REGULATION OF REGIONAL BLOOD-FLOW IN THE LATERODORSAL THALAMUS BY ASCENDING CHOLINERGIC NERVE-FIBERS FROM THE LATERODORSAL TEGMENTAL NUCLEUS

The laterodorsal tegmental nucleus (LDT) is the largest aggregation in the brainstem of cholinergic neurons whose axons reach the thalamus a s part of a diffuse projection to the forebrain. We measured the regio nal blood flow in the thalamus by means of laser Doppler flowmetry, an d examined whether the blood flow was regulated by the ascending choli nergic nerve fibers originating in the LDT. Experiments were performed on urethane-anesthetized rats whose upper cervical spinal cord was tr ansected to avoid response of systemic blood pressure following LDT st imulation. The ascending cholinergic nerve fibers were excited by elec trical or chemical stimulation applied to the LDT. The regional thalam ic blood flow increased in response to repetitive electrical stimulati on and chemical stimulation with L-glutamate to the LDT. The response, starting several seconds after the onset of electrical stimulation an d lasting as long as 1 min, was reduced by i.v. scopolamine, a choline rgic muscarinic receptor antagonist. The results indicate that regiona l blood flow in the thalamus is increased by excitation of the ascendi ng cholinergic nerve fibers originating in the LDT mainly through the cholinergic muscarinic receptors.