General anesthetic induced differential changes in latency of auditory evoked potential in the central nucleus of inferior colliculus of mouse.

Confirming the effect of general anesthetic on brainstem auditory evoked potential (BAEP) is important to interpret BAEP data, elucidate the neuroanatomical sites of action of general anesthetic and monitor the effect of general anesthetic. However, the effect of general anesthetic on BAEP is not thoroughly understood, which may be due to unreasonable acoustic stimulation scheme. This study aimed to redesign acoustic stimulation scheme and attempted to test our hypothesis that general anesthetic induces differential changes in BAEP latency in mouse. Auditory evoked potential in the central nucleus of inferior colliculus (AEP-ICC) was used to represent BAEP. Every 10 min after pentobarbital anesthesia, AEP-ICC was recorded by delivering tones with a rate of 1/s, and pentobarbital blood concentration (PBC) was measured, until the mice awoke. AEP-ICC latency to 80-dB SPL sounds (L) and latency change in nerve fibers (ΔL) did not present regular changes, and AEP-ICC latency to 50-dB SPL sounds (L) and latency change in synapses (ΔI) gradually decreased as pentobarbital was metabolized. L and ΔI changes were exponentially associated with decreased PBC, and L showed a linear relationship with ΔI. We conclude that, general anesthetic acts on auditory brainstem; general anesthetic does not alter L and ΔL but increases L and ΔI; L and ΔL can evaluate the function of auditory brainstem and its inferior structures under general anesthesia; L and ΔI exponentially reflect the blood concentration of a general anesthetic.