Abstract:
Hypoxic stress is known to induce depression, cognitive dysfunction and anxiety-related
complications through the activation of oxidative and inflammatory signaling pathways. Thus,
inhibition of these pathways might mitigate hypoxic stress-induced neurobehavioural deficits.
Experimental studies have shown that naringenin improves neurobehavioural disorders induced
by ischemic stroke via inhibition of oxidative stress, neuroinflammation and neurodegeneration.
However, there is paucity of information on its protective effects against neurobehavioural
deficits induced by Chronic Hypoxic Stress (CHS). Hence, this study was designed to evaluate the
effects and biochemical mechanisms of naringenin on CHS-induced depression, memory deficit
and anxiety related behaviours in mice.
Thirty-five male Swiss-mice (20-22 g) were distributed into 5 groups (n=7) and treated
intraperitoneally. Mice in groups I (non-stress control) and 2 (stress-control) received 5%-DMSO
(vehicle), while groups 3-5 were treated with 10, 25 and 50 mg/kg analytical grade of naringenin,
daily for 14 days. Thirty minutes after daily treatment, each mouse in group 2-5 was subjected to
15 minutes hypoxic-stress in an air-tight 250 mL cylindrical vessel for 14 consecutive days. The
neurobehavioural phenotypes (locomotor activity, anxiety, depression and memory) were
evaluated on day 15 using standard experimental procedures. Thereafter, the animals were
euthanized and the harvested brains were processed for determination of malondialdehyde,
reduced glutathione (GSH), nitrite, superoxide-dismutase and catalase using standard biochemical
techniques. Serum corticosterone and brain Tumor Necrosis Factor-alpha (TNF-α), and
interleukin-1β were assayed using ELISA kits. The expressions of Inducible Nitric Oxide
Synthase (iNOS), Nuclear Factor Kappa-B (NF-kB) and Brain Derived Neurotrophic Factor
(BDNF) were determined using immunohistochemical techniques. The histomorphological
changes of the amygdala were also determined using hematoxylin and eosin, and cresyl violet
stains. Data were analysed using descriptive statistics and ANOVA at α0.05.
Naringenin (25 and 50 mg/kg) relative to stress-control significantly attenuated CHS-induced
locomotor deficit (11.71±0.57 and 12.29±0.57 vs 8.29±0.68) and prolonged immobility time in
the test for depression (104.40±9.31 and 139.70±8.34 vs 197.40±6.83sec). It also reduced anxiety like behaviours but did not ameliorate memory deficit induced by CHS. Naringenin (10, 25 and
50 mg/kg) reduced malondialdehyde concentration (36.23±0.96, 40.65±1.60, 67.39±0.32 vs
79.86±4.26 μmol/g tissue) and increased GSH levels (20.85±0.63, 21.99±0.74, 21.65±0.46 vs
17.50±0.50 μmol/g tissue). It also restored the altered brain nitrite content and superoxide
dismutase activity but not catalase. Naringenin (25 and 50 mg/kg) reduced CHS-induced increase
in the brain contents of TNF-α (37.43±0.63 and 38.84±2.21 vs 50.14±2.26 pg/mL) and
interleukin-1β (190.60±11.19, 157.60±6.09 vs 245.70±8.54 pg/mL). The CHS-induced increased
brain expressions of iNOSand NF-kBimmunopositive cells were attenuated by naringenin. It also
increased BDNF expressions but did not alter serum corticosterone. Histomorphological
distortions and loss of neuronal cells in the amygdala induced by CHS was reduced by naringenin.
Naringenin attenuated depression and anxiety like behaviours induced by chronic hypoxic stress.
The mechanism was via neuroprotection relating to inhibition of oxidative stress,
proinflammatory cytokines, expressions of inducible nitric oxide synthase and nuclear factor
kappa-B, and upregulation of brain derived neurotrophic factor expressions.
