Abstract SNMP-1 (sensory neuron membrane protein 1) is an olfactory-specific membrane-bound protein which is homologous with the CD36 receptor family. Previous light level immunocytochemical studies suggested that SNMP-1 was localized in the dendrites and distal cell body of sex-pheromone-specific olfactory receptor neu- rons (ORN); these studies further suggested SNMP-1 was expressed in only one of two to three neurons in male- specific pheromone-sensitive trichoid sensilla. To better understand the expression and localization of SNMP-1, an immunocytochemical study was performed using elec- tron microscopy to visualize the distribution of SNMP-1 among the neurons of several classes of olfactory sensilla of both male and female antennae of the silkmoth Anthe- raea polyphemus. SNMP-1 antigenicity was primarily re- stricted to the receptive dendritic membranes of ORNs of all sensilla types examined and was observed in cytosolic granules, but not plasma membranes, of the cell soma. Mean labeling densities ranged from 1 to 16 gold parti- cles per micrometer of dendrite circumference; dendrites of trichoid and intermediate sensilla showed significantly higher labeling densities than those of basiconic sensilla. Larger dendrites of trichoid sensilla showed significantly higher mean labeling densities (13–16/μm) than smaller diameter dendrites (3–7/μm). Immunofluorescence stud- ies using baculovirus expressed SNMP-1 and multipho- ton photon laser scanning microscopy (MPLSM) indicat- ed that rSNMP-1, which was post-translationally pro- cessed to the in vivo molecular weight, was inserted into the plasma membrane in a topography presenting extra- cellular epitopes. These studies suggest SNMP-1 is a common feature of the ORNs, is asymmetrically ex- pressed among functionally distinct neurons, and possess- es a topography which permits interaction with compo- nents of the extracellular sensillum lymph. Keywords Baculovirus · CD36 · Pheromone · Receptor · MPLSM · Antheraea polyphenus (Insecta) Introduction Insects detect a range of odors using diverse classes of ol- factory sensilla on the antennae; each sensillum typically contains two to three olfactory receptor neurons (ORNs). Studies have shown that the different classes of sensilla are endowed with a variety of olfactory-specific proteins, including extracellular odorant-binding proteins (OBPs) and odorant-degrading enzymes (ODEs) (e.g., Vogt and Riddiford 1981; Vogt et al. 1985, 1999; Rybczynski et al. 1990; Laue and Steinbrecht 1997; Hekmat-Scafe et al. 1997; Rogers et al. 1999; Sandler et al. 2000), and neuro- nal odorant receptor proteins (ORs) (Clyne et al. 1999; Gao and Chess 1999; Vosshall et al. 1999). All three types of proteins are thought to interact with odor mole- cules within the extracellular compartment that surrounds the olfactory neuron and fills the sensillum: OBPs trans- port odor molecules to the ORs, and ODEs degrade odor molecules (see Fig. 8A). OBPs and ORs exist as multi- gene families, and ODEs exist as unrelated proteins (e.g., esterase, aldehyde oxidase; Rybczynski et al. 1990). Unique combinations of members of all three protein families are apparently expressed among the different classes of olfactory sensilla contributing to the overall odor-sensitive phenotypes of the sensilla. Research was supported by grants to R.G.V. from the United States Department of Agriculture (CGRP 94-37302-0615), the Na- tional Institutes of Health (NICDC DC-00588), and the National Science Foundation (IBN9731005) M.E. Rogers ( ✉ ) · R.G. Vogt Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA R.A. Steinbrecht Max-Planck-Institut für Verhaltenphysiologie, 82319 Seewiesen, Germany Present address: M.E. Rogers, Department of Biological Sciences, MC 2439, Columbia University, 1212 Amsterdam Ave., New York, NY 10027, USA e-mail: mr959@columbia.edu Tel.: +1-212-8544539, Fax: +1-212-5310425 R.G. Vogt, e-mail: vogt@biol.sc.edu Cell Tissue Res (2001) 303:433–446 DOI 10.1007/s004410000305 REGULAR ARTICLE Matthew E. Rogers · Rudolf A. Steinbrecht Richard G. Vogt Expression of SNMP-1 in olfactory neurons and sensilla of male and female antennae of the silkmoth Antheraea polyphemus Received: 18 July 2000 / Accepted: 11 October 2000 / Published online: 18 January 2001 © Springer-Verlag 2001