An increase in NMDA-sensitive [3H]glutamate and [3H]kainate binding in hippocampus 24 hours after PCP

Effects of risperidone on glutamate receptor subtypes in developing rat brain

Levels of ionotropic glutamate (Glu) N-methyl-d-aspartic acid (NMDA), 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA), and kainic acid (KA) receptors in forebrain regions of juvenile rats (age 42 days) were quantified after 3 weeks of treatment with three different doses of risperidone (0.3, 1.0 and 3.0 mg/kg) and compared findings to those in adult rats treated with risperidone (3.0 mg/kg/day) previously. Risperidone (at 0.3 mg/kg/day) did not alter levels of three ionotropic Glu receptors in all brain regions examined. Risperidone (at 1.0 and 3.0 mg/kg/day) significantly decreased NMDA binding in caudate-putamen of juvenile and adult animals. In contrast, the same two doses of risperidone decreased NMDA receptors in nucleus accumbens of juveniles and not adults. Risperidone (at 1.0 and 3.0 mg/kg/day) increased AMPA receptors in medial prefrontal cortex and caudate-putamen of juvenile animals, whereas risperidone (at 3.0 mg/kg) increased AMPA receptors in caudate-putamen and hippocampus of adults. Kainate receptors were not altered by any dose of risperidone in any brain region examined in developing and mature animals. The findings indicate that risperidone exerts dose-dependent effects on Glu receptor subtypes in developing animals, and that Glu receptor responses to repeated administration of risperidone are different in juvenile animals than adults.

Social memory in mice: disruption with an NMDA antagonist and attenuation with antipsychotic drugs

Social recognition reflects the ability of one animal to learn and remember the identity of another. Animal models of social learning and memory are pertinent to several different CNS diseases involving disruptions in cognition. Moreover, the increased understanding of the basic biology of memory increases the likelihood of discovery of memory-enhancing treatments in these human diseases. In the present study, we investigated the effects of the non-competitive NMDA antagonist ketamine on social recognition in mice across a broad dose range (5-30 mg/kg) and time-course (60 min-7 days). We also tested the ability of two antipsychotic drugs, haloperidol and olanzapine, to block the ketamine effect. Our results show that mice demonstrate social recognition over a several day period, with loss of recognition between 3-7 days. Ketamine disrupts social memory at doses which do not affect task performance. Chronic oral administration of haloperidol or olanzapine attenuates these ketamine-induced effects on social recognition, tending to normalize the memory behavior. The neural mechanisms of these actions are not known, although medial temporal lobe memory systems have been implicated.

Differential regulation of the NMDA receptor by acute and sub-chronic phencyclidine administration in the developing rat

Neurodegeneration induced by the NMDA receptor antagonist, phencyclidine (PCP), has been used to model the pathogenesis of schizophrenia in the developing rat. Acute and sub-chronic administration of PCP in perinatal rats results in different patterns of neurodegeneration. The potential role of an alteration in the membrane expression of NMDA receptors in PCP-induced degeneration is unknown. Acute PCP treatment on postnatal day 7 increased membrane levels of both NMDA receptor subunit 1 (NR1) and NMDA receptor subunit 2B (NR2B) proteins in the frontal cortex; conversely, NR1 and NR2B protein levels in the endoplasmic reticulum fraction were decreased. Acute PCP administration also resulted in increased membrane cortical protein levels of post-synaptic density-95, as well as the activation of calpain, which paralleled the observed increase in membrane expression of NR1 and NR2B. Further, administration of the calpain inhibitor, MDL28170, prevented PCP-induced up-regulation of NR1 and NR2B. On the other hand, sub-chronic PCP treatment on postnatal days 7, 9 and 11 caused an increase in NR1 and NR2A expression, which was accompanied by an increase in both NR1 and NR2A in the endoplasmic reticulum fraction. Sub-chronic PCP administration did not alter levels of post-synaptic density-95 and had no effect on activation of calpain. These data suggest that increased trafficking accounts for up-regulation of cortical NR1/NR2B subunits following acute PCP administration, while increased protein synthesis likely accounts for the increased expression of NR1/NR2A following sub-chronic PCP treatment of the developing rat. These results are discussed in the context of the differential neurodegeneration caused by acute and subchronic PCP administration in the developing rat brain.

Chronic phencyclidine administration reduces the expression and editing of specific glutamate receptors in rat prefrontal cortex

Phencyclidine (PCP) induces a form of psychosis that mimics naturally occurring schizophrenia in the most relevant domains of the psychopathology. In this report, we investigated the effect of chronic treatment with PCP on expression and RNA editing of alpha-amino-propionic acid (AMPA) and kainate (KA) glutamate receptor (GluR), in the rat prefrontal cortex and the hippocampus. We found that chronic, but not acute, PCP treatment decreased GluRs expression in the rat prefrontal cortex but not in the hippocampus. In particular, the mRNA coding for GluR2 and GluR3 subunits were reduced by 50%, whereas those coding for KA GluR5 and GluR6 were decreased by 30%. In addition, we observed a decrease of the editing levels of the R/G site in the flop form of both GluR2 and GluR3 and a significant increase in the editing level of GluR6 Q/R site. The variation in the editing level of the R/G sites suggests that chronic PCP treatment induced the formation of glutamate receptor subunits with slower resensitization kinetics and, with respect to kainate receptors, an increase in the Q/R editing level might generate receptor channels with a lower permeability to cations. Combining all the data, it can be inferred that the PCP treatment induced a specific and site-selective reduction of glutamatergic neurotransmission in the prefrontal cortex but not in the hippocampus.

Short and long term changes in NMDA receptor binding in mouse brain following chronic phencyclidine treatment

Phencyclidine (PCP) is an antagonist of the NMDA subtype of glutamate receptor. PCP treatment induces psychosis in normal humans, which provides a valuable model of schizophrenia. PCP administration also models some of the symptoms of schizophrenia in experimental animals. NMDA hypofunction has been hypothesized to explain these schizophrenia-like symptoms. Acute or chronic administration of the NMDA receptor antagonist PCP has been shown to induce several short or long-term effects in both humans and experimental animals. In an attempt to clarify the neurochemical substrates of these effects in the present study, we used quantitative autoradiography to examine the effects of chronic (14 days) PCP treatment on NMDA receptor binding in mouse brain following both a short- (1 and 24 h) and long-term (14 days) delay after the last PCP treatment. NMDA receptors were targeted using [(3)H]MK801. Chronic PCP treatment increased [(3)H]MK801 binding consistently in the hippocampus in the short-term (p < 0.01). Conversely in the long-term, there were widespread reductions in NMDA receptor binding and this effect was most evident in the hippocampus where a 35% reduction of binding was found (p < 0.001). These results suggest that the hippocampus has a strong involvement in both the short and long-term effects of PCP treatment and that reduced NMDA receptor function might be one of the neurochemical substrates of the long lasting actions of PCP or PCP-induced psychosis. Importantly, this study shows that the long-term delay following chronic PCP treatment more accurately represents a state of NMDA hypofunction than the short-term PCP model.

Glutamate receptor subunits are altered in forebrain and cerebellum in rats chronically exposed to the NMDA receptor antagonist phencyclidine

Phencyclidine (PCP) is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor subtype. It produces transient psychoses in normal individuals and exacerbates psychoses in schizophrenics. When administered to rodents, PCP elicits stereotypic behaviors including unrelenting head swaying, hyperlocomotion, and social withdrawal. In this study, we examined the relative distribution of the NMDA receptor subunits, as well as the subunits of its modulating receptor, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) in the forebrain, hippocampus, and cerebellum of rats chronically exposed to PCP. Rats were injected for 30 days with PCP (10 mg/kg) and age/sex-matched controls were injected for 30 days with saline vehicle. Brain NMDA and AMPA receptor subunit distribution patterns and protein levels were then analyzed by immunocytochemistry and Western blot analysis. Chronic PCP-treated animals showed significant alterations in glutamate receptor subunits, particularly for the NR1, NR2B, NR2C, and NR2D components of the NMDA receptor. AMPA receptor subunits demonstrated few significant changes in subunit availabilities. Western blot analysis largely confirmed the immunocytochemical findings. These results support the conclusion that subunits of the NMDA receptor are selectively altered by chronic PCP antagonism, with minimal to no changes observed in AMPA receptor subunits. Our findings are consistent with the interpretation that a dysfunctional NMDA receptor complex may mediate abnormal glutamatergic neurotransmission and potentially contribute to the complex etiology of cognitive disorders.

Activation of metabotropic glutamate receptor 5 is associated with effect of amphetamine on brain neurons

The role of metabotropic glutamate receptor 5 (mGluR5) was explored in mechanisms underlying the action of amphetamine (AMPH). The activity of mGluR5 was monitored by measuring the level of [3H]inositol monophosphates in brain neurons, in response to stimulation of 2-choloro-5-hydroxyphenylglycine (CHPG), a selective agonist of mGluR5. Treatment with 1 microM of AMPH for 1 h or 7 days increased the CHPG (1 mM, 30 min)-evoked phosphoinositide turnover by 46% or 92% and 26% or 84% in cultured cortical and hippocampal neurons, respectively, from that of CHPG-only treated cells. When AMPH was present during CHPG application post-1 h or 7 day AMPH incubation, the rate of phosphoinositide hydrolysis in cortical neurons became 121% or 142% higher than that treated with CHPG only. The postnatal day (P) 21 (juvenile) and P60 (adult) rats received three intraperitoneal injections of 5 mg/kg of AMPH or saline daily for 6 days. They were challenged on the eighth day with one dosage and sacrificed 3 h later. Reversible 3H-glutamate binding detected increases of 22-89% in the binding levels of cortex and hippocampus of both ages following the AMPH injections. Increases of 13-18% in the levels of mGluR5 mRNA were seen in the juvenile pyramidal neurons of hippocampal CA1-4, granular cells of dentate gyrus, and ventral thalamic nuclei, as shown by in situ hybridization. The AMPH-induced altered activity of mGluR5 is probably associated with changes in the expression of the glutamate receptors, including mGluR5. AMPH may modify the sensitivity of mGluR5 or interact with the receptor itself.

Synapse-associated protein 90/postsynaptic density-95-associated protein (SAPAP) is expressed differentially in phencyclidine-treated rats and is increased in the nucleus accumbens of patients with schizophrenia

Phencyclidine (PCP) induces a psychotomimetic state that closely resembles schizophrenia. Therefore, PCP-treated animals can provide a model for schizophrenia. Using differential display, we identified a gene regulated by the delayed action of PCP in rat nucleus accumbens (NAcs). Sequence analysis showed that the cDNA clone obtained was identical to rat synapse-associated protein 90/postsynaptic density-95-associated protein 1 (SAPAP1). Quantitative reverse transcriptase (RT)-PCR analysis showed that SAPAP1 mRNA had increased significantly in rat NAc (P<0.0001) and hippocampus (P<0.01) 24 h after a PCP (10 mg/kg) injection as compared to the controls. Immunoquantification using an anti-SAPAP1 antibody indicated that immunoreactivity for SAPAP1 increased significantly (P&<0.05) in the NAcs of unmedicated patients with schizophrenia, as compared to the control subjects and medicated patients with schizophrenia. Our findings support the hypothesis that there is abnormal glutamatergic neurotransmission in schizophrenia and show evidence of abnormalities in the intracellular signal transduction via N-methyl-D-aspartate (NMDA) receptors.

Long-term effects of olanzapine, risperidone, and quetiapine on ionotropic glutamate receptor types: implications for antipsychotic drug treatment

Levels of ionotropic glutamate (Glu) N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and kainic acid (KA) receptors in rat forebrain regions were compared by quantitative in vitro receptor autoradiography after continuous treatment for 28 days with the atypical antipsychotics olanzapine, risperidone, and quetiapine, or vehicle controls. All three treatments significantly decreased NMDA binding in caudate-putamen (CPu; by 30, 34, and 26%, respectively) but increased AMPA receptor levels in same region (by 22, 30, and 28%). Olanzapine and risperidone, but not quetiapine, also reduced NMDA receptor labeling in hippocampal CA1 (21 and 19%) and CA3 (23 and 22%) regions. KA receptors were unaltered by any treatment in the brain regions examined. These findings suggest that the antipsychotic effects of olanzapine and risperidone may be mediated in part by NMDA receptors in hippocampus, and perhaps AMPA receptors in CPu. The findings also support the hypothesis that down-regulation of NMDA receptors by atypical antipsychotic agents in CPu contributes to their low risk of extra-pyramidal side effects. Inability of olanzapine, risperidone, and quetiapine to alter KA receptors suggests their minimal role in mediating the central nervous system actions of these drugs.

Effect of amphetamine on the expression of the metabotropic glutamate receptor 5 mRNA in developing rat brain

Mechanisms underlying the acute effects of amphetamine (AMP) were examined by monitoring the expression of metabotropic glutamate receptor 5 (mGluR5) and specific 3H-glutamate binding in the developing rat brain. Each of the postnatal day (P) 4, P21 and P60 rats received one intraperitoneal injection of AMP, 5 mg/kg or saline and were sacrificed one hour later. In situ hybridization analysis revealed that the AMP treatment raised the levels of the mGluR5 mRNA by 9-28% in the neurons of the layer 5 of motor and somatosensory cortices, whereas reduced the levels by 12-28% in the layer 5 of perirhinal cortex and the ventromedial part of caudate-putamen of the 3 ages. In the layer 2/3 neurons of cingular cortex, an 18% higher and 14% and 22% lower than control levels of the mRNA were detected in the P4 and in the P21 and P60 rats injected with AMP. Moreover, the levels of mGluR5 mRNA in the hippocampi and dentate gyri were elevated by AMP to 110-151% of controls in the rats of 3 ages. Reversible 3H-glutamate binding assay showed an increase of 25% and a 12% decrease in the binding levels in the cortices of AMP-treated P4 and P21 rats. The AMP administration also produced a 27% reduction and 62% elevation in the binding of the hippocampi of P4 and P60 rats. The results reveal age- and region-dependent changes in the expression of the glutamate receptors induced by AMP and may indicate differential plastic capability of the neurons to the drug perturbation.

The delayed effects of DTG and MK-801 on latent inhibition in a conditioned taste-aversion paradigm

The delayed effects of phencyclidine (PCP) have been shown to disrupt latent inhibition (LI) in a conditioned taste-aversion paradigm. In an attempt to understand the mechanism of this disruption, the delayed effects of the selective sigma receptor agonist 1,3-Di(2-tolyl)guanidine (DTG) and the selective NMDA receptor antagonist MK-801 on latent inhibition were assessed in the same paradigm. Water-deprived male rats were allowed access to either water (nonpreexposed; NPE) or 5% sucrose (preexposed; PE) for 30 min on 2 consecutive days. On the third day, animals were allowed access to sucrose and subsequently injected with lithium chloride. On the forth day, animals were allowed access to both sucrose and water. LI was assessed by comparing the percent sucrose consumed in PE and NPE groups on the fourth day. DTG (1.0, 5.0, or 10.0 mg/kg), MK-801 (0.5, 1.0, or 2.0 mg/kg), or vehicle was administered IP 20 h before preexposure (days 1 and 2) and conditioning (day 3). In vehicle-treated groups, PE animals consumed a significantly higher percent sucrose on the test day than NPE animals, indicating the presence of LI. DTG (10.0 mg/kg) and MK-801 (2.0 mg/kg) decreased the percent sucrose consumed by animals in the PE group to the level observed in the NPE group, indicating disrupted LI. However, this dose of MK-801 was found to produce a decrease in percent sucrose consumed in PE animals not treated with lithium chloride, indicating that the decrease observed in the LI paradigm could be due to MK-801-induced decrease in taste preference for sucrose rather than a disruption of LI. Lower doses of MK-801 that did not produce a decrease in taste preference for sucrose did not significantly disrupt LI. None of the doses of DTG tested altered taste preference for sucrose. These data suggest a role for sigma receptors in the previously observed PCP-induced disruption of LI. Published by Elsevier Science Inc., 2000

Morphine tolerance and dependence in mice with history of repeated exposures to NMDA receptor channel blockers

Mice were subjected to two successive treatment protocols: first with NMDA receptor channel blockers (14 days, once a day) and second with morphine (5 mg/kg, 8 days, once a day). Treatment with the higher doses of dizocilpine (1 mg/kg), memantine (30 mg/kg), and MRZ 2/576 (30 mg/kg) upon discontinuation revealed only minor behavioral abnormalities attributable to the state of withdrawal. Following repeated administration of low-dose morphine, tolerance to morphine analgesia developed in mice preexposed to dizocilpine (1 mg/kg but not 0.3 mg/kg) but not memantine (10 and 30 mg/kg), MRZ 2/579 (10 and 30 mg/kg), or saline. There were no signs of morphine dependence in any treatment group. Overall, the present study found only minor effects of the subchronic administration of high doses of NMDA receptor channel blockers, suggesting that clinical use of NMDA receptor channel blockers such as memantine will not be accompanied by increased propensity to induction of morphine tolerance and dependence.

Long-term changes in brain following continuous phencyclidine administration: an autoradiographic study using flunitrazepam, ketanserin, mazindol, quinuclidinyl benzilate, piperidyl-3,4-3H(N)-TCP, and AMPA receptor ligands

Phencyclidine induces a model psychosis which can persist for prolonged periods and presents a strong drug model of schizophrenia. When given continuously for several days to rats, phencyclidine and other N-methyl-D-aspartate (NMDA) antagonists induce neural degeneration in a variety of limbic structures, including retrosplenial cortex, hippocampus, septohippocampal projections, and piriform cortex. In an attempt to further clarify the mechanisms underlying these degeneration patterns, autoradiographic studies using a variety of receptor ligands were conducted in animals 21 days after an identical dosage of the continuous phencyclidine administration employed in the previous degeneration studies. The results indicated enduring alterations in a number of receptors: these included decreased piperidyl-3,4-3H(N)-TCP (TCP), flunitrazepam, and mazindol binding in many of the limbic regions in which degeneration has been reported previously. Quinuclidinyl benzilate and (AMPA) binding were decreased in anterior cingulate and piriform cortex, and in accumbens and striatum. Piperidyl-3,4-3H(N)-TCP binding was decreased in most hippocampal regions. Many of these long-term alterations would not have been predicted by prior studies of the neurotoxic effects of continuous phencyclidine, and these results do not suggest a unitary source for the neurotoxicity. Whereas retrosplenial cortex, the structure which degenerates earliest, showed minimal alterations, some of the most consistent, long term alterations were in structures which evidence no immediate signs of neural degeneration, such as anterior cingulate cortex and caudate nucleus. In these structures, some of the receptor changes appeared to develop gradually (they were not present immediately after cessation of drug administration), and thus were perhaps due to changed input from regions evidencing neurotoxicity. Some of these findings, particularly in anterior cingulate, may have implications for models of schizophrenia.

Phencyclidine (PCP) and dizocilpine (MK801) exert time-dependent effects on the expression of immediate early genes in rat brain

The mRNA expression pattern for four different immediate early genes was examined dynamically in rat brain after administration of phencyclidine (PCP; 0.86 or 8.6 mg/kg) or MK801 (0.1 or 1.0 mg/kg). Following each treatment, the expression of cfos, cjun, junB, and zif268 mRNA changed distinctively and dynamically between 1 and 48 hours. cfos mRNA was induced in cortical areas at early times after either dose of PCP or of MK801; the change was especially prominent in cingulate and auditory cortices. zif268 mRNA showed an early (1 hour) activation and a delayed (24-48 hour) suppression after PCP and MK801 in neocortical areas. PCP also caused cjun and junB mRNA induction in cortical areas at early times, with a distribution and time course similar to its effects on cfos mRNA. No alterations in cfos, cjun, or junB mRNA were found in neocortical or hippocampal areas at any delayed time (>6 hours) after PCP treatment, whereas suppression of zif268 expression was prominent even at 48 hours post-treatment. CPP, a competitive NMDA antagonist, showed a similar pattern of effects on cfos and zif268 mRNA expression. These functional consequences of a PCP- or MK801-induced reduction in NMDA-sensitive glutamate transmission may be relevant to an understanding of animal NMDA pharmacology and/or to clinical psychotomimetic side effects of antiglutamatergic treatments.

Effect of up-regulation of NMDA receptors on cerebral O2 consumption and blood flow in rat

We tested the hypothesis that cerebrocortical blood flow and O2 consumption would be proportional to an up-regulated number of functional N-methyl-D-aspartate (NMDA) receptors. Previous work had shown a relationship between cerebral metabolism and NMDA receptor activity. We increased the specific binding to NMDA receptors in the cerebral cortex, from 2.2 +/- 0.9 to 4.5 +/- 0.8 (density units) in male Long-Evans rats by daily giving two intraperiotoneal injections (30 mg/kg) of CGS-19755, an NMDA receptor inhibitor, for 7 consecutive days (discontinued for 20 h before experiment). Twelve up-regulated (CGS treated) and 12 control rats were used in this study. Under isoflurane anesthesia and after topical stimulation of the right cerebral cortex with 10(-2) M NMDA, the blood flow (14C-iodoantipyrine method) increased from 98 +/- 11 ml/min/100 g in the unstimulated cortex of the control rats to 161 +/- 37 ml/min/100 g in the stimulated cortex. The unstimulated value for blood flow (95 +/- 7 ml/min/100 g) did not change in the upregulated group but it doubled (194 +/- 69 ml/min/100 g) in the stimulated, upregulated cortex. Similarly, O2 consumption (cryomicrospectrophotometrically determined) in normal rats increased 46%, from 9.3 +/- 1 ml/min/100 g to 13.6 +/- 4 after NMDA stimulation. While in the upregulated animals, O2 consumption increased 103% from 7.9 +/- 0.6 to 16 +/- 6.5 after NMDA stimulation. In conclusion, NMDA receptor upregulation does not alter basal cerebrocortical blood flow or O2 consumption but in the NMDA-stimulated cortex, the blood flow and O2 consumption increase is dependent on the number of NMDA receptors present.

[3H]MK-801 binding to well-washed rat brain membranes following cessation of chronic phencyclidine treatment

Rats were implanted with osmotic minipumps SC that infused either saline or 10 mg/kg/day phencyclidine (PCP) for 10 days, a regimen that produces dependence to PCP. At the end of this 10-day infusion period, the pumps were removed and the rats were sacrificed either immediately or at various time points (12 h, 1, 2, and 7 days) after pump removal. The saturation binding parameters of [3H]MK-801 were then determined in well-washed cortical/hippocampal membranes prepared from these rats. Neither the Bmax nor the Kd of [3H]MK-801 binding in membranes of PCP-treated rats differed from that determined using membranes from saline-treated rats at any time point studied. These results suggest that alterations in PCP receptors do not play a major role in the production of PCP dependence.

MK801 induces late regional increases in NMDA and kainate receptor binding in rat brain

We have previously shown that a single dose of PCP produces a dose-related increase in NMDA-sensitive 3H-glutamate binding in CA1 of hippocampus 24 hours later, and some regional changes in kainate binding. Here we report that dizocilpine (MK 801) (0.1 mg/kg and 1 mg/kg), a selective agonist at the PCP receptor and a noncompetitive antagonist of NMDA, produces a similar increase in NMDA-sensitive glutamate and kainate receptor binding in hippocampus 24 hours after a dose. These observations support the conclusion that blockade of glutamate-mediated transmission at the NMDA receptor selectively increases NMDA-sensitive glutamate receptor binding in CA1 of hippocampus and kainate binding in CA3 and dentate gyrus at putatively delayed time points. Several additional areas outside of hippocampus also showed receptor changes at 24 hours after MK801.