Microvascularization of thalamus and metathalamus in common tree shrew (Tupaia glis).

The microangioarchitecture of the thalamus and metathalamus in common tree shrew (Tupaia glis) was studied using vascular corrosion cast/stereomicroscope and SEM technique. The arterial supply of the thalamus and metathalamus was found to originate from perforating branches of the posterior communicating artery, the posterior cerebral artery, the middle cerebral artery, and the anterior choroidal artery. These perforating arteries gave rise to numerous bipinnate arterioles which in turn, with decreasing vessel diameters, branched into a non-fenestrated capillary bed. Venous blood from the superficial parts of the thalamus and metathalamus was collected into the thalamocollicular vein, whereas venous blood from internal aspects of the thalamus was conveyed to the internal cerebral vein. Some venous blood from the most rostral part of the thalamus flowed into tributaries of the middle cerebral vein before draining into the cavernous sinus. Further, the thalamic and metathalamic vascular arrangement was found to be of centripetal type. In addition, thalamic arterial anastomosis was rarely observed. Thus, obstruction of thalamic blood supply could easily lead to thalamic infraction.

Types of vascular wall as related to vasa vasorum in common tree shrew (Tupaia glis).

Blood vessels of the common tree shrew (Tupaia glis) were embedded in Araldite, sectioned at 0.5-1 microm thickness, and observed with light microscope (LM). It was found that the vascular wall could be classified into three categories: (1) those with proper vasa vasorum (PVV); (2) those with collaborative vasa vasorum in perimural tissues; (3) those without vasa vasorum. The PVV were located in the the tunica media, between the tunica media and the tunica adventitia, and in the tunica adventitia of the vascular wall. On studying the vascular casts with a scanning electron microscope (SEM), it was noted that what appeared to be vasa vasorum did not always conform to those found under the LM. Furthermore, the PVV seen in a particular blood vessel among different tree shrews were not always related to intraluminal partial pressure of oxygen, vascular size, and thickness of the wall. In contrast, the results of this study indicate that the activeness of the vascular wall in varying the amount of blood flow to certain organs is an important factor that is associated with the existence, density, and distribution of the vasa vasorum.