An Interactive Atlas of Zebrafish Vascular Anatomy

2 Days Post-Fertilization
By 2 dpf, most trunk and tail Se have lumenized (visible by angiography) and possess an active circulation [2 dpf overview]. The DLAVs are still two paired vessels rostrally, but caudally many anastomotic vessels are present between the right and left DLAVs. The trunk axial vessels (DA, PCV) are still relatively unchanged from earlier stages. Over the course of the next week the CV plexus becomes gradually remodeled down to a single, better-defined vascular tube. In the rostral trunk, vascularization of the pronephric glomus begins immediately ventral to the DA just caudal to its radix. The left paired PCV has begun a process of regression that will continue over the next several days with the right PCV eventually carrying the venous return from almost all of the trunk and the left PCV draining only the first few SeV. The supraintestinal artery (SIA) and the subintestinal veins (SIV), which will eventually provide blood supply to the digestive system, begin to appear at or after this stage (see [2.5 dpf overview]). The SIA is a continuation of the anterior mesenteric artery (AMA), which branches out from the DA just posterior to the pronephric glomus. Visualization of the AMA and SIA by fluorescent angiography is difficult because of the position of these vessels branch deep in the ventral trunk adjacent to the yolk ball. However, they are well visualized in Berlin blue dye-injected embryos (see [AMA & derivatives] and 2.5 dpf text). The SIV drains directly into the PCV and CCV at this stage. At later stages the hepatic sinusoid will be interposed between the SIV and CCV/PCV.

In the aortic arch system, the third and the forth aortic arches appear around 2 dpf, and the fifth and the sixth arches develop by 2.5 dpf (see [early 2.5 dpf head arches],[later 2.5 dpf head arches] for intermediate and "final" stages of arch emergence, and Fig. 6B,D,E and Fig. 8B-E for more details on arch anatomy). The second or hyoid aortic arch disappears and is replaced by a more superficial vessel, the opercular artery (ORA). A new venous vessel, the primary head sinus (PHS), begins to extend rostrally from the rostral tip of the ACV along the ventral-lateral wall of the otic capsule, joining to the rostral end of the PHBC. It is generally complete before 2.5 dpf (see below). The PHS is also called the "Lateral head vein" (in contrast to the "Medial head vein," or PHBC; see [2 dpf overview], and [early 2.5 dpf head arches],[later 2.5 dpf head arches]). The PHS becomes the main route for venous drainage from the head, subsuming in large part the early role of the PHBC.

The main arterial route for the brain, consisting of PICA, CaDI and BA, becomes robust by 2 dpf, and new branches appear from these vessels [2 dpf head, dorsal],[2 dpf head, ventral-anterior-lateral],[2 dpf head, dorsal-lateral]. The OA now feeds into a small plexus of vessels within the optic cup derived from the hyaloid artery and vein [2 dpf head, ventral-anterior-lateral]. A vessel circles the rostral half of the inner rim of the optic capsule, which will at later stages be part of the completed ring of the inner optic circle (IOC). The IOC drains ventrally into the OV and dorsally into the DCV [2 dpf head, ventral-anterior-lateral],[2 dpf head, dorsal-lateral]. The vascular connection allowing the CrDI to drain directly into the PMBC has now been severed, and all of its circulation is routed through the NCA. The connection between the PMsA and the PMBC also becomes severed. The distal portion of the PMsA drains the midbrain central arteries into the PMBC-PHBC junction [1-2 dpf head vessel changes]. The proximal portion of the PMsA becomes designated the mesencephalic artery (MsA). At slightly later stages the MsA will traverse the entire D-V extent of the head to drain via the mesencephalic veins (MsV) into the dorsal longitudinal vein (DLV; see [2.5 dpf head dorsal multilayer composite], tracing the course of the MsA). At this stage, however, the MsA does not yet connect to the MsV [2 dpf head, ventral-anterior-lateral],[2 dpf head, dorsal-lateral]. PLA extends rostrally from CrDI along the base of mid and forebrain, then loops medially and links to the corresponding vessel from the other side of the embryo (PLA’) at the PLA junction (PLAJ). Two new vessels, the communicating vessels CMV and CMV’, branch dorsal-laterally from the PLAJ, and link to the base of PrA or PrA’ [2 dpf head, ventral-anterior-lateral],[2.5 dpf head dorsal multilayer composite] lower layers, and [1-2 dpf head vessel changes]. Another new vessel also appears at or slightly after this stage, the median palatocerebral vein (MPLV). It takes off in a caudal direction from the midpoint of the PLA-PLA’ loop, and proceeds straight caudally along the cranial midline just above the pharynx, just below the diencephalon (3rd ventricle). At a level just posterior to the eye it ends in a "T," and its two branches, the palatocerebral veins (PLV) each drain laterally into the OV, and from there to the PMBC-PHBC junction [2.5 dpf head dorsal multilayer composite] or [3.5 dpf head dorsal multiulayer composite] lowest layers and [1-2 dpf head vessel changes].

At this stage, a number of central arteries (CtA) also begin to penetrate into the brain substance[2 dpf overview], [2.5 dpf head dorsal multilayer composite], and [1-2 dpf head vessel changes]. Three pairs of CtA extend from the BCA to irrigate the fore- and midbrain. The anterior mesencephalic central arteries (AMCtA), AMCtA and AMCtA’, extend arostrally. The PrA branch ventrally from the AMCtA, then irrigate the forebrain, draining via the ACeV and eventually into the PMBC [2.5 dpf head dorsal multilayer composite] (lower middle layer). The PLA also empties into the PrA via the CMV [2 dpf head, ventral-anterior-lateral], [2.5 dpf head dorsal multilayer composite], and [1-2 dpf head vessel changes]. The AMCtA irrigate rostral regions of the midbrain. The middle mesencephalic central arteries (MMCtA and MMCtA’) project rostrally and dorsally to irrigate the mid-portion of the midbrain [2.5 dpf head dorsal multilayer composite] middle layer and [1-2 dpf head vessel changes]. Another pair of CtA, the posterior mesencephalic central arteries (PMCtA), PMCtA and PMCtA’, project dorsally from BCA to irrigate the caudal part of the midbrain. These sets of vessels can often have common roots from the BCA (for example, see AMCtA’ MMCtA and PMCtA in [4.5 dpf head dorsal multilayer composite], lower middle and middle layers). Eventually the AMCtA, MMCtA and PMCtA all drain into the PMBC-PHBC junction via the remnant of the PMsA, as noted above. Still another pair of CtA, the cerebellar central arteries (CCtA and CCtA’), take off and extend upward from the PCS, branch to provide an arterial feed to the hindbrain, then drain back down into the PHBC ([4.5 dpf head dorsal multilayer composite], lower middle and middle layers and [1-2 dpf head vessel changes]). Many additional single central arteries extend dorsally from the BA, branch and intermingle, then loop down and drain into the PHBC. The BA and the paired PHBC extend caudally and make further interconnections on the ventral surface of the medulla oblongata. There is a prominent interconnection formed at the caudal most end of both sets of vessels. At this same point, a connection forms at 2-2.5 dpf linking the caudal ends of both PHBC to the paired DLAVs more dorsally in the cranial trunk. Eventually, this connection will detach from the PHBC and be solely from the BA at later stages. These and other changes in the vasculature of the head-trunk junction are detailed in [head-trunk connections]. In the cranial vascular system, the two MsV can be seen projecting rostrally from the DMJ or DLV and then diving ventrally. These vessels will eventually link to the MsA, but as noted above are not at this stage continuous through the head [2 dpf overview],[2 dpf head, dorsal-lateral]. The posterior cerebral veins (PCeV) also begin to appear at this stage, sprouting caudally from the DMJ or DLV and then eventually diving ventrally [2 dpf overview]. The PCeV are also not complete at this stage; they will eventually drain into the ACV [later 2.5 dpf head lateral], [2.5 dpf head dorsal multilayer composite]. As noted above in the 1.5 dpf section the "wiring pattern" of the cranial vasculature and changes that occur in this pattern between 1.5 and 2 dpf are diagrammed in [1-2 dpf head vessel changes].