Ultrastructural characteristics of spasm in intracerebral arterioles.

Following craniotomy, three groups of cats were subjected to three different stimuli: group A hyperventilation, group B electroshock, and group C direct electric current. During electric stimuli, pial vessels were observed through a cranial window. Immediately after electric current application, some arterial vessels showed segmental spastic constriction. Tissue samples for electron-microscopy were taken from the parietal lobe and nucleus caudatus. In all three groups of animals, different types of constriction of blood vessels were observed. The respiratory alkalosis achieved by hyperventilation led to physiological constriction of the arterioles. The electric stimuli led to spastic constriction of the meningeal and intracerebral arteries and arterioles in group B and C; the entire vessel wall was greatly deformed and the vessel lumen was almost obstructed. Electroshock resulted in only moderate structural changes of the smooth muscle cells. Direct current, however, caused an extreme and bizarre smooth muscle deformation. The results show that spastic constrictions of arterioles can be clearly distinguished from physiological, that is non-spastic constriction, by morphological parameters. Electric stimulation of cerebral vessels could be an experimental condition for further investigation of intracerebral vasospasm.