Resveratrol Mitigates Cognitive Impairments and Cholinergic Cell Loss in the Medial Septum in a Mouse Model of Gradual Cerebral Hypoperfusion

Abstract

Vascular cognitive impairment and dementia (VCID) is the second leading cause of dementia. There is currently no effective treatment for VCID. Resveratrol (RSV) is considered an antioxidant; however, our group has observed pleiotropic effects in stroke paradigms, suggesting more effects may contribute to mechanistic changes beyond antioxidative properties. The main goal of this study was to investigate if administering RSV twice a week could alleviate cognitive declines following the induction of a VCID model. Additionally, our aim was to further describe whether this treatment regimen could decrease cell death in brain areas vulnerable to changes in cerebral blood flow, such as the hippocampus and medial septum. We hypothesized RSV treatments in a mouse model of gradual cerebral hypoperfusion protect against cognitive impairment. We utilized gradual bilateral common carotid artery stenosis (GBCCAS) via the surgical implantation of ameroid constrictor devices. RSV treatment was administered on the day of implantation and twice a week thereafter. Cerebral perfusion was measured by laser speckle contrast imaging, and cognitive functions, including the recognition memory, the spatial working memory, and associative learning, were assessed by novel object recognition (NOR), Y-maze testing, and contextual fear conditioning (CFC), respectively. RSV treatment did not alleviate cerebral perfusion deficits but mitigated cognitive deficits in CFC and NOR after GBCCAS. Despite these deficits, no hippocampal pathology was observed; however, cholinergic cell loss in the medial septum was significantly increased after GBCCAS. This cholinergic cell loss was mitigated by RSV. This study describes a novel mechanism by which chronic RSV treatments protect against a VCID-induced cognitive decline through the preservation of cholinergic cell viability to improve memory performance.

Keywords: Alzheimer’s disease; basal forebrain; hippocampus; neuroprotection; septo-hippocampal pathway.

Figure 1

Experimental schematic for in vivo RSV treatments, LSCI measurements, and behavioral tests. LSCI was performed the day prior to AC or sham surgery and then 1, 14, and 33 days following surgery. RSV was administered on the day that the surgery occurred as well as twice per week thereafter, as indicated by the arrows. Behavioral testing occurred on days 27 through 32 following the surgery and consisted of open-field testing (OFT), two days of novel object recognition testing (NORT), Y-maze testing, and two days of contextual fear conditioning (CFC) testing. Arrows indicate days of RSV administration.

Figure 2

Resveratrol does not ameliorate deficits in cerebral blood flow in the VCID model. (A) Representative LSCI images in the four treatment groups. (B) Relative cerebral perfusion rates for all groups relative to baseline. Data are expressed as mean ± SEM. n = 8 for each of the VCID groups and 11 for each of the sham groups. dp = days post-surgery. # indicates significance between the VCID + Veh group compared to the Sham + Veh group, while @ indicates significance between the VCID + RSV and Sham + RSV groups. # and @ p < 0.05. ## and @@ p < 0.01. ### and @@@ p < 0.001.

Figure 3

General activity/locomotor function, anxiety-related behavior, and spontaneous alternation via Y-maze testing are not affected by VCID. An analysis was performed on (A) the distance traveled, (B) the time spent in the center of the open field, which was found among the groups, and (C) spontaneous alternations in Y-maze testing, which were found. Data are expressed as a mean ± SEM. n = 8 for each of the VCID groups and 11 for each of the sham groups.

Figure 3

General activity/locomotor function, anxiety-related behavior, and spontaneous alternation via Y-maze testing are not affected by VCID. An analysis was performed on (A) the distance traveled, (B) the time spent in the center of the open field, which was found among the groups, and (C) spontaneous alternations in Y-maze testing, which were found. Data are expressed as a mean ± SEM. n = 8 for each of the VCID groups and 11 for each of the sham groups.

Figure 4

Impairments in object recognition memory and contextual fear memory caused by VCID were reduced by resveratrol treatments. (A) VCID-induced impairment in recognition memory, which was ameliorated via resveratrol treatments. (B) VCID-induced impairment in contextual fear memory, which was prevented by resveratrol treatments. Data are expressed as a mean ± SEM. n = 8 for each of the VCID groups and 11 for each of the sham groups. * p < 0.05. ** p < 0.01.

Figure 5

The hippocampal neuronal count in the CA1 pyramidal layer was unaffected by the VCID model, as shown in (A) the representative images and the (B) the quantification of the CA1 pyramidal layer. Scale bar = 200 μm (main image) or 100 μm (inset image). Data are expressed as a mean ± SEM. n = 8 for each of the VCID groups and 9 for each of the sham groups.

Figure 6

Resveratrol mitigates medial septal cholinergic neuronal loss following 33 days of VCID. (A) Maximum intensity projection images showing expression of ChAT-positive neurons (yellow) in the medial septum at Bregma +0.88 mm. (B) Quantified number of ChAT-positive cells in the full medial septum. Scale bar = 200 μm (main image) or 100 μm (inset image). Data are expressed as a mean ± SEM. n = 8 for each of the VCID groups and 9 for each of the sham groups. * p < 0.05. ** p < 0.01.