Hyperammonemia induced gut microbiota dysbiosis and motor coordination disturbances in mice: new insight into gut­brain axis involvement in hepatic encephalopathy.

Hepatic encephalopathy (HE) is a neuropsychiatric hepatic­induced syndrome in which several factors are involved in promoting brain perturbations, with ammonia being the primary factor. Motor impairment, incoordination, and gut dysbiosis are some of the well­known symptoms of HE. Nevertheless, the link between the direct effect of hyperammonemia and associated gut dysbiosis in the pathogenesis of HE is not well established. Thus, this work aimed to assess motor function in hyperammonemia and gut dysbiosis in mice. Twenty­eight Swiss mice were distributed into three groups: two­week and four­week hyperammonemia groups were fed with an ammonia­rich diet (20% w/w), and the control group was pair­fed with a standard diet. Motor performance in the three groups was measured through a battery of motor tests, namely the rotarod, parallel bars, beam walk, and static bars. Microbial analysis was then carried out on the intestine of the studied mice. The result showed motor impairments in both hyperammonemia groups. Qualitative and quantitative microbiological analysis revealed decreased bacterial load, diversity, and ratios of both aerobic and facultative anaerobic bacteria, following two and four weeks of ammonia supplementation. Moreover, the Shannon diversity index revealed a time­dependent cutback of gut bacterial diversity in a treatment­time­dependent manner, with the presence of only Enterobacteriaceae, Streptococcaceae, and Enterococcaceaeat at four weeks. The data showed that ammonia­induced motor coordination deficits may develop through direct and indirect pathways acting on the gut­brain axis.

Neurobehavioral and neurophysiological effects of prolonged osmotic stress in rats: A focus on anxiety state and pain perception.

This study examined the effect of prolonged water deprivation, in rat, on 5-HT and TH- immuno-expression in Dorsal Raphe Nucleus (DRN), Substantia Nigra pars compacta (SNc), Ventral Tegmental Area (VTA), and Magnus Raphe Nucleus (MRN). In parallel, we evaluated the anxiety state and pain perception in dehydrated rats. Our Findings revealed that dehydrated rats exhibited more preference for the dark compartment, suggesting that prolonged water deprivation is associated to an anxiogenic effect. After one week, 5 H T IR in the DRN of dehydrated rates showed a significant decrease. This was reversed to a significant increase post week 2 of dehydration. Our findings also demonstrated that TH-IR in DRN, MRN, SNc and VTA neuronal systems is significantly and gradually enhanced after 1-and-2-week osmotic stress. In addition, our results proved that all dehydrated rats were characterized by a significant and proportional rise of the reaction time to the nociceptive response in the hot plate test, as water deprivation duration increased, suggesting that dehydration caused a significant decrease in pain perception. Finally, the data described here clearly showed the implication of serotonin and dopamine neurotransmitter systems in the resistance to osmotic stress. Therefore, in this study, such central impairments were traduced by a few peripheral outcomes manifested by changes in mood state and nociception.

Long term osmotic stress exposure outcomes on rat dopaminergic innervations and the associated motor behavior.

The osmotic stress is a powerful stimulus that elicits profound peripheral and central disturbances. In the mammalian brain, osmotic stress has been associated to several glial and neuronal changes. The lack of data regarding the impact on the dopaminergic system and locomotion led us to investigate the effect of prolonged water deprivation in rat on the midbrain dopaminergic system and locomotor performance by dehydrating rats for one and two weeks. Locomotor activity and tyrosine hydroxylase (TH) expression were assessed using the open field test and immunohistochemistry respectively. Water deprivation was accompanied with a significant increment of TH expression within substantia nigra compacta (SNc) and ventral tegmental area (VTA) gradually as the duration of dehydration increases. While locomotor activity showed the inverse tendency manifested by a drop of crossed boxes number following one and two weeks of water deprivation. Our data suggest a substantial implication of midbrain dopaminergic system in the central response to the osmotic stimuli accompanied with locomotor deficiencies.

Neuroprotective effect of curcumin-I in copper-induced dopaminergic neurotoxicity in rats: A possible link with Parkinson's disease.

Numerous findings indicate an involvement of heavy metals in the neuropathology of several neurodegenerative disorders, especially Parkinson's disease (PD). Previous studies have demonstrated that Copper (Cu) exhibits a potent neurotoxic effect on dopaminergic neurons and triggers profound neurobehavioral alterations. Curcumin is a major component of Curcuma longa rhizomes and a powerful medicinal plant that exerts many pharmacological effects. However, the neuroprotective action of curcumin on Cu-induced dopaminergic neurotoxicity is yet to be investigated. The aim of the present study was to evaluate the impact of acute Cu-intoxication (10mg/kg B.W. i.p) for 3days on the dopaminergic system and locomotor performance as well as the possible therapeutic efficacy of curcumin I (30mg/kg B.W.). Intoxicated rats showed a significant loss of Tyrosine Hydroxylase (TH) expression within substantia nigra pars compacta (SNc), ventral tegmental area (VTA) and the striatal outputs. This was correlated with a clear decrease in locomotor performance. Critically, curcumin-I co-treatment reversed these changes and showed a noticeable protective effect; both TH expression and locomotor performance was reinstated in intoxicated rats. These results demonstrate altered dopaminergic innervations following Cu intoxication and a new therapeutic potential of curcumin against Cu-induced dopaminergic neurotransmission failure. Curcumin may therefore prevent heavy metal related Parkinsonism.

Loss of tyrosine hydroxylase expression within the nigro-striato-cortical pathways in the cirrhotic rat: the possible restorative effect of the neurosteroid dehydroepiandrosterone sulfate.

Hepatic encephalopathy (HE) is a neuropsychiatric disorder occurring as a consequence of both acute and chronic liver failure. Advanced HE is generally accompanied with extrapyramidal symptoms including rigidity and tremor, which may reflect alterations of the dopaminergic system. Recently we reported a beneficial effect of the neuroactive steroid dehydroepiandrosterone sulfate (DHEAS) in cirrhotic rats, however the mechanisms of such an effect by DHEAS were not addressed. In the present study, we describe the changes of the dopaminergic system occurring in the cirrhotic rats and concomitantly we investigated the effect of DHEAS on this system in Sprague-Dawley rats using the expression of tyrosine hydroxylase (TH) as a neuronal marker. Rats were submitted to bile duct ligation (BDL) surgery and TH immunohistochemistry was assessed in the Substantia nigra pars compacta (SNc), striatum, ventral tegmental area (VTA) and the cortex. TH immunoreactivity showed a significant diminution in both SNc and VTA concomitantly with the cortical and the striatal outputs in the BDL rats vs. controls. Three daily injections of 5mg/kg of DHEAS to BDL rats significantly normalized TH expression decrease in both SNc and VTA as well as dopaminergic projections to the striatum and the cortex of BDL rats. The present data support an involvement of the dopaminergic system in mild HE and a possible beneficial effect of the neurosteroid DHEAS as a potential pharmacological treatment of mild HE.

The rat SCO responsiveness to prolonged water deprivation: implication of Reissner's fiber and serotonin system.

The osmotic stress is a potent stimulus that can trigger several peripheral as well as central impairments. The brain is a vulnerable target of the osmotic stress and particularly circumventricular organs (CVOs) regarding their strategic localization as sensory organs of biochemical changes in the blood and cerebrospinal fluid circulations. The subcommissural organ (SCO) is a CVO which releases doubly in the CSF and blood circulation a glycoprotein called Reissner's fiber (RF) that has been associated to several functions including electrolyte and water balances. The present work was aimed on the assessment of the secretory activity of the SCO and its serotoninergic innervation following 2 weeks of total water restriction in Wistar rat. Using the immunohistochemistry of RF and serotonin (5HT), our data showed a significant overall reduction of RF immunoreactivity within both ependymal and hypendymal cells of the SCO of dehydrated rats compared to their corresponding controls, this decrease was concomitant with an enhancement of fibers 5HT immunoreactivity in the SCO as well as in the classical ependyma and in the dorsal raphe nucleus (DRN), constituting the origin of this innervation. The present findings support the possible involvement of the SCO in the response to prolonged water deprivation by decreasing its secretory materials which may result from either a direct peripheral hormonal control and/or the consequence of the enhanced 5HT innervation of the SCO.