Report 2004

Report 2003

Projections to the rat pontine nuclei: separate channels or integration?

We find a remarkably high degree of overlap between inputs from homotopic representations in the pons. This finding has been compared to data (from the same cases) from another major projection system, the cortico-neostriatal system. The comparison shows that the overlap in the pontine nuclei is considerably larger than the corresponding overlap between these projections in the neostriatum. We conclude that the pontine nuclei are well suited for integrating related somatosensory inputs before passing the information onto the cerebellum.

Local organization of the inferior olive

Neurons in the olivary nuclei exhibit subthreshold oscillations of their membrane potential, thought to depend on gap-junctions between olivary neurons. Weused a strain of knockout mice that lack Connexin 36 (KO Cx36), the protein that forms gap junctions in the olive and other brain areas. Except for small deficits in vestibuloocular reflex(VOR) gain learning, the KO Cx36 mice appear normal. Despite the absence of electrotonic coupling, neurons from KO Cx36 mice maintained the ability to oscillate. Hence, knocking out the coupling transforms quiescent olivary neurons into oscillatory neurons. These results suggest that the lack of Cx36 proteins triggers compensatory mechanisms, which transform olivary neurons from quiescence to auto-rhythmicity. We propose that the ability of olivary neurons to produce oscillations using different strategies call attention to the importance of these oscillations to the normal function of the animal.

In vivo activity of granule cells

In continuation of the work reported last year we now also obtained sensory-evokedresponses in in vivogranule cells using airpuff stimulation of whiskers and face. These recordings have shown that the majority of granule cells fire in a burst pattern of discharge in response to sensory stimulation.

Bistability in Purkinje cells

In vivorecordings from Purkinje cells have revealed, surprisingly, that the majority of these neurons exhibit intrinsic membrane potential bistability. In most cases the transitions in membrane potential between states are preceded by spontaneously occurring complex spikes, with the transition between downstate and upstate being associated with a robust increase in simple spike frequency during the upstate. Analogous transitions between quiescent and spiking states following climbing fibre input have also been observed in non-invasive cell-attached recordings. Complex spikes evoked by sensory stimulation of the perioral areas were also efficient triggers of transitions between states, demonstrating the functional importance of this process for the integration of sensory input by the cerebellar cortex.