Detection and measurement of neurofibromatosis-1 mouse optic glioma in vivo

Abstract

One of the major limitations to preclinical mouse therapeutic evaluation is the inherent difficulty in imaging small tumors in vivo. We present a rapid and reliable method to detect optic glioma (OPG) in a mouse neurofibromatosis-1 model (Nf1(flox/mut)GFAP-Cre mice) in vivo using Manganese-Enhanced Magnetic Resonance Imaging (MEMRI). In a blinded study, 23 mice were chosen randomly from a cohort of Nf1(flox/mut)GFAP-Cre mice and two sets of age-matched controls. In all cases, OPG presence or absence was correctly identified. In addition, the OPG size and shape were accurately measured in vivo, facilitating the use of this model for preclinical drug studies.

Figure 1. Individual slices from T1-weighted, transaxial spin-echo MR images of the prechiasmatic region of mouse brain demonstrate the effect of Mn²⁺ enhancement

(A) Representative wild-type mouse without Mn²⁺ enhancement. (B) Expansion of the region marked “A” around the optic nerve (white box). (C) Same wild-type mouse with Mn²⁺enhancement. (D) Expansion of C around the optic nerve (white box). T1-weighted spin-echo images [repetition time (TR) = 300 ms, echo time (TE) = 14 ms, number of scans (NS) = 16] were collected in a transaxial orientation with a 1.5 × 1.5 cm² field of view and slice thickness of 0.5 mm. Before all imaging experiments, mice were anesthetized with isoflurane/O₂ [4% (v/v)], and they were maintained on isoflurane/O₂ [1% (v/v)] throughout the experiments. Mouse body temperature was maintained at 37 ± 1 °C using a heating pad formed by circulating warm water.

Figure 2. MEMRI accurately detects optic glioma in Nf1^flox/mutGFAP-Cre mice

MR images and optic nerve gross pathology are shown from one representative wild-type mouse (panels A-C), and two representative Nf1^flox/mutGFAP-Cre mice with optic glioma (panels D-F and G-I). The top panels show slices from T1-weighted, spin-echo MR images of the chiasmic region; the middle panels show expansions around the optic nerve region (white box); the bottom panels show corresponding the optic nerves. MEMRI was able to detect the asymmetric appearance of the optic glioma in one Nf1^flox/mutGFAP-Cre mouse (panels D-F) compared to the more symmetric-appearing optic glioma in another Nf1^flox/mutGFAP-Cre mouse (panels G-I).

Figure 3. Cross-sectional areas of prechiasmatic region optic nerve are larger in Nf1^flox/mutGFAP-Cre mice than in Nf1^flox/floxGFAP-Cre or control mice

Average optic nerve cross-sectional areas in Nf1^flox/mutGFAP-Cre mice (0.49 mm²; SD 0.09 mm²) are larger than those in Nf1^flox/floxGFAP-Cre (0.36 mm²; SD 0.03 mm²) or C57Bl/6J mice (0.32 mm²; SD 0.05 mm²). The differences between the optic nerve areas in the Nf1^flox/mutGFAP-Cre mice and the two other groups are both statistically significant; the difference between the Nf1^flox/floxGFAP-Cre and C57Bl/6J mice is not statistically significant, as determined by the Mann-Whitney Rank Sum Test.