Evaluation of avoidance memory
The avoidance memory test was performed in two days and two consecutive stages.
Accustomization session
All rats were placed in the laboratory at least 30 min before the onset of the experiment. Subsequently, each rat was placed in a light compartment, and after 5 sec, the guillotine door was opened and the animal was allowed to enter the dark compartment.
The initial delay time (the time to enter the dark compartment from the light compartment) was noted, and the criterion for the animal entering the dark compartment was the insertion of the hind legs into the compartment at which point the guillotine door was closed.
After 10 sec, the animal was returned to its cage, and the rats with a delay of more than 100 sec were excluded from the experiment
[20]. In the present study, two rats in the healthy control group did not enter the dark compartment after 100 seconds and were eliminated consequently.
Memory Acquisition Tutorial
The rat was placed in the light compartment again 30 min later, and after 5 sec, the guillotine door was opened, and as soon as the animal entered the dark compartment, the guillotine door was closed, and the animal was shocked through the floor bars (50 Hz, 1 milliampere, 3 seconds). Afterward, it was returned to its cage after 15 to 20 sec. The animal was placed in a light container again two minutes later. If the animal entered the black hole again, it would be shocked again. However, if animals had a memory and did not enter the dark compartment for two min, the test would be terminated, and the rats would be returned to the cage
[20].
Memory Recovery Test
A recovery test was performed 24 h after the memory acquisition tutorial session to check the animal's long-term memory. At this stage, each animal was placed in a light compartment, and after 20 sec, the guillotine door was opened, and the step-through latency (STL) in the dark compartment, as well as the
time spent in the dark compartment(
TDC) for each rat, were recorded during the test. The test lasted 5 min
[20], and after the test, the rats were returned to the cage. It should be noted that this step was performed without electrical stimulation and STL and TDC were measured for each rat for 300 sec. Therefore, the unit of measurement of these two variables was regarded as seconds. This test is a valid scale that is recommended by many researchers to measure avoidance memory
[21–23].
Evaluation of spatial memory
The Y-shaped maze device test consists of three arms and is made of Medium Density Fibreboard. Each arm is 46 cm long, 15 cm high, and 15 cm wide; moreover, the arms are placed at equal angles to each other and connected through a central area. To perform the test, the rat was first placed at the end of an arm, and it was possible to access all areas of the maze in a 5-min period. The number of times the animal entered each arm was observed and recorded in this study. The entry of the animal into the arm was considered when the animal's hind legs were completely inside the arm, and alternative behaviors were considered successful and consecutive entrances (series) into all arms in the overlapping 3 sets. Accordingly, the observed percentage of alternation (PA) was calculated as the maximum frequency (total number of arms imported) multiplied by 100
[20].
Data Analysis
The data were analyzed in SPSS software (version 22) through Shapiro-Wilk and one-way ANOVA with Tukey’s post-hoc tests. A p-value equal/less than 0.05 was considered statistically significant.
Results
Figures 1-3 present the STL, TDC, and PA levels of the research groups, respectively. The results of the one-way ANOVA test showed a significant difference among the research groups in terms of STL (F=8.148; P=0.001) and TDC (F=22.10; P=0.001). Furthermore, the results of Tukey’s post-hoc test revealed that the STL levels in the S group were significantly lower than those in the Sh group
Figure 1. Levels of step-through latency in the dark compartment in the seven research groups
*** (P≤0.001) showing a significant decrease, compared to that in the Sh group
## (P≤0.01) and # (P≤0.05) showing a significant increase, compared to that in the S group
δ (P≤0.05) showing a significant increase, compared to that in the SRTTT50 group
Figure 2. Levels of time spent in the dark compartment in the seven research groups
*** (P≤0.001) showing a significant increase, compared to that in the Sh group
## (P≤0.01) showing a significant decrease, compared to that in the S group
δδ (P≤0.01) showing a significant decrease, compared to that in the STT50, STT100, and SRTTT50 groups
βββ (P≤0.001) showing a significant decrease, compared to that in the STT100 group
εεε (P≤0.001) showing a significant decrease, compared to that in the SRTTT50 group
(P=0.001); however, the STL in the ST100 (P=0.0014), SRT (P=0.01), and SRTTT100 (P=0.003) groups were significantly higher than those in the S group. Moreover, the STL in the SRTTT100 group was significantly higher than that in the SRTTT50 group (P=0.018) (Figure 1).
The TDC levels in the S group were significantly higher than those in the Sh group (P=0.001). However, the TDC levels in the SRT (P=0.001) and SRTTT100 (P=0.001) groups were significantly lower than those in the S and SRT groups, compared to the STT50 (P=0.0018), STT100 (P=0.006), and SRTTT50 (P=0.001) groups. Additionally, the TDC in the SRTTT100 group was significantly lower than that in the STT100 (P=0.001) group. Moreover, the TDC in the SRTTT100 group was significantly lower than that in the SRTTT50 group (P=0.001) (Figure 2).
The results of the one-way ANOVA test indicated a significant difference among the research groups in terms of PA (P=0.001, F=5.83). Furthermore, the PA levels in the S group were significantly lower than those in the Sh group (P=0.02). However, this corresponding value was higher in the STT100 (P=0.004), SRT (P=0.001), SRTTT50 (P=0.001), and SRTTT100 (P=0.014) groups, compared to that in the S group (Figure 3).
Discussion
The results of the present study showed that the RT increased the STL in the dark compartment, reduced the TDC, and increased the percentage of
Figure 3. Levels of the non-repetitive percentage of alternation in the seven research groups
* (P≤0.001) showing a significant decrease, compared to that in the Sh group
# ## (P≤0.001,
##(P≤0.01), and # (P≤0.05) showing a significant increase, compared to that in the S group
non-repetitive alternations in rats exposed to stanozolol. Studies investigating the effect of long-term use of AAS on the structure of the brain show that exposure to these anabolic medications can lead to the induction of the extrinsic pathway of apoptosis through the mechanism of increased amyloid-beta and increased oxidative stress, thereby creating different structural abnormalities in the brain
[2]. The studies also found that AASs abuse with oxidative stress mechanisms led to the disruption of dopamine receptors and increased dopamine secretion from various parts of the brain and C1 hippocampus while inhibiting dopamine-like D1 receptors.
As a result, they reduced dopaminergic function and disrupted the androgen regeneration system. All of these events led to decreased neuronal flexibility and affected learning and memory
[24]. In this regard, the results of the studies demonstrated that long-term use of AAS led to a decrease in the number of healthy cells in the cortex, cerebellum, and hippocampus
[2]. The injections of 7.5 mg/kg testosterone for 14 days also impaired learning in rats, thereby increasing the rate of cognitive impairment
[24]. However, the mechanism of exercise activity has been known to increase neurotrophins, reduce oxidative stress, improve vascular circulation, and increase neuronal plasticity in the central nervous system
[25].
As a result, a long-term exercise in young and middle-aged people led to increased levels of brain-derived neurotrophic factor (BDNF) and cathepsin B; moreover, it decreased malondialdehyde and lipid peroxidation
[25]. On the other hand, studies show that the rate of damage to the nervous system was less observed in athletes consuming AAS. It seems that physical activity increases the body's metabolism and interaction with anabolic steroids and partly increases androgen receptors, which can improve the metabolism of lipoproteins in blood vessels and reduce the extent of AAS damage relative to non-athlete individuals
[26]. However, the impact of resistance activity on memory and learning in human and animal models exposed to S has not been yet fully understood.
The results of the present study showed that the consumption of TT with a dose of 100 mg/kg increased the STL in the dark compartment
and increased the percentage of non-repetitive alternations; nonetheless, the dose of 50 mg/kg had no significant effect on the research variables. Additionally, the consumption of TT decreased the levels of nuclear factor kappa beta (NF-κB), tumor necrosis factor-alpha, interleukin 1-beta, and malondialdehyde (MDA). However, it increased the peroxisome proliferator-activated receptor-gamma (PPARγ), anti-apoptotic protein Bcl-2, and superoxide dismutase, thereby inducing its protective effects on the central nervous system and hippocampus
[8, 27].
In the same line, the studies have shown that TT increased the expression of cyclooxygenase-2 and the enzyme nitric oxide synthase, thereby improving the function of the glia and increasing the levels of neurotrophin
[27]. Moreover, the findings of an
in vivo and
in vitro study indicated that 50 mg/kg and 100 mg/kg aqueous extract of TT with an antiapoptotic mechanism inhibited caspases, increased BDNF, and decreased NF-κB leading to the improved neuronal function
[28]. In line with the present study, the consumption of 14 days of 200 mg/kg TT improved the memory of rats
[8]. Additionally, the consumption of 150 and 300 mg/kg of TT extract also improved memory levels and learning of diabetic rats
[10]. On the other hand, TT extract also reduced MDA levels
and increased the percentage of non-repetitive alternations in diabetic rats
[29].
The results showed that RT with 100 mg/kg TT increased the STL in the dark compartment, reduced the TDC, and also increased the percentage of non-repetitive alternations, whereas RT with 50 mg/kg TT only increased the percentage of non-repetitive alternations.
Studies show that exercise can help enhance memory by improving neurotrophins and vascular circulation, reducing oxidative stress, and increasing neuronal plasticity
[25, 26]. The dose-dependent consumption of TT also has a protective effect on the central nervous system and hippocampus and improve memory by reducing the levels of inflammatory agents, antioxidants, and oxidative stress, followed by an increase in Peroxisome Proliferator Activated Receptor Gamma, B-cell lymphoma 2, cyclooxygenase-2 expression, nitric oxide synthase enzyme, and neurotrophins
[8, 27]. Furthermore, in line with the results of the present study, some studies have reported the desired effect of TT extract with high doses
[8, 27, 28]. Therefore, it seems that the effects of exercise and higher doses of TT extract on avoidance and working memory are more favorable than RT and RT with 50 mg/kg TT. Due to the role of neurotrophins, inflammatory factors, and oxidative-antioxidant stress system on memory disorders caused by stanozolol, one of the limitations of the present study is the lack of evaluation of these physiological variables; accordingly, it is recommended that future studies evaluate these physiological variables.
Conclusions
It seems that RT with TT administration has synergistic effects on improving memory in rats exposed to S; however, it is noteworthy to mention that the effect of TT is dose-dependent.
References