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Shitij Kapur

Publications and source records attributed to Shitij Kapur.

78 records · Page 5Linked to original sources
PubMed2002

Evidence for impaired cortical inhibition in schizophrenia using transcranial magnetic stimulation.

BACKGROUND: Cortical inhibition (CI) deficits have been proposed as a pathophysiologic mechanism in schizophrenia. This study employed 3 transcranial magnetic stimulation (TMS) paradigms to assess CI in patients with schizophrenia. Paired-pulse TMS involves stimulating with a lower-intensity pulse a few milliseconds before a higher-intensity pulse, thereby inhibiting the size of the motor evoked potential produced by the higher-intensity pulse. In the cortical silent period paradigm, inhibition is reflected by the silent period duration (ie, the duration of electromyographic activity cessation following a TMS-induced motor evoked potential). Transcallosal inhibition involves stimulation of the contralateral motor cortex several milliseconds prior to stimulation of the ipsilateral motor cortex, inhibiting the size of the motor evoked potential produced by ipsilateral stimulation. METHODS: We measured CI using these 3 paradigms in 15 unmedicated patients with schizophrenia (14 medication-naive and 1 medication-free for longer than 1 year) (13 were in the transcallosal inhibition paradigm), 15 medicated patients with schizophrenia (11 taking olanzapine, 1 risperidone, 1 quetiapine, 1 methotrimeprazine + perphenazine, 1 quetiapine + loxapine), and 15 healthy controls. RESULTS: Unmedicated patients demonstrated significant CI deficits compared with healthy controls across all inhibitory paradigms whereas medicated patients did not (at all inhibitory intervals, paired-pulse TMS: controls = 59.9%, medicated = 44.3%, unmedicated = 28.7%; cortical silent period: controls = 55.0 milliseconds, medicated = 60.4 milliseconds, unmedicated = 39.7 milliseconds; transcallosal inhibition: controls = 33.6%, medicated = 23.7%, unmedicated = 10.4%; P<.05). CONCLUSIONS: These results suggest that schizophrenia is associated with deficits in CI and that antipsychotic medications may increase CI.

Adult↗
PubMed2002

Brain serotonin 5-HT(1A) receptor binding in schizophrenia measured by positron emission tomography and [11C]WAY-100635.

BACKGROUND: Results of postmortem studies show an elevation in serotonin-1A (5-hydroxytryptamine-1A [5-HT(1A)]) receptor density in the prefrontal and temporal cortices of patients with schizophrenia. This study examined 5-HT(1A) receptors in vivo in patients with schizophrenia using positron emission tomography and [carbonyl-(11)C]-N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexane carboxamide ([(11)C]WAY-100635). METHODS: The 5-HT(1A) binding potential of 14 antipsychotic drug-naïve patients with a DSM-IV diagnosis of schizophrenia was compared with that of 14 age-matched healthy controls. Positron emission tomography data were analyzed using 9 cortical regions of interest, which were delineated on a coregistered magnetic resonance image and transferred to the positron emission tomographic image, with the cerebellum as the reference region for a simplified reference tissue model. We also performed a voxel-wise comparison using statistical parametric mapping. RESULTS: The region of interest-based analysis revealed a significant mean +/- SD cortical 5-HT(1A) receptor binding potential increase of 7.1% +/- 6.4% in patients with schizophrenia (F = 2.975; P =.02); local differences were +20% in the left medial temporal cortex (F = 9.339;P =.005) and +13% in the right medio temporal cortex (F = 4.453; P =.045). There were no significant differences in regional tracer delivery or cerebellar [(11)C]WAY-100635 uptake. The voxel-based analysis also confirmed a group difference in the left medial temporal cortex. CONCLUSIONS: The biological significance of elevated 5-HT(1A) receptor density in schizophrenia remains unclear. Given the location of 5-HT(1A) receptors on pyramidal cells, this elevation may reflect an abnormal glutamatergic network. Our finding needs to be viewed in light of preclinical evidence supporting a role for 5-HT(1A) receptors in mediating antipsychotic action and extrapyramidal adverse effects of drugs.

Adult↗
PubMed2002

Elevation of prolactin levels by atypical antipsychotics.

OBJECTIVE: Atypical antipsychotics are thought not to elevate prolactin levels. The authors examined data suggesting that atypical antipsychotics do elevate prolactin levels but more transiently than typical antipsychotics. METHOD: Prolactin levels in 18 male patients with schizophrenia who were receiving atypical antipsychotics were monitored over the 24-hour period following administration of their daily oral dose of risperidone, olanzapine, or clozapine. RESULTS: The baseline prolactin levels in patients receiving risperidone (mean=27 ng/ml, SD=14) were abnormally high, but baseline prolactin levels in patients receiving olanzapine (mean=9 ng/ml, SD=5) and clozapine (mean=9 ng/ml, SD=5) were not high. All three atypical antipsychotics caused a doubling of prolactin levels over baseline levels 6 hours after medication administration. CONCLUSIONS: These data suggest that these atypical antipsychotics raise prolactin levels, although the increases with olanzapine did not reach statistical significance. This suggests that the differences in the effects on prolactin levels of atypical and typical antipsychotics are not categorical but lie in the degree and duration of dose-induced prolactin elevation, attributable to the differential binding properties of each drug on pituitary dopamine D(2) receptors.

Adult↗
PubMed2002

Quetiapine: an effective antipsychotic in first-episode schizophrenia despite only transiently high dopamine-2 receptor blockade.

BACKGROUND: It has been suggested that transiently high dopamine-2 (D(2)) receptor occupancy by antipsychotic medication may be sufficient for inducing an antipsychotic response. We treated patients experiencing their first episode of schizophrenia with a single daily dose of quetiapine to achieve a transient daily peak of D(2) receptor blockade, to determine if this would lead to an antipsychotic response. METHOD: Fourteen patients with a DSM-IV diagnosis of schizophrenia or schizophreniform or schizoaffective disorder were treated with quetiapine titrated to a single daily dose (mean +/- SD dose at the time of the positron emission tomography [PET] scan = 427 +/- 69 mg) for 12 weeks. Peak D(2) occupancy approximately 2 hours postdose and trough D(2) occupancy approximately 20 hours postdose were determined using PET and [(11)C]raclopride. Clinical symptoms and side effects were measured at baseline and every 2 weeks during the treatment phase. RESULTS: Quetiapine administration led to a mean peak D(2) occupancy of 62% +/- 10% 2 hours postdose, which declined to 14% +/- 8% approximately 20 hours postdose. Ten (71%) of 14 patients responded to treatment with quetiapine, scoring "much improved" or greater on the Clinical Global Impressions-Improvement scale. Plasma drug levels and peak D(2) occupancy were highly correlated (r = 0.84; p =.003), as were prolactin and plasma drug levels when measured 2.5 hours after drug administration (r = 0.60; p <.05). Mean weight gain for the 10 subjects who completed the 12-week study was 4.2 +/- 4.6 kg (9.3 +/- 10.2 lb). No clinically relevant motor side effects occurred during the trial. CONCLUSION: Patients with a first episode of schizophrenia responded to treatment with a single daily dose of quetiapine despite only transiently high D(2) receptor occupancy. Our findings raise the question of whether continuously high D(2) blockade is necessary for obtaining an antipsychotic response. Future studies aimed at evaluating the relative merits of "transiently high" versus "continuously high" D(2) occupancy are warranted.

Adult↗
PubMed2001

Clozapine can induce high dopamine D(2) receptor occupancy in vivo.

RATIONALE: Clozapine is a unique antipsychotic with very low propensity to cause motor side effects. In contrast to most other antipsychotics that block more than 70% of dopamine D(2) receptors at therapeutic doses, clozapine occupies less than 70%. Furthermore, even at maximum occupancy, 70% is not exceeded. Several mechanisms have been proposed as explanations for this low D(2) receptor occupancy, but clear evidence is limited. OBJECTIVES: In patient studies the data are limited by the dose-range that can be safely used; therefore, the aims of this study were to examine the maximum occupancy of dopamine D(2) receptors with up to 5.0 mg/kg of bolus injection of clozapine to non-human primates and to measure the time course of occupancy. METHODS: PET examination with [(11)C]raclopride was performed to measure the dopamine D(2) receptor occupancy in the striatum of two monkeys after the bolus injection of 0.2-5.0 mg/kg clozapine. [(11)C]raclopride was injected sequentially to follow the time course of occupancy up to 7 h after the clozapine injection. RESULTS: Dopamine D(2) receptor occupancy reached up to 83% after 5.0 mg/kg clozapine injection. Occupancy decreased with a half-life of 7.22 h after 5.0 mg/kg clozapine and 5.25 h after 1.0 and 2.0 mg/kg clozapine. CONCLUSIONS: Clozapine could occupy a high proportion of dopamine D(2) receptors. The time course of occupancy was relatively fast, with a half-life of several hours.

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