Anatomical and immunohistological demonstration of the primary neural connections of the vomeronasal organ in the dog.

Macro- and microdissection methods together with conventional histology and lectin immunohistochemistry have been used to identify the course of the vomeronasal nerves and their site of termination (accessory olfactory bulb; AOB) in the dog. The AOB in this species is small and variable in size, situated on the medial surface of the main olfactory bulb, and has an anatomical structure unlike that described for other mammals. The vomeronasal nerves and their terminal glomeruli in the AOB are easily identifiable by selective immunohistochemical staining using Ulex europeus agglutinin I.     

Anatomical and immunohistological demonstration of the primary neural connections of the vomeronasal organ in the dog

Macro- and microdissection methods together with conventional histology and lectin immunohistochemistry have been used to identify the course of the vomeronasal nerves and their site of termination (accessory olfactory bulb; AOB) in the dog. The AOB in this species is small and variable in size, situated on the medial surface of the main olfactory bulb, and has an anatomical structure unlike that described for other mammals. The vomeronasal nerves and their terminal glomeruli in the AOB are easily identifiable by selective immunohistochemical staining using Ulex europeus agglutinin I. © 1992 Wiley-Liss, Inc.     

Projections of two subclasses of vomeronasal nerve fibers to the accessory olfactory bulb in the rabbit

The organization of the projections of subclasses of vomeronasal nerve fibers to the accessory olfactory bulb was analysed using monoclonal antibodies generated against a homogenate of the rabbit olfactory bulb. Monoclonal antibody R2D5 labels all the somata of vomeronasal receptor cells in the vomeronasal organ as well as all their axons (vomeronasal nerve fibers). Another monoclonal antibody (R4B12), which has been shown to selectively bind and thus identify a subclass of olfactory nerve fibers, also labels a subclass of vomeronasal nerve fibers. The R4B12-positive subclass of vomeronasal nerve fibers project to the glomeruli in the rostrolateral part of the accessory olfactory bulb. The third monoclonal antibody (R5A10) recognizes a complementary subclass of vomeronasal nerve fibers projecting to the glomeruli in the caudomedial part of the accessory bulb. In contrast to the clearly segregated terminations in the accessory bulb, the two subclasses of vomeronasal nerve fibers are intermingled with each other in the vomeronasal nerve bundles. Retrograde labeling of vomeronasal receptor cell somata following injection of horseradish peroxidase within the rostrolateral (R4B12-positive) part of the accessory bulb indicates that vomeronasal receptor cells of this subtype are widely distributed in the vomeronasal sensory epithelium. These results demonstrate the heterogeneity of vomeronasal receptor cells and the specificity of projections arising from subclasses of vomeronasal nerve fibers to the accessory olfactory bulb.     

Subdivision of the accessory olfactory bulb in the Japanese common toad, Bufo japonicus, revealed by lectin histochemical analysis

Lectin binding patterns in the olfactory bulb of the Japanese common toad, Bufo japonicus, were examined using 21 types of lectin. Ten out of 21 lectins, WGA, s-WGA, LEL, STL, DBA, VVA, SJA, RCA-I, PNA, and PHA-L, stained the olfactory nerve, the glomeruli in the main olfactory bulb (MOB), the vomeronasal nerve, and the glomeruli in the accessory olfactory bulb (AOB). The binding patterns of LEL, STL, DBA, and PHA-L subdivided AOB glomeruli into rostral and caudal regions, where LEL, STL, and DBA stained the rostral region more intensely than the caudal region, and PHA-L had the opposite effect. Another lectin, BSL-I, stained both AOB glomeruli and the vomeronasal nerve, but not MOB glomeruli or the olfactory nerve. This is the first report of histological subdivision in the AOB of an amphibian, which suggests that the AOB development in Bufo may be unique.     

Functional synapse formation between cultured rat accessory olfactory bulb neurons and vomeronasal pockets

To investigate the interaction between vomeronasal receptor neurons and accessory olfactory bulb neurons during pheromonal signal processing and specific synapse formation, partially dissociated rat vomeronasal receptor neurons were co-cultured with accessory olfactory bulb neurons. Between 7 and 14 days in co-culture, a few bundles of fibers from a spherical structure, termed the vomeronasal pocket, of cultured vomeronasal receptor neurons extended to the accessory olfactory bulb neurons. An optical recording of the intracellular Ca(2+) concentration was used to monitor the synaptic activation of cultured accessory olfactory bulb neurons. Electrical stimulation of the vomeronasal pocket between 7 and 14 days in co-culture had no effects on most of the cultured neurons tested, although it occasionally evoked weak responses in a small number of neurons. In contrast, vomeronasal pocket stimulation after 21 days in co-culture evoked clear calcium transients in a substantial number of cultured accessory olfactory bulb neurons. These responses of accessory olfactory bulb neurons were reversibly suppressed by the application of 6-cyano-7-nitroquinoxaline-2,3-dione; the calcium transients disappeared in most of the neurons and were diminished in the others. The application of d-2-amino-5-phosphonopentanoic acid partially affected the calcium transients, but blocked spontaneous calcium increases, which were observed repeatedly in accessory olfactory bulb-alone cultures. The application of both 6-cyano-7-nitroquinoxaline-2,3-dione and d-2-amino-5-phosphonopentanoic acid completely blocked the evoked calcium transients. These results suggest that functional glutamatergic synapses between vomeronasal receptor neurons and accessory olfactory bulb neurons were formed at around 21 days in co-culture.     

The terminal nerve projects centrally in the hamster

The projections of the peripheral and intracerebral portions of the hamster terminal nerve were examined with lesion and immunocytochemical techniques. After transection, proximal processes of the terminal nerve accumulate luteinizing hormone-releasing hormone-immunoreactive material, while the distal processes disintegrate and are no longer stained. It thus becomes possible to determine the direction of conduction of terminal nerve axons. The results of transection at the level of the cribriform plate, along the olfactory bulb, and in the ventral forebrain were all consistent in indicating a centripetal direction of conduction. Immunoreactive material collected distal to the lesion at each of these levels. All peripheral lesions eliminated processes coursing into and through the terminal ganglion at the base of the ventral forebrain. These lesions left intact, however, the terminal ganglion projections to the accessory olfactory bulb and ventral forebrain. These results indicate a centripetal projection from terminal neurons in the nasal cavity, along the olfactory bulbs and within the terminal ganglion to successively more caudal levels. This suggests that neural messages are conveyed from nasal cavity to the brain through this route. Because immunoreactive fibers were found within the sensory epithelium of the vomeronasal organ a sensory and/or sensory modulatory action is suggested.     

The bilateral bulbar projections of the primary olfactory neurons in the frog

Summary Whether or not the frog olfactory neuroreceptor cells project bilaterally to the olfactory bulb is still a debated question. We therefore decided to ascertain whether bilateral projections of the primary olfactory input exist and if so to investigate their extent. Reproducible extracellular bilateral bulbar potentials were recorded in the frog following electrical stimulation of dorsal or ventral olfactory nerve bundles. The general features of the contralateral evoked responses were very similar to those of the ipsilateral response. The contralateral response disappeared after transection of the rostral part of the olfactory interbulbar adhesion but not following transection of the habenular or anterior commissures. Horseradish peroxidase labelling showed that the fiber terminations of the olfactory nerve bundle was not restricted to the ipsilateral olfactory bulb but included the medial aspects of the contralateral bulb. The intertelencephalic sections increased the magnitude of the ipsilateral evoked responses. Olfactory bulb isopotential maps revealed a rough topographical correspondence between the olfactory neuroepithelium and bulb along the medio-lateral axis as well as along the dorso-ventral axis. In addition, a projection of the medial and central part of the olfactory sac to the medial part of the contralateral olfactory bulb through the interbulbar adhesion was confirmed. These findings suggest first, that the fibers from the neuro-receptors located in either the ventral or the dorsal olfactory mucosae project to both olfactory bulbs, and second, that the left and right bulbs exert a constant inhibition on each other via the habenular commissure.Abbreviations AON anterior olfactory nucleus - ax olfactory neuroreceptor axon - BA bulbar adhesion - D_I latero-dorsal olfactory nerve bundle - D_II centro-dorsal olfactory nerve bundle - D_III mediodorsal olfactory nerve bundle - EPL external plexiform layer - GL glomerular layer - gl glomerulus - GRL granular cell layer - MOB main olfactory bulb - m mitral cell - MBL mitral cell body layer - ON olfactory nerve - V lateral ventricule - V_I latero-ventral ol-factory nerve bundle - V_II centro-ventral olfactory nerve bundle - V_III medio-ventral olfactory nerve bundle - VN vomero-nasal nerve     

Tyrosine hydroxylase-like immunoreactive neurons in the olfactory bulb of the snake,Elaphe quadrivirgata,with special reference to the colocalization of tyrosine hydroxylase- and GABA-like immunoreactivities

Summary The distribution and structural features of tyrosine hydroxylase-like immunoreactive (TH-LI) neurons were studied in the olfactory bulb of a snake, Elaphe quadrivirgata, by using pre-and post-embedding immunocytochemistry at the light microscopic level. In contrast to rodent olfactory bulbs previously reported, many TH-LI neurons were seen not only in the main olfactory bulb (MOB) but also in the accessory olfactory bulb (AOB). With regard to the TH-like immunoreactivity, there appeared no appreciable differences between MOB and AOB. As in mammalian MOB, the majority of TH-LI neurons were clustered in the periglomerular region and appeared to send their dendritic branches into glomeruli, which as a whole make an intense TH-LI band in the glomerular layer (GML). In the external plexiform/mitral cell layer (EPL/ML) of MOB and AOB as well as in the outer sublamina of the internal plexiform layer (OSL) of AOB, an appreciable number of TH-LI neurons were scattered, extending dendritic processes which appeared to make a loose meshwork. TH-LI neurons in EPL/ML (including OSL) appeared to consist of at least two morphologically different types. The first had a small perikaryon and one or two smooth dendrites which usually extended to GML and were frequently confirmed to enter into glomeruli. The second had a larger perikaryon and 2–3 dendrites which branched into several varicose processes extending in EPL/ML/OSL but appeared not to enter into glomeruli. The TH-like immunoreactivity was rarely seen in the internal plexiform layer and internal granule cell layer. The colocalization of GABA-like and TH-like immunoreactivities was further studied. Almost all TH-LI neurons in both EPL/ ML/OSL and GML contained GABA-like immunoreactivity irrespectively of the type of TH-LI cells.Abbreviations in Figures AOB accessory olfactory bulb - MOB main olfactory bulb - Hem hemisphere - ON olfactory nerve layer - VN vomeronasal nerve layer - GM glomerular layer - EP/M external plexiform layer/Mitral cell layer - IP internal plexiform layer - IG internal granular layer - OS outer sublamina of the IPL of AOB - MS middle sublamina of the IPL of AOB - IS inner sublamina of the IPL of AOB     

Vomeronasal neurons promote synaptic formation on dendritic spines but not dendritic shafts in primary culture of accessory olfactory bulb neurons

To investigate the morphological changes of accessory olfactory bulb (AOB) neurons arising from pheromonal signals, a coculture system of AOB neurons and vomeronasal (VN) neurons had been established. Our previous study indicates that under coculture condition, the density of dendritic spines of an AOB neuron is less and the individual spine-head volume is larger than those under monoculture condition. In this study, to determine whether these differences in the dendrites of AOB neurons reflect the differences in synapse formation and synaptic properties, we observed these cultured cells by electron microscopy. Various synapses were observed under each culture condition. Synapses were classified on the basis of their postsynaptic structure and the size of postsynaptic density (PSD) was measured. Under the coculture condition with VN neurons, synapses on dendritic spines, which formed between AOB neurons, were observed frequently. In contrast, many synapses were formed on dendritic shafts under monoculture condition. The PSD of asymmetrical synapses on the spines under coculture condition was larger than that under monoculture condition. Moreover, some dendrodendritic reciprocal synapses were found only in coculture. We confirmed synapse formation between VN axons and AOB dendrites by immunohistochemical electron microscopy; thus, the characteristics of synapses between AOB neurons are considered to be modified by the synaptic contacts with VN axons.     

Neuropeptide Y in the olfactory system, forebrain and pituitary of the teleost, Clarias batrachus

Distribution of neuropeptide Y (NPY)-like immunoreactivity in the forebrain of catfish Clarias batrachus was examined with immunocytochemistry. Conspicuous immunoreactivity was seen in the olfactory receptor neurons (ORNs), their projections in the olfactory nerve, fascicles of the olfactory nerve layer in the periphery of bulb and in the medial olfactory tracts as they extend to the telencephalic lobes. Ablation of the olfactory organ resulted in loss of immunoreactivity in the olfactory nerve layer of the bulb and also in the fascicles of the medial olfactory tracts. This evidence suggests that NPY may serve as a neurotransmitter in the ORNs and convey chemosensory information to the olfactory bulb, and also to the telencephalon over the extrabulbar projections. In addition, network of beaded immunoreactive fibers was noticed throughout the olfactory bulb, which did not respond to ablation experiment. These fibers may represent centrifugal innervation of the bulb. Strong immunoreactivity was encountered in some ganglion cells of nervus terminalis. Immunoreactive fibers and terminal fields were widely distributed in the telencephalon. Several neurons of nucleus entopeduncularis were moderately immunoreactive; and a small population of neurons in nucleus preopticus periventricularis was also labeled. Immunoreactive terminal fields were particularly conspicuous in the preoptic, the tuberal areas, and the periventricular zone around the third ventricle and inferior lobes. NPY immunoreactive cells and fibers were detected in all the lobes of the pituitary gland. Present results describing the localization of NPY in the forebrain of C. batrachus are in concurrence with the pattern of the immunoreactivity encountered in other teleosts. However, NPY in olfactory system of C. batrachus is a novel feature that suggests a role for the peptide in processing of chemosensory information.     

Increase in the number of tyrosine hydroxylase-containing neurons in a primary culture system of the rat accessory olfactory bulb by co-culture with vomeronasal pockets

Previously, we established a culture system of the accessory olfactory bulb in order to investigate the functional role of each accessory olfactory bulb neurons in pheromonal signal processing. In the present study, we developed a co-culture system of cultured accessory olfactory bulb neurons with partially dissociated cells of the vomeronasal organ. The dissociated cells of the vomeronasal organ form spherical structures surrounding a central cavity in culture, referred to as the vomeronasal pockets. The projection and activity of olfactory receptor neurons affect the differentiation and maturation of main olfactory bulb neurons. It was also reported induction of tyrosine hydroxylase expression in main olfactory bulb neurons when they were co-cultured with explants of the olfactory epithelium. Thus, we investigated the effects of co-culture with vomeronasal pockets on the differentiation and/or maturation of cultured accessory olfactory bulb neurons in relation to tyrosine hydroxylase expression. The number of tyrosine hydroxylase-containing neurons developmentally increased over time in the accessory olfactory bulb culture. This increase was significantly enhanced by coculture with vomeronasal pockets. Interestingly, a significant change in tyrosine hydroxylase expression was not observed when main olfactory bulb neurons were co-cultured with vomeronasal pockets. Moreover, significant changes in tyrosine hydroxylase expression were not observed when accessory olfactory bulb neurons were co-cultured with olfactory epithelium explants, as was previously observed in co-culture of main olfactory bulb neurons and olfactory epithelium explants. These results suggest that the differentiation and/or maturation of accessory olfactory bulb neurons is modified by vomeronasal organ neurons via specific interactions between the sensory organ and its target.     

Shared and differential traits in the accessory olfactory bulb of caviomorph rodents with particular reference to the semiaquatic capybara

The vomeronasal system is crucial for social and sexual communication in mammals. Two populations of vomeronasal sensory neurons, each expressing Gαi2 or Gαo proteins, send projections to glomeruli of the rostral or caudal accessory olfactory bulb, rAOB and cAOB, respectively. In rodents, the Gαi2‐ and Gαo‐expressing vomeronasal pathways have shown differential responses to small/volatile vs. large/non‐volatile semiochemicals, respectively. Moreover, early gene expression suggests predominant activation of rAOB and cAOB neurons in sexual vs. aggressive contexts, respectively. We recently described the AOB of Octodon degus, a semiarid‐inhabiting diurnal caviomorph. Their AOB has a cell indentation between subdomains and the rAOB is twice the size of the cAOB. Moreover, their AOB receives innervation from the lateral aspect, contrasting with the medial innervation of all other mammals examined to date. Aiming to relate AOB anatomy with lifestyle, we performed a morphometric study on the AOB of the capybara, a semiaquatic caviomorph whose lifestyle differs remarkably from that of O. degus. Capybaras mate in water and scent‐mark their surroundings with oily deposits, mostly for male–male communication. We found that, similar to O. degus, the AOB of capybaras shows a lateral innervation of the vomeronasal nerve, a cell indentation between subdomains and heterogeneous subdomains, but in contrast to O. degus the caudal portion is larger than the rostral one. We also observed that four other caviomorph species present a lateral AOB innervation and a cell indentation between AOB subdomains, suggesting that those traits could represent apomorphies of the group. We propose that although some AOB traits may be phylogenetically conserved in caviomorphs, ecological specializations may play an important role in shaping the AOB.     

Coculture of the vomeronasal organ and olfactory bulb of the fetal rat

The vomeronasal organ and the olfactory bulb of the rat were cocultured from 15-day embryo siblings on collagen-coated membrane in Dulbecco's modified Eagle's medium containing fetal calf serum, horse serum, and antibiotics. At 4 days in vitro (DIV), vomeronasal axons forming two to three large fascicles were seen originating from the explants of the vomeronasal organ. Differential axonal growth was observed. Some fascicles made connections with the explants of the olfactory bulb. Twenty percent of the cocultures studied here showed the formation of connections. At 6–10 DIV many fascicles that did not connect with the olfactory bulb had degenerated, and large fascicles that were connected with the olfactory bulb survived for more than 10 DIV. The formation of connections between the vomeronasal organ and the olfactory bulb in coculture favors the survival of large nerve fascicles, but it could not be determined whether or not the presence of the olfactory bulb affects the initial orientation of the fibers and fascicles from the explants of the vomeronasal organ.     

A descriptive and comparative lectin histochemical study of the vomeronasal system in pigs and sheep

The accessory olfactory bulb (AOB) is the primary target of the sensory epithelium of the vomeronasal organ (VNO), and thus constitutes a fundamental component of the accessory olfactory system, which is involved in responses to behaviour-related olfactory stimuli. In this study we investigated the characteristics of the AOB, VNO, vomeronasal nerves (VNNs) and caudal nasal nerve (CdNN) in pigs and sheep, species in which olfaction plays a key behavioural role both in the neonatal period and in adulthood. The patterns of staining of the AOB by the Bandeiraea simplicifolia and Lycopersicon esculentum lectins were the same in the 2 species, whereas the Ulex europeus and Dolichos biflorus lectins gave different patterns. In both species, lectin staining of the AOB was consistent with that of the VNNs, while the CdNN did not label any of the structures studied. The entire sensory epithelium of the pig was labelled by Ulex europeus and Lycopersicum esculentum lectins, and all 4 lectins used labelled the mucomicrovillar surface of the sensory epithelium in sheep.     

Male hamster copulatory responses to a high molecular weight fraction of vaginal discharge: effects of vomeronasal organ removal

The importance of the vomeronasal (accessory olfactory) system for the copulatory responses of male hamsters to a high molecular weight fraction (HMF) of vaginal discharge was assessed in animals that had their vomeronasal organs (VNO) removed. These organs were extirpated bilaterally using an oral approach through the palate so as to eliminate the peripheral afferents to the accessory olfactory bulb (AOB) with minimal or no damage to the main olfactory system. The selective peripheral deafferentation procedure was verified by applying horseradish peroxidase intranasally following intraperitoneal injections of epinephrine to facilitate the vomeronasal pumping mechanism that draws fluids into the VNO. Heavy, bilateral anterograde labeling was evident in the olfactory nerve afferents within the main olfactory bulb of males that had their VNO removed and of animals that received sham surgery. Sham-operated males also had heavy, bilateral labeling in the vomeronasal nerve afferents within the AOB, whereas no such labeling occurred among animals with bilateral removal of the VNO. In sham-operated animals, both the HMF and the unfractionated discharge significantly increased the incidence of intromission attempts toward anesthetized males (surrogate females) whose hindquarters were scented with these stimuli. The unfractionated discharge also produced a significant elevation of overt copulatory behavior in males with selective peripheral deafferentation of the vomeronasal system, whereas the HMF did not facilitate copulatory behavior in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of olfactory and related structures in staged human embryos

Summary The staged sequence of development of the olfactory and related structures has been established from the serially sectioned human embryos of the Carnegie collection, from stage 11 to stage 23.The nasal epiblastic thickening appears at stage 11 and the nasal field is well outlined at stage 12. At stage 15, a continuous cellulovascular strand is observed between the nasal groove and the olfactory field. The vomeronasal groove appears at stage 16 (O'Rahilly 1967). During stage 17, the olfactory nerve is organized into two plexuses, lateral and medial, the latter mingled with the terminal-vomeronasal complex. The olfactory bulb begins to appear at stage 18. Stage 19 is characterized by the individualization of the olfactory bulb and nuclei. In addition, the distinction between olfactory structures and terminal and vomeronasal ones begins to be clear. The structure of the olfactory bulb is evident at stage 21. At stage 23, the olfactory strands are well individualized, and olfactory and terminal-vomeronasal fibers are easily distinguishable.The terminal ganglion is rather terminal-vomeronasal with an autonomic terminal contingent and a sensory one attached to the vomeronasal system.Supported by research programme project grant No. HD-08658, Institute of Child Health and Human Development, National Institutes of Health (USA)     

Immunocytochemical identification of luteinizing hormone-releasing hormone-positive fibres and terminals in the olfactory system of the rat

Luteinizing hormone-releasing hormone immunoreactivity was studied in the olfactory system of the rat in combination with acetylcholinesterase histochemistry. Neuronal perikarya containing luteinizing hormone-releasing hormone lie in the medial septal nucleus, the vertical limb of the diagonal band of Broca, the olfactory tubercule and the ganglionated plexus of the terminal nerve. Labelled fibres spread in the superficial layers of the main and accessory olfactory bulbs, some encompassing the strongly acetylcholinesterase-positive atypical glomeruli. Others are observed on the medial side of the bulb, running along the terminal nerve bundles and ganglia. These fibres join the vomeronasal nerve branches and proceed distally towards the nasal cavity. In the septal submucosa, immunoreactive fibres are partly associated with the terminal nerve network. Conspicuous endings filled with luteinizing hormone-releasing hormone are observed on blood vessels of the olfactory mucosa. Such well-differentiated terminals might be the neurosecretory afferents of a new neurohemal area. Immunoreactive terminals are also observed around the excretory ducts of the anterior medial glands. We have failed to observe any labelled fibres in the olfactory and vomeronasal epithelia. The results of the present study are discussed with respect to possible functional interpretations. It is suggested that significant amounts of luteinizing hormone-releasing hormone could be released in the submucosal capillaries in spite of the scarcity of immunoreactive fibres. Similar afferents could also modulate the secretory activity of some nasal glands. Synaptic events involving the neuropeptide might occur in the olfactory bulb, particularly in atypical glomerular areas previously characterized by their high acetylcholinesterase content. Finally, no anatomical support for a chemosensory function of fibres containing luteinizing hormone-releasing hormone has been brought out by our work.     

The organization of feedback projections in a pathway important for processing pheromonal signals

In most of the mammalian sensory systems there are massive cortical feedback projections to early processing stations. The mammalian accessory olfactory system is considered unique in several aspects. It is specialized for processing pheromonal signals and plays a critical role in regulating sociosexual behaviors. Furthermore, pheromonal signals are believed to bypass cortex and reach the hypothalamic behavioral centers after merely three forward projections. Because the organization of the feedback projections in the accessory olfactory system remains largely unclear, the importance of the feedback projections in the processing of pheromonal signals has been ignored. Here we show that in mice the feedback projections from the bed nucleus of stria terminalis (BST) and the vomeronasal amygdala to the accessory olfactory bulb (AOB) are topographically organized and use different neurotransmitters. By retrograde and anterograde tracing, we find that the feedback projection from the BST terminates in the AOB mitral cell layer, whereas that from the amygdala terminates in the AOB granule cell layer. By combining tracing, genetic labeling of GABAergic neurons, and immunostaining against a marker of glutamatergic synapses, we observe that the BST-to-AOB projection is GABAergic whereas the amygdala-to-AOB projection is glutamatergic. In addition, a substantial number of feedback neurons in the amygdala and BST express estrogen receptors. Thus, the accessory olfactory system, like other sensory systems, possesses extensive feedback projections. Moreover, our results suggest that central hormonal cues may modulate the processing of pheromonal signals at early stations through the precisely organized feedback projections.     

Selective binding of soybean agglutinin to the olfactory system of Xenopus

The binding patterns of four different lectins conjugated to horseradish peroxidase were investigated in the nervous system of juvenile Xenopus borealis. Only the lectin soybean agglutinin revealed a very selective binding pattern, which was restricted to the olfactory system. The olfactory and vomeronasal epithelia, the olfactory and accessory olfactory nerves and the olfactory and accessory olfactory bulbs were all labelled. The ventral portions of the olfactory nerve and bulb were however more intensely labelled than their dorsal portions. The rest of the brain and spinal cord did not bind this lectin except for a small discrete set of unmyelinated axons travelling in the medial forebrain bundle. Ultrastructural investigations revealed that soybean agglutinin was confined to the cell surface of olfactory neurons. The selective binding of this lectin of olfactory neurons suggests that specific cell surface glycoconjugates binding soybean agglutinin may have either a functional or developmental role in the olfactory system of Xenopus.     

Sex difference in Fos induced by male urine in medial amygdala-projecting accessory olfactory bulb mitral cells of mice

We previously reported that exposure to soiled male bedding induced Fos protein immunoreactivity (Fos-IR) in significantly more neurons of the vomeronasal organ (VNO) and medial amygdala of gonadectomized, estradiol-treated female than male mice whereas no such sex difference was seen in the intervening mitral cells of the accessory olfactory bulb (AOB). We asked whether a sexually dimorphic functional response to male urinary pheromones might be revealed in AOB mitral cells that project specifically to the medial amygdala. Gonadectomized mice of both sexes were treated with estradiol and 3 days later received bilateral injections of the retrograde tracer, Cholera toxin-B (CTB) into the medial amygdala. Five days later male urine or saline was applied nasally to each subject 90 min prior to sacrifice, and sections of the AOB were processed for double-label fluorescent immunocytochemistry for Fos protein and CTB. In both the rostral and caudal AOB, there were significantly more double-labeled mitral cells in female than in male subjects following exposure to male urine. A sex difference in the responsiveness of VNO sensory neurons seen previously to male soiled bedding is reflected in a parallel sex difference in the responsiveness of AOB mitral cells when only AOB cells that project to the amygdala are examined and when male urine as opposed to soiled male bedding is used as the activating stimulus.