Persistence of circadian rhythmicity in a mammalian hypothalamic "island" containing the suprachiasmatic nucleus.

TLDR

The study tested whether the suprachiasmatic nucleus functions as an autonomous circadian pacemaker. Researchers recorded neural activity from electrodes in the SCN and other brain sites, and also isolated a hypothalamic island containing the SCN using a Halasz knife. In intact rats, both SCN and other sites showed circadian neural rhythms, but in animals with an isolated SCN island and no eyes, rhythms disappeared elsewhere yet persisted within the island, indicating the SCN’s rhythmicity is independent of external inputs.

Abstract

The experimental work described tested the prosposition that the suprachiasmatic nucleus of the hypothalamus is an autonomous circadian pacemaker. Simultaneous recording from two extracellular electrodes indicated neural (multiple unit) activity at two sites in the brain, one of which is in or near the suprachiasmatic nucleus and the other in one of many other brain locations. Both sites in intact rats displayed clear circadian rhythmicity of spontaneous neural activity. In experimental animals, a Halasz knife was used to create an island of hypothalamic tissue that contained the suprachiasmatic nuclei. In such animals that were also blinded by bilateral ocular enucleation, circadian rhythmicity was lost at all brain locations recorded outside the island, but it persisted within the island that contained the suprachiasmatic nuclei. The rhythmicity of the island is thus not dependent on afferent inputs from elsewhere in the brain.