Depolarization of afferent fibers to the goll and burdach nuclei induced by stimulation of the brain-stem

1. In nembutalized cats the excitability of superficial radial (SR) and superficial peroneus (SP) primary afferents was tested by microelectrode stimulation (Wall's technique) within the dorsal column nuclei (DCN). SR and SP excitability increased for over 100 msec after conditioning stimulation of the brain-stem with a maximal effect at 50 msec interval. The conditioning curves did not change in decerebrated and cerebellectomized preparations. 2. In nembutalized intact and decerebrated cats a negative slow potential change (over 150 msec) was recorded from one isolated dorsal column (dorsal column potential, DCP) following stimulation of the brain-stem. In the same type of preparations the brain-stem stimulation induced from DCN surface a prolonged (over 150 msec) positive potential (P-wave) which inverted within the nuclei. 3. Interaction experiments have revealed an inhibitory effect of conditioning brain-stem stimulation on SR induced surface P-wave. The effect was maximal at 50 msec interval and was present up to 200 msec. SR stimulation also depressed the brain-stem induced P-wave for over 150 msec but with a maximal effect within the first 20–30 msec. 4. The effects reported above were maximal when the caudal-most brain-stem regions were stimulated. They were still present in control experiments where the sensorimotor cortex had been widely removed 15 days previously.