The use of general systemic manipulations to alter brain activity, often coupled with ex vivo biochemical analysis, has led to significant advances in our understanding of central nervous system (CNS) activity Nevertheless, the search for a clear understanding of the function of separate brain regions has necessitated the use of Intracranial preparations The advantages of this approach are twofold It allows stimulation of localized areas of brain tissue, which is important in the analysis of functions of separate nucler and neural pathways, furthermore the intracranial approach enables us to apply compounds to the CNS that do not readily cross the blood-brain barrier (see Oldendorf, 1971). It is notable that the majority of substances believed to be neurotransmitters fall into this category of compounds