Intracerebral pathways involved in arterial vasospasm following an experimental subarachnoid haemorrhage.

Subarachnoid blood does not induce vasospasm by a direct vascular effect, but via a neural and/or neurohumoral mechanism. Neurons in the A1 and A2 nuclei and in the median eminence region connected by fibres running in the central tegmental tract are necessary for the development of vasospasm following a SAH.