Golgi, Cajal, and the fine structure of the nervous system

Abstract

Towards the middle of the 20th century, neuroanatomy was on the decline. It was revived by the development of two new methods. One was the Nauta-Gygax method, which selectively stained nerve fibers that had been caused to degenerate by experimental lesions. This allowed connections between various parts of the nervous system to be better determined. The second was electron microscopy, which allowed the structure of neurons and the synapses between them to be examined in detail, and eventually this led to a revival of the Golgi impregnation methods. This occurred in the 1970s because of the desire of electron microscopists to determine the origins of the neuronal profiles they encountered in electron micrographs of various parts of the central nervous system. Eventually this led to the development of Golgi/EM techniques, whereby individual impregnated neurons could first be characterized by light microscopy and then thin sectioned for detailed analyses. Examining the axon terminals of such impregnated neurons, especially those in the cerebral cortex, for the first time revealed details of intercellular connections and allowed neuronal circuits to be postulated. However, Golgi/EM had only a brief, but fruitful existence. It was soon superceded by intracellular filling techniques, which allowed the added dimension that the physiological properties of identified neurons could also be determined.

Fig. 1

A transversely sectioned, gold toned, Golgi impregnated apical dendrite (Ap) of a layer 5 pyramidal cell. The small gold particles mark both the main shaft of the apical dendrite as well as the spines (sp) emanating from it. Scale bar = 1μm.

Fig.2

A gold toned axon terminal (At) from a smooth stellate cell in rat visual cortex forming a symmetric synapse (arrow) with the perikaryon of a pyramidal cell (pyr). Scale bar = 1μm.

Fig. 3

A gold toned, Golgi impregnated plexus of a chandelier cell in layer 3 of rat visual cortex. The plexus consists of vertical strings of axonal bouton (arrows) that extend along the initial axon segments of pyramidal cells. Scale bar = 50μm.

Fig.4

Light microscopic image of the axon terminal (At) from the axon plexus of a chandelier cell forming a symmetric synapse (arrow) with the initial axon segment (ais) of a layer 3 pyramidal cell. Scale bar = 1μm.

Fig. 5

The spine (sp) of a Golgi impregnated and gold toned apical dendrite (Ap) in rat visual cortex forming an asymmetric synapse with a degenerating geniculo-cortical axon terminal (d). Scale bar = 1μm.