. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 76 G. B. BRUMWELL AND V. J. MARTIN. Figure 5. Single-plane confocal images of controls. Scale bars are in /Mm. (a, b) Tentacles processed with the RFamide antibody revealed a nerve net (a), whereas tentacles processed without the RFamide antibody did not (b). (c, d) Tentacles stained with the JD1 antibody revealed a nerve net (o, whereas tentacles processed using the same protocol minus the JD1 anti- body did not (d). 2500 (Bode el ai, 1973). The authors report 5600 neurons in the adult. Similarly, regenerating heads show no
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 76 G. B. BRUMWELL AND V. J. MARTIN. Figure 5. Single-plane confocal images of controls. Scale bars are in /Mm. (a, b) Tentacles processed with the RFamide antibody revealed a nerve net (a), whereas tentacles processed without the RFamide antibody did not (b). (c, d) Tentacles stained with the JD1 antibody revealed a nerve net (o, whereas tentacles processed using the same protocol minus the JD1 anti- body did not (d). 2500 (Bode el ai, 1973). The authors report 5600 neurons in the adult. Similarly, regenerating heads show no de- creases in neuron number. A decapitated hydra generates its new head from the tissue below the old head (Bode et ai, 1988a). Initially about 250 neurons populate the subhead region, and this number increases to 300, 500. and 700 as this tissue becomes head: the adult head contains about 800 neurons (Bode ft al., 1973). Thus, in embryological devel- opment, budding, and head regeneration, the hydra neuron populations studied show no culling. This indicates that continuous increase in neuron numbers through adult levels may be a common mechanism of neurodevelopment in hydra. The hypothesis that large-scale neuronal PCD might not be part of adult hydra development is also supported by studies of tissue dynamics. First, loss of tissue to buds and to sloughing at the extremities balances the constant neuron production occurring in the adult hydra (David and Gierer, 1974; Bode etui, 1988a; Sakaguchi etui. 1996). If massive neuronal culling were occurring in the constantly develop- ing adult, then neuron loss through budding and sloughing would not balance neuron production. However, calcula- tions suggest that these two activities do balance neuron production (David and Gierer. 1974; Bode et ai. 1988a). This leaves little room for large-scale PCD of neurons between neurogenesis and sloughing. Second, if many neu- rons died between genesis and sloughing in adults, then neurons wo
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