STEREOLOGICAL ESTIMATION OF GAP JUNCTION SURFACE-AREA PER NEURON IN THE DEVELOPING NERVOUS-SYSTEM OF THE INVERTEBRATE MESOCESTOIDES-CORTI

As a major morphological feature in establishing the form of the nervo us system, it is recognized that neurons are initially overproduced, t hen naturally occurring cell death reduces the neuron number to the fu nctional requirement. However, the mechanisms controlling the selectiv e elimination of certain neurons during a general phase of cell death are not fully understood. One event that seems to be pivotal is the es tablishment of neural connections, the degree of which may be influent ial regarding the fate of specific neurons. However, little quantitati ve evidence is available to either support or refute this theory. In t his current study, a stereological measurement of gap junction per neu ron was carried out within the invertebrate model system of the tapewo rm metacestode Mesocestoides corti, which has previously been shown to overproduce neurons during the asexual reproduction stage of its life -cycle. Novel stereological estimation methods with 'vertical sections ' indicated that prior to asexual division the cerebral ganglion posse ssed approximately 268 neurons, each with a gap junction surface area of 250 mu m(2). As division progressed, the neuron number increased to approximately 700, while the total surface area of gap junction remai ned statistically unchanged. As a result the surface area of gap junct ion per neuron decreased to 106 mu m(2), less than half that in the un dividing stage. These results provide the first non-biased quantitativ e data regarding changes in the mean surface area of gap junction per neuron in a developing cerebral ganglion.