Long-term efficacy and safety of perampanel as an add-on therapy in patients with epilepsy

BACKGROUND

Perampanel (PER) is a newly developed amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor antagonist that has been globally approved for the treatment of both focal and generalized seizures. The efficacy and safety of PER have only been reported over short periods of treatment so far. This study aims to clarify the long-term efficacy and safety of PER as an add-on therapy.

METHOD

This retrospective observational study investigated 176 epilepsy patients who received PER as add-on medical therapy in two Japanese epilepsy centers between June 2016 and July 2022. The adherence, seizure frequency, and plasma concentration of PER were evaluated at three time points: 6 months, 12 months, and 24 months or longer after the start of adjunctive PER treatment.

RESULTS

112 patients undergoing PER treatment were evaluated at 6 months, 86 were evaluated at 12 months, and 52 were evaluated at 24 months or longer. Overall, 42.9 % (48/112), 45.4 % (40/86), and 44.2 % (23/52) of the patients were seizure-free at 6, 12, and 24 months or longer, respectively. The rate of PER tolerance was 78.3 %, 69.9 %, and 54.7 % at 6, 12, and 24 months or longer, respectively. At the latest timepoint, the seizure-free group was taking a significantly lower dose of PER than the seizure-remnant group, and the number of anti-seizure medications (ASMs) was associated with seizure outcomes. In addition, the seizure-free rate was significantly higher in patients who received PER as a first add-on than in those who received it as a late add-on. No significant difference was found in the plasma concentration of PER between the seizure-free and seizure-remnant groups at 24 months or longer. Among the patients receiving PER at dose of 2 mg, however, the plasma concentrations were significantly higher in the seizure-free group than in the seizure-remnant group (282.7 ± 109.8 μg/ml vs 94.7 ± 54.9 μg/ml, p = 0.0024).

CONCLUSION

This long-term retrospective observational study provides evidence of the efficacy and safety of PER over 2 years treatment period in Japan. Notably, patients who started on PER as the first add-on showed a better seizure outcome than those who received it as a late add-on over the long term. Measured plasma concentrations may provide valuable guidance for the management of patients. Higher plasma concentration at low dose PER may suggest the better seizure control.

Intrahippocampal injection of a selective blocker of NMDA receptors containing the GluN2B subunit, Ro25-6981, increases glutamate neurotransmission and induces antidepressant-like effects

Major depressive disorder (MDD) is a serious public health problem, as it is the most common psychiatric disorder worldwide. Antidepressant drugs increase adult hippocampal neurogenesis, which is required to induce some behavioral effects of antidepressants. Adult-born granule cells in the dentate gyrus (DG) and the glutamate receptors subunits 2 (GluN2B) subunit of N-methyl-D-aspartate (NMDA) ionotropic receptors play an important role in these effects. However, the precise neurochemical role of the GluN2B subunit of the NMDA receptor on adult-born GCs for antidepressant-like effects has yet to be elucidated. The present study aims to explore the contribution of the GluN2B-containing NMDA receptors in the ventral dentate gyrus (vDG) to the antidepressant drug treatment using a pharmacological approach. Thus, (αR)-(4-hydroxyphenyl)-(βS)-methyl-4-(phenylmethyl)-1-piperidinepropanol (Ro25-6981), a selective antagonist of the GluN2B subunit, was acutely administered locally into the ventral DG (vDG, 1 μg each side) following a chronic fluoxetine (18 mg/kg/day) treatment-known to increase adult hippocampal neurogenesis-in a mouse model of anxiety/depression. Responses in a neurogenesis-dependent task, the novelty suppressed feeding (NSF), and neurochemical consequences on extracellular glutamate and gamma-aminobutyric acid (GABA) levels in the vDG were measured. Here, we show a rapid-acting antidepressant-like effect of local Ro25-6981 administration in the NSF independent of fluoxetine treatment. Furthermore, we revealed a fluoxetine-independent increase in the glutamatergic transmission in the vDG. Our results suggest behavioral and neurochemical effects of GluN2B subunit independent of serotonin reuptake inhibition.

The protective effect of N-acetylcysteine against MK-801-induced neurodegeneration in mice

BACKGROUND

Neurological disorders result in not only a decline in the quality of life of patients but also a global economic burden. Therefore, protective medicine becomes more important for society. MK-801 is a chemical agent used to understand the etiology of behavioral disorders and brain degeneration in animal models. This study aims to determine whether N-acetylcysteine (NAC) is useful to treat brain degeneration caused by MK-801, an N-methyl-D-aspartate glutamate receptor antagonist.

METHODS AND RESULTS

Four groups were formed by dividing 24 male BALB/c mice into groups of six. The control group was given a saline solution (10 ml/kg-i.p.). MK-801 (1 mg/kg-i.p.) was given alone to one group, and it was given with NAC (100 mg/kg-i.p.) to another group, while the last group was given only NAC (100 mg/kg-i.p.). The administration of drugs lasted for fourteen days. After the behavioral tests (open field and elevated plus-maze), all animals were euthanised, and brain tissues were collected for real-time PCR, TAS-TOS analysis, hematoxylin-eosin, Kluver-Barrera, and TUNEL staining. In the MK-801 group, besides nuclear shrinkage in neurons, glial cell infiltration, vacuolization in cortical neurons, white matter damage, and apoptosis were observed.

CONCLUSION

In the mice given NAC as a protective agent, it was observed that behavioral problems improved, antioxidant levels increased, and nuclear shrinkage, glial cell infiltration, vacuolization in neurons, and white matter degeneration were prevented. Moreover, MBP expression increased, and the number of TUNEL-positive cells significantly decreased. As a result, it was observed that NAC may have a protective effect against brain degeneration.

Role of kainate receptors in pruriceptive processing in the mouse spinal cord

Pruritus, including neuropathic and psychogenic pruritus, is an unpleasant feeling that causes a desire to scratch, which negatively impacts physical and psychological aspects of daily life. Nonetheless, little is known about the neural mechanisms involved in pruritus. Glutamate is a predominant excitatory neurotransmitter in the mammalian central nervous system and exerts its effects by binding to various glutamate receptors, including kainate (KA) receptors; however, the precise involvement of each glutamate receptor in pruriceptive processing remains unclear, particularly that of KA receptors. Therefore, the roles of KA receptors in histamine-dependent and -independent itch were investigated using CNQX, an AMPA/KA receptors antagonist, UBP310 and UBP302, antagonists of KA receptors, and small interfering (si)RNAs against KA receptor subunits in mice with acute and chronic pruritus. The effects of KA receptor antagonists on histamine-induced c-Fos expression in the spinal cord were also examined. The intrathecal administration of CNQX reduced the number of scratching events induced by histamine and chloroquine. On the other hand, UBP310 or UBP302 and the siRNAs of KA receptor subunits 1-3 significantly inhibited the induction of scratching events in mice treated with histamine, while no significant change was observed in the induction of spontaneous scratching events in mice with chronic pruritus. In addition, antagonists of KA receptors attenuated c-Fos expression in the superficial layers of the dorsal horn induced by histamine. These results indicate that KA receptors are involved in acute pruriceptive processing in the spinal cord induced by histamine, but not chloroquine or chronic itch.

Hyperammonaemia disrupts daily rhythms reversibly by elevating glutamate in the central circadian pacemaker

Patients with cirrhosis exhibit features of circadian disruption. Hyperammonaemia has been suggested to impair both homeostatic and circadian sleep regulation. Here, we tested if hyperammonaemia directly disrupts circadian rhythm generation in the central pacemaker, the suprachiasmatic nuclei (SCN) of the hypothalamus. Wheel-running activity was recorded from mice fed with a hyperammonaemic or normal diet for ~35 days in a 12:12 light-dark (LD) cycle followed by ~15 days in constant darkness (DD). The expression of the clock protein PERIOD2 (PER2) was recorded from SCN explants before, during and after ammonia exposure, ±glutamate receptor antagonists. In LD, hyperammonaemic mice advanced their daily activity onset time by ~1 h (16.8 ± 0.3 vs. 18.1 ± 0.04 h, p = .009) and decreased their total activity, concentrating it during the first half of the night. In DD, hyperammonaemia reduced the amplitude of daily activity (551.5 ± 27.7 vs. 724.9 ± 59 counts, p = .007), with no changes in circadian period. Ammonia (≥0.01 mM) rapidly and significantly reduced PER2 amplitude, and slightly increased circadian period. The decrease in PER2 amplitude correlated with decreased synchrony among circadian cells in the SCN and increased extracellular glutamate, which was rescued by AMPA glutamate receptor antagonists. These data suggest that hyperammonaemia affects circadian regulation of rest-activity behaviour by increasing extracellular glutamate in the SCN.

Betaine prevents and reverses the behavioral deficits and synaptic dysfunction induced by repeated ketamine exposure in mice

As an N-methyl-D-aspartate (NMDA) receptor inhibitor, ketamine has become a popular recreational substance and currently is used to address treatment-resistant depression. Since heavy ketamine use is associated with persisting psychosis, cognitive impairments, and neuronal damage, the safety of ketamine treatment for depression should be concerned. The nutrient supplement betaine has been shown to counteract the acute ketamine-induced psychotomimetic effects and cognitive dysfunction through modulating NMDA receptors. This study aimed to determine whether the adjunctive or subsequent betaine treatment would improve the enduring behavioral disturbances and hippocampal synaptic abnormality induced by repeated ketamine exposure. Mice received ketamine twice daily for 14 days, either combined with betaine co-treatment or subsequent betaine post-treatment for 7 days. Thereafter, three-chamber social approach test, reciprocal social interaction, novel location/object recognition test, forced swimming test, and head-twitch response induced by serotonergic hallucinogen were monitored. Data showed that the enduring behavioral abnormalities after repeated ketamine exposure, including disrupted social behaviors, recognition memory impairments, and increased depression-like and hallucinogen-induced head-twitch responses, were remarkably improved by betaine co-treatment or post-treatment. Consistently, betaine protected and reversed the reduced hippocampal synaptic activity, such as decreases in field excitatory post-synaptic potentiation (fEPSP), long-term potentiation (LTP), and PSD-95 levels, after repeated ketamine treatment. These results demonstrated that both co-treatment and post-treatment with betaine could effectively prevent and reverse the adverse behavioral manifestations and hippocampal synaptic plasticity after repeated ketamine use, suggesting that betaine can be used as a novel adjunct therapy with ketamine for treatment-resistant depression and provide benefits for ketamine use disorders.

Graded heterogeneity of metabotropic signaling underlies a continuum of cell-intrinsic temporal responses in unipolar brush cells

Many neuron types consist of populations with continuously varying molecular properties. Here, we show a continuum of postsynaptic molecular properties in three types of neurons and assess the functional correlates in cerebellar unipolar brush cells (UBCs). While UBCs are generally thought to form discrete functional subtypes, with mossy fiber (MF) activation increasing firing in ON-UBCs and suppressing firing in OFF-UBCs, recent work also points to a heterogeneity of response profiles. Indeed, we find a continuum of response profiles that reflect the graded and inversely correlated expression of excitatory mGluR1 and inhibitory mGluR2/3 pathways. MFs coactivate mGluR2/3 and mGluR1 in many UBCs, leading to sequential inhibition-excitation because mGluR2/3-currents are faster. Additionally, we show that DAG-kinase controls mGluR1 response duration, and that graded DAG kinase levels correlate with systematic variation of response duration over two orders of magnitude. These results demonstrate that continuous variations in metabotropic signaling can generate a stable cell-autonomous basis for temporal integration and learning over multiple time scales.

Do NMDA-R antagonists re-create patterns of spontaneous gamma-band activity in schizophrenia? A systematic review and perspective

NMDA-R hypofunctioninig is a core pathophysiological mechanism in schizophrenia. However, it is unclear whether the physiological changes observed following NMDA-R antagonist administration are consistent with gamma-band alterations in schizophrenia. This systematic review examined the effects of NMDA-R antagonists on the amplitude of spontaneous gamma-band activity and functional connectivity obtained from preclinical (n = 24) and human (n = 9) studies and compared these data to resting-state EEG/MEG-measurements in schizophrenia patients (n = 27). Overall, the majority of preclinical and human studies observed increased gamma-band power following acute administration of NMDA-R antagonists. However, the direction of gamma-band power alterations in schizophrenia were inconsistent, which involved upregulation (n = 10), decreases (n = 7), and no changes (n = 8) in spectral power. Five out of 6 preclinical studies observed increased connectivity, while in healthy controls receiving Ketamine and in schizophrenia patients the direction of connectivity results was also inconsistent. Accordingly, the effects of NMDA-R hypofunctioning on gamma-band oscillations are different than pathophysiological signatures observed in schizophrenia. The implications of these findings for current E/I balance models of schizophrenia are discussed.

Excess extracellular K+ causes inner hair cell ribbon synapse degeneration

Inner hair cell (IHC) ribbon synapses are the first synapse in the auditory system and can be degenerated by noise and aging, thereby leading to hidden hearing loss (HHL) and other hearing disorders. However, the mechanism underlying this cochlear synaptopathy remains unclear. Here, we report that elevation of extracellular K+, which is a consequence of noise exposure, could cause IHC ribbon synapse degeneration and swelling. Like intensity dependence in noise-induced cochlear synaptopathy, the K+-induced degeneration was dose-dependent, and could be attenuated by BK channel blockers. However, application of glutamate receptor (GluR) agonists caused ribbon swelling but not degeneration. In addition, consistent with synaptopathy in HHL, both K+ and noise exposure only caused IHC but not outer hair cell ribbon synapse degeneration. These data reveal that K+ excitotoxicity can degenerate IHC ribbon synapses in HHL, and suggest that BK channel may be a potential target for prevention and treatment of HHL.

Recovery of cognitive functioning following abstinence from ketamine

BACKGROUND

Acute and adverse effects of ketamine on cognitive functioning have been documented. No longitudinal study has examined whether cognitive deficits can be reversed following ketamine abstinence although it has been suggested in some cross-sectional studies. This study aimed to investigate the changes in cognitive functioning among ketamine users following a 12-week abstinence from ketamine.

METHODS

In this longitudinal study, 114 ketamine users completed clinical and cognitive assessments at both baseline and 12-week follow-up with the following instruments: Severity of Dependence Scale, Beck Depression Inventory (BDI), Anxiety Subscale of the Hospital Anxiety Depression Scale (HADSA), and a cognitive battery.

RESULTS

BDI (p < 0.001) and HADSA (p = 0.044) scores were significantly reduced at the 12-week follow-up. Significant improvements were found in Wechsler Adult Intelligence Scale (Third edition) immediate recall (p < 0.001) and delayed recall (p < 0.001) on the Rey-Osterrieth Complex Figure Test, and in delayed recall (p < 0.001), and immediate recall (p = 0.001) on the Logical Memory component of the Wechsler Memory Scale (Third Edition) at the 12-week follow-up. Participants completed the Stroop Inference Test significantly faster (p < 0.001); and required fewer number of attempts (p < 0.001) and produced fewer perseverative errors (p < 0.001) on the Wisconsin Card Sorting Test at the 12-week follow-up.

CONCLUSION

Chronic ketamine users' verbal and visual memory and executive functions improved after 12 weeks of ketamine abstinence.

Prevalence of gabapentin in drug overdose postmortem toxicology testing results

BACKGROUND

The goal of this study was to establish and compare baseline data on the prevalence of gabapentin identified through postmortem toxicology testing among drug overdose decedents in several geographically diverse states/jurisdictions with differing levels of drug overdose fatality burdens in 2015.

METHODS

Death certificates and postmortem toxicology result reports from five U.S. jurisdictions were used to identify residents who died from drug overdoses in year 2015 and to calculate prevalence rates of gabapentin in postmortem toxicology by jurisdiction.

RESULTS

On average, 22% of all drug overdose decedents in our study tested positive for gabapentin. The percentage of gabapentin-positive overdose deaths varied significantly among jurisdictions: 4% in Northeast Tennessee, 7% in Maricopa County, 15% in West Virginia, 20% in North Carolina, and 41% in Kentucky (p < 0.0001). Among the drug overdose decedents who tested positive for opioids (including heroin), 26% also tested positive for gabapentin, with significant variation among states/jurisdictions (p < 0.0001). There was a significant difference in the gender distribution among drug overdose decedents who tested positive for gabapentin (46% male) vs. those who tested negative for gabapentin (65% male) (p < 0.0001). In Kentucky, gabapentin was listed as a contributing drug on the death certificate in 40% of the overdose deaths with gabapentin-positive toxicology; in North Carolina this percentage was 57%.

CONCLUSIONS

Routine gabapentin postmortem testing and linking of death certificate, medical examiner, coroner, toxicology, and prescription history data will provide more reliable information on the extent of gabapentin misuse, diversion, and implications for clinical care.

Ischemia-induced spreading depolarization in the retina

Cortical spreading depolarization is a metabolically costly phenomenon that affects the brain in both health and disease. Following severe stroke, subarachnoid hemorrhage, or traumatic brain injury, cortical spreading depolarization exacerbates tissue damage and enlarges infarct volumes. It is not known, however, whether spreading depolarization also occurs in the retina in vivo. We report now that spreading depolarization episodes are generated in the in vivo rat retina following retinal vessel occlusion produced by photothrombosis. The properties of retinal spreading depolarization are similar to those of cortical spreading depolarization. Retinal spreading depolarization waves propagate at a velocity of 3.0 ± 0.1 mm/min and are associated with a negative shift in direct current potential, a transient cessation of neuronal spiking, arteriole constriction, and a decrease in tissue O2 tension. The frequency of retinal spreading depolarization generation in vivo is reduced by administration of the NMDA antagonist MK-801 and the 5-HT(1D) agonist sumatriptan. Branch retinal vein occlusion is a leading cause of vision loss from vascular disease. Our results suggest that retinal spreading depolarization could contribute to retinal damage in acute retinal ischemia and demonstrate that pharmacological agents can reduce retinal spreading depolarization frequency after retinal vessel occlusion. Blocking retinal spreading depolarization generation may represent a therapeutic strategy for preserving vision in branch retinal vein occlusion patients.

Therapeutic options in Alzheimer’s disease

Alzheimer's disease (AD) places an enormous burden on individuals, families and society. Consequently, a tremendous effort is being devoted to the development of drugs that prevent or delay neurodegeneration. Current pharmacological treatments are based on the use of acetylcholinesterase inhibitors or memantine, a N-methyl-D-aspartate channel blocker. However, new therapeutic approaches, including those more closely targeted to the pathogenesis of the disease, are being developed. These potentially disease-modifying therapeutics include secretase inhibitors, cholesterol-lowering drugs, amyloid-beta immunotherapy, nonsteroidal anti-inflammatory drugs, hormonal modulation and the use of antioxidants. The possibility that oxidative stress is a primary event in AD indicates that antioxidant-based therapies are perhaps the most promising weapons against this devastating neurodegenerative disorder.

A potential association between Toxoplasma gondii infection and schizophrenia in mouse models

Schizophrenia is a serious neuropsychiatric disease of uncertain etiology, which causes human mental disorder and affects about 1% of the population. In recently years, some studies showed that some cases of schizophrenia may be associated with Toxoplasma gondii infection. In order to investigate a potential association between Toxoplasma infection and schizophrenia, we investigated the relative clinical symptom of schizophrenia such as learning and memory capability, depression and stereotypy to find some useful information by behavioral test in mouse models. Our results demonstrated that mice from Toxoplasma infection and MK-801 administration (as the model of schizophrenia) were impaired in learning and memory capability, and they had more serious depression and stereotypy compared with the control mice, especially the mice from congenital Toxoplasma infection. In addition, our results clearly showed that the number of cysts in brain tissue of congenital Toxoplasma infection mice was significantly low than in acquired Toxoplasma infected mice. Collectively, these results suggested a potential association between Toxoplasma infection and schizophrenia.

How Nox2-containing NADPH oxidase affects cortical circuits in the NMDA receptor antagonist model of schizophrenia

SIGNIFICANCE

Schizophrenia is a complex neuropsychiatric disorder affecting around 1% of the population worldwide. Its mode of inheritance suggests a multigenic neurodevelopmental disorder with symptoms appearing during late adolescence/early adulthood, with its onset strongly influenced by environmental stimuli. Many neurotransmitter systems, including dopamine, glutamate, and gamma-aminobutyric acid, show alterations in affected individuals, and the behavioral and physiological characteristics of the disease can be mimicked by drugs that produce blockade of N-methyl-d-aspartate glutamate receptors (NMDARs).

RECENT ADVANCES

Mounting evidence suggests that drugs that block NMDARs specifically impair the inhibitory capacity of parvalbumin-expressing (PV+) fast-spiking neurons in adult and developing rodents, and alterations in these inhibitory neurons is one of the most consistent findings in the schizophrenic postmortem brain. Disruption of the inhibitory capacity of PV+ inhibitory neurons will alter the functional balance between excitation and inhibition in prefrontal cortical circuits producing impairment of working memory processes such as those observed in schizophrenia.

CRITICAL ISSUES

Mechanistically, the effect of NMDAR antagonists can be attributed to the activation of the Nox2-dependent reduced form of nicotinamide adenine dinucleotide phosphate oxidase pathway in cortical neurons, which is consistent with the emerging role of oxidative stress in the pathogenesis of mental disorders, specifically schizophrenia. Here we review the mechanisms by which NMDAR antagonists produce lasting impairment of the cortical PV+ neuronal system and the roles played by Nox2-dependent oxidative stress mechanisms.

FUTURE DIRECTIONS

The discovery of the pathways by which oxidative stress leads to unbalanced excitation and inhibition in cortical neural circuits opens a new perspective toward understanding the biological underpinnings of schizophrenia.

[Activation of hippocampal D1 dopamine receptor inhibits glutamate-mediated depression induced by chronic unpredictable mild stress in rats]

The present study was to investigate the role of dopamine D1 receptors and its relationship with glutamate, N-methyl-D-aspartic acid (NMDA) receptor and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor in depression induced by chronic unpredictable mild stress (CUMS). CUMS-induced depression model was established in Sprague-Dawley rats, and intrahippocampal microinjections of D1 dopamine receptor agonist SKF38393, non-competitive NMDA receptor antagonist MK-801 and AMPA receptor antagonist NBQX were respectively adopted by rat brain stereotaxic coordinates. The behavioral observations were conducted by measurement of weight changes, sucrose preference test, open-field test and tail suspension test. The concentration of glutamic acid and the expression of its receptors' subunits were detected by HPLC and Western blot, respectively. The results showed that, compared with control group, CUMS rats showed depression-like behavioral changes, higher concentration of glutamic acid, lower expressions of NMDA receptor (NR1) and AMPA receptor (GluR2/3) in hippocampus. Pretreatment with injection of SKF38393 could rescue such depression effect of CUMS, decrease the concentration of glutamic acid, and increase the expressions of NMDA receptor (NR1), AMPA receptor (GluR2/3) in hippocampus. Pretreatment with MK-801 could enhance the antidepressant effect of SKF38393, while NBQX weakened. These results suggest that agonists of D1 dopamine receptor could reduce the concentration of glutamic acid in hippocampus, and its antidepressant effect may be mediated by AMPA receptor partially.

Effects of olanzapine, sertindole and clozapine on MK-801 induced visual memory deficits in mice

We investigated the effects of the second generation antipsychotics olanzapine, sertindole and clozapine on visual recognition memory using the novel object recognition (NOR) test in naive and MK-801-treated animals. The effects of drug treatment on locomotion and anxiety were also determined using the open field test. Male Balb-c mice were treated with olanzapine (0.2, 0.4 and 0.6 mg/kg; i.p.), sertindole (0.63, 1.3 and 2.5mg/kg; s.c.) or clozapine (0.5 and 1mg/kg; i.p.), and cognitive deficits were induced by MK-801 (0.2mg/kg; i.p.) administration. Olanzapine treatment decreased the ratio index in the NOR test, whereas sertindole and clozapine had no effect in naive mice. MK-801-induced cognitive impairment was reversed by treatment with olanzapine, sertindole or clozapine. While olanzapine, sertindole and clozapine had no effect on the anxiety of naive mice as determined by the open field test, MK-801 significantly increased the total distance traveled, time spent in the center zone and the velocity of the animals. MK-801-induced effects on locomotion and anxiety in the open field test were reversed by olanzapine, sertindole or clozapine treatment. The results of the present study demonstrated that olanzapine, sertindole and clozapine improved cognition in MK-801 treated mice, and indicate that these drugs have a potential to improve cognition in schizophrenia.

Typology of club drug use among young adults recruited using time-space sampling

The present study examined patterns of recent club drug use among 400 young adults (18-29) recruited using time-space sampling in NYC. Subjects had used at least one of six club drugs (methylenedioxymethamphetamine (MDMA), ketamine, gamma-hydroxybutyrate (GHB), cocaine, methamphetamine, and D-lysergic acid diethylamide (LSD)) within the prior 3 months. We used latent class analysis (LCA) to estimate latent groups based on patterns of recent club drug use and examined differences in demographic and psychological variables by class. A 3-class model fit the data best. Patterns were: Primary cocaine users (42% of sample), Mainstream users (44% of sample), and Wide-range users (14% of sample). Those most likely to be Primary cocaine users were significantly less likely to be heterosexual males and had higher educational attainment than the other two classes. Those most likely to be Wide-range users were less likely to be heterosexual females, more likely to be gay/bisexual males, dependent on club drugs, had significantly greater drug and sexual sensation seeking, and were more likely to use when experiencing physical discomfort or pleasant times with others compared to the other two groups. Findings highlight the utility of using person-centered approaches to understand patterns of substance use, as well as highlight several patterns of club drug use among young adults.

GABA inhibits ACh release from the rabbit retina: A direct effect or feedback to bipolar cells?

The cholinergic amacrine cells of the rabbit retina may be labeled with [3H]-Ch and the activity of the cholinergic population monitored by following the release of [3H]-ACh. We have tested the effect of muscimol, a potent GABAA agonist, on (1) the light-evoked release of ACh, presumably mediated via bipolar cells, which are known to have a direct input to the cholinergic amacrine cells and (2) ACh release produced by exogenous glutamate analogs that probably have a direct effect on cholinergic amacrine cells. Muscimol blocked the light-evoked release of ACh with an IC50 of 1.0 μM. In contrast, ACh release produced by nonsaturating doses of kainate or NMDA was not reduced even by 100 μM muscimol. Thus, we have been unable to demonstrate a direct effect of GABA on the cholinergic amacrine cells.

GABA antagonists, such as picrotoxin, caused a large increase in the base release and potentiated the light-evoked release of ACh. Both these effects were abolished by DNQX, a kainate antagonist that blocks the input to cholinergic amacine cells from bipolar cells. DNQX blocked the effects of picrotoxin even when controls showed that the mechanism of ACh release was still functional. Together, these results imply that the dominant site for the GABA-mediated inhibition of ACh release is on the bipolar cell input to the cholinergic amacrine cells. This is consistent with previous anatomical and physiological evidence that bipolar cells receive negative feedback from GABA amacrine cells.

Haloperidol and risperidone have specific effects on altered pain sensitivity in the ketamine model of schizophrenia

RATIONALE

The ketamine (ket) model reflects features of schizophrenia as well as secondary symptoms such as altered pain sensitivity.

OBJECTIVES

In the present study, we investigated the effect of subchronic oral treatment with haloperidol (hal, 0.075 mg/kg) and risperidone (ris, 0.2 mg/kg) on altered pain perception and locomotor activity in this model.

RESULTS

In reaction to 5 mg/kg morphine, ket pretreated animals showed a diminished analgesic response. Hal had no analgesic effect per se, but the compound normalised the analgesic reaction to morphine in the ket pretreated animals. The effect of ris was complex. First, there was no analgesic effect per se, and control animals showed a dose-dependent increase in the analgesic index after morphine injection. In the ket group treated with ris, the analgesic response to 5 mg/kg morphine was attenuated and in response to 10 mg/kg analgesia was comparable with that measured in controls. The reduced analgesic effect was not due to pharmacokinetic differences in morphine metabolism. After administration via drinking water in saline-injected control animals, the hal blood serum concentration was 2.6 +/- 0.45 ng/ml. In ket-injected animals, the mean serum concentration of hal amounted to 1.2 +/- 0.44 ng/ml. In the experiment using ris, animals in the control group had higher ris serum concentrations compared with ket-injected animals. In control animals, morphine dose dependently decreased locomotor activity. This effect was significantly stronger in the ket pretreated groups.

CONCLUSIONS

Hal and ris had different effects on altered pain sensitivity. It was hypothesised that these results are connected with alterations in dopamine D2 and mu opioid receptor binding.

Modulation of GABAergic and glutamatergic transmission by ethanol in the developing neocortex: an in vitro test of the excessive inhibition hypothesis of fetal alcohol spectrum disorder

Exposure to ethanol during development triggers neuronal cell death and this is thought to play a central role in the pathophysiology of fetal alcohol spectrum disorder (FASD). Studies suggest that ethanol-induced neurodegeneration during the period of synaptogenesis results from widespread potentiation of GABA(A) receptors and inhibition of NMDA receptors throughout the brain, with neocortical layer II being particularly sensitive. Here, we tested whether ethanol modulates the function of these receptors during this developmental period using patch-clamp electrophysiological and Ca(2+) imaging techniques in acute slices from postnatal day 7-9 rats. We focused on pyramidal neurons in layer II of the parietal cortex (with layer III as a control). Ethanol (70mM) increased spontaneous action potential-dependent GABA release in layer II (but not layer III) neurons without affecting postsynaptic GABA(A) receptors. Protein and mRNA expression for both the Cl(-) importer, NKCC1, and the Cl(-) exporter, KCC2, were detected in layer II/III neurons. Perforated-patch experiments demonstrated that E(Cl)((-)) is shifted to the right of E(m); activation of GABA(A) receptors with muscimol depolarized E(m), decreased action potential firing, and minimally increased [Ca(2+)](i). However, the ethanol-induced increase of GABAergic transmission did not affect neuronal excitability. Ethanol had no effect on currents exogenously evoked by NMDA or AMPA receptor-mediated spontaneous excitatory postsynaptic currents. Acute application of ethanol in the absence of receptor antagonists minimally increased [Ca(2+)](i). These findings are inconsistent with the excessive inhibition model of ethanol-induced neurodegeneration, supporting the view that ethanol damages developing neurons via more complex mechanisms that vary among specific neuronal populations.

[Association study of the SCN1 gene polymorphism and effective dose of lamotrigine]

An association between a polymorphism of the SCN1 gene, a therapeutical target of lamotrigine, and an effective dose (a blood plasma concentration) of the drug in patients with epilepsy has been studied. Fifty patients with different forms of epilepsy have been genotyped for the SCN1 IVS5N+5 G>A polymorphism using polymerase chain reaction. The distribution of allelic variants was as follows: 23 patients had the mutant homozygous genotype (V/V), 20 - the heterozygous genotype Wt/V and 7 were homozygous for the wild allele (Wt/Wt). Mean lamotrigine doses were 85,7+/-7,4 mg/day for carriers of the Wt/Wt genotype, 113,75+/-7,13 mg/day for the Wt/V genotype and 142,4+/-15,43 mg/day for the V/V genotype. Peak plasma concentrations corresponded to effective doses were 0,6+/-0,065 mg/ml for Wt/Wt, 0,96+/-0,1 mg/ml for V/V and 0,72+/-0,1 mg/ml for Wt/V. The hypothesis on the association between the SCN1 IVS5N+5 G>A polymorphism and the effective dose (concentration) of lamotrigine was confirmed. The significantly higher frequency of the SCN1A mutation in the group of patients with epilepsy compared to the control group of Caucasians (45,5 and 21,3%, respectively) implies that this polymorphism may contribute to the pathogenesis of epilepsy.

HDT-1, a new synthetic compound, inhibits glutamate release in rat cerebral cortex nerve terminals (synaptosomes)

AIM

Excessive glutamate release has been proposed to be involved in the pathogenesis of several neurological diseases. In this study, we investigated the effect of HDT-1 (3, 4, 4a, 5, 8, 8a-hexahydro-6,7-dimethyl-4a-(phenylsulfonyl)- 2-tosylisoquinolin-1(2H)-one), a novel synthetic compound, on glutamate release in rat cerebrocortical nerve terminals and explored the possible mechanism.

METHODS

The release of glutamate was evoked by the K+ channel blocker 4-aminopyridine (4-AP) or the high external [K+] and measured by one-line enzyme-coupled fluorometric assay. We also determined the loci at which HDT-1 impinges on cerebrocortical nerve terminals by using membrane potentialsensitive dye to assay nerve terminal excitability and depolarization, and Ca2+ indicator Fura-2 to monitor Ca2+ influx.

RESULTS

HDT-1 inhibited the release of glutamate evoked by 4-AP and KCl in a concentration-dependent manner. HDT-1 did not alter the resting synaptosomal membrane potential or 4-APevoked depolarization. Examination of the effect of HDT-1 on cytosolic [Ca2+] revealed that the diminution of glutamate release could be attributed to reduction in voltage-dependent Ca2+ influx. Consistent with this, the HDT-1-mediated inhibition of glutamate release was significantly prevented in synaptosomes pretreated with the N- and P/Q-type Ca2+ channel blocker omega-conotoxin MVIIC.

CONCLUSION

In rat cerebrocortical nerve terminals, HDT-1 inhibits glutamate release through a reduction of voltage-dependent Ca2+ channel activity and subsequent decrease of Ca2+ influx into nerve terminals, rather than any upstream effect on nerve terminal excitability.

17beta-estradiol affects GABAergic transmission in developing hippocampus

Estrogens are potent modulators of the nervous system. In particular, 17beta-estradiol was shown to affect GABAergic synaptic transmission in hippocampus of adult animals in vivo but much less is known on the impact of this hormone on the GABAergic system in the developing brains. We have recently shown that phasic and tonic GABAergic transmissions are strongly modulated upon long-term treatment with exogenous 17beta-estradiol in hippocampal neurons developing in vitro. To check for the long-term estrogen effect in a more physiological developmental model, we have investigated the GABAergic transmission in developing brains of P7-P40 animals, injected daily with 17beta-estradiol. We have found that such a treatment clearly increased GABAergic mIPSC frequency and amplitude while the onset and decay of mIPSCs were shortened. These effects were statistically significant in the youngest considered age group (P7-P13) with a tendency to disappear in older animals. Long-term treatment with estradiol did not change the susceptibility of mIPSC amplitude to upregulation by flurazepam while mIPSC decay was prolonged by this drug to a larger extent in 17beta-estradiol-treated animals. 17beta-estradiol strongly upregulated GABAergic tonic current but again this effect was restricted to the youngest group of animals. We conclude that 17beta-estradiol strongly modulates the GABAergic synaptic transmission but this effect critically depends on the animal age being the most prominent in youngest animals.

Lamotrigine in children with refractory epilepsy

We studied the efficacy and side effect profile oflamotrigine (LTG) in children with intractable epilepsy. We reviewed the database of our prolonged video-EEG laboratory to screen patients with intractable epilepsy who were on LTG either alone or in combination for three months or more. Of 75 patients, 28 patients (37%) had primary generalized seizures, 42 patients (56%) had partial onset seizures with or without secondary generalization, and 5 patients (7%) had two or more types of seizures. LTG reduced seizure frequency by at least 50% in 57.1% of patients with partial seizures and in 53.6% of patients with primary generalized seizures. The incidence of adverse events was relatively low (15%); the most common was skin rash. LTG should be considered in the treatment of pediatric patients with both partial onset and primary generalized seizures refractory to the major older antiepileptic drugs. LTG has a favorable side effect profile.

Pharmacological analysis of excitatory and inhibitory synaptic transmission in horizontal brainstem slices preserving three subnuclei of spinal trigeminal nucleus

Spinal trigeminal nucleus (Vsp) consists of three subnuclei: oralis (Vo), interpolaris (Vi) and caudalis (Vc). Previous anatomical studies using antero-/retro-grade tracers have suggested that intersubnuclear ascending/descending synaptic transmissions exist between subnuclei. However, pharmacological properties of the intersubnuclear synaptic transmission have not been studied yet. Since three subnuclei are located in Vsp along rostro-caudal axis, it will be necessary to prepare horizontal brainstem slices to perform pharmacological analysis of the intersubnuclear synaptic transmission. We here show horizontal brainstem slices retaining three subnuclei, and that, using blind whole-cell recordings in the slices, synaptic transmission may be abundantly retained between subnuclei in the horizontal slices, except for the transmission from Vo to Vc. Finally, pharmacological analysis shows that excitatory and inhibitory synaptic responses, respectively, are mediated by AMPA and NMDA receptors and by GABA(A) and glycine receptors, with a differential contribution to the synaptic responses between subnuclei. We therefore conclude that horizontal brainstem slices will be a useful preparation for studies on intersubnuclear synaptic transmission, modulation and plasticity between subnuclei, as well as, further, other brainstem nuclei.

The economic consequences of generic substitution for antiepileptic drugs in a public payer setting: the case of lamotrigine

Generic substitution of antiepileptic drugs (AEDs) may increase pharmacy utilization, thus counterbalancing per-pill savings. The purpose of our study was to analyze the economic impact of government-mandated switching from branded to generic lamotrigine. Patients in a Canadian public pharmacy claims database using branded lamotrigine (Lamictal GlaxoSmithKline, UK) in 2002 converted to generic lamotrigine in 2003 and were observed from July 2002 to March 2006. Patients used branded lamotrigine for >or=90 days pre-generic entry and had >or=1 claim for generic lamotrigine post-generic entry. For the generic period, observed per-patient monthly drug costs were calculated as the sum of costs for lamotrigine, other AEDs, and non-AEDs. Expected per-patient drug costs were estimated assuming lamotrigine dose and other prescription drug utilization in the generic period were identical to those observed during the brand period. Differences between observed and expected costs were compared. Among 1,142 branded lamotrigine users, overall average monthly drug costs per person were expected to decrease by $30.55 due to lower pill costs. Instead, they fell by $11.98 from the brand to the generic periods (p < 0.001). Because of dosage changes, lamotrigine costs decreased by $29.92 instead of the anticipated $33.87 (p < 0.001). Increased pharmacy utilization caused other AED costs to rise by $6.29 versus the expected $0.36 (p < 0.001), while non-AED drug cost increased by $11.64 rather than by $2.95 (p < 0.001). We concluded that conversion to generic lamotrigine resulted in lower than expected cost savings. Further research is necessary to determine whether this is due to reduced effectiveness and/or tolerability. Payers may weigh smaller-than-expected cost reductions against a possible decrease in effectiveness to assess the relevance of mandatory generic switching of lamotrigine.

Effects of schizophrenomimetics on the expression of the CCN1 (CYR 61) gene encoding a matricellular protein in the infant and adult neocortex of the mouse and rat

The acute systemic administration of a schizophrenomimetic phencyclidine [5 or 10 mg/kg, subcutaneously (s.c.)] markedly up-regulated the neocortical expression of the CCN1 gene encoding a secreted extracellular matrix-associated protein at postnatal day 56, but not at postnatal day 8, after 60 min in the mouse and rat. The development-dependent nature of the up-regulation between postnatal days 8 and 56 seems to be similar to that of the adult type phencyclidine-induced abnormal behaviours, which have been considered to be models of schizophrenic symptoms. In the young adult rat, 5, 10, and 20 mg/kg phencyclidine (given s.c.) induced an increase in the CCN1 gene transcripts in a dose-related and bell-shaped manner with a maximum at the dose of 10 mg/kg, 60 min post-injection. Other schizophrenomimetics, dizocilpine (1 mg/kg) and methamphetamine (4.8 mg/kg), also caused a prominent up-regulation of the neocortical expression of the CCN1 gene in adult rats. These results indicate that the CCN1 gene or protein could be implicated in a molecular cascade associated with the age-dependent onset of schizophrenia that usually occurs after puberty.

Direct inhibitory effect of fluoxetine on N-methyl-D-aspartate receptors in the central nervous system

BACKGROUND

Data accumulated in the last decade indicate that N-methyl-D-aspartate (NMDA) receptors might be involved in the pathophysiology of depression and the mechanism of action of antidepressants, although a direct inhibitory effect has been reported only in connection with tricyclic compounds, which interact with a wide range of receptors.

METHODS

Using whole-cell patch-clamp recording in rat cortical cell cultures, we investigated whether the selective serotonin reuptake inhibitor fluoxetine, which has a much better adverse effect profile, has a direct effect on NMDA receptors, and we compared its action to that of the tricyclic desipramine.

RESULTS

Both desipramine (concentration that causes 50% inhibition (IC(50)) = 3.13 microM) and fluoxetine (IC(50) = 10.51 microM) inhibited NMDA-evoked currents with similar efficacy in the clinically relevant low micromolar concentration range. However, in contrast to desipramine, the inhibition by fluoxetine was not voltage-dependent, and fluoxetine partially preserved its ability to associate with NMDA receptor in the presence of Mg(2+), suggesting different binding sites for the two drugs.

CONCLUSIONS

The fact that different classes of antidepressants were found to be low-affinity NMDA antagonists suggests that direct inhibition of NMDA receptors may contribute to the clinical effects of antidepressants.

Dietary Taurine Supplementation Ameliorates Diabetic Retinopathy via Anti-excitotoxicity of Glutamate in Streptozotocin-induced Sprague-Dawley Rats

The purpose of this study was to investigate whether taurine ameliorate the diabetic retinopathy, and to further explore the underlying mechanisms. The Sprague-Dawley rats were injected with streptozotocin to establish experimental diabetic model, then fed without or with 1.2% taurine for additional 4-12 weeks. After that, the protective effects of dietary taurine supplementation on diabetic retinopathy were estimated. Our results showed that chronic taurine supplement effectively improved diabetic retinopathy as changes of histopathology and ultrastructure. The supplementation could not lower plasma glucose concentration (P > 0.05), but caused an elevation in taurine content and a decline in levels of glutamate and gamma-aminobutyric acid (GABA) in diabetic retina (P < 0.05). Moreover, chronic taurine supplementation increased glutamate transporter (GLAST) expression (P < 0.05), decreased intermediate filament glial fibrillary acidic protein (GFAP) and N-methyl-D: -aspartate receptor subunit 1 (NR1) expression in diabetic retina (P < 0.05). These results demonstrated that chronic taurine supplementation ameliorates diabetic retinopathy via anti-excitotoxicity of glutamate in rats.

PAN-811 provides neuroprotection against glutamate toxicity by suppressing activation of JNK and p38 MAPK

In an earlier study, we demonstrated that PAN-811 (3-aminopyridine-2-carboxaldehyde thiosemicarbazone), a novel neuroprotectant, provides protection against glutamate, staurosporine, veratridine, or hypoxia/hypoglycemia toxicities in primary cortical neuronal cultures by upregulating Bcl-2 expression [R.-W. Chen, C. Yao, X.C. Lu, Z.-G. Jiang, R. Whipple, Z. Liao, H.A. Ghanbari, B. Almassian, F.C. Tortella, J.R. Dave. PAN-811 (3-aminopyridine-2-carboxaldehyde thiosemicarbazone), a novel neuroprotectant, elicits its function in primary neuronal cultures by upregulating Bcl-2 expression. Neuroscience 135 (2005) 191-201]. Both JNK (c-Jun N-terminal kinase) and p38 MAP (mitogen-activated protein) kinase activation have a direct inhibitory action on Bcl-2 by phosphorylation. In the present study, we continued to explore the mechanism of PAN-811 neuroprotection. Our results indicate that treatment of cultured cortical neurons with glutamate (100 microM) induces phosphorylation of both JNK and p38 MAPK. Specifically, pretreatment of neurons with 10 microM PAN-811 (an optimal neuroprotective concentration) for 1h, 4h, or 24h significantly suppresses glutamate-mediated activation of both JNK and p38 MAPK. Furthermore, the p38 MAPK-specific inhibitor SB203580 and the JNK-specific inhibitor SP600125 prevented glutamate-induced neuronal death in these primary cultures. Our results demonstrate that glutamate-induced phosphorylation of JNK and p38 MAPK is suppressed by PAN-811, which might contribute to Bcl-2 upregulation and PAN-811 neuroprotection.

Phencyclidine animal models of schizophrenia: Approaches from abnormality of glutamatergic neurotransmission and neurodevelopment

In humans, phencyclidine (PCP), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, reproduces a schizophrenia-like psychosis including positive symptoms, negative symptoms and cognitive dysfunction. Thus, the glutamatergic neuronal dysfunction hypothesis is one of the main explanatory hypotheses and PCP-treated animals have been utilized as an animal model of schizophrenia. The adult rodents treated with PCP repeatedly exhibit hyperlocomotion as an index of positive symptoms, a social behavioral deficit in a social interaction test and enhanced immobility in a forced swimming test as indices of negative symptoms. They also show a sensorimotor gating deficits and cognitive dysfunctions in several learning and memory tests. Some of these behavioral changes endure after withdrawal from repeated PCP treatment. Furthermore, repeated PCP treatment induces some neurochemical and neuroanatomical changes. On the other hand, the exposure to viral or environmental insult in the second trimester of pregnancy increases the probability of subsequently developing schizophrenia as an adult. NMDA receptor has been implicated in controlling the structure and plasticity of developing brain circuitry. Based on neurodevelopment hypothesis of schizophrenia, schizophrenia model rats treated with PCP at the perinatal stage is developed. Perinatal PCP treatment impairs neuronal development and induces long-lasting schizophrenia-like behaviors in adult period. Many findings suggest that these PCP animal models would be useful for evaluating novel therapeutic candidates and for confirming pathological mechanisms of schizophrenia.

Raloxifene acutely reduces glutamate-induced intracellular calcium increase in cultured rat cortical neurons via inhibition of high-voltage-activated calcium current

There is increasing evidence indicating that estrogen replacement therapy produces neuroprotective actions but has undesirable side effects on the reproductive system. Raloxifene is a selective estrogen receptor modulator that exerts estrogen agonist action in the brain while acting as an estrogen antagonist in the reproductive system. In the present study, we investigated whether raloxifene affected the glutamate-induced calcium (Ca2+) overload in rat cultured cortical neurons. The bulk cytosolic intracellular Ca2+ level was measured by using confocal microscopy with fluorescent Ca2+ probe fluo3. Whole-cell recording technique was used to observe the effects of raloxifene on N-methyl-D-aspartate (NMDA)-evoked and voltage-activated Ca2+ currents in cultured cortical neurons. Pre-exposure of cortical neurons to raloxifene (0.5 microM-10 microM) for 3 min attenuated intracellular Ca2+ increase induced by application of glutamate (300 microM) for 1 min. The action of raloxifene was reversible after washout. ICI 182,780 and thapsigargin did not block the action of raloxifene. In whole-cell recording experiments, raloxifene (10 microM) significantly reduced the amplitude of the high-voltage-activated Ca2+ current but had no effect on NMDA-evoked Ca2+ current. The present study demonstrates that raloxifene acutely reduces glutamate-induced intracellular Ca2+ increase probably via inhibition of high-voltage-activated calcium channels.

A rapid inhibition of NMDA receptor current by corticosterone in cultured hippocampal neurons

The stress level of corticosterone (CORT) may enhance the vulnerability of neurons to insult by increasing N-methyl-D-aspartate (NMDA) receptor activity. In this study, we present data showing that CORT could exert an inhibitory effect on NMDA currents in cultured neonatal hippocampal neurons. Extracellular application of 0.1,1,10 and 100 microM CORT significantly reduced the inward current evoked by co-application of NMDA (100 microM). Extracellular application of a membrane-impermeable CORT-BSA (10 microM) maintained the CORT effect. RU38486 (10 microM) failed to block the CORT (1 microM) inhibitory effect. Additionally, intracellular application of CORT (10 microM) showing the lack of effectiveness indicated that a non-genomic mechanism mediated the CORT suppression on NMDA receptors in hippocampal neurons. Furthermore, to elevate the activity of protein kinase A by intracellular 8-Br-cAMP maintained the suppressive effect of CORT on NMDA current. Intracellular blockade of protein kinase A by Rp-cAMP (10 microM) or staurosporine (50 nM) reduced NMDA currents and abolished CORT depression of NMDA currents. These data indicated that NMDA current itself is dependent on protein kinase A (PKA) activity and CORT depression of the current could be PKA-dependent at the same time. The rapid inhibitory effect of the stress level CORT on NMDA current might suggest a protective mechanism for neurons exposed to a transient increase in glucocorticoids.

Phenytoin- and carbamazepine-resistant spontaneous bursting in rat entorhinal cortex is blocked by retigabine in vitro

Hyperexcitability in the medial entorhinal cortex-hippocampal (mEC-HC) circuit in the initial weeks after prolonged seizure activity may contribute to the epileptogenic process in animal models of temporal lobe epilepsy (TLE). The present study examined combined mEC-HC slices (400 microm) using field potential recordings 1-2 weeks following the multiple administration, low-dose kainic acid (KA) model of TLE [Hellier, J.L., Patrylo, P.R., Buckmaster, P.S., Dudek, F.E., 1998. Recurrent spontaneous motor seizures after repeated low-dose systemic treatment with kainate: assessment of a rat model of temporal lobe epilepsy. Epilepsy Res. 31, 73-84]. Field potential recordings in slices from KA-treated rats demonstrated hallmarks of hyperexcitability in the mEC and in the CA1 and CA3 cell body regions of the HC. Spontaneous burst (SB) activity was observed under baseline recording conditions in the mEC of several slices from KA-treated rats, but not in the slices from saline-treated control rats. Elevating ACSF [K(+)](o) (6mM) in the presence of picrotoxin (50 microM) increased SB rates in all slices tested. However, there was a significantly shorter latency to onset of bursting and prolonged evoked response durations in layer II of the mEC of slices from KA-treated rats versus those from controls. Neither carbamazepine (CBZ) nor phenytoin (PHT) abolished SB activity in slices from KA-treated rats; whereas, SB activity in slices from control rats was dose-dependently reduced at 100 microM CBZ. In contrast, the novel anticonvulsant retigabine (RGB) dramatically reduced SB frequency in both control and KA-treated groups. The hyperexcitability observed in combined mEC-HC brain slices from KA-treated rats suggests that the mEC, as well as the HC, may contribute to the epileptogenic process after KA-induced seizure activity. This model may provide an efficient, flexible in vitro paradigm for differentiating novel AEDs in a model of pharmacoresistant bursting.

Prepulse inhibition of the startle reflex and its attentional modulation in the human S-ketamine and N,N-dimethyltryptamine (DMT) models of psychosis

Patients with schizophrenia exhibit diminished prepulse inhibition (PPI) of the acoustic startle reflex and deficits in the attentional modulation of PPI. Pharmacological challenges with hallucinogens are used as models for psychosis in both humans and animals. Remarkably, in contrast to the findings in schizophrenic patients and in animal hallucinogen models of psychosis, previous studies with healthy volunteers demonstrated increased levels of PPI after administration of low to moderate doses of either the antiglutamatergic hallucinogen ketamine or the serotonergic hallucinogen psilocybin. The aim of the present study was to investigate the influence of moderate and high doses of the serotonergic hallucinogen N,N-dimethyltryptamine (DMT) and the N-methyl-D-aspartate antagonist S-ketamine on PPI and its attentional modulation in humans. Fifteen healthy volunteers were included in a double-blind cross-over study with two doses of DMT and S-ketamine. Effects on PPI and its attentional modulation were investigated. Nine subjects completed both experimental days with the two doses of both drugs. S-ketamine increased PPI in both dosages, whereas DMT had no significant effects on PPI. S-ketamine decreased and DMT tended to decrease startle magnitude. There were no significant effects of either drug on the attentional modulation of PPI. In human experimental hallucinogen psychoses, and even with high, clearly psychotogenic doses of DMT or S-ketamine, healthy subjects failed to exhibit the predicted attenuation of PPI. In contrast, PPI was augmented and the startle magnitude was decreased after S-ketamine. These data point to important differences between human hallucinogen models and both animal hallucinogen models of psychosis and naturally occurring schizophrenia.

From prediction error to psychosis: ketamine as a pharmacological model of delusions

Recent cognitive neuropsychiatric models of psychosis emphasize the role of attentional disturbances and inappropriate incentive learning in the development of delusions. These models highlight a pre-psychotic period in which the patient experiences perceptual and attentional disruptions. Irrelevant details and numerous associations between stimuli, thoughts and percepts are imbued with inappropriate significance and the attempt to rationalize and account for these bizarre experiences results in the formation of delusions. The present paper discusses delusion formation in terms of basic associative learning processes. Such processes are driven by prediction error signals. Prediction error refers to mismatches between an organism's expectation in a given environment and what actually happens and it is signalled by both dopaminergic and glutamatergic mechanisms. Disruption of these neurobiological systems may underlie delusion formation. We review similarities between acute psychosis and the psychotic state induced by the NMDA receptor antagonist drug ketamine, which impacts upon both dopaminergic and glutamatergic function. We conclude by suggesting that ketamine may provide an appropriate model to investigate the formative stages of symptom evolution in schizophrenia, and thereby provide a window into the earliest and otherwise inaccessible aspects of the disease process.

Perceptual organization in ketamine users: preliminary evidence of deficits on night of drug use but not 3 days later

N-methyl-D-aspartate (NMDA)-receptor antagonists such as ketamine can induce transient schizophrenia-like symptoms and cognitive dysfunctions in healthy volunteers similar to those observed in patients with schizophrenia. Perceptual organization deficits have been documented in schizophrenia and are thought to be related to some symptoms associated with the illness. The current study was designed to determine whether people who repeatedly self-administer ketamine would also show deficits in perceptual organization. Using a psychophysically well-controlled measure of contour integration, we compared a group of recreational users (n = 16) to a group of poly-drug using controls (n = 16). Contour integration performance was measured on the night of drug use and 3 days later when drug free. The results showed that on the night of drug use, ketamine produced a dysfunction in contour integration however, this was not present 3 days later when drug free. Levels of dissociation were also higher in ketamine users only on the night of drug use. These preliminary data provide some support for the role of NMDA-receptor hypofunctioning in dysfunctional coordination of cognitive activity.

The excitatory and inhibitory effects of nitrous oxide on spinal neuronal responses to noxious stimulation

BACKGROUND

Because of the logistical obstacles to measurement under hyperbaric conditions, the effect of nitrous oxide (N2O) alone on spinal neuronal responses has not been tested. We hypothesized that, like other inhaled anesthetics, N2O would depress spinal neuronal responses to noxious stimulation.

METHODS

The lumbar spinal cord was exposed in rats anesthetized with isoflurane. Mechanically ventilated rats were placed into a hyperbaric chamber and needle electrodes were inserted into the hindpaws. Isoflurane administration was discontinued and anesthesia converted to N2O by pressurizing the chamber with N2O. A microelectrode was inserted into the lumbar cord using computer-controlled motors and a hydraulic microdrive. Neuronal responses to electrical stimulation of the hindpaw were sought at 1.5, 2, and 2.5 atm N2O (0.8-1.3 minimum alveolar concentration).

RESULTS

Increasing N2O partial pressures variably affected neuronal responses to a 2 s 100-Hz electrical stimulus. Neuronal depth and neuronal response were correlated, with superficial neurons tending to be facilitated, while deeper neurons were depressed; (overall responses were 1331 +/- 408, 1594 +/- 383, and 1578 +/- 500 impulses/min at 1.5, 2, and 2.5 atm N2O, respectively; mean, standard error). N2O did not affect neuronal responses to a repetitive "windup" stimulus. Infusion of the N-methyl-d-aspartate blocker MK-801 into separate rats increased the neuronal response to the 100-Hz stimulus (from 781 +/- 216 to 1352 +/- 269 impulses/min, P < 0.05).

CONCLUSIONS

N2O facilitated superficial spinal neuronal responses to noxious stimulation while depressing deeper neurons. These results suggest that anesthetic partial pressures of N2O have divergent effects on spinal neuronal responses to noxious stimulation, the specific responses depending on the depth of the spinal neurons.

Clozapine, SCH 23390 and alpha-flupenthixol but not haloperidol attenuate acute phencyclidine-induced disruption of conditional discrimination performance

RATIONALE

Forebrain dopamine (DA) manipulation has recently been shown to selectively disrupt a conditional discrimination task whose design parameters approximate tasks repeatedly shown to be impaired in schizophrenia.

OBJECTIVE

To investigate the reversal potential of the D(1)/D(2) receptor antagonist alpha-flupenthixol, the selective D(1) antagonist SCH 23390, the typical antipsychotic haloperidol and the atypical antipsychotic clozapine on acute phencyclidine (PCP)-induced disruption of a conditional discrimination task dependent on the ability to use task-setting cues that inform goal-directed performance.

MATERIALS AND METHODS

Rats learned a conditional discrimination task where reinforcement was contingent on an appropriate lever press during a specific auditory stimulus.

RESULTS

PCP disrupted task performance at 1.5 mg/kg, attenuated correct lever pressing at 2.5 mg/kg and abolished overall responding at 5 mg/kg (experiment 1). Pavlovian-instrumental transfer task results (experiment 2) showed that 1.5 and 2.5 mg/kg PCP had no disruptive effects on basic sensory, motor or motivational processes; however, such deficits were evident in 5-mg/kg-treated animals. PCP (1.5 mg/kg) disruption of conditional discrimination was attenuated by acute pretreatment with clozapine, SCH 23390 and alpha-flupenthixol; however, pretreatment with haloperidol did not attenuate task disruption.

CONCLUSION

The predictive validity of the conditional discrimination model is enhanced as the selective task disruption by the preeminent psychotomimetic PCP is reversed by clozapine (known to ameliorate cognitive deficits in schizophrenia) and the role of DA D(1) receptors as mediators of tasks that require conditional relationships is discussed.

Inhibition of glutamatergic activation of extracellular signal-regulated protein kinases in hippocampal neurons by the intravenous anesthetic propofol

BACKGROUND

Intravenous anesthetics cause amnesia, but the underlying molecular mechanisms are poorly understood. Recent studies reveal a significant role of extracellular signal-regulated protein kinases (ERKs) in controlling synaptic plasticity and memory formation. As a major synapse-to-nucleus superhighway, ERK transmits N-methyl-D-aspartate (NMDA) receptor signals to inducible transcriptional events essential for NMDA receptor-dependent forms of synaptic plasticity and memory. This study investigated the role of the widely used intravenous anesthetic propofol in regulating NMDA receptor-dependent ERK phosphorylation.

METHODS

The possible effect of propofol on NMDA receptor-mediated ERK phosphorylation was detected in cultured rat hippocampal neurons with Western blot analysis.

RESULTS

The authors found that propofol at clinical relevant concentrations (1-10 microm) reduced NMDA receptor-mediated ERK phosphorylation. This reduction was independent of gamma-aminobutyric acid transmission. The inhibition of the NMDA receptor seems to contribute to the effect of propofol on NMDA-stimulated ERK phosphorylation, because propofol reduced constitutive NMDA receptor NR1 subunit phosphorylation and impaired NMDA receptor-mediated Ca influx. Furthermore, by inhibiting the ERK pathway, propofol blocked NMDA receptor-dependent activation of two key transcription factors, Elk-1 and cyclic adenosine monophosphate response element-binding protein (CREB), and, as a result, attenuated Elk-1/CREB-dependent reporter gene (c-Fos) expression.

CONCLUSIONS

These results suggest that propofol possesses the ability to inhibit NMDA receptor activation of the ERK pathway and subsequent transcriptional activities in hippocampal neurons. These findings indicate a new avenue to explore a transcription-dependent mechanism that may underlie anesthetic interference with synaptic plasticity related to amnesic properties of intravenous anesthetics.