Odorant Responsiveness of Squid Olfactory Receptor Neurons

Abstract

In the olfactory organ of the squid, Lolliguncula brevis there are five morphological types of olfactory receptor neurons (ORNs). Previous work to characterize odor sensitivity of squid ORNs was performed on only two of the five types in dissociated primary cell cultures. Here, we sought to establish the odorant responsiveness of all five types. We exposed live squid or intact olfactory organs to excitatory odors plus the activity marker, agmatine (AGB), an arginine derivative that enters cells through nonselective cation channels. An antibody against AGB was used to identify odorant-activated neurons. We were able to determine the ORN types of AGB-labeled cells based on their location in the epithelium, morphology and immunolabeling by a set of metabolites: arginine, aspartate, glutamate, glycine, and glutathione. Of 389 neurons identified from metabolite-labeled tissue, 3% were type 1, 32% type 2, 33% type 3, 15% type 4, and 17% type 5. Each ORN type had different odorant specificity with type 3 cells showing the highest percentages of odorant-stimulated AGB labeling. Type 1 cells were rare and none of the identified type 1 cells responded to the tested odorants, which included glutamate, alanine and AGB. Glutamate is a behaviorally attractive odorant and elicited AGB labeling in types 2 and 3. Glutamate-activated AGB labeling was significantly reduced in the presence of the adenylate cyclase inhibitor, SQ22536 (80 mM). These data suggest that the five ORN types differ in their relative abundance and odor responsiveness and that the adenylate cyclase pathway is involved in squid olfactory transduction.

Emergence of sensory structures in the developing epidermis in sepia officinalis and other coleoid cephalopods

“…The description of the olfactory neurons of all three species studied here is consistent with previous studies in cephalopods that used classical histology and/or electron microscopy and described several classes of sensory neurons in the olfactory organs (Woodhams and Messenger, 1974;Emery 1975Emery , 1976Wildenburg and Fioroni, 1989;Mobley et al, 2008). One class possessed cilia projecting above the surface of the epithelium, and the existence of these cells likely explains, at least in part, the numerous cilia that we observed projecting into the lumen of the olfactory pit.…”

Mapping kainate activation of inner neurons in the rat retina

“…AGB labeling secondary to endogenous (basal) or exogenous (ligand) activation reports on the cation entry history of the cell and not the summed excitation/inhibitory history (Marc et al, 2005). Guanidinium compounds like AGB permeate cation channels and are immunodetectable when only a small fraction of glutamate receptors have been activated (Picco and Menini, 1993; Marc et al, 2005) using short incubation times secondary to ligand activation (Marc, 1999a,b; Michel et al, 1999; Edwards and Michel, 2003; Marc et al, 2005; Sun and Kalloniatis, 2006; Acosta et al, 2007; Edwards et al, 2007; Chang and Chiao, 2008; Mobley et al, 2008; Chang et al, 2010; Chen and Chiao, 2012). Factors that will affect AGB labeling include cell volume, channel size, number of open channels, ligand affinity of receptor channel, channel permeation, and channel desensitization (Marc, 1999a,b; Marc et al, 2005; Sun and Kalloniatis, 2006).…”

Amino Acid- vs. Peptide-Odorants: Responses of Individual Olfactory Receptor Neurons in an Aquatic Species

“…Amino acid odorants are widely used olfactory stimuli for aquatic vertebrates like fish [1]–[4], amphibia [5]–[7], as well as aquatic invertebrates [8]–[10]. As protein decomposition, in particular food decomposition, generates amino acids, these stimuli have been proposed to serve as cues in the search for food [11]–[13].…”