Temporary desynchronization among circadian rhythms with lateral fornix ablation

Area of Science:

• Neuroscience
• Chronobiology
• Endocrinology

Background:

• The suprachiasmatic nucleus (SCN) and hypothalamic areas regulate circadian rhythms.
• Fornix fibers play a role in transmitting signals to these hypothalamic regions.
• Understanding the specific roles of fornix tracts is crucial for deciphering circadian control.

Purpose of the Study:

• To investigate the role of lateral and medial fornix tracts in regulating circadian and ultradian rhythms.
• To determine the impact of fornix lesions on adrenal corticosteroid secretion, locomotor activity, body temperature, and feeding/drinking patterns.

Main Methods:

• Adult male rats underwent selective lateral or medial fornix suction ablations.
• Postoperative measurements of plasma adrenal corticosteroids, locomotor activity, body temperature, and food/water intake were recorded at 4-hour intervals over 48 hours.
• Least-squares spectrum analysis was used to analyze data for rhythmic patterns.

Main Results:

• Lateral fornix ablation specifically disrupted the periodicity of adrenal corticosteroid secretion.
• Corticosteroid secretion showed potential ultradian control after lateral fornix lesions.
• Locomotor activity rhythms remained normal, but feeding, drinking, and body temperature rhythms were occasionally aberrant, indicating a dissociation.

Conclusions:

• The anteroventral subiculum, through the medial corticohypothalamic tract, is vital for regulating specific circadian parameters.
• Lateral fornix pathways are critical for maintaining normal adrenal corticosteroid rhythmicity.
• Findings support the multi-oscillator theory of circadian organization and differentiate roles of fornix tracts in behavioral and endocrine rhythms.