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PubMed1976

Action potential fatigue in nonmyelinated nerve fibers: garfish olfactory and rabbit vagus nerve.

A decrease in amplitude and conduction speed in the compound action potential is observed with time in gar olfactory and rabbit vagus nerve when it is stimulated between 4 and 15 Hz at 26 degrees C in vitro. The amplitude decays exponentially for 1-3 min before reaching a steady state. Recs 15 s for gar olfactory nerve and 50 s for rabbit vagus nerve. The steady state values are 14% and 36% of the original amplitude, respectively, and conduction speeds are reduced by 25 % in both nerves. The effect results from completion between ion flow during the action potential and active transport. The accumulation of K+ions and depletion of Na+ ions in the restricted extracellular space contributes to the amplitude fatigue while the depletion of Na+ ions alone causes the decrease in conduction speed. Ouabain increases the fatigue rate in both preparations, but more so for gar. The fatigue and recovery measurements may provide a useful method to investigate active pumping, including both the total pumping rate and the electrogenic component.

Action Potentials↗
PubMedDate not supplied

The risk of olfactory disturbance from conchal plate injury during ethmoidectomy.

BACKGROUND: Even though the olfactory function usually is improved or unchanged after ethmoidectomy, some patients complain of olfactory disturbance, which may be caused by direct injury to the olfactory nerves. However, the detailed anatomic pathway of the olfactory nerves that leave the olfactory mucosa and after going through the cribriform plate insert into the olfactory bulb is uncertain. In the studies of lateral nasal wall, we referred to the thin bone that connects the middle, superior, and supreme turbinates to the skull base as the "conchal plate." We undertook this study to determine the anatomic relation between the conchal plate and the olfactory nerve. METHODS: Ten midsagittal sections from adult cadaver head specimens were used for gross anatomy and the midportion of the conchal plate was taken and fixed in 10% formalin. The microscopic structures of the conchal plate were observed after hematoxylin and eosin staining. RESULTS: The olfactory nerves originated from the olfactory mucosa lining the middle and superior turbinates and ran upward within the bone of the conchal plate. These results suggest that the olfactory nerve may be injured inadvertently in the conchal plate during ethmoidectomy and that this injury is likely to be one of the possible causes of olfactory disturbance. CONCLUSION: We propose a possibility that injury to the conchal plate can affect olfactory function. Therefore, care should be taken to avoid damage to the conchal plate during ethmoidectomy.

Adult↗
PubMed1994

Olfactory pathways in three patients with cryptococcal meningitis and acquired immune deficiency syndrome.

The olfactory mucosa, bulbs and tracts were examined for the presence of Cryptococcus neoformans in 3 patients with the acquired immune deficiency syndrome (AIDS) and cryptococcal meningitis. Two of them had antibodies against HIV-1 and one had positive serology for HIV-2. Cryptococci were seen in the subarachnoid space around olfactory tracts and bulbs and in the submucosal olfactory nerve fascicles. In one case, olfactory nerve fascicles from the lamina propria were also affected. Olfactory epithelium and respiratory mucosa were not involved. We suggest that Cryptococcus reached the olfactory nerve fascicles through the olfactory pathways for cerebrospinal fluid drainage which might serve as a source of latent cryptococcal infection.

AIDS-Related Opportunistic Infections↗
PubMed2001

Seasonal changes in beta-endorphin-like immunoreactivity in the olfactory system of the female catfish, Clarias batrachus (Linn).

In the olfactory system of the catfish Clarias batrachus, beta-endorphin-like immunoreactivity was seen in several olfactory receptor neurons (ORN) and their fiber projections extending caudally over the olfactory nerve to the olfactory bulb (OB). With beta-endorphin-like immunoreactivity as a cellular marker, the olfactory system in the female fish was investigated at different stages of its annual reproductive cycle. The reproductive cycle of the fish is divisible into four distinct phases: preparatory (February-April), prespawning (May-June), spawning (July-August), and postspawning (September-January). The gonosomatic index and the immunocytochemical profile of beta-endorphin-like immunoreactivity showed distinct changes as the fish progressed from one phase to another. In the preparatory phase, limited immunoreactivity was seen in the periphery of the bulb. However, the immunoreactivity showed a robust increase as the immunolabeled fibers extended progressively deeper into the bulb toward the mitral cell layer during the prespawning and spawning phases. Significant reduction in the immunoreactivity was noticed in the olfactory nerve layer of the fish in the postspawning phase. Several granule cells showed poor to moderate immunoreactivity during the spawning phase, although no immunoreactivity was seen in the inner cell layer during the rest of the year. The beta-endorphin-like immunoreactivity in the ORN also showed season-related changes, although these were less distinct. Whereas weak immunoreactivity confined to a few ORN was noticed in the fish collected in the preparatory phase, those in the prespawning phase showed conspicuous augmentation in immunoreactivity. During the spawning phase, the sensory layer of the olfactory epithelium showed reduced, homogenous immunoreactivity. In the postspawning phase, several ORN revealed distinct granular immunoreactivity, suggesting possibilities of de novo synthesis. These annual cyclic changes in the beta-endorphin-like immunoreactivity were consistently observed over a 30-month study period that spanned three consecutive spawning phases. The results suggest that the beta-endorphin-containing ORN, their fiber projections to the OB, and several granule cells in the inner cell layer may be involved in the processing of reproduction/reproductive behavior-related signals.

Animals↗
PubMed1982

Immunohistochemical demonstration of serotonin nerve fibers in the olfactory bulb of the rat, cat and monkey.

The distribution of serotonin (5-HT) positive fibers in the olfactory bulb of the rat, cat and monkey was studied using the peroxidase-anti-peroxidase (PAP) immunohistochemical method and highly specific antibodies to 5-HT. In general, 5-HT fibers were present throughout all layers in the olfactory bulb of these species except for the olfactory nerve layer and different as well as restricted laminar patterns of 5-HT distribution were observed. There were also species-related differences in the pattern of 5-HT distribution, in each layer. The most notable species difference was apparent in the glomerular layer of the main olfactory bulb. In case of the rat and cat, a very dense plexus of 5-HT fibers was observed to be diffuse in the glomerulus, while in the monkey, the distribution of 5-HT fibers was scanty and partial, as was seen in the accessory olfactory bulb of the rat.

Animals↗
PubMed1984

Three distinct morphological classes of receptors in fish olfactory organs.

Three morphologically distinct classes of receptor-neurons are proposed: (1) type I ciliar cells, (2) microvillar cells and (3) type II ciliar cells. Retrograde transport of horseradish peroxidase by axons in the olfactory nerve to the olfactory organs of goldfish (Carassius auratus) and channel catfish (Ictalurus punctatus) provided evidence that these axon-bearing cells are present in the organs of both species. Goldfish olfactory organs were also studied with scanning electron microscopy, dissociated with papain for isolated cell preparations, and processed for ultrastructural localization of acid phosphatase activity. Type I ciliar cells are similar to ciliar olfactory receptors found in all vertebrate classes. Microvillar cells are present in the olfactory organs of most fishes and in the tetrapod vomeronasal organ. In goldfish and catfish, type I ciliar and microvillar cells are concentrated on the inner third of each lamella, nearest to the median raphe. Type II ciliar cells have often been described as respiratory-type or ciliated nonsensory cells. They are structurally similar to respiratory epithelial cells in the nasal cavities of tetrapods and have motile cilia that beat synchronously, indicative of their role in mediating fluid flow over the olfactory epithelium. In goldfish they occur singly and in aggregates throughout the organ. In catfish they are segregated from type I ciliar and microvillar cells on the outer two-thirds of each lamella. In goldfish and catfish they have axons that pass through the olfactory nerve to the olfactory bulb; hence, they are receptor-neurons as well as analogous to respiratory epithelium. In addition to the three receptor types described above, cells resembling receptors with rodlike distal processes were seen filled with horseradish peroxidase and observed with scanning and transmission electron microscopy. Cells of similar structure have been documented elsewhere, often called "rod cells," and sometimes considered a separate receptor type in fishes. In this study, a number of rodlike processes were found with their ciliar or microvillar components partially fused. High levels of acid phosphatase activity were localized to these processes, and examples were found that corresponded to each of the three receptor types. Olfactory receptor turnover is believed to persist through life. The evidence presented supports the hypothesis that fusion of their dendritic apical processes marks an early stage of receptor cell senescence.

Acid Phosphatase↗
PubMed2005

Differential expression of neurofilament 200-like immunoreactivity in the main olfactory and vomeronasal systems of the Japanese newt, Cynops pyrrhogaster.

Expression of neurofilament 200 (NF200)-like immunoreactivity was examined in the main olfactory system and the vomeronasal system of the Japanese newt, Cynops pyrrhogaster, using anti-porcine NF200 monoclonal antibody (clone N52) to investigate the differences in phenotypical characteristics between these systems. The entire nasal cavity was a flattened single chamber consisting of the main nasal chamber (MNC) and the lateral nasal sinus (LNS) communicating with each other. The olfactory epithelium (OE) was present in the MNC, and the vomeronasal epithelium (VNE) was in the LNS. The OE possessed only a small number of NF200-like immunoreactive receptor neurons. The olfactory nerve and the olfactory nerve layer of the main olfactory bulb also contained a small number of NF200-like immunoreactive axons. In contrast, the VNE possessed many NF200-like immunoreactive receptor neurons. The vomeronasal nerve and the vomeronasal nerve layer of the accessory olfactory bulb contained many NF200-like immunoreactive axons. These findings in the Japanese newt indicate that NF200-like immunoreactive receptor neurons constitute a major subpopulation in the VNE and a minor subpopulation in the OE. In addition, NF200-like immunoreactivity seems to be a useful marker to distinguish the vomeronasal system from the other nervous systems including the main olfactory system in the Japanese newt. The localization of a few NF200-like immunoreactive receptor neurons in the OE might indicate that pheromone-sensitive receptor neurons are intermingled in the OE of the Japanese newt.

Animals↗
PubMed2003

Heterogeneous expression of connexin 36 in the olfactory epithelium and glomerular layer of the olfactory bulb.

Gap junctions regulate a variety of cell functions by directly connecting two cells through intercellular channels. Connexins are gap junction channel-forming protein subunits. In this study, we studied the expression of connexin 36 (Cx36) in the olfactory epithelium and olfactory bulb of adult mice. In situ hybridization revealed that mRNA for Cx36 was expressed in the olfactory sensory epithelium, main olfactory bulb and accessory olfactory bulb. Expression of mRNA encoding Cx36 was observed in the olfactory epithelium mainly in ventral and lateral regions of the turbinates. Immunohistochemical determination of Cx36 protein expression showed sparse punctuate staining in the olfactory epithelial layer. Intense Cx36-like immunostaining was found in the olfactory nerve bundles underlying the olfactory epithelium and in the olfactory nerve layer and glomerular layer of the olfactory bulb. Mapping of the intensity of Cx36-like immunofluorescence in glomeruli throughout the main olfactory bulb indicated a heterogeneous distribution. A set of approximately 50 glomeruli located in the anterior and posterior limits of the olfactory bulb was more intensely labeled than other glomeruli. There was intense immunofluorescence signal in the glomerular layer of the accessory olfactory bulb and in the vomeronasal nerve. beta-Galactosidase distribution in the olfactory epithelium and olfactory bulb in Cx36 knockout mice (Deans et al. [2001] Neuron 31:477-485) supported the findings with immunofluorescence. Cx36-like immunofluorescence was absent in the olfactory nerve bundles in Cx36 knockout mice. The immunolocalization of Cx36 to the olfactory and vomeronasal nerves, and a subset of olfactory glomeruli suggest a functional role for Cx36 in odor coding.

Animals↗
PubMed2002

Migration of LHRH neurons into the spinal cord: evidence for axon-dependent migration from the transplanted chick olfactory placode.

In the chick embryo, luteinizing hormone-releasing hormone (LHRH) neurons originate in the olfactory placode and migrate along the olfactory nerve to the forebrain. In previous studies, we demonstrated that LHRH neurons followed the trigeminal nerve when the olfactory nerve was physically interrupted. To examine whether LHRH neurons possess the capacity to migrate along the different type of axons, the olfactory placode was transplanted into the base of the forelimb. Three to five days after the transplantation, LHRH neurons were detectable in the spinal nerve, the dorsal root ganglion, the sympathetic ganglion and the spinal cord. Double or triple labelling studies for LHRH, somatostatin and/or axonin-1 showed that LHRH neurons entered the spinal nerve in contact with the olfactory axons, which are specifically immunoreactive to somatostatin. Migrating LHRH neurons continued to associate closely with the olfactory axons in the spinal nerve. However, some LHRH neurons often migrated along with the axonin-1 positive spinal sensory axons, maintaining a distance from the olfactory axons. Furthermore, a few LHRH neurons were observed in the ventral root and the ventral funiculus independent of olfactory axons. As LHRH neurons were observed in the motor component of the spinal nerve, it is probable that LHRH neurons also invaded the spinal cord using the motor axons as a guiding substrate for their migration. These results suggest that the migration mode of LHRH neurons is axon dependent in the peripheral region, however, chemical identity with regard to axonal substrate choice for migration was not specified in the present study.

Animals↗
PubMed1999

Beta-endorphin-like immunoreactivity in the forebrain and pituitary of the teleost Clarias batrachus (Linn.).

The organization of beta-endorphin-like immunoreactivity in the olfactory system, forebrain, and pituitary of the teleost Clarias batrachus was investigated. Immunoreactivity was prominently seen in the sensory neurons and basal cells in the olfactory epithelium and in some cells in the periphery and center (granule cells) of the olfactory bulb. Immunoreactive fibers in the olfactory nerve enter the olfactory nerve layer of the olfactory bulb and branch profusely to form tufts organized as spherical neuropils in the glomerular layer. While fascicles of immunoreactive fibers were seen in the medial olfactory tracts, the lateral olfactory tracts showed individual immunoreactive fibers. Immunoreactive fibers in the medial olfactory tract extend into the telencephalon and form terminal fields in discrete telencephalic and preoptic areas; some immunoreactive fibers decussate in the anterior commissure, while others pass into the thalamus. While neurons of the nucleus lateralis tuberis revealed weak immunoreactivity, densely staining somata were seen at discrete sites along the wall of the third ventricle. Although a large population of immunoreactive cells was seen in the pars intermedia of the pituitary gland, few were seen in the rostral pars distalis and proximal pars distalis; immunoreactive fibers were seen throughout the pituitary gland.

Animals↗
PubMed1997

The central pathway of primary olfactory axons is abnormal in mice lacking the N-CAM-180 isoform.

Although N-CAM has previously been implicated in the growth and fasciculation of axons, the development of axon tracts in transgenic mice with a targeted deletion of the 180-kD isoform of the neural cell adhesion molecule (N-CAM-180) appears grossly normal in comparison to wild-type mice. We examined the organization of the olfactory nerve projection from the olfactory neuroepithelium to glomeruli in the olfactory bulb of postnatal N-CAM-180 null mutant mice. Immunostaining for olfactory marker protein revealed the normal presence of fully mature primary olfactory neurons within the olfactory neuroepithelium of mutant mice. The axons of these neurons form an olfactory nerve, enter the nerve fiber layer of the olfactory bulb, and terminate in olfactory glomeruli as in wild-type control animals. The olfactory bulb is smaller and the nerve fiber layer is relatively thicker in mutants than in wild-type mice. Previous studies have revealed that the plant lectin Dolichos biflorus agglutinin (DBA) clearly stains the perikarya and axons of a subpopulation of primary olfactory neurons. Thus, DBA staining enabled the morphology of the olfactory nerve pathway to be examined at higher resolution in both control and mutant animals. Despite a normal spatial pattern of DBA-stained neurons within the nasal cavity, there was a distorted axonal projection of these neurons onto the surface of the olfactory bulb in N-CAM-180 null mutants. In particular, DBA-stained axons formed fewer and smaller glomeruli in the olfactory bulbs of mutants in comparison to wild-type mice. Many primary olfactory axons failed to exit the nerve fiber layer and contribute to glomerular formation. These results indicate that N-CAM-180 plays an important role in the growth and fasciculation of primary olfactory axons and is essential for normal development of olfactory glomeruli.

Animals↗
PubMed1986

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.

Animals↗
PubMed2004

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.

Animals↗
PubMed1998

Distribution of neuronal intermediate filament proteins in the developing mouse olfactory system.

The distribution of neuronal intermediate filament proteins in the developing mouse olfactory bulb and olfactory epithelium was characterized by immunocytochemical approach. Antibodies against alpha-internexin, neurofilament triplet proteins (NFTPs; NF-L, NF-M, and NF-H) and peripherin were used to determine their expression at different developmental stages. Alpha-internexin and peripherin were first found to be co-localized in the olfactory neuroepithelium during early development. At the perinatal stage, expression patterns of alpha-internexin and peripherin are distinguishable by spatial and temporal manner: peripherin is predominantly expressed in the olfactory nerves; whereas alpha-internexin is expressed in both olfactory nerves and olfactory bulb. Our observation suggests that peripherin as well as alpha-internexin may play some roles in the process formation of olfactory nerves during development. In the developing olfactory periglomerulus, alpha-internexin was found around postnatal Day 3, whereas NFTPs were not observed until postnatal Day 7. Our data showed that the expression of alpha-internexin preceded those of the NFTPs in most neurons of the developing olfactory bulb. Some small neurons in the adult olfactory bulb were uniquely labeled with antibody to alpha-internexin. Our results suggest that alpha-internexin may play a functional role in the neuronal cytoarchitecture of developing olfactory system, and can be a neuronal marker for detecting postmitotic migrating neurons in the adult olfactory bulb.

Animals↗
PubMed1992

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.

Animals↗
PubMed2004

Differential expression of cadherins in the developing and adult zebrafish olfactory system.

Cadherins are cell adhesion molecules that play important roles in development of a variety of tissues and maintenance of adult structures. Although cadherin expression has been studied in detail in the central nervous system of several vertebrate species, little is known of their distribution in the developing and adult olfactory structures, and there is no published report, to our knowledge, of cadherin expression in fish olfactory system. In this study, we examined expression patterns of three cadherins, cadherin-1 (E-cadherin), cadherin-2 (N-cadherin), and cadherin-4 (R-cadherin), in the olfactory system of developing and adult zebrafish by using both in situ hybridization and immunocytochemical methods. Cadherin-1 is detected in the newly formed olfactory placode, and its expression is maintained in the developing and adult olfactory epithelium and olfactory nerve. Cadherin-2 is expressed in the olfactory epithelium, olfactory nerve, and olfactory bulb of the embryonic and larval zebrafish, and its expression is reduced in the adult olfactory system. In contrast to the cadherin-1 and cadherin-2 expression, cadherin-4 is not found in the olfactory epithelium, but it is detected in the larval and adult olfactory bulb, in the olfactory tract, and its targets in the telencephalon. We hypothesize that the differential expression of these three cadherins in the developing zebrafish major olfactory structures reflects functionally different roles in the development of the vertebrate olfactory system.

Age Factors↗
PubMed1994

Olfactory ensheathing glia and platelet-derived growth factor B-chain reactivity in the transplanted rat olfactory bulb.

Using a monoclonal antibody against the B-chain of platelet-derived growth factor as a marker, we have examined the behavior of olfactory ensheathing glia in the normal and transplanted rat olfactory bulb. In the normal postnatal olfactory bulb, these glia are found to ensheath the bundles of incoming primary olfactory nerve fibers as well as those in the olfactory nerve layer. Olfactory marker protein antibody was used to identify the olfactory nerve proper. Within the transplant, the same glia: (1) ensheath bundles of both primary olfactory and non-primary olfactory axons, (2) ensheath axonal bundles deep within the donor tissue, and (3) eventually permit radiation of individual axons from bundles to surrounding neuropil. We believe that ensheathing glia (being rich in growth-related factors and extracellular matrix molecules) may be useful in providing trophic support and guidance for the reconstruction of developmentally or traumatically damaged neuronal pathways not directly related to the olfactory system. The evidence presented here indicates that ensheathing glia are capable of existing in deep brain areas and ensheathing other than primary olfactory axons. The special molecular characteristics of these glia along with the morphological findings presented here provide a foundation for further studies of these unique glia and their potential utility in the restoration of damaged neural pathways.

Animals↗
PubMed2003

Olfactory sensitivity of the gilthead seabream (Sparus auratus L) to conspecific body fluids.

The potential for intraspecific chemical communication in the gilthead seabream (a marine perciform) was investigated by assessing the olfactory sensitivity to conspecific body-fluids (water occupied by conspecifics, intestinal fluid, urine, semen, egg fluid) by multiunit electrophysiological recording from the olfactory nerve. The olfactory system was responsive to water previously occupied by conspecifics, and the active compound(s) could be extracted by solid-phase extraction. The olfactory system was extremely sensitive to body fluids of sexually mature conspecifics: thresholds of detection were 1:10(7.4) (intestinal fluid), 1:10(6.1) (gametes), and 1:10(4.2) (urine). The olfactory system was also sensitive to amino acids with thresholds of detection from 10(-8.1) M (L-leucine) to 10(-6.1) M (L-phenylalanine). However, a range of other known fish odorants (steroids, bile acids, and prostaglandins) failed to evoke significant responses. Given the high olfactory sensitivity to intestinal fluid and the low urine release rates of marine compared with freshwater fish, we suggest that chemical communication is likely to be mediated via compounds present in the intestinal fluid rather than urine. Furthermore, the types of chemicals involved are likely to be different from those of freshwater fish. Their exact chemical identity and biological roles remain to be established.

Animal Communication↗