Chromaffin, small granule-containing and ganglion cells in the adrenal gland of reptiles

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Abstract
Chromaffin, small granule-containing (SGC)-cells, neurons and the innervation of these cells was studied in the adrenal gland of three species of reptiles (Testudo graeca, Lacerta dugesi, Natrix natrix). After fixation with glutaraldehyde and osmium-tetroxide adrenaline (A)- and noradrenaline (NA)-storing cells can be distinguished by means of the different electron density of their granules: A-granules are moderately electron-dense, while NA-granules show a core of high electron density. The unusually high electron density of a few A-granules in Testudo occasionally required viewing of unstained sections which facilitated the discrimination of the two cell types in this species. In all species studied NA-granules display a remarkable polymorphism which is most pronounced in the tortoise. In this species A-granules are polymorphic, too. Both types of granules show wide variations in size, which are particularly great in the tortoise. This species also exhibits the largest average sizes for A-granules (285 nm), and NA-granules (354 nm). The corresponding parameters for Lacerta and Natrix, are 255 and 179 nm for A- and 323 and 304 nm for NA-granules, respectively. The rough ER in A- cells of the tortoise regularly occurs in the form of circular dilations (‘ergastosomes’, Kanerva and Hervonen, 1973). Mitochondria sometimes contain longitudinal cristae with a crystalloid internal pattern. Large dense bodies which incorporate granules are abundant in NA-cells. Smaller dense bodies containing a few dense patches and membranes are present in both A- and NA-cells. Intermediate stages between dense bodies and what appear to be A- or NA-granules (if the latter have lost some of their amine-content) are frequently observed. Small granule containing (SGC)-cells are regularly found in the adrenal of reptiles. Their granules have an average size of 146 nm in Testudo (188 and 107 nm in Lacerta and Natrix, respectively). The cells exhibit a high nucleo-cytoplasmic ratio and an electron-lucent cytoplasm. Various types of nerve cell are present in the reptilian adrenal. Small “light” neurons are similar to SGC-cells, but have only few granules, if any. Large “principal” neurons resemble ganglion cells in various autonomic ganglia. According to the morphology of their nuclei and the amounts and distribution of their ER, they may be divided into “light” and “dark” principal neurons. Chromaffin, SGC- and nerve cells are innervated by cholinergic nerve terminals containing small, clear (500–600 Å in diameter) and large, densecored vesicles measuring 730–1340 Å (Testudo). Synapses are usually found on the cell bodies. A-cells in the tortoise which form long processes have their synapses mostly along these processes. A-cell processes are occasionally found in the media of arterioles. Pre- and postsynaptic membrane specialisations are extremely rare on SGC-cells. Adrenergic nerve profiles, which are processes of neither chromaffin nor SGC-cells, may be identified after application of 5- and 6-hydroxydopamine in close proximity of chromaffin cells. This paper was presented in part at a Symposium on “Chromaffin, Enterochromaffin and Related Cells” held at Gifu, Japan, 22–24 August, 1975.