Quantitative immunocytochemical evaluation of serotonergic innervation in alcoholic rat brain

Neurotoxicity can be divided into three levels: depletion, degeneration and denervation. The first level is determined by the transmitter content, and the second and third levels, which require anatomical evaluation, can be analyzed by quantitative immunocytochemistry on a specific neurotransmitter system. An antibody specific to serotonin (5-HT) can reveal detailed normal as well as degenerative morphology of 5-HT neurons. Quantitative alterations of 5-HT fibers in a particular brain region indicate degenerative or plastic changes. This study demonstrates quantitative immunocytochemistry by using image analysis of immunostained 5-HT fibers in selectively-bred, alcohol-preferring and nonpreferring rats, which are known to have divergent drinking behaviors, and 5-HT contents in specific brain regions. The method of the image analysis is described in detail and the advantages and disadvantages of using this method to detect the degeneration of a particular fiber system are discussed. The 'area density' traditionally measured in image analysis was converted (with Zhou-Tam formula) into 'volume density' to correct the mismeasurement of fibers through the optical depth. Quantitative immunostaining shows that the difference in 5-HT fiber density in particular brain regions between the two rat lines is consistent with changes in content of the 5-HT/5-HIAA and hypersensitivity of 5-HT1 a receptor. This result indicates either (a) the 5-HT content is too low to be detected in the nerve terminals; (b) degeneration of 5-HT fibers occurs in P rats sometime during development; or (c) a smaller number of 5-HT fibers was preprogrammed in the brain regions of P than NP rats.(ABSTRACT TRUNCATED AT 250 WORDS)