Influence of norepinephrine-containing neurons derived from the locus coeruleus on lateral geniculate neuronal activities of cats

Facilitatory influences of conditioning stimulation of LC on evoked potentials in LGN to OTS were demonstrated in cats. These influences were observed when the stimulating electrode had been placed in areas histologically ascertained as having NE-containing cell bodies. The coeruleus modulation of geniculate potentials was not observed after reserpine pretreatment. However, a rapid recovery of the facilitation was produced by anl-dopa or NE injection. Injection of fusaric acid, a potent dopamine-β-hydroxylase inhibitor, also decreased the LC effects. In these cats, only an intraventricular NE injection was effective for the coeruleus modulation.The responsiveness of relay neurons to OTS, studied by extracellular recordings, was also enhanced y LC stimulation. Type-A interneurons, which responded to both orthodromic and antidromic stimulation, received influences similar to those on relay neurons after LC stimulation. Type-B interneurons, which failed to respond by antidromic spike discharges, received depressive effects. In reserpine-pretreated cats, LC effects on neuronal activities in the LGN were not observed. In these cats,l-dopa injection was effective in restoring the coeruleus modulation. It is suggested from these findings that enhanced responsiveness of relay neurons is due to an inhibitory effect on type-B interneurons after activation of NE-containing neurons derived from the LC.