Optical imaging of cerebellar functional architectures: parallel fiber beams, parasagittal bands and spreading acidification.

Publisher Summary An intriguing feature of the cerebellar cortex is its highly ordered circuitry and architectures, and understanding the function of this stereotypic circuitry and neuronal architectures is needed to unravel the nature of the neural computations performed by the cerebellar cortex. This chapter outlines the efforts put to develop and use optical imaging methodologies in the cerebellar cortex in vivo and emphasizes the significance of optical imaging in studying the interactions among the parallel fiber and climbing fiber systems, monitoring synaptic plasticity at the circuitry level, and observing novel phenomena such as spreading acidification and depression. Neutral red imaging has been used to map cerebellar cortical neuronal activity in vivo and has several useful properties for monitoring spatial patterns of neuronal activation in the cerebellar cortex. Thus, neutral red imaging provides a dramatic visualization that the cerebellar cortex is activated in parasagittal zones. Autofluorescence of flavoproteins and nicotinamide adenine dinucleotide has been used as an indirect measure of neuronal activity in isolated cell cultures and brain slice, but only to a limited extent in vivo . Spreading acidification and depression (SAD) appears to be a unique type of propagating activity, and multiple factors are likely to contribute to the spread of the acidification and depression such as hyperexcitability of the cerebellar circuitry. Conjunctive stimulation of climbing fiber and parallel fiber inputs results in long term depression at the parallel fiber–Purkinje cell synapse. Spreading acidification and depression in the cerebellar cortex is a newly described propagating activity in the central nervous system; however, much is still to be learned about SAD, including the mechanism of spread and the nature of the regenerative process.