Surface Of Olfactory Epithelium Research Articles

Comparative ultrastructure of the olfactory system in the East African root rat (Tachyoryctes splendens) and the naked mole rat (Heterocephalus glaber).

The ultrastructure of the olfactory system of most fossorial rodents remains largely unexplored. This study sought to investigate the functional structure of the olfactory mucosa and olfactory bulb of two species of fossorial rodents that have distinct behaviour and ecology, the East African root rat (RR) and the naked mole rat (NMR). Transmission electron microscopy and scanning electron microscopy were employed. The basic ultrastructural design of the olfactory system of the two species was largely comparable. In both species, the olfactory mucosa comprised an olfactory epithelium and an underlying lamina propria. The olfactory epithelium revealed olfactory knobs, cilia and microvilli apically and sustentancular cells, olfactory receptor neurons and basal cells in the upper, middle and basal zones, respectively. The lamina propria was constituted by Bowman's glands, olfactory nerve bundles and vasculature supported by loose connective tissue. Within the olfactory bulb, intracellular and extracellular structures including cell organelles, axons and dendrites were elucidated. Notable species differences were observed in the basal zone of the olfactory epithelium and on the luminal surface of the olfactory mucosa. The basal zone of the olfactory epithelium of the RR consisted of a single layer of flattened electron-dense horizontal basal cells while the NMR had juxtaposed electron-dense and electron-lucent heterogenous cells, an occurrence seen as being indicative of quiescent and highly proliferative states of the olfactory epithelia in the two species, respectively. The olfactory epithelial surface of the NMR comprised an elaborate cilia network that intertwined extensively forming loop-like structures whereas in the RR, the surface was rugged and consisted of finger-like processes and irregular masses. With gross and histological studies showing significant differences in the olfactory structures of the two species, these findings are a further manifestation that the olfactory system of the RR and the NMR have evolved differently to reflect their varied olfactory functional needs.

Ecological constraints on highly evolvable olfactory receptor genes and morphology in neotropical bats.

Although evolvability of genes and traits may promote specialization during species diversification, how ecology subsequently restricts such variation remains unclear. Chemosensation requires animals to decipher a complex chemical background to locate fitness-related resources, and thus the underlying genomic architecture and morphology must cope with constant exposure to a changing odorant landscape; detecting adaptation amidst extensive chemosensory diversity is an open challenge. In phyllostomid bats, an ecologically diverse clade that evolved plant visiting from a presumed insectivorous ancestor, the evolution of novel food detection mechanisms is suggested to be a key innovation, as plant-visiting species rely strongly on olfaction, supplementarily using echolocation. If this is true, exceptional variation in underlying olfactory genes and phenotypes may have preceded dietary diversification. We compared olfactory receptor (OR) genes sequenced from olfactory epithelium transcriptomes and olfactory epithelium surface area of bats with differing diets. Surprisingly, although OR evolution rates were quite variable and generally high, they are largely independent of diet. Olfactory epithelial surface area, however, is relatively larger in plant-visiting bats and there is an inverse relationship between OR evolution rates and surface area. Relatively larger surface areas suggest greater reliance on olfactory detection and stronger constraint on maintaining an already diverse OR repertoire. Instead of the typical case in which specialization and elaboration are coupled with rapid diversification of associated genes, here the relevant genes are already evolving so quickly that increased reliance on smell has led to stabilizing selection, presumably to maintain the ability to consistently discriminate among specific odorants-a potential ecological constraint on sensory evolution.

Expression of CD36 by Olfactory Receptor Cells and Its Abundance on the Epithelial Surface in Mice.

CD36 is a transmembrane protein that is involved in the recognition of certain amphiphilic molecules such as polar lipids in various tissues and body fluids. So far, CD36 homologues in insects have been demonstrated to be present on the surface of olfactory dendrites and to participate in the perception of exogenous compounds. However, little is known about the relationship between CD36 and mammalian olfaction. Indeed, the detection of only CD36 mRNA in the mouse olfactory epithelium has been reported to date. In the present study, to provide potential pieces of evidence for the involvement of CD36 in mammalian olfactory perception, we extensively investigated the localisation of this protein in the mouse olfactory mucosa. In situ hybridisation analysis using antisense oligonucleotides to CD36 mRNA detected aggregated signals within the deeper epithelial layer of olfactory mucosa. The mRNA signals were also detected consistently in the superficial layer of the olfactory epithelium, which is occupied by supporting cells. Immunostaining with an anti-CD36 polyclonal antibody revealed that CD36 localises in the somata and dendrites of distinct olfactory receptor cells and that it occurs abundantly on the olfactory epithelial surface. However, immunoreactive CD36 was rarely detectable in the nerve bundles running in the lamina propria of olfactory mucosa, the axons forming the olfactory nerve layer in the outermost layer of the bulb and axon terminals in the glomeruli. We also obtained electron microscopic evidence for the association of CD36 protein with olfactory cilia. Altogether, we suggest that CD36 plays a role in the mammalian olfaction. In addition, signals for CD36 protein were also detected on or around the microvilli of olfactory supporting cells and the cilia of nasal respiratory epithelium, suggesting a role for this protein other than olfaction in the nasal cavity.

Morphological assessment of the luminal surface of olfactory epithelium in mice deficient in tissue plasminogen activator following bulbectomy

This study aimed to investigate the function of tissue plasminogen activator in the olfactory epithelium of mice following neural injury. Transmission electron microscopy was used to study the changes in the morphology of the olfactory epithelium 1-7 days after surgical ablation of the olfactory bulb (bulbectomy). Prior to bulbectomy, a uniformly fine material was observed within some regions of the olfactory epithelium of mice deficient in tissue plasminogen activator. At 2-3 days after bulbectomy, there were degenerative changes in the olfactory epithelium. At 5-7 days after bulbectomy, we noted drastic differences in olfactory epithelium morphology between mice deficient in tissue plasminogen activator and wild-type mice (comparisons were made using findings from a previous study). The microvilli seemed to be normal and olfactory vesicles and receptor neuron dendrites were largely intact in the olfactory epithelium of mice deficient in tissue plasminogen activator. The tissue plasminogen activator plasmin system may inhibit the regeneration of the olfactory epithelium in the early stages following neural injury.

Olfactory morphology of carcharhinid and sphyrnid sharks: Does the cephalofoil confer a sensory advantage?

Many hypotheses have been advanced to explain the adaptive significance of the sphyrnid cephalofoil, including potential advantages of spacing the olfactory organs at the distal tips of the broad surface. We employed comparative morphology to test whether the sphyrnid cephalofoil provides better stereo-olfaction, increases olfactory acuity, and samples a greater volume of the medium compared to the situation in carcharhiniform sharks. The broadly spaced nares provide sphyrnid species with a significantly greater separation between the olfactory rosettes, which could lead to an enhanced ability to resolve odor gradients. In addition, most sphyrnid species possess prenarial grooves that greatly increase the volume of water sampled by the nares and thus increase the probability of odorant encounter. However, despite a much greater head width, and a significantly greater number of olfactory lamellae, scalloped hammerhead sharks do not possess a greater amount of olfactory epithelial surface area than the carcharhiniform sandbar sharks. Therefore, sphyrnid sharks might not possess any greater olfactory acuity than carcharhinids. Despite this, there are clear olfactory advantages to the cephalofoil head morphology that could have led to its evolution, persistence, and diversification. persistence, and diversification.

Chloride cells--a component of the fish olfactory epithelium

Electron microscopic study of the surface and of ultrathin sections of the olfactory lining performed in seven species of freshwater fish of the Acipenserformes, Salmoniformes, Cypriniformes, and Perciformes orders. The cells that contain numerous mitochondria and well-developed tubular reticulum and have a peculiar shape of the apical surface were found in the olfactory epithelium of all the fish studied. They were identified as chloride cells, i.e., cells with a clearly seen ion-transporting specialization. The excretory character of their activity and a possible participation in maintaining a certain and constant ion composition of the mucus on the olfactory epithelium surface is discussed.

DOSIMETRIC ADJUSTMENT FACTORS FOR METHYL METHACRYLATE DERIVED FROM A STEADY-STATE ANALYSIS OF A PHYSIOLOGICALLY BASED CLEARANCE-EXTRACTION MODEL

Cells within the epithelial lining of the nasal cavity metabolize a variety of low-molecularweight, volatile xenobiotics. In common with terminology developed for other metabolizing organs, the nose extracts these chemicals from the airstream, thereby clearing some portion of the total nasal airflow. In this article, a physiologically based clearance-extraction (PBCE) model of nasal metabolism is used to predict extraction for steady-state conditions. This model, developed by simplification of existing physiologically based pharmacokinetic (PBPK) nasal models, has three tissue regions in two flow paths. A dorsal flow stream sequentially passes over a small area of respiratory epithelium and then over the entire olfactory epithelial surface within the nose. A ventral airstream, consisting of most of the total flow, passes over the larger portion (>80%) of the respiratory epithelium. Each underlying tissue stack has a mucus layer, an epithelial tissue compartment, and a blood exchange region. Metabolism may occur in any of the subcompartments within the tissue stacks. The model, solved directly for a steady-state condition, specifies the volumetric airflow over each stack. Computational fluid dynamic (CFD) solutions for the rat and human for the case with no liquid-phase resistance provided a maximum value for regional extraction, E max'. Equivalent air-to-liquid phase permeation coefficients (also referred to as the air-phase mass transfer coefficient) were calculated based on these E max' values. The PBCE model was applied to assess expected species differences in nasal extraction and in localized tissue metabolism of methyl methacrylate (MMA) in rats and in humans. Model estimates of tissue dose of MMA metabolites (in mumol metabolized/h/ ml tissue) in both species were used to evaluate the dosimetric adjustment factor (DAF) that should be applied in reference concentration (RfC) calculations for MMA. For human ventilation rates equivalent to light exercise, the DAF was estimated to be 3.02 at 28.4 ppm, the benchmark concentration for nasal lesions. Depending on specific assumptions about distribution of esterase activities in human tissues, the range of DAF values was 1.56-8.00. The DAF for heavy exercise with a ventilation rate of 42 L/min was still 2.98. Estimated DAFs were concentration dependent, varying between 2.4 and 4.76 in the inhaled concentration range from 1 and 400 ppm. Present default methods utilize a DAF of 0.145. These steady-state calculations with this PBCE model should be useful in risk assessment calculations for a variety of vapors and gases that are converted to toxic metabolites in cells in the respiratory tract.

Ultrastructural localization of amiloride-sensitive sodium channels and Na+,K(+)-ATPase in the rat's olfactory epithelial surface.

Several studies have indicated that olfactory responses are impeded by amiloride. Therefore, it was of interest to see whether, and if so which, olfactory epithelial cellular compartments have amiloride-sensitive structures. Using ultrastructural methods that involved rapid freezing, freeze-substitution and low temperature embedding of olfactory epithelia, this study shows that, in the rat, this tissue is immunoreactive to antibodies against amiloride sensitive Na(+)-channels. However, microvilli of olfactory supporting cells, as opposed to receptor cilia, contained most of the immunoreactive sites. Apices from which the microvilli sprout and receptor cell dendritic knobs had much less if any of the amiloride-antibody binding sites. Using a direct ligand-binding cytochemical method, this study also confirms earlier ones that showed that olfactory receptor cell cilia have Na+, K(+)-ATPase. It is proposed that supporting cell microvilli and the receptor cilia themselves have mechanisms, different but likely complementary, that participate in regulating the salt concentration around the receptor cell cilia. In this way, both structures help to provide the ambient mucous environment for receptor cells to function properly. This regulation of the salt concentration of an ambient fluid environment is a function that the olfactory epithelium shares with cells of transporting epithelia, such as those of kidney.

A banded topography in the developing rat's olfactory epithelial surface

In situ hybridization studies from various laboratories have shown that the rat's olfactory epithelium has four distinct regions in which most putative odor receptors are located. To determine whether morphological features accompany this biochemical patterning, olfactory epithelial surfaces of rat nasal endoturbinates and septa were examined with scanning electron microscopy, placing particular emphasis on endoturbinate IIb. There was some morphological patterning at embryonic day 15 (E15), but distinct regions were not yet discernible. Regionalization became distinct at E16 and E18. Posterior regions (Regions 1 and 2) had much higher receptor cell knob densities than more anterior regions closer to the respiratory epithelium (Regions 3 and 4). Supporting cell microvilli were longer in Region 1 than in Region 2. Apices of cells surrounding the receptor cells were flatter in Regions 1 and 2 than in Regions 3 and, especially, Region 4. In Regions 1-3, these surrounding cells were made up mainly of supporting cells; in Region 4 they included respiratory cells. Regions 3 and 4 also had glandular openings and scattered microvillous cells that resemble hair cells of the ear. Older fetuses and adults showed similar evidence of patterning, but detailed examination was precluded by the increased length and entanglement of receptor cell cilia and supporting cell microvilli. In conclusion, a distinct topographic pattern, involving both receptor and surrounding cells, emerges during development of the rat olfactory epithelial surface. Location of the bands roughly matches the zones seen by in situ hybridization.

A banded topography in the developing rat's olfactory epithelial surface

In situ hybridization studies from various laboratories have shown that the rat's olfactory epithelium has four distinct regions in which most putative odor receptors are located. To determine whether morphological features accompany this biochemical patterning, olfactory epithelial surfaces of rat nasal endoturbinates and septa were examined with scanning electron microscopy, placing particular emphasis on endoturbinate IIb. There was some morphological patterning at embryonic day 15 (E15), but distinct regions were not yet discernible. Regionalization became distinct at E16 and E18. Posterior regions (Regions 1 and 2) had much higher receptor cell knob densities than more anterior regions closer to the respiratory epithelium (Regions 3 and 4). Supporting cell microvilli were longer in Region 1 than in Region 2. Apices of cells surrounding the receptor cells were flatter in Regions 1 and 2 than in Regions 3 and, especially, Region 4. In Regions 1–3, these surrounding cells were made up mainly of supporting cells; in Region 4 they included respiratory cells. Regions 3 and 4 also had glandular openings and scattered microvillous cells that resemble hair cells of the ear. Older fetuses and adults showed similar evidence of patterning, but detailed examination was precluded by the increased length and entanglement of receptor cell cilia and supporting cell microvilli. In conclusion, a distinct topographic pattern, involving both receptor and surrounding cells, emerges during development of the rat olfactory epithelial surface. Location of the bands roughly matches the zones seen by in situ hybridization. J. Comp. Neurol. 388:293–306, 1997. © 1997 Wiley-Liss, Inc.

The Morphology of the Olfactory Epithelium in Larval, Juvenile and Upstream Migrant Stages of the Sea Lamprey, <i>Petromyzon marinus</i>

The structure of the olfactory epithelium in the larval, juvenile and upstream migrant stages of the sea lamprey, Petromyzon marinus, was investigated by light microscopy and by scanning and transmission electron microscopy. Ciliated olfactory receptor cells (ORC) were present in all stages. In larval specimens, the number of ORC was 20 +/- 8 ORC per 100 microns length of olfactory epithelial surface. In juveniles and in upstream migrants the ORC density dropped to 9 +/- 2 and 6 +/- 2 ORC/100 microns, respectively. Sustentacular cells were microvillar in the smallest larval stage (with a body length of 15 mm) and ciliated in larger larvae and later life stages. The morphological characteristics of the olfactory mucosa suggest that the sea lamprey's capacity for use of the olfactory system extends into the larval stage, and that there are specific changes associated with metamorphosis.

Histopathologic changes in the olfactory epithelium in mice after exposure to sulfur dioxide.

To investigate the effects of sulfur dioxide (SO2) on olfactory epithelium, an experiment was performed with 56 mice from the same colony. Experimental animals were divided into three groups consisting of a 30-min exposure group (group 1), a 60-min exposure group (group 2), and a 120-min exposure group (group 3). The olfactory mucosa in these mice were studied by light microscopy immediately, and after 24 h, 48 h, or 72 h exposure to 20 ppm of SO2. Edema, loss of cilia, epithelial thinning, and epithelial desquamation in the olfactory epithelium were observed in groups 2 and 3. The basal lamina and the connective tissue were well preserved throughout the entire mucosa. Injuries to olfactory epithelium became severer with exposure time. These changes were further pronounced 24 h after exposure. Regenerated epithelia were not observed in any group. Scanning electron microscopic findings were consistent with light microscopic findings. Olfactory epithelial surface were consistent with light microscopic findings. Olfactory epithelial surface was sloughed off and revealed, underlining intact basal lamina. The results of this study suggest that early lesions of olfactory epithelium after exposure to SO2 may be primarily degenerative.

Turtle olfactory responses are unchanged by perfusing olfactory epithelium with salt free solution

1. 1. Turtle olfactory bulbar responses to various odorants were essentially unchanged by perfusing the olfactory epithelium with the salt free solution or solutions containing various concentrations of salts such as NaCl, CaCl 2, choline chloride and Tris chloride. 2. 2. It was confirmed that salt concentrations on the surface of olfactory epithelium were sufficiently lowered by perfusing the epithelium with the salt free solution. 3. 3. The results obtained suggested that ion transport across cation channels located at apical membranes of olfactory cells including ciliary membranes does not contribute to generation of olfactory responses in the turtle.

Effects of long-term unilateral naris closure on the olfactory epithelia of adult mice

This study investigated the effects of long-term unilateral naris closure on the olfactory epithelia of adutt mice. The results support and extend the findings of our previous paper in which we examined the effects of unilateral closure for up to 3 months. In the present study naris closures were performed for 4, 5, 6, 7 or 8 months. The observed effects depended on the length of closure and the position of the sampling site along the rostral-caudal axis of the olfactory epithelium. The closed sides appeared to be unaffected by naris closure at all time points when compared to controls. A number of time-dependent changes were characteristic of the open-side olfactory epithelium. The most deleterious effects occured in the rostral regions of the epithelium where there were dramatic losses of receptor neurons at 3 months, regrowth at 4 months, and losses at 5, 6, 7 and 8 months of closure. The effects of naris closure on the morphology of the epithelium on the open sides were often striking. In mice that had significant losses of receptor neurons, the epthhelium frequently had only supporting and basal cell layers with virtually the entire neuronal layer absent. Depending on the length of closure, the middle regions of the open side showed either no effect, losses, or else an increase in the number of receptor neurons. Naris closure resulted in an increase in the number of receptor neurons in the caudal regions of the open side at all time points. In the 7 and 8 month closure groups, 2 additional abnormalities were observed on the open sides. Some animals showed an increased rugosity of the olfactory epithelial surface. In others large numbers of polymorphonuclear leukocytes were visible on the epithelial surface indicating active inflammation.

Ultrastructural evidence for peptidergic innervation of the apical region of frog olfactory epithelium

Ultrastructural examination of the region near the olfactory epithelial surface of leopard frogs revealed the presence of nerve terminals just proximal to the zonula adherens between adjacent sustentacular cells, and between sustentacular cells and olfactory receptor neurons. Terminal varicosities, located about 20 nm from sustentacular cell membranes, contained numerous large-diameter dense-cored vesicles, small-diameter agranular vesicles, and mitochondria. On the basis of ultrastructural characteristics, they are identified as peptidergic sensory terminals.

Tight-junctional strands first appear in regions where three cells meet in differentiating olfactory epithelium: a freeze-fracture study.

Tight junctions of the olfactory epithelium of rat embryos were studied at the 14th day of gestation and during their subsequent development. Two different epithelial morphologies could be distinguished at the 14th gestational day. In one group of embryos the epithelial surface appeared undifferentiated, with tight-junctional strands found exclusively in regions where three cells met. The main orientation of these strands is in a direction parallel to the longitudinal orientation of the epithelial cells. These junctions resemble tight junctions that interconnect three cells, i.e. tricellular tight junctions, in that respect. However, unlike these the junctions mainly have single strands of particles, whereas tricellular junctions usually consist of paired strands of particles. Tight-junctional strands were completely absent in areas where two cells met. These areas, i.e. those of incipient bicellular tight junctions, had gap-junction-like aggregates of intramembranous particles. Another group of 14-day-old embryos displayed a differentiating olfactory epithelial surface with bicellular as well as tricellular tight-junctional strands. The latter ones were paired. Here too the tight-junctional belts displayed some gap-junction-like aggregates of particles, but there were considerably fewer of these than earlier. As one or the other tight-junctional appearance was always seen in a single freeze-fracture replica, it is reasonable to assume that the two tight-junctional appearances reflect a sequential pattern of differentiation peculiar to the whole surface of the olfactory epithelium, i.e. to surfaces of receptor cells as well as to surfaces of supporting cells. It would appear that, at the onset of olfactory epithelial differentiation, tight junctions first interconnect cells in regions where three cells meet and that tricellular strand formation precedes the formation of bicellular strands. When strands were present at the 14th day of embryonic development, their numbers were lower than those found later. However, strand packing, expressed as the density per micrometre of strands parallel to the epithelial surface, increased beginning at the 16th day of embryonic development.

Isolated frog olfactory cilia: a preparation of dendritic membranes from chemosensory neurons

The recently introduced frog olfactory cilia preparation (Chen and Lancet, 1984; Pace et al., 1985) has been useful for studies of molecular chemosensory mechanisms. Here we describe in detail the properties of this cilia preparation. The "calcium shock" procedure leads to a complete removal of the cilia from the olfactory epithelial surface. Isolated cilia constitute segments of proximal regions with 9 X 2 + 2 microtubular arrangement and a large proportion of membrane vesicles, probably derived from the ciliary distal segments. Polypeptides unique to the olfactory cilia preparation, compared to a control preparation of palate respiratory cilia, are identified by Coomassie brilliant blue staining, silver staining, and radiolabeled lectin overlays, as well as by biosynthetic labeling with 35S-methionine in epithelial explants and protein phosphorylation in isolated cilia. The olfactory cilia preparation contains odorant-sensitive adenylate cyclase, which is absent in control membranes from deciliated epithelium. High activities of tyrosine and serine/threonine protein kinases are also present. The olfactory cilia preparation described should be instrumental in the further elucidation of the biochemistry and molecular biology of vertebrate olfaction.

Genesis of cilia and microvilli of rat nasal epithelia during pre-natal development. I. Olfactory epithelium, qualitative studies.

Rat foetuses from intra-uterine days E13 through E22 (day before parturition) and adults were used for a qualitative electron-microscopic investigation of the development of ciliated/microvillous surfaces of the olfactory epithelium. In the E13 and most of the E14 embryos the epithelial surface is not yet characteristically olfactory. Apical cell profiles show primary cilia. These can arise at the epithelial surface or below. From E14 onwards the epithelial surface acquires olfactory characteristics. Dendritic endings of the olfactory receptor cells can be found amidst microvillous profiles of supporting cells. Either cell type may bear primary cilia. From E16 onwards the receptor cells sprout multiple olfactory cilia, but cells with primary cilia are found throughout pre-natal development. These primary cilia are, at least for a while, retained during the formation of the secondary cilia. Primary cilia always have distinct necklaces at their base. Otherwise, especially with respect to their tips, their morphology can vary. Originally they have expanded tips (up to E14); later on such wide tips are no longer encountered (E16 and E17). Primary cilia of receptor cells never have wide tips. Appreciable numbers of endings with tapering olfactory cilia are discerned around E18 and especially E19. Throughout pre-natal development posterior/superior parts of the septal olfactory epithelium are more precocious than anterior/inferior parts, in particular in the region of transition with the respiratory epithelium. This advance in development includes total densities of dendritic endings of olfactory receptor cells, densities of multiciliated endings alone and lengths of supporting cell microvilli. This difference is discussed with respect to the topography of the olfactory epithelial surface in adult animals. In addition to the systematic topographic variation, a number of more local, apparently not-systematically distributed, topographic variations present during development are described. Most of these also occur in adult animals and they include heterogeneity in length of supporting cell microvilli and the presence of patches of supporting cells with rounded apical protuberances, of patches displaying dendrites with polyaxonemes rather than individual cilia and of scattered atypical cells (neither typical olfactory receptor nor olfactory supporting cells). At their surfaces such atypical cells can resemble inner-ear hair cells. Relative to olfactory receptor and supporting cells there are only very few atypical cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Olfactory and non-olfactory epithelia in the nasal cavity of the mouse, Peromyscus.

AbstractThe nasal cavities of 14 deer mice, Peromyscus maniculatus, were examined histologically to determine the variability in surface area of the olfactory epithelium and its correlation with nasal cavity volume, area of non‐olfactory epithelial surface, and body size.Forty‐four per cent of the nasal cavity surface of P. maniculatus is covered by a non‐olfactory epithelium with an area of 129.8 mm2; the epithelial surface consists of gradations in type from keratinized stratified squamous rostrally to ciliated pseudostratified columnar caudally. An extensive portion of this epithelium is non‐ciliated and devoid of goblet cells. Situated dorsocaudal to the non‐olfactory epithelium is the olfactory epithelial surface measuring 166.8 mm2 in area.The areas of total, non‐olfactory and olfactory epithelial surfaces are highly variable in a sample of mice containing two subspecies, both sexes and various ages. Surface area measurements of non‐olfactory and olfactory epithelia are correlated significantly with body length, body weight and volume of the nasal cavity. A relatively constant epithelial area to volume ratio is present in the nasal cavity of P. maniculatus. It is surmised that a stable ratio of molecules in the air to epithelial area may occur within a species.