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PubMed1989

Olfaction in schizophrenia.

It was hypothesised that schizophrenic patients tested for olfactory discrimination would show a left nostril deficit. 15 tested were slightly but not significantly better than a control group of 15.

Adult↗
PubMed2002

Brain imaging studies of the functional organization of human olfaction.

It is believed that sensory functions are organized in a hierarchical and parallel manner. The sense of smell differs in several aspects from other senses: odors can immediately elicit emotional evocations, they are remembered after a long time, and they are difficult to label. This raises the question of whether odorous stimuli may be processed differently from the other sensory stimuli. New data from brain imaging studies suggest that this is not the case and that the specific characteristics of the sense of smell can be attributed to the engagement of limbic structures at an early stage in the signal processing.

Animals↗
PubMed2005

Her odours make him deaf: crossmodal modulation of olfaction and hearing in a male moth.

All animals have to cope with sensory conflicts arising from simultaneous input of incongruent data to different sensory modalities. Nocturnal activity in moths includes mate-finding behaviour by odour detection and bat predator avoidance by acoustic detection. We studied male moths that were simultaneously exposed to female sex pheromones indicating the presence of a potential mate, and artificial bat cries simulating a predation risk. We show that stimulation of one sensory modality can modulate the response to information from another, suggesting that behavioural thresholds are dynamic and depend on the behavioural context. The tendency to respond to bat sounds decreased as the quality and/or the amount of sex pheromone increased. The behavioural threshold for artificial bat cries increased by up to 40 dB when male moths where simultaneously exposed to female sex pheromones. As a consequence, a male moth that has detected the pheromone plume from a female will not try to evade an approaching bat until the bat gets close, hence incurring increased predation risk. Our results suggest that male moths' reaction to sensory conflicts is a trade-off depending on the relative intensity of the input to CNS from the two sensory modalities.

Acoustic Stimulation↗
PubMed1994

Transduction diversity in olfaction.

Odors are powerful stimuli that can focus the attention, elicit behaviors (or misbehaviors) and even resurrect forgotten memories. These actions are directed by the central nervous system, but they depend upon the initial transduction of chemical signals by olfactory receptor neurons. Electrophysiological recordings suggest that the responses of olfactory receptor neurons to odors are more diverse than was initially believed, being mediated by effects on several different conductances. Both excitatory and inhibitory responses are produced by these effects and some, if not all, odors can affect more than one component of the membrane conductance. The extent of this diversity is reviewed here, and its impact on our understanding of odor discrimination is discussed.

Animals↗
PubMed1996

Temporal resolution in olfaction: stimulus integration time of lobster chemoreceptor cells

The stimulus integration time of lobster olfactory receptor cells in situ was determined using extracellularly recorded spiking responses from receptor cells and on-line high-resolution measurement of odor square pulses. At a fixed odor concentration, odor steps of 200 ms duration elicited maximum responses; shorter odor steps did not drive the cells to their maximum response and longer odor steps added spikes but did not result in higher firing rates. Excitatory processes peaked within 220 ms of stimulus onset. At 160­300 ms, stimulus intensity discrimination was most evident. Adaptation processes reduced response magnitude to near-zero levels within 1000 ms of stimulus onset. Olfactory receptor cells thus resolve odor peak onsets within the first few hundred milliseconds: this time window corresponds to the 4­5 Hz frequency of olfactory sampling (i.e. 'sniffing') as well as the rapid fluctuations in odor concentration that are common in natural odor plumes. The stimulus integration time of 200 ms may play a role in the filtering of information used by lobsters to orient to distant odor sources.

Journal Article↗
PubMed1996

Olfaction and prey search in the carnivorous leech Haemopis marmorata

Haemopis marmorata, the green horse leech, is carnivorous and readily eats earthworms. Using a Y-maze with flowing water, we show that specimens of H. marmorata are attracted to live earthworms. Ablating the dorsal lip, the presumed site of the chemoreceptors that this species uses in prey search, disrupts the ability of the leeches to find the earthworms in the Y-maze. Earthworm wash, a preparation of the collagen coating of earthworm skin, shock-induced earthworm secretion, mammalian blood and a salt­arginine mixture are not attractive to the green horse leech. The tails of freshly killed earthworms are attractive to the leeches, but tails from worms killed 8­12 h previously and stored cold are not. Our conclusion is that the earthworms produce a metabolite that attracts the leeches.

Journal Article↗
PubMed1997

Perireception in olfaction: molecular mass sieving by aesthetasc sensillar cuticle determines odorant access to receptor sites in the Caribbean spiny lobster Panulirus argus.

The responsiveness of chemoreceptor neurons depends on a combination of perireceptor and receptor events. Olfactory neurons of crustaceans are packaged into distinctive cuticular sensilla called aesthetascs. The cuticle of aesthetascs is thin and permeable, even though it does not contain any obvious surface pores or pore tubules. This suggests that this 'spongy' aesthetasc cuticle may act as a molecular sieve that restricts large odorant molecules from entering the sensilla and binding to the olfactory neurons. We examined whether this is so for the aesthetasc cuticle of the Caribbean spiny lobster Panulirus argus. We used a chromatographic column packed with aesthetasc cuticle and connected to a flow-through ultraviolet spectrophotometer to measure the elution times of ultraviolet-absorbent molecular mass markers between 165 and 2 x 10(6) Da. Molecules larger than approximately 8.5 kDa had similar elution times, indicating that they did not penetrate the cuticle. Molecules smaller than 8.5 kDa had longer elution times that were directly and inversely proportional to their molecular mass. These results suggest that aesthetasc cuticle excludes molecules larger than 8.5 kDa from having access to the olfactory receptor neurons. We conclude that the molecular sieving capacity of the aesthetasc cuticle of P. argus is a perireceptor mechanism that is a critical determinant of the types of molecules capable of stimulating its olfactory receptors.

Animals↗
PubMed1997

Perireceptor mechanisms sustaining olfaction at low salinities: insight from the euryhaline blue crab Callinectes sapidus

As the blue crab Callinectes sapidus moves from sea water to fresh water, the 'exposed' chemosensory dendrites in the olfactory sensilla (aesthetascs) undergo changes in length that are positively correlated with environmental salinity. In this study, we demonstrate the following. (1) The responses of the olfactory receptor cells of freshwater-acclimated crabs are reduced relative to those of seawater-acclimated animals, but increase with a time course comparable to the increase in dendrite length when these crabs are transferred to sea water. (2) The olfactory response of seawater-acclimated crabs is lost and the chemosensory dendrites osmotically ablated if the aesthetascs are acutely exposed to low salinity. However, maintaining iso-osmotic conditions with mannitol preserves both the physiological response and the structural integrity of the dendrites. (3) The flux of [14C]thiocyanate and 22Na between the hemolymph and sensillar lymph of the aesthetascs indicates continuity between these fluid compartments. (4) There is a net efflux of Na+ from the hemolymph through the aesthetascs in freshwater-acclimated crabs, and measurements of electrical potential across the antennules suggest that this efflux largely derives from passive diffusion. (5) Dendrites in the aesthetascs of crabs acclimated to brackish water are intermediate in length between those of freshwater- and seawater-acclimated animals. Together, our findings suggest that, at low salinities, the efflux of Na+ (and probably other ions) from the hemolymph generates an ionic/osmotic microenvironment within the aesthetascs that sustains the structural and functional integrity of the olfactory dendrites. We propose that the length of these dendrites, and consequently the olfactory response, is constrained by the distance over which this microenvironment can be effectively maintained.

Journal Article↗
PubMed2000

Sustaining olfaction at low salinities: mapping ion flux associated with the olfactory sensilla of the blue crab Callinectes sapidus.

To test the hypothesis of a diffusion-generated, ionic/osmotic microenvironment within the olfactory sensilla (aesthetascs), flux gradients of Ca(2+) and K(+) associated with the external surfaces of these sensilla were spatially mapped using self-referencing, ion-selective microelectrodes. Blue crabs (Callinectes sapidus) acclimated to low-salinity conditions (15% sea water and fresh water) showed a net efflux of ions from the aesthetascs. The region of maximum flux associated with each aesthetasc conformed to that predicted from structural data and corresponded to the permeable region of the cuticle separating the olfactory dendrites from the external environment. Estimates of net flux from the entire tuft of aesthetascs for both Ca(2+) and K(+) fell within the predicted range on the basis of comparisons with (22)Na(+) flux measured previously and assuming a passive diffusion model of ion movement from the hemolymph to the sensillar lymph and, ultimately, to the external environment. The maximum concentrations of these ions measured deep within the tuft are discussed in the light of a potential across the aesthetascs that may limit ion efflux at low salinities.

Animals↗
PubMed1988

The relationship between nasal anatomy and human olfaction.

The relationship between nasal anatomy and olfactory ability was evaluated by correlating measurements from nasal cavity CT scans with the results of an established clinical measure of olfactory function (Odorant Confusion Matrix, or OCM). The most appropriate mathematical model of this relationship was developed by analyzing the logarithms of 30 anatomical measures and a logistic transform of the OCM percent correct score. Two nasal cavity regions were found to be the most important factors in accounting for the olfactory test results, with a third region modifying the effects of the first two. The results of this study suggest that nasal anatomy may play a role in controlling the access of an odorant to the olfactory receptor area. The conclusions of this study have implications for nasal surgeons who, when possible, should make attempts to repair or preserve these nasal regions which seem to be so important to olfactory function.

Humans↗
PubMed1994

The effect of human olfactory biopsy on olfaction: a preliminary report.

Normal human olfactory function is subject to a wide variety of factors. Although biopsy of human olfactory neuroepithelium has been reported by several researchers, there are no studies which have evaluated the effect of this procedure on olfactory function. In this retrospective study, we sought to determine if tissue removal from the olfactory cleft has an adverse influence on the sense of smell. Nineteen subjects underwent bilateral olfactory testing and subsequent endoscopic olfactory mucosal biopsy. All subjects were retested 6 weeks to 1 year after olfactory neuroepithelial biopsy. No statistical difference was found between olfactory tests performed before or after biopsy. These data suggest that biopsy of human olfactory neuroepithelium has no discernible adverse effect on the ability to smell.

Alzheimer Disease↗
PubMed2004

Olfaction in olfactory bulbectomized rats.

Experimental rats had their right olfactory bulb removed on postnatal day 2 (P2) and their left olfactory bulb removed on P90. Control rats had one or both olfactory bulbs removed on P90. Before and after their adult-stage surgery, rats were trained using olfactometry and operant conditioning to detect and discriminate odors. Anterograde transport of horseradish peroxidase applied to the olfactory epithelium revealed numerous axons of olfactory sensory neurons in the right hemisphere of 27 experimental rats. These axons terminated in glomerular-like clusters within the frontal neocortex (n = 5) or anterior olfactory nucleus with some axons extending into the subventricular epithelium (n = 22). Seventeen of the experimental rats were able to detect a variety of odors and to discriminate between odors. Performance accuracy was related to the location and density of these anomalous inputs; experimental rats with inputs confined to frontal neocortex and those lacking any inputs to the forebrain were anosmic, as were adult-operated bilaterally bulbectomized rats. Our results provide strong support for the contention that, in the absence of the olfactory bulbs, olfactory connections to novel forebrain sites can support both odor detection and odor discrimination.

Animals↗
PubMed2006

The role of the amygdala and olfaction in unconditioned fear in developing rats.

Early in ontogeny, young rats must be able to detect dangerous stimuli and to exhibit appropriate defensive behaviors. Different nuclei of the amygdala mediate unconditioned and conditioned fear responses to threat in adult rats. The aim of this study was to determine the role of the amygdala in unlearned fear behavior in young rats. When exposed to an unfamiliar adult male rat, preweaning rat pups freeze, with peak levels on postnatal day 14 and declining levels on day 18. Pups were made anosmic to block olfactory input to the amygdala, and amygdala activation was assessed by quantifying the neuronal marker c-fos. Anosmic pups did not freeze in the presence of the male rat and had decreased c-fos expression in the medial amygdala on day 14 and in the medial and lateral amygdala on day 18. However, the decrease in freezing between days 14 and 18 was not associated with a decrease in c-fos expression in the medial amygdala. The medial and lateral amygdala were then inactivated by local muscimol infusion on day 14. Muscimol infusion into the medial amygdala decreased freezing to the male rat but not to a loud noise, whereas infusion into the lateral amygdala blocked freezing to a loud noise but not to the male. These findings indicate that different nuclei of the amygdala process sensory information of different modalities, mediate unconditioned freezing, and may be involved in developmental changes in the fear response in young rats.

Amygdala↗