Evaluation of a system for serial biopsy of cerebral cortical tissue in an awake goat

No techniques to date have been developed that allow investigators to obtain serial, rapidly frozen brain tissue samples in unanesthetized animals. The design and methods for implantation of cranial windows in goats are described in detail. The cranial window allows one direct and repeated access to the cerebral cortical surface. With each window, a parietal cortical area of 7.9 cm2 (minus the dura) is available for biopsy. Serial tissue samples are obtained using a suction-freezing system. Samples (100-250 mg) are frozen in less than 1 s. Up to six samples can be taken from each site. Goats were studied over a period of 2-5 days. No signs of sampling or immobilization stress were present as evidenced by a relatively constant level of arterial catecholamines and CO2 partial pressure (PCO2). Local cerebral blood flow (CBF) in the tissue under the window was of the same magnitude as that in other cerebral cortical regions and was unaffected by serial sampling. Levels of labile phosphates and of some glycolytic and tricarboxylic acid cycle-associated intermediates were minimally influenced by serial sampling. Greater variability in metabolite levels was seen for biopsies taken 2-5 days apart than for biopsies taken at 1- to 2-min intervals. However, variations within animals were less than variations among animals. This was especially true for acutely biopsied samples. The described methods provide a model for studies of cerebral metabolism in unstressed goats where anesthetic influences are avoided and where each animal can be utilized as its own control.