ABSTRACT
Synaptic transmission, based on precise neurone-to-neurone signalling, is proposed to be the basic tenet of the neurone doctrine. Over the last decade, however, another mode for interneuronal communication in the central nervous system (CNS) has been advanced and has gained experimental support (Otellin and Arushanian, 1989; Sakharov, 1990; Agnati et al., 1995; Bach-y-Rita, 1993; Grace, 1991; Zigmond et al., 1990). This new concept is based on diffusion of neurotransmitters and other biologically active compounds through the brain extracellular fluid to distant receptors. Agnati et al. suggested the term “volume transmission” to define this complementary means of intercellular communication (Agnati et al., 1995). By volume transmission, neurotransmitters may spread for distances beyond the point of release through the extracellular space and exert their activity at multiple receptor sites within a brain area; this may permit the area to operate as a unified whole.
