Abstract
The vestibular nucleus (VN) is a center for stabilizing gaze and posture in response to the head rotation and tilt. VN neurons are physiologically classified into regularly and irregularly discharging neurons on the basis of the regularity of spacing of action potentials. The segregation of VN neurons is involved in different response properties to head movements. Although the discharge regularity has been considered to be attributed to afterhyperpolarization (AHP), the relationships between the discharge regularity and profiles of AHP are still unclear. In this study, we investigated discharge patterns of VN neurons using whole-cell patch clamp technique not only in vitro slice preparations but in vivo preparations obtained from young rats. Previously, AHPs were classified into AHP without a slow component [AHP(s-)], AHP with a slow component [AHP(s+)], and AHP with a slow component and an afterdepolarization [AHP(s+) with ADP]. Both in vitro and in vivo, neurons exhibiting AHP(s+) fired more regularly than the other types of neurons. Application of 100 μM apamin to block Ca2+-dependent K+ channels abolished the slow component of AHP(s+) and made regular discharges of neurons exhibiting AHP(s+) to be irregular. These suggest that neurons exhibiting AHP(s+) are regularly discharging neurons, whereas neurons exhibiting AHP(s-) and AHP(s+) with ADP are irregularly discharging neurons. The regular firings of neurons exhibiting AHP(s+) are attributed to activation of apamin-sensitive Ca2+-dependent K+ channels. [J Physiol Sci. 2006;56 Suppl:S20]
