Basal gene expression in male and female Sprague-Dawley rat nasal respiratory and olfactory epithelium

Nose, Larynx, and Trachea

Chapter 22 outlines the morphology of the nose, larynx, and trachea. The text includes descriptions of spontaneous and treatment-related lesions observed in the tissues in toxicity and carcinogenicity studies.

The text begins with a description of the normal upper respiratory tract through the stages of embryonic development. Anatomy and histology are discussed before delving into the various degenerative, regenerative, and adaptive lesions found in toxicology studies. Included in the text is information on inflammatory and vascular lesions, and how trauma and injury, as well as exposure to irritants, can elicit inflammatory responses.

Molecular pathology of the upper respiratory tract is investigated, as well as an examination of the molecular alterations within specific cell types, providing a better understanding of the mechanisms of tissue injury.

Sex differences in the acute nasal antioxidant/antielectrophilic response of the rat to inhaled naphthalene

Naphthalene is a nasal carcinogen, inducing respiratory adenomas in male and olfactory neuroblastomas in female rats, respectively. The reasons for the site and sex-specific tumorigenic response are unknown. Naphthalene is bioactivated to electrophilic metabolites; cytotoxicity followed by regenerative cell proliferation is likely involved in the tumorigenic response. To examine sex differences in the acute nasal response to naphthalene, male and female F344 rats were nose-only exposed to 0, 1, 3, 10, or 30 ppm naphthalene vapor for 4 or 6 h. Following exposure, respiratory/transitional mucosa (RTM) and olfactory mucosa (OM) were isolated and analyzed for markers of oxidant/electrophilic stress and/or toxicity, including reduced/oxidized glutathione levels (GSH/GSSG), mRNA levels of electrophile-responsive genes, and epithelial cytoxicity (as measured by membrane permeability to ethidium homodimer-1). Naphthalene caused significant depletion of GSH in RTM and OM with no increase in GSSG. Cytotoxicity was apparent at concentrations of 15 and 30 ppm. No consistent sex differences were observed in these responses. Sex differences were observed in the induction of antielectrophilic genes in OM: glutamyl cysteine ligase (catalytic subunit) (Gclc), NADPH quinone oxidase 1 (Nqo1), and heme oxygenase 1 (Hmox1) were all induced to a greater extent in the male OM compared with the female. No consistent sex differences were observed in the RTM. Although the mechanism of the sex difference in the RTM adenoma response remains enigmatic, sex differences in the induction of antioxidant/electrophile-responsive genes may contribute to the heightened sensitivity of the female OM to the carcinogenic effects of naphthalene.

RNA profiles of rat olfactory epithelia: individual and age related variations

Background

Mammalian genomes contain a large number (~1000) of olfactory receptor (OR) genes, many of which (20 to 50%) are pseudogenes. OR gene transcription is not restricted to the olfactory epithelium, but is found in numerous tissues. Using microarray hybridization and RTqPCR, we analyzed the mRNA profiles of the olfactory epithelium of male and female Brown Norway rats of different origins and ages (newborn, adult and old).

Results

(1) We observed very little difference between males and females and between rats from two different suppliers. (2) Different OR genes were expressed at varying levels, rather than uniformly across the four endoturbinates. (3) A large proportion of the gene transcripts (2/3 of all probes) were detected in all three age groups. Adult and older rats expressed similar numbers of OR genes, both expressing more OR genes than newborns. (4) Comparisons of whole transcriptomes or transcription profiles of expressed OR genes only showed a clear clustering of the samples as a function of age. (5) Most OR genes were expressed at lower levels at birth than in older animals, but a small number of OR genes were expressed specifically or were overexpressed in newborns.

Conclusion

Not all OR genes are expressed at a detectable level. Pups expressed fewer OR genes than adult rats, and generally at a lower level; however, a small subset of OR genes were more strongly expressed in these newborn rats. The reasons for these differences are not understood. However, the specific expression of some OR genes in newborn olfactory epithelia may be related to the blindness and deafness of pups at birth, when these pups are heavily reliant on olfaction and their mother.