The purpose of this qualitative morphological study was the immunocytochemical and ultrastructural comparison of perivascular nerves of the basilar artery (BA) of young (6-month-old) and adult (12-month-old) capybaras - adult capybaras showed regression of the internal carotid artery (ICA). The study focused on immunolabeling for the vasoactive peptide endothelin-1 (ET-1) and endothelin A receptor (ETA) as well as for the synapse marker synaptophysin (SYP). In the BA of young capybaras, immunoreactivity for ET-1, ETA receptor and SYP was detected in perivascular nerve varicosities and/or intervaricosities. Immunoreactivity for ET-1 and ETA receptor was also displayed by some Schwann cells, which accompanied perivascular nerves. In addition to the presence of the above-described perivascular nerve characteristics, the BA of adult animals also revealed structurally altered perivascular nerves, where axon profiles were irregular in shape with dense axoplasm, while the cytoplasm of Schwann cells was vacuolated and contained myelin-like figures. These structurally altered perivascular nerves displayed immunoreactivity for ET-1, ETA receptor and SYP. These results show that the ET-1 system is present in some of the BA perivascular nerves and it is likely that this system is affected during animal maturation when ICA regression takes place. The role of ET-1 in cerebrovascular nerves is still unclear but its involvement in neural (sensory) control of cerebral blood flow and nerve function is possible.

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