Different effects of phencyclidine and methamphetamine on firing activity of medial prefrontal cortex neurons in freely moving rats

Potential antipsychotic action of the selective agonist of adenosine A1 receptors, 5'-Cl-5'-deoxy-ENBA, in amphetamine and MK-801 rat models

Background

Disturbances of dopaminergic and glutamatergic transmissions have been suggested to be involved in the pathomechanisms underlying psychotic symptoms of schizophrenia. In line with this concept, hyperlocomotion induced by the dopaminomimetic amphetamine and the uncompetitive antagonist of NMDA receptors MK-801 (dizocilpine) in rodents is a generally established model for screening of new potential antipsychotic drugs. Since recent studies have indicated that receptors for adenosine may be targets for antipsychotic therapy, the aim of the present study was to investigate an influence of 5′-Cl-5′-deoxy-ENBA, a potent and selective adenosine A₁ receptor agonist, on hyperlocomotion induced by amphetamine and MK-801.

Methods

Locomotor activity was measured by Force Plate Actimeters where four force transducers located below the corners of the floor of the cage tracked the animal position on a Cartesian plane at each time point.

Results

Hyperlocomotion induced by either amphetamine (1 mg/kg sc) or MK-801 (0.3 mg/kg ip) was inhibited by 5′-Cl-5′-deoxy-ENBA (0.1 mg/kg ip). The effect of 5′-Cl-5′-deoxy-ENBA on the amphetamine- and MK-801-induced hyperlocomotion was antagonized by the selective antagonist of adenosine A₁ receptor DPCPX at doses of 1 and 2 mg/kg ip, respectively.

Conclusion

The present study suggests that stimulation of adenosine A₁ receptors may produce antipsychotic effects.

Optogenetic inhibition of ventral hippocampal neurons alleviates associative motor learning dysfunction in a rodent model of schizophrenia

Schizophrenia (SZ) is a serious and incurable mental disorder characterized by clinical manifestations of positive and negative symptoms and cognitive dysfunction. High-frequency deep brain stimulation (DBS) of the ventral hippocampus (VHP) has been recently applied as a therapeutic approach for SZ in both experimental and clinical studies. However, little is known about the precise mechanism of VHP-DBS treatment for SZ and the role of hippocampal cell activation in the pathogenesis of SZ. With optogenetic technology in this study, we tried to inhibit neuronal activity in the VHP which has dense projections to the prefrontal cortex, before measuring long stumulus-induced delay eyeblink conditioning (long-dEBC) in a rodent model of SZ. Rats were administrated with phencyclidine (PCP, 3 mg/kg, 1/d, ip) for successive 7 days before optogenetic intervention. The current data show that PCP administration causes significant impairment in the acquisition and timing of long-dEBC; the inhibition of bilateral VHP neurons alleviates the decreased acquisition and impaired timing of longd-dEBC in PCP-administered rats. The results provide direct evidence at the cellular level that the inhibition of VHP neuronal cells may be a prominent effect of hippocampal DBS intervention, and increased activity in the hippocampal network play a pivotal role in SZ.

Bidirectional variation in glutamate efflux in the medial prefrontal cortex induced by selective positive and negative allosteric mGluR5 modulators

Dysregulation of prefrontal cortical glutamatergic signalling via NMDA receptor hypofunction has been implicated in cognitive dysfunction and impaired inhibitory control in such neuropsychiatric disorders as schizophrenia, attention‐deficit hyperactivity disorder and drug addiction. Although NMDA receptors functionally interact with metabotropic glutamate receptor 5 (mGluR5), the consequence of this interaction for glutamate release in the prefrontal cortex (PFC) remains unknown. We therefore investigated the effects of positive and negative allosteric mGluR5 modulation on changes in extracellular glutamate efflux in the medial PFC (mPFC) induced by systemic administration of the non‐competitive NMDA receptor antagonist dizocilpine (or MK801) in rats. Extracellular glutamate efflux was measured following systemic administration of the positive allosteric mGluR5 modulator [S‐(4‐Fluoro‐phenyl)‐{3‐[3‐(4‐fluoro‐phenyl)‐[1,2,4]‐oxadiazol‐5‐yl]‐piperidin‐1‐yl}‐methanone] (ADX47273; 100 mg/kg, p.o.) and negative allosteric mGluR5 modulator [2‐chloro‐4‐{[1‐(4‐fluorophenyl)‐2,5‐dimethyl‐1H‐imidazol‐4‐yl]ethynyl}pyridine] (RO4917523; 0.3 mg/kg, p.o.), using a wireless glutamate biosensor in awake, freely moving rats. The effect of MK801 (0.03–0.06 mg/kg, s.c.) on mPFC glutamate efflux was also investigated in addition to the effects of MK801 (0.03 mg/kg, s.c.) following ADX47273 (100 mg/kg, p.o.) pre‐treatment. ADX47273 produced a sustained increase in glutamate efflux and increased the effect of NMDA receptor antagonism on glutamate efflux in the mPFC. In contrast, negative allosteric mGluR5 modulation with RO4917523 decreased glutamate efflux in the mPFC. These findings indicate that positive and negative allosteric mGluR5 modulators produce long lasting and opposing actions on extracellular glutamate efflux in the mPFC. Positive and negative allosteric modulators of mGluR5 may therefore be viable therapeutic agents to correct abnormalities in glutamatergic signalling present in a range of neuropsychiatric disorders.

Afferent drive of medial prefrontal cortex by hippocampus and amygdala is altered in MAM-treated rats: evidence for interneuron dysfunction

Evidence indicates that the prefrontal cortex and its regulation by afferent inputs are disrupted in schizophrenia. Using a validated rat model of schizophrenia based on prenatal administration of the mitotoxin methyl azoxymethanol acetate (MAM), we examined the convergent projections from the ventral hippocampus (vHipp) and the basolateral amygdala (BLA) in the medial prefrontal cortex (mPFC). In vivo extracellular recordings were done in anesthetized rats to assess how prior stimulation of the BLA or vHipp input to the mPFC affected mPFC responses to subsequent stimulation of these regions. The interstimulus interval (ISI) of the BLA and vHipp pulse stimulation was varied randomly between 0 and 130 ms, and the probability of evoked spike response in the mPFC measured. We found that BLA input increased vHipp-evoked spike probability at ISIs 40-130 ms, but decreased spike probability at ISIs 10-20 ms. This would be consistent with activation of inhibitory interneurons at shorter ISIs by BLA stimulation. In contrast, in MAM-treated rats BLA stimulation increased vHipp-evoked spike probability in mPFC at all ISIs tested. Given that interneurons are driven primarily by N-methyl-D-aspartate (NMDA) channel activation, the effects of the NMDA channel blocker, phencyclidine (PCP), were tested. PCP was found to completely attenuate the inhibitory effect of BLA input on vHipp-evoked responses in mPFC at shorter ISIs, causing the response in control rats treated with PCP to resemble that observed in the MAM rat. In contrast to the effects of BLA stimulation on vHipp-mPFC-evoked responses, there was no inhibitory period when examining the effects of vHipp stimulation on BLA-mPFC-evoked responses in control rats, but in MAM-treated rats there was a significant inhibition at short intervals. Thus, both affective input arising from the BLA and context-dependent input from the vHipp exert a modulatory effect on mPFC neural activity in response to these inputs. Whereas the BLA potentiated vHipp input to the mPFC at long intervals, there was a short-interval inhibitory period that appeared to be mediated by an NMDA-dependent drive of interneurons. This inhibitory modulation was absent in the model of schizophrenia and following PCP, which is consistent with an interneuron disruption in this disorder.

The role of the hippocampo-prefrontal cortex system in phencyclidine-induced psychosis: a model for schizophrenia

Phencyclidine (PCP) is a psychotomimetic drug that induces schizophrenia-like symptoms in healthy individuals and exacerbates pre-existing symptoms in patients with schizophrenia. PCP also induces behavioral and cognitive abnormalities in non-human animals, and PCP-treated animals are considered a reliable pharmacological model of schizophrenia. However, the exact neural mechanisms by which PCP modulates behavior are not known. During the last decade several studies have indicated that disturbed activity of the prefrontal cortex (PFC) may be closely related to PCP-induced psychosis. Systemic administration of PCP produces long-lasting activation of medial PFC (mPFC) neurons in rats, almost in parallel with augmentation of locomotor activity and behavioral stereotypies. Later studies have showed that such PCP-induced behavioral abnormalities are ameliorated by prior administration of drugs that normalize or inhibit excess excitability of PFC neurons. Similar activation of mPFC neurons is not induced by systemic injection of a typical psychostimulant such as methamphetamine, even though behavioral hyperactivity is induced to almost the same level. This suggests that the neural circuits mediating PCP-induced psychosis are different to those mediating methamphetamine-induced psychosis. Locally applied PCP does not induce excitation of mPFC neurons, indicating that PCP-induced tonic excitation of mPFC neurons is mediated by inputs from regions outside the mPFC. This hypothesis is strongly supported by experimental results showing that local perfusion of PCP in the ventral hippocampus, which has dense fiber projections to the mPFC, induces tonic activation of mPFC neurons with accompanying augmentation of behavioral abnormalities. In this review we summarize current knowledge on the neural mechanisms underlying PCP-induced psychosis and highlight a possible involvement of the PFC and the hippocampus in PCP-induced psychosis.

Differences in responsiveness of mediodorsal thalamic and medial prefrontal cortical neurons to social interaction and systemically administered phencyclidine in rats

Phencyclidine (PCP) is a psychotomimetic drug that induces schizophrenia-like symptoms in healthy individuals and behavioral abnormalities with corresponding symptoms of schizophrenia in non-human animals. Our previous studies showed that systemically administered PCP produces tonic activation of neurons in the medial prefrontal cortex (mPFC) of rats and that this activation is mainly via excitatory inputs from regions outside the mPFC. Such long-lasting activation of PFC neurons is now considered to be a pivotal factor in PCP-induced behavioral abnormalities. Although our previous study identified the ventral hippocampus as a possible source of the excitatory inputs, it is not the only source innervating the mPFC. Several regions such as the thalamus also have monosynaptic projections to the mPFC. Recently, increased c-fos expression by systemic PCP administration was reported in the mediodorsal nucleus of the thalamus (MD) and the centromedial nucleus of the thalamus (CM), which have strong reciprocal innervations with the mPFC. However, few studies have reported effects of PCP on the firing activity of MD/CM neurons in unanesthetized animals. In the current study in freely moving rats, we examined effects of systemically administered PCP on the spontaneous firing activity of the MD/CM, after identifying the response properties of recorded neurons in social interaction with an unfamiliar partner. About 30% of MD/CM neurons recorded exhibited tonic excitation following systemic PCP administration, whereas only a few neurons (7%) were inhibited by PCP. The proportion of MD neurons activated by systemic PCP administration was about half of that in the mPFC. Although the proportion of neurons responsive to social interaction did not differ between the two regions (40%), neurons activated during social interaction in the mPFC (90%) were more likely to be affected by systemic PCP administration than those in the MD/CM (45%). These results suggest that neurons responsive to social interaction in the mPFC may be differently affected by PCP than those in the MD/CM.

Clozapine and haloperidol differently suppress the MK-801-increased glutamatergic and serotonergic transmission in the medial prefrontal cortex of the rat

The administration of noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine and ketamine has been shown to increase the extracellular concentration of glutamate and serotonin (5-HT) in the medial prefrontal cortex (mPFC). In the present work, we used in vivo microdialysis to examine the effects of the more potent noncompetitive NMDA receptor antagonist, MK-801, on the efflux of glutamate and 5-HT in the mPFC, and whether the MK-801-induced changes in the cortical efflux of both transmitters could be blocked by clozapine and haloperidol given systemically or intra-mPFC. The systemic, but not the local administration of MK-801, induced an increased efflux of 5-HT and glutamate, which suggests that the NMDA receptors responsible for these effects are located outside the mPFC, possibly in GABAergic neurons that tonically inhibit glutamatergic inputs to the mPFC. The MK-801-induced increases of extracellular glutamate and 5-HT were dependent on nerve impulse and the activation of mPFC AMPA/kainate receptors as they were blocked by tetrodotoxin and NBQX, respectively. Clozapine and haloperidol blocked the MK-801-induced increase in glutamate, whereas only clozapine was able to block the increased efflux of 5-HT. The local effects of clozapine and haloperidol paralleled those observed after systemic administration, which emphasizes the relevance of the mPFC as a site of action of these antipsychotic drugs in offsetting the neurochemical effects of MK-801. The ability of clozapine to block excessive cortical 5-HT efflux elicited by MK-801 might be related to the superior efficacy of this drug in treating negative/cognitive symptoms of schizophrenia.

Abnormal glutamate receptor expression in the medial temporal lobe in schizophrenia and mood disorders

Pharmacological and anatomical evidence suggests that abnormal glutamate neurotransmission may be associated with the pathophysiology of schizophrenia and mood disorders. Medial temporal lobe structural alterations have been implicated in schizophrenia and to a lesser extent in mood disorders. To comprehensively examine the ionotropic glutamate receptors in these illnesses, we used in situ hybridization to determine transcript expression of N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate receptor subunits in the medial temporal lobe of subjects with schizophrenia, bipolar disorder (BD), or major depression (MDD). We used receptor autoradiography to assess changes in glutamate receptor binding in the same subjects. Our results indicate that there are region- and disorder-specific abnormalities in the expression of ionotropic glutamate receptor subunits in schizophrenia and mood disorders. We did not find any changes in transcript expression in the hippocampus. In the entorhinal cortex, most changes in glutamate receptor expression were associated with BD, with decreased GluR2, GluR3, and GluR6 mRNA expression. In the perirhinal cortex we detected decreased expression of GluR5 in all three diagnoses, of GluR1, GluR3, NR2B in both BD and MDD, and decreased NR1 and NR2A in BD and MDD, respectively. Receptor binding showed NMDA receptor subsites particularly affected in the hippocampus, where MK801 binding was reduced in schizophrenia and BD, and MDL105,519 and CGP39653 binding were increased in BD and MDD, respectively. In the hippocampus AMPA and kainate binding were not changed. We found no changes in the entorhinal and perirhinal cortices. These data suggest that glutamate receptor expression is altered in the medial temporal lobe in schizophrenia and the mood disorders. We propose that disturbances in glutamate-mediated synaptic transmission in the medial temporal lobe are important factors in the pathophysiology of these severe psychiatric illnesses.

Ketamine dose-dependently induces high-frequency oscillations in the nucleus accumbens in freely moving rats

BACKGROUND

In humans, subanesthetic doses of ketamine and recovery from ketamine anesthesia are associated with psychotic-like behavior. In rodents, ketamine produces hyperactivity, stereotypies, and abnormal social interaction used to model certain features of schizophrenia. Increasing evidence has implicated aberrant activity in the nucleus accumbens (NAc) with the pathophysiology of schizophrenia.

METHODS

Here, we examined the effect of an IP injection of ketamine (10, 25, 50, and 200 mg/kg) and d-amphetamine (3 mg/kg) on local field potentials in the rodent NAc. Locomotor activity was recorded simultaneously.

RESULTS

Spontaneous high-frequency oscillations (HFO) (140-180 Hz) were present in local field potentials recorded from the NAc. Ketamine dose-dependently induced rapid and substantial increases in HFO that correlated with behavioral hyperactivity. Similarly, large increases in HFO occurred during recovery from ketamine anesthesia. In contrast, d-amphetamine, which induced locomotor activity, produced only small increases in HFO.

CONCLUSIONS

We propose that ketamine-induced abnormal increases in HFO form part of the complex neurological changes in this model of schizophrenia. Ketamine-induced increases in HFO, although sharing similar temporal dynamics to hyperactivity, may not be functionally related to increased movement.

The 5-HT(1A) receptor agonist 8-OH-DPAT prevents prefrontocortical glutamate and serotonin release in response to blockade of cortical NMDA receptors

We studied the role of 5-HT(1A) receptors in controlling the release of glutamate (GLU) in the medial prefrontal cortex (mPFC) of conscious rats with the in vivo microdialysis technique. The effect of the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin infused in the prefrontal cortex was examined under basal conditions and on the rise of extracellular GLU (+106%) induced by co-infusion of the competitive N-methyl-d-aspartate receptor antagonist 3-[(R)-2-carboxypiperazin-4yl]-propyl-1-phosphonic acid (CPP). 8-OH-DPAT (0.3 and 3 microm) had no effect on basal extracellular GLU, but the higher concentration completely abolished the rise of extracellular GLU induced by CPP. CPP also increased extracellular serotonin (5-HT) in the mPFC (+50%) and this effect was antagonized by 3 microm 8-OH-DPAT which, by itself, had no effect on basal 5-HT release. The effects of 8-OH-DPAT on extracellular GLU and 5-HT were reversed by the 5-HT(1A) receptor antagonist WAY100 635 (100 microm), indicating a selective involvement of 5-HT(1A) receptors. WAY100 635 had no effect by itself. These results show that the stimulation of cortical 5-HT(1A) receptors prevents the CPP-evoked rise of extracellular GLU and 5-HT and suggest that these effects may contribute to the ability of intracortical 8-OH-DPAT to counteract cognitive deficits caused by the blockade of NMDA receptors.

Ketamine induces dopamine-dependent depression of evoked hippocampal activity in the nucleus accumbens in freely moving rats

Noncompetitive NMDA receptor antagonists, such as ketamine, induce a transient schizophrenia-like state in healthy individuals and exacerbate psychosis in schizophrenic patients. In rodents, noncompetitive NMDA receptor antagonists induce a behavioral syndrome that represents an experimentally valid model of schizophrenia. Current experimental evidence has implicated the nucleus accumbens in the pathophysiology of schizophrenia and the psychomimetic actions of ketamine. In this study, we have demonstrated that acute systemic administration of ketamine, at a dose known to produce hyperlocomotion and stereotypy, depressed the amplitude of the monosynaptic component of fimbria-evoked field potentials recorded in the nucleus accumbens. A similar effect was observed using the more selective antagonist dizocilpine maleate, indicating the depression was NMDA receptor dependent. Paired-pulse facilitation was enhanced concomitantly with, and in proportion to, ketamine-induced depressed synaptic efficacy, indicative of a presynaptic mechanism of action. Notably, the depression of field potentials recorded in the nucleus accumbens was markedly reduced after a focal 6-hydroxydopamine lesioning procedure in the nucleus accumbens. More specifically, pretreatment with the D2/D4 antagonist haloperidol, but not the D1 antagonist SCH23390 blocked ketamine-induced depression of nucleus accumbens responses. Our findings provide supporting evidence for the contemporary theory of schizophrenia as aberrant excitatory neurotransmission at the level of the nucleus accumbens.

Serial analysis of gene expression in methamphetamine- and phencyclidine-treated rodent cerebral cortices: are there common mechanisms?

Pharmacological actions of methamphetamine (METH) and phencyclidine (PCP) are different, but both of them can induce similar psychiatric disorders including abuse, intoxication, withdrawal, and psychotic symptoms like those of schizophrenia. These mental disorders are caused not only by their direct pharmacological effects, but also by secondary brain damage containing gene expression changes. In order to broadly grasp these alterations, we used serial analysis of gene expression (SAGE), a transcriptome analysis. We analyzed three cDNA libraries from cerebral cortices of saline (1 mL/kg)-, METH (4 mg/kg)-, or PCP (10 mg/kg)-treated Wistar rats (one hour after i.p. administration). The numbers of total tags were about 50,000 in each library, and approximately 18,000 kinds of tags were identified respectively. From the comparisons of three groups, we found both METH- and PCP-reactive genes. Upregulated genes contained calmodulin 2, stromal cell-derived factor receptor 1, brain-specific angiogenesis inhibitor 1-associated protein 2, ras homologue enriched in brain, basigin and thyrotropin-releasing hormone receptor. Downregulated genes contained lipocalin 2, aldolase A, importin 13, fatty acid binding protein 3, and glycine receptor alpha2 subunit. These data suggest important clues of common molecular basis in METH- and PCP-related psychiatric disorders.

The 5-HT receptor antagonist M100,907 prevents extracellular glutamate rising in response to NMDA receptor blockade in the mPFC

We recently found that intracortical injection of the selective and competitive N-methyl-D-aspartate (NMDA) receptor antagonist 3-(R)-2-carboxypiperazin-4-propyl-1-phosphonic acid (CPP) impaired attentional performance in rats and blockade of 5-hydroxytryptamine (5-HT)2A receptors antagonized this effect. Here, we used the microdialysis technique in conscious rats to study the effect of CPP on extracellular glutamate (GLU) in the medial prefrontal cortex (mPFC) and the regulation of this effect by 5-HT2A receptors. Intraperitoneal injection of 20 mg/kg CPP increased extracellular GLU in the mPFC (201% of basal levels) but had no effect on 5-HT. Intracortical infusion of 100 microm CPP increased extracellular GLU (230% of basal values) and 5-HT (150% of basal values) in the mPFC, whereas 30 microm had no significant effect. The effect of 100 microm CPP on extracellular GLU was abolished by tetrodotoxin, suggesting that neuronal activity is required. Subcutaneous injection of 40 microg/kg M100,907 completely antagonized the effect of 100 microm cpp on extracellular GLU, whereas 10 microg/kg caused only partial attenuation. Likewise, intracortical infusion of 0.1 microm M100,907 completely reversed the increase of extracellular GLU induced by CPP. These findings show that blockade of NMDA receptors in the mPFC is sufficient to increase extracellular GLU locally. The increase of cortical extracellular GLU may contribute to CPP-induced cognitive deficits and blockade of 5-HT2A receptors may provide a molecular mechanism for reversing these deficits caused by dysfunctional glutamatergic transmission in the mPFC.

Activation of Medial Prefrontal Cortex by Phencyclidine is Mediated via a Hippocampo-prefrontal Pathway

Phencyclidine (PCP) is a psychotomimetic drug that elicits schizophrenia-like symptoms in healthy persons, and administration of PCP to animals is used as a pharmacological model of schizophrenia. We recently demonstrated that systemic administration of PCP to rats produces long-lasting activation of medial prefrontal cortex (mPFC) neurons with augmentation of locomotor activity, whereas direct application of PCP to mPFC neurons has little effect on their firing activity. These findings suggest that PCP-induced activation of mPFC neurons is elicited mainly via excitatory inputs from regions outside the mPFC. In the present study, we examined effects of local application of PCP to the ventral hippocampus (vHIP) on firing activity of PFC neurons in freely moving rats. PCP locally perfused into the vHIP increased spontaneous discharges of PFC neurons during perfusion with augmentation of locomotor activity. Local application of a more selective NMDA receptor antagonist, MK801, to vHIP neurons under anesthesia increased the spontaneous firing rates of most neurons directly projecting to the mPFC, whereas local application of MK801 to mPFC neurons did not induce excitatory responses in any of those neurons. The present results indicate that tonic excitatory inputs from the vHIP to the PFC may trigger development of behavioral abnormalities.