Data from: Avian cephalic vascular anatomy, sites of thermal exchange, and the rete ophthalmicum

The general anatomy of avian cephalic blood vessels is well known and there are published details of their role in physiological thermoregulation. Unfortunately, the finer details of vascular pathways to and from sites of thermal exchange are not well known. Additionally, the role of the rete ophthalmicum (RO), a vascular heat exchanger in the temporal region, has been investigated in terms of brain temperature regulation, yet only the arteries have received substantial attention. Without anatomical details of both the arterial and venous pathways, the role of blood vessels in physiological thermoregulation is incomplete. Cephalic vascular anatomy of multiple avian taxa was investigated using a differential-contrast, dual-vascular injection technique and high-resolution X-ray microcomputed tomography. Sites of thermal exchange (oral, nasal, and orbital regions) and the RO were given special attention due to their known roles in cephalic thermoregulation. Blood vessels to and from sites of thermal exchange were investigated to detect conserved vascular patterns and their ability to deliver cooled blood to the RO and dural venous sinus. Sites of thermal exchange were supplied by arteries directly and through collateral pathways. Veins were found to offer multiple pathways that could influence the temperature of neurosensory tissues, as well as pathways that would bypass neurosensory tissues. These results question the paradigm that arterial blood from the RO is the primary method of brain cooling in birds. A shift in the primary role of the RO from brain cooling to regulating and maintaining the temperature of the avian eye should be further investigated.

鸟类头部血管的大体解剖结构已广为人知，且已有文献详细阐述了其在生理性体温调节（physiological thermoregulation）中的作用。然而，关于通往热交换部位以及从中发出的血管通路的精细细节，目前仍不甚明确。此外，颞区的血管性热交换器（vascular heat exchanger）——眼周血管网（rete ophthalmicum, RO）——的功能已围绕脑部温度调节展开研究，但相关探讨仅聚焦于动脉血管，尚未对静脉通路给予充分关注。若缺乏动静脉通路的解剖学细节，关于血管在生理性体温调节中作用的认知便不够完整。本研究采用微分对比双血管注射技术与高分辨率X射线显微计算机断层扫描（high-resolution X-ray microcomputed tomography），对多个鸟类类群的头部血管解剖结构展开了探究。鉴于口腔、鼻腔与眶区以及眼周血管网（RO）在头部体温调节中的已知功能，本研究对这些区域予以重点关注。本研究对通往热交换部位的血管进行了分析，以探寻保守的血管模式，以及其向RO与硬脑膜静脉窦输送低温血液的能力。热交换部位通过动脉直接供血，并可经由侧支通路获取血液。研究发现，静脉存在多条可影响神经感觉组织温度的通路，同时也存在绕过神经感觉组织的通路。上述研究结果对“鸟类脑部降温的主要方式为来自眼周血管网（RO）的动脉血液”这一学术范式提出了质疑。未来应进一步探究将眼周血管网（RO）的核心功能从脑部降温，转变为调节并维持鸟类眼部温度的可能性。