ASSOCIATION BETWEEN DENDRITIC LAMELLAR BODIES AND COMPLEX SPIKE SYNCHRONY IN THE OLIVOCEREBELLAR SYSTEM

Dendritic lamellar bodies have been reported to be associated with den drodendritic gap junctions. In the present study we investigated this association at both the morphological and electrophysiological level i n the olivocerebellar system. Because cerebellar GABAergic terminals a re apposed to olivary dendrites coupled by gap junctions, and because lesions of cerebellar nuclei influence the coupling between neurons in the inferior olive, we postulated that if lamellar bodies and. gap ju nctions are related, then the densities of both structures will change together when the cerebellar input is removed. Lesions of the cerebel lar nuclei in rats and rabbits resulted in a reduction of the density of lamellar bodies, the number of lamellae per lamellar body, and the density of gap junctions in the inferior olive, whereas the number of olivary neurons was not significantly reduced. The association between lamellar bodies and electrotonic coupling was evaluated electrophysio logically in alert rabbits by comparing the occurrence of complex spik e synchrony in different Purkinje cell zones of the flocculus that rec eive their climbing fibers from olivary subnuclei with different densi ties of lamellar bodies. The complex spike synchrony of Purkinje cell pairs. that receive their climbing fibers from an olivary subnucleus w ith a high density of lamellar bodies, was significantly higher than t hat of Purkinje cells, that receive their climbing fibers from a subnu cleus with a low density of lamellar bodies. To investigate whether th e complex spike synchrony is related to a possible synchrony between s imple spikes, we recorded simultaneously the complex spike and simple spike responses of Purkinje cell pairs during natural visual stimulati on. Synchronous simple spike responses did occur, and this synchrony t ended to increase as the synchrony between the complex spikes increase d. This relation raises the possibility that synchronously activated c limbing fibers evoke their effects in part via the simple spike respon se of Purkinje cells. The present results indicate that dendritic lame llar bodies and dendrodendritic gap junctions can be downregulated con comitantly, and that the density of lamellar bodies in different oliva ry subdivisions is correlated with the degree of synchrony of their cl imbing fiber activity. Therefore these data support the hypothesis tha t dendritic lamellar bodies can be associated with dendrodendritic gap junctions. Considering that the density of dedritic lamellar bodies i n the inferior olive is higher than in any other area of the brain, th is conclusion implies that electrotonic coupling is important for the function of the olivocerebellar system.