REGIONAL CEREBRAL BLOOD-FLOW RESPONSES TO NEUROCHEMICAL STIMULATION OF THE SUBSTANTIA INNOMINATA IN THE ANESTHETIZED RAT

Since electrical stimulation of neurones may activate not only cell bo dies but also neuronal fibres, this study aimed to test a selectively cholinergic neurochemical stimulation of the rat substantia innominata (SI) by the local microinjection of carbachol; the effects of this ac etylcholine agonist were compared with glutamate. Cortical and subcort ical cerebral blood flow (CBF) were measured in anaesthetized rats wit h the [C-14]iodoantipyrine method by the tissue sampling technique imm ediately following the intracerebral (SI) microinjection of saline, 50 nmol of carbachol or glutamate. Carbachol microinjection into the SI induced a transient but significant vasodilatation in frontoparietal m otor (+28%) and temporal (+41%) cortices, that lasted for less than 10 min. Glutamate did not elicit any significant CBF modifications when compared to control rats although a significant interhemispheric asymm etry after microinjection was observed in the frontoparietal motor cor tex. This latter observation would suggest that the glutamate-induced cortical response is less pronounced than that elicited by carbachol. Overall, these results demonstrate that a selective cholinergic stimul ation of the SI can induce a transient cortical vasodilatation and fur ther confirms the hypothesis of a muscarinic modulation of CBF via thi s basal structure.