The Role of Cutaneous Receptors in the Menton Tap Silent Period

The neuromuscular mechanisms of the electromyographic silent period are poorly understood but clinically significant. Our purpose was to isolate the contribution of cutaneous afferents from the chin to the latency and the duration of the EMG silent period. Under the conditions of our experiment, the afferents of the mental nerve have no observable influence on the latency or the duration of the silent period educed by a menton tap.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66492/2/10.1177_00220345790580011001.pd

SUPERFICIAL AND DEEP CONVERGENT NOCICEPTIVE NEURONS ARE DIFFERENTIALLY AFFECTED BY N-METHYL-D-ASPARTATE APPLIED ON THE BRAINSTEM SURFACE OF THE RAT MEDULLARY DORSAL HORN

International audienceThe activation of N-methyl-D-aspartate receptors is implicated in the spinal and trigeminal processing of nociceptive information conveyed by convergent (wide dynamic range) neurons and particularly in C-¢ber-evoked responses elicited by repetitive and high-intensity electrical stimulation of the neuronal receptive ¢eld. In this study, the e¡ects of intrathecal NMDA application on the electrically evoked nociceptive responses of trigeminal subnucleus caudalis convergent neurons have been investigated. The total C-¢ber-evoked activity triggered by 30 successive stimuli was divided into two components: the C-¢ber input response and thèwind-up' response. Application of 0.1 Wg (in 50 Wl) of NMDA evoked a bi-directional e¡ect on the total C-¢ber-evoked activity of 19 neurons tested. A signi¢cant increase in the total C-¢ber-evoked activity was observed 15^25 min after the NMDA application for nine neurons located in super¢cial laminae II and III. In contrast, a signi¢cant decrease in the total C-¢ber-evoked activity was observed 5^25 min after the NMDA application for 10 neurons located more deeply, in lamina V. The NMDA-induced modi¢cations seen in the total C-¢ber-evoked activity were likely a re£ection of a signi¢cant increase or decrease in neuronal activity evoked by the C-¢ber input rather than wind-up of the responses since the latter was not signi¢cantly modi¢ed by the NMDA application. These results provide evidence for a possible inhibitory role for NMDA-dependent interneurons of the super¢cial laminae of the medullary dorsal horn on the nociceptive activity of deep convergent neurons.