Repeated phencyclidine administration alters glutamate release and decreases GABA markers in the prefrontal cortex of rats
Highlights
► Repeated PCP administration increased glutamate release in the PFC of rats. ► The repeated PCP-induced increase in PFC glutamate was blunted compared with that seen after a single PCP injection. ► Repeated PCP administration decreased markers of GABA function in the PFC. ► Clozapine attenuated the PCP-induced changes in glutamate and GABA function.
Introduction
Glutamate abnormalities reported in schizophrenia patients (Tamminga, 1998) are proposed to be involved in schizophrenia pathology (Olney and Farber, 1995), including cognitive deficits that are core features of the disorder (Elvevag and Goldberg, 2000). N-methyl-d-aspartate (NMDA) glutamate receptor antagonists induce a psychosis-like state in healthy humans that mimics most major symptoms of schizophrenia (Javitt and Zukin, 1991), including cognitive impairment (Krystal et al., 1994). Acute NMDA receptor antagonist administration increases extracellular glutamate levels in the prefrontal cortex (PFC; Moghaddam et al., 1997), a brain region critically involved in cognition (Fuster, 1973, Robbins, 1996) and implicated in cognitive deficits in schizophrenia (Weinberger et al., 1986). Thus, excessive glutamate transmission, possibly through non-NMDA glutamate receptors, has been hypothesized to underlie schizophrenia pathology, including cognitive deficits (Mathé et al., 1998, Moghaddam et al., 1997).
The increase in PFC glutamate efflux induced by NMDA receptor antagonists may be attributable to blockade of excitatory NMDA receptors located on inhibitory γ-aminobutyric acid (GABA) interneurons, leading to disinhibition of glutamate release from neurons targeted by those interneurons (Adams and Moghaddam, 1998, Farber et al., 1998, Olney and Farber, 1995). NMDA receptor antagonist treatment has been shown to decrease markers of GABA function both in vitro and in vivo (Behrens et al., 2007, Cochran et al., 2003, Kinney et al., 2006, Morrow et al., 2007, Paulson et al., 2003). Two important markers that are reduced after NMDA receptor antagonist exposure are parvalbumin, a calcium binding protein located within a subpopulation of fast-spiking GABAergic interneurons centrally involved in information processing in the brain (Bartos et al., 2007, Cardin et al., 2009, Sohal et al., 2009), and glutamic acid decarboxylase-67 (GAD67), the main isoform of the synthesizing enzyme for GABA in the brain (Asada et al., 1997). The reductions in these two markers occur in the same neuronal population, the parvalbumin-positive fast-spiking inhibitory interneurons. Interestingly, disturbances in GABA systems, including reductions in parvalbumin and GAD67 in the PFC, have also been found in schizophrenia patients (Benes and Berretta, 2001, Guidotti et al., 2000, Hashimoto et al., 2003, Lewis et al., 2004, Olney and Farber, 1995). Disruption of GABA function in parvalbumin-positive fast-spiking interneurons may thus drive the glutamate disinhibition and cognitive impairment induced by NMDA receptor antagonists, as well as glutamate dysregulation and cognitive deficits in schizophrenia.
The schizophrenia-like state evoked by NMDA receptor antagonists in humans is present only during intoxication and dissipates after clearance of the drug from the body (Adler et al., 1998, Cho et al., 2005, Krystal et al., 1994, Krystal et al., 2003, Malhotra et al., 1996, Meltzer et al., 1972, Pradhan, 1984, Rosenbaum et al., 1959). However, a single administration of an NMDA receptor antagonist, such as phencyclidine (PCP), induces severe nonspecific behavioral disruptions (for review, see Amitai and Markou, 2010a, Jentsch and Roth, 1999), which often preclude the precise quantification of cognitive deficits that are likely induced by the first PCP administration. Repeated administration of PCP allows tolerance to develop to the initial nonspecific behavioral disruptions induced by PCP (Melnick et al., 2002). Upon administration of acute re-challenges with PCP, selective cognitive deficits can be observed (Podhorna and Didriksen, 2005). We therefore developed a repeated PCP administration regimen in which two initial PCP injections are followed by two drug-free weeks, after which several additional daily PCP injections are administered. This PCP regimen has been shown to induce robust, significant, and selective cognitive deficits with relevance to schizophrenia in the 5-choice serial reaction time task (Amitai et al., 2007, Amitai and Markou, 2009a, Amitai and Markou, 2009b, Amitai and Markou, 2010b), as well as impulsive-like response disinhibition in the intracranial self-stimulation procedure (Amitai et al., 2009). These PCP-induced deficits were sensitive to partial attenuation by chronic treatment with the atypical antipsychotic clozapine (Amitai et al., 2007, Amitai et al., 2009). By examining the potential of an atypical antipsychotic medication to prevent the disruptive effects of a re-challenge with a psychotomimetic drug, this experimental design parallels the prevention of recurrence of a psychotic episode in schizophrenia by antipsychotic treatment.
Repeated PCP administration alters the effects of PCP on neurotransmitter levels compared with a single acute administration. For example, while a single acute administration of PCP strongly increases dopamine levels in the PFC, repeated PCP administration decreases baseline PFC dopamine levels in the drug-free state and blunts the increase in PFC dopamine release immediately after acute re-challenges with PCP (Jentsch et al., 1998). However, little is known about the effects of repeated PCP exposure on glutamate function. To address this question, we investigated the effects of repeated PCP administration on glutamate in the PFC using in vivo microdialysis combined with the repeated PCP administration regimen that we developed previously (Amitai et al., 2007) and compared the resulting glutamate levels with the effects of a single PCP injection. Furthermore, we treated an independent group of rats with the repeated PCP regimen, harvested their brains at different time points during treatment, and assessed levels of the GABA markers parvalbumin and GAD67 in the PFC using immunohistochemistry. Finally, we assessed the effects of clozapine, an atypical antipsychotic that partially ameliorates cognitive deficits in schizophrenia, on the changes in PFC glutamate efflux and GABA markers induced by repeated PCP administration.
Section snippets
Subjects
Eighty male Wistar rats (Charles River Laboratories, Wilmington, MA) were housed two per cage on a 12 h/12 h reverse light/dark cycle (lights off at 8:00 am). All behavioral testing was conducted during the animals’ dark cycle. Rats were allowed to reach a body weight of at least 300 g before being restricted to 20 g of food per day and before initiating drug treatment. Food restriction was introduced to match as closely as possible the experimental conditions of previous studies in which
Experiment 1: effects of single or repeated PCP administration and chronic clozapine on extracellular glutamate in the PFC
Baseline glutamate levels (Single PCP group: 2.58 ± 0.65 μM; Vehicle/Repeated PCP group: 3.50 ± 0.72 μM; Clozapine/Repeated PCP group: 4.59 ± 0.70 μM; Clozapine/Saline group: 2.92 ± 0.43 μM) did not differ significantly among groups. ANOVA of the effects of PCP/saline administration detected significant main effects of both Time Point (F8,216 = 14.95, p < 0.0001) and Drug Treatment (F3,216 = 10.23, p = 0.0001), as well as a Drug Treatment × Time Point interaction (F24,216 = 6.41, p < 0.0001).
Discussion
Confirming previous studies (Abekawa et al., 2003, Abekawa et al., 2006, Abekawa et al., 2007, Adams and Moghaddam, 1998, Adams and Moghaddam, 2001), acute PCP exposure significantly elevated extracellular glutamate levels in the PFC of rats. This PCP-induced glutamate efflux was observed after a single PCP injection as well as after repeated PCP administration.
Interestingly, the increase in PFC glutamate in response to PCP appeared blunted after repeated PCP exposure compared to that seen
Acknowledgments
The authors would like to thank Mrs. Jessica Benedict for outstanding technical assistance, Mr. Michael Arends for excellent editorial assistance, and Dr. Daniel Hoyer from Novartis Pharma AG for providing us with clozapine.
References (71)
- et al.
The effect of atypical and classical antipsychotics on sub-chronic PCP-induced cognitive deficits in a reversal-learning paradigm
Behav. Brain Res.
(2006) - et al.
Effect of clozapine, haloperidol, or M100907 on phencyclidine-activated glutamate efflux in the prefrontal cortex
Biol. Psychiatry
(2001) - et al.
Effects of ketamine on thought disorder, working memory, and semantic memory in healthy volunteers
Biol. Psychiatry
(1998) - et al.
Increased impulsivity and disrupted attention induced by repeated phencyclidine are not attenuated by chronic quetiapine treatment
Pharmacol. Biochem. Behav.
(2009) - et al.
Disruption of performance in the five-choice serial reaction time task induced by repeated administration of N-methyl-D-aspartate receptor antagonists: relevance to cognitive dysfunction in schizophrenia
Biol. Psychiatry
(2010) - et al.
Effects of metabotropic glutamate receptor 2/3 agonism and antagonism on schizophrenia-like cognitive deficits induced by phencyclidine in rats
Eur. J. Pharmacol.
(2010) - et al.
Clozapine attenuates disruptions in response inhibition and task efficiency induced by repeated phencyclidine administration in the intracranial self-stimulation procedure
Eur. J. Pharmacol.
(2009) - et al.
Parvalbumin-immunoreactive neurons are reduced in the prefrontal cortex of schizophrenics
Schizophr. Res.
(1997) - et al.
Selective deficits in prefrontal cortical GABAergic neurons in schizophrenia defined by the presence of calcium-binding proteins
Biol. Psychiatry
(2002) - et al.
GABAergic interneurons: implications for understanding schizophrenia and bipolar disorder
Neuropsychopharmacology
(2001)
The glutamate synapse in neuropsychiatric disorders: focus on schizophrenia and Alzheimer’s disease
Prog. Brain Res.
Atypical antipsychotics attenuate a sub-chronic PCP-induced cognitive deficit in the novel object recognition task in the rat
Behav. Brain Res.
Phencyclidine-induced cognitive deficits in mice are improved by subsequent subchronic administration of clozapine, but not haloperidol
Eur. J. Pharmacol.
Reduced prefrontal cortical dopamine, but not acetylcholine, release in vivo after repeated, intermittent phencyclidine administration to rats
Neurosci. Lett.
The neuropsychopharmacology of phencyclidine: from NMDA receptor hypofunction to the dopamine hypothesis of schizophrenia
Neuropsychopharmacology
NMDA receptor function and human cognition: the effects of ketamine in healthy volunteers
Neuropsychopharmacology
A simple procedure for assessing ataxia in rats: effects of phencyclidine
Pharmacol. Biochem. Behav.
Phencyclidine (PCP): some human studies
Neurosci. Biobehav. Rev.
Involvement of γ-aminobutyric acid neurotransmission in phencyclidine-induced dopamine release in the medial prefrontal cortex
Eur. J. Pharmacol.
Effects of NRA0045, a novel potent antagonist at dopamine D4, 5-HT2A, and a1 adrenaline receptors, and NRA0160, a selective D4 receptor antagonist, on phencyclidine-induced behavior and glutamate release in rats
Psychopharmacology (Berl)
Role of the simultaneous enhancement of NMDA and dopamine D1 receptor-mediated neurotransmission in the effects of clozapine on phencyclidine-induced acute increases in glutamate levels in the rat medial prefrontal cortex
Naunyn Schmiedebergs Arch. Pharmacol.
Different effects of a single and repeated administration of clozapine on phencyclidine-induced hyperlocomotion and glutamate releases in the rat medial prefrontal cortex at short- and long-term withdrawal from this antipsychotic
Naunyn Schmiedebergs Arch. Pharmacol.
Corticolimbic dopamine neurotransmission is temporally dissociated from the cognitive and locomotor effects of phencyclidine
J. Neurosci.
Gene expression for glutamic acid decarboxylase is reduced without loss of neurons in prefrontal cortex of schizophrenics
Arch. Gen. Psychiatry
Chronic nicotine improves cognitive performance in a test of attention but does not attenuate cognitive disruption induced by repeated phencyclidine administration
Psychopharmacology (Berl)
Cognitive-disruptive effects of the psychotomimetic phencyclidine and attenuation by atypical antipsychotic medications in rats
Psychopharmacology (Berl)
Cleft palate and decreased brain γ-aminobutyric acid in mice lacking the 67-kDa isoform of glutamic acid decarboxylase
Proc. Natl. Acad. Sci. U. S. A.
Synaptic mechanisms of synchronized gamma oscillations in inhibitory interneuron networks
Nat. Rev. Neurosci.
Ketamine-induced loss of phenotype of fast-spiking interneurons is mediated by NADPH-oxidase
Science
Driving fast-spiking cells induces gamma rhythm and controls sensory responses
Nature
Absence of behavioral sensitization in healthy human subjects following repeated exposure to ketamine
Psychopharmacology (Berl)
Induction of metabolic hypofunction and neurochemical deficits after chronic intermittent exposure to phencyclidine: differential modulation by antipsychotic drugs
Neuropsychopharmacology
Reversal of PCP-induced learning and memory deficits in the Morris’ water maze by sertindole and other antipsychotics
Psychopharmacology (Berl)
Cognitive impairment in schizophrenia is the core of the disorder
Crit. Rev. Neurobiol.
Unit activity in prefrontal cortex during delayed-response performance: neuronal correlates of transient memory
J. Neurophysiol.
Cited by (69)
Phencyclidine Disrupts Neural Coordination and Cognitive Control by Dysregulating Translation
2024, Biological Psychiatry Global Open ScienceTargeting α6GABA<inf>A</inf> receptors as a novel therapy for schizophrenia: A proof-of-concept preclinical study using various animal models
2022, Biomedicine and PharmacotherapyPhencyclidine-induced cognitive impairments in repeated touchscreen visual reversal learning tests in rats
2021, Behavioural Brain ResearchGlutamate in schizophrenia: Neurodevelopmental perspectives and drug development
2020, Schizophrenia ResearchCitation Excerpt :As glutamate levels, particularly in the ACC, may remain elevated in patients who do not respond adequately to antipsychotic treatment, together this could suggest that standard antipsychotics are ineffective in modulating glutamate level in this subgroup. Interestingly, there is some suggestion that the additional efficacy of clozapine, an antipsychotic reserved for otherwise antipsychotic-resistant schizophrenia, may arise from its ability to reduce cortical glutamate levels or facilitate NMDAR activation (Abekawa et al., 2006; Amitai et al., 2012; Fukuyama et al., 2019; Javitt et al., 2005; López-Gil et al., 2007; Melone et al., 2001; Williams et al., 2004). Nonetheless, currently available antipsychotics, including clozapine, are not effective in reducing positive symptoms in all patients and also do not adequately address negative symptoms and cognitive impairment.
Treatment effects on neurometabolite levels in schizophrenia: A systematic review and meta-analysis of proton magnetic resonance spectroscopy studies
2020, Schizophrenia ResearchCitation Excerpt :For example, preclinical studies have suggested that excessive activation of glutamatergic neurotransmission following NMDA receptor hypofunction can cause excitotoxic effects, possibly leading to some of the structural alterations observed in schizophrenia (Olney and Farber, 1995; Plitman et al., 2014; Schobel et al., 2013). Meanwhile, past animal studies have reported that increased extracellular glutamate, caused by NMDA antagonists, was attenuated by antipsychotic treatments (Amitai et al., 2012; Kehr et al., 2018). It has also been reported that regulating excess extracellular glutamate and reducing abnormal hippocampal hypermetabolism might have protective effects on the volume of the hippocampus, in which volume loss is shown in schizophrenia (Schobel et al., 2013).