Figure 2.

TR-Dex3 disposition in plasma and brain after intranasal or intraarterial administration. (A) Schematic of the ventral rat brain surface depicting key areas of focus for our study: the entry zones of cranial nerves I (olfactory) and V (trigeminal) along with the cerebral arteries and their associated PVS. (B) Ventral view of the unperfused brain surface from a nontreated animal showing the approximate regions imaged in (I–L). A putative PVS surrounding the lumen of numerous arteries can be realized upon close inspection because the vessels remain filled with blood. The PVS associated with a proximal branch of the MCA is indicated in B1. (C) TR-Dex3 plasma concentration over time after intranasal or intraarterial administration. Intranasal administration of 1.2 mg of TR-Dex3 was performed dropwise over 15 minutes. Intraarterial administration of 2 μg TR-Dex3 was infused through the abdominal aorta over the first 1 to 2 minutes of the experiment. Plasma samples were acquired at 10 and 20 minutes after initiation of the experiment. The concentration of TR-Dex3 at time zero after intraarterial administration was estimated by dividing the dose by the plasma volume of female Sprague–Dawley rats (3.4 mL/100 g).⁴⁰ Values are presented as means±s.e.m. (n=5 for each condition). (D) Ex vivo fluorescence imaging of the ventral brain surface after intranasal TR-Dex3 and saline upper body perfusion. Representative image showing TR-Dex3 fluorescent signal on the olfactory bulb, the trigeminal nerve (V) entry zone of the brainstem, and in the PVS of arteries on the ventral surface of the brain 20 minutes after intranasal administration. A representative image obtained under identical imaging and image processing conditions revealed no visible fluorescence on the ventral brain surface after intraarterial administration of TR-Dex3 (D1; scale bar=1 mm). Boxes in D are shown at higher magnification (E–H), with significant perivascular fluorescent signal observed along the VOA at the ventrocaudal olfactory bulb (E), at the bifurcation of the ICA into the MCA and ACA (F), at the level of the basilar artery dividing into two trunks yielding the SCA and PCA within the interpeduncular fossa (G), and at the lateral branching of the AICA off of the basilar artery (H). Representative images of the lateral brain surface in different animals consistently revealed significant perivascular fluorescence associated with the MCA after intranasal (I) but not intraarterial (J) administration of TR-Dex3 under identical imaging and image processing conditions. Similarly, representative images of the ventral brainstem also consistently revealed significant perivascular fluorescence associated with the posterior circulation after intranasal (K) but not intraarterial (L) administration of TR-Dex3 under identical imaging and image processing conditions. Scale bars for E–H=400 μm. ACA, anterior cerebral artery; AICA, anterior inferior cerebellar artery; ICA, internal carotid artery; MCA, middle cerebral artery; OFA, olfactofrontal artery; PCA, posterior cerebral artery; PVA, posterior ventral artery; PVS, perivascular space; SCA, superior cerebellar artery; TR-Dex3, Texas Red-labeled 3 kDa dextran; VOA, ventral olfactory artery.