Dysrhythmia in the suprachiasmatic nucleus inhibits memory processing

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Science  14 Nov 2014:
Vol. 346, Issue 6211, pp. 854-857
DOI: 10.1126/science.1259652

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  1. Fig. 1 Phase-resetting responses of the Siberian hamster circadian system.

    (A) Phase response (left) and transition (right) curves are typical for nocturnal rodents. Hamsters were housed in 16 hours of light followed by 8 hours of dark. Each animal was given a single light pulse (300 lux, 30 min) at different phases of the first circadian cycle in constant darkness (22). Each filled black circle represents a single animal (n = 98); means of each time point are connected by the red line. The phase transition curve has a slope of 1, which indicates type 1 (i.e., weak) phase resetting (27). (B) The DPS protocol. Actograms show daily locomotor activity on each line, with successive days plotted from top to bottom. A phase-advancing signal (2-hour light pulse, red rectangle), followed by a phase-delaying signal (3-hour delay of the light-dark cycle, blue arrow) on the next day drives the system into arrhythmia. Night is indicated by the gray shaded area. The progressive daily shortening of the nightly active phase (i.e., alpha compression) after DPS treatment reliably predicts arrhythmia (17).

  2. Fig. 2 An intact SCN is necessary for circadian arrhythmia to impair recognition and spatial memory.

    (A) Representative actograms of DPS (top) and SCNx (bottom) animals; red triangle indicates day of treatment. Chi-square periodograms confirm robust rhythms during entrainment (blue peaks above black line are significant; P = 0.001) and arrhythmia. (B) SCNx animals (n = 11) performed significantly better than random chance (i.e., 50 for SA, 0 for NOR), whereas DPS-treated animals (n = 8) failed both memory tests (upper panels). ENT (n = 10) and sham-operated (SHAM) (n = 11) hamsters also performed significantly better than chance. Arrhythmic groups shown in blue. Scores significantly different from chance indicated by * (one-sample t test; 0.0001 < P < 0.01). For DPS animals, P > 0.05. Number of T-maze arm entries and NOR exploration times did not differ significantly among ENT, DPS, SCNx, and SHAM groups (P > 0.05; middle panels). No left-right positional biases were found in the T maze or NOR arena (P > 0.05; lower panels) (22). (C) Representative Nissl-stained tissue sections from intact (left) and SCNx (right) hamsters. Optic tracts are labeled OT. Black scale bar, 100 μm.

  3. Fig. 3 SCN ablation rescues memory in arrhythmic animals.

    (A) Representative actogram of a hamster during ENT, DPS, and SCNx phases of the experiment. Phases were separated by 4 to 6 weeks. Days of DPS and SCNx treatments are indicated (red arrowheads). Periodograms evaluated the last 10 days of data from each phase of the experiment. (B) Locomotor activity was redistributed across the 24-hour day when animals became arrhythmic (left), but total daily activity is conserved across all conditions (right). (C) Performance on both memory tests (upper panels) was normal while animals were entrained but was impaired after the DPS protocol made them arrhythmic. SCN ablation subsequently rescued test performance (Lesion; n = 11; red circles). Scores significantly different from chance indicated by * (one-sample t test; 0.0001 < P < 0.05). Memory did not improve in SHAM animals (Lesion; n = 8; white circles) or in animals with partial damage to the SCN (Lesion; n = 9; gray circles). Surgery did not alter the number of arm entries or exploration time (middle panels) among SCNx (red bars), PSCNx (gray bars), or SHAM (white bars) animals (22). (C) None of the treatment groups showed any positional bias in the T maze or NOR arena (lower panels) (22).