Induction and suppression of immediate early genes in specific rat brain regions by the non-competitive N-methyl-D-aspartate receptor antagonist MK-801

Increasing Adiponectin Signaling by Sub-Chronic AdipoRon Treatment Elicits Antidepressant- and Anxiolytic-Like Effects Independent of Changes in Hippocampal Plasticity

(1) Background: Adiponectin is an adipocyte-secreted hormone that has antidepressant- and anxiolytic-like effects in preclinical studies. Here, we investigated the antidepressant- and anxiolytic-like effects of sub-chronic treatment with AdipoRon, an adiponectin receptor agonist, and its potential linkage to changes in hippocampal adult neurogenesis and synaptic plasticity. (2) Methods: Different cohorts of wild-type C57BL/6J and CamKIIα-Cre male mice were treated with sub-chronic (7 days) AdipoRon, followed by behavioral, molecular, and electrophysiological experiments. (3) Results: 7-day AdipoRon treatment elicited antidepressant- and anxiolytic-like effects but did not affect hippocampal neurogenesis. AdipoRon treatment reduced hippocampal brain-derived neurotrophic factor (BDNF) levels, neuronal activation in the ventral dentate gyrus, and long-term potentiation of the perforant path. The knockdown of N-methyl-D-aspartate (NMDA) receptor subunits GluN2A and GluN2B in the ventral hippocampus did not affect the antidepressant- and anxiolytic-like effects of AdipoRon. (4) Conclusions: Increasing adiponectin signaling through sub-chronic AdipoRon treatment results in antidepressant- and anxiolytic-like effects independent of changes in hippocampal structural and synaptic function.

Region-Specific Enhancement of c-fos Expression by Combined Treatment With NMDA Receptor Agonists and Antagonists With Antidepressant Potential

Rapastinel, formerly Glyx-13, is a novel positive allosteric modulator of the N-methyl-D-aspartate-receptor (NMDAR) that counteracts psychotomimetic actions of NMDAR antagonists. We set out to evaluate the effect of rapastinel alone or in combination with the global and GluN2B subunit-specific NMDAR antagonists MK-801 and Ro25-6981, respectively, on neuronal activation in relevant regions using c-fos brain mapping. Whereas rapastinel alone did not trigger significant c-fos expression beyond the prelimbic cortex, it strongly increased the c-fos expression induced by MK-801 in hippocampal, cingulate, and retrosplenial areas. Similar results were obtained when rapastinel was replaced by D-cycloserine. Our results reveal new interactions at network level between NMDAR modulators with possible implications regarding their therapeutic effects.

Distinct retrosplenial cortex cell populations and their spike dynamics during ketamine-induced unconscious state

Ketamine is known to induce psychotic-like symptoms, including delirium and visual hallucinations. It also causes neuronal damage and cell death in the retrosplenial cortex (RSC), an area that is thought to be a part of high visual cortical pathways and at least partially responsible for ketamine's psychotomimetic activities. However, the basic physiological properties of RSC cells as well as their response to ketamine in vivo remained largely unexplored. Here, we combine a computational method, the Inter-Spike Interval Classification Analysis (ISICA), and in vivo recordings to uncover and profile excitatory cell subtypes within layers 2&3 and 5&6 of the RSC in mice within both conscious, sleep, and ketamine-induced unconscious states. We demonstrate two distinct excitatory principal cell sub-populations, namely, high-bursting excitatory principal cells and low-bursting excitatory principal cells, within layers 2&3, and show that this classification is robust over the conscious states, namely quiet awake, and natural unconscious sleep periods. Similarly, we provide evidence of high-bursting and low-bursting excitatory principal cell sub-populations within layers 5&6 that remained distinct during quiet awake and sleep states. We further examined how these subtypes are dynamically altered by ketamine. During ketamine-induced unconscious state, these distinct excitatory principal cell subtypes in both layer 2&3 and layer 5&6 exhibited distinct dynamics. We also uncovered different dynamics of local field potential under various brain states in layer 2&3 and layer 5&6. Interestingly, ketamine administration induced high gamma oscillations in layer 2&3 of the RSC, but not layer 5&6. Our results show that excitatory principal cells within RSC layers 2&3 and 5&6 contain multiple physiologically distinct sub-populations, and they are differentially affected by ketamine.

Molecular and cellular dissection of NMDA receptor subtypes as antidepressant targets

A growing body of evidence supports the idea that drugs targeting the glutamate system may represent a valuable therapeutic alternative in major depressive disorders (MDD). The rapid and prolonged mood elevating effect of the NMDA receptor (NMDAR) antagonist ketamine has been studied intensely. However, its clinical use is hampered by deleterious side-effects, such as psychosis. Therefore, a better understanding of the mechanisms of the psychotropic effects after NMDAR blockade is necessary to develop glutamatergic antidepressants with improved therapeutic profile. Here we review recent experimental data that addressed molecular/cellular determinants of the antidepressant effect mediated by inactivating NMDAR subtypes. We refer to results obtained both in pharmacological and genetic animal models, ranging from global to conditional NMDAR manipulation. Our main focus is on the contribution of different NMDAR subtypes to the psychoactive effects induced by NMDAR ablation/blockade. We review data analyzing the effect of NMDAR subtype deletions limited to specific neuronal populations/brain areas in the regulation of mood. Altogether, these studies suggest effective and putative specific NMDAR drug targets for MDD treatment.

Facilitated c-Fos Induction in Mice Deficient for the AMPA Receptor-Associated Protein Ckamp44

The recently identified Cystine-knot containing AMPAR-associated protein (Ckamp44) represents a novel AMPAR-related protein that critically controls AMPAR-mediated currents and short-term plasticity. However, the effects of the lack of this protein at network level are not entirely understood. Here we used c-Fos brain mapping to analyse whether the excitatory/inhibitory balance is altered in the absence of the Ckamp44. We found that Ckamp44(-/-) mice treated with an NMDAR antagonist exhibited a very robust c-Fos expression pattern, similar with that seen in mice lacking the GluN2A subunit of NMDAR treated with the same compound. This finding is unexpected, in particular, since Ckamp44 expression is strongest in dentate gyrus granule cells and less abundant in the rest of the brain.

REVIEW ■ : Neuroprotection in Brain Ischemia: An Update (Part I

Ischemic brain injury produced by stroke or cardiac arrest is a major cause of human neurological disability. Steady advances in the neurosciences have elucidated pathophysiological mechanisms of brain ischemia and have suggested many therapeutic approaches directed at specific injury mechanisms to achieve neuroprotection of the acutely ischemic brain. The first portion of this two-part review highlights the differentiating features and pathological mechanisms of focal and global cerebral ischemic injury and summarizes a wealth of recent evidence as to how antagonism of excitatory amino acid neurotoxicity, mediated via NMDA as well as non-NMDA receptors, may offer a means of diminishing the extent of ischemic injury. The Neuroscientist 1:95-103, 1995

Puberty marks major changes in the hippocampal and cortical c-Fos activation pattern induced by NMDA receptor antagonists

Non-selective and subunit (GluN2B)-specific N-methyl-d-aspartate receptor (NMDAR) antagonists represent promising alternative antidepressant drugs with fast onset of the therapeutic action. The neuronal activation pattern induced by NMDAR antagonists is well characterized by c-Fos expression analysis only in the adult rodent brain. In contrast, there is little information available regarding their effects during postnatal development. Here we performed a systematic c-Fos brain mapping of the non-selective NMDAR antagonist MK-801 and the GluN2B-specific antagonist Ro 25-6981 from postnatal day 16 (P16) to P40. We found significant regional differences with gender-specificity in the activation pattern compared to the adult. Surprisingly, in the hippocampus, MK-801 triggered at pre-pubertal stages (especially at P24) very strong c-Fos expression, followed by low levels after P30, the approximate time point of puberty onset in mice. The cortical distribution of MK-801-triggered c-Fos expression before puberty differed also substantially from the adult brain, showing high levels only in deep cortical layers at pre-pubertal stages. In comparison, the cortical activation induced by Ro 25-6981 diminished from high pre-pubertal levels and was in comparison with that triggered by MK-801 low in the hippocampus. These results reveal highly dynamic changes in the c-Fos activation pattern induced by NMDAR antagonists during puberty. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

Development of NMDAR antagonists with reduced neurotoxic side effects: a study on GK11

The NMDAR glutamate receptor subtype mediates various vital physiological neuronal functions. However, its excessive activation contributes to neuronal damage in a large variety of acute and chronic neurological disorders. NMDAR antagonists thus represent promising therapeutic tools that can counteract NMDARs' overactivation. Channel blockers are of special interest since they are use-dependent, thus being more potent at continuously activated NMDARs, as may be the case in pathological conditions. Nevertheless, it has been established that NMDAR antagonists, such as MK801, also have unacceptable neurotoxic effects. Presently only Memantine is considered a safe NMDAR antagonist and is used clinically. It has recently been speculated that antagonists that preferentially target extrasynaptic NMDARs would be less toxic. We previously demonstrated that the phencyclidine derivative GK11 preferentially inhibits extrasynaptic NMDARs. We thus anticipated that this compound would be safer than other known NMDAR antagonists. In this study we used whole-genome profiling of the rat cingulate cortex, a brain area that is particularly sensitive to NMDAR antagonists, to compare the potential adverse effects of GK11 and MK801. Our results showed that in contrast to GK11, the transcriptional profile of MK801 is characterized by a significant upregulation of inflammatory and stress-response genes, consistent with its high neurotoxicity. In addition, behavioural and immunohistochemical analyses confirmed marked inflammatory reactions (including astrogliosis and microglial activation) in MK801-treated, but not GK11-treated rats. Interestingly, we also showed that GK11 elicited less inflammation and neuronal damage, even when compared to Memantine, which like GK11, preferentially inhibits extrasynaptic NMDAR. As a whole, our study suggests that GK11 may be a more attractive therapeutic alternative in the treatment of CNS disorders characterized by the overactivation of glutamate receptors.

Pharmacological blockade of GluN2B-containing NMDA receptors induces antidepressant-like effects lacking psychotomimetic action and neurotoxicity in the perinatal and adult rodent brain

NMDA receptor (NMDAR) antagonists like ketamine and MK-801 possess remarkable antidepressant effects with fast onset. However, they over-stimulate the retrosplenial cortex, evoking psychosis-like effects and neuronal injury, revealed by de novo induction of the heat shock protein 70 (Hsp70). Moreover, early in the development MK-801 triggers widespread cortical apoptosis, inducing extensive caspase-3 expression. Altogether these data raise strong concerns on the clinical applicability of NMDAR antagonist therapies. Therefore, the development of novel therapeutics targeting more specifically NMDAR to avoid psychotomimetic effects is necessary. Here we investigated a GluN2B (NR2B) antagonist in behavioral and neurotoxicity paradigms in rats to assess its potential as possible alternative to unspecific NMDA receptor antagonists. We found that treatment with the GluN2B specific antagonist Ro 25-6981 evoked robust antidepressant-like effects. Moreover, Ro 25-6981 did not cause hyperactivity as displayed after treatment with unspecific NMDAR antagonists, a correlate of psychosis-like effects in rodents. Additionally, Ro 25-6981, unlike MK-801, did not induce caspase-3 and HSP70 expression, markers of neurotoxicity in the perinatal and adult brain, respectively. Moreover, unexpectedly, in the adult retrosplenial cortex Ro 25-6981 pretreatment significantly reduced MK-801-triggered neurotoxicity. Our results suggest that GluN2B antagonists may represent valuable alternatives to unspecific NMDAR antagonists with robust antidepressant efficacy and a more favorable side-effect profile.

Neurochemical and molecular characterization of ketamine-induced experimental psychosis model in mice

Ketamine, an NMDA receptor antagonist has been shown to induce aberrant behaviour phenotypes in rodents, some of which are known to simulate the behaviour abnormalities observed in patients suffering from schizophrenia. Thus, developing ketamine-induced animal models became an important tool of choice to study the mechanistic details of some critical symptoms associated with schizophrenia. In this study, our goal was to characterize and correlate the ketamine-induced changes in the behavioural phenotypes to the changes in neurochemical and molecular profile(s) in the brain tissues implicated in the pathophysiology of schizophrenia. We studied the effects of ketamine in mice using 'acute' and 'chronic' treatment regimens along with the 'drug withdrawal' effects on their biochemical and molecular parameters in the pre-frontal cortex, hippocampus, and striatum. Our results demonstrated that the acute and chronic ketamine administration, differentially and site specifically, modulated the levels of acetylcholine, dopamine, serotonin and noradrenaline. In addition, the chronic ketamine doses dramatically suppressed the levels of glycine among some of the amino acids examined and induced alternations in gene expression of the key neurotransmitter receptor systems, including some members of the dopamine and the serotonin receptor families. The acute and chronic ketamine treatment induced "signature" neurochemical and gene-expression patterns that are implicated in the pathophysiology of schizophrenia. Our analyses tend to support the "chronic ketamine" mice model for experimental psychosis as a tool for deeper investigation of the mechanistic paradigm associated with the schizophrenia spectrum disorder and for screening next-generation antipsychotic drugs.

The role of endogenous neurotensin in psychostimulant-induced disruption of prepulse inhibition and locomotion

The neuropeptide neurotensin (NT) is closely associated with dopaminergic and glutamatergic systems in the rat brain. Central injection of NT into the nucleus accumbens (NAcc) or peripheral administration of NT receptor agonists, reduces many of the behavioral effects of psychostimulants. However, the role of endogenous NT in the behavioral effects of psychostimulants (e.g. DA agonists and NMDA receptor antagonists) remains unclear. Using a NTR antagonist, SR142948A, the current studies were designed to examine the role of endogenous NT in DA receptor agonist- and NMDA receptor antagonist-induced disruption of prepulse inhibition of the acoustic startle response (PPI), locomotor hyperactivity and brain-region specific c-fos mRNA expression. Adult male rats received a single i.p. injection of SR142948A or vehicle followed by D-amphetamine, apomorphine or dizocilpine challenge. SR142948A had no effect on baseline PPI, but dose-dependently attenuated d-amphetamine- and dizocilpine-induced PPI disruption and enhanced apomorphine-induced PPI disruption. SR142948A did not significantly affect either baseline locomotor activity or stimulant-induced hyperlocomotion. Systemic SR142948A administration prevented c-fos mRNA induction in mesolimbic terminal fields (prefrontal cortex, lateral septum, NAcc, ventral subiculum) induced by all three psychostimulants implicating the VTA as the site for NT modulation of stimulant-induced PPI disruption. Further characterization of the NT system may be valuable to find clinical useful compounds for schizophrenia and drug addiction.

Neurodegeneration and prolonged immediate early gene expression throughout cortical areas of the rat brain following acute administration of dizocilpine

N-methyl-d-aspartate receptor antagonist drugs (NMDA-A), such as dizocilpine (MK801), induce long-lasting behavioral disturbances reminiscent to psychotic disorders in humans. To identify cortical structures affected by NMDA-A, we used a single dose of MK801 (10 mg/kg) that caused low and high neurodegeneration in intact and orchiectomized male rats, respectively. Degenerating somas (neuronal death) and axonal/synaptic endings (terminal degeneration) were depicted by a silver technique, and functionally affected cortical neuronal subpopulations by Egr-1, c-Fos, and FosB/DeltaFosB-immunolabeling. In intact males, MK801 triggered a c-Fos induction that remained high for more than 24 h in selected layers of the retrosplenial, somatosensory and entorhinal cortices. MK801-induced neurodegeneration reached its peak at 72 h. Degenerating somas were restricted to layer IV of the granular subdivision of the retrosplenial cortex, and were accompanied by suppression of Egr-1 immunolabeling. Terminal degeneration extended to selected layers of the retrosplenial, somatosensory and parahippocampal cortices, which are target areas of retrosplenial cortex. Induction of FosB/DeltaFosB by MK801 also extended to the same cortical layers affected by terminal degeneration, likely reflecting the damage of synaptic connectivity. In orchiectomized males, the neurodegenerative and functional effects of MK801 were exacerbated. Degenerative somas in layer IV of the retrosplenial cortex significantly increased, with a parallel enhancement of terminal degeneration and FosB/DeltaFosB-expression in the mentioned cortical structures, but no additional areas were affected. These observations reveal that synaptic dysfunction/degeneration in the retrosplenial, somatosensory and parahippocampal cortices might underlie the long-lasting impairments induced by NMDA-A.

Differential c-Fos induction by different NMDA receptor antagonists with antidepressant efficacy: potential clinical implications

Preclinical and clinical studies have shown that N-methyl-D-aspartate (NMDA) receptor antagonists can exert antidepressant effects. Thus, a single intravenous injection of ketamine, a non-competitive NMDA receptor antagonists, has been recently demonstrated to produce a rapid and relatively sustained antidepressant effect in patients. Therefore, the role of NMDA receptors and their signalling pathways for pathophysiology and therapy of depression are under intense research.

Reduction in the protein level of c-Jun and phosphorylation of Ser73-c-Jun in rat frontal cortex after repeated MK-801 treatment

Repeated administration of NMDA antagonists can induce behavioral alterations that mimic symptoms of psychosis, as seen in schizophrenia. JNK, one of the MAPKs, and c-Jun, its downstream target molecule, play important roles in regulating apoptosis in neural cells, and have been suggested as being associated with the pathophysiology of psychosis and the mechanism of action of some antipsychotics. We investigated changes in the JNK-c-Jun pathway and other Jun family proteins in the rat frontal cortex after single and repeated administration of MK-801 to examine acute and chronic responses. Neither the protein level nor the phosphorylation of JNK changed after single or repeated doses of MK-801. However, after repeated treatments, but not a single treatment, with MK-801, a down-regulation occurred in the protein level and of Ser73 phosphorylation of c-Jun in the rat frontal cortex. Other members of the Jun family, JunB and JunD, were unchanged. Repeated exposure to MK-801 down-regulated the phosphorylation and protein level of c-Jun in the rat frontal cortex, which may be related to the long-term effects of chronic treatment with MK-801.

Distinct functions of egr gene family members in cognitive processes

The different gene members of the Egr family of transcriptional regulators have often been considered to have related functions in brain, based on their co-expression in many cell-types and structures, the relatively high homology of the translated proteins and their ability to bind to the same consensus DNA binding sequence. Recent research, however, suggest this might not be the case. In this review, we focus on the current understanding of the functional roles of the different Egr family members in learning and memory. We briefly outline evidence from mutant mice that Egr1 is required specifically for the consolidation of long-term memory, while Egr3 is primarily essential for short-term memory. We also review our own recent findings from newly generated forebrain-specific conditional Egr2 mutant mice, which revealed that Egr2, as opposed to Egr1 and Egr3, is dispensable for several forms of learning and memory and on the contrary can act as an inhibitory constraint for certain cognitive functions. The studies reviewed here highlight the fact that Egr family members may have different, and in certain circumstances antagonistic functions in the adult brain.

Lamotrigine prevents MK801-induced alterations in early growth response factor-1 mRNA levels and immunoreactivity in the rat brain

MK801 (dizocilpine) induces selective neurotoxic effects in the retrosplenial cortex, ranging from neuronal vacuolization to irreversible neurodegeneration depending on the dose administered. Although lamotrigine prevents MK801-induced neuronal vacuolization in the retrosplenial cortex 4 h after injection, it is not clear whether lamotrigine attenuates the subsequent neurodegeneration that occurs 3-4 days later. Because early growth response factor-1 (egr-1) plays a key role in neurodegeneration and its expression is induced in the retrosplenial cortex following MK801 treatment, it is possible that lamotrigine may attenuate MK801-induced neurodegeneration via inhibition of egr-1 expression in the retrosplenial cortex. To address this issue, we treated rats with lamotrigine (10 or 20 mg/kg) followed by MK801 (2 mg/kg) and measured changes in the levels of egr-1 mRNA and immunoreactivity in the retrosplenial cortex and other brain regions 3 h later. We also evaluated the effects of these treatments on neurodegeneration 4 days following treatment using Fluoro-Jade B staining. MK801 treatment increased egr-1 mRNA and immunoreactivity in the restrosplenial, cingulate, entorhinal and piriform cortices, but decreased levels in hippocampal subfields. These MK801-induced changes in egr-1 expression were significantly inhibited by lamotrigine pretreatment. In addition, MK801-induced neurodegeneration in the retrosplenial cortex was partially blocked by lamotrigine pretreatment in a dose dependent manner. These results demonstrate that lamotrigine pretreatment prevents the MK801-induced upregulation of egr-1 expression in a region-selective manner, and suggest that this effect may contribute, in part, to the attenuation of MK801-induced neurodegeneration in the retrosplenial cortex.

Suppressive effect of clozapine but not haloperidol on the increases of neuropeptide-degrading enzymes and glial cells in MK-801-treated rat brain regions

MK-801, a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, produces neurotoxicity in adult rodent brain, and causes schizophrenia-like psychosis and cognitive dysfunction. Since neuropeptides and neuropeptide-degrading enzymes play important roles in cognitive function, we examined whether or not MK-801-induced schizophrenia-like psychosis is co-related with the changes of these enzymes in rat brain regions. In the present study, we investigated the effect of systemic treatment with MK-801 (0.5mg/kg) on neuropeptide-degrading enzymes, prolyl oligopeptidase (POP) and thimet oligopeptidase (EP 24.15), and glial marker proteins GFAP and CD11b in rat brain regions. The levels of POP and EP 24.15 activities increased significantly three days after treatment with MK-801 in the posterior cingulate/retrosplenial cortices (PC/RSC). Since atypical neuroleptic clozapine but not typical neuroleptic haloperidol prevents the MK-801-induced schizophrenia-like symptoms, we further examined the pretreated effects of the neuroleptics. Clozapine, but not haloperidol, significantly attenuated MK-801-induced changes in the levels of the neuropeptide-degrading enzymes. Immunohistochemical studies on GFAP and CD11b showed the increase in the PC/RSC of MK-801-treated rat brain and the pretreatment with clozapine suppressed these changes. Double immunostain experiments of EP 24.15 and GFAP antibodies demonstrated some co-localization of the neuropeptidase with astrocytes. The present findings suggest that change of neuropeptidases in the brain is in part correlated with changes of glial cells, and may play an important role in the control of schizophrenia-like psychotic disorders.

Acute D2/D3 dopaminergic agonism but chronic D2/D3 antagonism prevents NMDA antagonist neurotoxicity

BACKGROUND

Antagonists of the N-methyl-D-aspartate (NMDA) glutamate receptor, most likely by producing disinhibtion in complex circuits, acutely produce psychosis and cognitive disturbances in humans, and neurotoxicity in rodents. Studies examining NMDA Receptor Hypofunction (NRHypo) neurotoxicity in animals, therefore, may provide insights into the pathophysiology of psychotic disorders. Dopaminergic D2 and/or D3 agents can modify psychosis over days to weeks, suggesting involvement of these transmitter system(s).

METHODS

We studied the ability of D2/D3 agonists and antagonists to modify NRHypo neurotoxicity both after a one-time acute exposure and after chronic daily exposure.

RESULTS

Here we report that D2/D3 dopamine agonists, probably via D3 receptors, prevent NRHypo neurotoxicity when given acutely. The protective effect with D2/D3 agonists is not seen after chronic daily dosing. In contrast, the antipsychotic haloperidol does not affect NRHypo neurotoxicity when given acutely at D2/D3 doses. However, after chronic daily dosing of 1, 3, or 5 weeks, haloperidol does prevent NRHypo neurotoxicity with longer durations producing greater protection.

CONCLUSIONS

Understanding the changes that occur in the NRHypo circuit after chronic exposure to dopaminergic agents could provide important clues into the pathophysiology of psychotic disorders.

Clozapine but not haloperidol suppresses the changes in the levels of neuropeptides in MK-801-treated rat brain regions

Noncompetitive NMDA receptor antagonist (+)MK-801 is known to induce neurotoxicity and schizophrenia-like symptomatology where atypical neuroleptic clozapine is effective in contrast to typical neuroleptic, haloperidol. Although neuropeptides are implicated in memory and cognition, their roles in schizophrenia are not well understood. In the present study, we therefore examined the possible roles of neuropeptides, cholecystokinin (CCK) and somatostatin (SS) in the posterior cingulate/retrosplenial cortices (PC/RSC), frontal cortex, and hippocampus of a MK-801-induced schizophrenia-like model rat brain. This study further investigated the pretreated effect of atypical versus typical neuroleptics on the peptidergic system. SS mRNA and peptide levels significantly decreased in the PC/RSC and hippocampus but not in the frontal cortex 3 days after 0.5 mg/kg MK-801 treatment whereas CCK mRNA and peptide levels significantly decreased in all of the brain regions examined. Pretreatment with clozapine but not haloperidol completely recovered the changes in both mRNA and peptide levels of SS and CCK in those brain regions. These data suggest that peptidergic system in the brain presumably plays an important role in the control of negative schizophrenia.

Dose-response characteristics of ketamine effect on locomotion, cognitive function and central neuronal activity

The present dose-response study sought to determine the effects of subanesthetic dosages (4-16 mg/kg) of ketamine on locomotion, sensorimotor gating (PPI), working memory, as well as c-fos expression in various limbic regions implicated in the pathogenesis of schizophrenia. In addition, we examined whether ketamine-induced locomotion was influenced by the dark/light cycle. We found that ketamine increased locomotor activity in a dose dependent manner, but found no influence of the dark-light cycle. Additionally, ketamine dose-dependently interrupted PPI, resulting in prepulse facilitation at doses of 8 and 12 mg/kg. The dose of 12 mg/kg also induced impairments in working memory assessed by the discrete-trial delayed-alternation task. C-fos expression indicated that the dose-dependent behavioral effects of ketamine might be related to changes in the activity of limbic regions, notably hippocampus and amygdala.

A gene for neuronal plasticity in the mammalian brain: Zif268/Egr-1/NGFI-A/Krox-24/TIS8/ZENK?

Zif268 is a transcription regulatory protein, the product of an immediate early gene. Zif268 was originally described as inducible in cell cultures; however, it was later shown to be activated by a variety of stimuli, including ongoing synaptic activity in the adult brain. Recently, mice with experimentally mutated zif268 gene have been obtained and employed in neurobiological research. In this review we present a critical overview of Zif268 expression patterns in the naive brain and following neuronal stimulation as well as functional data with Zif268 mutants. In conclusion, we suggest that Zif268 expression and function should be considered in a context of neuronal activity that is tightly linked to neuronal plasticity.

Effects of NMDA-receptor antagonist treatment on c-fos expression in rat brain areas implicated in schizophrenia

1. The noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists produce behavioral responses that closely resemble both positive and negative symptoms of schizophrenia. These drugs also induce excitatory and neurotoxic effects in limbic cortical areas. 2. We have here mapped the brain areas which show increased activity in response to noncompetitive NMDA-receptor antagonist administration concentrating especially to those brain areas that have been suggested to be relevant in the pathophysiology of schizophrenia. 3. Rats were treated intraperitoneally with a NMDA-receptor antagonist MK801 and activation of brain areas was detected by monitoring the expression of c-fos mRNA by using in situ hybridization. 4. MK801 induced c-fos mRNA expression of in the retrosplenial, entorhinal, and prefrontal cortices. Lower c-fos expression was observed in the layer IV of the parietal and frontal cortex. In the thalamus, c-fos mRNA expression was detected in the midline nuclei and in the reticular nucleus but not in the dorsomedial nucleus. In addition, c-fos mRNA was expressed in the anterior olfactory nucleus, the ventral tegmental area, and in cerebellar granule neurons. 5. NMDA-receptor antagonist ketamine increased dopamine release in the parietal cortex, in the region where NMDA-receptor antagonist increased c-fos mRNA expression. 6. Thus, the psychotropic NMDA-receptor antagonist induced c-fos mRNA expression in most, but not all, brain areas implicated in the pathophysiology of schizophrenia. The high spatial resolution of in situ hybridization may help to define regions of interest for human imaging studies.

Identification of genes regulated by memantine and MK-801 in adult rat brain by cDNA microarray analysis

In this study, we monitored gene expression profiles using cDNA microarrays after an acute systemic administration of the high affinity N-methyl-D-aspartate (NMDA) uncompetitive antagonist MK-801 (1 mg/kg; 4 h), and the clinically used moderate affinity antagonist memantine (25 mg/kg; 4 h) in adult rat brains. From a microarray containing 1090 known genes, 13 genes were regulated by both treatments of which 12 were upregulated and one was downregulated. In addition, 28 and 34 genes were regulated (> or = 1.5- or < or = 0.67-fold change) by either memantine or MK-801, respectively. Genes commonly regulated by both treatments and not previously reported were confirmed by in situ hybridization (ISH) and include regenerating liver inhibitory factor-1 (RL/IF-1), GDP-dissociation inhibitor 1 (GDI-1), neural visinin Ca2+-binding protein 2 (NVP-2), neuromedin B receptor, and Na+/K+ transporting ATPase 2beta. ISH with memantine (5-50 mg/kg) revealed regulation of these genes in other cortical and hippocampal regions. RL/IF-1 induction occurred at 1 h and returned to basal levels by 8 h, consistent with the profile of an immediate early gene. Western blot analysis showed increases (approximately 30-65%) in GDI-1 protein present in both cytosolic and membrane fractions that were significant in the 84-kDa Rab bound form, suggesting that memantine influences Ras-like GTPase function. Genes regulated by a 5 mg/kg dose of memantine might be important in its therapeutic effects. These findings increase the number of known, differentially altered genes after treatment of uncompetitive NMDA receptor antagonists and suggest broader actions of these agents than previously realized.

The NMDA receptor hypofunction model of psychosis

Antagonists of the NMDA glutamate receptor, including phencyclidine (PCP), ketamine, and CGS-19755, produce cognitive and behavioral changes in humans. In rodents these agents produce a myriad of histopathological and neurochemical changes. Several lines of evidence suggest that a large number of these drug-induced effects are dose-dependent manifestations of the same general disinhibition process in which NMDA antagonists abolish GABAergic inhibition, resulting in the simultaneous excessive release of acetylcholine and glutamate. Progressive increases in the severity of NMDA receptor hypofunction (NRHypo) within the brain produce an increasing range of effects on brain function. Underexcitation of NMDA receptors, induced by even relatively low doses of NMDA antagonist drugs, can produce specific forms of memory dysfunction without clinically evident psychosis. More severe NRHypo can produce a clinical syndrome very similar to a psychotic schizophrenic exacerbation. Finally, sustained and severe NRHypo in the adult brain is associated with a form of neurotoxicity with well-characterized neuropathological features. In this paper several of these effects of NMDA antagonists and a likely mechanism responsible for producing them will be reviewed. In addition the possible role of NRHypo in the pathophysiology of idiopathic psychotic disorders will be considered.

Postnatal expression of the plasticity-related nerve growth factor-induced gene A (NGFI-A) protein in the superficial layers of the rat superior colliculus: Relation to N-methyl-d-aspartate receptor function

Immediate early gene expression in the CNS is induced by sensory stimulation and seems to be involved in long-term synaptic plasticity. We have used an immunohistochemical method to detect the nerve growth factor-induced gene A (NGFI-A) protein expression in the superficial layers of the rat superior colliculus during postnatal development. Our goal was to correlate the expression of this candidate plasticity protein with developmental events, especially the activity-dependent refinement of the retinocollicular and corticocollicular pathways. We have also investigated the N-methyl-D-aspartate (NMDA)-receptor dependence of the NGFI-A expression. Animals of various postnatal ages were used. Postnatal day (P) 12 and older animals were submitted to a protocol of dark adaptation followed by light stimulation. NGFI-A expression was never observed during the first 2 postnatal weeks. The first stained cells were observed at P15, 2 days after eye opening (P13). The highest number of stained cells was observed at the end of the third postnatal week (P22). Adult-like level of expression was reached at P30, since at this age, the number of stained cells was comparable to that found in adult rats (P90). Both P22 animals submitted to an acute treatment with MK-801 (i.p. injection) and adult animals submitted to chronic intracranial infusion of a MK-801 presented a clear decrease in the NGFI-A expression in response to light stimulation. These results suggest that the NGFI-A expression is dependent on the NMDA receptor activation, and the observed pattern of expression is in close agreement with previous descriptions of the changes in the NMDA receptor-mediated visual activity in the developing rat superior colliculus (SC). Our results suggest that the plasticity-related NGFI-A protein might play a role in the developmental plasticity of the superficial layers of the rat SC after eye opening.

Dose-dependent effect of MK-801 on the levels of neuropeptides processing enzymes in rat brain regions

The appropriate levels of neuropeptides and their processing enzyme activities are required to continue a normal cell life, and the dysfunction of these peptides and enzymes are responsible for many neuronal abnormalities. Systemic administration of (+) MK-801 (dizocilpine maleate), a noncompetitive N-methyl-[D]-aspartate (NMDA) receptor antagonist, causes both neuroprotective and neurotoxic activities depending on doses and conditions. In the present study, we investigated the dose dependent effect of (+) MK-801 on prolyl endopeptidase (PEP), endopeptidase EC 24.15 (EP 24.15) and beta-D-glucuronidase activities as well as the protein levels of EP 24.15 and neuron specific enolase (NSE) in the posterior cingulate/retrosplenial cortices (PC/RSC), hippocampus, frontal cortex and striatum of female rats 3 days after the treatment. The activity of PEP was significantly increased compared with controls (saline) in the PC/RSC at 1.0 and 5.0 mg/kg doses, and in the frontal cortex at 5.0 mg/kg dose. beta-D-Glucuronidase activity was dose-dependently increased in all brain regions examined. The activity of EP 24.15 was unchanged in all regions after the treatment, whereas the Western blot analysis for EP 24.15 showed the increased protein level in the PC/RSC. These results suggest that a low dose treatment with MK-801 causes neurotoxicity in the PC/RSC and hippocampus, and the high dose treatment causes neurotoxicity in all the brain regions examined.

Induction of heat shock protein (HSP)-70 in posterior cingulate and retrosplenial cortex of rat brain by dizocilpine and phencyclidine: lack of protective effects of sigma receptor ligands

The role of sigma receptors in the induction of heat shock protein (HSP)-70 by non-competitive N-methyl-Daspartate (NMDA) receptor antagonists (+)-MK-801 (dizocilpine) and phencyclidine (PCP) was studied. HSP-70 is induced in the posterior cingulate and retrosplenial cortex of rat brain 24 hours after a single administration of dizocilpine (1 mg/kg) or PCP (50 mg/kg). The induction of heat shock protein HSP-70 by dizocilpine or PCP was attenuated partially by pre-treatment with the antipsychotic drug haloperidol (3 mg/kg, i.p., 15 minutes previously). However, pre-treatment with high potent and selective sigma receptor ligands, 4-phenyl-4-(1-phenylbutyl)piperidine (4-PPBP, 3 mg/kg, i.p., 15 minutes previously) and N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride) (NE-100, 3 mg/kg, i.p., 15 minutes previously) did not alter the induction of HSP-70 by dizocilpine or PCP. These findings suggest that sigma receptors may not play a significant role in the induction of HSP-70 by non-competitive NMDA receptor antagonists dizocilpine and PCP, and that protective effects of haloperidol on induction of HSP-70 protein by dizocilpine or PCP may be due to other effect(s) except sigma receptors.

NMDA-antagonist MK-801-induced neuronal degeneration in Wistar rat brain detected by the Amino-Cupric-Silver method

The neurotoxic effect following a single intraperitoneal injection of MK-801 (10 mg/kg) in adult female Wistar rats at different survival times was studied with the 1994 version of de Olmos' Amino-Cupric-Silver (A-Cu-Ag) technique for detection of neural degeneration. In addition to the well documented somatodendritic degeneration observable in cortical olfactory structures, dentate gyrus, retrosplenial and sensory cortices, we detected this type of neuronal degeneration also in the main olfactory bulb, motor and anterior cingulate cortices, thalamus and cerebellum. Terminal degeneration, not reported by previous authors, was detected in cortical olfactory structures, hippocampal formation, sensory, infralimbic, prelimbic, agranular insular, ectorhinal, perirhinal and lateral orbital cortices. These results demonstrate that the A-Cu-Ag procedure is more efficient than other silver methods for detecting the degeneration induced by MK-801. In fact, the use of the A-Cu-Ag method has made it possible to infer the connectional relations between the damaged cell bodies and corresponding terminal degeneration. Our results also indicate that the A-Cu-Ag technique may be a suitable method for the staining of neurons undergoing apoptotic-like degeneration. The probable degenerative mechanism of MK-801 in the main olfactory system is discussed.

Inhibitory effect of propofol on ketamine-induced c-Fos expression in the rat posterior cingulate and retrosplenial cortices is mediated by GABAA receptor activation

BACKGROUND

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, including ketamine, have psychotomimetic activities and cause neuronal damage in the posterior cingulate and retrosplenial cortices (PC/RS), which are suggested to be the brain regions responsible for their psychotomimetic activities. We previously demonstrated that ketamine induced marked c-Fos (c-fos protein) expression in the rat PC/RS, which was inhibited by propofol, and the expression was closely related to ketamine-induced abnormal behavior. In the present study, we investigated whether the inhibition by propofol was mediated by GABAA receptor receptor activation.

METHODS

Using Wistar rats, propofol alone, propofol with bicuculline or propofol with flumazenil was injected intravenously and then continuously infused. Fifteen minutes later, 100 mg kg-1 of ketamine or normal saline was injected intraperitoneally. Two hours after the ketamine or saline injection, the brain was extracted and brain sections were prepared, and c-Fos expression was detected using immunohistochemical methods.

RESULTS

Ketamine induced marked c-Fos expression in the PC/RS (171 +/- 9/0.4 mm2), which was significantly inhibited by propofol (5 +/- 5/0.4 mm2). The inhibition by propofol was disinhibited dose-dependently by both bicuculline (0.5 and 1.0 mg kg-1 bicuculline groups: 46 +/- 15 and 143 +/- 16, respectively) and flumazenil (0.1 and 1.0 mg kg-1 flumazenil groups: 79 +/- 6 and 130 +/- 15, respectively).

CONCLUSION

These results demonstrate that the inhibitory effect of propofol on ketamine-induced c-Fos expression in the PC/RS is mediated by GABAA receptor activation, and suggests that ketamine-induced psychoneuronal adverse effects may be suppressed by propofol via the activation of GABAA receptors.

Basal EGR-1 (zif268, NGFI-A, Krox-24) expression in developing striatal patches: role of dopamine and glutamate

Egr-1 (also known as zif268, NGFI-A, or Krox 24) is an immediate-early gene of the zinc finger family that exhibits relatively high constitutive expression in the brain, as well as inducibility by seizure activity, stimulants, and salient physiological stimuli. Immunocytochemical detection of the Egr-1 protein in the developing striatum revealed that in the late prenatal and early postnatal period, Egr-1 protein was expressed selectively in patches of striatal neurons under basal conditions. Egr-1 immunoreactivity was co-expressed with known markers of striatal patch neurons, indicating that expression was greatest in the striatal patch compartment. This patchy expression of Egr-1 transitioned to a nearly homogeneous pattern of Egr-1-immunoreactive cells by postnatal day 10, at which time most striatal neurons appeared to be Egr-1-immunoreactive. The dopamine D1 antagonist SCH23390 (0.5-1.0 mg/kg) reduced Egr-1 expression during the first week postnatal, but it was no longer effective at postnatal day 10. On the other hand, the noncompetitive NMDA antagonist MK-801 (0.5-1.0 mg/kg) became more effective at reducing Egr-1 expression with age. Neonatal destruction of nigrostriatal dopamine afferents reduced the basal pattern of Egr-1 expression for 2-3 days after the lesion, but then Egr-1 expression returned. Thus, Egr-1 expression in the developing striatum appears to be driven first by dopaminergic afferents, and then later in development by excitatory glutamatergic afferents.

The anesthetics propofol and ketamine inhibit cocaine-induced egr-1 gene expression in rat forebrain

Acute cocaine injection to rats is known to induce the expression of immediate early genes in the forebrain, the effect being primarily mediated by the dopaminergic system. We examined the effect of the anesthetics ketamine and propofol on cocaine-induced egr-1 mRNA expression. Using in situ hybridization, we show that both compounds did not induce egr-1 gene by themselves, but were able to dose-dependently reduce cocaine-induced egr-1 mRNA synthesis in the nucleus accumbens, caudate-putamen and cingulate cortex. Our data suggest that in addition to glutamate NMDA receptors, propofol may act via GABA(A) receptors or ion channels.

Effects of MK-801 and electroconvulsive shock on c-Fos expression in the rat hippocampus and frontal cortex

Both the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and electroconvulsive shock (ECS) have been reported to induce c-Fos in rat brain. However, the former has anticonvulsant and psychotomimetic effects and the latter has proconvulsant and antipsychotic effects. To understand the mode of action of these treatments, the authors examined the effect of MK-801 and the interaction between MK-801 and ECS on the induction of c-Fos in the rat hippocampus and frontal cortex. MK-801 induced c-Fos in these brain regions in a nonlinear dose-response relationship. Maximum effect was achieved with 1-2 mg/kg of MK-801. The level of c-Fos paralleled animal hyperkinetic behavior, suggesting the role of c-Fos in the induced psychotomimetic behaviors. Pretreatment with MK-801 dose-dependently attenuated both the seizures and c-Fos expression by ECS. However, at an MK-801 pretreatment dose of 8 mg/kg, which completely blocked ECS-induced seizure, the induction of c-Fos was not completely blocked, suggesting non-NMDA mediated pathways of the induction of c-Fos by ECS.

Expression of c-Fos, ICER, Krox-24 and JunB in the whisker-to-barrel pathway of rats: time course of induction upon whisker stimulation by tactile exploration of an enriched environment

Modified tactile information has been shown to induce adaptive plasticity in the somatosensory cortex of rat. The cellular mechanisms resulting in plastic neuronal responses, however, are largely unknown. Inducible transcription factors have been proposed as one major link in the cascade from modified input to altered neuronal structure and function. We investigated the spatial and temporal patterns of transcription factor induction in the rat whisker-to-barrel pathway by placing the animals in a novel, enriched environment while having clipped sets of whiskers on one side of the face. Such stimulation resulted not only in a specific c-Fos induction in brainstem barrelettes and thalamic barreloids, but also in the barrel-related cortical columns, each with different time courses. In the barrel cortex, c-Fos and Krox-24 immunostaining showed a rapid induction with peak levels at 1 h and a return to basal levels after 14 h. JunB was induced after 1 h of exploration, declined at 6 h and returned to basal levels after this time point. The inducible cyclic AMP early repressor (ICER), a transcription factor of the cAMP signaling pathway, showed a maximum after 6 h, decreased slowly, but elevated levels were still detectable after 5 days. Our data demonstrate that upon whisker stimulation by exploration of a novel, enriched environment, (i) subcortical relay stations in the whisker-to-barrel pathway are able to express elevated levels of c-Fos and (ii) in the barrel cortex c-Fos, JunB, Krox-24 and ICER are differentially regulated in the temporal domain.

Cerebral glucose utilization in transgenic mice overexpressing heat shock protein 70 is altered by dizocilpine

Heat shock protein (HSP70), a member of the 70 kDa HSP superfamily, has been widely implicated in the cellular stress response to numerous insults. HSP70 may be a significant factor in cell survival following stresses such as cerebral ischaemia. The precise mechanisms by which HSP70 facilitates cell survival remain unclear. The aim of this study was to ascertain whether any differences in local cerebral glucose utilization (LCGU) existed between transgenic mice overexpressing HSP70 (HSP70 Tg) and wild- type littermate (WT) mice. LCGU was assessed using (14)C-2-deoxyglucose in HSP70 Tg and WT mice under basal conditions (intraperitoneal injection of saline) and during metabolic activation produced by NMDA receptor blockade (intraperitoneal injection of dizocilpine, 1 mg/kg). No significant alterations in LCGU were observed between saline injected HSP70 Tg and WT mice in any of the 35 brain regions analyzed. Dizocilpine injection produced significant heterogeneous alterations in LCGU in HSP70 Tg mice (24 of 35 brain regions) and in WT mice (22 of 35 brain regions) compared with saline injected mice. The distribution of altered LCGU produced by dizocilpine was similar in HSP70 Tg and WT mice. However in five brain regions, dizocilpine injected HSP70 Tg mice displayed significantly altered LCGU compared to dizocilpine injected WT mice (anterior thalamic nucleus +27%, dorsal CA1 stratum lacunosum molecularae +22%, dorsal CA1 stratum oriens + 14%, superior olivary body -26%, and the nucleus of the lateral lemniscus -16%). These data highlight that while overexpression of HSP70 transgene does not significantly alter LCGU in the basal state, mice overexpressing the HSP70 transgene respond differently to metabolic stress produced by NMDA receptor blockade in some important brain regions.

Ketamine-induced c-Fos expression in the mouse posterior cingulate and retrosplenial cortices is mediated not only via NMDA receptors but also via sigma receptors

Ketamine induces marked c-fos expression in the posterior cingulate and retrosplenial cortices (PC/RS). We investigated whether NMDA and/or sigma receptors were involved in the c-Fos expression. The number of Fos-LI positive boutons in NMDA receptor knockout mice was significantly lower than that in wild-type mice. Rimcazole but not haloperidol significantly suppressed the c-Fos expression. The results indicate that the ketamine-induced c-Fos expression is mediated not only via NMDA receptors but also via sigma receptors.

Sexually dimorphic effects of morphine and MK-801: sex steroid-dependent and -independent mechanisms

Rats show gender differences in responses to morphine and the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801); the role of sex steroids in mediating these differences is unclear. We tested the overall hypothesis that circulating gonadal steroids determine the gender differences in morphine- and MK-801-induced behavior and c-Fos expression. Morphine caused a greater expression of c-Fos in the striatum of intact males than of that females, which was independent of sex steroids. MK-801 completely inhibited morphine-induced c-Fos in intact females but only caused partial inhibition in intact males; castrated males showed complete inhibition, which was reversed by testosterone, but gonadal steroids had no effect on this response in females. In thalamus, there was a large sex difference in the response to MK-801 that was independent of gonadal steroids. Behavioral responses to morphine were greater in males, but responses to MK-801 were greater in females; both were sex steroid independent. These findings show significant sex differences in response to morphine and MK-801 that are mediated by sex steroid-dependent and -independent mechanisms, which may be important in treatment outcomes of drug addiction.

Expression of c-Fos, Fos B, Jun B, and Zif268 transcription factor proteins in rat barrel cortex following apomorphine-evoked whisking behavior

Apomorphine-evoked expression of transcription factor proteins: c-Fos, Fos B, Jun B, and Zif268 (also named Krox-24, NGFI-A, Egr-1), was investigated in rat somatosensory (barrel) cortex. The effect of the N-methyl-D-aspartate receptor antagonist MK-801 on their expression was also analyzed. Apomorphine is a dopamine receptor agonist, eliciting motor activity, including enhanced whisking leading to the activation of vibrissae representation in the barrel cortex. Rats had their whiskers clipped on one side of the snout. The Zif268 levels were markedly reduced by this procedure alone. In contrast, apomorphine (5.0 mg/kg) evoked marked c-Fos elevation, less pronounced changes in Jun B and Zif268 and no change in Fos B. The greatest apomorphine-evoked c-Fos accumulation was observed in layers IV and V/VI of non-deprived barrel cortex and was not significantly influenced by MK-801 injection at 0.1 mg/kg. A higher dose of MK-801 (1.0 mg/kg) produced abnormalities in locomotor behavior and diminished c-Fos levels on the non-deprived side to the ones observed in the sensory stimulus-deprived cortex. We conclude that the response of the somatosensory cortex is selective with respect to both the gene activated and its cortical layer localization. Furthermore, sensory stimulation provides a major but not the only component to apomorphine-evoked barrel cortex gene activation.