REAPPEARANCE OF ACTIVITY IN THE VESTIBULAR NEURONS OF LABYRINTHECTOMIZED GUINEA-PIGS IS NOT DELAYED BY CYCLOHEXIMIDE

1. In mammals, unilateral labyrinthectomy; induces an immediate depres sion of the resting discharges in the neurones of the ipsilateral vest ibular nuclei. Later on, a spontaneous restoration of this activity oc curs. The aim of the present study was to test the possibility that pr otein synthesis could be involved in the start of this process in the guinea-pig. 2. Cycloheximide (CHX), a protein synthesis inhibitor, was injected intramuscularly 1 h before (30 mg kg(-1)) and 5 h after (15 mg kg(-1)) labyrinthectomy. 3. In a first group of animals, CHX was fo und to induce an inhibition of protein synthesis at levels ranging fro m 71 to 93 % for 9 h after labyrinthectomy. 4. In a second group of al ert animals, we studied single unit activity of second-order vestibula r neurones. It was found that, in the 12-16 h post-labyrinthectomy per iod, at a time when restoration began in guinea-pigs not treated with CHX, the discharges in the labyrinthectomized group treated with CHX w ere not different from those observed in a previous study in labyrinth ectomized animals not treated with CHX. 5. We conclude that protein sy nthesis is not required for the start of restoration of activity in th e vestibular neurones deprived of their ipsilateral labyrinthine input .