Evaluations of memory, anxiety, and the growth factor IGF-1R after post-surgical menopause treatment with a highly selective progestin

Abstract

Progestogens are a key component of menopausal hormone therapies. While some progestogens can be detrimental to cognition, there is preclinical evidence that progestogens with a strong progesterone-receptor affinity benefit some molecular mechanisms believed to underlie cognitive function. Thus, a progestin that maximizes progesterone-receptor affinity and minimizes affinities to other receptors may be cognitively beneficial. We evaluated segesterone-acetate (SGA), a 19-norprogesterone derivative with a strong progesterone-receptor affinity and no androgenic or estrogenic-receptor activity, hypothesizing that it would enhance cognition. Middle-aged rats underwent Sham or Ovariectomy (Ovx) surgery followed by administration of medroxyprogesterone-acetate (MPA; used as a positive control as we have previously shown MPA-induced cognitive deficits), SGA (low or high dose), or vehicle (one Sham and one Ovx group). Spatial working and reference memory, delayed retention, and anxiety-like behavior were assessed, as were memory- and hormone- related protein assays within the frontal cortex, dorsal hippocampus, and entorhinal cortex. Low-dose SGA impaired spatial working memory, while high-dose SGA had a more extensive detrimental impact, negatively affecting spatial reference memory and delayed retention. Replicating previous findings, MPA impaired spatial reference memory and delayed retention. SGA, but not MPA, alleviated Ovx-induced anxiety-like behaviors. On two working memory measures, IGF-1R expression correlated with better working memory only in rats without hormone manipulation; any hormone manipulation or combination of hormone manipulations used herein altered this relationship. These findings suggest that SGA impairs spatial cognition after surgical menopause, and that surgical menopause with or without progestin administration disrupts relationships between a growth factor critical to neuroplasticity.

Keywords: Learning; Memory; Ovariectomy; Progestin; Rat; WRAM.

Figure 1.. Experimental Timeline.

The study timeline, depicting surgeries, hormone administration, and completion of the behavioral battery, which included the WRAM, MWM, VP, and OFT, before euthanasia and tissue collection.

Figure 2.. WMC Errors during Acquisition on the WRAM.

(A) During task acquisition, Ovx rats administered the low dose of SGA made more WMC errors than Ovx-Vehicle rats. (B) A Trial x Treatment interaction for this comparison, and SGA-induced impairments were present (C) at the highest working memory load trial, Trial 4. *p < 0.05. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 3.. WMI Errors during Acquisition on the WRAM.

(A) During task acquisition, rats administered the low dose of SGA made more WMI errors than Ovx-Vehicle rats. (B) The Trial x Treatment interaction for this comparison was significant, revealing SGA-induced impairments (C) at the highest working memory load trial, Trial 4. *p < 0.05, **p < 0.01, ***p < 0.001. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 4.. Delayed Memory Retention on the WRAM.

Where Sham-Vehicle rats (A) did not show delay-induced impairment, Ovx-Vehicle rats (B) demonstrated marginal deficits following the delay. Ovx-MPA (C) and Ovx-SGA High (E) rats demonstrated delay-induced working memory impairments, where Ovx-SGA Low rats (D) did not show an increase in WMC errors following the delay. ^p < 0.10, *p < 0.05. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 5.. Reference Memory Performance on the MWM.

(A) Rats treated with the high dose of SGA, as well as rats treated with MPA, demonstrated reference memory deficits on the MWM compared to Vehicle-treated rats across all 5 baseline days of testing, demonstrated by swimming a greater path length on average for a given trial before finding the platform. (B) The probe trial revealed that all groups were able to spatially localize to the platform. *p < 0.05, **p < 0.01, ****p < 0.0001. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 6.. Performance on the VP Task.

Rats demonstrated visual and motor acuity, as well as the ability to complete the procedural elements of a water-escape spatial navigation task, as trial latency decreased across the 6 testing trials. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 7.. Anxiety-like and Locomotive Behavior on the OFT.

(A) Rats treated with the low dose of SGA demonstrated increased locomotion overall compared with Ovx-Vehicle rats. While there were no effects for corner distance (B) on the OFT, evaluations of distance travelled in the center (C) and small center (D) revealed that Ovx-Vehicle rats demonstrated a trend towards elevated anxiety-like behavior, while SGA at the low dose and the high dose prevented Ovx-induced elevation in anxiety-like profile. There were no effects of Treatment for time spent in the corners or center of the OFT (E and F). Findings for time spent in the small center (G) reflected a similar pattern observed in distance analyses on the OFT, where SGA reversed the Ovx-induced decreased time in the small center. ^p < 0.10, *p < 0.05. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 8, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 8.. Body and Uterine Weights Collected at Euthanasia.

(A) Ovx-Vehicle rats had elevated body weights as compared to Sham-Vehicle rats; administration of MPA attenuated Ovx-induced weight gain. (B) Ovx led to a significant reduction in uterine weight collected at euthanasia relative to Sham rats, but MPA attenuated this Ovx-induced decrease, suggesting some uterine stimulation as a result of MPA administration. *p < 0.05, ***p < 0.001, ****p < 0.0001. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.

Figure 9.. Correlations between Neurobiological and Behavioral Outcomes.

Assessment of relationships between WRAM performance and neurobiological outcomes demonstrated significant negative correlations for the Sham-Vehicle rats between relative IGF-1R expression within the dorsal hippocampus and (A) WMC or (B) WMI errors made during learning on the WRAM. **p < 0.01. Sham-Vehicle n = 9, Ovx-Vehicle n = 9, Ovx-MPA n = 10, Ovx-SGA Low n = 10, Ovx-SGA High n = 10.