A histochemical study of the innervation of cerebral blood vessels in the turtle

Specific histochemical techniques for the demonstration of noradrenaline and of acetylcholinesterase have been used to study the distribution of adrenergic and cholinergic nerves to the cerebral blood vessels of turtle, Geoclemys reevesii . The major and medium‐sized cerebral arteries were supplied with dense adrenergic nerve plexuses, the plexuses were particularly dense in the medium‐sized pial arteries of very thick vascular wall, indicating the functional significance of these arteries in the cerebral circulation. The parenchymal arterioles and capillaries were also supplied with adrenergic nerves. On the other hand, the cholinergic innervation was less dense than the adrenergic one and the acetylcholinesterase activity of the nerve fibres was remarkably weak. By contrast, the parenchymal small arterioles and capillaries exhibited heavy acetylcholinesterase activity on the vascular wall and, in addition, the capillaries were supplied with the well‐stained acetylcholinesterase‐positive nerve fibres. These fibres and also the adrenergic fibres associating with the capillaries appear to be of central origin. It is suggested that the cholinergic mechanisms in the parenchymal small vessels also play an important role in the cerebral circulation. The basophil leucocytes observed abundantly in the blood of turtle emitted an intensive greenish yellow fluorescence after formaldehyde gas‐treatment.