Intracellular studies in the facial nucleus illustrating a simple new method for obtaining viable motoneurons in adult rat brain slices.

In general, it has been difficult to preserve electrophysiologically viable motoneurons in brain slices from adult mammals. The present study describes a new method for obtaining viable motoneurons in the facial nucleus of adult rat brain slices. The essence of the method was to use a modified artificial cerebrospinal fluid (ACSF) in which NaCl was replaced initially by sucrose; the modified ACSF was used during 1) preparation and 2) a 1 hr recovery period. The rationale for the modification is discussed in terms of the proposed acute neurotoxic effects of passive chloride entry and subsequent cell swelling and lysis. The actual recordings were made only after switching back to normal ACSF. Use of this method yielded large numbers of viable motoneurons that were suitable for intracellular recording; no motoneurons survived when normal ACSF (i.e., with NaCl) was used during slice preparation. A survey of some electrophysiological and pharmacological properties of facial motoneurons in this preparation, by means of current-clamp and voltage-clamp recording, revealed close similarities to the properties of adult motoneurons previously observed in vivo (e.g., time-dependent inward rectification, apamin-sensitive afterhyperpolarization, and serotonin-induced slow depolarization).