The loss of ganglionic cells that followed the integrity of the pupillary reflex could be observed from week on and was most dramatic from days on. The differential degeneration of the retina caused by bilateral occlusion of the common carotid arteries in the rat.Twelve weeks after the vessel ligations, the hematoxylineosinstained retina sections of some rats appeared spared. In order to distinguish the contribution of visual impairment from the hippocampal neuronal damage to the spatial learning dysfunction, various approaches have been employed.When VO rats were divided into groups based on the presence or absence of the pupillary reflex, both groups comm itted more errors in the arm rad ialmaze as compared with the shamoperated controls, but the rats with an impaired pupillary reflex performed noticeably worse than the group with an intact reflex. In another study, the learning capacities of rats with bilateral internal carotid artery occlusion or with VO were compared.In the arm radial maze, the results resembled those obtained with the groups based on pupillary reflex integrity: both the internal carotid arteryoccluded and the VO groups committed more errors than the controls, and the VO group gave the worst performance. These experiments suggest that cerebral hypoperfusion itself compromises the learning process, but damage to the visual system aggravates the test results that depend on visual cues.It is highly likely that hypoperfusion severe enough to damage the retina has a more dramatic impact on the hippocampus and the related memory processes. Auditory and tactile stimuli also guide rats in spatial learning; this is especially true for albino rats with limited vision.The concerns as to the exact role of impaired vision in spatial learning in the VO model remain unresolved because of the lack of unequivocal evidence.On postoperative days and, a loss in body weight can be observed in both the shamoperated and VO groups.Since certain muscles in the ventralcervical reg ion are slightly damaged during the preparation of the carotid arteries, discomfort during movement of the head, mastication, and swallowing may B R A I N R E S E A R C H R E V I E W S contribute to this initial weight loss.The shamoperated animals start to regain weight rapidly, while the VO animals lag somewhat behind, even up to weeks after the onset of VO. The slower gain in body weight following VO cannot be attributed to the surgical method since the control animals are exposed to the same procedures.A potential increase in sympathetic tone or hormonal changes due to the ligation may be considered responsible for the delayed weight gain.On the other hand, the blood flow to the hypothalamus, a major center of autonomic control, is also markedly reduced in the VO model, which may compromise the hypothalamic function.Early reports described the hypertensive response after VO surgery, indicated by increases in blood pressure and heart rate. Our experiments followed the longterm changes in systolic blood pressure measured with the tail cuff method in unrestrained, awake rats from hup to weeks after the onset of permanent VO.