Chemosensory function and dysfunction

Taste and smell are fundamental sensory systems essential in nutrition and food selection, for the hedonic and sensory experience of food, for efficient metabolism, and, in general, for the maintenance of a good quality of life. The gustatory and olfactory systems demonstrate a diversity of transduction mechanisms, and during the last decade, considerable progress has been made toward our understanding of the basic mechanisms of taste and smell. Understanding normal chemosensory function helps clarify the molecular events that underlie taste and smell disorders. At least 2,000,000 Americans suffer from chemosensory disorders--a number that is likely to grow as the aging segment of the population increases. Smell disorders are more frequent than taste disturbances, due to the vulnerability and anatomical distinctiveness of the olfactory system, and because a decline in olfactory function is part of the normal aging process. Common gustatory and olfactory complaints are due to a number of medications, to upper respiratory infections, to nasal and paranasal sinus diseases, and to damage to peripheral nerves supplying taste and smell. Most chemosensory complaints have an identifiable cause. Although diagnosis of taste and smell disorders has improved considerably over the last two decades, treatment of these disorders is still limited to conditions with discernible and reversible causes. Future research is needed for a better understanding of chemosensory mechanisms, establishing improved diagnostic procedures, and disseminating knowledge on chemosensory disorders among practitioners and the general public.     

What are affects?

In an attempt to answer the question, "what is affect?", this paper considers Freud's metapsychological formulation in the light of recent developments in psychoanalysis and neuroscience. It argues that the problem of affect-perhaps more than any other-forces us to acknowledge the intrinsic connexion between mind and body, and to accommodate it in our theoretical formulations. A review of the problem from this point of view leads to the following formulation: affect is a primary sensory modality, analogous to the senses of vision, hearing, somatic sensation, taste, and smell. These modalities are the elementary constituents of the envelope of consciousness, from which it is impossible to free ourselves. Whereas the sensory modalities of vision, hearing, somatic sensation, taste, and smell represent aspects of the external object world ("unknowable" in itself), affect is the primary sensory modality through which we perceive as aspect of the internal world of the subject ("unconscious" in itself).     

Mutations in a cyclic nucleotide-gated channel lead to abnormal thermosensation and chemosensation in C. elegans

The C. elegans tax-4 mutants are abnormal in multiple sensory behaviors: they fail to respond to temperature or to water-soluble or volatile chemical attractants. We show that the predicted tax-4 gene product is highly homologous to vertebrate cyclic nucleotide-gated channels. Tax-4 protein expressed in cultured cells functions as a cyclic nucleotide-gated channel. The green fluorescent protein (GFP)-tagged functional Tax-4 protein is expressed in thermosensory, gustatory, and olfactory neurons mediating all the sensory behaviors affected by the tax-4 mutations. The Tax-4::GFP fusion is partly localized at the sensory endings of these neurons. The results suggest that a cyclic nucleotide-gated channel is required for thermosensation and chemosensation and that cGMP is an important intracellular messenger in C. elegans sensory transduction.     

Influence of smell loss on taste function.

The influence of damage to one sensory system on the functioning of other sensory systems has been of scientific interest for over a century. Recently it has been suggested that damage to the olfactory system (CN I) decreases the ability to taste; that is, to perceive sweet, sour, bitter and salty sensations via CN VII, IX, and X. If true, this would be in contrast to most other sensory systems, where compromise typically leads to either cross-modal enhancement of function or to no effects at all. In the present study, data from both regional and whole-mouth taste tests of 581 patients presenting to a smell and taste center with varying degrees of olfactory function were evaluated to address whether olfactory loss is associated with taste loss. No significant influence of olfactory dysfunction on any measure of taste perception was found when the effects of sex, age, and etiology were controlled. These data suggest that smell loss, per se, has no meaningful influence on taste function, and that clinical associations between smell and taste dysfunction, when observed, likely reflect comorbid influences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Award for Distinguished Scientific Early Career Contributions to Psychology: Paul A. S. Breslin.

Presents a citation for Paul A. S. Breslin, who received the 2001 Award for Distinguished Scientific Early Career Contributions to Psychology, "for innovative and definitive work in the chemical senses: taste, smell, and chemesthesis." A biography and selected bibliography accompany the citation. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Olfactory associative learning in Caenorhabditis elegans is impaired in lrn-1 and lrn-2 mutants.

The C. elegans mutants, lrn-1 and lrn-2, are impaired in associative learning using conditioned taste cues. Both mutants are defective in associative learning about appetitive and aversive events, indicating that lrn-1 and lrn-2 exert effects across motivational boundaries. In a new olfactory associative learning paradigm, in which wild type worms learn to avoid a previously attractive diacetyl odor after it has been paired with an aversive acetic acid solution, lrn-1 and lrn-2 are impaired. Although defective in associative learning using a conditioned olfactory cue, nonassociative learning (habituation and dishabituation) using this same olfactory cue is unaffected. The discovery that lrn-1 and lrn-2 are defective in associative learning with both taste and olfactory cues may suggest that associative learning in different sensory modalities converges on a common genetic pathway in C. elegans that is subserved by lrn-1 and lrn-2. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two heteromeric kinesin complexes in chemosensory neurons and sensory cilia of Caenorhabditis elegans

Chemosensation in the nervous system of the nematode Caenorhabditis elegans depends on sensory cilia, whose assembly and maintenance requires the transport of components such as axonemal proteins and signal transduction machinery to their site of incorporation into ciliary structures. Members of the heteromeric kinesin family of microtubule motors are prime candidates for playing key roles in these transport events. Here we describe the molecular characterization and partial purification of two heteromeric kinesin complexes from C. elegans, heterotrimeric CeKinesin-II and dimeric CeOsm-3. Transgenic worms expressing green fluorescent protein driven by endogenous heteromeric kinesin promoters reveal that both CeKinesin-II and CeOsm-3 are expressed in amphid, inner labial, and phasmid chemosensory neurons. Additionally, immunolocalization experiments on fixed worms show an intense concentration of CeKinesin-II and CeOsm-3 polypeptides in the ciliated endings of these chemosensory neurons and a punctate localization pattern in the corresponding cell bodies and dendrites. These results, together with the phenotypes of known mutants in the pathway of sensory ciliary assembly, suggest that CeKinesin-II and CeOsm-3 drive the transport of ciliary components required for sequential steps in the assembly of chemosensory cilia.     

Human thalamic nucleus mediating taste and multiple other sensations related to ingestive behavior

Until now, taste was the only primary sensory modality for which the human central nervous system pathways were unknown. We report sensations evoked by stimulation at microampere current levels in the region of the human thalamic nucleus (ventralis caudalis parvocellularis internis) corresponding to the monkey taste relay nucleus. Stimulation in this region during awake neurosurgical procedures evoked special visceral/somatic (taste/pungent smell), general visceral (fullness of a hollow viscus), as well as painful and nonpainful general somatic sensations. General somatic or visceral sensation was evoked by stimulation at 80% of sites where special visceral/somatic sensation was evoked. These results suggest that primate taste relay mediates multiple sensations in addition to taste.     

Functional and molecular characterization of individual olfactory neurons

To gain an understanding of the olfactory signal transduction process, individual chemosensory neurons have been assessed for odor-induced Ca2+ responses and the molecular elements of transduction cascades using Ca2+ imaging technique in combination with single-cell RT-PCR approaches. It has been demonstrated that responsiveness of cells to cyclic AMP or inositol trisphosphate odorants was blocked by specific adenylyl cyclase inhibitors or phospholipase C inhibitors, respectively. Using specific primers in single-cell RT-PCR analysis, olfactory marker protein, two G protein subtypes (G(olf) and G(o)), and adenylyl cyclase (subtype III) and a phospholipase C (phospholipase Cbeta2-related subtype) were identified. For a subpopulation of sensory neurons it was demonstrated that both transduction cascades coexist and are active in the same cell. These data support the notion that two second messenger pathways are active in olfactory sensory neurons and emphasize the concept of dual transduction cascades in olfaction.     

OSM-9, a novel protein with structural similarity to channels, is required for olfaction, mechanosensation, and olfactory adaptation in Caenorhabditis elegans

Although cyclic nucleotide-gated channels mediate sensory transduction in olfaction and vision, other forms of sensory transduction are independent of these channels. Caenorhabditis elegans cyclic nucleotide-gated channel mutants respond normally to some olfactory stimuli and to osmotic stimuli, suggesting that these chemosensory responses use an alternative sensory transduction pathway. One gene that may act in this pathway is osm-9, which is required for each of these responses as well as a mechanosensory response to nose touch. osm-9 encodes a protein with ankyrin repeats and multiple predicted transmembrane domains that has limited similarity to the Drosophila phototransduction channels transient receptor potential (TRP) and TRP-like (TRPL). The sequence of OSM-9 and other TRP-like genes reveals a previously unsuspected diversity of mammalian and invertebrate genes in this family. osm-9 is required for the activity of the predicted G-protein-coupled odorant receptor ODR-10, which acts in the AWA olfactory neurons; its similarity to other G-protein-regulated transduction channels suggests that OSM-9 is involved in AWA signaling. osm-9:: GFP fusion genes are expressed in a subset of chemosensory, mechanosensory, and osmosensory neurons. osm-9 also affects olfactory adaptation within neurons that require the cyclic nucleotide-gated channel for olfaction; in these neurons, the gene has a regulatory function and not a primary role in sensory transduction.     

The afferent code for sensory quality.

"Many of the more recent findings in sensory psychology and physiology derive from the application of electrophysiology to the study of sensory processes." Experiments involving the taste sense and utilizing the recording and amplifying of nerve impulse traffic in sensory fibers "en route" to the brain are reviewed, and their general implications for the theory of afferent coding are discussed. An important principle of sensory coding is that "the same afferent fiber may convey different information depending upon the amount of activity in another parallel fiber." The relative rather than the absolute amount of activity in any one set of afferent fibers may determine the quality of sensation. "It is not only the activity in parallel fibers that is important, it is the relative amount of such parallel activity. Studies of the other senses indicate that these principles are not unique to taste." 21 refs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Specification of anteroposterior cell fates in Caenorhabditis elegans by Drosophila Hox proteins

Antennapedia class homeobox (Hox) genes specify cell fates in successive anteroposterior body domains in vertebrates, insects and nematodes. The DNA-binding homeodomain sequences are very similar between vertebrate and Drosophila Hox proteins, and this similarity allows vertebrate Hox proteins to function in Drosophila. In contrast, the Caenorhabditis elegans homeodomains are substantially divergent. Further, C. elegans differs from both insects and vertebrates in having a non-segmented body as well as a distinctive mode of development that involves asymmetric early cleavages and invariant cell lineages. Here we report that, despite these differences, Drosophila Hox proteins expressed in C. elegans can substitute for C. elegans Hox proteins in the control of three different cell-fate decisions: the regulation of cell migration, the specification of serotonergic neurons, and the specification of a sensory structure. We also show that the specificity of one C. elegans Hox protein is partly determined by two amino acids that have been implicated in sequence-specific DNA binding. Together these findings suggest that factors important for target recognition by specific Hox proteins have been conserved throughout much of the animal kingdom.     

On the nature of taste qualities.

The concept of 4 basic tastes developed historically on the basis of a number of criteria. Modern evidence, largely electrophysiological, has led some investigators to reject the concept of basic tastes in favor of a taste continuum or multidimensional space. The present article reviews data that support the validity of the basic tastes. It is concluded that this concept, as well as the separate question of taste as an analytic or synthetic sense, is compatible with either of the 2 major positions on sensory coding in taste, labeled line theory and pattern theory. Taste may profitably be considered to comprise 4 distinct but interacting sensory modalities or submodalities analogous to the (other) skin senses. (97 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of taste transduction

Taste cells use a wide variety of mechanisms for transduction. Ionic stimuli, such as salts and acids, interact directly with ion channels to depolarize taste cells. More complex stimuli, such as sugars and amino acids, utilize apically located receptors for transduction. Recent molecular biological results suggest that the metabotropic glutamate receptor mGluR4 may function in glutamate taste transduction. New biochemical studies have identified a bitter-responsive receptor that activates gustducin. Unexpected results with knockout mice suggest that gustducin may be directly involved in both bitter and sweet transduction. Electrophysiological experiments indicate that both inositol trisphosphate and cyclic nucleotides function in both bitter and sweet transduction events.     

Taste and smell complaints in HIV-infected patients

OBJECTIVES: To define the scope of taste and smell (chemosensory) complaints amongst HIV-infected persons in the study population; to evaluate the clinical factors associated with chemosensory complaints; and to determine the impact of chemosensory complaints on quality of life. DESIGN: Cross-sectional survey. SETTING: Tertiary care university medical center clinic. PARTICIPANTS: A total of 207 HIV-infected patients. MAIN OUTCOME MEASURES: Chemosensory complaint score from taste and smell questionnaire and quality of life scores from the Medical Outcomes Study HIV Health Survey (MOS-HIV). RESULTS: A total of 144 patients (70%) reported chemosensory complaints, 91 (44%) reported both taste and smell complaints, 47 (23%) reported only taste complaints, and six (3%) reported only smell complaints. Many patients complained that drugs interfered with their sense of taste, or that medications tasted bad. Higher chemosensory complaint scores were associated with a greater number of medications taken, tobacco use, and hay fever. Patients with chemosensory complaints had significantly lower scores in all domains of the MOS-HIV than those without complaints. Quality of life as measured by the MOS-HIV was lower in patients with chemosensory complaints even after controlling for number of AIDS diagnoses, number of medications, CD4 cell count, and HIV-1 viral load. CONCLUSIONS: Chemosensory complaints were common in the patient population and were associated with a poor quality of life. Medications played an important role in chemosensory complaints. Measures to optimize taste and smell function may improve quality of life and medication adherence, and prevent complications such as inadequate oral intake, malnutrition, weight loss, and ultimately wasting.     

Long-term toxicity study quillaia extract in rats

Tannic acid fixation reveals differences in the number of protofilaments between microtubules (MTs) in the nematode Caenorhabditis elegans. Most cells have MTs with 11 protofilaments but the six touch receptor neurons (the microtubule cells) have MTs with 15 protofilaments. No 13-protofilament (13-p) MT has been seen. The modified cilia of sensory neurons also possess unusual structures. The cilia contain nine outer doublets with A subfibers of 13 protofilaments and B subfibers of 11 protofilaments and a variable number of inner singlet MTs containing 11 protofilaments. The 15-p MTs but not the 11-p MTs are eliminated by colchicine-treatment or by mutation of the gene mec-7. Concomitantly, touch sensitivity is also lost. However, whereas colchicine treatment leads to the loss of all MTs from the microtubule cells, mutations in mec-7 result in the partial replacement of the 15-p MTs with 11-p MTs. Benzimidazoles (benomyl and nocodazole) have more general effects on C. elegans (slow growth, severe uncoordination, and loss of processes from the ventral cord) but do not affect the 15-p MTs. Benomyl will, however, disrupt the replacement 11-p MTs found in the microtubule cells of mec-7 mutants. The 11-p and 15-p MTs also respond differently to temperature and fixation conditions. It is likely that either type of MT will suffice for the proper outgrowth of the microtubule cell process, but only the 15-p MT can function in the specialized role of sensory transduction of the microtubule cells.     

Psychophysical Isolation of the Modality Responsible for Detecting Multimodal Stimuli: A Chemosensory Example.

Multiple sense modalities can be stimulated conjointly by a physically complex item, such as a predator, and also by a physically solitary stimulus that acts on multiple receptor classes. As a prime example of this latter group, l-menthol from mint stimulates taste, smell, and several somatosensory submodalities. In 6 experiments that used a variety of psychometric techniques, the authors experimentally isolated the modality by which l-menthol is detected in the upper airways (the nose and mouth). Interestingly, absolute detection in both the nasal and oral cavities was based on olfaction and not stinging, cooling, or taste. These experiments illustrate how the sensory modality responsible for detecting a multimodal or multisensory stimulus can be psychophysically isolated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shifting strategies for behavioral thermoregulation in developing golden hamsters.

Studied developmental changes in the golden hamster pup's capacity for behavioral temperature regulation. Groups of 3 pups aged 4-24 days were tested at room temperature (22°C), on a strong gradient (34-22°C), and on a mild gradient (30-22°C). The proportion of time engaged in the following behaviors was recorded: contact with the warm edge (thermotaxis), active huddling, and quiet huddling. Results show that Ss tested at 22° engaged in active huddling, and their temperature dropped rapidly. Only on Day 14 were they able to maintain their temperature constant with a combination of vigorous exploration and quiet huddling. On the strong gradient, Ss were able to regulate their temperature at all ages. Young Ss (4-5 days) depended on thermotaxis rather than huddling, separating when their temperature started to rise. With age, quiet huddling replaced thermotaxis as a dominant behavior. On the mild gradient, Ss combined active and quiet huddling with thermotaxis, so that their temperature dropped at a slow steady rate. It is concluded that hamster pups have a well-developed capacity for behavioral temperature regulation. Whether they attempt to keep their temperature constant or tolerate a slow rate of drop depends on the amount of exogenous heat available, which under natural conditions would be supplied predominantly by the mother. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Roles of chemical mediators in the taste system

Recent advances in neural mechanisms of taste are reviewed with special reference to neuroactive substances. In the first section, taste transduction mechanisms of basic tastes are explained in two groups, whether taste stimuli directly activate ion channels in the taste cell membrane or they bind to cell surface receptors coupled to intracellular signaling pathways. In the second section, putative transmitters and modulators from taste cells to afferent nerves are summarized. The candidates include acetylcholine, catecholamines, serotonin, amino acids and peptides. Studies favor serotonin as a possible neuromodulator in the taste bud. In the third section, the role of neuroactive substances in the central gustatory pathways is introduced. Excitatory and inhibitory amino acids (e.g., glutamate and GABA) and peptides (substance P and calcitonin gene-related peptide) are proved to play roles in transmission of taste information in both the brainstem relay and cortical gustatory area. In the fourth section, conditioned taste aversion is introduced as a model to study gustatory learning and memory. Pharmacobehavioral studies to examine the effects of glutamate receptor antagonists and protein kinase C inhibitors on the formation of conditioned taste aversion show that both glutamate and protein kinase C in the amygdala and cortical gustatory area play essential roles in taste aversion learning. Recent molecular and genetic approaches to disclose biological mechanisms of gustatory learning are also introduced. In the last section, behavioral and pharmacological approaches to elucidate palatability, taste pleasure, are described. Dopamine, benzodiazepine derivatives and opioid substances may play some roles in evaluation of palatability and motivation to ingest palatable edibles.