Biogenic amine changes in brain regions and attenuating action of Ocimum sanctumin noise exposure

Noise exposure in early adulthood causes age-dependent and brain region-specific impairments in cognitive function

Hearing loss is a chronic health condition that affects millions of people worldwide. In addition to age-related hearing impairment, excessive noise exposure is a leading cause of hearing loss. Beyond the devastating effects of hearing impairment itself, epidemiological studies have identified hearing loss as a major risk factor for age-related cognitive decline, including dementia. At present, we currently lack a full understanding of the brain regions and underlying molecular changes that are responsible for mediating the link between hearing loss and cognitive impairment across aging. In the present study, we exposed 6-month-old rats to an occupational-like noise (100 dB SPL, 4 h/day × 30 days) or sham exposure and investigated both hippocampal-dependent (i.e., spatial learning and memory, assessed using the Morris water maze) and striatal-dependent (i.e., visuomotor associative learning, assessed using an operant-conditioning task) cognitive function across aging at 7, 10, and 13 months of age. We also investigated brain region-specific changes in microglial expression following noise/sham exposure in order to assess the potential contribution of this cell type to noise-induced cognitive impairments. Consistent with human studies, the occupational-like noise exposure resulted in high-frequency hearing loss, evidenced by a significant increase in hearing thresholds at 20 kHz. Ultimately, our results suggest that not all higher-level cognitive tasks or their associated brain regions appear to be equally susceptible to noise-induced deficits during aging, as the occupational-like noise exposure caused an age-dependent deficit in spatial but not visuomotor associative learning, as well as altered microglial expression in the hippocampus but not the striatum. Interestingly, we found no significant relationships between spatial learning ability and the level of hearing loss or altered microglial density in the hippocampus following noise exposure, suggesting that other changes in the brain likely contribute to hippocampal-dependent cognitive dysfunction following noise exposure. Lastly, we found that a subset of younger animals also showed noise-induced deficits in spatial learning; findings which suggest that noise exposure may represent an increased risk for cognitive impairment in vulnerable subjects. Overall, our findings highlight that even a mild occupational-like noise exposure earlier in adulthood can have long lasting implications for cognitive function later in life.

To cope with a changing aquatic soundscape: Neuroendocrine and antioxidant responses to chronic noise stress in fish

Anthropogenic underwater noises that change aquatic soundscapes represent an important issue in marine conservation. While it is evident that strong underwater acoustic pollutants may cause significant damage to fish at short ranges, the physiological effects of long-term exposure to relatively quiet but continuous noise are less well understood. Here, we present a summary of the known impacts of long-term underwater noise on hypothalamic-pituitary-interrenal (HPI) axis-mediated physiological responses, oxidant/antioxidant balance, and neurotransmitter regulation in fish. Cortisol is known to play a central role in physiological stress response, most often as a mediator of acute response. However, recent research indicates that noise exposure may also induce chronic corticosteroid responses, which involve increased rates of cortisol turnover. Moreover, continuous noise affects oxidative stress and antioxidant systems in vertebrates and fish, suggesting that oxidative species may mediate some noise-induced physiological responses and make these systems valuable noise stress markers. Lastly, noise stress is also known to affect neurotransmitters in the brain that may cause neurophysiological and behavioral changes. The neurochemical mechanisms underlying observed behavioral disorders in fish after exposure to changing acoustic environments are a topic of active research. Overall, a growing body of evidence suggests that chronic noise pollution could be a threat to fish populations. In future work, systematic and comparative investigations into long-term and transgenerational adaptive neuronal and metabolic responses to noise will be important to understand the physiological patterns and dynamics of noise response relevant to fish conservation.

Differential Plasticity in Auditory and Prefrontal Cortices, and Cognitive-Behavioral Deficits Following Noise-Induced Hearing Loss

Excessive exposure to loud noise causes hearing loss and neural plasticity throughout the auditory pathway. Recent studies have identified that non-auditory regions, such as the hippocampus, are also susceptible to noise exposure; however, the electrophysiological and behavioral consequences of noise-induced hearing loss on the prefrontal cortex (PFC) are unclear. Using chronically-implanted electrodes in awake rats, we investigated neural plasticity in the auditory and prefrontal cortices in the days following noise exposure via metrics associated with spontaneous neural oscillations and the 40-Hz auditory steady-state response (ASSR). Noise exposure did not alter the profile of spontaneous oscillations in either of the cortices, yet it caused a differential plasticity in the sound-evoked activity, which was characterized by enhanced event-related potentials (ERPs) in the auditory cortex (i.e., central gain), and decreased inter-trial coherence (ITC) of the 40-Hz ASSR within the PFC. Moreover, phase synchrony between auditory and prefrontal cortices was decreased post-exposure, suggesting a reduction in functional connectivity. Cognitive-behavioral testing using the Morris water maze and a series of lever-pressing tasks revealed that noise exposure impaired spatial learning and reference memory, as well as stimulus-response habit learning, whereas cognitive flexibility tasks requiring set-shifting and reversal learning appeared unaffected. Collectively, our findings identify the complex and region-specific cortical plasticity associated with noise-induced hearing loss, and highlight the varying degrees of susceptibility of non-auditory, cognitive tasks of learning, memory and executive function to noise exposure.

Magnesium treatment palliates noise-induced behavioral deficits by normalizing DAergic and 5-HTergic metabolism in adult male rats

Magnesium (Mg) is the fourth most abundant biological mineral essential for good health. Neuroprotective, anxiolytic and antidepressant effects of magnesium following stress and brain injuries are well established. In present study, we analyzed the protective effects of magnesium in rats exposed to sub-chronic noise stress. Magnesium Chloride (MgCl2, 100 mg/kg) was administered intraperitoneally once daily for 15 days prior exposure to noise stress. Rats were exposed to noise stress for 4 h after administration of magnesium for 15 days. At the end of treatment behavioral alterations were assessed. Animals were decapitated following behavioral testing and the brains were dissected out for neurochemical estimations by HPLC-EC. Improvement in noise-induced memory deficits as assessed by novel object recognition (NOR) test and elevated plus maze (EPM) test was found in magnesium treated rats. This improvement in noise-induced behavioral deficits following treatment with magnesium may be attributed to a significant decrease (p < 0.01) in dopamine (DA) and serotonin (5-hydroxytryptamine; 5-HT) turnover as compared to control rats observed in present work. These results suggest that treatment with magnesium can attenuate the noise-induced deficits and may be used as a therapy against noise-induced neurodegeneration. Moreover an adequate amount of magnesium in daily diet may help to develop the ability to resist against or cope up with stressful conditions encountered in daily life.

Decreased Hippocampal 5-HT and DA Levels Following Sub-Chronic Exposure to Noise Stress: Impairment in both Spatial and Recognition Memory in Male Rats

Mankind is exposed to a number of stressors, and among them noise is one which can cause intense stress. High levels of background noise can severely impair one’s ability to concentrate. The present study was aimed to investigate the effect of sub-chronic noise stress on cognitive behavior and hippocampal monoamine levels in male rats. The study was performed on 12 male Wistar rats, divided into two groups; the control and noise-exposed. The rats in the test group were subjected to noise stress, 4h daily for 15 days. Cognitive testing was performed by the Elevated Plus Maze test (EPM) and Novel Object Recognition test (NOR). HPLC-EC was used to determine hippocampal monoamine levels and their metabolites. The data obtained revealed a significant decrease in hippocampal serotonin (5-hydroxytryptamine; 5-HT) and dopamine (DA) levels, whereas turnover ratios of 5-HT and DA were significantly increased compared to the controls. Rats exposed to noise exhibited a significant decrement in spatial memory. A significantly decreased recognition index of rats exposed to noise as compared to the control was also observed in the NOR test. Results of the present findings suggest the role of decreased hippocampal 5-HT and DA in the impairment of cognitive function following noise exposure.

A review on animal models for screening potential anti-stress agents

Stress is a state of threatened homeostasis that produces different physiological as well as pathological changes depending on severity, type and duration of stress. The animal models are pivotal for understanding the pathophysiology of stress-induced behavioral alterations and development of effective therapy for its optimal management. A battery of models has been developed to simulate the clinical pain conditions with diverse etiology. An ideal animal model should be able to reproduce each of the aspects of stress response and should be able to mimic the natural progression of the disease. The present review describes the different types of acute and chronic stress models including immersion in cold water with no escape, cold environment isolation, immobilization/restraint-induced stress, cold-water restraint stress, electric foot shock-induced stress, forced swimming-induced stress, food-deprived activity stress, neonatal isolation-induced stress, predatory stress, day-night light change-induced stress, noise-induced stress, model of post-traumatic stress disorder and chronic unpredictable stress models.

Effects of Ocimum sanctum and Camellia sinensis on stress-induced anxiety and depression in male albino Rattus norvegicus

Objective:

The aim of this study was to study the ameliorative effects of Ocimum sanctum and Camellia sinensis on stress-induced anxiety and depression.

Materials and Methods:

The study was carried out using male albino rats (200 ± 50 g). The effect of O. sanctum and C. sinensis was evaluated for anxiety and depression using elevated plus maze (EPM) test, open field test (OFT), forced swim test (FST), and tail suspension test (TST).

Result:

Restraint stress (3 h/day for six consecutive days) induced a significant reduction in both the percentage number of entries and time spent in open arms in EPM, and these changes were reversed with post-treatment of aqueous extract of O. sanctum and C. sinensis (100 mg/kg for 6 days). Restraint stress-induced (a) increased latency and (b) decreased ambulation and rearing were also reversed by O. sanctum and C. sinensis in OFT. A significant increase in immobility period was observed in FST and TST after restraint stress. O. sanctum and C. sinensis significantly reduced the immobility times of rats in FST and TST.

Conclusion:

O. sanctum and C. sinensis possess anxiolytic and antidepressant activities.

Evaluation of ethanol leaf extract of Ocimum sanctum in experimental models of anxiety and depression

CONTEXT

Recent studies reveal the co-occurrence of both anxiety and depressive disorders in many clinical conditions, which has introduced the concept of mixed anxiety and depressive disorders (MADD).

OBJECTIVE

The study evaluated the ethanol leaf extract of Ocimum sanctum (OS) Linn. (Labiatae), a prominent medicinal plant, against both anxiety and depressive disorder, to evaluate its potency in combating MADD.

MATERIALS AND METHODS

Swiss albino mice weighing 20-25 g were used. Gross behavior was observed through Digiscan animal activity monitor. Depression was studied through tail suspension test (TST) and forced swim test (FST). Anxiety experiments included light dark test, elevated plus maze test, and holeboard test. Further, rotarod test was also used to study any defects in motor coordination.

DISCUSSION AND CONCLUSION

OS at 200 mg/kg showed motor-depressant activity as evaluated with locomotor activity and stereotypy measures. OS at 50 mg/kg shortened the immobility time in the TST and FST, respectively, indicating a possible antidepressant activity. Further, a diminution in the anxiety response at a dose of 50 mg/kg, p.o. body weight was also observed against light dark, elevated plus maze, and holeboard tests, which signifies its antianxiety activity. No defects were observed in the motor coordination of the mice in the rotarod test. Thus, the OS extract shows antianxiety and antidepressant properties at the same dose and can be a potential therapeutic agent against mixed anxiety and depressive syndrome.

Ocimum sanctum Linn. A reservoir plant for therapeutic applications: An overview

The medicinal plants are widely used by the traditional medicinal practitioners for curing various diseases in their day to day practice. In traditional system of medicine, different parts (leaves, stem, flower, root, seeds and even whole plant) of Ocimum sanctum Linn. have been recommended for the treatment of bronchitis, malaria, diarrhea, dysentery, skin disease, arthritis, eye diseases, insect bites and so on. The O. sanctum L. has also been suggested to possess anti-fertility, anticancer, antidiabetic, antifungal, antimicrobial, cardioprotective, analgesic, antispasmodic and adaptogenic actions. Eugenol (1-hydroxy-2-methoxy-4-allylbenzene), the active constituents present in O. sanctum L. have been found to be largely responsible for the therapeutic potentials. The pharmacological studies reported in the present review confirm the therapeutic value of O. sanctum L. The results of the above studies support the use of this plant for human and animal disease therapy and reinforce the importance of the ethno-botanical approach as a potential source of bioactive substances.

Effects of four Indian medicinal herbs on Isoniazid-, Rifampicin- and Pyrazinamide-induced hepatic injury and immunosuppression in guinea pigs

AIM: To evaluate and compare the hepatoprotective and immunomodulatory effects of Curcuma longa (CL), Ocimum sanctum (OS), Tinospora cordifolia (TC) and Zizyphus mauritiana (ZM) on liver injury and immunosuppression induced by Isoniazid (INH), Rifampicin (RIF) and Pyrazinamide (PZA).

METHODS: Duncan Hartley guinea pigs, weighing 700-1050 g, were treated orally with 50 mg/kg of INH, 100 mg/kg of RIF and 300 mg/Kg of PZA for 21-d. 200 mg/kg (bw) of each herb crude extract was administered to the herb control group and 2-h previous to INH + RIF + PZA (AKT) doses to the Herb + AKT groups. Serum alanine aminotransferase (ALT), aspertate aminotransferase (AST) bilirubin and Alkaline Phosphatase (ALP) were assessed on d 0 and 21 in all the groups. Phagocytic % (P%), Phagocytic Index (PI) and Chemotactic Index (CI) were also measured as immunologic parameters. Histological analysis was carried out to assess injury to the liver.

RESULTS: The AKT treated control group showed hepatotoxicity as judged by elevated serum AST 5-fold, AST/ALT ratio 4-fold, ALP 2-fold and hepatological changes, such as focal necrosis, portal triaditis and steatosis. Immune function was suppressed as judged by decreased P% (51.67 ± 1.68 vs 40.61 ± 1.28, P < 0.01), PI (2.0725 ± 0.05 vs 0.61 ± 0.05, P < 0.001) and CI (1.8525 ± 0.04 vs 0.695 ± 0.07, P < 0.001). All four herb treated groups showed normal liver histology, enzyme levels and increased P%, while PI and CI were enhanced in the TC and ZM treated groups, respectively. CL + AKT, TC + AKT and ZM + AKT showed nearly normal histology with minimal inflammation and microvesicular steatosis, while OS + AKT showed partial protection. Hepatotoxicity was prevented by restricting the rise of AST by 2-fold in CL + AKT and TC + AKT groups and by 3-fold in OS + AKT and ZM + AKT groups, AST/ALT by 2-fold and ALP to normal levels in all four groups. All four herb + AKT groups showed normal to enhanced neutrophil function.

CONCLUSION: All four herbs showed hepatoprotective potential and prevented immunosuppression. CL and TC showed the highest hepatoprotective activity, while TC and ZM showed strong immunostimulatory activity.

Oxidative stress in brain and antioxidant activity of Ocimum sanctum in noise exposure

Noise is a pervasive aspect of many modern communities, work environments and its damaging effects, particularly the production of free radicals are not limited to the auditory organ. The oxidative stress in three discrete brain regions, in wistar strain male albino rats subjected to three different durations of noise exposures (acute, sub-acute and chronic noise stress) and the in vivo as well as the in vitro antioxidant activity of Ocimum sanctum has been analyzed. Broadband white noise (100dB) exposure significantly increased the levels of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), glutathione peroxidase (EC 1.11.1.9), lipid peroxidation, oxidized glutathione (GSSG) and decreased the levels of reduced glutathione (GSH), GSH/GSSG ratio. However, administration of ethanolic extract of O. sanctum attenuates the alterations induced by noise exposure. The antioxidant activity of O. sanctum is also evident from its effectiveness in scavenging the free radicals in a dose dependent manner in the herbal antioxidant assays. The results indicate that adaptation to noise does not occur in the brain regions even after 30 days of noise exposure. The abundance of phytochemicals such as phenolics and flavanoids in O. sanctum may be held responsible for its attenuating activity. Therefore, this study indicates that O. sanctum has the potential for further evaluation as an ideal antioxidant for the noise induced oxidative stress.

Stress response in rat brain after different durations of noise exposure

The alteration in the levels of plasma corticosterone, brain norepinephrine (NE), and expression of brain heat shock proteins (Hsp70) after different durations of noise exposure (acute, 1 day; sub-acute, 15 days; chronic, 30 days) has been studied to analyze their role in combating time-dependent stress effects of noise. Broadband white noise (100dB) exposure to male Wistar albino rats significantly increased the levels of plasma corticosterone and NE in all three durations of noise exposure. The sustained increase observed in their levels in the chronic group suggests that animals are not getting adapted to noise even after 30 days of exposure. The important role of Hsp70 in combating noise induced stress is evident from the significant increase in its expression after chronic exposure, while there was a reciprocal decrease in the NE and corticosterone when compared with their levels after acute and sub-acute noise exposure. This clearly indicates that the time-dependent stress response to noise exposure is a complex mechanism involving highly interconnected systems such as hypothalamo-pituitary-adrenal (HPA) axis, heat shock proteins and may have serious implications in vital organs, particularly in the brain when there is a prolonged noise exposure.