FREQUENCY-ANALYSIS OF CATECHOLAMINE AXONAL MORPHOLOGY IN HUMAN BRAIN .1. EFFECTS OF POSTMORTEM DELAY INTERVAL

The diverse morphologies of catecholamine axons in the human brain wer e examined by using tyrosine hydroxylase immunocytochemistry. Human br ain tissue was obtained by either rapid autopsy (mean postmortem delay < 1 h) or routine autopsy (mean postmortem delay 5 h). Tissue blocks from the superior frontal cortex (Brodmann area 9), the hippocampal gy rus and the calcarine cortex (Brodmann area 17) were processed for tyr osine hydroxylase immunoreactivity. First, a quantitative method was d eveloped to reliably identify differing morphologies of catecholamine axons in human brain tissue. A total of 625 tyrosine hydroxylase immun oreactive axons were randomly sampled from coded sections and classifi ed into one of six distinct morphological categories. These categories were based upon axonal morphologies which were readily distinguished by trained observers, and moreover, further investigations demonstrate d that entire tissue sections could be reliably re-sampled at interval s of up to six months. Second, regional variations in axonal distribut ion and the effects of increasing postmortem delay in tissue processin g on the categories of tyrosine hydroxylase immunoreactive axon morpho logies were examined. Postmortem delays of up to 6.5 hours were found to decrease the frequency of fine axons with varicosities (axon type 2 ) and increase thick-caliber straight axons (axon type 5) in all regio ns examined. The frequency of other morphological axon types did not c hange as a function of postmortem delay. In summary, the use of quanti tative neuroanatomical measures of the catecholaminergic system in hum an brain tissue was found to be reliable and valid. It was furthermore demonstrated that postmortem delays affect selected morphological typ es of catecholamine axons. These results indicate that interpretation of immunostained human material must include careful consideration of the effects of postmortem delay on immunoreactive axonal morphology.