Induction of c-fos mRNA expression in an in vitro hippocampal slice model of adult rats after kainate but not gamma-aminobutyric acid or bicuculline treatment

Spatiotemporal Correlation of Epileptiform Activity and Gene Expression in vitro

Epileptiform activity alters gene expression in the central nervous system, a phenomenon that has been studied extensively in animal models. Here, we asked whether also in vitro models of seizures are in principle suitable to investigate changes in gene expression due to epileptiform activity and tested this hypothesis mainly in rodent and additionally in some human brain slices. We focused on three genes relevant for seizures and epilepsy: FOS proto-oncogene (c-Fos), inducible cAMP early repressor (Icer) and mammalian target of rapamycin (mTor). Seizure-like events (SLEs) were induced by 4-aminopyridine (4-AP) in rat entorhinal-hippocampal slices and by 4-AP/8 mM potassium in human temporal lobe slices obtained from surgical treatment of epilepsy. SLEs were monitored simultaneously by extracellular field potentials and intrinsic optical signals (IOS) for 1–4 h, mRNA expression was quantified by real time PCR. In rat slices, both duration of SLE exposure and SLE onset region were associated with increased expression of c-Fos and Icer while no such association was shown for mTor expression. Similar to rat slices, c-FOS induction in human tissue was increased in slices with epileptiform activity. Our results indicate that irrespective of limitations imposed by ex vivo conditions, in vitro models represent a suitable tool to investigate gene expression. Our finding is of relevance for the investigation of human tissue that can only be performed ex vivo. Specifically, it presents an important prerequisite for future studies on transcriptome-wide and cell-specific changes in human tissue with the goal to reveal novel candidates involved in the pathophysiology of epilepsy and possibly other CNS pathologies.

Immediate and delayed hippocampal neuronal loss induced by kainic acid during early postnatal development in the rat

The degree to which the neonatal hippocampus is resistant to the effects of excitotoxins, such as kainic acid (KA) remains uncertain. Previously, we showed delayed loss of hippocampal neurons during pubescence in neonatal rats subjected to intracerebroventricular (i.c.v.) KA administration (10 nmol) at postnatal day 7 (P7). To further characterize the time course as well as the underlying mechanisms of this neuronal loss, we administered i.c.v. KA (10 or 50 nmol) to P7 preweanling rats. Brain sections were then examined at several neurodevelopmental time points (i.e., P8, P14, P25, P40, P60 and P75) using thionin staining and three-dimensional, non-biased cell counting to assess neuronal loss, and immunohistochemistry and electron microscopy to search for evidence of necrosis and apoptosis. Dose-dependent acute neuronal loss was observed at P8-P14 in hippocampal subfields CA3a and CA3c. Transient heat shock protein (HSP-70) immunostaining accompanied this acute neuronal loss. Progressive neuronal loss then continued in CA3 until P75, but without concomitant HSP-70 immunostaining. Progressive neuronal cell loss was also observed in the CA1 subfield of the hippocampus beginning at pubescence (i.e., P40) and continuing until P75. The appearance of TUNEL-positive hippocampal neurons accompanied the delayed neuronal loss in both CA3 and CA1 and electron micrographs confirmed that neurons in these subfields were undergoing apoptosis. KA administration (i.c.v.) to preweanling rats caused both immediate and delayed damage to hippocampal neurons. The effect of KA was dose-dependent, and the delayed neuronal damage occurred through an apoptosis-mediated mechanism. These findings may be relevant to the pathogenesis of some neuropsychiatric disorders, where early CNS injury is not apparent until the onset of clinical symptoms in young adulthood.

Double immunocytochemistry for the detection of Fos protein in retrogradely identified neurons using cholera toxin B subunit

The focus of this paper was to describe a method combining the neuroanatomical technique of retrograde transport of cholera toxin B subunit (CTB) with the technique of Fos functional labeling. This method allowed us to evaluate whether neurons identified by retrograde tracing were activated following chemical stimulation of another brain area. We have used this method at the light microscopic level to determine whether the stimulation of the rostral ventrolateral medulla activated retrogradely labeled adrenal sympathetic preganglionic neurons in the spinal cord. CTB-containing neurons, Fos immunoreactive neurons and double labeled neurons were observed in spinal autonomic areas. These results suggest that the rostral ventrolateral medulla exerts a descending activation upon identified adrenal preganglionic neurons. The method described in this protocol can be applied for other brain areas in order to establish if a given structure can activate an identified population of neurons linked with a particular target of central or peripheral nervous system.

c-fos expression and redox state of cytochrome oxidase of rat brain in hypoxia

Hypoxic induction of c-fos was studied in rat brains as a function of the cerebral oxygenation state using near-infrared spectroscopy by which the hemoglobin oxygenation state and redox state of mitochondrial cytochrome oxidase could be monitored noninvasively. Following reoxygenation after hypoxia, the expression of c-fos and MAP2 mRNAs was followed by reverse transcription-coupled PCR. The expression of MAP2 remained unchanged throughout all the conditions from 21 to 8% FiO2. Under mildly hypoxia conditions, c-fos mRNA was not induced. Hemoglobin was partially deoxygenated but cytochrome oxidase remained fully oxidized. Severe hypoxia, where cytochrome oxidase was reduced, caused a significant induction of c-fos mRNA At this stage, the oxygen concentration in cerebral tissue fell to < 10(-7) M. These data suggest that the decline in oxidative phosphorylation might be a trigger for the induction of c-fos mRNA.

Delayed neuronal loss after administration of intracerebroventricular kainic acid to preweanling rats

Excitotoxins, such as kainic acid (KA), have been shown to produce both immediate and delayed neuronal degeneration in adult rat brain. While preweanling rats have been shown to be resistant to the immediate neurotoxicity of KA, the presence of delayed neuronal loss has not been investigated in such animals. To determine whether intracerebroventricular (i.c.v.) administration of KA would produce delayed neuronal loss, preweanling rats were administered 5 nmol or 10 nmol KA i.c.v. on postnatal day 7 (P7) and then examined at P14, P45, and P75. Using three-dimensional, non-biased cell counting, neuronal loss was observed in the CA3 subfield of the hippocampal formation at P45 and P75 in animals administered 10 nmol KA, as compared to animals administered 5 nmol KA or artificial cerebrospinal fluid. Further, the amount of immunoreactivity to jun, the protein product of the immediate early gene, c-jun, adjusted for the number of remaining neurons was increased in the same brain areas. Antibody labeling of inducible heat shock protein and glial fibrillary acidic protein was not similarly increased in animals administered i.c.v. KA. The data suggest that while i.c.v. KA does not produce immediate neuronal loss in preweanling rats, the hippocampus is altered so that neuronal loss occurs after a delay, perhaps through apoptosis. These findings may be relevant to the pathogenesis of neuropsychiatric disorders, such as schizophrenia, that are characterized by early limbic-cortical deficits but onset of illness in young adulthood.

Progressive neurodegeneration after intracerebroventricular kainic acid administration in rats: implications for schizophrenia?

BACKGROUND

Intracerebroventricular (ICV) administration of kainic acid to rats produces limbic-cortical neuronal damage that has been compared to the neuropathology of schizophrenia.

METHODS

Groups of adult rats were administered ICV kainic acid and then assessed for neuronal loss and the expression of proteins relevant to mechanisms of neuronal damage after one and fourteen days. Neuronal loss was assessed by two-dimensional cell counting and protein expression was assessed by immunohistochemistry.

RESULTS

ICV kainic acid administration was associated with both immediate (day 1) and delayed (day 14) neuronal loss in the dorsal hippocampus. The immediate injury was largely limited to the CA3 hippocampal subfield, while the delayed injury included the CA1 subfield. Multiple mechanisms of cell death appeared to be involved in the delayed neuronal loss, as evidenced by changes in the expression of glutamate receptor subunits, heat shock protein and jun protein.

CONCLUSIONS

ICV kainic acid administration to adult rats produces progressive damage to limbic-cortical neurons, involving both fast and slow mechanisms of cell death. Given the evidence for clinical deterioration, cognitive deficits and hippocampal neuropathy in some cases of schizophrenia, this animal model may be relevant for hypotheses regarding mechanisms of neurodegeneration in that disorder.

c-fos expression in isolated rat spinal cord

Expression of c-fos-immunoreactivity (c-fos-ir) has been demonstrated in the dorsal horn of lumbar segments of an isolated spinal cord preparation from 3 week old rats. The method of preparation generated a low level of c-fos-ir activity which was not significantly altered by low intensity (1.5 times threshold) dorsal root stimulation, but was significantly increased by high intensity (20 times threshold) stimulation. Replacement of the calcium in the bathing medium by 2 mM manganese suppressed all detectable c-fos-ir, whereas inclusion of 0.5 microM capsaicin caused intense c-fos-ir expression in the absence of stimulation. The number of dorsal horn cells exhibiting c-fos-ir increased between 0.5 and 1 h after stimulation, reaching a maximum at 2 h, with no further increase at longer intervals. Few positive cells were found when the incubation temperature was reduced from 27 to 20 degrees C. The strongest increase in c-fos-ir was found in the dorsal horn ipsilateral to the stimulated dorsal root and a smaller, but significant, increase was also seen in the contralateral dorsal horn. Cords obtained from animals treated at 1 day old with capsaicin to destroy afferent C fibres showed a reduction in the number of c-fos-ir positive cells induced by high intensity dorsal root stimulation. This preparation will aid detailed investigation of the pharmacology of nociceptive pathways.

Immediate early gene expression and delayed cell death in limbic areas of the rat brain after kainic acid treatment and recovery in the cold

Systemic injection of kainic acid (KA) results in characteristic behaviors and programmed cell death in some regions of the rat brain. We used KA followed by recovery at 4 degrees C to restrict damage to limbic structures and compared patterns of immediate early gene (IEG) expression and associated DNA binding activity in these damaged areas with that in spared brain regions. Male Wistar rats were injected with KA (12 mg/kg, i.p.) and kept at 4 degrees C for 5 h. This treatment reduced the severity of behaviors and restricted damage (observed by Nissl staining) to the CA1 and CA3 regions of the hippocampus and an area including the entorhinal cortex. DNA laddering, characteristic of apoptosis, was first evident in the hippocampus and the entorhinal cortex 18 and 22 h after KA, respectively. The pattern of IEG mRNA induction fell into three classes: IEGs that were induced in both damaged and spared areas (c-fos, fos B, jun B, and egr-1), IEGs that were induced specifically in the damaged areas (fra-2 and c-jun), and an IEG that was significantly induced by saline injection and/or the cold treatment (jun D). The pattern of immunoreactivity closely followed that of mRNA expression. Binding to the AP-1 and EGR DNA consensus sequences increased in all three regions studied. This study describes a unique modification of the animal model of KA-induced neurotoxicity which may prove a useful tool for dissecting the molecular cascade that ultimately results in programmed cell death.

Widespread neuronal expression of c-Fos throughout the brain and local expression in glia following a hippocampal injury

Fos oncoprotein is an immediate early gene product and a marker of cell activation following a variety of insults. We have previously shown that a mechanical lesion to the hippocampus of adult mice induces a neuronal expression of the cytokines interleukin-1alpha (IL-1alpha) and tumor necrosis factor-alpha (TNF alpha) whereas a lesion to the striatum does not. The role of these inflammatory cytokines in the pathophysiology of central neurons is still unclear. The present work was undertaken to study a possible correlation between the central expression patterns of c-Fos on the one hand and IL-1alpha and TNF alpha on the other hand. We show that Fos is expressed in a majority of brain neurons after a unilateral lesion to the hippocampus whereas it is confined to the site of injury when applied to the striatum, as previously described for the expression of the cytokines.

Differential temporal patterns of expression of immediate early genes in cerebral cortex induced by intracerebral excitotoxin injection: sensitivity to dexamethasone and MK-801

A number of conditions associated with persistent excitation such as electrically and chemically-induced seizures cause a rapid increase in the expression of immediate early genes (IEG) such as c-fos. In this study the time-course of induction of c-jun, jun-B and zif 268 mRNA by kainate was characterized in rat cerebral cortex and compared to that of c-fos mRNA induction. Unilateral injection of kainate into the nucleus basalis caused a significant induction of c-jun mRNA in cerebral cortex from 4 hr which was maximal at 8 hr, being 3 times greater in ipsilateral cortex than in control cortex. This pattern was also shown for jun-B and was similar, but of small magnitude, to that obtained with c-fos mRNA, with a maximal increase at 8 hr, whilst the maximal induction of zif-268 mRNA preceded these responses occurring at 4 hr. A marked difference was seen in duration in the c-jun induction which was maintained at a high level for at least 24 hr. Treatment of animals with MK-801 (within 30 min of injection of kainate) or dexamethasone (2-30 mg/kg) at the time of kainate injection significantly attenuated the response. The induction of c-fos mRNA by kainate injection was most sensitive to dexamethasone (2 mg/kg), whereas a higher dose (30 mg/kg) was required to attenuate the induction of zif-268 mRNA. These results show that a time-dependent and co-ordinated induction of c-fos, c-jun, jun-B and zif-268 mRNA in cerebral cortex occurs in response to the persistent excitation caused by excitotoxin injection which is mediated by glutamate and shows a differential sensitivity to dexamethasone.