RESUMEN
OBJECTIVES: Transcranial magnetic stimulation (TMS) allows exploration of the mode of action of neuroactive substances in the human brain, and allows evaluation of neuronal networks, which might be involved in the action of nicotine. The aim of the present study was to explore motor cortex excitability in chronic smokers and non-smokers using TMS. METHODS: The study included 50 healthy subjects, of whom 25 were chronic smokers and 25 were age- and sex-matched non-smokers. Number of cigarettes per day and duration of smoking in years were documented. Serum level of cotinine was measured. Resting and active motor threshold (RMT, AMT) and input-output curves (I/O) were performed to assess corticospinal excitability. The duration of the contralateral silent period (cSP) at different ranges of stimulation intensities and ipsilateral silent period (iSP) were used as measures of inhibition. RESULTS: There were no significant differences either in RMT or AMT between groups. I/O curve showed a significant intensity×group interaction (P=0.008). This was attributable to significantly higher amplitudes of MEP among smokers than non-smokers especially at 130, 140 and 150% of RMT (P=0.0001 and P=0.03 and 0.02 respectively). The mean duration of the cSP at different intensities and iSP duration were similar in both groups. Nicotine level and smoking index were correlated respectively with rMT and iSP (P=0.03 and 0.01). CONCLUSION: The present results confirm previous findings by Grundey et al. (2013) that chronic nicotine consumption is characterized by hyperexcitability of corticospinal output. We speculate that it is a secondary adaptation to long-term nicotine use with high inter-individual variance.
Asunto(s)
Excitabilidad Cortical/efectos de los fármacos , Potenciales Evocados Motores/efectos de los fármacos , Corteza Motora/efectos de los fármacos , Nicotina/farmacología , Adulto , Excitabilidad Cortical/fisiología , Potenciales Evocados Motores/fisiología , Humanos , Masculino , Persona de Mediana Edad , Corteza Motora/fisiología , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Nicotina/efectos adversos , Estimulación Magnética Transcraneal/métodosRESUMEN
BACKGROUND: Essential tremor (ET) is thought to emerge from activity in a distributed cerebello-thalamo-cortical network. It has been proposed that the network goes into oscillation because of abnormal GABAergic inhibitory transmission. OBJECTIVE: To test this idea by investigating GABAergic circuitry in motor cortex using transcranial magnetic stimulation (TMS). METHODS: Motor cortex excitability was examined using TMS in 21 patients with essential tremor and in 20 control subjects. Resting and active motor threshold (RMT, AMT) and input-output curves examined corticospinal excitability. Contralateral silent period (cSP) at a different range of stimulation intensities, and the ipsilateral silent period (iSP) using a stimulus intensity of 150% RMT were used as measures of GABAergic function. RESULTS: RMT and AMT were significantly lower in patients than controls and patients had a steeper I/O curve. However, there were no significant differences in either cSP at different intensities or in iSP. CONCLUSION: We found no evidence in favour of the GABA hypothesis in ET.
Asunto(s)
Excitabilidad Cortical , Temblor Esencial/fisiopatología , Corteza Motora/fisiopatología , Tractos Piramidales/fisiopatología , Estimulación Magnética Transcraneal , Ácido gamma-Aminobutírico/fisiología , Adolescente , Adulto , Potenciales Evocados Motores , Femenino , Humanos , Masculino , Persona de Mediana Edad , Inhibición Neural , Adulto JovenRESUMEN
OBJECTIVES: It has recently been suggested that drug-induced tardive syndromes (TS) might be due to maladaptive plasticity, which increases motor excitability in cerebral cortex and basal ganglia. In order to test this hypothesis, we performed the first measurements of cortical excitability in TS. METHODS: Motor cortex excitability was examined using transcranial magnetic stimulation (TMS) in 22 TS patients and compared with that in 20 age and sex-matched healthy individuals. Resting and active motor threshold (RMT, AMT) and input-output curves (I/O curves) assessed corticospinal excitability. The duration of the contralateral silent period (cSP) at a range of stimulation intensities and ipsilateral silent period (iSP) were used as measures of inhibition. RESULTS: There were no significant differences in RMT and AMT between patients and controls, although the input-output curves were significantly steeper in patients. The cSP (at different stimulus intensities) and iSP were both longer in the patients compared to the control group. However, most of this difference could be accounted for by increased recruitment of motor evoked potentials (MEPs) in patients. CONCLUSION: TS is characterized by hyperexcitability of corticospinal output that might contribute to the lack of selectivity in muscle recruitment and contribute to excess involuntary movement. The findings are opposite to those in naturally-occurring hyperkinesia such as Sydenham's and Huntington's chorea, suggesting a fundamental difference in the pathophysiology.