ABSTRACT
From studies using extracellular recording in behaving animals, it has been known for some time that the activity of monoamine cells of the locus coeruleus (LC) and dorsal raphe vary with the waking state of the animal. Calcium currents in LC neurons were indicated by the presence of slowly rising action potentials after treatment with tetrodotoxin. These action potentials were blocked by removing the calcium from the extracellular solution or by the addition of calcium channel blockers to the extracellular solution. Although the LC has been proposed to play a principal role in the various stages of the sleep/waking cycle, it appears that control of LC cell firing is determined by intrinsic properties during only certain parts of the cycle. Locus coeruleus neurons are spontaneously active in the absence of synaptic input such that the silence during rapid eye movement sleep must be mediated by active inhibition.
