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Changes in continuously recorded intracranial pressure of conscious rabbits at different time-periods after superior cervical sympathectomy.

The intracranial pressure, measured as the ventricular fluid pressure (VFP), was recorded continuously during about 2 days via a cannula inserted into the left lateral ventricle of the brain of conscious rabbits. The effect of bilateral removal of the superior cervical ganglia on the VFP was studied at various time-periods after operation, and the results were compared with those from unoperated control animals. The pressure changes attributed to the sympathectomy are referred to as the net VFP. The operation ultimately caused a disappearance of noradrenaline from intracranial sympathetic nerves. The net VFP was not affected during an 8-hr period of the recording starting 5–8 hrs after sympathectomy. During the following 35 hrs it was reduced by approximately 25 mm physiological saline followed by a return to initial or somewhat higher levels. Four days after sympathectomy the net VFP was significantly increased throughout the recording period. Two weeks after the operation the pressure had returned to the same, or even lower level compared with the non-sympathectomized control animals. The variations in the net VFP at different time-periods after sympathectomy are considered to reflect mainly changes in the intracranial vascular bed due to the leakage and disappearance of the noradrenaline transmitter from the degenerating nerve terminals followed by denervation supersensitivity. The results are discussed in terms of a sympathetic influence on the intracranial pressure mediated through the volume of the intracranial vascular bed, and/or the cerebrospinal fluid production in the choroid plexuses.