Ultrastructural organization of giant neurones of the mollusc Lymnaea stagnalis under different environmental temperatures.

The ultrastructure of identified giant neurones of the visceral ring of Lymnaea stagnalis ganglion alters with the seasonal change of the animal and, experimentally, from the inactive physiological state (winter time or at +4 degrees C) to an active one (spring-summer time or at +18 degrees C). The ultrastructural organization of the active animal's neurones is characterized by morphological alteration pointing to an increased metabolic activity, viz., an increased number of nucleoli, an enlarged surface of nuclear membrane and an increase in the nuclear membrane pores, appearance of a zone of free ribosomes near the nuclear membrane, changing the structure of cytosomes, abundant granular endoplasmic reticulum, increase in the number of mitochondria.