Amino Acid Odorants Stimulate Microvillar Sensory Neurons

Abstract

The olfactory epithelium (OE) of zebrafish is populated with ciliated and microvillar olfactory sensory neurons (OSNs). Whether distinct classes of odorants specifically activate either of these unique populations of OSNs is unknown. Previously we demonstrated that zebrafish OSNs could be labeled in an activity-dependent fashion by amino acid but not bile acid odorants. To determine which sensory neuron type was stimulated by amino acid odorants, we labeled OSNs using the ion channel permeant probe agmatine (AGB) and analyzed its distribution with conventional light- and electron-microscope immunocytochemical techniques. Approximately 7% of the sensory epithelium was labeled by AGB exposure alone. Following stimulation with one of the eight amino acids tested, the proportion of labeled epithelium increased from 9% for histidine to 19% for alanine; amino acid stimulated increases in labeling of 2-12% over control labeling. Only histidine failed to stimulate a significant increase in the proportion of labeled OSNs compared to control preparations. Most amino acid sensitive OSNs were located superficially in the epithelium and immuno-electron microscopy demonstrated that the labeled OSNs were predominantly microvillar. Large numbers of nanogold particles (20-60 per 1.5 microm(2)) were associated with microvillar olfactory sensory neurons (MSNs), while few such particles (<15 per 1.5 microm(2)) were observed over ciliated olfactory sensory neurons (CSNs), supporting cells (SCs) and areas without tissue, such as the lumen above the OE. Collectively, these findings indicate that microvillar sensory neurons are capable of detecting amino acid odorants.

Immunohistochemical and Histochemical Characteristics of the Olfactory System of the Guppy, Poecilia reticulata (Teleostei, Poecilidae)

“…Previous works in Carassius carassius showed that this synaptic region, connected with the lateral olfactory tract, mediates feeding behavior (Hamdani et al, 2001b). Retrograde axonal transport studies (Hamdani et al, 2001a;Valentinčič et al, 2005) discovered that the lateral glomerular layer is innervated by microvillous olfactory neurons, known to be stimulated by amino acids (Lipschitz and Michel, 2002). We could hypothesize that in Poecilia reticulata calretinin prevalently identifies the subtypes of crypt and microvillous cells in the mucosa.…”

Mutually Exclusive Glomerular Innervation by Two Distinct Types of Olfactory Sensory Neurons Revealed in Transgenic Zebrafish

“…One of the goldfish V2R-type receptors and its zebrafish ortholog are activated by amino acids with preferences for arginine and glutamate, respectively (Speca et al, 1999;Kuang et al, 2003;Luu et al, 2004). Activity-dependent labeling of OSNs using a cation channel-permeant probe, agmatine, has shown that amino acid odorants stimulate at least microvillous OSNs in zebrafish (Lipschitz and Michel, 2002). Functional imaging of OB glomeruli in zebrafish using calcium-and voltage-sensitive dyes has revealed that various amino acids and nucleotides elicit activation of glomeruli in the lateral region of the OB Korsching, 1997, 1998).…”

Visualizing a set of olfactory sensory neurons responding to a bile salt

“…In fishes there are three types of sensory neuron; the ciliated and microvillous sensory neurons, and crypt cells. The sensory neurons express different types of odorant receptors and respond to different classes of stimuli (Hansen et al, 2003;Lipschitz and Michel, 2002;Sato and Suzuki, 2001). These classes of sensory neurons send their axons to distinct and segregated regions in the olfactory bulb (Hansen et al, 2003;Koide et al, 2009;Sato et al, 2005).…”