Volume transmission in the CNS and its relevance for neuropsychopharmacology

The terms 'wiring' and 'volume' transmission (WT and VT) have been introduc ed to provide a systematic categorization of intercellular communication in the brain. WT is one-to-one transmission and includes classical synapses, gap junctions and membrane juxtapositions, whereas VT is a one-to-many tran smission and includes paracrine and endocrine-like transmissions in the bra in extracellular space and cerebrospinal fluids. Any brain cell can partici pate in WT and VT and any kind of substance (e.g. ions, classical transmitt ers, peptides, neurosteroids) can be a signal in WT and VT. These concepts are relevant for the pharmacokinetics and actions of neuropsychoactive drug s. These drugs can be regarded as exogenous VT signals in that they diffuse in the cerebral extracellular space and are constrained there by the same factors that influence migration of endogenous VT signals. In addition, neu ropsychoactive drugs can better mimic and more effectively interact with th e relatively unconstrained VT-type transmissions than with the rigidly cons trained WT mechanisms, such as synaptic transmission.