Ketamine Alters Lateral Prefrontal Oscillations in a Rule-Based Working Memory Task.

Acute administration of N-methyl-D-aspartate receptor (NMDAR) antagonists in healthy humans and animals produces working memory deficits similar to those observed in schizophrenia. However, it is unclear whether they also lead to altered low-frequency (≤60 Hz) neural oscillatory activities similar to those associated with schizophrenia during working memory processes. Here, we recorded local field potentials (LFPs) and single-unit activity from the lateral prefrontal cortex (LPFC) of three male rhesus macaque monkeys while they performed a rule-based prosaccade and antisaccade working memory task both before and after systemic injections of a subanesthetic dose (≤0.7 mg/kg) of ketamine. Accompanying working-memory impairment, ketamine enhanced the low-gamma-band (30-60 Hz) and dampened the beta-band (13-30 Hz) oscillatory activities in the LPFC during both delay periods and intertrial intervals. It also increased task-related alpha-band activities, likely reflecting compromised attention. Beta-band oscillations may be especially relevant to working memory processes because stronger beta power weakly but significantly predicted shorter saccadic reaction time. Also in beta band, ketamine reduced the performance-related oscillation as well as the rule information encoded in the spectral power. Ketamine also reduced rule information in the spike field phase consistency in almost all frequencies up to 60 Hz. Our findings support NMDAR antagonists in nonhuman primates as a meaningful model for altered neural oscillations and synchrony, which reflect a disorganized network underlying the working memory deficits in schizophrenia.SIGNIFICANCE STATEMENT Low doses of ketamine, an NMDAR blocker, produce working memory deficits similar to those observed in schizophrenia. In the lateral prefrontal cortex, a key brain region for working memory, we found that ketamine altered neural oscillatory activities in similar ways that differentiate schizophrenic patients and healthy subjects during both task and nontask periods. Ketamine induced stronger gamma (30-60 Hz) and weaker beta (13-30 Hz) oscillations, reflecting local hyperactivity and reduced long-range communications. Furthermore, ketamine reduced performance-related oscillatory activities, as well as the rule information encoded in the oscillations and in the synchrony between single-cell activities and oscillations. The ketamine model helps link the molecular and cellular basis of neural oscillatory changes to the working memory deficit in schizophrenia.

Ketamine Alters Outcome-Related Local Field Potentials in Monkey Prefrontal Cortex.

A subanesthetic dose of the noncompetitive N-methyl-d-aspartate receptor antagonist ketamine is known to induce a schizophrenia-like phenotype in humans and nonhuman primates alike. The transient behavioral changes mimic the positive, negative, and cognitive symptoms of the disease but the neural mechanisms behind these changes are poorly understood. A growing body of evidence indicates that the cognitive control processes associated with prefrontal cortex (PFC) regions relies on groups of neurons synchronizing at narrow-band frequencies measurable in the local field potential (LFP). Here, we recorded LFPs from the caudo-lateral PFC of 2 macaque monkeys performing an antisaccade task, which requires the suppression of an automatic saccade toward a stimulus and the initiation of a goal-directed saccade in the opposite direction. Preketamine injection activity showed significant differences in a narrow 20-30 Hz beta frequency band between correct and error trials in the postsaccade response epoch. Ketamine significantly impaired the animals' performance and was associated with a loss of the differences in outcome-specific beta-band power. Instead, we observed a large increase in high-gamma-band activity. Our results suggest that the PFC employs beta-band synchronization to prepare for top-down cognitive control of saccades and the monitoring of task outcome.

Ketamine-Induced Changes in the Signal and Noise of Rule Representation in Working Memory by Lateral Prefrontal Neurons.

Working memory dysfunction is an especially debilitating symptom in schizophrenia. The NMDA antagonist ketamine has been successfully used to model working memory deficits in both rodents and nonhuman primates, but how it affects the strength and the consistency of working memory representations remains unclear. Here we recorded single-neuron activity in the lateral prefrontal cortex of macaque monkeys before and after the administration of subanesthetic doses of ketamine in a rule-based working memory task. The rule was instructed with a color cue before each delay period and dictated the correct prosaccadic or antisaccadic response to a peripheral stimulus appearing after the delay. We found that acute ketamine injections both weakened the rule signal across all delay periods and amplified the trial-to-trial variance in neural activities (i.e., noise), both within individual neurons and at the ensemble level, resulting in impaired performance. In the minority of postinjection trials when the animals responded correctly, the preservation of the signal strength during the delay periods was predictive of their subsequent success. Our findings suggest that NMDA receptor function may be critical for establishing the optimal signal-to-noise ratio in information representation by ensembles of prefrontal cortex neurons. SIGNIFICANCE STATEMENT: In schizophrenia patients, working memory deficit is highly debilitating and currently without any efficacious treatment. An improved understanding of the pathophysiology of this symptom may provide critical information to treatment development. The NMDA antagonist ketamine, when injected at a subanesthetic dose, produces working memory deficit and other schizophrenia-like symptoms in humans and other animals. Here we investigated the effects of ketamine on the representation of abstract rules by prefrontal neurons, while macaque monkeys held the rules in working memory before responding accordingly. We found that ketamine weakened the signal-to-noise ratio in rule representation by simultaneously weakening the signal and augmenting noise. Both processes may be relevant in an effective therapy for working memory impairment in schizophrenia.

N-methyl-d-aspartate receptor antagonist ketamine impairs action-monitoring activity in the prefrontal cortex.

Failures in monitoring of self-generated actions are thought to underlie the positive symptoms in schizophrenia. It has been hypothesized that these deficits may be caused by a dysfunction of N-methyl-d-aspartate receptors (NMDARs). Here we recorded the activity of prefrontal neurons in monkeys performing an antisaccade task, while we administered a subanesthetic dose of the noncompetitive NMDAR antagonist ketamine. Many neurons discriminated between correct antisaccades and response errors in their postresponse activity. Ketamine increased the activity for the neurons' nonpreferred response, thereby decreasing the neurons' performance selectivity. Ketamine also affected the monkeys' behavior after an error, consistent with a deficit in error detection. The results show that NMDARs play an important role in action monitoring in primates. The decrease in performance selectivity of prefrontal neurons after ketamine can help to explain the deficits in action monitoring found in humans after ketamine administration and provides support for the hypothesis that an NMDAR dysfunction underlies self-monitoring deficits and psychotic symptoms in schizophrenia.

NMDA antagonist ketamine reduces task selectivity in macaque dorsolateral prefrontal neurons and impairs performance of randomly interleaved prosaccades and antisaccades.

Ketamine, an NMDA receptor antagonist, has been shown to induce behavioral abnormalities in humans that mimic the positive, negative, and most importantly cognitive deficits observed in schizophrenia. Similar cognitive deficits have been observed in nonhuman primates after a subanesthetic dose of ketamine, including an impairment in their ability to perform the antisaccade task, which requires the suppression of a prosaccade toward a flashed stimulus and the generation of a saccade in the opposite direction. The neural basis underlying these cognitive impairments remains unknown. Here, we recorded single-neuron activity in the lateral prefrontal cortex of macaque monkeys before and after the administration of subanesthetic doses of ketamine during the performance of randomly interleaved prosaccade and antisaccade trials. Ketamine impeded the monkeys' ability to maintain and apply the correct task rule and increased reaction times of prosaccades and antisaccades. These behavioral changes were associated with an overall increase in activity of PFC neurons and a reduction in their task selectivity. Our results suggest that the mechanism underlying ketamine-induced cognitive abnormalities may be the nonspecific increase in PFC activity and the associated reduction of task selectivity.

An Emergency Department Survey on Research Participation in the Patient With Suicidal Ideation or Suicide Attempt.

The patient expressing suicidal ideation is a common mental health presentation in the emergency department (ED) but a notion exists that this psychiatric crisis precludes them from research participation. In order to better understand the potential research participation of suicidal patients, this study surveyed patients in the ED with suicide attempt or ideation. This was an anonymized survey study interviewing 50 patients in a tertiary care ED with a chief complaint of suicide attempt or suicidal ideation. A script was read by the research assistant regarding a hypothetical research study using ketamine to treat suicidality in the ED and asked to rate their interest in participation in the study as well as their interest in a 1-week follow-up call. Most patients (84%) reported that they would be interested in participating in this research project while 96% of all 50 patients would be interested in a follow-up phone call at 1 week. The data from this study should help other emergency medicine and psychiatry researchers advance projects in this underserved ED patient population.

Flow through the Emergency Department for Patients Presenting with Substance Use Disorder in Alberta, Canada.

INTRODUCTION: Since 2016 the province of Alberta, Canada, has seen a significant increase in substance use disorder (SUD) presentations to the emergency department (ED) with a large surge during the COVID-19 pandemic. In this retrospective study we deconstruct the total length of stay (LOS) in the ED into stages for patients presenting with SUD and estimate the effects of covariates on the time to transition between stages. METHODS: Using the Canadian Coding Standards for International Classification of Diseases, 10th Modification, codes F10.0-F19.9 and T36.0-T50.9, we extracted data from the National Ambulatory Care Reporting System between April 1, 2019-March 31, 2020 on all ED presentations for SUD by Alberta residents. We used a multistate model to deconstruct the EDLOS into eight mutually exclusive states and determine which factors affected the time spent in each state. RESULTS: We analyzed 66,880 presentations (37,530 patients). The mean age was 37.2 years, and 61% were male. The median total LOS in the ED was 6 hours 13 minutes. Patients presenting with methamphetamines (METH) intoxication and patients from low-income neighborhoods had significantly increased transition times between all states. Opposite this, opiate use was associated with faster transition times between almost all states. Metro EDs experienced slower transitions when attempting to discharge or admit patients when compared to urban or rural EDs. Emergency department crowding also had a dramatic effect on physician initial assessment times, while discharge and admission times in patients presenting with SUD were also significantly affected. CONCLUSION: Patients with SUD experience a variety of delays during their ED stay. Those with METH intoxication and those from the lowest income neighborhoods were most likely to experience slower transitions from state to state in the ED and may benefit from a focused approach to improve ED flow.

Intravenous ketamine for depression: A clinical discussion reconsidering best practices in acute hypertension management.

Ketamine is a versatile medication with an emerging role for the treatment of numerous psychiatric conditions, including treatment resistant depression. Current psychiatry guidelines for its intravenous administration to treat depression recommend regular blood pressure monitoring and an aggressive approach to potential transient hypertensive episodes induced by ketamine infusions. While this approach is aimed at ensuring patient safety, it should be updated to align with best practice guidelines in the management of hypertension. This review defines and summarizes the currently recommended approach to the hypertensive emergency, the asymptomatic hypertensive urgency, and discusses their relevance to intravenous ketamine therapy. With an updated protocol informed by these best practice guidelines, ketamine treatment for depression may be more accessible to facilitate psychiatric treatment.

Behavioral abnormalities in synapsin II knockout mice implicate a causal factor in schizophrenia.

Recent studies on the phosphoprotein synapsin II have revealed reduced expression in postmortem medial prefrontal cortex tissues from subjects with schizophrenia, and chronic antipsychotic drug treatment has resulted in concurrent increases in synapsin II mRNA and protein levels. Collectively, this research suggests a role of synapsin II in the pathophysiology of schizophrenia; however, whether synapsin II plays a causal role in this disease process still remains unclear. Therefore, the goal of this investigation was to examine whether synapsin II knockout mice display behavioral abnormalities commonly expressed in preclinical animal models of schizophrenia, namely deficits in prepulse inhibition (PPI), decreased social behavior, and locomotor hyperactivity. Results indicate that mice with knockout of the synapsin II gene demonstrate deficits in PPI at three prepulse intensities (67, 70, and 73 dB), along with deficits in habituation to startle to a 110 dB acoustic pulse. Knockout animals also expressed decreased social behavior and increased locomotor activity when compared to wildtype and heterozygous populations. Complete knockout of the synapsin II gene was confirmed in postmortem brain tissues via immunoblotting. In conclusion, these results confirm that synapsin II knockout mice display behavioral endophenotypes similar to established preclinical animal models of schizophrenia, and lend support to the notion that abnormalities in synapsin II expression may play a causal role in the underlying pathophysiological mechanisms of schizophrenia.

Allosteric modulation of the dopamine receptor by conformationally constrained type VI beta-turn peptidomimetics of Pro-Leu-Gly-NH2.

A peptidomimetic of Pro-Leu-Pro-NH2, 7, possessing an indolizidinone type VI beta-turn mimic was synthesized via improved high-yielding protocols for the preparation and Cbz protection of alpha-allylproline. Bicyclic peptidomimetic 7 and spirobicylic peptidomimetic 8 enhanced the binding of [3H] N-propylnorapomorphine to dopamine receptors indicating that a type VI beta-turn is a possible bioactive conformation of the homochiral Pro-Leu-Pro-NH2 and Pro-Pro-Pro-NH 2 analogues of Pro-Leu-Gly-NH2 at the dopamine receptor allosteric regulatory site.

MIF-1 and its peptidomimetic analogs attenuate haloperidol-induced vacuous chewing movements and modulate apomorphine-induced rotational behavior in 6-hydroxydopamine-lesioned rats.

Two melanocyte-stimulating hormone release inhibiting factor-1 (MIF-1) also known as L-prolyl-L-leucyl-glycinamide (PLG) peptidomimetic analogs, 3(R)-[[[2(S)-pyrrolidinyl]carbonyl]-amino]-3-(butyl)-2-oxo-1-pyrrolidineacetamide trifluoroacetate (A) and 3(R)-[[[2(S)-pyrrolidinyl]carbonyl]amino]-3-(benzyl)-2-oxo-1-pyrrolidineacetamide trifluoroacetate (B), were evaluated for their ability to modulate dopaminergic activity by measuring apomorphine-induced rotations in 6-hydroxydopamine (6-OHDA)-lesioned rats, and haloperidol (HP)-induced vacuous chewing movements (VCMs) in rats; animal models of Parkinson's disease (PD) and human tardive dyskinesia (TD), respectively. In the 6-OHDA model, both analogs were found to potentiate the contralateral rotational behavior induced by apomorphine dose-dependently and with approximately the same potency. Furthermore, each analog was able to significantly attenuate HP-induced VCMs with almost equal efficacy. The potency and efficacy of these analogs were significantly greater than their parent compound, PLG. These results suggest that both analogs can modulate dopaminergic activity in vivo, likely by the same mechanisms recruited by PLG previously reported.

Alpha-phenyl-N-tert-butylnitrone prevents oxidative stress in a haloperidol-induced animal model of tardive dyskinesia: investigating the behavioural and biochemical changes.

Haloperidol (HP) is a widely prescribed antipsychotic drug used for the treatment of mental disorders. However, while providing therapeutic benefits, this drug also causes serious extrapyramidal side effects, such as tardive dyskinesia (TD). Upon chronic administration, HP causes behavioural supersensitivity to dopamine D2 receptor agonists, as well as the development of vacuous chewing movements (VCMs), in an animal model of human TD. Currently, a prevailing hypothesis to account for these behavioural abnormalities implicates oxidative stress. This study was undertaken to examine whether the free radical trapping agent, α-phenyl-N-tert-butylnitrone (PBN), can prevent the development of behavioural supersensitivity to dopamine D2 receptor agonists and the development of VCMs. Additionally, the study examined whether increased synthesis of apoptosis inducing factor (AIF) can result from HP-induced oxidative stress. Male Sprague-Dawley rats were treated with HP in conjunction with PBN, or its vehicle, for 4weeks. After a 24-hour washout period, behavioural observations were recorded along with the estimation of lipid peroxidation and antioxidant enzyme activities. The free radical trapping agent, PBN, prevented the development of behavioural supersensitivity, reduced lipid peroxidation and prevented the reduction of antioxidant enzyme activities. AIF concentrations at the mRNA and protein levels remained unchanged; therefore increased AIF gene expression is unlikely to be involved in HP-induced oxidative stress. The findings of the present study suggest the involvement of striatal free radicals in the development of behavioural supersensitivity, and free radical trapping agents, such as PBN, as possible options for the treatment of extrapyramidal side effects in humans.

Specific binding of photoaffinity-labeling peptidomimetics of Pro-Leu-Gly-NH2 to the dopamine D2L receptor: evidence for the allosteric modulation of the dopamine receptor.

The present study was undertaken to investigate the mechanistic role of l-prolyl-l-leucyl-glycinamide (PLG) in modulating agonist binding to the dopamine D(2L) receptor. Competition and displacement assays indicate that the photoaffinity-labeling peptidomimetics of PLG, 3(R)-[(4(S)-(4-azido-2-hydroxy-benzoyl) amino-2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide hydrochloride (1a) and 3(R)-[(4(S)-(4-azido-2-hydroxy-5-iodo-benzoyl)amino-2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide hydrochloride (1b) bind at the same site as PLG. Autoradiography was used to establish the covalent binding of [(125)I]-1b to an approximately 51kDa protein in bovine striatal membranes. Western blot analysis with a dopamine D(2L)-specific antibody, in combination with autoradiography, following a two-dimensional gel separation, suggested this approximately 51kDa protein to be the dopamine D(2L) receptor. Further evidence for binding of 1b to dopamine D(2L) was provided by samples immunoprecipitated with the D(2L) antibody. These samples were analyzed by western blotting in parallel with autoradiography of [(125)I]-1b labeled protein. Both methods revealed bands at approximately 51kDa. Furthermore, PLG is shown to compete with 1b for binding to the dopamine D(2L) receptor as determined by autoradiography, as well as competition experiments with PLG and 1a. Collectively, these findings suggest the successful development of a photoaffinity-labeling agent, compound 1b, that has been used to elucidate the interaction of PLG specifically with the dopamine D(2L) receptor.

Role of AP-2alpha transcription factor in the regulation of synapsin II gene expression by dopamine D1 and D2 receptors.

Synapsins are a family of neuron-specific phosphoproteins involved in synaptic vesicle docking, synaptogenesis, and synaptic plasticity. Previous studies have reported an increase in synapsin II protein by dopaminergic agents in the striatum, medial prefrontal cortex, and nucleus accumbens. This study investigated the mechanistic pathway involved in synapsin II regulation by dopaminergic drugs using primary midbrain neurons to determine which of several transcription factors regulates synapsin II expression. Protein kinase A (PKA) participation in the signaling pathway was examined using selective PKA inhibitors, which reduced synapsin II expression in cell cultures while dopaminergic agents were unable to increase synapsin II in the presence of the PKA inhibitor. Transcription factor involvement was further investigated using separate cultures treated with antisense deoxyoligonucleotides (ADONs) against the following transcription factors: activating protein 2 alpha (AP-2alpha), early growth response factor 1 (EGR-1), or polyoma enhancer activator-3 (PEA-3). Selective knockdown of AP-2alpha by ADONs reduced synapsin II levels, whereas treatment with EGR-1 and PEA-3 ADONs did not affect synapsin II expression. Furthermore, dopaminergic agents were no longer able to influence synapsin II concentrations following AP-2alpha knockdown. Collectively, these results indicate that a cyclic adenosine-3',5'-monophosphate/PKA-dependent mechanism involving the AP-2alpha transcription factor is likely responsible for the increase in neuronal synapsin II following dopamine D1 receptor stimulation or dopamine D2 receptor inhibition.

Allosteric modulation of the dopamine D2 receptor by Pro-Leu-Gly-NH2 peptidomimetics constrained in either a polyproline II helix or a type II beta-turn conformation.

Type II beta-turn mimics and polyproline II helix mimics based upon diastereoisomeric 5.6.5 spiro bicyclic scaffolds have provided two pairs of Pro-Leu-Gly-NH(2) (PLG) peptidomimetics with contrasting dopamine receptor modulating activities. Compounds 1a and 3a were found to be positive allosteric modulators of the dopamine receptor, while the corresponding diastereoisomeric compounds 1b and 3b provided the first PLG peptidomimetics with the ability to decrease the binding of agonists to the dopamine receptor. The positive allosteric modulating activity of 3a supported the hypothesis that a polyproline II helix conformation is the bioactive conformation for the PLG analogue Pro-Pro-Pro-NH(2). The results also show that a change in the bridgehead chirality of the 5.6.5 scaffold brings about opposite effects in terms of the modulation of the dopamine receptor.

Cloning, characterization, and functional studies of a human 40-kDa catecholamine-regulated protein: implications in central nervous system disorders.

Catecholamine-regulated proteins (CRPs) have been shown to bind dopamine and other structurally related catecholamines; in particular, the 40-kDa CRP (CRP40) protein has been previously cloned and functionally characterized. To determine putative human homologs, BLAST analysis using the bovine CRP40 sequence identified a human established sequence tag (EST) with significant homology (accession #BQ224193). Using this EST, we cloned a recombinant human brain CRP40-like protein, which possessed chaperone activity. Radiolabeled dopamine binding studies with recombinant human CRP40 protein demonstrated the ability of this protein to bind dopamine with low affinity and high capacity. The full-length human CRP40 nucleotide sequence was elucidated (accession #DQ480334) with RNA ligase-mediated rapid amplification of complementary DNA ends polymerase chain reaction, while Northern blot hybridization suggested that human CRP40 is an alternative splice variant of the 70-kDa mitochondrial heat shock protein, mortalin. Human SH-SY5Y neuroblastoma cells treated with the antipsychotic drug, haloperidol, exhibited a significant increase in CRP40 messenger RNA expression compared to untreated control cells, while other dopamine agonists/antagonists also altered CRP40 expression and immunolocalization. In conclusion, these results show that we have cloned a splice variant of mortalin with a novel catecholamine binding function and that this chaperone-like protein may be neuroprotective in dopamine-related central nervous system disorders.

Modulation of agonist binding to human dopamine receptor subtypes by L-prolyl-L-leucyl-glycinamide and a peptidomimetic analog.

The present study was undertaken to investigate the role of the hypothalamic tripeptide L-prolyl-L-leucyl-glycinamide (PLG) and its conformationally constrained analog 3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA) in modulating agonist binding to human dopamine (DA) receptor subtypes using human neuroblastoma SH-SY5Y cells stably transfected with respective cDNAs. Both PLG and PAOPA enhanced agonist [3H]N-propylnorapomorphine (NPA) and [3H]quinpirole binding in a dose-dependent manner to the DA D2L,D2S, and D4 receptors. However, agonist binding to the D1 and D3 receptors and antagonist binding to the D2L receptors by PLG were not significantly affected. Scatchard analysis of [3H]NPA binding to membranes in the presence of PLG revealed a significant increase in affinity of the agonist binding sites for the D2L, D2S, and D4 receptors. Analysis of agonist/antagonist competition curves revealed that PLG and PAOPA increased the population and affinity of the high-affinity form of the D2L receptor and attenuated guanosine 5'-(beta,gamma-imido)-triphosphate-induced inhibition of high-affinity agonist binding sites for the DA D2L receptor. Furthermore, direct NPA binding with D2L cell membranes pretreated with suramin, a compound that can uncouple receptor/G protein complexes, and incubated with and without DA showed that both PLG and PAOPA had only increased agonist binding in membranes pretreated with both suramin and DA, suggesting that PLG requires the D2L receptor/G protein complex to increase agonist binding. These results suggest that PLG possibly modulates DA D2S, D2L, and D4 receptors in an allosteric manner and that the coupling of D2 receptors to the G protein is essential for this modulation to occur.