Cellular localization of aquaporin-1 in the human and mouse trigeminal nervous system.

<p>+ represents AQP1 immunoreactivity is detectable and − represents is not.</p

Mouse AQP1 positive trigeminal neurons innervate the oral mucosa but not skin.

<p>(<b>A–C</b>) Representative combined fluorescent and light images showing the injection site of retrograde tracer FG (red asterisks) within the cheek mucosa and submucosa of mice. (<b>D–I</b>) Representative double fluorescent images showing the co-distribution of AQP1 immunoreactive neurons (blue) with FG-labeled neurons (green) innervating cheek mucosa (D–F) or skin (G–I). AQP1 and FG double-labeled neurons are marked with arrowheads. AQP1 single-labeled neurons are marked with the double-arrowheads, and FG single-labeled neurons with arrows. Note that some FG-labeled small-size mucosal neurons are co-labeled with AQP1. No FG-labeled cutaneous neurons are positive for AQP1. Scale bars = 500 µm in A–C; 40 µm in D–I.</p

Localization of AQP1 in the brain stem of humans (A, B, G–L) and mice (C–F).

<p>(<b>A–F</b>) Representative images of immunohistochemistry for AQP1. (<b>G–L</b>) Representative images of double immunofluorescence of AQP1 (red) with GFAP (green in H) or β-tubulin III (green in K) in the sp5. There is extensive expression of AQP1 throughout the human medulla oblongata including the spinal trigeminal tract (sp5) and spinal trigeminal nucleus (Sp5, A and B). AQP1 and GFAP are highly colocalized at the glial lamellae along the medulla surface as well as astrocyte processes within the brain parenchyma (G–I). Interestingly, astrocyte cell bodies (arrowheads in I) do not express AQP1. No β-tubulin III positive axons coexpress AQP1 in the sp5 (L). In the mouse brain stem, dense dot-like AQP1 labeled nerve fibers are present in the caudal part of sensory root of the trigeminal nerve (s5, E) and sp5 (C and D), but not at the rostral part of s5 or at the motor root of the trigeminal nerve (m5, F). Moreover, AQP1 positive axonal terminals are observed in the caudal and interpolar parts of the trigeminal nucleus (Sp5C and Sp5I, C and D), but not in the principal sensory trigeminal nucleus (Pr5, E). Scale bars = 1 mm in A; 200 µm in B, G–L; 400 µm in C–F.</p

Localization of AQP1 in the trigeminal ganglion of humans (A, C–E) and mice (B, F–H).

<p>(<b>A–B)</b> Representative images of immunohistochemistry for AQP1. (<b>C–H)</b> Representative images of double immunofluorescence with AQP1 (red) and β-tubulin III (green). Some small-sized (white asterisks) and medium-sized (yellow asterisks) trigeminal neurons of humans and mice are positive for AQP1 which is localized to the cell membrane and cytoplasm. Large-sized trigeminal neurons (black asterisks) of the two species are negative for AQP1. Satellite cells expressing AQP1 (arrowheads) are observed around both AQP1-negative and -positive trigeminal neurons in humans, but only around AQP1-positive trigeminal neurons in mice. Both human and mouse capillary endothelial cells (arrows) express AQP1. (<b>I–J</b>) Immunolocalization of glutamine synthetase (I) and AQP1 (J) in the 10 µm adjacent sections of mouse trigeminal ganglion. Each neuron is wrapped tightly by GS-positive satellite glial cells (arrowheads in I). However, AQP1 immunoreaction (arrowheads in J) is only localized to satellite cells surrounding AQP1-positive trigeminal neurons. Scale bars = 50 µm in A–H; 15 µm in I and J.</p

Cellular Localization of Aquaporin-1 in the Human and Mouse Trigeminal Systems

<div><p>Previous studies reported that a subpopulation of mouse and rat trigeminal neurons express water channel aquaporin-1 (AQP1). In this study we make a comparative investigation of AQP1 localization in the human and mouse trigeminal systems. Immunohistochemistry and immunofluorescence results showed that AQP1 was localized to the cytoplasm and cell membrane of some medium and small-sized trigeminal neurons. Additionally, AQP1 was found in numerous peripheral trigeminal axons of humans and mice. In the central trigeminal root and brain stem, AQP1 was specifically expressed in astrocytes of humans, but was restricted to nerve fibers within the central trigeminal root and spinal trigeminal tract and nucleus in mice. Furthermore, AQP1 positive nerve fibers were present in the mucosal and submucosal layers of human and mouse oral tissues, but not in the muscular and subcutaneous layers. Fluorogold retrograde tracing demonstrated that AQP1 positive trigeminal neurons innervate the mucosa but not skin of cheek. These results reveal there are similarities and differences in the cellular localization of AQP1 between the human and mouse trigeminal systems. Selective expression of AQP1 in the trigeminal neurons innervating the oral mucosa indicates an involvement of AQP1 in oral sensory transduction.</p> </div

Colocalization of AQP1 and β-tubulin III in the oral submucosa, muscle and skin of humans (A–C, G–I, M–O) and mice (D–F, J–L, P–R).

<p>(<b>A–F</b>) AQP1 (red) and β-tubulin III (green) are coexpressed within a number of the nerve bundles (arrowheads) of the cheek submucosa from the two species. AQP1 positive microvessels (arrows) are also scatted among the nerve bundles. (<b>G–R</b>) There are a large number of β-tubulin III (green) positive nerve fibers, and a few AQP1 positive microvessels (arrowheads), within the cheek intermusclar (G–L) and subcutaneous regions (M–R). No overlap between β-tubulin III and AQP1 immunoreactivity is observed. Scale bars = 100 µm.</p

Localization of AQP1 in the peripheral and central branches of human (A–C,G–L) and mouse (D–F,M–S) trigeminal neurons.

<p>(<b>A–F</b>) Representative images of immunohistochemistry for AQP1. (<b>G–R</b>) Representative images of double immunofluorescence with AQP1 (red) and GFAP (green in H and N) or β-tubulin III (green in K and Q). A considerable proportion of axons are positive for AQP1 within the human (transverse section, A) and mouse (longitude section, D) mandibular nerve. The human trigeminal central root exhibits dense immunoreactivity for AQP1 (B, C, G, J), which is colocalized with GFAP (I), but not β-tubulin III (L). In contrast, in the mouse trigeminal central root, there are a population of AQP1 positive axons (E, F, M, P) that coexpress β-tubulin III (R) but not GFAP (O). Scale bars = 100 µm in A, D, F; 300 µm in B; 200 µm in E; 50 µm in C, G–R.</p

The percentage of AQP1-immunoreactive neurons in the trigeminal ganglia of humans and mice.

<p>The Data were expressed as a percentage of positive neurons respect to the total neuronal population in each class of neurons (small- medium- and large-sized neurons) (n = 3 in humans and n = 5 in mice).</p

Localization of AQP1 in the oral tissues of humans (the left panels) and mice (the right panel).

<p>(<b>A–F</b>) Representative images showing that AQP1 is localized to nerve fibers (arrowheads in A–F) and microvascular walls (arrows in A–F) within the mucosa and submucosa of the tongue (A–D) and cheek (E and F) of the two species. There is AQP1 immunoreactivity within the filiform papillae of humans (A) and mice (B). Note that AQP1 immunoreactivity is distinctively localized to the apex of the mouse filiform papillae (stars in B). In addition, AQP1 immunoreactivity is found within the human stratum corneum of the tongue (A). AQP1 staining is present below the taste buds, but there is no staining within the taste buds (star in D). (<b>G–J</b>) Representative images showing that AQP1 immunoreactivity is present in blood vessels (arrows in G–J) in the human and mouse cheek muscle (G and H) and skin (I and J). Note that intramuscular nerve fibers (double arrowheads) are negative for AQP1. Scale bars = 200 µm in A; 50 µm in B and G–J; 100 µm in C–F.</p

Reactive microgliosis in the hippocampus of 4-week-old Bmi-1^−/− mice.

<p>Compared with WT littermates (A and C), strong immunostaining for the microglial marker Iba-1 was observed in the hippocampus of Bmi-1^−/− mice (B and D). Activated microglia with large soma and thick processes (arrowheads) were present at Bmi-1^−/− mice (D).</p