Changes of the biophysical properties of voltage-gated Na+ currents during maturation of the sodium-taste cells in rat fungiform papillae.

Taste cells are a heterogeneous population of sensory receptors that undergo continuous turnover. Different chemo-sensitive cell lines rely on action potentials to release the neurotransmitter onto nerve endings. The electrical excitability is due to the presence of a tetrodotoxin-sensitive, voltage-gated sodium current (INa ) similar to that found in neurons. Since the biophysical properties of neuronal INa change during development, we wondered whether the same also occurred in taste cells. Here, we used the patch-clamp recording technique to study INa in salt-sensing cells (sodium cells) of rat fungiform papillae. We identified these cells by exploiting the known blocking effect of amiloride on ENaC, the sodium (salt) receptor. Based on the amplitude of INa , which is known to increase during development, we subdivided sodium cells into two groups: cells with small sodium current (SSC cells; INa  < 1 nA) and cells with large sodium current (LSC cells; INa  > 1 nA). We found that: the voltage dependence of activation and inactivation significantly differed between these subsets; a slowly inactivating sodium current was more prominent in LSC cells; membrane capacitance in SSC cells was larger than in LSC cells. mRNA expression analysis of the α-subunits of voltage-gated sodium channels in fungiform taste buds supported the functional data. Lucifer Yellow labelling of recorded cells revealed that our electrophysiological criterion for distinguishing two broad groups of taste cells was in good agreement with morphological observations for cell maturity. Thus, all these findings are consistent with developmental changes in the voltage-dependent properties of sodium-taste cells. KEY POINTS: Taste cells are sensory receptors that undergo continuous turnover while they detect food chemicals and communicate with afferent nerve fibres. The voltage-gated sodium current (INa ) is a key ion current for generating action potentials in fully differentiated and chemo-sensitive taste cells, which use electrical signalling to release neurotransmitters. Here we show that, during the maturation of rat taste cells involved in salt detection (sodium cells), the biophysical properties of INa , such as voltage dependence of activation and inactivation, change significantly. Our results help reveal how taste cells gain electrical excitability during turnover, a property critical to their operation as chemical detectors that relay sensory information to nerve fibres.

Coding of pheromones by vomeronasal receptors.

Communication between individuals is critical for species survival, reproduction, and expansion. Most terrestrial species, with the exception of humans who predominantly use vision and phonation to create their social network, rely on the detection and decoding of olfactory signals, which are widely known as pheromones. These chemosensory cues originate from bodily fluids, causing attractive or avoidance behaviors in subjects of the same species. Intraspecific pheromone signaling is then crucial to identify sex, social ranking, individuality, and health status, thus establishing hierarchies and finalizing the most efficient reproductive strategies. Indeed, all these features require fine tuning of the olfactory systems to detect molecules containing this information. To cope with this complexity of signals, tetrapods have developed dedicated olfactory subsystems that refer to distinct peripheral sensory detectors, called the main olfactory and the vomeronasal organ, and two minor structures, namely the septal organ of Masera and the Grueneberg ganglion. Among these, the vomeronasal organ plays the most remarkable role in pheromone coding by mediating several behavioral outcomes that are critical for species conservation and amplification. In rodents, this organ is organized into two segregated neuronal subsets that express different receptor families. To some extent, this dichotomic organization is preserved in higher projection areas of the central nervous system, suggesting, at first glance, distinct functions for these two neuronal pathways. Here, I will specifically focus on this issue and discuss the role of vomeronasal receptors in mediating important innate behavioral effects through the recognition of pheromones and other biological chemosignals.

Author Correction: Female mouse tears contain an anti-aggression pheromone.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Female mouse tears contain an anti-aggression pheromone.

Tears contain pheromones that trigger specific behavioral responses. In the mouse, male tear fluid is involved in long and short-term effects such as the receptive behavior and pregnancy block in females and the aggression in males. In contrast, pup tears exert an inhibitory effect on male mating behavior, also promoting sexual rejection in females. In the rat, a male lacrimal protein acts as an intraspecific and heterospecific signal enhancing sexual behavior in females and evoking avoidance behavior in mouse. However, behavioral effects of female tears on male behavior have yet to be described. Here, we report that female lacrimal fluid of different mouse strains contains a relatively small and involatile factor that abolishes inter-male aggression switching it into a copulatory behavior. The production of this molecule by the lacrimal glands is not affected by the estrous cycle but it is sensitive to ovariectomy, thus suggesting a control mediated by hormones. Moreover, this lacrimal anti-aggression pheromone modulates the activity of the lateral habenula, a brain area responsible for the valence of the aggressive interactions.

In-vivo activation of vomeronasal neurons shows adaptive responses to pheromonal stimuli.

In most mammals, the vomeronasal system has a pivotal role in mediating socio-sexual behaviours. The vomeronasal organ senses pheromones through the activation of specific receptors. Pheromone binding to cognate receptors activates Ca-influx via the gating of a cation channel that generates membrane depolarisation. The ex-vivo activation of vomeronasal neurons (VSNs) by pheromonal stimuli has been largely investigated by electrophysiological and imaging techniques; however, few studies have been carried out to determine the physiological responses of VSNs, in-vivo. By tracking the phosphorylation of S6 ribosomal protein as a marker of neuronal activity, we show that S6 becomes phosphorylated (pS6) in mouse VSNs stimulated by intraspecific and heterospecific pheromonal cues. We observed that female scent induces pS6 immunoreactivity in the apical VSNs of male vomeronasal epithelium, whereas male cues stimulate S6 phosphorylation in both the basal and apical VSNs of females. We also show that this dimorphic pattern of pS6 immunoreactivity is reproduced when heterospecific stimuli are used. Moreover, we found that a consistent proportion of VSNs is activated by both heterospecific and intraspecific pheromones. Additionally, we have evidence of adaptive responses to S6 phosphorylation when stimulation with cues of the same and opposite sex and of different species is sustained.

Evolution of spatially coexpressed families of type-2 vomeronasal receptors in rodents.

The vomeronasal organ (VNO) is an olfactory structure for the detection of pheromones. VNO neurons express three groups of unrelated G-protein-coupled receptors. Type-2 vomeronasal receptors (V2Rs) are specifically localized in the basal neurons of the VNO and are believed to sense protein pheromones eliciting specific reproductive behaviors. In murine species, V2Rs are organized into four families. Family-ABD V2Rs are expressed monogenically and coexpress with family-C V2Rs of either subfamily C1 (V2RC1) or subfamily C2 (V2RC2), according to a coordinate temporal diagram. Neurons expressing the phylogenetically ancient V2RC1 coexpress family-BD V2Rs or a specific group of subfamily-A V2Rs (V2RA8-10), whereas a second neuronal subset (V2RC2-positive) coexpresses a recently expanded group of five subfamily-A V2Rs (V2RA1-5) along with vomeronasal-specific Major Histocompatibility Complex molecules (H2-Mv). Through database mining and Sanger sequencing, we have analyzed the onset, diversification, and expansion of the V2R-families throughout the phylogeny of Rodentia. Our results suggest that the separation of V2RC1 and V2RC2 occurred in a Cricetidae ancestor in coincidence with the evolution of the H2-Mv genes; this phylogenetic event did not correspond with the origin of the coexpressing V2RA1-5 genes, which dates back to an ancestral myomorphan lineage. Interestingly, the evolution of receptors within the V2RA1-5 group may be implicated in the origin and diversification of some of the V2R putative cognate ligands, the exocrine secreting peptides. The establishment of V2RC2, which probably reflects the complex expansion and diversification of family-A V2Rs, generated receptors that have probably acquired a more subtle functional specificity.

Lacrimal gland removal impairs sexual behavior in mice.

Exocrine gland-secreting peptides (ESPs) are a protein family involved in the pheromonal communication of rodents. ESP1 is a lacrimal peptide synthesized by the extraorbital glands of males of specific mouse strains that modulates the sexual behavior in females. Reportedly, BALB/c males, that produce high level of ESP1 in the tear fluid, were shown to enhance the lordosis behavior in C57BL/6 females during mating. In contrast, C57BL/6 and ICR males, both unable to express ESP1, failed to modulate this sexual behavior. Nonetheless, ICR males did become competent to enhance lordosis behavior in C57BL/6 females providing these were pre-exposed to ESP1. To exclude any strain differences, here, we investigated the pheromonal role of the extraorbital glands and indirectly of ESP1 in animals of the same strain. This was performed by applying the lordosis experimental paradigm in BALB/c mice before and after the surgical removal of these glands in males. The excision of the extraorbital glands reduced but did not abolish the production of ESP1 in the lacrimal fluid of BALB/c mice. An immunological analysis on soluble extracts of the glands that drain into the conjunctival sac revealed that the intraorbital glands (ILGs) are also responsible for the production of ESP1. The removal of both the extra and ILGs completely eliminated the tear secretion of ESP1. Extraorbital gland-deficient BALB/c mice were still able to induce lordosis behavior in sexually receptive females. In contrast, males with the removal of both the extra and ILGs failed to enhance lordosis behavior in females. Unexpectedly, C57BL/6 males did improve this sexual performance in BALB/c females. However, an analysis of the tear fluid of C57BL/6 males revealed low but detectable levels of ESP1. Overall, our study highlights the relevance of the orbital glands in modulating reproductive behavior and the sensitivity of the vomeronasal system to detect trace amount of ESP1.

Facilitation of action planning in children with autism: the contribution of the maternal body odor.

Imitation is a key socio-cognitive skill impaired in individuals with Autism Spectrum Conditions (ASC). It is known that the familiarity with an actor facilitates the appearance of imitative abilities. Here, we explore whether a highly familiar and socially relevant stimulus presented in the olfactory modality is able to improve spontaneous imitation as early as at the level of action planning. A group of 20 children with ASC and 20 controls observed their own mother or the mother of another child performing a reach-to-grasp action towards an object, under the exposure to their maternal odor, the odor of the mother of another child or no odor. Subsequently, children acted upon the same object with no specific instruction to imitate. Child's movement initiation time (MIT) served as an indicator of motor planning facilitation induced by action observation. Results suggest that for children with ASC (but not controls) MIT was significantly lower when exposed to the maternal odor both when interacting with a familiar or an unfamiliar model. In the former case, the performance is comparable to controls. The familiar model in the absence of any olfactory cue is able to induce a facilitation effect, but the maximal facilitation on MIT is evident when maternal odor and familiar model are paired. We hypothesize that for children with ASC the maternal odor provides relevant social motivation for taking advantage of others' actions when planning movements in an imitative context.

Aggressive behaviour and physiological responses to pheromones are strongly impaired in mice deficient for the olfactory G-protein -subunit G8.

Heterotrimeric G-proteins are critical players in the transduction mechanisms underlying odorant and pheromonal signalling. In the vomeronasal organ (VNO) of the adult mouse, two different G-protein complexes have been identified. Gαoß2γ8 is preferentially expressed in the basal neurons and coexpresses with type-2 vomeronasal pheromone receptors (V2Rs) whereas Gαi2ß2γ2 is found in the apical neurons and coexpresses with type-1 vomeronasal pheromone receptors (V1Rs). V2R-expressing neurons project to the posterior accessory olfactory bulb (AOB) whereas neurons expressing V1Rs send their axon to the anterior AOB. Gγ8 is also expressed in developing olfactory neurons where this protein is probably associated with Go. Here, we generated mice with a targeted deletion of the Gγ8 gene and investigated the behavioural effects and the physiological consequences of this mutation. Gγ8(-/-) mice show a normal development of the main olfactory epithelium; moreover, they do not display major deficits in odour perception. In contrast, the VNO undergoes a slow but remarkable loss of basal neurons starting from the fourth postnatal week, with a 40% reduction of cells at 2 months and 70% at 1 year. This loss is associated with a reduced early-gene expression in the posterior AOB of mice stimulated with pheromones. More interestingly, the Gγ8 deletion specifically leads to a reduced pheromone-mediated aggressiveness in both males and females, all other socio-sexual behaviours remaining unaltered. This study defines a specific role for Gγ8 in maintenance of the neuronal population of the VNO and in the mechanisms of pheromonal signalling that involve the aggressive behaviour towards conspecifics.

Body odors promote automatic imitation in autism.

BACKGROUND: Autism spectrum disorders comprise a range of neurodevelopmental pathologies characterized, among other symptoms, by impaired social interactions. Individuals with this diagnosis are reported to often identify people by repetitively sniffing pieces of clothing or the body odor of family members. Since body odors are known to initiate and mediate many different social behaviors, smelling the body odor of a family member might constitute a sensory-based action promoting social contact. In light of this, we hypothesized that the body odor of a family member would facilitate the appearance of automatic imitation, an essential social skill known to be impaired in autism. METHODS: We recruited 20 autistic and 20 typically developing children. Body odors were collected from the children's mothers' axillae. A child observed a model (their mother or a stranger mother) execute (or not) a reach-to-grasp action toward an object. Subsequently, she performed the same action. The object was imbued with the child's mother's odor, a stranger mother's odor, or no odor. The actions were videotaped, and movement time was calculated post hoc via a digitalization technique. RESULTS: Automatic imitation effects-expressed in terms of total movement time reduction-appear in autistic children only when exposed to objects paired with their own mother's odor. CONCLUSIONS: The maternal odor, which conveys a social message otherwise neglected, helps autistic children to covertly imitate the actions of others. Our results represent a starting point holding theoretical and practical relevance for the development of new strategies to enhance communication and social behavior among autistic individuals.

Implicit olfactory processing attenuates motor disturbances in idiopathic Parkinson's disease.

Many reports in the literature indicate that idiopathic Parkinson's disease (IPD) patients have substantial olfactory dysfunctions even before motor symptoms become evident. It has not yet been clarified, however, if some form of implicit olfactory processing is preserved in this population. An olfactory visuomotor priming paradigm, which detects implicit olfactory processing in neurologically healthy participants, was utilized to investigate motor control in relation to olfactory signals in a group of IPD patients. Two control groups were also considered: 12 vascular Parkinson's disease (VPD) in whom normal olfactory abilities are typically reported and 12 neurologically healthy participants. All of the participants were asked to perform reach-to-grasp movements toward large or small targets following olfactory cues delivered by a computer-controlled olfactometer. The odor was either 'size' congruent with the target (e.g., strawberry or apple, respectively) or incongruent (e.g., apple or strawberry, respectively). A bend sensor glove (CyberGlove) was used to measure the hand kinematics. Facilitation effects were noted in all the groups with regard to movement time. If a congruent rather than an incongruent odor was delivered, the movement time of the reach-to-grasp was shortened and facilitation effects in maximum grip amplitude were noted in both the IPD and the VPD groups. The maximum grip amplitude was smaller when no odor, as compared to a congruent odor, was delivered. The present results suggest that implicit olfactory processing affects motor control in IPD patients favoring less severe bradykinesia and hand movement hypometria. Once confirmed, these findings could be useful when rehabilitation strategies are being hypothesized for these patients.

Implicit olfactory abilities in traumatic brain injured patients.

To investigate implicit olfactory abilities in a group of anosmic traumatic brain injured (TBI) patients, an olfactomotor priming paradigm was administered. A group of matched normosmic/mildly microsmic TBI patients and a group of neurologically healthy participants served as controls. For all the groups, an interference effect was evident on the peak velocity of grip aperture when participants grasped a large target preceded by a "small" odor. The present results suggest that some form of implicit olfactory processing is preserved in TBI patients even when diagnosed as anosmic on the basis of explicit olfactory testing.

Calcium-activated chloride channels in the apical region of mouse vomeronasal sensory neurons.

The rodent vomeronasal organ plays a crucial role in several social behaviors. Detection of pheromones or other emitted signaling molecules occurs in the dendritic microvilli of vomeronasal sensory neurons, where the binding of molecules to vomeronasal receptors leads to the influx of sodium and calcium ions mainly through the transient receptor potential canonical 2 (TRPC2) channel. To investigate the physiological role played by the increase in intracellular calcium concentration in the apical region of these neurons, we produced localized, rapid, and reproducible increases in calcium concentration with flash photolysis of caged calcium and measured calcium-activated currents with the whole cell voltage-clamp technique. On average, a large inward calcium-activated current of -261 pA was measured at -50 mV, rising with a time constant of 13 ms. Ion substitution experiments showed that this current is anion selective. Moreover, the chloride channel blockers niflumic acid and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid partially inhibited the calcium-activated current. These results directly demonstrate that a large chloride current can be activated by calcium in the apical region of mouse vomeronasal sensory neurons. Furthermore, we showed by immunohistochemistry that the calcium-activated chloride channels TMEM16A/anoctamin1 and TMEM16B/anoctamin2 are present in the apical layer of the vomeronasal epithelium, where they largely colocalize with the TRPC2 transduction channel. Immunocytochemistry on isolated vomeronasal sensory neurons showed that TMEM16A and TMEM16B coexpress in the neuronal microvilli. Therefore, we conclude that microvilli of mouse vomeronasal sensory neurons have a high density of calcium-activated chloride channels that may play an important role in vomeronasal transduction.

Subliminally perceived odours modulate female intrasexual competition: an eye movement study.

BACKGROUND: Evidence suggests that subliminal odorants influence human perception and behavior. It has been hypothesized that the human sex-steroid derived compound 4,16-androstadien-3-one (androstadienone) functions as a human chemosignal. The most intensively studied steroid compound, androstadienone is known to be biologically relevant since it seems to convey information about male mate quality to women. It is unclear if the effects of androstadienone are menstrual cycle related. METHODOLOGY/PRINCIPAL FINDINGS: In the first experiment, heterosexual women were exposed to androstadienone or a control compound and asked to view stimuli such as female faces, male faces and familiar objects while their eye movements were recorded. In the second experiment the same women were asked to rate the level of stimuli attractiveness following exposure to the study or control compound. The results indicated that women at high conception risk spent more time viewing the female than the male faces regardless of the compound administered. Women at a low conception risk exhibited a preference for female faces only following exposure to androstadienone. CONCLUSIONS/SIGNIFICANCE: We contend that a woman's level of fertility influences her evaluation of potential competitors (e.g., faces of other women) during times critical for reproduction. Subliminally perceived odorants, such as androstadienone, might similarly enhance intrasexual competition strategies in women during fertility phases not critical for conception. These findings offer a substantial contribution to the current debate about the effects that subliminally perceived body odors might have on behavior.

A recent class of chemosensory neurons developed in mouse and rat.

In most animal species, the vomeronasal organ ensures the individual recognition of conspecifics, a prerequisite for a successful reproduction. The vomeronasal organ expresses several receptors for pheromone detection. Mouse vomeronasal type-2 receptors (V2Rs) are restricted to the basal neurons of this organ and organized in four families. Family-A, B and D (family ABD) V2Rs are expressed monogenically (one receptor per neuron) and coexpress with either Vmn2r1 or Vmn2r2, two members of family-C V2Rs. Thus, basal neurons are characterized by specific combinations of two V2Rs. To investigate this issue, we raised antibodies against all family-C V2Rs and analyzed their expression pattern. We found that six out of seven family-C V2Rs (Vmn2r2-7) largely coexpressed and that none of the anti-Vmn2r2-7 antibodies significantly stained Vmn2r1 positive neurons. Thus, basal neurons are divided into two complementary subsets. The first subset (Vmn2r1-positive) preferentially coexpresses a distinct group of family-ABD V2Rs, whereas the second subset (Vmn2r2-7-positive) coexpresses the remaining group of V2Rs. Phylogenetic reconstruction and the analysis of genetic loci in various species reveal that receptors expressed by this second neuronal subset are recent branches of the V2R tree exclusively present in mouse and rat. Conversely, V2Rs expressed in Vmn2r1 positive neurons, are phylogenetically ancient and found in most vertebrates including rodents. Noticeably, the more recent neuronal subset expresses a type of Major Histocompatibility Complex genes only found in murine species. These results indicate that the expansion of the V2R repertoire in a murine ancestor occurred with the establishment of a new population of vomeronasal neurons in which coexists the polygenic expression of a recent group of family-C V2Rs (Vmn2r2-7) and the monogenic expression of a recent group of family-ABD V2Rs. This evolutionary innovation could provide a molecular rationale for the exquisite ability in individual recognition and mate choice of murine species.

When flavor guides motor control: an effector independence study.

Research on multisensory integration during natural tasks has revealed how chemical senses contribute to plan and control movements. An aspect which has yet to be investigated regards whether the motor representations evoked by chemosensory stimuli, once established for a particular movement, can be used to control different effectors. Here, we investigate this issue by asking participants to drink a sip of flavored solution, grasp with the hand a visual target, and then bring it to the mouth, miming the action of biting. Results show that hand and lip apertures were scaled according to the size of the object evoked by the flavor. Maximum hand and lip apertures were greater when the action toward a small visual target (e.g., strawberry) was preceded by a sip of a "large" (e.g., orange) than a "small" (e.g., almond) flavor solution. Conversely, maximum hand and lip apertures were smaller when the action toward a large visual target (e.g., apple) was preceded by the presentation of a "small" (e.g., strawberry) rather than a "large" flavor solution. These findings support previous evidence on the presence of a unique motor plan underlying the act of grasping with-the-hand and with-the-mouth, extending the knowledge of chemosensorimotor transformations to motor equivalence.

Grasping a fruit. Hands do what flavour says.

Previous research on multisensory integration during goal-directed natural actions reported that visual, proprioceptive, auditory and orthonasal olfactory stimulation has the ability to influence motor control. In this study, we used kinematics to investigate the integration between vision and flavour perception during reach-to-grasp movements. Participants were requested to drink a sip of flavoured solution and then grasp an object presented in central vision. The results indicate that when the objects evoked by the flavour and by the visual target were of a similar size (i.e., large or small) and evoked the same kind of hand shaping in order to be grasped (i.e., congruent condition) facilitation effects emerged. Conversely, when the object evoked by the flavour and by the visual target was of a different size and evoked a different kind of hand shaping in order to be grasped (i.e., incongruent condition) interference effects emerged. Interference effects, however, were only evident for the combination involving a large visual target and a 'small' flavour. When comparing hand kinematics between the congruent and a 'no flavour' condition (i.e., water), facilitation effects emerged in favour of the former condition. Taken together, these results indicate the contribution of complex chemosensory stimuli for the planning and execution of visually guided reach to grasp movements. And, contribute to the current debate regarding the multisensory nature of the sensorimotor transformations underlying motor performance.

Smelling odors, understanding actions.

Previous evidence indicates that we understand others' actions not only by perceiving their visual features but also by their sound. This raises the possibility that brain regions responsible for action understanding respond to cues coming from different sensory modalities. Yet no studies, to date, have examined if this extends to olfaction. Here we addressed this issue by using functional magnetic resonance imaging. We searched for brain activity related to the observation of an action executed towards an object that was smelled rather than seen. The results show that temporal, parietal, and frontal areas were activated when individuals observed a hand grasping a smelled object. This activity differed from that evoked during the observation of a mimed grasp. Furthermore, superadditive activity was revealed when the action target-object was both seen and smelled. Together these findings indicate the influence of olfaction on action understanding and its contribution to multimodal action representations.

Calcium concentration jumps reveal dynamic ion selectivity of calcium-activated chloride currents in mouse olfactory sensory neurons and TMEM16b-transfected HEK 293T cells.

Ca(2+)-activated Cl(-) channels play relevant roles in several physiological processes, including olfactory transduction, but their molecular identity is still unclear. Recent evidence suggests that members of the transmembrane 16 (TMEM16, also named anoctamin) family form Ca(2+)-activated Cl(-) channels in several cell types. In vertebrate olfactory transduction, TMEM16b/anoctamin2 has been proposed as the major molecular component of Ca(2+)-activated Cl(-) channels. However, a comparison of the functional properties in the whole-cell configuration between the native and the candidate channel has not yet been performed. In this study, we have used the whole-cell voltage-clamp technique to measure functional properties of the native channel in mouse isolated olfactory sensory neurons and compare them with those of mouse TMEM16b/anoctamin2 expressed in HEK 293T cells. We directly activated channels by rapid and reproducible intracellular Ca(2+) concentration jumps obtained from photorelease of caged Ca(2+) and determined extracellular blocking properties and anion selectivity of the channels. We found that the Cl(-) channel blockers niflumic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and DIDS applied at the extracellular side of the membrane caused a similar inhibition of the two currents. Anion selectivity measured exchanging external ions and revealed that, in both types of currents, the reversal potential for some anions was time dependent. Furthermore, we confirmed by immunohistochemistry that TMEM16b/anoctamin2 largely co-localized with adenylyl cyclase III at the surface of the olfactory epithelium. Therefore, we conclude that the measured electrophysiological properties in the whole-cell configuration are largely similar, and further indicate that TMEM16b/anoctamin2 is likely to be a major subunit of the native olfactory Ca(2+)-activated Cl(-) current.

Calcium-activated chloride currents in olfactory sensory neurons from mice lacking bestrophin-2.

Olfactory sensory neurons use a chloride-based signal amplification mechanism to detect odorants. The binding of odorants to receptors in the cilia of olfactory sensory neurons activates a transduction cascade that involves the opening of cyclic nucleotide-gated channels and the entry of Ca(2+) into the cilia. Ca(2+) activates a Cl(-) current that produces an efflux of Cl(-) ions and amplifies the depolarization. The molecular identity of Ca(2+)-activated Cl(-) channels is still elusive, although some bestrophins have been shown to function as Ca(2+)-activated Cl(-) channels when expressed in heterologous systems. In the olfactory epithelium, bestrophin-2 (Best2) has been indicated as a candidate for being a molecular component of the olfactory Ca(2+)-activated Cl(-) channel. In this study, we have analysed mice lacking Best2. We compared the electrophysiological responses of the olfactory epithelium to odorant stimulation, as well as the properties of Ca(2+)-activated Cl(-) currents in wild-type (WT) and knockout (KO) mice for Best2. Our results confirm that Best2 is expressed in the cilia of olfactory sensory neurons, while odorant responses and Ca(2+)-activated Cl(-) currents were not significantly different between WT and KO mice. Thus, Best2 does not appear to be the main molecular component of the olfactory channel. Further studies are required to determine the function of Best2 in the cilia of olfactory sensory neurons.