Abstract
Nucleus prepositus hypoglossi (NPH) is involved in the velocity-position integration for horizontal eye movements. To clarify which types of neurons compose the NPH, we investigated membrane properties, such as afterhyperpolarization (AHP), responses to hyperpolarizing currents, and firing patterns, of NPH neurons using whole-cell patch clamp technique in rat brainstem slices. AHPs were classified into three types: AHP without a slow component, AHP with a slow component, and AHP with a slow component and an afterdepolarization. Responses to hyperpolarizing current pulses were classified into three types: time-dependent inward rectification, time-independent inward rectification, and no inward rectification. Firing patterns were classified into continuous-spiking neurons that exhibited repetitive firings with relatively constant interspike intervals (ISIs), late-spiking neurons that exhibited a delay in the generation of the first spike, and neurons exhibiting an extremely low firing rate. Continuous-spiking neurons were further divided into two types according to whether the first ISI was markedly longer than the second. Neurons exhibiting the long first ISI were designated as FIL neurons. Application of 100μM apamin abolished the long ISI of FIL neurons, suggesting that the long ISI is attributed to activation of SK-type Ca2+ activated K+ conductances. All these results suggest that the NPH consists of heterogeneous neuronal population with various membrane properties and these neurons contribute to the neural integrator. [J Physiol Sci. 2006;56 Suppl:S190]
