Three-dimensional mapping of norepinephrine and serotonin in human thalamus

Detailed quantitative information on catecholamines and 5-hydroxytryptamine (serotonin) in the human thalamus is much needed because of increasing interest in norepinephrine and serotonin as modulators of thalamic behavioral state control and overall information processing. This study provides three-dimensional distribution patterns of these monoamines in postmortem thalami from 13 normal subjects (no known neurological or psychiatric histories). The patterns come from a relatively fine-grained grid mapping procedure on successive coronal sections. Samples were analyzed by high performance liquid chromatography with electrochemical detection. The highest endogenous concentrations of norepinephrine are found in a ventromedial core that includes a number of the medial and intralaminar sub-nuclei but extends only slightly into the sensory regions of the lateral ties. The posterior portion of the thalamus, the pulvinar, contains low levels of norepinephrine. The distribution of 5-hydroxytryptamine is quite similar to that of norepinephrine in the rostral two-thirds of thalamus: however, in the pulvinar region, levels of serotonin are considerably increased and differ markedly between individual thalami. The study provides the first definitive mapping of serotonin levels in human thalamus. Consistent with many animal studies, there is no evidence for major dopaminergic innervation of human thalamus. By emphasizing the pattern distribution of the monoamines rather than the absolute values, it can be shown that the ambiguities of postmortem degradation frequently associated with biochemical assays are largely avoided. The terminal field distribution of norepinephrine is an essentially constant neurochemical signature in all thalami examined. The utility of the biochemical grid mapping procedure may be especially significant in terms of matching with data from functional neuroimaging techniques.