Noradrenergic axon terminals in the cerebral cortex of rat. III. Topometric ultrastructural analysis.

A new fixation method has been developed for localizing biogenic amines in nervous tissue. The method is a modification of the chromaffin reaction in which all fixation steps are buffered with mixtures of sodium chromate and potassium dichromate. In this way the fixation and cytochemical reaction are carried out almost simultaneously. Using the rat vas deferens as a model tissue, it was found that the preservation of electron dense (chromaffin) cores in the vesicles of adrenergic nerve terminals depended on several factors: a short primary fixation using low concentrations of aldehydes, the presence of the chromate/ dichromate buffer during all fixation steps and, finally, a long incubation period in a slightly acidic (pH 6.0) solution of this buffer before postflxation in osmium tetroxide. Using this method it was possible to identify not only small and large dense-cored vesicles as storage sites for amines but also a tubular reticulum (neuronal endoplasmic reticulum), the latter especially in nerve terminals of mesenteric arteries and iris. Biogenic amines were also visualized in sympathetic ganglion cells and in the central nervous system e.g., supraependymal nerve terminals, tissues that up to now proved the most difficult in terms of amine localization. In all the tissues examined the cytochemical reaction was highly selective and present in well preserved tissue, which is a significant advance over previously available techniques. It therefore offers new opportunities for further studies on the role of biogenic amines as neurotransmitters.

Ultrastructural cytochemistry of biogenic amines in nervous tissue: methodologic improvements.

The origin and fate of secretory packages, especially synaptic vesicles.

Serotonin nerve terminals in the locus coeruleus of adult rat: a radioautographic study.

Publisher Summary This chapter discusses the neuronal secretory systems to critically examine the processes in the magnocellular neurons, and considers to what extent they are variations of Palade's model, and whether they display any unique characteristics, particularly in comparison with other types of neurons. Vasopressin (VP) and oxytocin (OT) are designated as neurohypophysial hormones, for the hypothalamic neurohypophysial system (HNS), which was the first neuronal secretory system in which they are identified in profusion. The specific enzymes could vary the cleavage products of propressophysin and prooxyphysin in different central nervous system (CNS) sites. In addition, modifying influences are probably exerted by the different co-peptides and co-transmitters within VP and OT neurons. The rich efferent input from other neuronal systems, the feedback relays, and the selective coordination between neurosecretory cells contribute to the extended repertoire of the so-called neurohypophysial peptides. The diversity and versatility of the peptidergic neurosecretory cells that produce VP and OT reveal affinities with other neurons in the CNS.

Neuronal secretory systems

Localization of amine storage sites in the adrenergic cell body. A study of the superior cervical ganglion of the rat by fine structural cytochemistry.

J.P. Tranzer

Papers

Localization of amine storage sites in the adrenergic cell body. A study of the superior cervical ganglion of the rat by fine structural cytochemistry.

The nature of rat "specific heart granules" with regard to catecholamines: an investigation by ultrastructural cytochemistry.