Sampling and analysis of cerebrospinal fluid for chronic studies in awake rats

A method is described whereby cerebrospinal fluid (CSF) may be sampled repeatedly from awake rats over a period of 1 to 10 wk. Stainless steel or Teflon catheters (22-gauge) were implanted in the cisterna magna of anesthetized rats (n = 19) via a midline hole immediately rostral to the interparietal-occipital suture. Several days later almost simultaneous CSF and blood samples from the same air-breathing animals were slowly drawn into glass capillary tubes. pH was determined immediately by electrode and total CO2 by microgasometer. Because sampling via Tygon microbore tubing attached to the implanted catheters allowed part of CSF CO2 content to be lost through the tube wall, stainless steel tube is preferred to make this connection. For mock CSF, total CO2 calculated from pH and PCO2 values was closely comparable to that directly measured by microgasometer. CSF pH, PCO2, and [HCO-3] in five awake rats were found to be similar to those reported in the literature for the briefly anesthetized rat. The sampling procedure did not of itself significantly alter breathing patterns (n = 14). Thus, chronic CSF sampling is feasible in awake rats for purposes of studies of ventilatory control.