Autoradiographic study of the cerebrovascular effects of stimulation of the substantia innominata: convenient stimulation paradigm.

The aim of this study was to determine the distribution within the whole brain of the vascular effects of stimulation of the substantia innominata. This basal forebrain nucleus is the major cholinergic input in the neocortex in the rodent. The local cerebral blood flow was measured by the autoradiographic [14C]iodoantipyrine technique in a group of control and a group of stimulated unanesthetized rats. The substantia innominata was electrically stimulated through a chronically implanted electrode. The stimulation induced blood flow increases exceeding 200% in the hemisphere ipsilateral to the stimulation and 100% in the contralateral hemisphere compared to the control group. The ipsilateral vasodilations were observed not only in the cortical areas but also in some subcortical structures. Comparison with previous data suggests that part of the effects is due to cholinergic neurons of the substantia innominata and part to non-cholinergic neurons and indirect effects. However, only two out of eight stimulated rats displayed this response. The low reproducibility of the results is discussed, considering the stimulation paradigm which has been developed for future measurements of the cerebral glucose utilization which requires a long duration stimulation period.