The circadian activity rhythms of rats with mid- and parasagittal ‘split-SCN’ knife cuts and pinealectomy

Dec 24, 1990Brain research

Daily activity patterns in rats with divided brain clock areas and removed pineal gland

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

25% of rats with knife cuts through one suprachiasmatic nucleus (SCN) exhibited disturbed circadian activity rhythms under constant illumination.

Rhythmic disturbances were not observed in rats with sham knife cuts or those with cuts on the midline or lateral to the SCN.
Rats with both a knife cut through the SCN and pinealectomy (PX) were twice as likely to show severe rhythmic disruptions under free-running conditions compared to those with only the SCN cut and sham PX.
Rats with only PX or only SCN cuts displayed coherent activity rhythms until subjected to a second surgical procedure, after which 35% showed disruptions.
The activity rhythms of rats with knife cuts on the midline or lateral to the SCN remained unaffected when combined with PX.
The findings suggest that the pineal gland may be involved in maintaining coupling in the multioscillator system that regulates circadian activity rhythms.

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To explore the multioscillator nature of the neurohumoral circuitry controlling the expression of circadian rhythmicity, rats' wheel running circadian activity rhythms were compared following sagittal knife cuts in the region of the suprachiasmatic nucleus (SSCN), following pinealectomy (PX) and following the combination of SSCN and PX. 25% of animals with knife cuts that passed through one SCN had disturbed running activity under constant illumination; rhythmic disturbances were seen neither in animals with sham knife cuts nor in rats with knife cuts on the midline or lateral to the SCN. Animals with both SSCN and PX were twice as likely to show severe rhythmic disruptions under free-running conditions as rats with SSCN and sham PX. Rats with PX and sham SSCN did not display disrupted activity rhythms. When animals with PX alone or SSCN alone were first observed under free-running conditions and then subjected to a second surgical procedure so that all animals underwent both PX and SSCN, all PX and most SSCN animals demonstrated coherent activity rhythms after the first operation, but 35% showed disruptions in circadian activity patterns only following the second surgery. The activity rhythms of rats with knife cuts placed either on the midline or lateral to the SCN did not deteriorate when combined with PX. Rats with coherent rhythms following knife cuts damaging one SCN had rhythm disruptions after the addition of PX. The effects of pinealectomy may indicate that the pineal gland plays a role in maintaining the coupling relationships in the multioscillator system controlling circadian activity rhythms. The results of this study also suggest that neither the direct commissural connection of the SCNs nor the humoral output of the pineal gland is indispensable for the expression of coherent circadian activity rhythms in the rat.

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The circadian activity rhythms of rats with mid- and parasagittal ‘split-SCN’ knife cuts and pinealectomy

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