Identification of the rostral migratory stream in the canine and feline brain

Abstract

In the adult rodent brain, neural progenitor cells migrate from the subventricular zone of the lateral ventricle towards the olfactory bulb in a track known as the rostral migratory stream (RMS). To facilitate the study of neural progenitor cells and stem cell therapy in large animal models of CNS disease, we now report the location and characteristics of the normal canine and feline RMS. The RMS was found in Nissl-stained sagittal sections of adult canine and feline brains as a prominent, dense, continuous cellular track beginning at the base of the anterior horn of the lateral ventricle, curving around the head of the caudate nucleus and continuing laterally and ventrally to the olfactory peduncle before entering the olfactory tract and bulb. To determine if cells in the RMS were proliferating, the thymidine analog 5-bromo-2-deoxyuridine (BrdU) was administered and detected by immunostaining. BrdU-immunoreactive cells were present throughout this track. The RMS was also immunoreactive for markers of proliferating cells, progenitor cells and immature neurons (Ki-67 and doublecortin), but not for NeuN, a marker of mature neurons. Luxol fast blue and CNPase staining indicated that myelin is closely apposed to the RMS along much of its length and may provide guidance cues for the migrating cells. Identification and characterization of the RMS in canine and feline brain will facilitate studies of neural progenitor cell biology and migration in large animal models of neurologic disease.

Figure 1. Rostral migratory stream in the dog brain.

(A) Schematic of a sagittal view of a canine brain. The red line indicates the location of the RMS in relationship to the anterior horm of the lateral ventricle (LV), caudate nucleus (CN), olfactory bulb (OB), cortex (Ctx) and cerebellum (Cb). (B) Nissl staining showing the orientation and nomenclature of the canine RMS. (C) anti-BrdU immunostaining in brown with hematoxylin counterstain in purple. C1 shows BrdU staining at the boundary of the white matter and caudate nucleus in the descending limb; C2 shows BrdU staining in the olfactory peduncle/rostral limb. (D) anti-Dcx immunostaining. D1 shows morphology of cells in the funnel; D2 shows leading and trailing processes of migrating cells in the descending limb. (E) Immunoreactivity for BrdU (green, in the RMS) and NeuN (red, in the CN) does not overlap in the descending limb. Section is counterstained with DAPI (blue). (F) BrdU immunostaining (brown) in the olfactory peduncle in tissue from dog 5, analyzed at 6 hr after a single 75 mg/kg i.v., indicating that BrdU is taken up by dividing cells all along the RMS. Scale bar in B, C, D: 1 mm. Scale bars in C1, C2, E: 100 microns. Scale bars in D1, D2, F: 50 microns. Please view the figures on a computer monitor for accurate RGB color representation.

Figure 2. Rostral migratory stream in the cat brain.

(A) Nissl staining demonstrating the RMS orientation and location from the anterior horn of the lateral ventricle (LV) to the olfactory bulb (OB). (B) anti-BrdU immunostaining. (C) anti-Ki67 immunostaining, demonstrating the presence of dividing cells along the entire RMS. (D, E) T2-weighted MRI images of a cat head in the dorsal (D) and transverse (E) planes, showing cerebrospinal fluid in the open olfactory ventricles of an adult (5 year old) cat (arrows). Scale bars in main panels A–D: 500 microns. Scale bars in insets B1–2, C1–3∶100 microns.

Figure 3. Relationship of white matter and the RMS.

(A) Luxol fast blue staining of a saggital section from dog 4. Inset shows the approximate location of the RMS in red and part of the white matter in blue. (B–D) Confocal maximum projection images of CNPase staining (red) and doublecortin staining (green) in the SVZ (B), funnel (C), and olfactory peduncle (D) in dog 1.

Figure 4. Areas of dog brain (A–C) and cat brain (D–E) embedded for sectioning.

(A, D): Lateral view. (C, E): Ventral view. (B): View from the midline. Hemispheres were separated and an ∼40×22×22 mm block (including the olfactory bulb when possible) was isolated from each side (B’–E’). Scale bar in B’ and D’ is 1 cm. Labels are based on the atlas of Singer.