5‐HYDROXYTRYPTAMINE (SEROTONIN, ENTERAMINE) CONTENT OF STRUCTURES OF THE LIMBIC SYSTEM *

IN PREVIOUS articles, evidence has been cited from bioelectric and behavioural studies that allows one to infer a dichotomy in the function of the phylogenetic+ly old and new cortex (MACLEAN, 1954; MACLEAN et al., 195S-56). This dichotomy has important implications because it bears upon the distinctive attributes of emotional and intellectual behaviour. The ‘old’ cortex comprises the so-called archicortex and mesocortex. The archicortex and the greater part of the mesocortex are contained in the great limbic lobe which is found in the brains of all mammals. The “old” cortex and its associated nuclear structures constitute a functionally integrated system which may be appropriately referred to as the limbic system (MACLEAN, 1952). In a study of the effect of neuropharmacological agents on the bioelectrical activity of the brain it was found that, following the administration of reserpine, distinctive changes could be localized in the hippocampus (MACLEAN et al., 1955-56), a structure which contains the greater part of the archicortex and which has important connections with the hypothalamus. Corresponding, but less pronounced, changes could also be localized in the region of the posterior hypothalamus. Subsequently, with the publication of the findings of PLETSCHER, SHORE, and BRODIE (1956), it became apparent that the evolution of the electroencephalographic changes (MACLEAN et al., 1955-56) followed a time course strikingly similar to that of the depletion and restoration of 5-hydroxytryptamine (5-HT) in the brain which they found after administering large doses of reserpine to rabbits. Heretofore it has been claimed that the amount of 5-HT in the cerebral cortex is negligible compared with that in the hypothalamus (AMIN, CRAWFORD, and GADDUM, 1954; PAASONEN and VOGT, 1956). In view of the foregoing observations and the suggestion that 5-HT might be of neurophysiological importance (GADDUM, 1954; WOOLLEY and SHAW, 1954; BRODIE and SHORE, 1957), a study was made of the 5-HT content of the hippocampus and other cortical and subcortical structures of the limbic system. This communication reports the findings.