Fewer glutamate receptors are immunocytochemically detectable in sec8 mutants. A: Confocal images showing NMJs on ventral longitudinal muscles 15, 6/7, 13 and 12 in first instar larvae (24–28 h AEL). NMJs were visualized using the neuronal membrane marker anti-HRP (magenta). Postsynaptic glutamate receptors were visualized using antibodies raised against the glutamate receptor subunit GluRIIA (green). Scale bar: 10 μm. Quantification of GluRIIA cluster sizes is shown in B. B: Top: Average GluRIIA cluster size was significantly reduced in sec8 mutant first instar larvae. Middle: Frequency histogram of GluRIIA cluster sizes. Bottom: Average GluRIIA cluster size was significantly reduced in sec8P1 mutant third instar larvae, and this phenotype is rescued by a precise excision of the P-element ('sec8rev5'). Similar results were obtained using antibodies against GluRIIB and GluRIIC (see text). C: Confocal images showing ventral longitudinal NMJs in first instar larvae, as in A, stained using antibodies against cysteine string protein (CSP; top panels), discs-large (DLG; middle panels), and synaptotagmin (SYT; bottom panels). Scale bar: 10 μm. D: Quantification of staining in C. sec8 mutants showed no significant difference in cysteine string protein (CSP, top), discs-large (DLG, middle) or synaptotagmin (SYT, bottom) immunofluorescence compared with controls.