ABSTRACT
The majority of studies on the nonadrenergic innervation of cerebral vessels have been performed in vitro. Nonadrenergic neurotransmitters may stimulate or depress other fiber tracts and changes in flow may not correspond to the anatomical distribution of the substance under study. Most putative neurotransmitters influence cerebral metabolism, for instance serotonin and γ-amino butyric acid decrease both cerebral oxygen uptake and local glucose consumption provided they can be made to cross the blood-brain barrier or a suitable analogue used. The problems of the inability of most neurotransmitters to cross the blood-brain barrier must be overcome. The blood-brain barrier has to be artificially disrupted to allow intravascular serotonin to reach the smooth muscle cells of the cerebral arterioles. The effects on cerebral metabolic activity and net alterations in cerebral blood flow are based on investigations where problems of blood-brain barrier permeability have been circumvented.
