Joaquín García-Estrada

Beneficial effects of α-lipoic acid plus vitamin E on neurological deficit, reactive gliosis and neuronal remodeling in the penumbra of the ischemic rat brain

During cerebral ischemia-reperfusion, the enhanced production of oxygen-derived free radicals contributes to neuronal death. The antioxidants alpha-lipoic acid and vitamin E have shown synergistic effects against lipid peroxidation by oxidant radicals in several pathological conditions. A thromboembolic stroke model in rats was used to analyze the effects of this mixture under two oral treatments: intensive and prophylactic. Neurological functions, glial reactivity and neuronal remodeling were assessed after experimental infarction. Neurological recovery was only found in the prophylactic group, and both antioxidant schemes produced down-regulation of astrocytic and microglial reactivity, as well as higher neuronal remodeling in the penumbra area, as compared with controls. The beneficial effects of this antioxidant mixture suggest that it may be valuable for the treatment of cerebral ischemia in humans.

Astrocytic and microglia cells reactivity induced by neonatal administration of glutamate in cerebral cortex of the adult rats

Recent studies confirm that astrocytes and neurons are associated with the synaptic transmission, particularly with the regulation of glutamate (Glu) levels. Therefore, they have the capacity to modulate the Glu released from neurons into the extracellular space. It has also been demonstrated an intense astrocytic and microglia response to physical or chemical lesions of the central nervous system. However, the persistence of the response of the glial cells in adult brain had not been previously reported, after the excitotoxic damage caused by neonatal dosage of monosodium glutamate (MSG) to newborn rats. In this study, 4 mg/g body weight of MSG were administered to newborn rats at 1, 3, 5, and 7 days after birth, at the age of 60 days the astrocytes and the microglia cells were analyzed with immunohistochemical methods in the fronto‐parietal cortex. Double labeling to glial fibrillary acidic protein (GFAP) and BrdU, or isolectin‐B4 and BrdU identified astrocytes or microglia cells that proliferated; immunoblotting and immunoreactivity to vimentin served for assess immaturity of astrocytic intermediate filaments. The results show that the neonatal administration of MSG‐induced reactivity of astrocytes and microglia cells in the fronto‐parietal cortex, which was characterized by hyperplasia; an increased number of astrocytes and microglia cells that proliferated, hypertrophy; increased complexity of the cytoplasm extension of both glial cells and expression of RNAm to vimentin, with the presence of vimentin‐positive astrocytes. This glial response to neuroexcitotoxic stimulus of Glu on the immature brain, which persisted to adulthood, suggests that the neurotransmitter Glu could trigger neuro‐degenerative illnesses.

An alpha-lipoic acid–vitamin E mixture reduces post-embolism lipid peroxidation, cerebral infarction, and neurological deficit in rats

Oxidative stress increases delayed neuronal death in the brain following ischemia. As a consequence, many attempts to reduce the damage resulting from cerebral ischemia under more highly oxidized conditions have focused on treatments aimed at maintaining the redox equilibrium of the local environment. This study demonstrates the synergistic effects of combining treatments with alpha-lipoic acid (LA) and vitamin E (VE) as an efficient measure to reduce the damage caused by cerebral ischemia. Two oral therapeutic protocols were examined: intensive treatment (100 mg/kg LA and 140 mg/kg VE for 7 days after ischemia) and prophylactic treatment (20 mg/kg LA and 50 mg/kg VE from 30 days before infarction up to the day of sacrifice). The prophylactic treatment reduced serum lipid peroxidation, and diminished brain infarct volume by approximately 50%. Furthermore, prophylactically treated rats showed a reduction in post-ischemia neurological scores. No significant differences were found in the intensively treated group. Our data indicate that pre-ischemia administration of the LA-VE antioxidant mixture reduced the volume of brain damaged and the functional consequences of embolic infarction. These findings suggest that prophylaxis with an LA-VE mixture may be valuable in reducing cerebral damage levels in patients with a high risk of stroke.

Prednisone induces cognitive dysfunction, neuronal degeneration, and reactive gliosis in rats.

Background High glucocorticoid serum levels and prednisone (PDN) therapy have been associated with depression, posttraumatic stress disorder, and some types of cognitive dysfunction in humans. Objective The aim of this study was to assess whether chronic (90 days) PDN administration produces disturbance in learning and memory retention associated with neuronal degeneration and cerebral glial changes. Methods Male Wistar rats were studied. Controls received 0.1 ml distilled water vehicle orally. The PDN group was treated orally with 5 mg/kg/d PDN, which is equivalent to moderate doses used in clinical settings. Learning and memory retention were assessed with the Morris water maze. The index of degenerated neurons as well as the number and cytoplasmic transformation of astrocytes and microglia cells were evaluated in the prefrontal cortex and the CA1 hippocampus. Results PDN-treated rats showed a significant delay of 20% in learning and memory retention as compared with controls. In addition, in the PDN group, the neuronal degeneration index was two times higher in the prefrontal cortex, and approximately 10 times higher in the CA1 hippocampus, than in control animals. The number and cytoplasmic transformation of astrocytes were also significantly higher in the PDN group than in control animals. In the PDN-treated group, isolectin-B4-labeled microglia cells were higher in the prefrontal cortex but not in the hippocampus. Conclusion These results suggest that chronic exposure to PDN produces learning and memory impairment, reduces neural viability, and increases glial reactivity in cerebral regions with these cognitive functions.

Casimiroa edulis seed extracts show anticonvulsive properties in rats

A single dose of 5, 10 and 100 mg/kg of Casimiroa edulis aqueous extract (AQ); 10, 100 and 1000 mg/kg of C. edulis ethanolic extract (E-OH); in addition, 10, 30 and 12 mg/kg of propyleneglycol (Pg), phenytoin (Phen) and phenobarbital (Phb) was orally given to adult male Wistar rat groups. Thereafter, all groups were assayed for protection against maximal electroshock (MES) and pentylenetetrazole (METsc) seizure inducing tests at hourly intervals throughout 8 h. For MES, a maximal protection of 70% at the 2nd and 4th h with 10 mg/kg AQ and 100 mg/kg E-OH doses, occurred. That of Phen, Phb and Pg was 80, 90 and 10% at the 8th, 6th and 2nd h, respectively. The averaged values of the MES unprotected rats under 10 and 100 mg/kg of AQ and E-OH extracts, showed that a shortened reflex duration as well as a delayed latency and uprising times occurred. On the other hand, just an enlarged latency and no protection against METsc device in AQ and EOH was observed. Phen and Phb maximal protection was 80 and 100% at the 4th and 6th hour against METsc. Thus, AQ is tenfold more potent anticonvulsive extract than E-OH against MES.

Dietary tryptophan restriction in rats triggers astrocyte cytoskeletal hypertrophy in hippocampus and amygdala

We have previously reported that dietary tryptophan (TRP) restriction in a rat crucial postnatal developmental stage induces depression-like behavior and alters dendritic spine density in CA1 pyramidal neurons and granule cells of the hippocampus. Due to astrocyte involvement in critical brain mechanisms, it seems worth to investigate possible adaptive changes in the glial population with TRP restriction. Experimental rats were fed with low TRP diet (20% of TRP level of the laboratory rat chow) from postnatal days 30-60. Antibody against glial fibrillary acidic protein (GFAP), a principal intermediate filament in astrocytes, was used to evaluate cytoskeletal hypertrophy and glial proliferation. Our results showed an increase in size and branching of GFAP-immunoreactive (IR) cells in the dorsal hippocampus and amygdala, characteristics of an astrocytic activation. No significant differences were found regarding the number of GFAP-IR cells in both regions. These results indicate that dietary TRP restriction can induce astrocytic activation, hence, provide further evidences supporting the hypothesis that serotonin may also modulate glial morphology.

Nitric oxide in the commissural nucleus tractus solitarii regulates carotid chemoreception hyperglycemic reflex and c-Fos expression

Carotid body chemoreceptors function as glucose sensors and contribute to glucose homeostasis. The nucleus tractus solitarii (NTS) is the first central nervous system (CNS) nuclei for processing of information arising in the carotid body. Here, we microinjected a nitric oxide (NO) donor sodium nitroprusside (SNP), an NO-independent activator of the soluble guanylyl cyclase (sGC) (YC₁) or an NO-synthase (NOS) inhibitor Nω-nitro-l-arginine methyl ester (L-NAME) into the commissural NTS (cNTS) before carotid chemoreceptor anoxic stimulation and measured arterial glucose and the expression of Fos-like immunoreactivity (Fos-ir). Male Wistar rats (250-300 g) were anesthetized, and the carotid sinus was vascularly isolated. Either artificial cerebrospinal fluid (aCSF), SNP, YC₁ or L-NAME were stereotaxically injected into the cNTS. The SNP and YC₁ infused into the cNTS before carotid chemoreceptor stimulation (SNP-2 and YC₁-2 groups) similarly increased arterial glucose compared to the aCSF-2 group. By contrast, infusion of L-NAME into the cNTS before carotid chemoreceptor stimulation (L-NAME-2 group) decreased arterial glucose concentration. The number of cNTS Fos-ir neurons, determined in all the groups studied except for YC₁ groups, significantly increased in SNP-2 rat when compared to the aCSF-2 or SNP-2 groups. Our findings demonstrate that NO signaling, and the correlative activation of groups of cNTS neurons, plays key roles in the hyperglycemic reflex initiated by carotid chemoreceptor stimulation.

Nitric oxide infused in the solitary tract nucleus blocks brain glucose retention induced by carotid chemoreceptor stimulation

Previous work has shown that the carotid body glomus cells can function as glucose sensors. The activation of these chemoreceptors, and of its afferent nucleus in the brainstem (solitary tract nucleus - STn), induces rapid changes in blood glucose levels and brain glucose retention. Nitric oxide (NO) in STn has been suggested to play a key role in the processing of baroreceptor signaling initiated in the carotid sinus. However, the relationship between changes in NO in STn and carotid body induced glycemic changes has not been studied. Here we investigated in anesthetized rats how changes in brain glucose retention, induced by the local stimulation of carotid body chemoreceptors with sodium cyanide (NaCN), were affected by modulation of NO levels in STn. We found that NO donor sodium nitroprusside (SNP) micro-injected into STn completely blocked the brain glucose retention reflex induced by NaCN chemoreceptor stimulation. In contrast, NOS inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) increased brain glucose retention reflex compared to controls or to SNP rats. Interestingly, carotid body stimulation doubled the expression of nNOS in STn, but had no effect in iNOS. NO in STn could function to terminate brain glucose retention induced by carotid body stimulation. The work indicates that NO and STn play key roles in the regulation of brain glucose retention.

Hippocampal cytogenesis and spatial learning in senile rats exposed to chronic variable stress: effects of previous early life exposure to mild stress

In this study, we exposed adult rats to chronic variable stress (CVS) and tested the hypothesis that previous early-life exposure to stress changes the manner in which older subjects respond to aversive conditions. To this end, we analyzed the cytogenic changes in the hippocampus and hippocampal-dependent spatial learning performance. The experiments were performed on 18-month-old male rats divided into four groups as follows: Control (old rats under standard laboratory conditions), Early-life stress (ELS; old rats who were exposed to environmental noise from postnatal days, PNDs 21–35), CVS + ELS (old rats exposed to a chronic stress protocol who were previously exposed to the early-life noise stress) and CVS (old rats who were exposed only to the chronic stress protocol). The Morris Water Maze (MWM) was employed to evaluate the spatial learning abilities of the rats at the end of the experiment. Immunohistochemistry against 5′Bromodeoxyuridine (BrdU) and glial fibrillar acidic protein (GFAP) was also conducted in the DG, CA1, CA2 and CA3 regions of the hippocampus. We confocally analyzed the cytogenic (BrdU-labeled cells) and astrogenic (BrdU + GFAP-labeled cells) changes produced by these conditions. Using this procedure, we found that stress diminished the total number of BrdU+ cells over the main proliferative area of the hippocampus (i.e., the dentate gyrus, DG) but increased the astrocyte phenotypes (GFAP + BrdU). The depleted BrdU+ cells were restored when the senile rats also experienced stress at the early stages of life. The MWM assessment demonstrated that stress also impairs the ability of the rats to learn the task. This impairment was not present when the stressful experience was preceded by the early-life exposure. Thus, our results support the idea that previous exposure to mild stressing agents may have beneficial effects on aged subjects.

BDNF and AMPA receptors in the cNTS modulate the hyperglycemic reflex after local carotid body NaCN stimulation

The application of sodium cyanide (NaCN) to the carotid body receptors (CBR) (CBR stimulation) induces rapid blood hyperglycemia and an increase in brain glucose retention. The commissural nucleus tractus solitarius (cNTS) is an essential relay nucleus in this hyperglycemic reflex; it receives glutamatergic afferents (that also release brain derived neurotrophic factor, BDNF) from the nodose-petrosal ganglia that relays CBR information. Previous work showed that AMPA in NTS blocks hyperglycemia and brain glucose retention after CBR stimulation. In contrast, BDNF, which attenuates glutamatergic AMPA currents in NTS, enhances these glycemic responses. Here we investigated the combined effects of BDNF and AMPA (and their antagonists) in NTS on the glycemic responses to CBR stimulation. Microinjections of BDNF plus AMPA into the cNTS before CBR stimulation in anesthetized rats, induced blood hyperglycemia and an increase in brain arteriovenous (a-v) of blood glucose concentration difference, which we infer is due to increased brain glucose retention. By contrast, the microinjection of the TrkB antagonist K252a plus AMPA abolished the glycemic responses to CBR stimulation similar to what is observed after AMPA pretreatments. In BDNF plus AMPA microinjections preceding CBR stimulation, the number of c-fos immunoreactive cNTS neurons increased. In contrast, in the rats microinjected with K252a plus AMPA in NTS, before CBR stimulation, c-fos expression in cNTS decreased. The expression of AMPA receptors GluR2/3 did not change in any of the studied groups. These results indicate that BDNF in cNTS plays a key role in the modulation of the hyperglycemic reflex initiated by CBR stimulation.