γ‐Aminobutyric acid (GABA) signaling components in Drosophila: Immunocytochemical localization of GABA_B receptors in relation to the GABA_A receptor subunit RDL and a vesicular GABA transporter

Abstract

gamma-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in insects and is widely distributed in the central nervous system (CNS). GABA acts on ion channel receptors (GABA(A)R) for fast inhibitory transmission and on G-protein-coupled ones (GABA(B)R) for slow and modulatory action. We used immunocytochemistry to map GABA(B)R sites in the Drosophila CNS and compared the distribution with that of the GABA(A)R subunit RDL. To identify GABAergic synapses, we raised an antiserum to the vesicular GABA transporter (vGAT). For general GABA distribution, we utilized an antiserum to glutamic acid decarboxylase (GAD1) and a gad1-GAL4 to drive green fluorescent protein. GABA(B)R-immunoreactive (IR) punctates were seen in specific patterns in all major neuropils of the brain. Most abundant labeling was seen in the mushroom body calyces, ellipsoid body, optic lobe neuropils, and antennal lobes. The RDL distribution is very similar to that of GABA(B)R-IR punctates. However, the mushroom body lobes displayed RDL-IR but not GABA(B)R-IR material, and there were subtle differences in other areas. The vGAT antiserum labeled punctates in the same areas as the GABA(B)R and appeared to display presynaptic sites of GABAergic neurons. Various GAL4 drivers were used to analyze the relation between GABA(B)R distribution and identified neurons in adults and larvae. Our findings suggest that slow GABA transmission is very widespread in the Drosophila CNS and that fast RDL-mediated transmission generally occurs at the same sites.

GABAB receptors play an essential role in maintaining sleep during the second half of the night in Drosophila melanogaster

“…Previous studies have shown that there are large numbers of GABA-producing neurons in the adult brain of Drosophila (Enell et al, 2007;Okada et al, 2009). The processes of some of these arborise in the region of the accessory medulla that contains presumed dendrites of the PDF neurons (Hamasaka et al, 2005).…”

“…In western blots of brain tissue from Drosophila the antiserum detected a band of appropriate size (Hamasaka et al, 2005), and in GABA B -R2 immunohistochemistry on Drosophila brains the antiserum labelled neurons that were in close proximity to neural elements immunopositive for a vesicular GABA transporter, GAD and a GABA A receptor (RDL), strongly indicating that the GABA B -R2 antiserum is reliably detecting a GABA B receptor (Enell et al, 2007). The anti-GABA B -R2 specificity was further established by diminished GABA B -R2 immunolabelling after GABA B -R2 RNAi in specific neurons (OSNs) in the antenna/antennal lobe (Root et al, 2008).…”

“…Because the latter is significantly reduced after silencing the GABAergic neurons , other GABA receptors must be responsible for maintaining sleep. Suitable candidates are slow metabotropic GABA B receptors that are often co-localised with ionotropic GABA A receptors (Enell et al, 2007). In Drosophila, like in mammals, the metabotropic GABA B receptors are G-protein-coupled seven-transmembrane proteins composed of two subunits, GABA B -R1 and GABA B -R2 (Kaupmann et al, 1998;Mezler et al, 2001).…”

Responses ofDrosophilagiant descending neurons to visual and mechanical stimuli

“…In larger fly species (Strausfeld and Bassemir, 1983;Heisenberg and Wolf, 1984), electron microscopical observations confirm that these Col A-GDN synapses are monosynaptic, comprising mixed chemical and electrical junctions. If the chemical synapses between Col A neurons and the GDN are excitatory (Enell et al, 2007;Strausfeld et al, 2007), inhibitory response seen in the GDN to some light-on stimuli are likely to derive from a separate neural pathway. Pathways carrying information about light-on and light-off may indeed be interdependent because the intensity of response to light-off is related to the prior duration of light-on.…”

A GABAergic Inhibitory Neural Circuit Regulates Visual Reversal Learning inDrosophila

“…In Drosophila MBs, the GABA A receptor subunit RDL is expressed throughout the substructures except the cell body area (Liu et al, 2007), whereas the GABA B receptor R2 (GABA B -R2) subunit is expressed only in calyx (Enell et al, 2007). Of the various MB Gal4 lines, we focused our attention principally on the 17d-Gal4 (Fig.…”