Prophylactic effect of all-trans retinoic acid in an amyloid-beta rat model of Alzheimer's disease

Retinoid signaling has been argued to have favorable effects on Alzheimer's disease (AD). We studied the role of chronic intracerebroventricular (ICV) injection of all-trans retinoic acid (ATRA) on the amyloid-beta (Aβ) model of AD.
Adult male rats weighing 260-330 g were divided into 12 groups of 8 each. Six groups of rats received ATRA (3nM, 30nM, 3μM, 0.3mM, 30mM/rat; ICV) or DMSO 1% (2μl/rat; ICV), bilaterally and in a chronic manner (6 times, twice a week). Forty eight hours following the last injection, memory performance was assessed using a passive avoidance paradigm. One group received Aβ (10μg/rat; ICV), bilaterally. The control group received DMSO 1% (2μl/rat; ICV). Twenty days later memory performance was assessed. Three groups of rats received Aβ (10μg/rat; ICV) and then ATRA (3nM or 30nM/rat; ICV) or DMSO 1%, chronically (6 times, twice a week). Another group received DMSO 1% (2μl/rat; ICV) and then, DMSO 1%, chronically (6 times, twice a week).
ATRA at doses 0.3mM and 30mM/rat impaired memory retrieval by decreasing step-through latency (STL) and increasing time spent in the dark compartment (TDC), significantly. However, moderate doses (3nM and 30nM/rat) did not change memory performance. ATRA (30nM/rat) increased STL and decreased TDC and NST in the Aβ-treated rats, significantly compared to the group received Aβ-DMSO 1%.
The results propose a potential prophylactic effect of ATRA in the ICV Aβ model of AD and indicate the prominence of retinoic acid signaling as a target for AD prevention.