Low levels of muscarinic M1 receptor-positive neurons in cortical layers III and V in Brodmann areas 9 and 17 from individuals with schizophrenia.

BACKGROUND: Results of neuroimaging and postmortem studies suggest that people with schizophrenia may have lower levels of muscarinic M1 receptors (CHRM1) in the cortex, but not in the hippocampus or thalamus. Here, we use a novel immunohistochemical approach to better understand the likely cause of these low receptor levels. METHODS: We determined the distribution and number of CHRM1-positive (CHRM1+) neurons in the cortex, medial dorsal nucleus of the thalamus and regions of the hippocampus from controls (n = 12, 12 and 5, respectively) and people with schizophrenia (n = 24, 24 and 13, respectively). RESULTS: Compared with controls, levels of CHRM1+ neurons in people with schizophrenia were lower on pyramidal cells in layer III of Brodmann areas 9 (-44%) and 17 (-45%), and in layer V in Brodmann areas 9 (-45%) and 17 (-62%). We found no significant differences in the number of CHRM1+ neurons in the medial dorsal nucleus of the thalamus or in the hippocampus. LIMITATIONS: Although diagnostic cohort sizes were typical for this type of study, they were relatively small. As well, people with schizophrenia were treated with antipsychotic drugs before death. CONCLUSION: The loss of CHRM1+ pyramidal cells in the cortex of people with schizophrenia may underpin derangements in the cholinergic regulation of GABAergic activity in cortical layer III and in cortical/subcortical communication via pyramidal cells in layer V.

Low levels of muscarinic M1 receptor-positive neurons in cortical layers III and V in Brodmann areas 9 and 17 from individuals with schizophrenia.

BACKGROUND: Results of neuroimaging and postmortem studies suggest that people with schizophrenia may have lower levels of muscarinic M1 receptors (CHRM1) in the cortex, but not in the hippocampus or thalamus. Here, we use a novel immunohistochemical approach to better understand the likely cause of these low receptor levels. METHODS: We determined the distribution and number of CHRM1-positive (CHRM1+) neurons in the cortex, medial dorsal nucleus of the thalamus and regions of the hippocampus from controls (n = 12, 12 and 5, respectively) and people with schizophrenia (n = 24, 24 and 13, respectively). RESULTS: Compared with controls, levels of CHRM1+ neurons in people with schizophrenia were lower on pyramidal cells in layer III of Brodmann areas 9 (-44%) and 17 (-45%), and in layer V in Brodmann areas 9 (-45%) and 17 (-62%). We found no significant differences in the number of CHRM1+ neurons in the medial dorsal nucleus of the thalamus or in the hippocampus. LIMITATIONS: Although diagnostic cohort sizes were typical for this type of study, they were relatively small. As well, people with schizophrenia were treated with antipsychotic drugs before death. CONCLUSION: The loss of CHRM1+ pyramidal cells in the cortex of people with schizophrenia may underpin derangements in the cholinergic regulation of GABAergic activity in cortical layer III and in cortical/subcortical communication via pyramidal cells in layer V.

Lower cortical serotonin 2A receptors in major depressive disorder, suicide and in rats after administration of imipramine.

We have attempted to replicate studies showing higher levels of serotonin 2A receptors (HTR2A) in the cortex of people with mood disorders and to determine the effects of treating rats with antidepressant drugs on levels of that receptor. In situ [3H]ketanserin binding and autoradiography was used to measure levels of HTR2A in Brodmann's area (BA) 46 and 24 from people with major depressive disorders (MDD, n = 16), bipolar disorders (BD, n = 14) and healthy controls (n = 14) as well as the central nervous system (CNS) of rats (20 per treatment arm) treated for 10 or 28 d with fluoxetine (10 mg/kg/d) or imipramine (20 mg/kg/d). Compared with controls, HTR2A were lower in BA 24, but not BA 46, from people with MDD (p = 0.005); HTR2A were not changed in BD. Levels of HTR2A were lower in BA 24 (p = 0.007), but not BA 46, from people who had died by suicide. Finally, levels of HTR2A were lower in the CNS of rats treated with imipramine, but not fluoxetine, for 28 d, but not 10 d. From our current and previous data we conclude cortical HTR2A are lower in schizophrenia, MDD, people with mood disorders who died by suicide, rats treated with some antipsychotic or some antidepressant drugs. As levels of cortical HTR2A can be affected by the aetiologies of different disorders and mechanisms of action of different drugs, a better understanding of how such changes can occur needs to be elucidated.

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.

Repeated electroconvulsive seizure induces c-Myc down-regulation and Bad inactivation in the rat frontal cortex.

Repeated electroconvulsive seizure (ECS), a model for electroconvulsive therapy (ECT), exerts neuroprotective and proliferative effects in the brain. This trophic action of ECS requires inhibition of apoptotic activity, in addition to activation of survival signals. c-Myc plays an important role in apoptosis of neurons, in cooperation with the Bcl-2 family proteins, and its activity and stability are regulated by phosphorylation and ubiquitination. We examined c-Myc and related proteins responsible for apoptosis after repeated ECS. In the rat frontal cortex, repeated ECS for 10 days reduced the total amount of c-Myc, while increasing phosphorylation of c-Myc at Thr58, which reportedly induces degradation of c-Myc. As expected, ubiquitination of both phosphorylated and total c-Myc increased after 10 days ECS, suggesting that ECS may reduce c-Myc protein level via ubiquitination-proteasomal degradation. Bcl-2 family proteins, caspase, and poly(ADP-ribose) polymerase (PARP) were investigated to determine the consequence of down-regulating c-Myc. Protein levels of Bcl-2, Bcl-X(L), Bax, and Bad showed no change, and cleavage of caspase-3 and PARP were not induced. However, phosphorylation of Bad at Ser-155 and binding of Bad to 14-3-3 increased without binding to Bcl-X(L) after repeated ECS, implying that repeated ECS sequesters apoptotic Bad and frees pro-survival Bcl-XL. Taken together, c-Myc down-regulation via ubiquitination-proteasomal degradation and Bad inactivation by binding to 14-3-3 may be anti-apoptotic mechanisms elicited by repeated ECS in the rat frontal cortex. This finding further supports the trophic effect of ECS blocking apoptosis as a possible therapeutic effect of ECT.

The effect of MK-801 on mTOR/p70S6K and translation-related proteins in rat frontal cortex.

In experimental animals, including rats, MK-801 produces characteristic behavioural changes that model schizophrenia. It has been hypothesized that these changes accompany long-term synaptic changes, which require protein neosynthesis. We observed the effect of MK-801 on the "mammalian target of rapamycin" (mTOR)/70-kDa ribosomal protein S6 kinase (p70S6K) pathway that regulates protein synthesis in the rat frontal cortex. A single injection of MK-801 (0.5, 1, or 2mg/kg) induced an acute increase in the phosphorylation of Akt (Ser-473) eIF4E-binding protein (4E-BP1) (Thr-37/46) and p70S6K (Thr-389). In contrast, after repeated treatment with MK-801 (1mg/kg for 5 or 10 days), the phosphorylation of Akt (Ser-473), mTOR (Ser-2481), 4E-BP1 (Thr-37/46), p70S6K (Thr-389), and S6 (Ser-240/244) increased. Thus, proteins in the mTOR/p70S6K pathway are modulated in chronic MK-801 animal models. These findings may suggest that repeated MK-801 treatment activates the signal transduction pathways involved in the initiation of protein synthesis in the rat frontal cortex.

Haloperidol and clozapine differentially regulate signals upstream of glycogen synthase kinase 3 in the rat frontal cortex.

Glycogen synthase kinase 3 (GSK3) was recently suggested to be a potential target of psychotropics used in psychiatric illnesses such as schizophrenia and bipolar disorder. Relevant studies have found that antipsychotic drugs regulate GSK3 activity via an increase in either inhibitory serine phosphorylation or amount of GSK3 after acute or subchronic treatment. Recent evidence shows that GSK3 is regulated by dopaminergic or serotonergic systems implicated in the pathophysiology and treatment mechanisms of schizophrenia and bipolar disorder. Therefore, antipsychotics may regulate GSK3 via antagonizing dopaminergic or serotonergic activity. However, the signaling pathway that is involved in GSK3 regulation by dopaminergic or serotonergic systems has not been well established. Haloperidol is a typical antipsychotic with potent dopamine D(2) receptor antagonism. Clozapine is an atypical antipsychotic with potent serotonin 5HT(2) receptor antagonism. We injected rats with haloperidol or clozapine and examined the phosphorylation and amount of GSK3alpha/beta and its well-known upstream regulators Akt and Dvl in the rat frontal cortex by Western blotting. Both haloperidol and clozapine induced Ser21/9 phosphorylation of GSK3GSK3alpha/beta. Haloperidol increased the Ser473 phosphorylation of Akt transiently, whereas clozapine maintained the increase for 1 h. Haloperidol did not affect the phosphorylation and amount of Dvl, whereas clozapine increased both phosphorylation and the amount of Dvl. Our results suggest that GSK3 activity may be regulated by both typical and atypical antipsychotics and that Akt or Dvl, depending on the D(2)- or 5HT(2)- receptor antagonism properties of typical and atypical antipsychotics, mediate the regulation differently.

The distribution of muscarinic M1 receptors in the human hippocampus.

The muscarinic M1 receptor plays a significant role in cognition, probably by modulating information processing in key regions such as the hippocampus. To understand how the muscarinic M1 receptor achieves these functions in the hippocampus, it is critical to know the distribution of the receptor within this complex brain region. To date, there are limited data on the distribution of muscarinic M1 receptors in the human hippocampus which may also be confounded because some anti-muscarinic receptor antibodies have been shown to lack specificity. Initially, using Western blotting and immunohistochemistry, we showed the anti-muscarinic M1 receptor antibody to be used in our study bound to a single 62kDa protein that was absent in mice lacking the muscarinic M1 receptor gene. Then, using immunohistochemistry, we determined the distribution of muscarinic M1 receptors in human hippocampus from 10 subjects with no discernible history of a neurological or psychiatric disorder. Our data shows the muscarinic M1 receptor to be predominantly on pyramidal cells in the hippocampus. Muscarinic M1 receptor positive cells were most apparent in the deep polymorphic layer of the dentate gyrus, the pyramidal cell layer of cornu ammonis region 3, the cellular layers of the subiculum, layer II of the presubiculum and layer III and V of the parahippocampal gyrus. Positive cells were less numerous and less intensely stained in the pyramidal layer of cornu ammonis region 2 and were sparse in the molecular layer of the dentate gyrus as well as cornu ammonis region 1. Although immunoreactivity was present in the granular layer of the dentate gyrus, it was difficult to identity individual immunopositive cells, possibly due to the density of cells. This distribution of the muscarinic M1 receptors in human hippocampus, and its localisation on glutamatergic cells, would suggest the receptor has a significant role in modulating excitatory hippocampal neurotransmission.

Activation of Cdk2-pRB-E2F1 cell cycle pathway by repeated electroconvulsive shock in the rat frontal cortex.

BACKGROUND: Recent reports indicate that repeated electroconvulsive shock (ECS) induces cortical cell proliferation, suggesting the possibility that ECS may activate cell cycle progression in the rat brain cortex. METHODS: Sprague-Dawley rats (150-200g) were divided into four treatment groups and then given sham treatment or ECS treatment for 1, 5, and 10 days, respectively. The activity of cyclin-dependent kinase 2 (Cdk2), phosphorylation, and total protein amount of cyclin D1, cyclin E, pocket retinoblastoma family of protein (pRB), and E2F1 were analyzed in the rat cerebral cortex. RESULTS: The activity of Cdk2, the protein amount of pRB, Ser795 phosphorylation of pRB, and the protein amount of E2F1 were all increased compared with the sham-treated control subjects, and these increases were enhanced with the increasing number of ECS. In contrast, the protein amounts of Cdk2, cyclin D1, and cyclin E were not changed by repeated ECS. CONCLUSIONS: The Cdk2-pRB-E2F1 cell cycle pathway is activated by repeated ECS in the rat frontal cortex.

Implication of reactive oxygen species, ERK1/2, and p38MAPK in sodium salicylate-induced heat shock protein 72 expression in C6 glioma cells.

Sodium salicylate, one of anti-inflammatory agents, is known to partially induce the heat shock response: it stimulates the DNA-binding of heat shock factor 1 (HSF1) without inducing heat shock gene expression. Here we show that when C6 glioma cells are recovered from sodium salicylate treatment, they highly induce heat shock protein 72 (HSP72), but not HSP73 and HSP90, demonstrating that salicylate-induced inert HSF1 can be fully activated into a transcriptionally competent form by sodium salicylate recovery (SR)-specific mechanism. Fluorescent analysis using 2',7'-dichlorodihydrofluorescein diacetate revealed that sodium salicylate enhanced reactive oxygen species (ROS) production. N-acetyl-L-cysteine (NAC, a ROS scavenger) completely suppressed SR-induced HSP72 synthesis and HSP72 promoter-driven CAT reporter gene transcription as well as salicylate-induced HSF1-DNA binding, indicating a critical role(s) of ROS in the SR-induced HSP72 gene regulation. We also show that treatment of C6 cells with sodium salicylate activated p38MAPK and inactivated ERK1/2 in a ROS-independent manner and activities of these protein kinases returned during recovery period to the control level. Inhibiting p38MAPK and ERK1/2 with the p38MAPK inhibitors (SB203580 and SB202190) and the MEK1/2 inhibitor (PD98059 and U0126) or with expression of dominant negative p38MAPK and ERK1/2 abolished SR-induced HSP72 synthesis and HSP70 promoter-driven CAT activity. However, sodium salicylate-induced HSF1-DNA binding was not affected by the p38MAPK inhibitor or the MEK1/2 inhibitor. These findings suggest that sodium salicylate partially activates HSF1 via ROS production and p38MAPK activation and the salicylate-induced inert HSF1 can be fully activated into a transcriptionally competent form by the ERK1/2 signaling pathways that are activated independently of ROS during SR.

The effects of clozapine on the GSK-3-mediated signaling pathway.

We investigated the effect of 10 microM clozapine on the activity of glycogen synthase kinase-3beta (GSK-3beta) and its upstream and downstream molecules in SH-SY5Y human neuroblastoma cells. Clozapine activates both Akt- and Dvl-mediated phosphorylation of GSK-3beta through phosphorylation at Ser9, and increased total cellular and intranuclear levels of beta-catenin. Pretreatment with the specific inhibitor of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway, LY294002 (20 microM), prevented the phosphorylation of Akt but did not affect the phosphorylation of GSK-3beta. These results suggest that clozapine regulates the phosphorylation of GSK-3beta through Wnt signal pathways involving Dvl upstream but not through the PI3K-Akt pathway in SH-SY5Y cells.

An investigation of the factors that regulate muscarinic receptor expression in schizophrenia.

We previously identified a group of subjects with schizophrenia who, on average, have a 75% decrease in cholinergic receptor, muscarinic 1 (CHRM1) in Brodmann's area (BA) 9. To extend this finding, we determined i) if the decrease in CHRM1 was present in another functionally related CNS region (BA6), ii) whether the marked decrease in CHRM1 was accompanied by changes in levels of other CHRMs and iii) potential factors responsible for the decreased CHRM1 expression. We measured CHRM1 and CHRM3 using in situ radioligand binding with [(3)H]pirenzepine and [(3)H]4-DAMP respectively in BA6 from 20 subjects with schizophrenia who had low levels of CHRM1 in BA9 (SzLow[(3)H]PZP), 18 subjects with schizophrenia whose levels of CHRM1 were similar to controls (SzNormal[(3)H]PZP) and 20 control subjects. Levels of CHRM1, 3 and 4 mRNA were measured using qPCR and levels of the transcription factors, SP1 and SP3, were determined using Western blots. In BA6, the density of [(3)H]pirenzepine binding was decreased in subjects with SzLow[(3)H]PZP (p<0.001) compared to controls. The density of [(3)H]4-DAMP binding, levels of CHRM1, 3 and 4 mRNA and levels of SP1 and SP3 was not significantly different between the three groups. This study shows that the previously identified decrease in CHRM1 expression is not confined to the dorsolateral prefrontal cortex but is present in other cortical areas. The effect shows some specificity to CHRM1, with no change in levels of binding to CHRM3. Furthermore, this decrease in CHRM1 does not appear to be associated with low levels of CHRM1 mRNA or to simply be regulated by the transcription factors, SP1 and SP3, suggesting that other mechanisms are responsible for the decreased CHRM1 in these subjects.

Potential molecular and cellular mechanism of psychotropic drugs.

Psychiatric disorders are among the most debilitating of all medical illnesses. Whilst there are drugs that can be used to treat these disorders, they give sub-optimal recovery in many people and a significant number of individuals do not respond to any treatments and remain treatment resistant. Surprisingly, the mechanism by which psychotropic drugs cause their therapeutic benefits remain unknown but likely involves the underlying molecular pathways affected by the drugs. Hence, in this review, we have focused on recent findings on the molecular mechanism affected by antipsychotic, mood stabilizing and antidepressant drugs at the levels of epigenetics, intracellular signalling cascades and microRNAs. We posit that understanding these important interactions will result in a better understanding of how these drugs act which in turn may aid in considering how to develop drugs with better efficacy or increased therapeutic reach.

Role of MKP-1 (DUSP1) in clozapine-induced effects on the ERK1/2 signaling pathway in the rat frontal cortex.

RATIONALE: Clozapine affects the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway in the brain, which plays an important role in its antipsychotic action. However, previous findings are inconsistent, and related molecular mechanisms require further clarification. OBJECTIVES: Time- and dose-dependent effects of clozapine on the ERK1/2 pathway and its regulatory mechanism were investigated in rat frontal cortex. METHODS AND RESULTS: At 15, 30, 60, and 120 min after intraperitoneal injection of clozapine (5, 10, and 20 mg/kg), changes in ERK1/2, its upstream canonical kinases (Raf1 and mitogen-activated protein kinase kinase 1/2 [MEK1/2]), and its downstream molecule (p90 ribosomal S6 kinase [p90RSK]) were investigated in rat frontal cortex. At 15 min, p-Raf1, p-MEK1/2, p-ERK1/2, and p-p90RSK all increased dose-dependently. At 30 min, p-ERK1/2 and p-p90RSK showed no significant changes, while dose-dependent increases in p-Raf1 and p-MEK1/2 were found. At 60 and 120 min, although p-ERK1/2 and p-p90RSK decreased, increases in p-Raf1 and p-MEK1/2 were maintained. A clozapine-induced reduction in ERK1/2 phosphorylation was evident at both tyrosine and threonine residues, suggesting the involvement of dual specificity phosphatases (DUSPs; mitogen-activated protein kinase phosphatases [MKPs]). mRNA expression of seven Dusps that can dephosphorylate ERK1/2 were examined; Mkp-1 (Dusp1) mRNA increased following clozapine treatment. Moreover, MKP-1 protein and phosphatase activity increased, and binding of MKP-1 to ERK1/2 was also upregulated by clozapine administration. CONCLUSIONS: In rat frontal cortex, clozapine regulates ERK1/2 phosphorylation via MKP-1, which induces uncoupling between Raf1-MEK1/2 and ERK1/2-p90RSK activity. These findings suggest an important role of MKP-1 in the mechanism of action of clozapine.

The neurobiology of APOE in schizophrenia and mood disorders.

APOE is a major component of several lipoproteins. In addition to its role as a lipid transport protein APOE also serves a dual role as a glial derived, synaptic signalling molecule and thought to play an important role in synaptic plasticity and cognition. Polymorphisms within the APOE gene have been associated with the incidence of Alzheimer's disease. In light of the similarities in the cognitive deficits experienced in both Alzheimer's disease and schizophrenia as well as the comorbidity of depression in Alzheimer's disease, aberrant APOE signalling has been implicated in the pathologies of schizophrenia and mood disorders. The schizophrenia candidate gene, reelin, also shares common receptors with APOE, further supporting a role for APOE in the pathology of these disorders. This review will summarise the current understanding of the involvement of APOE and its receptors in the symptomatology and pathology of schizophrenia and mood disorders and the implications of this involvement for drug treatment.

Haloperidol regulates the phosphorylation level of the MEK-ERK-p90RSK signal pathway via protein phosphatase 2A in the rat frontal cortex.

Haloperidol, a classical antipsychotic drug, affects the extracellular signal-regulated kinase (ERK) pathway in the brain. However, findings are inconsistent and the mechanism by which haloperidol regulates ERK is poorly understood. Therefore, we examined the ERK pathway and the related protein phosphatase 2A (PP2A) in detail after haloperidol administration. Haloperidol (0.5 and 1 mg/kg) induced biphasic changes in the phosphorylation level of mitogen-activated protein kinase kinase (MEK), ERK, and p90 ribosomal S6 kinase (p90RSK) without changing Raf-1 phosphorylation. Fifteen minutes after haloperidol administration, MEK-ERK-p90RSK phosphorylation increased, whilst PP2A activity decreased. At 60 min, the reverse was observed and the binding of PP2A to MEK and ERK increased. Higher dosages of haloperidol (2 and 4 mg/kg), affected neither MEK-ERK-p90RSK phosphorylation nor PP2A activity. Accordingly, PP2A regulates acute dose- and time-dependent changes in MEK-ERK-p90RSK phosphorylation after haloperidol treatment. These findings suggest the involvement of a dephosphorylating mechanism in the acute action of haloperidol.

The effects of repeated administrations of MK-801 on ERK and GSK-3beta signalling pathways in the rat frontal cortex.

Repeated administrations of NMDA receptor antagonists induce behavioural changes which resemble the symptoms of schizophrenia in animals. ERK and GSK-3beta associated signalling pathways have been implicated in the pathogenesis of psychosis and in the action mechanisms of various psychotropic agents. Here, we observed the phosphorylations of ERK and GSK-3beta and related molecules in the rat frontal cortex after repeated intraperitoneal injections of MK-801, over periods of 1, 5, and 10 d. Repeated treatment with 0.5, 1, and 2 mg/kg MK-801 increased the phosphorylation levels of the MEK-ERK-p90RSK and Akt-GSK-3beta pathways and concomitantly and significantly increased CREB phosphorylation in the rat frontal cortex. However, single MK-801 treatment did not induce these significant changes. In addition, the immunoreactivities of HSP72, Bax, and PARP were not altered, which suggests that neuronal damage may not occur in the rat frontal cortex in response to chronic MK-801 treatment. These findings suggest that chronic exposure to MK-801 may induce pro-survival and anti-apoptotic activity without significant neuronal damage in the rat frontal cortex. Moreover, this adaptive change might be associated with the psychotomimetic action of MK-801.

The effects of MK-801 on the phosphorylation of Ser338-c-Raf-MEK-ERK pathway in the rat frontal cortex.

MK-801 induces psychotomimetic behavioural changes in animals. ERKs play an important role in the pathogenesis of schizophrenia and in the action of antipsychotics and psychotomimetics. We observed phosphorylation of ERK-signalling-pathway-associated molecules in the rat frontal cortex and their association with rat behaviour after MK-801 administration. After injecting 0.25-1 mg/kg MK-801, ERK phosphorylation decreased compared to vehicle treatment, and rats showed increased locomotion. After 2 mg/kg treatment, ERK phosphorylation increased and rat motility started to decrease. After treating with 4-8 mg/kg, ERK phosphorylation once again decreased and rats showed hypomotility and ataxia. ERK phosphorylation levels were maintained from 15 min to 90 min after 1 or 2 mg/kg treatment. Ser338-c-Raf and MEK phosphorylation showed similar dose-dependent and temporal patterns to those of ERK. Taken together, Ser338-c-Raf-MEK-ERK phosphorylation by MK-801 in the rat frontal cortex showed a specific pattern and may be associated with behavioural changes induced by MK-801.

Increased phosphorylation of Ser473-Akt, Ser9-GSK-3beta and Ser133-CREB in the rat frontal cortex after MK-801 intraperitoneal injection.

GSK-3beta is regarded as playing an important part in the pathogenesis of schizophrenia and the action of psychotomimetic agents. We observed phosphorylation of molecules associated with the GSK-3beta signalling pathway in the rat brain after MK-801 injection, which induces a schizophrenia-like state in humans. Ser9-GSK-3beta phosphorylation was increased after injection of 1 mg/kg MK-801 in the rat frontal cortex but not in the hippocampus or cerebellum. This increase peaked at 30 min and was maintained until 90 min after injection. The phosphorylation showed a dose-dependent increase up to 1 mg/kg MK-801, followed by a decrease at higher dosage. Furthermore, phosphorylation of Ser473-Akt and Ser133-CREB showed similar temporal, dose-dependent and regionally specific patterns with those of Ser9-GSK-3beta. However, phosphorylation of Dvl and Ser33-beta-catenin was not affected by MK-801. These results suggest that GSK-3beta phosphorylation by MK-801 may be associated with the Akt-GSK-3beta pathway rather than with the Wnt-Dvl-GSK3beta pathway.