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Arquivos de Neuro-Psiquiatria

On-line version ISSN 1678-4227

Arq. Neuro-Psiquiatr. vol.61 no.2A São Paulo June 2003 



Efffect of clozapine and typical antipsychotics on P50 suppression in patients with schizophrenia. (Abstract)*. Dissertation. Porto Alegre, 2003.


Jefferson Becker**


INTRODUCTION: The P50 is a mid-latency evoked potential used to characterize differences in auditory sensory gating among psychiatric patients and normal controls. Attenuation of the amplitude of the P50 component with stimulus repetition is widely used to study sensory gating. In the P50 suppression paradigm, when a pair of auditory stimuli is presented 500 ms apart, the amplitude of the second response, compared with the first one, is markedly attenuated in healthy subjects. Most schizophrenic patients, on the other hand, fail to inhibit the P50 response to the second stimulus, which is assumed to reflect an inhibitory deficit.
OBJECTIVE: To verify if clozapine has distinct effects in the P50 suppression compared to typical antipsychotics. To replicate in our population the findings, which showed that a sensory gating suppression deficit persists in schizophrenics, treated with typical antipsychotics compared to healthy subject. To find out if there is a relation between the P50 suppression failure in schizophrenic patients and the Brief Psychiatry Rating Scale (BPRS) scores.
METHOD: Fifty schizophrenic patients who fulfilled DSM-IV criteria for schizophrenia, selected from the private and public health system, and 25 healthy volunteers were selected for the study. Exclusion criteria were another DSM-IV axis I psychiatric diagnosis evaluated with MINI, use of any atypical antipsychotic medication but clozapine or use of drugs of abuse in the last month. This population was divided in three groups (n=25): group 1 - schizophrenics treated with typical antipsychotics; group 2 - patients with schizophrenia in use of clozapine; group 3 - normal controls. All participants were submitted to P50 recordings according to Ghisolfi et al. (Neuropsychopharmacology 2002;27:629-37) protocol. BPRS were assessed by a board-certified psychiatrist before the P50 recording. Critical variables for the analysis included conditioning (S1) and test (S2) P50 amplitude and latency, S2/S1 ratio, S1-S2 difference and BPRS scores. ANOVA was performed for comparable data among the groups. Post hoc T-test was used to compare the mean values between 2 groups.
RESULTS: There was no statistically significant difference in the mean ages and gender distribution among the 3 groups. After comparing latency and amplitude mean values, it has been found that S1 amplitude in the group 1 was significantly smaller than in the group 2 (p=0.037). There were no differences in other groups' analysis. The mean S2/S1 ratio was 0.82 ± 0.45 in the group 1, 0.57 ± 0.41 in the group 2 and 0.44 ± 0.27 in the group 3. ANOVA showed significant difference in these ratios (p=0.003). When comparison between two groups was done, it has been found significant difference in the findings of the group 1 in the relation to group 2 (p=0.045) and 3 (p=0.001). There was no statistically significant difference between groups 2 and 3 (p=0.182). The S1-S2 means difference was significant only in the comparison of the groups 1 and 3 (p=0.007). However, there was a very strong tendency in the S1-S2 analysis of the groups 1 and 2 (p=0.067). There was no relation among BPRS scores and S2/S1 ratio, S1-S2 difference, S1 and S2 P50 amplitude and latency.
CONCLUSION: This study showed P50 suppression impairment in schizophrenics in use of typical antipsychotics. It was not found a relation among BPRS scores and P50 parameters. On the other hand, P50 suppression was significantly better among patients with schizophrenia in use of clozapine than in use of typical antipsychotics.

Key words: antipsychotics, clozapine, P50 evoked potentials, schizophrenia.


* Efeito da clozapina e dos antipsicóticos típicos na supressão do potencial evocado P50 em pacientes com esquizofrenia (Resumo). Dissertação de Mestrado, Pontifícia Universidade Católica do Rio Grande do Sul (Área: Neurociências). Orientador: Jaderson Costa da Costa
** Address: Rua General Caldwell 661/307 - 90130-051 Porto Alegre RS - Brasil. E-mail:

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