Immunocytochemical Techniques for the Identification of Peptidergic Neurons

Abstract

Immunocytochemistry overcomes disadvantages of unspecificity common to most classical histochemical techniques used for the identification of neuronal pathways. However, it cannot simply replace these techniques. The problem is to produce highly specific antisera against various substances of the nervous tissue. Thus, progress in neuroimmunochemistry mainly depends upon the chemical isolation of many different types of neuronal antigens. Especially in vertebrates (mostly over the past 10 years), it has been shown that immunocytochemistry is a powerful tool in the study of the nervous system (Livett 1978; Setalo and Flerko 1978; Hökfelt et al. 1980 b). Immunohistochemical investigations have led to the discovery of previously unknown neurotransmitter pathways, the distribution of neuropeptides in the central and peripheral nervous system, and the coexistence of classical neurotransmitters and neuropeptides within one neuron. Knowledge of the distribution of neuropeptides in the nervous system of vertebrates has been greatly increased. In evolutionary terms, vertebrate neuropeptides are obviously very ancient functional molecules, since they act as “neuroregulators” throughout the whole animal kingdom. Compounds with a high resemblance to vertebrate neuropeptides have also been identified immunohistochemically in the lowest invertebrates, for example in Hydra (Taban and Cathieni 1979; Grimmelikhuijzen et al. 1981 a, b).