The cholinergic pathway to cerebral blood vessels

Summary The effect of stimulating the greater superficial petrosal nerve (g.s.p.n.) upon retroglenoid venous blood flow has been tested in anaesthetized, paralysed and artificially ventilated rats. In 11 out of 15 tests, blood flow increased by an average of 25% with a time to peak response of 28 s. This response was abolished with the injection of atropine 0.1 mg kg^–1 injected intra-arterially. With both petrosal nerves intact, the administration of 6–7% CO₂ in air or 15% O₂ in N₂ caused average increases in blood flow of 105% and 45% respectively. These responses were not affected by bilateral section of the g.s.p.n. Similar experiments were carried out in 5 anaesthetized, spontaneously breathing rabbits in which, in addition toPaCO₂ andPaO₂,PO₂,PCO₂ and blood flow in the caudate nucleus were measured continuously using chronically implanted mass spectrometer catheters and heated thermistors. Caudate nucleus blood flow increased in response to hypoxia and hypercapnia and this response was not significantly affected by section of one or both g.s.p.n., sinus or vagus nerves. With section of sinus and vagus nerves, blood flow changed passively with arterial pressure.