Quick Freezing of the Murine Cns: Comparison of Regional Cooling Rates and Metabolite Levels When Using Liqujd Nitrogen or Freon‐121

Abstract— Murine brains were frozen in situ , either in liquid N 2 or in Freon‐12 cooled to its freezing point. The effect of these coolants on cooling rates and times in various CNS regions was determined. In addition, levels of ATP, P‐creatine and lactate were measured in selected regions of brains from both intact animals and severed heads frozen in either coolant. For both the intact animals and severed heads, superficial regions of brain cooled to 0°C and deeper regions to 25°C, at the same rate in either liquid N 2 or Freon. Subsequent cooling was more rapid in liquid N 2 in both regions. Levels of ATP, P‐creatine and lactate were similar in brains frozen in either coolant, probably because CNS utilization of highenergy phosphates decreased markedly as body temperature fell. In brains of animals frozen intact, levels of ATP and P‐creatine were higher and levels of lactate were lower than those in brains from heads which were severed prior to freezing. This difference may be a result of the marked stimulation which accompanies decapitation and may also reflect continued cerebral circulation in the intact animal for a brief time after immersing the animal in the coolant.