Figure 2.

Pharmacological identification of the two types of the VLPO neurons in in vitro brain slices. A multipolar neuron (a) and a fusiform or bipolar neuron (c), scale bar, 10 μm. Noradrenaline (NA, 10 μM) inhibited the firing rate of the multipolar triangular neuron (a) but increased the firing rate of the bipolar fusiform neuron (c). The neurons inhibited by NA (10 μM) were identified as the sleep-promoting neurons, and the neurons excited by NA were interneurons. (b) NA-inhibited neurons (sleep-promoting neurons) are characterized by a low-threshold spike (LTS) (asterisk) when depolarized from a hyperpolarized level or when released from a hyperpolarized level (inset). (d) NA-excited neurons (interneurons) never show LTSs when they are depolarized from any level of membrane hyperpolarization. They usually show a slowing of the voltage response toward the first action potential (arrow).