Studies of Connections Between Locus Coeruleus and Cerebral Cortex

Abstract

Abstract-Small tracking electrodes were inserted into the cat locus eoeruleus (LC), and the effects of LC stimulation were determined on the transcallosal potential (TCP) evoked in cerebral cortex on the same side. LC stimulation at 8 volts inhibited TCP amplitude an average of II Rostral LC placements appeared most effective. LC stimulation, without drugs, did not affect the peak latency of the TCP. dl-Propranolol and FLA-63 blocked LC inhibition of the TCP and also increased TCP amplitude per se. Propranolol first increased the latency of the TCP during LC stimulation, then decreased it, while also prolonging the latency of the TCP per se. Phenoxybenzamine increased rather than blocked the LC inhibitory effect and also increased TCP amplitude. dl-Erythro-DOPS slightly increased the LC inhibitory effect, and substantially increased TCP amplitude. dl-Threo-DOPS produced somnolence in unanesthetized animals, led to increased norepinephrine levels in cortex and brain stem, and caused cortical po tentials to fluctuate widely. A midbrain lesion of the dorsal ascending NE bundle blocked the LC inhibitory effect. LC stimulation alone, or in combination with evoked cortical stimulation, did not affect the interstimulus electrocorticogram or the heart rate. In the transcallosal system of the cortical regions studied, the LC appears to play mainly an inhibitory role. What is the net effect of locus coeruleus (LC) stimulation on nerve cells of cerebral cortex?A simple inhibitory role might be proposed, because LC stimulation slows the spontaneous firing rate of hippocampal neurons (1), and also reduces both the amplitude of field potentials and the number of spike potentials of relay neurons within the spinal trigeminal nucleus (2 Further to illustrate the complexity of the issue, it is worth noting the ion tophoretic evidence that some cortical neurons are stimulated by local norepinephrine (NE) (4, 5), whereas others are inhibited (6, 7).

Effect of Stimulation of Locus Coeruleus on the Evoked Potential in the Amygdala in Rats

“…Hoffer et al (9) found that discrete stimulation of LC decreased the spontaneous discharge rate of cerebellar Purkinje cells through noradrenaline mediated mechanism. Similar inhibitory effects of LC stimulation on hippocampal pyra midal cells (10), relay neurons of the spinal trigeminal nucleus (11) and the transcallosal potential in cerebral cortex (12) have also been found. However, electrophysiological evidence for the role of LC in modulating the amygdaloid activity has apparently not been reported.…”