Résumé:
The widespread use of Imidacloprid (IMI), a neonicotinoid pesticide, raises concerns about its
neurotoxic effects. Chronic exposure induces oxidative stress, mitochondrial dysfunction, and
behavioral impairments. Melissa officinalis L. (MOE), a medicinal plant known for its
antioxidant properties, may offer neuroprotective effects. The present study investigates the
dose-dependent neurotoxic effects of IMI and the protective role of MOE in Wistar rats,
focusing on regional brain differences.
In the first phase, the aqueous extract of MOE was analyzed for its active constituents.
Phytochemical screening revealed high levels of polyphenols, flavonoids, and condensed
tannins—compounds known for their potent antioxidant activity. In vitro assays, including
DPPH, ABTS, CUPRAC, and FRAP, confirmed significant free radical scavenging activities
(85% and 80% scavenging in DPPH and ABTS assays, respectively). Structural analysis
through X-ray diffraction (XRD), infrared spectroscopy (IR), and scanning electron
microscopy (SEM) validated the presence of bioactive compounds.
The second phase assessed the neurotoxic effects of chronic IMI exposure (5 mg/kg/day and
50 mg/kg/day) in Wistar rats for 90 days. IMI induced neurotoxicity in a dose-dependent
manner, with more severe damage in the striatum and hippocampus. IMI exposure led to
metabolic disruptions, including a significant reduction in body weight and brain mass at the
higher dose (50 mg/kg/day, p ≤ 0.001), with MOE administration partially counteracting these
effects. Additionally, IMI exposure caused significant depletion of oxidative stress markers
(SOD, CAT, GPx, GSH, GST, MDA) and mitochondrial dysfunction, evidenced by
increasing mitochondrial swelling and reduced oxygen consumption (p ≤ 0.001) and altering
membrane permeability.
Neurobehavioral assessments included tests for anxiety (open field and labyrinth tests),
cognition (novel object and olfactory recognition tests), social behavior (Vsoc-Maze), and
anhedonia (sucrose preference test). showed substantial cognitive and motor dysfunction in
IMI-exposed rats. With a 40% decrease in memory retention and a 50% decrease in motor
coordination at the higher dose (p ≤ 0.001). Lysosomal stability was compromised by IMI
exposure, as evidenced by a 45% reduction in Neutral Red Retention Time (NRRT) (p ≤
0.001) with MOE treatment restoring lysosomal stability. Lysosomal pH variations were also
measured to assess functional changes, with lysosomal destabilization further confirmed by
morphological alterations observed under light microscopy. These changes included
lysosomal expansion, leakage of neutral red dye, and cell rounding, all of which indicated
progressive lysosomal damage. The degree of damage progressed over time, from minor
structural disruptions to more severe alterations, which were clearly visible at the microscopic
level. Histopathological examination revealed severe neuronal damage, particularly at the
higher IMI dose, whereas MOE co-treatment preserved neuronal integrity. AChE activity was
significantly inhibited, especially in the hippocampus and striatum, and was partially restored
with MOE administration.
