Carbon dioxide and fruit odor transduction in Drosophila olfactory neurons. What controls their dynamic properties?

We measured frequency response functions between odorants and action potentials in two types of neurons in Drosophila antennal basiconic sensilla. CO2 was used to stimulate ab1C neurons, and the fruit odor ethyl butyrate was used to stimulate ab3A neurons. We also measured frequency response functions for light-induced action potential responses from transgenic flies expressing H134R-channelrhodopsin-2 (ChR2) in the ab1C and ab3A neurons. Frequency response functions for all stimulation methods were well-fitted by a band-pass filter function with two time constants that determined the lower and upper frequency limits of the response. Low frequency time constants were the same in each type of neuron, independent of stimulus method, but varied between neuron types. High frequency time constants were significantly slower with ethyl butyrate stimulation than light or CO2 stimulation. In spite of these quantitative differences, there were strong similarities in the form and frequency ranges of all responses. Since light-activated ChR2 depolarizes neurons directly, rather than through a chemoreceptor mechanism, these data suggest that low frequency dynamic properties of Drosophila olfactory sensilla are dominated by neuron-specific ionic processes during action potential production. In contrast, high frequency dynamics are limited by processes associated with earlier steps in odor transduction, and CO2 is detected more rapidly than fruit odor

Multiple Biogenic Amine Receptor Types Modulate Spider, Cupiennius salei, Mechanosensory Neurons

The biogenic amines octopamine (OA), tyramine (TA), dopamine (DA), serotonin (5-HT), and histamine (HA) affect diverse physiological and behavioral processes in invertebrates, but recent findings indicate that an additional adrenergic system exists in at least some invertebrates. Transcriptome analysis has made it possible to identify biogenic amine receptor genes in a wide variety of species whose genomes have not yet been sequenced. This approach provides new sequences for research into the evolutionary history of biogenic amine receptors and allows them to be studied in experimentally accessible animal models. The Central American Wandering spider, Cupiennius salei, is an experimental model for neurophysiological, developmental and behavioral research. We identified ten different biogenic amine receptors in C. salei transcriptomes. Phylogenetic analysis indicated that, in addition to the typical receptors for OA, TA, DA, and 5-HT in protostome invertebrates, spiders also have α1- and α2-adrenergic receptors, but lack TAR2 receptors and one invertebrate specific DA receptor type. In situ hybridization revealed four types of biogenic amine receptors expressed in C. salei mechanosensory neurons. We used intracellular electrophysiological experiments and pharmacological tools to determine how each receptor type contributes to modulation of these neurons. We show that arachnids have similar groups of biogenic amine receptors to other protostome invertebrates, but they lack two clades. We also clarify that arachnids and many other invertebrates have both α1- and α2-adrenergic, likely OA receptors. Our results indicate that in addition to an OAβ-receptor that regulates rapid and large changes in sensitivity via a Gs-protein activating a cAMP mediated pathway, the C. salei mechanosensory neurons have a constitutively active TAR1 and/or α2-adrenergic receptor type that adjusts the baseline sensitivity to a level appropriate for the behavioral state of the animal by a Gq-protein that mobilizes Ca2+

Carbon dioxide and fruit odor transduction in Drosophila olfactory neurons. What controls their dynamic properties?

We measured frequency response functions between odorants and action potentials in two types of neurons in Drosophila antennal basiconic sensilla. CO2 was used to stimulate ab1C neurons, and the fruit odor ethyl butyrate was used to stimulate ab3A neurons. We also measured frequency response functions for light-induced action potential responses from transgenic flies expressing H134R-channelrhodopsin-2 (ChR2) in the ab1C and ab3A neurons. Frequency response functions for all stimulation methods were well-fitted by a band-pass filter function with two time constants that determined the lower and upper frequency limits of the response. Low frequency time constants were the same in each type of neuron, independent of stimulus method, but varied between neuron types. High frequency time constants were significantly slower with ethyl butyrate stimulation than light or CO2 stimulation. In spite of these quantitative differences, there were strong similarities in the form and frequency ranges of all responses. Since light-activated ChR2 depolarizes neurons directly, rather than through a chemoreceptor mechanism, these data suggest that low frequency dynamic properties of Drosophila olfactory sensilla are dominated by neuron-specific ionic processes during action potential production. In contrast, high frequency dynamics are limited by processes associated with earlier steps in odor transduction, and CO2 is detected more rapidly than fruit odor

Molecular phylogenetic analysis of putative nACh channel subunits.

<p>Evolutionary history inferred by the Maximum Likelihood method. The unrooted radiation tree is drawn to scale, with branch lengths measured in numbers of substitutions per site. The analysis involved 36 amino acid sequences and was run with 1000 bootstraps. Numbers indicate bootstrap values. There were a total of 903 positions in the final dataset. Evolutionary analyses were conducted in MEGA6 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138068#pone.0138068.ref035" target="_blank">35</a>]. Accession numbers for <i>C</i>. <i>salei</i> sequences are in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138068#pone.0138068.t001" target="_blank">Table 1</a> and for other sequences in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138068#pone.0138068.s004" target="_blank">S1 Table</a>.</p

Structural model of the <i>C</i>. <i>salei</i> GABA_Aβ subunit and its evaluation by Ramachandran plot analysis.

<p>(A) Homology model of CsGABA_Aβ created by I-TASSER server is shown in blue as cartoon representation aligned with the human HsGABA_Aβ3 crystal structure in green ribbon representation. The structures are shown as viewed from the outside of the pentameric ring. The agonist binding Loops A-B in the principal face and D-F in the complementary face and the transmembrane helices TM1-M4 are indicated. Image was created with PYMOL software. (B) Ramachandran plot analysis of CsGABA_Aβ protein structure calculated by the Rampage server.</p

<i>Cupiennius salei</i> Cys loop subunits.

<p>GluCl = glutamate-gated chloride channel; GABA = γ-amino butyric acid; rdl = resistance to dieldrin; pHCl = pH gated chloride channel; grd = GABA and glycine-like receptor; nACh = nicotinic acetylcholine receptor; HisCl = histamine gated chloride channel; NC-LGCl = Not characterized ligand gated chloride channel; AChBP = acetylcholine binding protein. N/A = not available yet, submitted to GeneBank. F indicates forward and R reverse orientation in the clone direction. Sequences indicated with “yes” were identical to the transcriptome database and SNP indicates single nucleotide polymorphism. “missing T” means that a nucleotide with the nitrogenous base thymine was deleted.</p><p><i>Cupiennius salei</i> Cys loop subunits.</p

Alignment of the amino acid sequences in transmembrane domain 2 (TM2).

<p>Residues that line the pore in most Cys-loop receptors are shown in red. Arginine in position 0’ is critical for Cl-selective channels. The equivalent position for cation selective channels (-1’) generally has negatively charged residue (E or D). Note that the two isomers of <i>C</i>. <i>salei</i> nACh1 have a positively charged amino acid in this location. Position 13’, which is occupied by hydrophobic residues in cation permeable channels, is shown in green. Sequences were aligned with MAFFT.</p