Evidence for a functional cholinergic innervation of cerebral arteries.

Cat and rabbit cerebral arteries were compared to determine whether cholinergic nerves are present in both species. Low levels of acetylcholine and high affinity choline accumulation were found in noncerebral vessels of both species. Since it is doubtful that these low levels reflect the presence of a cholinergic innervation, they can be seen as indicators of background levels of these parameters in blood vessels. Cerebral arteries of both species contained much higher amounts of acetylcholine; levels ranged from 9 to 36 nmol/g. Accumulation of choline was also measured. Choline accumulation that was blocked with hemicholinium-3 was taken as a measure of high-affinity uptake and considered to be associated with cholinergic nerves. Levels of choline accumulation were much higher in cerebral arteries of both cats and rabbits than in noncerebral vessels. After labeling acetylcholine stores by preincubation with [3H]choline at a low concentration (5 X 10(-8) M), transmural electrical stimulation caused a marked increase in tritium efflux from both cat and rabbit cerebral arteries. Fractional release of acetylcholine per stimulation pulse averaged 8.6 X 10(-6). Treatment with tetrodotoxin or removal of calcium from the superfusing solution blocked stimulation-evoked tritium release, confirming its neurogenic origin. These findings provide strong evidence that cerebral arteries of both cats and rabbits are innervated with cholinergic nerves. However, the relationship between a neurogenic dilator response of cerebral arteries and the presence of a cholinergic innervation remains unclear.