Uncoupling of cerebral blood flow and glucose utilization in the regenerating facial nucleus after axotomy

Axotomy is known to activate various metabolic processes including protein synthesis and glucose utilization in the motor nucleus. Although it is generally assumed that the local cerebral blood flow (CBF) fluctuates in response to the axonal reaction, there has been no direct evidence for changes in CBF in the motor nucleus following axotomy. In this study, the CBF in the facial nuclei was measured after axotomy of the facial nerve employing the [14C]iodoantipyrine method to evaluate the relation between the CBF and axonal reaction. Following unilateral facial nerve axotomy in neonates, which induced neuronal degeneration in the facial nucleus, the CBF and glucose uptake was significantly decreased on the operated nucleus, suggesting that CBF and glucose metabolism are coupled in the degenerating nucleus. In contrast, after axotomy in adults, which induced regeneration of neurons and glial reactions, glucose uptake was increased on the operated nucleus, while the CBF did not differ significantly between the operated and unoperated nucleus. These findings imply that glucose metabolism and CBF are uncoupled in the regenerating nucleus, suggesting that the relation between CBF and metabolism in the regenerating nucleus following axotomy may clearly contradict the classical concept of a tight coupling between CBF and metabolism.