The strength and variability of electrical synaptic connections between GABAergic
interneurons are key determinants of spike synchrony within neuronal networks. However,
little is known about how electrical coupling strength is determined due to the inaccessibility
of gap junctions on the dendritic tree. We investigated the properties of gap junctions
in cerebellar interneurons by combining paired somato-somatic and somato-dendritic
recordings, anatomical reconstructions, immunohistochemistry, electron microscopy,
and modeling. By fitting detailed compartmental models of Golgi cells to their somato-dendritic
voltage responses, we determined their passive electrical properties and the mean
gap junction conductance (0.9 nS). Connexin36 immunofluorescence and freeze-fracture
replica immunogold labeling revealed a large variability in gap junction size and
that only 18% of the 340 channels are open in each plaque. Our results establish that
the number of gap junctions per connection is the main determinant of both the strength
and variability in electrical coupling between Golgi cells.
