurotransmitter release in microdialysis procedures we administered KCl (100 mM) into the hippocampus. Proto-oncogene c-FOS-like immunoreactivity is upregulated in granule cells of the dentate gyrus, pyramidal cells of the hippocampus, cingulate, piriform and frontoparietal cortices at 2 h, but not 24 h after K+ administration. Neither implantation of the probes nor perfusion with artificial cerebrospinal fluid resulted in similar patterns of c-FOS immunoreactivity. In addition, we investigated whether the impairment of the cholinergic septohippocampal pathway would modify the K(+)-induced expression of the immediate early gene c-fos in the hippocampus. The expression of c-fos induced by KCl was not altered in the animals with fimbria-fornix lesion despite the marked decrease in acetylcholine release in the hippocampus. Glutamate concentrations measured in the same superfusates showed that a significantly greater glutamate release occurs in denervated hippocampi. Furthermore, abolishment of seizure-like activity (induced by KCl) in anesthetized animals did not alter expression of c-FOS immunoreactivity in the K(+)-stimulated hippocampi. The results from these studies confirm that most of the releasable acetylcholine of the hippocampus is linked to the fimbrial input and may suggest that c-FOS upregulation in this model does not respond to any cholinergic input from the medial septum via the fimbria-fornix.

Stress protein and proto-oncogene expression as indicators of neuronal pathophysiology after ischemia

Induction of hsp70 mRNA and protein appear to provide useful markers for delineating stages in the progression of neuronal pathophysiology after ischemia. Detection of hsp70 encoded by the induced mRNA is dependent on complex interactions between the time course of mRNA expression and recovery of protein synthesis in a given neuron population, and perhaps other factors relating to specific aspects of hsp70 physiology, during recirculation intervals of hours to days. Transient mRNA expression and subsequent detection of immunoreactive hsp70 protein appear to identify neurons more likely to survive ischemia and other insults, while prolonged expression of hsp70 mRNA is associated with more severe neuronal injury. Fos and Jun immunoreactivities are also increased after ischemia, and provide indexes of functional gene expression during earlier recirculation periods. The accumulation of Fos immunoreactivity in particular designates neurons in which rapid recovery of protein synthesis during 1-3 h recirculation has allowed translation of the very transiently expressed c-fos mRNA. Jun-like immunoreactivity allows an evaluation of events at later recirculation intervals, and provides a clear demonstration of synthesis and accumulation of induced protein in CA1 neurons at 6 h following 2 min ischemia. Detailed understanding of the significance of such interactions between transcriptional and translational events will continue to evolve as information accumulates regarding the expression of additional mRNAs and proteins after ischemia. The present demonstration that Jun-like immunoreactivity accumulates in CA1 neurons after brief ischemia indicates that widespread changes in gene expression, expected as a consequence of such primary effects on transcription factor activity, are likely to contribute to the phenomenon of induced ischemic tolerance and to other persistent changes in the brain following diverse insults.

Fos family member changes in nucleus caudalis neurons after primary afferent stimulation: enhancement of fos B and c-fos

In situ hybridization using cDNAs complementary to specific regions of the mRNAs encoding four members of the FOS transcription factor gene family reveals modest levels of hybridization over superficial lamina of the nucleus caudalis of the spinal tract of the trigeminal in sections taken from unstimulated brains. Fos B expression is markedly and rapidly enhanced ipsilateral to electrical stimulation of the trigeminal ganglia. c-fos mRNA also changes; these differences contrast with the lack of significant changes in the low basal levels of expression of fra-1 and fra-2 mRNAs. The prominent change in fos B mRNA is mediated largely by an increase in the number of neurons that express hybridization densities above background after stimulation. This result, taken together with data on stimulation-induced changes in expression of preproenkephalin and other AP-1 transcription factors in wild-type animals and stimulation-induced changes in CAT activity in transgenic mice expressing portions of the proenkephalin promoter, is consistent with a role for the enhanced fos B expression in upregulation of expression of preproenkephalin in these neurons.

Distribution of c-fos expression in brainstem neurons associated with conditioning and pseudo-conditioning of the rabbit nictitating membrane reflex

Experiments were performed to test the hypothesis that there is a characteristic distribution of neuronal c-fos expression associated with the classical conditioning of the rabbit nictitating membrane reflex (NMR). Rabbits were divided into two groups: a conditioning group that received paired tone and airpuff stimuli in a traditional delay NMR conditioning paradigm and a pseudo-conditioning group in which the same number of tone and airpuff stimuli were applied but without being paired. Labeling was present in similar brainstem nuclei in both groups of animals. The labeled sites included trigeminal and auditory nuclei in the classical pathway for the nictitating membrane reflex as well as other nuclei such as the raphe nuclei and those in the ventrolateral medulla (VLM). However, there were quantitative differences in the labeling between the two groups. There were significantly more labeled nuclear profiles in the trigeminal nucleus of the pseudoconditioned rabbits, but more labeled nuclear profiles in the raphe nuclei in the conditioned animals. Interestingly, the ratio of the labeling in the raphe versus the VLM strongly differed between the two groups.

The dopamine D1 receptor antagonist SCH-23390 decreases the mRNA levels of the transcription factor zif268 (krox-24) in adult rat intact striatum--an in situ hybridization study

By in situ hybridization with an oligonucleotide probe, we have studied the cellular distribution of the messenger RNA encoding the transcription factor zif268 (krox-24) in the adult intact rat striatum and regulation of its synthesis by acute treatment with the dopamine D1 receptor antagonist SCH-23390. Zif268 mRNA was found in the striatal medium-sized neurons and not in the large cells. Its levels were decreased by SCH-23390, suggesting activation of this immediate early gene in the striatum through dopamine D1 receptor stimulation.

Regional expression of c-fos antigen in the basal forebrain following intraventricular infusions of angiotensin and its modulation by drinking either water or saline

The expression of c-fos protein was examined in the basal forebrains of male rats 60 min following intracerebroventricular infusions of 250 pmol angiotensin II. Levels of corticosterone and vasopressin were also measured at the same time point. In animals not allowed access to water after infusion, angiotensin II induced intense c-fos expression in a band of neurons extending throughout the anterior region of the third ventricle region, including the organum vasculosum of the lamina terminalis, the median preoptic nucleus (nucleus medianus) and the subfornical organ. There were also high levels of expression in the hypothalamic supraoptic nucleus and the paraventricular nucleus, particularly its lateral (magnocellular) region, though other, parvicellular areas were also affected. No other area of the hypothalamus was altered. There was increased c-fos expression in the central nucleus of the amygdala and the bed nucleus of the stria terminalis. Allowing rats to drink during the 60-min survival period modified this pattern of response. c-fos was markedly reduced in the supraoptic nucleus and the paraventricular nucleus but not in the other areas examined, including the anterior region of the third ventricle and the amygdala. When water was withheld for 15 min, but then allowed, rats drank the same total volume but c-fos expression was no longer inhibited in either the supraoptic nucleus or paraventricular nucleus. When rats were given 0.9% saline to drink, they ingested about three times as much as water, but angiotensin II-induced c-fos expression was similar to that in rats denied access to water. The pattern was similar following access to 1.8% saline, though levels in the organum vasculosum of the lamina terminalis were reduced. There was a marked correlation between the number of c-fos-positive neurons in the supraoptic nucleus or paraventricular nucleus and plasma levels of corticosterone 60 min after infusion, but not with arginine-vasopressin levels. These experiments show that angiotensin II induces highly localized expression of c-fos in areas known to be concerned with the dipsogenic and endocrine actions of this peptide, and that this pattern is selectively altered by allowing the animal to drink solutions of different tonicity. Immediate-early gene expression is a novel and valuable method of determining the neural response to peptides at the cellular level.

Neurotransmitter-stimulated immediate-early gene responses are organized through differential post-synaptic receptor mechanisms

The products of the cellular immediate-early genes (IEGs) are thought to act as messengers in the coupling of trans-synaptic stimuli with altered neuronal gene expression. However, the manner in which neurotransmission specifies particular responses through the IEGs is undefined. In this report, mRNA and transcription analysis of a precisely-timed, physiological IEG response illustrates how an IEG signal may be organized through differential neurotransmitter receptor activation. The nocturnal pattern of IEG expression in the rat pineal gland has been shown to be differentially regulated through post-synaptic adrenergic receptors. Induction of the c-fos gene is primarily mediated through alpha 1-receptors, whereas the coordinately regulated jun-B gene exhibits dual regulation through alpha 1- and beta-receptors. A simultaneous repression of c-jun expression is partly mediated through a beta-receptor mechanism. In vitro analysis of IEGs in cultured pineal glands has confirmed the receptor-specific link between adrenergic neurotransmission and IEG induction. The pineal is a unique neuroendocrine model in which the characteristics and function of the IEG third messenger system may be defined.

Administration of quinolinic acid in the rat hippocampus induces expression of c-fos and NGFI-A

We have studied the effect of intrahippocampal administration of quinolinic acid (QUIN) on the temporal expression of mRNAs encoding the immediate early genes (IEGs) c-fos and NGFI-A, by in situ hybridization histochemistry. After administration of QUIN to the left hippocampus, expression of mRNA of both IEGs was transiently stimulated. Maximal expression was found between 1 and 3 h. mRNA of both IEGs was simultaneously expressed in the ipsilateral and contralateral sides in the granule cell layer of the dentate gyrus, the pyramidal cell layer of the CA1 and CA3 fields as well as in the cortex. After pretreatment with the non-competitive NMDA antagonist MK-801 (2 mg/kg i.p. -30 min) the increased expression of both IEGs was partially prevented in the hippocampus and completely in the cortex. No inhibition was observed after treatment with the AMPA antagonist NBQX (30 mg/kg i.p. -15, -5 and +10 min). Additional delayed expression of both IEGs was observed in the ipsilateral hippocampus. This expression was related to cell damage. Twelve h after QUIN administration, c-fos and NGFI-A mRNAs were present in the dentate gyrus. After 4 days, only c-fos mRNA was observed in the dentate gyrus and CA1 field while no NGFI-A mRNA was detected. The present results show that the effect of QUIN is mediated by NMDA and not by AMPA receptors.

Fos-like expression and nuclear size in osmotically stimulated supraoptic nucleus neurons

This study has analysed by immunocytochemistry the pattern of expression of Fos-related proteins, as well as variations in nuclear size, after the osmotically induced activation of supraoptic nucleus neurons of the rat. In control rats most supraoptic nucleus neurons were Fos-like negative. After acute and chronic dehydration by salt-loading, the number of Fos-like positive neurons increased dramatically. The level of Fos-like immunoreactivity was higher in chronically stimulated rats, and also the neurons of the ventral region of the supraoptic nucleus were more intensely stained than those of the dorsal region. The karyometric analysis was made on electron micrographs. The mean nuclear profile area showed a significant increase in dehydrated rats with respect to the controls (73 +/- 16 microns 2 in those dehydrated for six days vs 54 +/- 13 in controls, mean +/- S.D.). However, no significant differences in this parameter were found when one-day and six-day dehydrated groups were compared. The invagination factor of the nuclear membrane, a nuclear shape indicator, decreased significantly in dehydrated rats, indicating a tendency towards spherical nuclei. It is noteworthy that the nuclear profile perimeter was constant, about 32 microns, in control and osmotically simulated rats. The higher nuclear accumulation of Fos-related antigens after six days of dehydration suggests that in chronically stimulated supraoptic nucleus neurons there is a sustained induction of cell-specific genes. Moreover, the transcription rate of the target genes containing the consensus DNA sequence TGAC/GTCA or c-AMP responsive elements recognition sites may depend upon the nuclear concentration of Fos-related antigens in supraoptic nucleus neurons. Our results also suggest that the initial Fos-related antigen expression and nuclear size increase are triggered concomitantly in supraoptic nucleus neurons after a short period of osmotic stimulation. On the other hand, we propose that nuclear envelope invaginations represent a reservoir of nuclear membrane which allows dynamic changes in nuclear size and shape depending on the metabolic status of the supraoptic nucleus neurons.

Induction of FOS and JUN proteins after focal ischemia in the rat: differential effect of the N-methyl-D-aspartate receptor antagonist MK-801

FOS and JUN proteins are transcription factors thought to be involved in coupling neuronal excitation to target gene expression. Cortical infarction of consistent size and location was produced by irradiating the rat brain with Xenon light through the intact skull for 20 min following systemic injection of the photo-sensitizing dye, rose bengal. To investigate the time course and distribution pattern of five cellular immediate early gene (IEG)-encoded proteins after focal ischemia, the expression of c-FOS, FOS B, c-JUN, JUN B and JUN D was studied immunocytochemically in sham-operated control animals and at different postischemic time intervals up to 24 h. A separate group of animals was pretreated with the non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801. Photochemically induced focal ischemia caused a rapid induction of FOS and JUN proteins in the entire ipsilateral cortex apart from the ischemic focus. Immunoreactivity in the ipsilateral subcortical gray and white matter and in the entire contralateral hemisphere was indistinguishable from control animals. Individual IEG-encoded proteins were sequentially induced with increased levels of immunoreactivity persisting for different time periods up to 24 h. c-FOS, FOS B, c-JUN and JUN B exhibited a characteristic distribution pattern as reflected by different staining intensities in individual cortical layers. The rapid IEG induction in the entire ipsilateral sensorimotor and limbic structure-associated cortices after photochemically induced infarction most likely reflects spreading depression caused by ischemia and mediated by NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Narine occlusion decreases basal levels of Fos protein in the cerebral cortex of the lizard Podarcis hispanica

Immunocytochemical study of cerebral cortex of the lizard Podarcis hispanica using an antibody directed to the M peptide of the rat c-Fos protein showed a distinct pattern of Fos distribution. Abundant Fos-immunoreactive neuronal nuclei were detected in the cell layers of the medial, the dorsal and the lateral cortices, whereas only a few nuclei were found in the cell layer of the dorsomedial cortex. The Fos immunoreactivity was characterized by Western blot analysis of nuclear extracts from lizard brain and showed a distinct band with an apparent molecular weight of 30,000. In band-shift assays, nuclear extracts from lizard brain were shown to contain AP-1 complexes. The basal expression of Fos immunoreactivity is related to sensory olfactory input in the cerebral cortex of the lizard since experiments with olfactory-deprived animals resulted in a complete absence of Fos immunoreactivity in the cortical areas.

cFos labeling in rat superior colliculus: activation by normal retinal pathways and pathways from intracranial retinal transplants

Previous studies in this laboratory have shown that intracranial retinal transplants can establish both anatomical and functional connections with the host brain. Embryonic rat retinae transplanted intracranially into neonatal host brains are capable of evoking appropriate physiological and behavioral responses when illuminated. The present study employs the specific expression of the cFos protein to identify brain regions in which immediate-early gene activation can be recognized in response to flash stimuli delivered to retinal transplants and to normal intact retinae. Stimulation of the intact eye induced significant cFos expression in various visual centers, including the stratum griseum superficiale of the superior colliculus and the pretectal area, but not in the dLGN, suprachiasmatic nucleus, or retina. Animals with functional transplants expressed cFos throughout the depth of the stratum griseum superficiale and stratum opticum of the superior colliculus, thus apparently activating an additional population of superior collicular cells. Like the eye-stimulated animals, animals with functional transplants failed to elicit significant cFos expression in the dLGN or transplanted retina. This study indicates that intracranial retinal transplants are capable of forming functional connections with the host superior colliculus which not only mediate transient changes in electrical activity but also may affect gene expression through the induction of the c-fos gene.

Stimulus-induced coordinate changes in mRNA abundance in single postsynaptic hippocampal CA1 neurons

The molecular effects of use-dependent changes in synaptic transmission were studied in individual CA1 pyramidal neurons from rat hippocampal slices. Potentiation of excitatory postsynaptic currents was associated with coordinate changes in the relative abundance of several mRNAs 30 min to 3 hr after stimulation. There was a 300% increase in calcium/calmodulin-dependent protein kinase II mRNA levels concordant with a 50% decrease in protein kinase C beta 1 isoform mRNA. A 2-fold increase in zif-268 mRNA was seen, while increases in c-fos and c-jun mRNA levels were inconsistent, gamma-Aminobutyric acid A receptor beta 1 subunit mRNA levels increased 3-fold. Potentiation-induced changes were prevented by N-methyl-D-aspartate receptor blockade. Changes in mRNA abundance in individual cells, with synaptic and glial interactions intact, combine to produce a molecular fingerprint of a potentiated CA1 neuron.

Induction of fos expression by activity in the spinal rhythm generator for scratching

Fos expression was evaluated immunohistochemically in L7-S1 spinal segments after inducing fictive scratching in paralysed, unanaesthetized, decerebrate cats. The activity was induced by cutaneous stimulation of the pinna on one side and recorded from peripheral nerves. A cumulative duration of scratching of 60 to 90 min was effective in inducing fos expression. Most Fos-positive neurones were found in the dorsolateral part of the ventral horn and in the intermediate region of the spinal cord on the scratching side. In sham-operated animals the finding of Fos-positive neurones in these areas was very rare.

Song presentation induces gene expression in the songbird forebrain

We investigated the participation of genomic regulatory events in the response of the songbird brain to a natural auditory stimulus of known physiological and behavioral relevance, birdsong. Using in situ hybridization, we detected a rapid increase in forebrain mRNA levels of an immediate-early gene encoding a transcriptional regulator (ZENK; also known as zif-268, egr-1, NGFI-A, or Krox-24) following presentation of tape-recorded songs to canaries (Serinus canaria) and zebra finches (Taeniopygia guttata). ZENK induction is most marked in a forebrain region believed to participate in auditory processing and is greatest when birds hear the song of their own species. A significantly lower level of induction occurs when birds hear the song of a different species and no induction is seen after exposure to tone bursts. Cellular analysis indicates that the level of induction reflects the proportion of neurons recruited to express the gene. These results suggest a role for genomic responses in neural processes linked to song pattern recognition, discrimination, or the formation of auditory associations.

The transcription factors c-JUN, JUN D and CREB, but not FOS and KROX-24, are differentially regulated in axotomized neurons following transection of rat sciatic nerve

In adult rats, expression of c-JUN, JUN B, JUN D, c-FOS, FOS B, KROX-24 and CREB proteins was investigated by immunocytochemistry in L4 and L5 dorsal root ganglia and lumbar spinal cord for up to 300 days following transection of the left sciatic nerve. In dorsal root ganglia, expressions of c-JUN and JUN D were increased 10 h and 15 h after sciatic nerve transection, respectively. c-JUN was still at an elevated level after 300 days predominantly in small diameter neurons, whereas JUN D had declined to control levels after 100 days. In contrast to the JUN proteins, expression of CREB showed a delayed onset after 10 days and reached a maximum between 70 and 150 days. In motoneurons, expression of c-JUN and JUN D was increased 15 h and 25 h after sciatic nerve transection, respectively. Expression of c-JUN remained increased after 150 days, whereas JUN D had declined to control levels after 70 days. In contrast, expression of CREB declined within 30 h in axotomized motoneurons and remained on a reduced level for up to 150 days. JUN B, c-FOS, FOS B and KROX-24 were not induced either following axotomy or following a repeated nerve crush. Sciatic nerve transection including the surgical procedure transynaptically provoked a transient expression of all JUN, FOS and KROX-24 proteins in neurons of spinal dorsal horn which disappeared after 5 days except the expression of JUN D which lasted for up to 20 days. In contrast, CREB immunoreactivity was not at all altered in neurons of spinal dorsal horn. In untreated animals, CREB and to a lesser extent JUN D showed an ubiquitous expression in neurons and glia cells of spinal cord, whereas expression of c-JUN and a weak expression of FOS B were restricted to motoneurons. In neurons of the dorsal root ganglia, a basal expression was found for c-JUN, JUN D and CREB and, at a low level, for FOS B and KROX-24. c-JUN and JUN D were colocalized with CREB in many cells such as interneurons, motoneurons, dorsal root ganglion cells and glial cells indicating the possibility for both the control of c-jun and jun D expression by CREB and the competition of JUN and CREB proteins for CRE consensus sequences.

The expression of the immediate-early genes c-fos, egr-1 and c-jun in the accessory olfactory bulb during the formation of an olfactory memory in mice

Female mice form a memory for the pheromones of the male with which they mate. It has been proposed that the site of the synaptic changes underlying this memory is the accessory olfactory bulb, at the first level of the accessory olfactory system. In this study we have examined the expression of the immediate-early genes c-fos, c-jun and egr-1 in the mitral and granule cells of the accessory olfactory bulb immediately after mating, during the period of memory formation. Transient increases were seen in the number of granule cell nuclei expressing c-fos and the number of granule and mitral cell nuclei expressing egr-1, during the period of memory formation. No changes were observed in the expression of c-jun during this period. The increase in the number of cells expressing c-fos and egr-1 required the association of mating and pheromonal exposure, conditions also required for memory formation. Large increases in the number of mitral and granule cell nuclei expressing c-fos and egr-1 were also observed following the infusion of the drug bicuculline into the accessory olfactory bulb in the absence of mating. This procedure has previously been shown to result in the formation of a nonspecific memory for male pheromones. These results associate the expression of c-fos and egr-1 in the accessory olfactory bulb with the conditions required for the formation of an olfactory memory for male pheromones.

Rearrangement of centromeric satellite DNA in hippocampal neurons exhibiting long-term potentiation

In situ hybridization in conjunction with three-dimensional reconstruction was used to examine the topology of satellite DNA (sDNA) sequences in hippocampal CA1 neurons. In slices fixed immediately after preparation, 4-5 signals/nucleus were detected in CA1, CA3 and dentate neurons. 70-80% of 154 neurons examined in these 3 areas displayed all signals at the nuclear periphery. In the remaining fraction of neurons, sDNA signals were divided between the nucleolus and the nuclear periphery. sDNA signals were consistently localized to the nuclear midplane. Slices left to equilibrate in artificial cerebral spinal fluid for 1 h, in the absence of potentiation, exhibited a significant increase in the total number of signals/nucleus in CA1 and dentate neurons. This increase in the number of signals occurred in both nucleolar and peripheral compartments, with the number of the nucleolar compartment nearly doubling. The total number of signals/nucleus was found to be consistently reduced in tetanized CA1 neurons (4.89 +/- 0.09 signals/nucleus, n = 195, P less than 0.05) as compared to neurons from unpotentiated slices (5.27 +/- 0.10 signals/nucleus, n = 81). A similar decrease in the total number of signals/nucleus was also observed in CA1 neurons exposed to N-methyl-D-aspartate (NMDA), from 5.27 +/- 0.10 signals/nucleus (n = 81) to 5.00 +/- 0.08 signals/nucleus (n = 215, P less than 0.05). In contrast, dentate neurons, employed as internal controls, did not exhibit any change in number and compartmentalization of sDNA signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Trans-synaptic regulation of gene expression

Neurotransmitters regulate gene expression through second messenger cascades that transmit the signal from the plasma membrane to the nucleus of the postsynaptic cell. Ca2+ and cAMP are two of the second messengers that regulate gene expression in response to neurotransmitters. The Ca2+ and cAMP signals induce expression of a class of genes, termed immediate early genes, within minutes of neurotransmitter receptor activation. Many of these genes encode transcription factors that regulate the expression of late response genes. The results of recent experiments have elucidated mechanisms by which neurotransmitter-induced Ca2+ and cAMP signals regulate immediate early gene expression.

c-fos expression in rat lumbar spinal cord during the development of adjuvant-induced arthritis

A parallel clinical and behavioral study of adjuvant-induced arthritis in the rat showed four stages in the time-course of the disease: preclinical (first week), acute (weeks 2-4), post-acute (weeks 5-8) and recovery weeks 9-11) [Calvino et al. (1987) Behav. Brain Res. 24, 11-29]. As several studies have reported the expression of the proto-oncogene c-fos in spinal cord neurons following acute noxious peripheral stimuli, the aim of this study was to quantitatively assess Fos-like immunoreactivity in lumbar spinal cord neurons at various times of adjuvant-induced arthritis development, i.e. one, two, three, 11 and 22 weeks post-inoculation. The total number of Fos-like immunoreactive neurons in the lumbar enlargement correlated with the observed development of adjuvant-induced arthritis, i.e. Fos-like immunoreactivity was absent at one week, moderate at two weeks, greatly increased at three weeks, decreased at 11 weeks and returned to control values at 22 weeks. At three weeks, at the peak of Fos-like immunoreactivity distribution and acute stage of hyperalgesia, maximal labeling was observed in L3 and L4 spinal segments. In these segments, the most densely labeled region was the neck (laminae V and VI) of the dorsal horn (55%) and the ventral horn (35%) as compared to the superficial laminae (laminae I and II; 5%) and the nucleus proprius (laminae III and IV; 5%). These data indicate that c-fos expression induced by chronic inflammation is better expressed in deeper laminae than in the superficial ones, and that the number of Fos-positive cells correlates with behavioral studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian variation in photic regulation of immediate-early gene mRNAs in rat suprachiasmatic nucleus cells

Exposure of rodents to light at daily times at which it can phase-shift circadian rhythms (subjective night) induces an increase in immunoreactivity for the immediate-early gene product Fos in cells of the circadian pacemaker, the suprachiasmatic nuclei (SCN). Light exposure at other phases (subjective day) does not increase Fos immunoreactivity in SCN cells, but it is not known whether this failure reflects the inability of light to induce transcription of appropriate mRNAs, or a post-transcriptional block. We used in situ hybridization studies to examine levels of mRNA in the SCN of rats exposed to light during the subjective day and subjective night. We studied levels of mRNAs for several immediate-early genes: c-fos, NGFI-A, NGFI-B, c-jun, junB and junD, before and after light exposure at these phases. Levels of mRNAs for all of the genes tested were unaffected by light exposure during the subjective day, and all were increased in response to light during the subjective night. With the exception of a weak constitutive label for junD, none of the genes were expressed in the SCN in darkness at either phase. Light-induced increases in the levels of several mRNAs in the SCN occur only during the subjective night; the mechanisms which prevent such responses during the subjective day remain unknown.

Correlation between the induction of an immediate early gene, zif/268, and long-term potentiation in the dentate gyrus

Expression of the immediate early gene zif/268 (also termed NGFI-A, Krox 24, TIS8 and Egr-1) was investigated in awake rats following various long-term potentiation (LTP) induction protocols. zif/268 mRNA (Northern blots) and protein (immunohistochemistry) levels sharply increased following LTP, and followed a time course characteristic of other immediate early genes. When measured across 3 tetanization protocols known to produce differing degrees of LTP persistence, zif/268 induction was found to be more highly correlated with LTP duration than with the magnitude of initial LTP. These data support the hypothesis that the immediate early gene zif/268 plays a role as a third messenger in the cascade of cellular and nuclear events that govern the persistence of LTP.

Neural-specific expression, genomic structure, and chromosomal localization of the gene encoding the zinc-finger transcription factor NGFI-C

The nerve growth factor-induced clone C (NGFI-C) gene encodes a zinc-finger transcription factor that is rapidly induced by nerve growth factor in rat pheochromocytoma PC12 cells and by seizure in brain. NGFI-C is closely related to the previously described early response genes, nerve growth factor-induced clone A (NGFI-A or EGR1), EGR2, and EGR3. These four early response (immediate early) proteins all contain very similar zinc-finger DNA binding domains; in addition, analysis of the non-zinc-finger region revealed that they share an additional five highly homologous subdomains, four of which are within the amino terminus. The 5' flanking region of NGFI-C contains several cAMP response elements but does not contain any serum-response elements or CArG boxes [CC(A/T)6GG], cis-acting elements commonly involved in early response gene regulation. NGFI-C mRNA was detected in neural tissues of postnatal animals, but no expression was found in rat embryos. In situ hybridization demonstrated that NGFI-C is rapidly induced in the dentate gyrus of the hippocampus after seizure, but in contrast to NGFI-A, increases in NGFI-C mRNA were not detected in the overlying cortex. By using fluorescence in situ hybridization, NGFI-C was localized to human chromosome 2p13. This region contains a constitutive fragile site that is associated with chromosomal breakpoints and translocations characteristic of some chronic lymphocytic leukemias.

The effect of stimulus duration on noxious-stimulus induced c-fos expression in the rodent spinal cord

C-fos is a proto-oncogene that is expressed within some neurons following depolarization. The protein product, fos, has been proposed as an anatomical marker for neuronal activity following noxious peripheral stimulation. However, the literature on noxious-stimulus induced fos expression contains several puzzling observations on the time course and laminar distribution of neuronal labeling within the spinal cord. This study has analyzed the effect of stimulus duration on the expression of fos-like immunoreactivity (FLI) within the spinal cord of anesthetized rats. In order to examine the time course of fos expression following brief periods of stimulation, we required a type of stimulus that was intense enough to activate nociceptors but that did not produce tissue damage. We have therefore employed pulsed, high intensity electrical stimulation, with stimulus durations ranging from 3 s to 24 h. The results indicate that stimulus duration has a profound effect upon the number of labeled cells, the intensity of neuronal labeling, the laminar pattern of FLI, and the time course of fos expression. Brief stimulation periods induce relatively few and relatively lightly labeled neurons, located predominantly within the most superficial laminae of the dorsal horn. Maximal immunoreactivity appears approximately 2 h after stimulation has ceased, and disappears within hours. Continuous stimulation produces many more labeled cells, darker labeling, and FLI within both dorsal and ventral laminar regions. Maximal FLI is seen after approximately 4.5 h of continuous stimulation, with reduction in the number of labeled cells thereafter. These data indicate that the results of any study employing c-fos as a marker for neuronal activity may be affected by the duration of the exciting stimulus.

C-fos protooncogene expression in rat brain after long-term training of two-way active avoidance reaction

C-fos nuclear protooncogene encodes a regulatory protein (Fos), able to directly influence both expression of itself and other genes. It has been repeatedly shown that c-fos expression coincides with different forms of cell activation, probably being functionally involved in the coupling of extracellular ligands to long-term cellular responses. In this study it has been found that c-fos mRNA accumulation in rat brain, as measured by northern blotting coincides with increase of performance level of learned behavior of a two-way active avoidance task. We have previously reported (Nikolaev et al., Brain Res. Bull., in press) that a single training session of two-way active avoidance strongly induces c-fos mRNA accumulation but that after long-term training up to the asymptotic level of performance no c-fos expression was detectable. In this paper we show that c-fos still remains inducible even after long-term, asymptotic training to darkness as conditioned stimulus (CS), provided that a novel stimulus, wide band noise, which elevated performance level, was given together with darkness as compound CS.

Induction of immediate early gene encoded proteins in the rat hippocampus after bicuculline-induced seizures: differential expression of KROX-24, FOS and JUN proteins

Immunocytochemistry with specific antisera was used to assess regional levels of six immediate early gene encoded proteins (KROX-24, c-FOS, FOS B, c-JUN, JUN B and JUN D) in the rat hippocampus after 15 min of bicuculline-induced seizures. Serial sections of the dorsal hippocampus were examined at various postictal recovery periods up to 24 h. The results demonstrate a complex temporal and spatial pattern of immediate early gene synthesis and accumulation. Three major categories of immediate early gene products could best be distinguished in the dentate gyrus: KROX-24 and c-FOS showed a concurrent rapid rise with peak levels at 2 h and a return to baseline levels within 8 h after seizure termination. FOS B, c-JUN and JUN B levels increased more gradually with peak intensities in the dentate gyrus reached at 4 h. These immediate early gene products showed above normal levels in various hippocampal subpopulations up to 24 h. JUN D exhibited the most delayed onset combined with a prolonged increase of seizure-induced immunoreactivity. Irrespective of this differential temporal expression profile of individual transcription factors, the sequence of induction in the hippocampal subpopulations was identical for all immediate early gene-encoded proteins examined: first in the dentate gyrus granule cells followed by CA1 and CA3 neurons, respectively. Our data indicate an asynchronous synthesis of several immediate early gene-encoded proteins in the brain after status epilepticus. FOS and JUN proteins act via homo- or heterodimer complexes at the AP-1 and other DNA binding sites. The different time-courses for individual immediate early gene products strongly suggest, that at different time-points after status epilepticus, different AP-1 complexes are effective. In vitro studies have shown that different AP-1 complexes possess different DNA binding affinities as well as different transcriptional regulatory effects. Our results suggest that these molecular mechanisms are also effective in vivo.

Expression of c-fos and other genes encoding transcription factors in long-term potentiation

The genes encoding transcription factors are known to be induced in many different biological phenomena of transition from one long-lasting state of cell functioning to another. It is widely believed that transcription factors control this transition by regulating the expression of other genes. Recently, several reports on gene expression after the induction of long-term potentiation (LTP) have been published. In particular, the c-fos nuclear protooncogene, encoding the Fos transcription factor, has been extensively investigated. However, the results of those studies were seemingly contradictory. The present commentary reviews available data in an attempt to resolve the apparent contradictions, showing that long-lasting LTP (i.e., lasting longer than a few hours) may involve c-fos expression, while shorter LTP may not.

Expression of c-fos and NGFI-A messenger RNA in the medulla oblongata of the anaesthetized rat following stimulation of vagal and cardiovascular afferents

Messenger RNA encoding the immediate early genes (IEGs) c-fos and NGFI-A was localized by in situ hybridization of specific 35S-labelled oligonucleotides to detect activated neurones in the medulla oblongata following unilateral electrical stimulation of the vagus (nX) and aortic depressor nerve (ADN), and following mechanical stimulation of the left carotid sinus (CS). In electrically stimulated rats, c-fos and NGFI-A mRNA was strongly expressed in the nucleus tractus solitarius (NTS) (predominantly ipsilaterally), area postrema (AP) and in a dorsal subregion of the paratrigeminal nucleus (PTN). Lower levels of c-fos and NGFI-A mRNA were seen in the ipsilateral NTS and PTN following mechanical stimulation of the left CS. In general these data correlate with the topography of innervation by the different nerve afferents, although the expression in the PTN (and in some cases the AP) would not be predicted on the basis of neuronal innervation patterns reported for the rat. Expression of these IEGs also occurred in the rostral and caudal ventrolateral medulla and inferior olive of both stimulated and sham-operated rats; presumably due to effects of the anaesthesia and surgical procedures. In conclusion the localization of the expression of c-fos and NGFI-A mRNAs represents a useful neuroanatomical technique for detecting the cell bodies of neurones that are activated by cardiovascular nerve afferents and should allow the further characterization of the neurochemical identity of these neurones.

Induction of c-fos mRNA in rat brain by conditioned and unconditioned stressors

Intense depolarizing stimuli induce the expression of the proto-oncogene c-fos which may be useful as a marker of neuronal activity. To determine if mild physical and behavioral stressors may also induce c-fos expression, we subjected rats to an unconditioned stressor (footshock) or a conditioned stressor (a tone previously paired with footshock) and measured c-fos mRNA levels in various brain regions using in situ hybridization. Removing rats from their home cage and exposing them to a tone was sufficient to cause increases in c-fos mRNA in several forebrain areas while further increases in c-fos occurred in the septum, cingulate cortex, and endopiriform nucleus in response to acute footshock stress. Both unconditioned and conditioned stressors increased c-fos mRNA levels in the locus ceruleus which correlated with stress-induced plasma corticosterone concentrations. Unconditioned footshock stress also increased c-fos mRNA in the hypothalamic paraventricular nucleus (PVN). However, neither conditioned nor unconditioned stressors induced c-fos in the PVN in rats which had been previously exposed to footshock. C-fos appears to be a sensitive marker for stress-responsive brain areas and may be important in mediating long-term neurochemical changes that result from stress.

D1Dopamine Receptor Activation of Multiple Transcription Factor Genes in Rat Striatum

Recent studies have shown that dopamine receptor agonists induce expression of Fos-like immunoreactivity in rat striatal neurons. The protooncogene c-fos belongs to a family of immediate early genes that are rapidly induced in fibroblasts by growth factors. In light of previous findings that several immediate early gene mRNAs that encode proven or putative transcription factors are differentially regulated by neuronal stimulation in vivo, we have examined the effect of dopaminergic agents on mRNA levels of several such genes using in situ hybridization and northern blot analysis. d-Amphetamine (2.5-10 mg/kg i.p.) causes a rapid but transient dose-dependent increase in zif268 and jun-B mRNA levels in striatum that was abolished by striatal 6-hydroxydopamine lesions or by pretreatment with the specific D1 receptor antagonist SCH-23390 but not by specific D2 receptor antagonists. Apomorphine, a dopamine agonist that acts at both D1 and D2 receptors, and SKF-38393, a specific D1 receptor agonist, produce similar mRNA changes in rats pretreated with either 6-hydroxydopamine or reserpine, whereas LY-171,555, a specific D2 receptor agonist, has no effect. Direct dopamine agonist effects on these immediate early gene mRNA levels are also blocked by D1 but not by D2 antagonists. We observed similar, although less robust, changes in c-fos and fos-B mRNA levels. These results demonstrate that striatal D1 dopamine receptors are coupled to activation of multiple transcription factor genes, including zif268 and jun-B as well as members of the fos family.

Activation of the zinc finger encoding gene krox-20 in adult rat brain: comparison with zif268

Zif268 and krox-20 are transcription regulatory factors that contain highly homologous zinc finger DNA-binding domains. Recent studies have demonstrated that zif268 expression is rapidly regulated in brain by neuronal stimulation. We now report that, like zif268, krox-20 is rapidly and transiently activated by electroconvulsive shock treatment (ECT), D1 dopamine receptor activation, and opiate withdrawal. These studies indicate that, as found for the leucine zipper family of transcription factors, multiple members of the zinc finger family of transcription factors are induced by neuronal stimulation.

Primary afferent stimulation acts through a 193 base pair promoter region to upregulate preproenkephalin expression in dorsal horn of transgenic mice

The expression of the principal opioid peptide gene, preproenkephalin A, is exquisitely regulated by primary afferent inputs to the spinal and medullary dorsal horns. This regulated expression in response to neural synaptic activity has been referred to as trans-synaptic regulation. To define which DNA regions could mediate this trans-synaptic regulation, transgenic 'HEC' mice whose genomes include 193 bp of the human preproenkephalin A promoter fused to a chloramphenicol acetyltransferase (CAT) reporter gene were studied. Mice received unilateral electrical stimulation of the trigeminal ganglion or adjuvant injection into the hindpaw, stimuli known to regulate dorsal horn proenkephalin expression in vivo. CAT activity conferred by this promoter displayed trans-synaptic upregulation with both stimuli. Although the level of the upregulation was 2- to 3-fold higher than the change in the wild type gene, several features of this induction paralleled aspects of the behavior of the wild-type gene: the rapidity of responses to trigeminal ganglion stimulation, the stimulation intensity dependence of responses to trigeminal ganglion stimulation and the time course of upregulation noted following adjuvant injection. Regulatory proteins binding to this restricted promoter region are thus likely to mediate aspects of dorsal horn enkephalin regulation by pain and other somatic stimuli.

Induction of expression of genes encoding transcription factors in the rat brain elicited by behavioral training

c-fos and zif/268 are regulatory genes encoding transcription factors able to influence gene expression directly. It has been shown repeatedly that expression of transcription factors correlates with different forms of cell activation, probably being functionally involved in the coupling of extracellular signals with long-term cellular responses. This study describes that c-fos and zif/268 mRNA accumulation, as measured by northern blot analysis, occurs in the rat hippocampus as well as the visual cortex following behavioral training of two-way active avoidance response.

Induction of immediate-early gene proteins in dentate granule cells and somatostatin interneurons after hippocampal seizures

The expression of the protein products of the immediate-early genes c-fos, Fos B, Fos-related proteins (FRAs), c-jun, jun B, jun D and krox-24 was investigated in the rat hippocampus at various times after electrically-induced hippocampal seizures. Hippocampal seizures induced all the immediate-early gene proteins in dentate granule cells with differing time-courses. In addition, Krox-24, Fos and Jun D were also induced in somatostatin-containing interneurons throughout the hippocampus and also in a small percentage of parvalbumin-containing interneurons. Thus, hippocampal seizures induce waves of immediate-early gene protein expression in dentate granule cells and a selective expression of krox-24, Fos and Jun D in hippocampal somatostatin interneurons. These results suggest that biochemical and/or morphological changes occurring in dentate granule cells and somatostatin interneurons after seizures may be regulated by immediate-early gene expression, and that these immediate-early gene proteins may be involved in seizure development in the nervous system.

Activity-dependent neuronal plasticity following tissue injury and inflammation

Increases in neuronal activity in response to tissue injury lead to changes in gene expression and prolonged changes in the nervous system. These functional changes appear to contribute to the hyperalgesia and spontaneous pain associated with tissue injury. This activity-dependent plasticity involves neuropeptides, such as dynorphin, substance P and calcitonin gene-related peptide, and excitatory amino acids, such as NMDA, which are chemical mediators involved in nociceptive processing. Unilateral inflammation in the hindpaw of the rat results in an increase in the expression of preprodynorphin and preproenkephalin mRNA in the spinal cord, which parallels the behavioral hyperalgesia associated with the inflammation. Cellular intermediate-early genes, such as c-fos, are also expressed in spinal cord neurons following inflammation and activation of nociceptors. Peripheral inflammation results in an enlargement of the receptive fields of many of these neurons. Dynorphin applied to the spinal cord also induces an enlargement of receptive fields. NMDA antagonists block the hyperexcitability produced by inflammation. A model has been proposed in which dynorphin, substance P and calcitonin gene-related peptide enhance excitability at NMDA receptor sites, leading first to dorsal horn hyperexcitability and then to excessive depolarization and excitotoxicity.

c-fos may code for a common transcription factor within the hypothalamic neural circuits involved in osmoregulation

Conscious rats were given an intraperitoneal (i.p.) injection of isotonic or hypertonic saline, and killed 10-240 min later. In the hypothalamus of hypertonic saline-injected rats, c-fos-mRNA positive cells were mainly restricted to the supraoptic and paraventricular nuclei and to structures associated with the lamina terminalis of the third ventricle, including in particular the subfornical organ, the organum vasculosum of the lamina terminalis (OVLT) and the median preoptic nucleus. These structures comprise the proposed anterior hypothalamic 'osmoreceptor complex' for regulation of vasopressin release. The time course of the appearance and disappearance of c-fos mRNA signals was similar in all regions. Thus c-fos protein (Fos) may be a common transcription factor in the hypothalamic neural circuits involved in osmoregulation.

Morphine or U-50,488 suppresses Fos protein-like immunoreactivity in the spinal cord and nucleus tractus solitarii evoked by a noxious visceral stimulus in the rat

Immunohistochemical visualization of Fos protein, the nuclear phosphoprotein product of the early-immediate gene c-fos, permits identification of populations of neurons that are activated in response to a variety of stimuli. This study examined the distribution of Fos-like immunoreactive (FLI) neurons in the spinal cord and the nucleus tractus solitarii (NTS) of the caudal medulla evoked by a noxious visceral stimulus in the unanesthetized rat. It also compared the inhibition of pain behavior and Fos expression by a mu-selective opioid agonist, morphine, and a kappa-selective opioid agonist, U-50,488. Intraperitoneal injection of 3.5% acetic acid in the unanesthetized rat evoked the expression of FLI in a discrete population of spinal cord neurons, the distribution of which closely mirrored the spinal terminations of visceral primary afferents. Specifically, FLI neurons were concentrated in laminae I, IIo, V, VII, and X. Large numbers of Fos-immunoreactive neurons were also present in the NTS of the caudal medulla, most likely as a result of spinosolitary tract and vaginal afferent input. The number of labeled neurons in both the spinal cord and the NTS was significantly correlated with the number of abdominal stretches, a pain behavior measure. Both morphine (1-10 mg/kg s.c.) and U-50,488 (3-30 mg/kg s.c.) produced a dose-dependent inhibition of the pain behavior in these animals and a dose-dependent suppression of the number of FLI neurons in both the spinal cord and in the NTS; complete suppression of FLI neurons was, however, not necessary for the production of antinociception. Furthermore, although equianalgesic doses of morphine and U-50,488 reduced the number of labelled neurons in the spinal cord to a comparable extent, morphine reduced the number of immunoreactive neurons in the NTS to a greater extent than did U-50,488. These results suggest that morphine and U-50,488 have comparable effects on the transmission of visceral nociceptive messages by spinal neurons, but differentially affect the autonomic response to noxious visceral stimuli.

fos-lacZ transgenic mice: mapping sites of gene induction in the central nervous system

A transgenic mouse line containing a fos-lacZ fusion gene was derived in which beta-galactosidase activity identified cell populations expressing fos either constitutively or after stimulation. Seizures and light pulses induced nuclear lacZ activity in defined populations of neurons in vivo, and an array of neurotransmitters, including glutamate, induced the transgene in primary brain cultures. In unstimulated mice, the major sites of fos-lacZ expression were skin, hair follicle, and bone. fos-lacZ mice provide a new avenue for activity mapping studies based on gene expression.

Expression of the proto-oncogene c-fos in three-dimensional fetal brain cell cultures and the lack of correlation with maturation-inducing stimuli

Previous work has shown that aggregating fetal brain cell cultures are able to attain a highly differentiated state, and that their development is greatly enhanced by growth and/or differentiation factors such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and the protein kinase C-activating tumor promoter mezerein. The present study shows that in these 3-dimensional cultures the peptide growth factors EGF and bFGF as well as mezerein are able to induce the expression of the proto-oncogene c-fos. This induction was rapid and transient, in good agreement with observations reported from a wide variety of cell types in vitro. The maximal levels of c-fos mRNA found after stimulation were low in immature cultures and increased greatly as maturation progressed. Of the three factors tested, mezerein was the most potent inducer of c-fos. In contrast to the peptide growth factors EGF and bFGF which were found to induce c-fos only in glial cells, mezerein was stimulatory in glial cells as well as in neurons. A similar cell type specificity has been observed previously for the maturation-enhancing response in immature aggregate cultures. However, in the present study no correlation was found between the degree of c-fos induction and the extent of the maturation-enhancing stimulation. Immature cultures known to be most sensitive and responsive to these maturation-enhancing agents required relatively high doses of peptide growth factors for the induction of c-fos, and the maximal levels of c-fos mRNA elicited were much lower than those in differentiated cultures which did not show any long-term response to these stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential induction of immediate early genes by excitatory amino acid receptor types in primary cultures of cortical and striatal neurons

In primary cultures of neurons from cerebral cortex and striatum, 30 s stimulation with the excitatory amino acid glutamate elicited a 5 to 9-fold increase in immediate early gene (IEG) mRNAs. Glutamate increased c-fos, c-jun, jun-B, and NGFI-A (zif/268) mRNAs by binding to both alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor types, and increased c-fos, jun-B, and NGFI-A mRNAs by binding to the metabotropic receptor. NMDA receptor activation elicited IEG expression by a transmembrane calcium influx; AMPA receptor-induced depolarization played a permissive role for the opening of the NMDA receptor channel. The protein kinase C (PKC) inhibitor H-7 (but not inhibitors of cyclic nucleotide-dependent and calcium/calmodulin-dependent protein kinases) partially blocked IEG expression induced by glutamate.

Distributed changes in rat brain DNA synthesis with long-term habituation and potentiation of the perforant path-granule cell synapse

The involvement of brain deoxyribonucleic acid (DNA) synthesis in adaptive neural events was studied in the adult rat during long-term habituation (LTH) or potentiation (LTP) of the perforant path-granule cell synapse. Male Long-Evans rats were given 50 muCi [3H]thymidine intraventricularly under urethane anesthesia. Soon thereafter, field excitatory postsynaptic potential (EPSP) slope and population spike were monitored from the right dentate gyrus before and at various times (5, 10, 15, 60 min) following the delivery to the ipsilateral perforant bundle of a low frequency (LFS: 1.0 Hz, 160 s) or a high-frequency train (HFS: 400 Hz, 200 ms), repeated once after 5 min. Unstimulated implanted rats served as controls. DNA synthesis was evaluated by the incorporation of the radioactive precursor into DNA of several brain areas at the end of a 1 h incorporation period. In CA1, LTH and LTP increased DNA synthesis by 30% on the stimulated side. In the entorhinal cortex, LTH but not LTP increased DNA synthesis (by 30%) on the stimulated side. Conversely, in the frontal cortex, LTP but not LTH increased DNA synthesis (by 100%) on both sides. Long-lasting changes in synaptic efficacy covaried non-linearly with DNA synthesis in mono- and polysynaptically stimulated hippocampal regions, and in functionally associated neocortical areas. The co-variations of population spike amplitude were positive for LTH and negative for LTP in the dentate gyrus and frontal cortex of both sides, and in CA3/CA1 of the stimulated side, indicating higher DNA synthesis at lower values of LTH and LTP, and viceversa. Further, regional cross-correlation analyses revealed a high degree of synchronization among brain sites, following low- or high-frequency train pulses, indicating that (i) extra-target sites participate on the stimulated and on the contralateral side, and (ii) small distributed changes take place across the sampled neural networks. A modulatory role of information flow on brain DNA synthesis is inferred to take place in a diffuse, distributed manner.

Induction of somatostatin by kainic acid in pyramidal and granule cells of the rat hippocampus

Seizures were induced in rats by systemic administration of kainic acid and, 1.5-12 h after, expression of preprosomatostatin and c-fos mRNAs in 9 hippocampal areas and in the cerebral perirhinal cortex was investigated using in situ hybridization histochemistry. Immunohistochemistry was also performed to study somatostatin peptide. In the control animals preprosomatostatin mRNA was expressed in some cells in the dentate hilus, the stratum oriens and the stratum radiatum of Ammon's horn, the subiculum and the cortex. Starting 3 h after kainic acid administration preprosomatostatin mRNA was expressed in a subpopulation of granule and pyramidal cells which did not normally express it. Preprosomatostatin mRNA-positive cells were markedly increased in the subiculum. Immunohistochemical examination confirmed that preprosomatostatin mRNA in granule and pyramidal cells was translated into peptide. In contrast, c-fos mRNA was induced in most hippocampal and cortical neurons starting 1.5 h after the kainic acid injection. When diazepam was injected to suppress the generalized seizures, preprosomatostatin mRNA was still expressed in pyramidal and subicular cells but not in granule cells.

Synaptic regulation of immediate early gene expression in primary cultures of cortical neurons

Neuronal stimulation can rapidly activate several immediate early genes that code for transcription factors. We have used primary cortical cultures to study the regulation of four of these genes, c-fos, c-jun, jun-B, and zif268. Immunocytochemical studies with antibodies to Jun-B, c-Jun, and c-Fos demonstrate intense staining in the nuclei of a subset of cortical neurons in mature cultures (21-25 days in vitro) but not young cultures (3-7 days in vitro). To assess whether this immunoreactivity may be induced by spontaneous synaptic activity that develops with a similar profile, we examined the effects of agents that reduce this synaptic activity. Tetrodotoxin or N-methyl-D-aspartate receptor antagonists suppress basal immunoreactivity to Jun-B and c-Fos, but not c-Jun, indicating that the basal level of c-Jun expression is not dependent on electrical activity. Picrotoxin, an agent that increases synaptic excitation indirectly by blocking inhibitory synaptic currents mediated by gamma-aminobutyric acidA receptors, markedly increases the percentage of neurons displaying immunoreactivity to c-Fos, c-Jun, Jun-B, and Zif268. Northern analysis suggests that the increases in immunostaining induced by picrotoxin are secondary to a rapid increase in mRNA for these proteins. These findings provide evidence for rapid transcriptional regulation of immediate early genes in cortical neurons by synaptic activity.

Electrical activation and c-fos mRNA expression in rat neurosecretory neurones after systemic administration of cholecystokinin

1. The expression of c-fos mRNA in the rat hypothalamus was examined by in situ hybridization following systemic administration of cholecystokinin (CCK), a procedure known to activate magnocellular oxytocin neurons but not magnocellular vasopressin neurones. 2. Conscious male rats were given a single I.P. injection of 50 micrograms/kg CCK, c-fos mRNA signal was apparent in the supraoptic and paraventricular nuclei in rats killed 10 min after injection but not in uninjected or saline-(vehicle) injected rats. The density of c-fos mRNA at both sites was further elevated in rats killed 30 min or 60 min following injection, and was absent in rats killed 4 h after injection. 3. In the paraventricular nucleus the most dense expression of c-fos mRNA following CCK administration was in the medial, mainly parvocellular portion of the nucleus, in an area corresponding to the distribution of corticotrophin-releasing factor mRNA determined by in situ hybridization in adjacent sections. 4. The I.P. injection of CCK increased plasma oxytocin concentrations, measured by specific radioimmunoassay from 13 +/- 5 pg/ml in control rats to 107 +/- 9 pg/ml in the rats killed 10 min after injection, a similar response to that observed previously in urethane-anaesthetized rats. 5. In each of six urethane-anaesthetized rats, recordings were made from single neurones in the supraoptic nucleus, identified antidronomically as projecting to the posterior pituitary and identified electrophysiologically as putative oxytocin neurones. Following I.P. injection of 50 micrograms/kg CCK, the neurones increased their firing rate by a mean of 1.3 +/- 0.2 spikes/s averaged over the 10 min following injection. 6. From the appearance of c-fos mRNA in supraoptic neurones following CCK administration we conclude that this message is expressed in magnocellular oxytocin neurones, since vasopressin neuronal activity and vasopressin release is known to be unaffected by this stimulus, and since the supraoptic nucleus contains essentially only oxytocin neurones and vasopressin neurones. 7. We conclude that c-fos mRNA expression can be induced in supraoptic oxytocin neurones following brief and modest episodes of electrical activation, suggesting that c-fos may be involved in the gene regulation of these neurones under physiological conditions.