Deep Brain Stimulation Improves Parkinson's Disease-Associated Pain by Decreasing Spinal Nociception.

Dopamine exerts antinociceptive effects on pain in PD at cortical and spinal levels, whereas only cortical effects have been described for DBS, so far. By assessing the nociceptive flexion reflex (NFR) threshold at medication on, and DBS ON and OFF in two patients, we showed that DBS additionally decreases spinal nociception.

Ethanol reduces motoneuronal excitability and increases presynaptic inhibition of Ia afferents in the human spinal cord.

INTRODUCTION: Already low blood concentrations of ethanol acutely impair motor control and coordination. In vitro experiments have given evidence that spinal effects of ethanol contribute to this by reducing spinal excitability and enhancing presynaptic inhibition of Ia fibers. In this study, we investigated the influence of 0.7 g per kilogram of bodyweight ethanol on motoneuronal excitability and presynaptic inhibition in humans. METHODS: The study was performed in 10 volunteers. Spinal excitability was measured by the maximal H-reflex of the soleus muscle normalized to the maximal muscular response (Hmax/Mmax). Presynaptic inhibition was measured by changes in heteronymous Ia-facilitation of the soleus H-reflex, which is achieved by stimulation of the femoral nerve. A decrease in facilitation can be ascribed to an increase in presynaptic inhibition. Changes of these parameters under the influence of 0.7 g per kilogram of bodyweight ethanol were assessed in comparison to control measurements before ethanol application. RESULTS: Both parameters, Hmax/Mmax and Heteronymous facilitation, were significantly reduced under the influence of ethanol (Wilcoxon signed-rank test with Bonferroni correction for each, p<0.01). DISCUSSION: The increase in presynaptic inhibition by ethanol is probably caused by an increase in GABAA receptor-mediated Cl-conductance, which has been shown in spinal cord cultures. The role of presynaptic inhibition in movement is assumed to be there to control the afferent input of muscle spindles and tendon organs as a mechanism of specific input-selection. This study demonstrated that ethanol reduces spinal excitability and increases GABAergic presynaptic inhibition on Ia afferent fibers in humans.

Introduction of a continual RIII reflex threshold tracking algorithm.

INTRODUCTION: The RIII reflex is used in fundamental and clinical pain research. Here we introduce a continual reflex threshold tracking algorithm to facilitate investigations of the time courses of influences on the threshold. METHODS: First we investigated the probability of reflex occurrence at the threshold estimated by the continual algorithm and the changes of the threshold over the time during continual recordings of 100 min duration in 10 subjects. Secondly we compared the threshold estimates of the continual algorithm with those of a standard algorithm of threshold estimation in 52 subjects and compared the differences between the two methods with the test-retest-variability of each method. RESULTS: The average probability of reflex occurrence at the threshold estimated by the continual algorithm was 48.7% (SD = 3.2%). Changes of the RIII reflex threshold over the time were not significant (Friedman test, p>0.05). The variability between the thresholds determined by the different algorithms (test: SD = 2.50 mA, retest: SD = 1.80 mA) was lower than the variability between test and retest (standard algorithm: SD = 4.32 mA, continual algorithm: SD = 4.44 mA). DISCUSSION: The continual algorithm can be used for a continuous estimation of the reflex threshold at the 50% probability of reflex-occurrence. No evidence of habituation was detected. This allows for investigations of the time courses of pharmacological and physiological influences on the reflex threshold by using this algorithm. The lower variability between the continual algorithm and the standard algorithm compared to the variability between tests and retests of the methods allows for interchangeable conclusions drawn from data obtained with both methods.