Membrane properties of excitatory and inhibitory neurons in the rat prepositus hypoglossi nucleus.

The prepositus hypoglossi nucleus (PHN) is thought to be a neural structure involved in transforming eye or head velocity signals into eye position signals for horizontal eye movements. In this study, we investigated the relationship between electrophysiological membrane properties and expression patterns of cellular markers for excitatory and inhibitory neurons by whole-cell patch clamp recordings followed by reverse transcription polymerase chain reaction (RT-PCR) analysis in rat brainstem slices. Three types of voltage response properties, namely afterhyperpolarization (AHP), firing pattern, and response to hyperpolarizing current pulses, were characterized in each neuron. Following RT-PCR analysis, we identified PHN neurons as either glutamatergic (n = 22) or GABAergic (n = 43), although a small number of cholinergic (n = 2) and glycinergic neurons (n = 1) were also identified. Both glutamatergic and GABAergic neurons showed a wide variety of membrane properties; however, we found several characteristic relationships between neuronal type and membrane properties. Most neurons exhibiting (i) AHP without a slow component, (ii) a firing pattern with a delay in the generation of the first spike, (iii) a firing pattern with a transient burst and (iv) a firing pattern with a prolonged initial interspike interval were GABAergic. On the other hand, glutamatergic neurons were primarily characterized by a low firing rate. These results indicate that there is a close relationship between specific electrophysiological membrane properties and expression of chemical markers in some types of glutamatergic and GABAergic PHN neurons.