Differential expression of synapsin in visual neurons of the locust Schistocerca gregaria

Abstract

In many taxa, photoreceptors and their second-order neurons operate with graded changes in membrane potential and can release neurotransmitter tonically. A common feature of such neurons in vertebrates is that they have not been found to contain synapsins, a family of proteins that indicate the presence of a reserve pool of synaptic vesicles at synaptic sites. Here, we provide a detailed analysis of synapsin-like immunoreactivity in the compound eye and ocellar photoreceptor cells of the locust Schistocerca gregaria and in some of the second-order neurons. By combining confocal laser scanning microscopy with electron microscopy, we found that photoreceptor cells of both the compound eye and the ocellus lacked synapsin-like immunostaining. In contrast, lamina monopolar cells and large ocellar L interneurons of the lateral ocellus were immunopositive to synapsin. We also identified the output synapses of the photoreceptors and of the L interneurons, and, whereas the photoreceptor synapses lacked immunolabeling, the outputs of the L interneurons were clearly labeled for synapsin. These findings suggest that the photoreceptors and the large second-order neurons of the locust differ in the chemical architecture of their synapses, and we propose that differences in the time course of neurotransmission are the reason for this.

Sprouting interneurons in mushroom bodies of adult cricket brains

“…By light microscopy, immunostaining of the cricket MBs gave results identical to those of our previous study (Frambach et al, 2004). Selective marking of synaptic vesicle-containing fiber profiles by immunoelectron microscopy has previously been demonstrated in MBs of the cricket (Frambach et al, 2004) and for grasshoppers (Leitinger et al, 2004), whereas fibers devoid of vesicles were not stained.…”

“…The antibody specificity was confirmed in Drosophila nervous tissue by the absence of immunolabelling in mutants lacking synapsin (Godenschwege et al, 2004). The antibody directed against Drosophila synapsin, marking brain compartments in Drosophila (Godenschwege et al, 2004), has been used for selectively labelling neuropil with synaptic vesicle pools in several arthropods (crustaceans: Harzsch et al, 1997;spiders: Fabian-Fine et al, 1999;insects: Frambach et al, 2004;Leitinger et al, 2004), including also corresponding MB compartments in bees and crickets (Frambach et al, 2004;Okada et al, 2007). Synapsin-like labelling was visualized using goat-anti-mouse IgG coupled to Cy3 (dilution 1:100; Jackson, Dianova; Hamburg, Germany).…”

Neuroarchitecture of the central complex of the desert locust: Intrinsic and columnar neurons

“…The specificity of the antibody has been characterized by Klagges et al (1996). It labels synaptic neuropil as demonstrated in Drosophila (Klagges et al, 1996), honeybees (Brandt et al, 2005), and locusts (Leitinger et al, 2004;Kurylas et al, 2008). The anti-serotonin antiserum (Diasorin, Dietzenbach, Germany) was raised in rabbit against paraformaldehyde-coupled conjugates of bovine serum albumin and 5-hydroxytryptamine.…”

Confocal microscopy in large insect brains: Zinc–formaldehyde fixation improves synapsin immunostaining and preservation of morphology in whole-mounts

“…It has been employed to construct threedimensional models of the Drosophila optic lobes (Rein et al, 1999), the antennal lobes of moths (Berg et al, 2002), and for standard brain atlases for Drosophila (Rein et al, 2002) and honeybee (Brandt et al, 2005). Synapsin antibodies show poor penetration, however, and analysis of large brains has therefore been carried out on cryostat or vibratome sections (e.g., Leitinger et al, 2004;Sullivan and Beltz, 2004).…”

“…Synapsins are phosphoproteins that associate selectively with the cytoplasmic surface of small synaptic vesicles (Klagges et al, 1996;Leitinger et al, 2004;Fdez and Hilfiker, 2006;Evergren et al, 2007) and are therefore expressed abundantly in regions of high synaptic density. Immunostaining against synapsin is used widely in the functional, comparative and evolutionary neuroanatomy of arthropods (e.g., Watson and Schürmann, 2002;Sullivan and Beltz, 2004;Kleineidam et al, 2005).…”