Rajib Paul

Differential expression of HR38 in the mushroom bodies of the honeybee brain depends on the caste and division of labor

We used a cDNA microarray to identify genes expressed in a caste (worker)‐ and division of labor (nurse bees or foragers)‐dependent manner in the honeybee brain. Among the identified genes, one encoded a putative orphan receptor (HR38) homologue that mediates ecdysteroid‐signaling. Real‐time reverse transcription‐polymerase chain reaction indicated that expression of this gene is higher in forager brains, as compared to nurse bees and queens. In the forager brain, expression was concentrated in a subset of the mushroom body neurons, suggesting that ecdysteroid‐signaling in the mushroom bodies might be involved in the division of labor of the workers.

Gene expression of ecdysteroid-regulated gene E74 of the honeybee in ovary and brain

To facilitate studies of hormonal control in the honeybee (Apis mellifera L.), a cDNA for a honeybee homologue of the ecdysteroid‐regulated gene E74 (AmE74) was isolated and its expression was analysed. Northern blot analysis indicated strong expression in the adult queen abdomen, and no significant expression in the adult drone and worker abdomens. In situ hybridization demonstrated that this gene was expressed selectively in the ovary and gut in the queen abdomen. Furthermore, this gene was also expressed selectively in subsets of mushroom body interneurones in the brain of the adult worker bees. These findings suggest that AmE74 is involved in neural function as well as in reproduction in adult honeybees.

Expression of Two Ecdysteroid-Regulated Genes, Broad-Complex and E75, in the Brain and Ovary of the Honeybee (Apis mellifera L.)

Abstract We previously demonstrated that two ecdysteroid-regulated genes, Mblk-1/E93 and E74, are expressed selectively in Kenyon cell subtypes in the mushroom bodies of the honeybee (Apis mellifera L.) brain. To further examine the possible involvement of ecdysteroid-regulated genes in brain function as well as in oogenesis in the honeybee, we isolated cDNAs for two other ecdysteroid-regulated genes, Broad-Complex (BR-C) and E75, and analyzed their expression in the worker brain as well as in the queen abdomen. In situ hybridization revealed that BR-C, like Mblk-1/E93, is expressed selectively in the large-type Kenyon cells of the mushroom bodies in the worker brain, whereas E75 is expressed in all mushroom body neuron subtypes, suggesting a difference in the mode of response to ecdysteroid among Kenyon cell subtypes. In the queen ovary, both BR-C and E75 are expressed preferentially in the follicle cells that surround egg cells at the late stage, suggesting their role in oogenesis. These results suggest that BR-C and E75 are involved in the regulation of brain function as well as in reproductive physiology in the adult honeybee.

EcR-A Expression in the Brain and Ovary of the Honeybee (Apis mellifera L.)

Abstract We previously demonstrated that six genes involved in ecdysteroid signaling are expressed preferentially in Kenyon-cell subtypes in the mushroom bodies of the honeybee (Apis mellifera L.). To further examine the possible involvement of ecdysteroid signaling in honeybee brain function, we isolated a cDNA for the A isoform of the ecdysone receptor gene homolog AmEcR-A and analyzed its expression in the brain. In situ hybridization revealed that AmEcR-A is expressed selectively in the small-type Kenyon cells of the mushroom bodies in the worker and queen brain, like AmE74 and AmHR38, suggesting a possible association of these gene products. Analysis of AmEcR-A expression in queen and worker abdomens demonstrated that AmEcR-A is strongly expressed in nurse cells of the queen ovary, suggesting that ecdysteroid and ecdysteroid signaling have roles in oogenesis. Our present results further support the possible involvement of ecdysteroid signaling in brain function, as well as in regulating queen reproductive physiology in the adult honeybee.

Division of labor in the honey bee (Apis mellifera): The role of tyramine β-hydroxylase

SUMMARY The biogenic amine octopamine (OA) is involved in the regulation of honey bee behavioral development; brain levels are higher in foragers than bees working in the hive, especially in the antennal lobes, and treatment causes precocious foraging. We measured brain mRNA and protein activity of tyramineβ -hydroxylase (T βh), an enzyme vital for OA synthesis, in order to begin testing the hypothesis that this enzyme is responsible for the rising levels of OA during honey bee behavioral development. Brain OA levels were greater in forager bees than in bees engaged in brood care, as in previous studies, but T βh activity was not correlated with bee behavior. Tβ h mRNA levels, however, did closely track OA levels during behavioral development, and T βh mRNA was localized to previously identified octopaminergic neurons in the bee brain. Our results show that the transcription of this neurotransmitter synthetic enzyme is associated with regulation of social behavior in honey bees, but other factors may be involved.

Neuroprotective Potential of Silymarin against CNS Disorders: Insight into the Pathways and Molecular Mechanisms of Action

Silymarin, a C25 containing flavonoid from the plant Silybum marianum, has been the gold standard drug to treat liver disorders associated with alcohol consumption, acute and chronic viral hepatitis, and toxin‐induced hepatic failures since its discovery in 1960. Apart from the hepatoprotective nature, which is mainly due to its antioxidant and tissue regenerative properties, Silymarin has recently been reported to be a putative neuroprotective agent against many neurologic diseases including Alzheimers and Parkinsons diseases, and cerebral ischemia. Although the underlying neuroprotective mechanism of Silymarin is believed to be due to its capacity to inhibit oxidative stress in the brain, it also confers additional advantages by influencing pathways such as β‐amyloid aggregation, inflammatory mechanisms, cellular apoptotic machinery, and estrogenic receptor mediation. In this review, we have elucidated the possible neuroprotective effects of Silymarin and the underlying molecular events, and suggested future courses of action for its acceptance as a CNS drug for the treatment of neurodegenerative diseases.

Cholesterol contributes to dopamine-neuronal loss in MPTP mouse model of Parkinson’s disease: Involvement of mitochondrial dysfunctions and oxidative stress

Hypercholesterolemia is a known contributor to the pathogenesis of Alzheimer’s disease while its role in the occurrence of Parkinson’s disease (PD) is only conjecture and far from conclusive. Altered antioxidant homeostasis and mitochondrial functions are the key mechanisms in loss of dopaminergic neurons in the substantia nigra (SN) region of the midbrain in PD. Hypercholesterolemia is reported to cause oxidative stress and mitochondrial dysfunctions in the cortex and hippocampus regions of the brain in rodents. However, the impact of hypercholesterolemia on the midbrain dopaminergic neurons in animal models of PD remains elusive. We tested the hypothesis that hypercholesterolemia in MPTP model of PD would potentiate dopaminergic neuron loss in SN by disrupting mitochondrial functions and antioxidant homeostasis. It is evident from the present study that hypercholesterolemia in naïve animals caused dopamine neuronal loss in SN with subsequent reduction in striatal dopamine levels producing motor impairment. Moreover, in the MPTP model of PD, hypercholesterolemia exacerbated MPTP-induced reduction of striatal dopamine as well as dopaminergic neurons in SN with motor behavioral depreciation. Activity of mitochondrial complexes, mainly complex-I and III, was impaired severely in the nigrostriatal pathway of hypercholesterolemic animals treated with MPTP. Hypercholesterolemia caused oxidative stress in the nigrostriatal pathway with increased generation of hydroxyl radicals and enhanced activity of antioxidant enzymes, which were further aggravated in the hypercholesterolemic mice with Parkinsonism. In conclusion, our findings provide evidence of increased vulnerability of the midbrain dopaminergic neurons in PD with hypercholesterolemia.

L-DOPA-induced hyperhomocysteinemia in Parkinson's disease: Elephant in the room.

BACKGROUND Dopamine replacement therapy by its precursor, L-3.4-dihydroxyphenylalanine (L-DOPA), has been the treatment of choice for Parkinsons disease. However, the possible contributory effect of L-DOPA therapy on the progression of Parkinsons disease mediated by the L-DOPA-induced toxic metabolites remains elusive. SCOPE OF REVIEW Prolong use of L-DOPA leads to behavioral impediments and instigate the generation of several toxic metabolites. One such metabolite is homocysteine, the level of which increases in the plasma of Parkinsons disease patients undergoing L-DOPA therapy, as well as in brain of animal models of the disease. In concoction with parkinsonian neurotoxins, Hcy exaggerates dopaminergic neurodegeneration, while its intranigral infusion has been demonstrated to decrease the dopamine level as well as causes dopaminergic neurodegeneration. Therefore, it can be propounded that elevated level of Hcy (hyperhomocysteinemia) is one of the underlying causes of L-DOPA-induced side-effects and aggravates the progressive nature of Parkinsons disease, which has been focused here. We have provided a conjectural discussion on the involvement of Hcy in L-DOPA-induced dyskinesia in Parkinsons disease. CONCLUSION Hyperhomocysteinemia as a result of prolonged L-DOPA therapy is the emerging cause of L-DOPA-induced behavioral abnormalities and progressive nature of Parkinsons disease. GENERAL SIGNIFICANCE This review highlights that hyperhomocysteinemia could be a putative contributor of the side-effects of chronic L-DOPA therapy because of its neurotoxic potency.

Chronic exposure of homocysteine in mice contributes to dopamine loss by enhancing oxidative stress in nigrostriatum and produces behavioral phenotypes of Parkinson’s disease

Increased homocysteine (Hcy) level has been implicated as an independent risk factor for various neurological disorders, including Parkinson’s disease (PD). Hcy has been reported to cause dopaminergic neuronal loss in rodents and causes the behavioral abnormalities. This study is an attempt to investigate molecular mechanisms underlying Hcy-induced dopaminergic neurotoxicity after its chronic systemic administration. Male Swiss albino mice were injected with different doses of Hcy (100 and 250 mg/kg; intraperitoneal) for 60 days. Animals subjected to higher doses of Hcy, but not the lower dose, produces motor behavioral abnormalities with significant dopamine depletion in the striatum. Significant inhibition of mitochondrial complex-I activity in nigra with enhanced activity of antioxidant enzymes in the nigrostriatum have highlighted the involvement of Hcy-induced oxidative stress. While, chronic exposure to Hcy neither significantly alters the nigrostriatal glutathione level nor it causes any visible change in tyrosine hydroxylase-immunoreactivity of dopaminergic neurons. The finding set us to hypothesize that the mild oxidative stress due to prolonged Hcy exposure to mice is conducive to striatal dopamine depletion leading to behavioral abnormalities similar to that observed in PD.

β-Phenethylamine—A Phenylalanine Derivative in Brain—Contributes to Oxidative Stress by Inhibiting Mitochondrial Complexes and DT-Diaphorase: An In Silico Study

Till date, the mode of action of β‐PEA on neurons is not well illustrated. We tested the hypothesis that β–PEA has the ability to cause oxidative stress by inhibiting the antioxidant enzyme DT‐diaphorase and mitochondrial complexes (Complex‐I and complex‐III).