Effects of Goldblatt hypertension on rats' hippocampal cholinergic system

Abstract

Background: The classical renin-angiotensin system (RAS) has an important role in the cardiovascular system and water homeostasis in the body. Recently, the existence of RAS with all of its components has been shown in the mammalian brain. RAS participates in many brain activities, including memory acquisition and consolidation. Since the cholinergic neurotransmission in the hippocampus is crucial for these functions, this study aims to evaluate the hippocampal angiotensin receptors (ATs) and choline acetyltransferase (ChAT) mRNA in the renovascular hypertensive rats in captopril- and losartan-treated hypertensive rats.

Methods: The rats were randomly divided into four groups of eight animals; sham, Goldblatt two kidney one clip (2K1C) hypertensive rats and Goldblatt 2K1C hypertensive rats received 5 mg/kg captopril and Goldblatt 2K1C hypertensive rats received 10 mg/kg losartan. After 8 days of treatment, the rats were sacrificed and angiotensin-converting enzyme (ACE), ChAT, AT1, and AT2 receptor mRNAs in the hippocampus of rats were assessed by real-time PCR. The Morris water maze test was applied to measure the cognitive functioning of the rats.

Results: Hypertensive rats showed impaired acquisition and memory function in the Morris water maze test. Treatment with ACE inhibitor (captopril) and AT1 receptor antagonist (losartan) reversed the observed acquisition and memory deficit in hypertensive rats. Overexpression of AChE, AT1, and AT2 and low expression of ChAT were noted in the hippocampus of rats with Goldblatt hypertension compared with that of the sham group. Treatment with captopril significantly reversed these changes, while treatment with losartan slightly reduced the mentioned effects.

Conclusion: The memory-enhancing effect of captopril in renovascular hypertensive rats might lead to increased hippocampal ChAT expression.

Keywords: AT receptors; ChAT; Goldblatt hypertension; hippocampus.

Figure 1

Diagram of experimental protocol for drug administration, surgery, behavioral, and gene expression analysis.

Figure 2

Systolic blood pressure levels of groups. Each group consists of eight animals. Treatments were started 3 weeks after surgery and continued for 8 consecutive days. Blood pressure levels were measured at the end of the study. RHR: renal hypertensive rats. Data are expressed as mean ± SEM. Data are analyzed with ANOVA followed by Tukey multiple comparison tests. RHR rats showed a significant higher systolic blood pressure compared to the control group. Both of the treatments significantly decreased the systolic blood pressure levels (***P < 0.001; **P < 0.01).

Figure 3

(a) Escape latency to reach the platform in each day during five training days or acquisition trials. The two-way ANOVA repeated-measure test followed by Tukey is used to analyze the data. (b) Time spent in target quadrant during the probe trial on day 6. In the probe-trial test, one-way ANOVA revealed that RHR rats spent a short time in the target quadrant compared to the sham group (P < 0.001). (Tukey pairwise multiple comparison test comparing percent search time in target quadrant versus each of the other quadrants after one-way ANOVA.) Losartan- and captopril-treated hypertensive groups spent more time in the target quadrant compared to the RHR group (P < 0.001). RHR, renal hypertensive rats; Sham, sham operated control; Asterisks indicate a significant difference from the sham (***P < 0.001, **P < 0.01, and *P < 0.05). Data are expressed as mean ± SEM (n = 8).

Figure 4

Q-PCR analysis of ACE, ChAT, AT1, and AT2 expression in the hippocampus of hypertensive and control rats; mRNA levels were measured using gene-specific primers, and the values were normalized to β-actin expression (*P < 0.05, **P < 0.01, mean ± SD, n = 5).