Immunohistochemical and lectin histochemical studies on the developing olfactory organs of fetal camel

Little is known about the development of the olfactory organs of camel. In this study, prenatal development and neuronal differentiation of the vomeronasal organ (VNO) and the olfactory epithelium (OE) of the one‐humped camel were studied by immunohistochemistry and lectin histochemistry. A neuronal marker, protein gene product (PGP) 9.5, but not a marker of fully differentiated olfactory receptor cells, olfactory marker protein, intensely labeled the olfactory receptor cells of the VNO and OE at 395 mm, 510 mm, and 530 mm fetal ages, indicating that the olfactory receptor cells are differentiated, but not fully matured both in the VNO and the OE. In 187 mm and 190 mm fetuses, PGP 9.5 yielded faint immunoreactive signals in the VNO, but not in the OE, although the presence of olfactory receptor cells were demonstrated in both tissues by intense WGA and LEL stainings. We conclude that the camel VNO and OE bear differentiated, but still immature receptor cells; in addition, the onset of neuronal differentiation seems to be somewhat earlier in the VNO than in the OE till half of the prenatal life. Microsc. Res. Tech. 78:613–619, 2015. © 2015 Wiley Periodicals, Inc.     

Ultrastructural neurobiology of the olfactory mucosa of the brown trout, Salmo trutta.

This paper describes four investigations of the olfactory mucosa of the brown trout: 1) the ultrastructure of the olfactory mucosa as revealed by scanning (SEM), conventional transmission (TEM), and high voltage (HVEM) electron microscopy; 2) light and electron-microscopic investigations of retrograde transport of the tracer macromolecule horseradish peroxidase (HRP) when applied to the cut olfactory nerve; 3) SEM and TEM investigations of the effects of olfactory nerve transection on cell populations within the olfactory epithelium; and 4) ultrastructural investigations of reversible degeneration of olfactory receptors caused by elevated copper concentrations. The trout olfactory epithelium contains five cell types: ciliated epithelial cells, ciliated olfactory receptor cells, microvillar olfactory receptor cells, supporting cells, and basal cells. The ciliated and microvillar olfactory receptor cells and a small number of basal cells are backfilled by HRP when the tracer is applied to the cut olfactory nerve. When the olfactory nerve is cut, both ciliated and microvillar olfactory receptor cells degenerate within 2 days and are morphologically intact again within 8 days. When wild trout are taken from their native stream and placed in tanks with elevated copper concentrations, ciliated and microvillar cells degenerate. Replacement of these trout into their stream of origin is followed by morphologic restoration of both types of olfactory receptor cells. Ciliated and microvillar receptor cells are primary sensory bipolar neurons whose dendrites make contact with the environment; their axons travel directly to the brain. Consequently, substances can be transported directly from the environment into the brain via these "naked neurons." Since fish cannot escape from the water in which they swim, and since that water may occasionally contain brain-toxic substances, the ability to close off--and later reopen--this anatomic gateway to the brain would confer a tremendous selective advantage upon animals that evolved the "brain-sparing" capacity to do so. Consequently, the unique regenerative powers of vertebrate olfactory receptor neurons may have their evolutionary origin in fishes.     

Ultrastructural histopathology of human olfactory dysfunction.

This paper presents electron-microscopic observations on biopsies of the olfactory mucosae of several classes of patients with smell disorders: 1) patients with loss of smell function following head injury (post-traumatic anosmics or hyposmics); 2) patients with loss of smell function following severe head colds and/or sinus infections (post-viral olfactory dysfunction, or PVOD); and 3) patients that have lacked smell function since birth (congenital anosmics). Of these, the traumatic anosmics' olfactory epithelia were quite disorganized; the orderly arrangement of supporting cells, ciliated olfactory receptor neurons, microvillar cells, and basal cells was disrupted. Although many somata of ciliated olfactory receptors were present, few of their dendrites reached the epithelial surface. The few olfactory vesicles present usually lacked olfactory cilia. The post-viral anosmics, too, had a greatly reduced number of intact ciliated olfactory receptor neurons, and most of those present were aciliate. The post-viral hyposmics had a larger population of intact, ciliated olfactory receptor cells. In the seven cases of congenital anosmia studied, no biopsies of olfactory epithelium were obtained, indicating the olfactory epithelium is either absent--or greatly reduced in area--in these individuals.     

Neurotrophins and their receptors in the primary olfactory neuraxis

The primary olfactory pathway is an elegant and simple system in which to study neurogenesis and neuronal plasticity because of the simple fact that olfactory receptor neurons (ORNs) are continually generated throughout the adult lifetimes of vertebrates. Thus, neuronal birth, differentiation, survival, axon pathfinding, target recognition, synapse formation, and cell death are developmental events that can be examined in the mature olfactory epithelium (OE). Neurotrophins (nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3, and 4/5) are a family of bioactive peptides that exert their effects by interacting with high- and low-affinity receptors on the surfaces of responsive cells, and have been implicated in several stages of neuronal development throughout the central and peripheral nervous system (CNS and PNS). There has been significant interest within the olfactory community as to how these multifunctional peptides might regulate the cycle of degeneration and regeneration of olfactory receptor neurons. The focus of this review is to highlight what is known about the actions of neurotrophins in the primary olfactory pathway, and to pinpoint future directions that will enable us to further understand their role in olfactory receptor neuron development and turnover.     

Introduction to olfactory neuroepithelium

Among the five senses, the sense of smell (olfaction) is the most sensitive and emotional window on the outside world (Stern and Marx, 1999). The olfactory system recognizes and discriminates myriad odorants of diverse molecular structures. What makes the olfactory system so specific and sensitive? OE harboring the olfactory receptor neurons (ORNs) also has an another unusual characteristic ability that fascinates scientists. Neurogenesis in this tissue continues throughout lifetime. This unique character provides an elegant model to study neurogenesis and neuronal plasticity, since neuronal birth, differentiation, survival, axon pathfinding, target recognition, synapse formation, and cell death can be examined in the mature OE. This special issue of Microscopic Research and Technique presents the recent developments in this exciting field of neuroscience, “structure and function of olfactory neuroepithelium.” Microsc. Res. Tech. 58:133–134, 2002. © 2002 Wiley-Liss, Inc.     

Apoptosis in the mature and developing olfactory neuroepithelium

Neuronal apoptosis is important in the developmental sculpting of a normal nervous system and also in the loss of neurons caused by neurodegenerative disease, ischemia or trauma. In a developing embryo, exquisite mechanisms of regulation exist to balance factors that control neuronal birth and death within a given neuronal group, so that sufficient neurons develop and survive to elicit normal function. Postnatally, the only part of the mammalian nervous system where many of these regulatory balance mechanisms are retained is the olfactory epithelium (OE). During the last 30 years, researchers investigating olfactory receptor neuron cellular and developmental biology have focussed on the regeneration of the neuronal population within the olfactory neuroepithelium, following the induced death of the mature neuronal population. This body of work has thus far overshadowed the equally important and intrinsically linked phenomenon of the death of mature olfactory receptor neurons, which is required to initiate regeneration. The purpose of this review is to reveal what has been established about the different forms of cell death that can occur in neurons of the olfactory epithelium, and highlight the identified pro- and anti-apoptotic pathways that control the normal and induced turnover of olfactory receptor neurons.     

Fine structural aspects of secretion and extrinsic innervation in the olfactory mucosa.

The mucus at the surface of the olfactory mucosa constitutes the milieu in which perireceptor events associated with olfactory transduction occur. In this review, the ultrastructure of olfactory mucus and of the secretory cells that synthesize and secrete olfactory mucus in the vertebrate olfactory mucosa is described. Bowman's glands are present in the olfactory mucosa of all vertebrates except fish. They consist of acini, which may contain mucous or serous cells or both, and ducts that traverse the olfactory epithelium to deliver secretions to the epithelial surface. Sustentacular cells are present in the olfactory epithelium of all vertebrates. In fish, amphibia, reptiles, and birds, they are secretory; in mammals, they generally are considered to be "non-secretory," although they may participate in the regulation of the mucous composition through micropinocytotic secretion and uptake. Goblet cells occur in the olfactory epithelium of fish and secrete a mucous product. Secretion from Bowman's glands and vasomotor activity in the olfactory mucosa are regulated by neural elements extrinsic to the primary olfactory neurons. Nerve fibers described in early anatomical studies and characterized by immunohistochemical studies contain a variety of neuroactive peptides and have several targets within the olfactory mucosa. Ultrastructural studies of nerve terminals in the olfactory mucosa have demonstrated the presence of adrenergic, cholinergic and peptidergic input to glands, blood vessels, and melanocytes in the lamina propria and of peptidergic terminals in the olfactory epithelium. The neural origins of the extrinsic nerve fibers and terminals are the trigeminal, terminal, and autonomic systems.     

Development,growth, and plasticity in the crayfish olfactory system

Decapod crustaceans have a well-defined olfactory system characterised by a set of chemosensitive sensilla grouped together in an array (the olfactory organ) on their antennules. Olfactory receptor neurons in the olfactory organ project exclusively to, and terminate in, cone-shaped olfactory glomeruli in a discrete neuropil in the brain, the olfactory lobe. The olfactory organ appears to be the only afferent input to the olfactory lobe, making the system convenient for the study of its development and growth. The progression of development of the olfactory system is a continuum and can be traced from the first appearance of peripheral receptor cells and central stem cells through to the construction of the tracts and neuropils that constitute the adult system. Cell proliferation leading to the production of peripheral and central olfactory neurons can be observed with mitotic markers in both embryonic stages and in postembryonic growth. Cell proliferation in the olfactory system in crayfish persists throughout the lives of the animals and can be modulated by manipulating the living conditions imposed on growing animals. Large serotonergic neurons that are associated with the olfactory system may play a role in the regulation of cell proliferation.     

Fine structure of olfactory epithelia of gastropod molluscs.

Among gastropod molluscs the chemical senses are most important for location of distant objects. They are used in food finding, locating mates, avoiding predators, trail following, and homing. Chemoreceptors are commonly associated with the oral area, the tentacles, and the osphradium, which lies in the mantle cavity. Most chemosensory neurons are primary sensory neurons, although secondary sensory cells have been reported in the osphradium of some prosobranch gastropods. Most chemosensory organs contain sensory cells with ciliated sensory endings that are in contact with the external environment. Some sensory endings have only microvilli or have no surface elaborations. Cilia on sensory endings are commonly of the conventional type, but some species have modified cilia; some lack rootlets, some have an abnormal microtubular content, and some have paddle-shaped endings. The perikarya of sensory neurons may be within the sensory epithelium, below it, or in ganglia near the sensory surface. In some groups of gastropods there are peripheral ganglia in the olfactory pathway; in others chemosensory axons appear to pass directly to the CNS. Olfactory epithelia of terrestrial pulmonates have modified brush borders with long branching plasmatic processes and a spongy layer of cytoplasmic tubules which extend from the epithelial cells. Sensory endings of the olfactory receptors are entirely within this spongy layer. Aquatic pulmonates may have a similar spongy layer in their olfactory epithelia, but the cilia of sensory endings, as well as motile cilia of epithelial cells, extend well beyond the spongy layer.     

Odor discrimination by G protein-coupled olfactory receptors

The vertebrate olfactory system possesses a remarkable capacity to recognize and discriminate a variety of odorants by sending the coding information from peripheral olfactory sensory neurons in the olfactory epithelium to the olfactory bulb of the brain. The recognition of odorants appear to be mediated by a G protein-coupled receptor superfamily that consists of approximately 1% of total genes in vertebrates. Since the first discovery of the olfactory receptor gene superfamily in the rat, similar chemosensory receptors have been found in various species across different phyla. The functions of these receptors, however, had been uncharacterized until the recently successful functional expression and ligand screening of some olfactory receptors in various cell expression systems. The functional cloning of odorant receptors from single olfactory neurons allowed for the identification of multiple receptors that recognized a particular odorant of interest. Reconstitution of the odorant responses demonstrated that odorant receptors recognized various structurally-related odorant molecules with a specific molecular receptive range, and that odor discrimination is established based on a combinatorial receptor code model in which the identities of different odorants are encoded by a combination of odorant receptors. The receptor code for an odorant changes at different odorant concentrations, consistent with our experience that perceived quality of an odorant changes at different concentrations. The molecular bases of odor discrimination at the level of olfactory receptors appear to correlate well with the receptive field in the olfactory bulb where the input signal is further processed to create the specific odor maps.     

Presynaptic inhibition of olfactory receptor neurons in crustaceans

Presynaptic inhibition of transmitter release from primary sensory afferents is a common strategy for regulating sensory input to the arthropod central nervous system. In the olfactory system, presynaptic inhibition of olfactory receptor neurons has been long suspected, but until recently could not be demonstrated directly because of the difficulty in recording from the afferent nerve terminals. A preparation using the isolated but intact brain of the spiny lobster in combination with voltage-sensitive dye staining has allowed stimulus-evoked responses of olfactory receptor axons to be recorded selectively with optical imaging methods. This approach has provided the first direct physiological evidence for presynaptic inhibition of olfactory receptor neurons. As in other arthropod sensory systems, the cellular mechanism underlying presynaptic afferent inhibition appears to be a reduction of action potential amplitude in the axon terminal. In the spiny lobster, two inhibitory transmitters, GABA and histamine, can independently mediate presynaptic inhibition. GABA- and histaminergic interneurons in the lobster olfactory lobe (the target of olfactory receptor neurons) constitute dual, functionally distinct inhibitory pathways that are likely to play different roles in regulating primary olfactory input to the CNS. Presynaptic inhibition in the vertebrate olfactory system is also mediated by dual inhibitory pathways, but via a different cellular mechanism. Thus, it is possible that presynaptic inhibition of primary olfactory afferents evolved independently in vertebrates and invertebrates to fill a common, fundamental role in processing olfactory information.     

Role of nerve growth factor in the olfactory system

Olfactory neurons are unique in the mammalian nervous system because of their capacity to regenerate in adult animals. It has been shown that olfactory receptor cells located in the olfactory epithelium are replaced on a continuous basis and in response to injury throughout the life span of most species. NGF, which is one of the neurotrophic factors, is present in many areas of the central and peripheral nervous system. It has been shown that NGF in the olfactory bulb plays a role in the survival of cholinergic neurons in the horizontal limb of the diagonal band (HDB). Recent studies of NGF in the olfactory bulb suggest that it is involved in the development, maintenance, and regeneration of olfactory receptor cells. In this study, we review reports examining the relationship between NGF in the olfactory bulb and neuronal regeneration and development in the mammalian olfactory systems. Low- and high-affinity NGF receptor immunoreactivity is markedly expressed during regeneration and at different stages of development in the mouse olfactory system. This level of immunoreactivity is no longer present after completion of regeneration and at maturation. Other findings indicate that NGF injected into the olfactory bulb is transported retrogradely to the olfactory epithelium. It has also been shown that continuous anti-NGF antibody injection into the olfactory bulb causes degeneration and olfactory dysfunction. Administration of NGF directory into nasal cavity results in an increase in the expression of olfactory marker protein within the olfactory epithelium in axotomized rats. These findings suggested that the presence of NGF in the olfactory bulb plays an essential role in regeneration, maintenance, and development in the olfactory system of mammals.     

The nasal cavity of the sheep and its olfactory sensory epithelium

Macro and microdissection methods, conventional histology and immunohistochemical procedures were used to investigate the nasal cavity and turbinate complex in fetal and adult sheep, with special attention to the ethmoturbinates, the vestibular mucosa, and the septal mucosa posterior to the vomeronasal organ. The ectoturbinates, which are variable in number and size, emerge and develop later than the endoturbinates. The olfactory sensory epithelium is composed of basal cells, neurons, and sustentacular cells organized in strata, but numerous different types are distinguishable on the basis of their thickness and other properties; all variants are present on the more developed turbinates, endoturbinates II and III. Mature neurons and olfactory nerve bundles express olfactory marker protein. We found no structure with the characteristics that in mouse define the septal organ or the ganglion of Grüneberg. Our results thus suggest that in sheep olfactory sensory neurons are exclusively concentrated in the main olfactory epithelium and (to a lesser extent) in the vomeronasal organ. Microsc. Res. Tech. 77:1052–1059, 2014. © 2014 Wiley Periodicals, Inc.     

The terminal nerve and its relation with extrabulbar "olfactory" projections: lessons from lampreys and lungfishes

The definition of the terminal nerve has led to considerable confusion and controversy. This review analyzes the current state of knowledge as well as diverging opinions about the existence, components, and definition of terminal nerves or their components, with emphasis on lampreys and lungfishes. I will argue that the historical terminology regarding this cranial nerve embraces a definition of a terminal nerve that is compatible with its existence in all vertebrate species. This review further summarizes classical and more recent anatomical, developmental, neurochemical, and molecular evidence suggesting that a multitude of terminalis cell types, not only those expressing gonadotropin-releasing hormone, migrate various distances into the forebrain. This results in numerous morphological and neurochemically distinct phenotypes of neurons, with a continuum spanning from olfactory receptor-like neurons in the olfactory epithelium to typical large ganglion cells that accompany the classical olfactory projections. These cell bodies may lose their peripheral connections with the olfactory epithelium, and their central projections or cell bodies may enter the forebrain at several locations. Since "olfactory" marker proteins can be expressed in bona fide nervus terminalis cells, so-called extrabulbar "olfactory" projections may be a collection of disguised nervus terminalis components. If we do not allow this pleiomorphic collection of nerves to be considered within a terminal nerve framework, then the only alternative is to invent a highly species- and stage-specific, and, ultimately, thoroughly confusing nomenclature for neurons and nerve fibers that associate with the olfactory nerve and forebrain.     

Ultrastructural changes of the olfactory bulb in manganesetreated mice

The effect of manganese toxicity on the ultrastructure of the olfactory bulb was evaluated. Male albino mice were injected intraperitoneally with MnCl₂ (5 mg/Kg/day) five days per week during nine weeks. The control group received NaCl (0.9%). The olfactory bulbs of five mice from each group were processed for transmission electron microscopy after 2, 4, 6 and 9 weeks of manganese treatment. On week 2, some disorganization of the myelin sheaths was observed. After 4 weeks, degenerated neurons with dilated cisternae of rough endoplasmic reticulum and swollen mitochondria appeared. A certain degree of gliosis with a predominance of astrocytes with swollen mitochondria, disorganization of the endomembrane system, dilation of the perinuclear cisternae and irregularly shaped nuclei with abnormal chromatin distribution were observed after 6 weeks. Some glial cells showed disorganization of the Golgi apparatus. On week 9, an increase in the number of astrocytes, whose mitochondrial cristae were partially or totally erased, and a dilation of the rough endoplasmic reticulum were found. Neurons appear degenerated, with swollen mitochondria and a vacuolated, electron dense cytoplasm. These changes seem to indicate that the olfactory bulb is sensitive to the toxic effects of manganese.     

Impulse conduction of olfactory receptor neuron axons

Compound action potentials were recorded from rat olfactory receptor neuron axons at measured distances from the stimulation electrode along the lateral surface of the main olfactory bulb. Distances were plotted as a function of the latencies measured from stimulus onset to the prominent negative trough of the triphasic compound action potential. A straight line was fitted to these data to calculate impulse conduction velocity, 0.42 +/- 0.01 m/s (n = 25). Two procedures were used to investigate whether those axons that project to caudal regions of the bulb had faster conduction velocities than axons projecting to rostral bulb. First, the stimulating electrode was moved to mid-bulb and the recording electrode was placed on the caudal bulb. Alternatively, axons were stimulated antidromically at the caudal bulb. These two procedures stimulate those axons projecting to caudal bulb and bypass olfactory receptor neuron axons that synapse in the rostral bulb. The mean impulse conduction velocities from these caudal and antidromic recordings were 0.58 +/- 0.19 m/s (n = 8) and 0.57 +/- 0.19 m/s (n = 9), respectively. Though both of these means are higher than the impulse conduction velocity calculated for stimulation at the rostral bulb, the differences were not statistically significant.     

Endocytic pathways in the olfactory and vomeronasal epithelia of the mouse: ultrastructure and uptake of tracers.

Mammalian olfactory neurons possess a well-developed system of endocytic vesicles, endosomes, and lysosomes in their dendrites and perikarya. Vomeronasal neurons are similar and also contain much perikaryal agranular endoplasmic reticulum (AER). Olfactory supporting cells contain endocytic vesicles and endosomes associated closely with abundant fenestrated AER, and vesicles and numerous large dense vacuoles are present basally. Vomeronasal supporting cells have little AER, and few dense vacuoles occur in their bases. In olfactory neurons, ultrastructural tracers (0.08% horseradish peroxidase, thorium dioxide, ferritin) are endocytosed by olfactory receptor endings and transported to the cell body, where their movement is halted in lysosomes. Higher concentrations (1%) of horseradish peroxidase penetrate olfactory receptor plasma membranes and intercellular junctions. In olfactory supporting cells, endocytosed tracers pass through endosomes to accumulate in dense basal vacuoles. These observations indicate that olfactory sensory membranes are rapidly cycled and that endocytosed materials are trapped within the epithelium. It is proposed that in the olfactory epithelium, endocytosis presents redundant odorants to the enzymes of the supporting cell AER to prevent their accumulation, whereas in the vomeronasal epithelium the receptor cells carry out this activity.     

Drosophila as a focus in olfactory research: mapping of olfactory sensilla by fine structure, odor specificity, odorant receptor expression, and central connectivity.

This review intends to integrate recent data from the Drosophila olfactory system into an up-to-date account of the neuronal basis of olfaction. It focuses on (1) an electron microscopic study that mapped a large proportion of fruitfly olfactory sensilla, (2) large-scale electrophysiological recordings that allowed the classification of the odor response spectra of a complete set of sensilla, (3) the identification and expression patterns of candidate odorant receptors in the olfactory tissues, (4) central projections of neurons expressing a given odorant receptor, (5) an improved glomerular map of the olfactory center, and (6) attempts to exploit the larval olfactory system as a model of reduced cellular complexity. These studies find surprising parallels between the olfactory systems of flies and mammals, and thus underline the usefulness of the fruitfly as an olfactory model system. Both in Drosophila and in mammals, odorant receptor neurons appear to express only one type of receptor. Neurons expressing a given receptor are scattered in the olfactory tissues but their afferents converge onto a few target glomeruli only. This suggests that in both phyla, the periphery is represented in the brain as a chemotopic map. The major difference between mammals and fruitflies refers to the numbers of receptors, neurons, and glomeruli, which are largely reduced in the latter, and particularly in larvae. Yet, if activated in a combinatorial fashion, even this small set of elements could allow discrimination between a vast array of odorants.     

Lectins bind differentially to cilia and microvilli of major and minor cell populations in olfactory and nasal respiratory epithelia.

Binding of colloidal gold-conjugated lectins was studied in cilia and microvilli of rat olfactory and respiratory epithelia. This was done in sections of rapidly frozen, freeze-substituted specimens embedded in Lowicryl K11M or, for wheat germ agglutinin (WGA) alone, in deep-etched replicas. Olfactory dendritic endings and cilia labeled with WGA and faintly with soybean agglutinin (SBA); olfactory supporting cell microvilli bound only Dolichos biflorus agglutinin (DBA). Microvilli of an infrequent cell bound peanut agglutinin (PNA), SBA, and WGA. These microvilli labeled more strongly with the last two lectins than the olfactory cilia. Respiratory cilia bound WGA and, somewhat more weakly, PNA; microvilli of ciliated respiratory cells bound all four lectins. Visualization of specific labeling improved after preincubation of sections with neuraminidase, except for DBA where lectin binding was abolished. PNA labeling was seen only after neuraminidase preincubation. The densities of membrane surface particles that labeled with WGA corresponded with those of fracture plane particles in a quantitative freeze-fracture, deep-etch analysis. Therefore, a considerable fraction of the WGA-bound particles could reflect transmembrane proteins in olfactory dendritic endings and cilia and in respiratory cilia. The possible nature of these particles is discussed.     

Structure of the olfactory receptor organs,their GABAergic neural pathways,and modulation of mating behavior,in the giant freshwater prawn,Macrobrachium rosenbergii

In the giant male prawn, Macrobrachium rosenbergii, the olfactory system is thought to be the main pathway for modulating sexual behavior through pheromone perception. In this report, we first used gross anatomical, histological, and SEM methods to describe the structures of the olfactory receptors (sensilla setae), their neural pathways, and possible role in modulating mating behavior. On the surfaces of antennule and antenna filaments there are four types of sensory receptors, viz single spike‐like setae, single flagellum‐like setae, multiple flagella‐like setae, and aesthetascs (ASs). The ASs, which had previously been proposed to be odor receptor setae, are found only on the short filament of lateral antennule (slAn). Each AS on the slAn connects with olfactory receptor neurons (ORNs), whose axons form an outer central antennule nerve (ocAnNv), which then connects with the olfactory neutrophil (ON) of the brain. Thus, the slAn is the major olfactory organ that conveys sensory inputs from each AS to the ON within the deutocerebrum. GABA immunoreactivity was present in ASs, neurons of ORNs, inner central antennular, lateral tegumentary nerve, ocAnNv and the ON, inferring that GABA is the likely neurotransmitter in modulating olfaction. Disruption of the slAn by ablation or covering with Vaseline, resulted in significant reduction of mating behavior, indicating that this organ is crucial for sex pheromone perception. Identification of the active pheromones and further bioassays are now being performed. Microsc. Res. Tech. 76:572–587, 2013. © 2013 Wiley Periodicals, Inc.