Expression of transient receptor potential (TRP) channel mRNAs in the mouse olfactory bulb

Transient receptor potential (TRP) channels are a large family of cation channels. The 28 TRP channel subtypes in rodent are divided into 6 subfamilies: TRPC1-7, TRPV1-6, TRPM1-8, TRPP2/3/5, TRPML1-3 and TRPA1. TRP channels are involved in peripheral olfactory transduction. Several TRPC channels are expressed in unidentified neurons in the main olfactory bulb (OB), but the expression of most TRP channels in the OB has not been investigated. The present study employed RT-PCR as an initial survey of the expression of TRP channel mRNAs in the mouse OB and in 3 cell types: external tufted, mitral and granule cells. All TRP channel mRNAs except TRPV5 were detected in OB tissue. Single cell RT-PCR revealed that external tufted, mitral and granule cell populations expressed in aggregate 14 TRP channel mRNAs encompassing members of all 6 subfamilies. These different OB neuron populations expressed 7–12 channel mRNAs. Common channel expression was more similar among external tufted and mitral cells than among these cells and granule cells. These results indicate that a large number of TRP channel subtypes are expressed in OB neurons, providing the molecular bases for these channels to regulate OB neuron activity and central olfactory processing.     

Expression of neuron-specific markers by the vomeronasal neuroepithelium in six species of primates

Vomeronasal organ (VNO) morphology varies markedly across primate taxa. Old World monkeys display no postnatal VNO. Humans and at least some apes retain a vestigial VNO during postnatal life, whereas the strepsirrhines and New World Monkeys present a morphologically well-defined VNO that, in many species, is presumed to function as an olfactory organ. Available microanatomical and behavioral studies suggest that VNO function in these species does not precisely duplicate that described in other mammalian taxa. The questions of which species retain a functional VNO and what functions they serve require inquiry along diverse lines but, to be functional, the vomeronasal epithelium must be neuronal and olfactory. We used immunohistochemistry to establish these criteria in six primate species. We compared the expression of two neuronal markers, neuron-specific beta-tubulin (BT) and protein gene product 9.5, and olfactory marker protein (OMP), a marker of mature olfactory sensory neurons, in paraffin-embedded VNO sections from two strepsirrhine and four haplorhine species, all of which retain morphologically well-defined VNOs during postnatal life. The infant Eulemur mongoz, adult Otolemur crassicaudatus, neonatal Leontopithicus rosalia, and adult Callithrix jacchus express all three proteins in their well-defined vomeronasal neuroepithelia. The infant Tarsius syrichta showed some BT and OMP immunoreactivity. We establish that two strepsirrhine species and at least some New World haplorhines have mature sensory neurons in the VNO. In contrast, at all ages examined, Saguinus geoffroyi VNO expresses these markers in only a few cells.     

Protective effect of gliclazide on diabetic peripheral neuropathy through Drp-1 mediated-oxidative stress and apoptosis

To further understand the roles of growth factors in the olfactory neurogenesis, we studied the mRNA levels of diverse genes in olfactory bulb (OB) and olfactory epithelium (OE) during the regeneration process of OE. mRNA expression levels of various genes in the OB and OE during the regeneration processes of OE from damage induced by methimazole administration were studied by DNA microarray analysis. The results were confirmed by quantitative real-time RT-PCR and immunohistochemistry. Expression levels of various genes dramatically changed during the observation period. Among them, mRNA expression of BDNF dramatically increased in OE during the first 7 days and then decreased. In contrast, mRNA expression of BDNF in OB significantly decreased during the first 7 days after administration and then gradually increased. The changes in the mRNA levels of OMP in OB precisely followed those of OMP in OE and OB. The present results suggest that BDNF in OE contributes to the early stage of regeneration, and BDNF in OB has its role in the late stage of regeneration of olfactory receptor neurons (ORNs).     

Distribution of OMP-, PGP 9.5- and CaBP-like immunoreactive chemoreceptor neurons in the developing human olfactory epithelium

We have examined the distribution of olfactory marker protein (OMP), protein gene product 9.5 (PGP 9.5) and calcium-binding protein D-28k (CaBP) in the olfactory epithelium of mid- to late fetal and newborn humans using immunocytochemistry. Olfactory chemoreceptor neurons (ORNs) in a 24-week-old female fetus, a 31-week-old male fetus and a newborn male were examined. OMP-like immunoreactivity (-LI) and PGP 9.5-LI were distributed throughout ORNs at all ages. CaBP-like immunoreactivity, however, was found only in clustered or isolated fetal ORNs; in the newborn, CaBP-LI was seen only in isolated ORNs sparsely distributed throughout the OE. These findings demonstrate that human ORNs express OMP-LI nearly 4 weeks earlier in development than previously reported. PGP 9.5-LI is coincidentally abundant within these cells, suggesting it may have an important role in mature ORNs. Because the number of ORNs expressing CaBP-LI decreases during perinatal development, CaBP may be important in intracellular calcium regulation during ORN growth and maturation in the developing OE.     

Immunolocalization of VEGF/VEGFR system in human fetal vomeronasal organ during early development

The vomeronasal system (VNS) is an accessory olfactory structure present in most mammals adhibited to the detection of specific chemosignals implied in social and reproductive behavior. The VNS comprises the vomeronasal organ (VNO), vomeronasal nerve and accessory olfactory bulb. VNO is characterized by a neuroepithelium constituted by bipolar neurons and supporting and stem/progenitor cells. In humans, VNO is present during fetal life and is supposed to possess chemoreceptor activity and participate in gonadotropin-releasing hormone neuronal precursor migration toward the hypothalamus. Instead, the existence and functions of VNO in postnatal life is debated. Vascular endothelial growth factor (VEGF) and its receptors (VEGFRs) have been demonstrated to play fundamental roles in various neurogenic events. However, there are no data regarding the localization and possible function of VEGF/VEGFRs in human fetal VNO. Therefore, this study was conceived to investigate the expression of VEGF/VEGFRs in human VNO in an early developmental period (9–12 weeks of gestation), when this organ appears well structured. Coronal sections of maxillofacial specimens were subjected to peroxidase-based immunohistochemistry for VEGF, VEGFR-1 and VEGFR-2. Double immunofluorescence for VEGF, VEGFR-1 or VEGFR-2 and the neuronal marker protein gene product 9.5 (PGP 9.5) was also performed. VEGF expression was evident in the entire VNO epithelium, with particularly strong reactivity in the middle layer. Strongly VEGF-immunostained cells with aspect similar to bipolar neurons and/or their presumable precursors were detected in the middle and basal layers. Cells detaching from the basal epithelial layer and detached cell groups in the surrounding lamina propria showed moderate/strong VEGF expression. The strongest VEGFR-1 and VEGFR-2 expression was detected in the apical epithelial layer. Cells with aspect similar to bipolar neurons and/or their presumable precursors located in the middle and basal layers and the detaching/detached cells displayed a VEGFR-1 and VEGFR-2 reactivity similar to that of VEGF. The basal epithelial layer exhibited stronger staining for VEGFRs than for VEGF. Cells with morphology and VEGF/VEGFR expression similar to those of the detaching/detached cells were also detected in the middle and basal VNO epithelial layers. Double immunofluorescence using anti-PGP 9.5 antibodies demonstrated that most of the VEGF/VEGFR-immunoreactive cells were neuronal cells. Collectively, our findings suggest that during early fetal development the VEGF/VEGFR system might be involved in the presumptive VNO chemoreceptor activity and neuronal precursor migration.     

Distribution of GAP-43 nerve fibers in the skin of the adult human hand

Skin is an important region of somatic sensory input, and is one of the most innervated areas of the human body. In this study, we investigated in human hand skin the distribution of nervous structures immunoreactive for the growth-associated protein 43 (GAP-43) and the protein gene product 9.5 (PGP 9.5). GAP-43 is a neuronal presynaptic membrane protein that is generally considered to be a marker of neuronal plasticity. PGP 9.5 is a neuron-specific soluble protein that is widely used as general marker for the peripheral nervous system. The entire neural network of the dermis and epidermis was stained with antibody to PGP 9.5. In the dermis, there were fewer GAP-43-immunostained nerve fibers than PGP 9.5-immunostained nerve fibers, whereas in the epidermis the numbers were equal. Only some Merkel cells and Meissner corpuscles were GAP-43-immunoreactive. In conclusion, our results show that GAP-43 protein is expressed in a subset of PGP 9.5-immunoreactive nerve structures.     

Sex hormone binding globulin in the rat olfactory system

Ovarian steroids are known to act on the olfactory system. Their mode of action, however, is mostly unclear to date since nuclear receptors are lacking in sensory neurons. Here we used immunocytochemistry and RT-PCR to study expression and distribution of sex hormone binding globulin (SHBG) in the rat olfactory system. Single sensory cells in the olfactory mucosa and their projections in the olfactory bulb showed specific SHBG immunostaining as determined by double immunofluorescence with olfactory marker protein OMP. Larger groups of SHBG stained sensory cells occurred in the vomeronasal organ (VNO). A portion of the olfactory glomeruli in the accessory olfactory bulb showed large networks of SHBG positive nerve fibres. Some of the mitral cells showed SHBG immune fluorescence. RT-PCR revealed SHBG encoding mRNA in the olfactory mucosa, in the VNO and in the olfactory bulbs indicating intrinsic expression of the binding globulin. The VNO and its related projections within the limbic system are known to be sensitive to gonadal steroid hormones. We conclude that SHBG may be of functional importance for rapid effects of olfactory steroids on limbic functions including the control of reproductive behaviours through pheromones.     

Notch 2 and Notch 1/3 segregate to neuronal and glial lineages of the developing olfactory epithelium.

The murine olfactory epithelium (OE) generates olfactory receptor neurons (ORNs) throughout development and into adulthood, but only a few of the factors regulating olfactory neuro- and glio-genesis have been delineated. Notch receptors maintain CNS neuronal progenitors and drive glial differentiation, and the Notch effectors Hes 1 and 5 are expressed in the OE, but the Notch receptors that stimulate Hes gene activation in defined lineages during OE development have not been determined. Here, we first use RT-PCR to reveal which Notch receptors and ligands are expressed in the developing and adult OE. This is followed by immunofluorescent detection, combined with lineage-specific markers to define the stage-specific developmental expression of different Notch family members. We show that throughout development, Notch 1 and 3 are expressed in cells retained within the lamina propria, where Notch 3 is expressed in olfactory ensheathing cells (OECs). In contrast, Notch 2 is expressed in apical embryonic and early postnatal OE neuronal progenitors. In postnatal and adult OE, Notch 1 is expressed predominantly in Bowman's glands, and Notch 2 in sustentacular cells. Notch 2 and Notch 1/3 may, therefore, have different roles in the commitment and differentiation of neuronal and glial lineages of the OE during development, and the maintenance of non-neuronal phenotypes postnatally.     

Neuronal gap junctions in the mouse main olfactory bulb: morphological analyses on transgenic mice

In the present study we analyzed the structural features of extraglomerular gap junction-forming processes in mouse olfactory bulb electron microscopically. This work complements a previous study in which we analyzed the structural features of neuronal gap junction-forming processes within the glomerulus itself. Furthermore we examined connexin 36 expressing cells in the mouse olfactory bulb by analyzing transgenic mice in which the connexin 36 coding sequence was replaced with histological reporters. In extraglomerular regions, the mitral/tufted cell somata, dendrites and axon hillocks made gap junctions and mixed synapses with interneuronal processes. These gap junctions and synapses were associated with various types of interneuronal processes, including a particular type of sheet-like or calyx-like process contacting the somata or large dendrites of mitral/tufted cells. In the olfactory bulbs of the transgenic mice, connexin 36 was expressed in mitral cells, tufted cells, presumed granule cells and periglomerular cells. Multiple immunofluorescent labelings further revealed that presumed interneurons expressing connexin 36 in the periglomerular region rarely expressed calbindin, calretinin or tyrosine hydroxylase and are likely to comprise a chemically uncharacterized class of neurons. Similarly, interneurons expressing connexin 36 in the granule cell layer were rarely positive for calretinin, which was expressed in numerous presumed granule cells in the mouse main olfactory bulb. In summary, these findings revealed that mitral/tufted cells make gap junctions with diverse types of neurons; in the glomeruli gap junction-forming interneuronal processes originated from some types of periglomerular cells but others from a hitherto uncharacterized neuron type(s), and in the extraglomerular region gap-junction forming processes originate mainly from a subset of cells within the granule cell layer.     

Dopamine modulates synaptic transmission between rat olfactory bulb neurons in culture

The glomerular layer of the olfactory bulb (OB) contains synaptic connections between olfactory sensory neurons and OB neurons as well as connections among OB neurons. A subpopulation of external tufted cells and periglomerular cells (juxtaglomerular neurons) expresses dopamine, and recent reports suggest that dopamine can inhibit olfactory sensory neuron activation of OB neurons. In this study, whole cell electrophysiological and primary culture techniques were employed to characterize the neuromodulatory properties of dopamine on glutamatergic transmission between rat OB mitral/tufted (M/T) cells and interneurons. Immunocytochemical analysis confirmed the expression of tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, in a subpopulation of cultured neurons. D2 receptor immunoreactivity was also observed in cultured M/T cells. Dopamine reduced spontaneous excitatory synaptic events recorded in interneurons. Although the D1 receptor agonist SKF38393 and the D2 receptor agonist bromocriptine mesylate mimicked this effect, evoked excitatory postsynaptic potentials (EPSPs) recorded from monosynaptically coupled neuron pairs were attenuated by dopamine and bromocriptine but not by SKF38393. Neither glutamate-evoked currents nor the membrane resistance of the postsynaptic interneuron were affected by dopamine. However, evoked calcium channel currents in the presynaptic M/T cell were diminished during the application of either dopamine or bromocriptine, but not SKF38393. Dopamine suppressed calcium channel currents even after nifedipine blockade of L-type channels, suggesting that inhibition of the dihydropyridine-resistant high-voltage activated calcium channels implicated in transmitter release may mediate dopamine's effects on spontaneous and evoked synaptic transmission. Together, these data suggest that dopamine inhibits excitatory neurotransmission between M/T cells and interneurons via a presynaptic mechanism.     

A morphological study of the vomeronasal organ and the accessory olfactory bulb in the Korean roe deer, Capreolus pygargus

The vomeronasal organ (VNO) and accessory olfactory bulb (AOB) of the Korean roe deer (Capreolus pygargus) were studied histologically to evaluate their morphological characteristics. Grossly, the VNO, encased by cartilage, has a paired tubular structure with a caudal blind end and a rostral connection through incisive ducts on the hard palate. In the VNO, the vomeronasal sensory epithelium (VSE) consists of galectin-3-positive supporting cells, protein gene product (PGP) 9.5-positive receptor cells, and basal cells. The vomeronasal respiratory epithelium (VRE) consists of a pseudostratified epithelium. The AOB strata included a vomeronasal nerve layer (VNL), a glomerular layer (GL), a mitral/tufted cell layer, and a granular cell layer. All lectins used in this study, including Bandeiraea simplicifolia agglutinin isolectin B4 (BSI-B4), soybean agglutinin (SBA), Ulex europaeus agglutinin I (UEA-I), and Triticum vulgaris wheat germ agglutinin (WGA), labeled the VSE with varying intensity. In the AOB, both the VNL and the GL reacted with BSI-B4, SBA, and WGA with varying intensity, but not with UEA-I. This is the first morphological study of the VNO and AOB of the Korean roe deer, which are similar to those of goats.     

Tonic and synaptically evoked presynaptic inhibition of sensory input to the rat olfactory bulb via GABA(B) heteroreceptors

Olfactory receptor neurons of the nasal epithelium send their axons, via the olfactory nerve (ON), to the glomeruli of the olfactory bulb (OB), where the axon terminals form glutamatergic synapses with the apical dendrites of mitral and tufted cells, the output cells of the OB, and with juxtaglomerular (JG) interneurons. Many JG cells are GABAergic. Here we show that, despite the absence of conventional synapses, GABA released from JG cells activates GABA(B) receptors on ON terminals and inhibits glutamate release both tonically and in response to ON stimulation. Field potential recordings and current-source density analysis, as well as intracellular and whole cell recording techniques were used in rat OB slices. Baclofen (2-5 microM), a GABA(B) agonist, completely suppressed ON-evoked synaptic responses of both mitral/tufted cells and JG cells, with no evidence for postsynaptic effects. Baclofen (0.5-1 microM) also reversed paired-pulse depression (PPD) of mitral/tufted cell responses to paired-pulse facilitation (PPF), and reduced depression of JG cell excitatory postsynaptic currents (EPSCs) during repetitive ON stimulation. These results suggest that baclofen reduced the probability of glutamate release from ON terminals. The GABA(B) antagonists CGP35348 or CGP55845A increased mitral/tufted cell responses evoked by single-pulse ON stimulation, suggesting that glutamate release from ON terminals is tonically suppressed via GABA(B) receptors. The same antagonists reduced PPD of ON-evoked mitral/tufted cell responses at interstimulus intervals 50-400 ms. This finding suggests that a single ON impulse evokes sufficient GABA release, presumably from JG cells, to activate GABA(B) receptors on ON terminals. Thus GABA(B) heteroreceptors on ON terminals are activated by ambient levels of extrasynaptic GABA, and by ON input to the OB. The time course of ON-evoked, GABA(B) presynaptic inhibition suggests that neurotransmission to M/T cells and JG cells will be significantly suppressed when ON impulses arrive in glomeruli at 2.5-20 Hz. GABA(B) receptor-mediated presynaptic inhibition of sensory input to the OB may play an important role in shaping the activation pattern of the OB glomeruli during olfactory coding.     

A comparative study of an olfactory epithelial area lacking olfactory neurons and a nearby presence of TGF-α-like immunoreactive olfactory neurons

Our previous study has shown that ddY mice have special patches of nasal epithelium in the posterior roof of the nasal cavity that exclusively consists of olfactory supporting cells and horizontal basal cells. Here, we extend this finding to Balb/c and DBA/2 mice, Wistar and Sprague-Dawley rats, hamsters, and guinea pigs. In the mice, rats, and hamsters studied, the patches lacked olfactory cells and their precursor, globose basal cells. In rats and hamsters, the supporting cells were arranged in a single layer, in mice as three or four layers. Horizontal basal cells were located in a single layer in these species. In the guinea pigs, the specialized roof structure was less clear and could be seen at the level of ultrastructure as an olfactory neuron-lacking area. Distinct populations of transforming growth factor (TGF)-α-like immunoreactive olfactory cells occupied an area close to the epithelial patches. In this region, the TGF-α-like immunoreactive neurons were negative for the usual olfactory markers, either OMP or protein gene product (PGP) 9.5 or β-tubulin. These cells are suggested to project to the so-called ’necklace glomeruli’ and use a different cGMP-driven, transduction pathway. Three-dimensional analysis of double- labeled (TGF-α, PGP9.5) serial sections revealed a unique relation among the epithelial patches, TGF-α-like immunoreactive neurons and olfactory epithelium.     

Distribution of olfactory marker protein in the rat vomeronasal organ

Olfactory marker protein (OMP) may act as a modulator within the olfactory signal-transduction cascade. It has also been shown to have some importance in development of olfactory sensory organs. Here we used high resolution immunocytochemistry to localize OMP in the rat vomeronasal organ (VNO). Immunofluorescence for OMP was abundant in cilia and in apical dendrites of sensory cells, mostly associated with intraepithelial capillaries. Perikarya were stained to a lesser extent while intense OMP immunoreactivity was seen in axons of sensory neurons. Single cells within the non-sensory portion of the VNO exhibited intense OMP immunofluorescence in apical cilia and weak cytoplasmic staining. Some of the exocrine cells in the vomeronasal glands contained OMP positive secretory granules. Electron microscopy revealed that non-sensory ciliated cells had short rod like kinocilia as well as microvilli. These cells contained secretory vesicles. Their basal portion was in close apposition to nerve endings. Our findings suggest that the sensory part of the VNO contains OMP positive sensory neurons and that the non-sensory epithelium may contain secondary sensory cells. In addition OMP may be liberated from secretory glands into vomeronasal secretions.     

Immunohistochemistry of the canine vomeronasal organ

The canine's olfactory acuity is legendary, but neither its main olfactory system nor its vomeronasal system has been described in much detail. We used immunohistochemistry on paraffin-embedded sections of male and female adult dog vomeronasal organ (VNO) to characterize the expression of proteins known to be expressed in the VNO of several other mammals. Basal cell bodies were more apparent in each section than in rodent VNO and expressed immunoreactivity to anticytokeratin and antiepidermal growth factor receptor antibodies. The thin layer of neurone cell bodies in the sensory epithelium and axon fascicles in the lamina propria expressed immunoreactivity to neurone cell adhesion molecule, neurone-specific beta tubulin and protein gene product 9.5. Some neurones expressed growth-associated protein 43 (GAP43): and a number of those also expressed neurone-specific beta tubulin-immunoreactivity. Some axon fascicles were double labelled for those two proteins. The G-protein alpha subunits Gi and Go, involved in the signal transduction pathway, showed immunoreactivity in the sensory cell layer. Our results demonstrate that the canine vomeronasal organ contains a population of cells that expresses several neuronal markers. Furthermore, GAP43 immunoreactivity suggests that the sensory epithelium is neurogenic in adult dogs.     

Immunohistochemistry of the canine vomeronasal organ

The canine's olfactory acuity is legendary, but neither its main olfactory system nor its vomeronasal system has been described in much detail. We used immunohistochemistry on paraffin-embedded sections of male and female adult dog vomeronasal organ (VNO) to characterize the expression of proteins known to be expressed in the VNO of several other mammals. Basal cell bodies were more apparent in each section than in rodent VNO and expressed immunoreactivity to anticytokeratin and antiepidermal growth factor receptor antibodies. The thin layer of neurone cell bodies in the sensory epithelium and axon fascicles in the lamina propria expressed immunoreactivity to neurone cell adhesion molecule, neurone-specific beta tubulin and protein gene product 9.5. Some neurones expressed growth-associated protein 43 (GAP43): and a number of those also expressed neurone-specific beta tubulin-immunoreactivity. Some axon fascicles were double labelled for those two proteins. The G-protein alpha subunits Gi and Go, involved in the signal transduction pathway, showed immunoreactivity in the sensory cell layer. Our results demonstrate that the canine vomeronasal organ contains a population of cells that expresses several neuronal markers. Furthermore, GAP43 immunoreactivity suggests that the sensory epithelium is neurogenic in adult dogs.     

Heterotopically transplanted embryonic olfactory bulb projection neurons form selective and appropriate axonal projections over considerable distances in adult host brains

Embryonic olfactory primordia were transplanted into the region of the septum, the adjacent lateral ventricle (LV) and olfactory tubercle (Tu) in adult host rats. After a minimum of 7 weeks, wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were injected into the host anterior olfactory nucleus (AO). The injection retrogradely labeled the neural cell bodies in the large neuron area (the mitral and tufted cells) of the olfactory bulb (OB) transplant. In addition, the anterogradely labeled fibers projected from the host AO to the transplant. These results indicated that the transplanted mitral and tufted neurons were able to grow axons selectively to an appropriate host terminal region (the AO) and receive fibers from the AO, even when the transplant itself was in an inappropriate host site, at a considerable distance from the host AO.     

成年小鼠嗅觉功能与嗅上皮中成熟嗅觉神经元数量的实验研究

目的　探讨成年BALB/C小鼠维持嗅觉功能所需嗅上皮中成熟嗅神经元的数量,研究小鼠嗅上皮中嗅神经元数量与小鼠嗅觉功能的相关性。  方法    用0.7%的Triton X-100灌注8~10周大小的BALB/C小鼠鼻腔以诱导小鼠嗅觉障碍,分别于灌鼻后第3,7,21,49,56天行觅食实验检测小鼠觅食行为的改变,并联合免疫荧光染色（IFC）的方法,检测小鼠嗅上皮（OE）中成熟嗅神经元（ORNs）的数量与其嗅觉功能的相关性。  结果　小鼠经Triton X-100灌注鼻腔后第3、7天,其觅食时间明显延长（F=32.04,P<0.001),Bonferroni法两两比较示第3,7天觅食时间均长于对照组及造模后第21、49、56天组,P<0.001差异有统计学意义。嗅上皮中成熟嗅神经元（ORNs）的数量亦于第3、7天为低(F=223.97, P<0.001),觅食时间与嗅上皮成熟ORNs的数量呈负相关（r=－0.757,P<0.001）。小鼠嗅觉障碍于造模后第21天左右开始恢复,此时嗅上皮中OMP（+）细胞占28.66%。  结论　小鼠嗅觉功能与其嗅上皮中成熟ORNs数量具有明显的相关性;当成年BALB/C小鼠嗅上皮中成熟ORNs数量恢复至对照组的28.66%时即可使小鼠嗅觉功能得以恢复。