Intranasal instillation techniques are used to deliver various substances to the upper and lower respiratory tract (URT and LRT) in mice. Here, we quantify the relative distribution achieved with intranasal delivery of a nonabsorbable tracer, 99m Tc-labeled sulfidecolloid. Relative distribution was determined by killing mice after instillation and quantifying the radioactivity in dissected tissues using gamma scintigraphy. A significant effect of delivery volume on relative distribution was observed when animals were killed 5 min after instillation delivered under gas anesthesia. With a delivery volume of 5 l, no radiation was detected in the LRT; this increased to a maximum of 55.7 Ϯ 2.5% distribution to the LRT when 50 l were delivered. The majority of radiation not detected in the LRT was found in the URT. Over the course of the following 1 h, radiation in the LRT remained constant, while that in the URT decreased and appeared in the gastrointestinal tract. Instillation of 25 l into anesthetized mice resulted in 30.1 Ϯ 6.9% distribution to the LRT, while only 5.3 Ϯ 1.5% (P Ͻ 0.05) of the same volume was detected in the LRT of awake mice. Varying the body position of mice did not affect relative distribution. When using intranasal instillation, the relative distribution between the URT and LRT and the gastrointestinal tract is heavily influenced by delivery volume and level of anesthesia. gamma scintigraphy; topical treatment; upper respiratory tract; lower respiratory tract THE ADMINISTRATION OF SUBSTANCES to mice by the intranasal route is an effective, noninvasive technique employed for the delivery of allergens (3, 4, 26), drugs or gene therapy (4, 20), immunotherapy (1, 7, 11), and pathogens (12,16,18) to the upper and lower respiratory tracts (URT and LRT). In published studies, volumes of substances intranasally instilled into mice range from 5 l (22) to 100 l (3), with little justification for the chosen volumes. Intranasal delivery is often carried out after intraperitoneal (9, 19) or inhalation (5, 14, 15) anesthesia but has also been performed with fully awake mice (1,6,17). The position of the mouse during intranasal delivery has also varied between studies, with horizontal (13) and head-down supine (12) positions having been used. The specific delivery protocols used in these studies are thought to influence the relative distribution of the delivered substance to the URT, LRT, and gut. However, to our knowledge, very little published information is available describing the distribution of intranasally delivered substances or how the distribution can be influenced by delivery techniques.Preliminary studies by Tsuyuki et al. (23) have shown that 75% of a 50-l dose of intranasally administered Evans blue dye is deposited in the airways, with no dye detectable in the esophagus or stomach. Eyles et al. (7) reported that 48% of a 50-l dose of intranasally instilled 7-m-diameter 46 Sc-labeled styrene-divinyl benzene microspheres was evident in the lungs 15 min after challenge, while Takafuji et al. (21) ...

The mechanisms underlying airway hyperresponsiveness remain unclear, although airway inflammation and remodeling are likely important contributing factors. We hypothesized that airway physiology would differ between mice subjected to brief or chronic allergen exposure, and that these differences would be associated with characteristic inflammatory markers and indices of airway remodeling. BALB/c mice were sensitized to ovalbumin and studied at several time points following brief or chronic allergen challenge protocols. By measuring airway responses to methacholine, we demonstrated increases in maximal inducible bronchoconstriction that persisted for 8 wk following either brief or chronic allergen challenge; we also observed increases in airway reactivity, although it was only in chronically challenged mice that these changes persisted beyond the resolution of allergen-induced inflammation. Using airway morphometry, we further demonstrated that increases in maximal bronchoconstriction were associated with increases in airway contractile tissue in both models, and that chronic, but not brief, allergen challenge resulted in subepithelial fibrosis. Our observations that different aspects of sustained airway dysfunction and remodeling persist beyond the resolution of acute inflammatory events support the concept that remodeling occurs as a consequence of allergic airway inflammation, and that these structural changes contribute independently to the persistence of airway hyperresponsiveness.

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SUMMARY:Understanding the mechanisms of airway remodeling in chronic allergic conditions such as asthma is increasingly dependent on the use of animal models. Techniques for quantifying structural changes are required that are reproducible and responsive and that can be applied to different staining techniques in both human and animal airway tissues. Here, we characterize a morphometric technique to quantify changes in extracellular matrix and contractile tissue as two indices of airway remodeling in mice. Specific aims were to establish the optimum projection beneath the epithelium to assess remodeling changes and to determine whether such changes are reproducible within different areas of the lung. Finally, based on the variance within measurements, we calculated sample size requirements for research applications of this technique. BALB/c mice were sensitized to ovalbumin and studied after chronic allergen challenge. Lungs were formalin fixed and sectioned were then assayed for extracellular matrix or contractile tissue using morphometric/colorimetric techniques. In this model, the optimum projected distance to measure changes in extracellular matrix or contractile tissue was 20 m beneath the epithelium; projecting beyond this depth resulted in decreased ability to detect allergen-induced changes (signal) because of increased irrelevant staining of surrounding parenchymal tissue (noise). The technique was responsive, because an allergen-induced signal was detected in all airway sections and all lung regions studied (p Ͻ 0.05). The power of this analysis was such that allergen-induced changes can be reliably (Ͼ80% power) detected using 8 to 10 mice. This morphometric technique provides a valid and objective method to assess structural changes in the airways of mice after chronic allergen exposure. (Lab Invest 2003, 83:1285-1291.

SUMMARYExperimental mouse models of asthma have broadened our understanding of the mechanisms behind allergen-induced asthma. Typically, mouse models of allergic asthma explore responses to a single allergen; however, patients with asthma are frequently exposed to, and tend to be allergic to, more than one allergen. The aim of the current study was to develop a new and more relevant mouse model of asthma by measuring the functional, inflammatory and structural consequences of chronic exposure to a combination of two different allergens, ovalbumin (OVA) and house dust mite (HDM), in comparison with either allergen alone. BALB/c mice were sensitized and exposed to OVA, HDM or the combination of HDM and OVA for a period of 10 weeks. Following allergen exposure, airway responsiveness was measured using the flexiVent small animal ventilator, and mice were assessed for indices of airway inflammation and remodeling at both 24 hours and 4 weeks after the final allergen exposure. Mice exposed to the HDM-OVA combination exhibited increased numbers of inflammatory cells in the bronchoalveolar lavage (BAL) when compared with mice exposed to a single allergen. Mice exposed to HDM-OVA also exhibited an elevated level of lung tissue mast cells compared with mice exposed to a single allergen. Following the resolution of inflammatory events, mice exposed to the allergen combination displayed an elevation in the maximal degree of total respiratory resistance (Max R RS ) compared with mice exposed to a single allergen. Furthermore, trends for increases in indices of airway remodeling were observed in mice exposed to the allergen combination compared with a single allergen. Although concurrent exposure to HDM and OVA resulted in increased aspects of airway hyperresponsiveness, airway inflammation and airway remodeling when compared with exposure to each allergen alone, concurrent exposure did not result in a substantially more robust mouse model of allergic asthma than exposure to either allergen alone.

T-cell-mediated airway inflammation is considered to be critical in the pathogenesis of airway hyperresponsiveness (AHR). We have described a mouse model in which chronic allergen exposure results in sustained AHR and aspects of airway remodeling and here sought to determine whether eliminating CD4(+) and CD8(+) cells, at a time when airway remodeling had occurred, would attenuate this sustained AHR. Sensitized BALB/c mice were subjected to either brief or chronic periods of allergen exposure and studied 24 h after brief or 4 wk after chronic allergen exposure. In both models, mice received three treatments with anti-CD4 and -CD8 monoclonal antibodies during the 10 days before outcome measurements. Outcomes included in vivo airway responsiveness to intravenous methacholine, CD4(+) and CD8(+) cell counts of lung and spleen using flow cytometric analysis, and airway morphometry using a computer-based image analysis system. Compared with saline control mice, brief allergen challenge resulted in AHR, which was eliminated by antibody treatment. Chronic allergen challenge resulted in sustained AHR and indexes of airway remodeling. This sustained AHR was not reversed by antibody treatment, even though CD4(+) and CD8(+) cells were absent in lung and spleen. These results indicate that T-cell-mediated inflammation is critical for development of AHR associated with brief allergen exposure, but is not necessary to maintain sustained AHR.

These findings suggest that certain corticosteroid treatment regimes may actually potentiate airway remodeling and dysfunction in patients with asthma and lead to increased exacerbations and worsening of asthma symptoms.