A transcranial magnetic stimulation study of the effects of olanzapine and risperidone on motor cortical excitability in patients with schizophrenia.
BACKGROUND
There has been a progressive increase in interest in the functioning of the main inhibitory and excitatory neurotransmitters in the pathophysiology of schizophrenia. Limited information is available as to how these neurotransmitters are affected by commonly prescribed antipsychotic agents.


OBJECTIVE
We investigated whether the atypical antipsychotics olanzapine and risperidone differ in their effects on inhibitory and excitatory cortical markers measured with transcranial magnetic stimulation.


METHODS
Electromyographic recordings from the abductor pollicis brevis muscle were made during focal transcranial magnetic stimulation to the contralateral motor cortex and during bilateral cortical stimulation. Twenty patients on each drug and 22 controls were studied with measures of the resting motor threshold, motor evoked potential size, post-excitatory silent period duration, cortical inhibition and facilitation to paired-pulse transcranial magnetic stimulation and transcallosal inhibition.


RESULTS
The patient groups differed from the controls in the silent period and transcallosal inhibition measures, both of which assess cortical inhibitory activity. The two medication groups differed in the magnitude of the resting motor threshold and several measures of transcallosal inhibition that reflect the spread of inhibitory activity between hemispheres.


CONCLUSIONS
These findings suggest that olanzapine and risperidone differ subtly in their effects on cortical inhibitory mechanisms. Further evaluation is required to establish whether these differences may reflect or underlie differences seen between these medications in their clinical profiles, including their effects on cognitive symptoms of schizophrenia.
Fitzgerald
Paul B
PB
Dandenong Psychiatry Research Centre, Monash University School of Psychology, Psychiatry and Psychological Medicine, P.O. Box 956, Dandenong, Victoria 3175, Australia. paul.fitzgerald@med.monash.edu.au
Brown
Timothy L
TL
Daskalakis
Z Jeff
ZJ
Kulkarni
J
J
D000328:Adult; D000704:Analysis of Variance; D001569:Benzodiazepines; D016009:Chi-Square Distribution; D004574:Electromagnetic Fields; D019054:Evoked Potentials, Motor / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000187:drug effects* / Q000502:physiology; D000077152:Olanzapine; D010361:Patients; D010890:Pirenzepine / Q000031:analogs & derivatives* / Q000494:pharmacology* / Q000627:therapeutic use; D018967:Risperidone / Q000494:pharmacology* / Q000627:therapeutic use; D012559:Schizophrenia / Q000188:drug therapy* / Q000503:physiopathology
D001569:Benzodiazepines; D010890:Pirenzepine; D018967:Risperidone; D000077152:Olanzapine