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Advanced Neurology Stress accelerates parkinsonism in rats

catalepsy duration starting from block 2, whereas those
treated with reserpine without stress exposure showed
motor impairment only in block 4.
In the open field test, no significant differences were
detected between the groups on the first observation day
(day 19 of the protocol), although there was a trend toward
increased ambulation in the groups exposed to the UMS
protocol. Conversely, rats treated with reserpine exhibited
reduced spontaneous ambulation compared with that in
rats treated with vehicle in the second evaluation (day 29
of the protocol). Although the decrease in spontaneous
motor activity due to reserpine was expected, the effect was
subtle throughout the treatment. This is consistent with
previous studies indicating that motor activity in the open
Figure 6. Effects of repeated administration of 0.1 mg/kg reserpine (Res) field is the least affected, or is the last to decline, following
or vehicle (Veh) on lipid peroxidation (MDA formation) in the striatum repeated reserpine treatment. 27,29,41
of rats subjected to chronic unpredictable mild stress for 1 week (St) or
those who remained in their home cages (Ctl). Data were expressed as Remarkably, the spontaneous activity evaluated in the
mean ± SEM (n = 6 for all groups). Statistical analysis did not reveal any open field test reflects a more general measure of motor
significant effects
Abbreviations: SEM: Standard error of mean; MDA: Malondialdehyde. function compared with that evaluated in the catalepsy test.
This outcome is explained primarily by the motivation to
explore a new environment, which significantly influences
the UMS protocol, plasma CORT levels were measured behavior in the open field arena. Interestingly, irrespective
after different durations of the protocol, which revealed of experimental manipulations, ambulation decreased over
significantly elevated levels of the stress hormone after the repeated exposures to the open field arena, probably due to
1 week of the UMS protocol. habituation to the apparatus, which reduces the novelty-
st
When prolonged stress protocols are used, animals tend induced motivation to explore.
to habituate to the stressors, and the rate of habituation Conversely, the stress procedure increased the distance
depends on the type of stressor. Using a protocol with a traveled in the open field, an effect that was reversed by
variety of stressors, creating unpredictability has been reserpine administration. The hyperlocomotion observed
shown to delay this adaptation. 18,40 Nevertheless, although in stressed rats is consistent with the literature showing
unpredictable repeated stress may delay habituation, increased motor activity in open field tests and heightened
the delay eventually occurs as animals adapt to different anxiety-like behaviour. The absence of increased
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stressors. This may facilitate the activation of the HPA axis locomotor activity in the St-Res group is probably
after exposure to subsequent stressors. 40 explained by the strong negative impact of reserpine on the
In Experiment I, we aimed to determine the optimal spontaneous motor activity. To summarize, Experiment
duration of exposure to unpredictable mild stressors. II demonstrated the following: (1) an increase in plasma
Results indicated that animals subjected to 1 week of CORT levels in the stress groups compared with that in
unpredictable stress showed an increase in plasma CORT the controls, (2) a progressive induction of motor deficit
levels compared with those who were not. A trend toward by repeated administration of reserpine, and (3) an
decreasing CORT levels was observed with prolonged accelerated and worsened onset of motor impairment in
exposure periods, supporting the abovementioned stressed rats treated with reserpine compared with that in
habituation mechanism. Based on these results, we opted control rats undergoing the same treatment, as indicated
for a 1-week duration of exposure to unpredictable stress by the catalepsy test results.
in Experiment II. Previous studies by our group. 27-30,33,41 Investigations using other animal models of
have already demonstrated that low doses of reserpine parkinsonism have demonstrated that acute or chronic
can progressively increase catalepsy duration and reduce stress exacerbates motor symptoms. 43-46 However, these
locomotor activity in the open field test. Our current studies used protocols of predictable stress. In the present
findings indicate that exposure to the stress protocol study, we used the UMS protocol with various stressors.
applied before reserpine treatment accelerated the onset of Specifically, we adapted a model of induction of moderate
motor impairment. Specifically, rats subjected to the stress chronic stress, which is generally used in mood disorder
protocol and reserpine treatment exhibited increased research. This was an interesting approach because
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Volume 3 Issue 4 (2024) 7 doi: 10.36922/an.4037