Association Between Dendritic Lamellar Bodies and Complex Spike Synchrony in the Olivocerebellar System

Dendritic lamellar bodies have been reported to be associated with\n dendrodendritic gap junctions. In the present study we investigated this\n association at both the morphological and electrophysiological level in\n the olivocerebellar system. Because cerebellar GABAergic terminals are\n apposed to olivary dendrites coupled by gap junctions, and because lesions\n of cerebellar nuclei influence the coupling between neurons in the\n inferior olive, we postulated that if lamellar bodies and gap junctions\n are related, then the densities of both structures will change together\n when the cerebellar input is removed. Lesions of the cerebellar nuclei in\n rats and rabbits resulted in a reduction of the density of lamellar\n bodies, the number of lamellae per lamellar body, and the density of gap\n junctions in the inferior olive, whereas the number of olivary neurons was\n not significantly reduced. The association between lamellar bodies and\n electrotonic coupling was evaluated electrophysiologically in alert\n rabbits by comparing the occurrence of complex spike synchrony in\n different Purkinje cell zones of the flocculus that receive their climbing\n fibers from olivary subnuclei with different densities of lamellar bodies.\n The complex spike synchrony of Purkinje cell pairs, that receive their\n climbing fibers from an olivary subnucleus with a high density of lamellar\n bodies, was significantly higher than that of Purkinje cells, that receive\n their climbing fibers from a subnucleus with a low density of lamellar\n bodies. To investigate whether the complex spike synchrony is related to a\n possible synchrony between simple spikes, we recorded simultaneously the\n complex spike and simple spike responses of Purkinje cell pairs during\n natural visual stimulation. Synchronous simple spike responses did occur,\n and this synchrony tended to increase as the synchrony between the complex\n spikes increased. This relation raises the possibility that synchronously\n activated climbing fibers evoke their effects in part via the simple spike\n response of Purkinje cells. The present results indicate that dendritic\n lamellar bodies and dendrodendritic gap junctions can be downregulated\n concomitantly, and that the density of lamellar bodies in different\n olivary subdivisions is correlated with the degree of synchrony of their\n climbing fiber activity. Therefore these data support the hypothesis that\n dendritic lamellar bodies can be associated with dendrodendritic gap\n junctions. Considering that the density of dedritic lamellar bodies in the\n inferior olive is higher than in any other area of the brain, this\n conclusion implies that electrotonic coupling is important for the\n function of the olivocerebellar system

The evolution of hippocampus volume and brain size in relation to food hoarding in birds

Food-hoarding birds frequently use spatial memory to relocate their caches, thus they may evolve a larger hippocampus in their brain than non-hoarder species. However, previous studies testing for such interspecific relationships provided conflicting results. In addition, food hoarding may be a cognitively complex task involving elaboration of a variety of brain regions, even outside of the hippocampus. Hence, specialization to food hoarding may also result in the enlargement of the overall brain. In a phylogenetic analysis of distantly related birds, we studied the interspecific association between food hoarding and the size of different brain regions, each reflecting different resolutions. After adjusting for allometric effects, the relative volume of the hippocampus and the relative size of the entire brain were each positively related to the degree of food-hoarding specialization, even after controlling for migration and brood parasitism. We also found some significant evidence for the relative volume of the telencephalon being associated with food hoarding, but this relationship was dependent on the approach we used. Hence, neural adaptation to food hoarding may favour the evolution of different brain structures