Noriyo Suzuki

Olfactory epithelium consisting of supporting cells and horizontal basal cells in the posterior nasal cavity of mice

Abstract. The olfactory epithelium of mice generally consists of olfactory cells, progenitors of olfactory cells (globose basal cells), supporting cells, and horizontal basal cells. However, in the dorsal fossa (the roof) of the posterior nasal cavity of mice, we found seven epithelial patches consisting of only non-neuronal cell types, i.e., supporting cells and horizontal basal cells, among the normal olfactory epithelium. The supporting cells occupied three or four layers in the apical to middle regions; in the basal region, horizontal basal cells were localized in a single row adjacent to the basement membrane. Bowmans gland ducts were also present in the epithelium. Neuronal cells (olfactory cells and globose basal cells) were totally absent. The ultrastructure of the supporting cells, horizontal basal cells, and Bowmans glands was essentially similar to that in the normal olfactory epithelium. In the early postnatal period (P1–P7), cell types in the epithelium were the same as those in the normal olfactory epithelium. From P10 to P21, olfactory cells and globose basal cells had disappeared from the olfactory epithelium. At this period, the number of TUNEL-positive cells was significantly higher than that in the surrounding olfactory epithelium; ultrastructurally, many apoptotic figures were observed. This suggests that the epithelium consisting of supporting cells and horizontal basal cells is generated by the apoptotic death of olfactory cells and globose basal cells during postnatal development.

Distinct expression pattern of insulin-like growth factor family in rodent taste buds.

The insulin‐like growth factor (IGF) system is an important regulator of growth and differentiation in a variety of tissues. In the present study, the expression of IGF family members in the taste buds of mice and rats was examined. By reverse transcriptase polymerase chain reaction (RT‐PCR) analysis, mRNA of IGF‐I and ‐II, IGF‐I receptor (IGF‐IR), insulin receptor (insulin R), and IGF‐binding protein (IGFBP)‐2, ‐3, ‐4, ‐5, and ‐6 was detected in the taste bud‐containing epithelium of the circumvallate papillae of mice. As suggested by the study using degenerate PCR (McLaughlin [2000] J. Neurosci. 20:5679–5688), IGF‐IR was expressed in most of the taste bud cells of adult mice, as found by immunohistochemistry, and in those of postnatal day (P) 6 mice by in situ hybridization. Insulin R, which has strong homology to IGF‐IR, was also detected in most of the taste bud cells of mice by immunohistochemistry and in situ hybridization. IGF‐I immunoreactivity was detected in a few taste bud cells and in the epithelium surrounding taste buds. Northern blot analysis revealed that the amount of IGF‐I mRNA in taste bud‐containing epithelium was very low compared with that in liver. IGF‐II immunoreactivity was weakly detected in mouse taste buds and the surrounding epithelium. In the rat tissue, a subset of the taste bud cells was positive for IGF‐II. Among the six IGFBPs, IGFBP‐2, ‐5, and ‐6 were detected in the mouse taste buds: IGFBP‐2 and ‐5 immunoreactivity was seen in the majority of the taste bud cells, whereas IGFBP‐6 immunoreactivity was found in the nerve fibers innervating the taste buds. In situ hybridization study also revealed that IGFBP‐2 and ‐5 mRNA was synthesized in the taste buds of P6 mice and that the expression of these mRNAs overlapped in von Ebners glands. These data reveal that IGF‐I and ‐II might be produced in taste bud cells and (or) surrounding lingual epithelium and act through IGF‐IR and insulin R locally in a paracrine and autocrine manner. The activity of these IGFs may be modulated through their interaction with IGFBP‐2, ‐5, and 6. J. Comp. Neurol. 482:74–84, 2005.

IP3-Activated Ion Channel Activities in Olfactory Receptor Neurons from Different Vertebrate Species

It is now widely accepted that vertebrate olfactory transduction is mediated through a cAMP pathway in which an odorant-occupied receptor molecule activates a G-protein-linked adenylate cyclase that produces a second messenger, adenosine 3′,5′-cyclic monophosphate (cAMP). cAMP then gates cyclic nucleotide-activated cation channels localized in the membrane of olfactory cilia [1–7]. In addition, recent experiment on fish and rats suggest that not only cAMP, but also inositol 1,4,5-trisphosphate (IP3), serves as a second messenger in an additional transduction pathway in vertebrate olfaction.

Bulbectomy of neonatal mice induces migration of basal cells from the olfactory epithelium

Bulbectomy of neonatal mice induced cell migration from the olfactory epithelium in the nasal septum. We examined cell types of migrating clusters by immunohistochemistry using anti-keratin and anti-BrdU antibodies, and by electron microscopy. At 1-2 days after unilateral bulbectomy of P1 mice, cells migrated from the olfactory epithelium to the lamina propria of the septal olfactory mucosa. Horizontal basal cells that reacted specifically with anti-keratin antibody, and globose basal cells characterized by a round shape and poor content of organellae in their cytoplasm, were contained in the cluster. At 1 week, migrated clusters that contained keratin-positive horizontal basal cells were observed in both the lamina propria and olfactory bulb on the unoperated side. At 1 month, not only basal cells but also olfactory cells and presumed supporting cells were involved in the clusters in the lamina propria and olfactory bulb, suggesting that migrated cells do not transform to other phenotypes.

Voltage-Dependent Conductances in Solitary Olfactory Receptor Cells

To elucidate the chemoelectrical transduction mechanism in olfactory perception, the basic membrane properties of enzymatically isolated olfactory receptor cells from the bullfrog were studied in different ionic environments using the “Gigaseal ” whole-cell clamp technique.’ The receptor cells had resting potentials between -40 mV and 112 mV (mean -73.6 mV, n = 14). They had high input resistance (2-6 Gohm) and low input capacitance (3.7-5.0 pF, mean 4.5 pF, n = 29). The specific membrane capacitance was calculated as 0.8 pF/cm* from the estimated value of the surface area of receptor cells (573 pm). Repetitive action potentials were evoked in the receptor cells by the injection of depolarizing current. The frequency of the repetitive firing was a function of the magnitude of the injected current. Anode break spikes were observed on the cessation of hyperpolarizing current injection of appreciable strength. The membrane currents of the receptor cells associated with depolarizing voltage pulses in normal saline were characterized by an initial inward current followed by a slowly developing outward current. No currents were activated by the hyperpolarizing voltage pulses. The inward current activated by the membrane depolarization consisted of two different current components; Na current (INa) and Ca current (I,). I, was activated by membrane depolarization beyond -40 mV, was maximum at -10 mV and reversed its polarity at 4-40 mV. Most of I,, was suppressed by the ordinary blocking dose of TTX for Na+channels, but about one-tenth of I,, was left intact even with a high dose of TTX (20 pg/ml). This indicates that Na+ channels of a different type are distributed in the receptor cells. I, was activated by membrane depolarization beyond -20 mV, was maximal at + 10 mV, and reversed its polarity at +40 mV. I, showed a sustained response to depolarizing voltage pulses and no discernible inactivation was observed. Tail currents of I,, were observed on the cessation of the voltage pulses as in other tissue preparations?’ The outward current activated by membrane depolarization consisted of at least three different current components; delayed rectifier K current ( IKdr), Ca-activated K current ( I,(,)), and the transient outward current (Im). Both I,,, and I,,,,, were activated by membrane depolarization beyond -20 mV and were suppressed completely by the substitution of external K + and Ca2+ with TEA+ and Co2+, respectively. I,, was observed when the external NaCl and KCl were substituted with TEA-Cl, which suggests that anions are involved in this current.