Neurons in the third abdominal ganglion of the early postnatal crayfish: a quantitative and ultrastructural study

Ultrastructural data on the third abdominal ganglion of the crayfish was heretofore only available for adult individuals. The fine structure of neurons in the adult that are involved in the escape response has been described in detail, but no similar data existed for the postnatal individual. An increase in the number of neurons in the third abdominal ganglion during postnatal stages had been reported, which suggested that several changes in the features of neurons may occur. Here we describe the general anatomy and ultrastructure of the early postnatal third abdominal ganglion, with emphasis on neurons, and we compare their characteristics to those of the adult. Abdominal ganglia of 56 crayfish of 0, 8, 10, 18, 25, 50, 110, and 150 postnatal days were processed under cacodylate buffered aldehyde fixatives, osmicated, embedded in plastic, sectioned, and examined by light and electron microscopy. The anatomy of postnatal ganglia is homologous to the anatomy of the adult ganglia except that the perineurium is not developed in postnatals. The area of neurons within the postnatal ganglion shows no stratification, but neurons are grouped in nuclei according to their size. Neurons constitute a homogeneous population in different stages of maturity, as revealed particularly by the ultrastructure of the nucleolus. Postnatal development is evident in the perineurium, which may provide structural support to the ganglion.