Elevated prostacyclin biosynthesis in mice impacts memory and anxiety-like behavior

Abstract

Prostacyclin is an endogenous lipid metabolite with properties of vasodilation and anti-platelet aggregation. While the effects of prostacyclin on the vascular protection have been well-documented, the role of this eicosanoid in the central nervous system has not been extensively studied. Recently, a transgenic mouse containing a hybrid enzyme, of cyclooxygenase-1 linked to prostacyclin synthase, was developed that produces elevated levels of prostacyclin in vivo. The goal of this study was to investigate whether increased prostacyclin biosynthesis could affect behavioral phenotypes in mice. Our results uncovered that elevated levels of prostacyclin broadly affect both cognitive and non-cognitive behaviors, including decreased anxiety-like behavior and improved learning in the fear-conditioning memory test. This study demonstrates that prostacyclin plays an important, but previously unrecognized, role in central nervous system function and behavior.

Keywords: Anxiety; Behavior; Eicosanoid; Memory; Prostacyclin.

Figure 1. Measurement of PGI₂ production in brain

(A) Examples showing 6-Keto-PGF1α detected using HPLC, using a positive control (COX-1-10aa-PGIS positive cell lysate), non-transgenic mouse, and TG-Cp mouse brain tissue. (B) This figure demonstrates that CP-Tg mouse tissue exhibits enhanced conversion of arachidonic acid to PGI₂ (n=3, for each group, p<0.05), compared with control.

Figure 2. PGIS overexpression had significant effect on non-cognitive behavior

(A) Exploratory behavior measured by the open field activity in 3 month old mice shows no significant differences. (B) At 6 months of age, exploratory behavior measured in CP-Tg mice is significantly decreased compared to NTg mice. (MOVE) = Total time moving, (REST) = time at rest, (STEREO) = time moving in stereotypic fashion. (C). In 3 month old mice, CP-Tg showed improved coordination on the rotarod, compared with NTg mice on trials 1, 2, and 4. (D) At 6 months of age, there was no significant difference between groups. * p < 0.05.

Figure 3. Effect of PGIS on anxiety-like behavior measured by the open field activity

(A) Three month old CP-Tg mice exhibit greater time spent on the periphery of the open field, compared with NTg. (B) At 6 months of age, there is no significant difference between NTg and CP-Tg mice between the perimeter and thecenter of the open field). * p < 0.05.

Figure 4. PGIS overexpression decreased anxiety-like behavior at six months in light dark exploration

(A) At three months of age, there was no significant difference in time or number of transitions between the two groups. (B) At six months of age, CP-Tg mice spent a significantly greater time in light, and had a reduced number of transitions, compared to NTg mice. * p < 0.05.

Figure 5. Anxiety-like behavior measured by elevated plus maze

(A) Time spent in open arms is similar between CP-Tg and NTg lines in three month old mice, but CP-Tg mice show significantly more transitions than NTg mice. (B) In six month old mice, the time spent in open arms and the number of transitions is similar between the two groups. * p < 0.05.

Figure 6. PGIS overexpression had a significant effect on associative learning

(A) CP-Tg has a significant increase in percentage freezing time during the third shock of the training trial. (B) CP-Tg mice exhibited an increased average motion index compared with NTg mice. Mice were tested in both cue and context trials. (C) CP-Tg exhibited an enhanced response in the short-term memory component in the contextual fear conditioning (p < 0.05). (D) No significant differences were seen in long term memory contextual fear conditioning. (E) No significant differences were seen in short term cue fear conditioning. (F) No significant differences were observed in long term cue fear conditioning.