Kinin B1 receptor deficiency protects mice fed by cafeteria diet from abnormal glucose homeostasis.

The kallikrein-kinin system has been implicated in body weight and glucose homeostasis. Their major effectors act by binding to the kinin B2 and B1 receptors. It was assessed the role of the kinin B1 receptor in weight and glucose homeostasis in B1 receptor knockout mice (B1RKO) subjected to a cafeteria diet (CAF). Wild-type (WT) and B1RKO male mice (C57BL/6 background; 8 weeks old) were fed a standard diet (SD) or CAF for 14 weeks, ad libitum, and four groups were formed: WT-SD; B1RKO-SD; WT-CAF; B1RKO-CAF. Body weight and food intake were assessed weekly. It was performed glucose tolerance (GTT) and insulin tolerance tests (ITT), and HOMA-IR, HOMA-ß and HOMA-ß* 1/HOMA-IR were calculated. Islets from WT and B1RKO were isolated in order to measure the insulin secretion. Western blot was used to assess the hepatic AKT phosphorylation and qPCR to assess gene expression. CAF induced a higher body mass gain in B1RKO compared to WT mice. CAF diet increased epididymal fat depot mass, hepatic fat infiltration and hepatic AKT phosphorylation in both genotypes. However, B1RKO mice presented lower glycemic response during GTT when fed with CAF, and a lower glucose decrease in the ITT. This higher resistance was overcomed with higher insulin secretion when stimulated by high glucose, resulting in higher glucose uptake in the GTT when submitted to CAF, despite lower insulin sensitivity. Islets from B1RKO delivered 4 times more insulin in 3-month-old mice than islets from WT. The higher insulin disposition index and high insulin delivery of B1RKO can explain the decreased glucose excursion during GTT. In conclusion, CAF increased the ß-cell function in B1RKO mice, compensated by the diet-induced insulin resistance and resulting in a healthier glycemic response despite the higher weight gain.

Sex-specific effects of dehydroepiandrosterone (DHEA) on glucose metabolism in the CNS.

DHEA is a neuroactive steroid, due to its modulatory actions on the central nervous system (CNS). DHEA is able to regulate neurogenesis, neurotransmitter receptors and neuronal excitability, function, survival and metabolism. The levels of DHEA decrease gradually with advancing age, and this decline has been associated with age related neuronal dysfunction and degeneration, suggesting a neuroprotective effect of endogenous DHEA. There are significant sex differences in the pathophysiology, epidemiology and clinical manifestations of many neurological diseases. The aim of this study was to determine whether DHEA can alter glucose metabolism in different structures of the CNS from male and female rats, and if this effect is sex-specific. The results showed that DHEA decreased glucose uptake in some structures (cerebral cortex and olfactory bulb) in males, but did not affect glucose uptake in females. When compared, glucose uptake in males was higher than females. DHEA enhanced the glucose oxidation in both males (cerebral cortex, olfactory bulb, hippocampus and hypothalamus) and females (cerebral cortex and olfactory bulb), in a sex-dependent manner. In males, DHEA did not affect synthesis of glycogen, however, glycogen content was increased in the cerebral cortex and olfactory bulb. DHEA modulates glucose metabolism in a tissue-, dose- and sex-dependent manner to increase glucose oxidation, which could explain the previously described neuroprotective role of this hormone in some neurodegenerative diseases.

Dehydroepiandrosterone protects male and female hippocampal neurons and neuroblastoma cells from glucose deprivation.

Dehydroepiandrosterone (DHEA) modulates neurogenesis, neuronal function, neuronal survival and metabolism, enhancing mitochondrial oxidative capacity. Glucose deprivation and hypometabolism have been implicated in the mechanisms that mediate neuronal damage in neurological disorders, and some studies have shown that these mechanisms are sexually dimorphic. It was also demonstrated that DHEA is able to attenuate the hypometabolism that is related to some neurodegenerative diseases, eliciting neuroprotective effects in different experimental models of neurodegeneration. The aim of this study was to evaluate the effect of DHEA on the viability of male and female hippocampal neurons and SH-SY5Y neuroblastoma cells exposed to glucose deprivation. It was observed that after 12h of pre-treatment, DHEA was able to protect SH-SY5Y cells from glucose deprivation for 6h (DHEA 10(-12), 10(-8) and 10(-6)M) and 8h (DHEA 10(-8)M). In contrast, DHEA was not neuroprotective against glucose deprivation for 12 or 24h. DHEA (10(-8)M) also protected SH-SY5Y cells when added together or even 1h after the beginning of glucose deprivation (6h). Furthermore, DHEA (10(-8)M) also protected primary neurons from both sexes against glucose deprivation. In summary, our findings indicate that DHEA is neuroprotective against glucose deprivation in human neuroblastoma cells and in male and female mouse hippocampal neurons. These results suggest that DHEA could be a promising candidate to be used in clinical studies aiming to reduce neuronal damage in people from both sexes.

Effect of low doses of progesterone in the expression of the GABA(A) receptor α4 subunit and procaspase-3 in the hypothalamus of female rats.

Progesterone is a steroid which regulates neural function, thereby modulating neurotransmission, cell survival, and behavior. Previous studies by our group have shown that chronic administration of low doses of progesterone in diestrus II female rats has an antidepressant-like effect in the forced swimming test (FST). Depression is associated with the several neurotransmitters systems, including GABA and serotonin, and with neurodegeneration and cell death in some brain circuits. The aim of this study was to verify the effect of progesterone on the protein expression of the GABA(A) receptor α4 subunit, serotonin transporter (SERT), Akt, extracellular signal-regulated kinase (Erk), and caspase-3 in the hypothalamus of diestrus II female rats exposed to the FST. Female rats were treated with a daily injection of progesterone (0.4 mg/kg) or vehicle, during two complete oestrous cycles. On the day of the experiment, the animals were euthanized 30 min after the FST, the hypothalamus was dissected and protein expression of GABA(A) receptor α4 subunit, SERT, Akt, Erk, and caspase-3 was evaluated. Progesterone increased the expression of GABA(A) receptor α4 subunit but did not change the expression of SERT. Progesterone decreased the expression of procaspase-3 in the hypothalamus without changing the activation of Akt and Erk in this structure. In summary, our results suggest that progesterone acts to increase the expression of the GABA(A) receptor α4 subunit and decrease the expression of procaspase-3 in the hypothalamus of female rats. Such effects may be involved in the antidepressant-like effect of progesterone in female rats exposed to the FST.

Effect of progesterone on the expression of GABA(A) receptor subunits in the prefrontal cortex of rats: implications of sex differences and brain hemisphere.

Progesterone is a neuroactive hormone with non-genomic effects on GABA(A) receptors (GABA(A)R). Changes in the expression of GABA(A)R subunits are related to depressive-like behaviors in rats. Moreover, sex differences and depressive behaviors have been associated with prefrontal brain asymmetry in rodents and humans. Thus, our objective was to investigate the effect of progesterone on the GABA(A)R α1 and γ2 subunits mRNA expression in the right and left prefrontal cortex of diestrus female and male rats exposed to the forced swimming test (FST). Male and female rats (n = 8/group) were randomly selected to receive a daily dose of progesterone (0·4 mg·kg⁻¹) or vehicle, during two complete female estrous cycles (8-10 days). On the experiment day, male rats or diestrus female rats were euthanized 30 min after the FST. Our results showed that progesterone significantly increased the α1 subunit mRNA in both hemispheres of male and female rats. Moreover, there was an inverse correlation between depressive-like behaviors and GABA(A)R α1 subunit mRNA expression in the right hemisphere in female rats. Progesterone decreased the GABA(A)R γ2 mRNA expression only in the left hemisphere of male rats. Therefore, we conclude that the GABA(A) system displays an asymmetric distribution according to sex and that progesterone, at lower doses, presents an antidepressant effect after increasing the GABA(A) R α1 subunit expression in the right prefrontal cortex of female rats.

Increase in reactive oxygen species and activation of Akt signaling pathway in neuropathic pain.

Neuropathic pain occurs as a result of peripheral or central nervous system injury. Its pathophysiology involves mainly a central sensitization mechanism that may be correlated to many molecules acting in regions involved in pain processing, such as the spinal cord. It has been demonstrated that reactive oxygen species (ROS) and signaling molecules, such as the serine/threonine protein kinase Akt, are involved in neuropathic pain mechanisms. Thus, the aim of this study was to provide evidence of this relationship. Sciatic nerve transection (SNT) was used to induce neuropathic pain in rats. Western blot analysis of Akt and 4-hydroxy-2-nonenal (HNE)-Michael adducts, and measurement of hydrogen peroxide (H(2)O(2)) in the lumbosacral spinal cord were performed. The main findings were found seven days after SNT, when there was an increase in HNE-Michael adducts formation, total and p-Akt expression, and H(2)O(2) concentration. However, one and 15 days after SNT, H(2)O(2) concentration was raised in both sham (animals that were submitted to surgery without nerve injury) and SNT groups, showing the high sensibility of this ROS to nociceptive afferent stimuli, not only to neuropathic pain. p-Akt also increased in sham and SNT groups one day post injury, but at 3 and 7 days the increase occurred exclusively in SNT animals. Thus, there is crosstalk between intracellular signaling pathways and ROS, and these molecules can act as protective agents in acute pain situations or play a role in the development of chronic pain states.

Dendritic spines in the posterodorsal medial amygdala after restraint stress and ageing in rats.

Several evidences suggest that the posterodorsal medial amygdala (MePD) can be a relevant part of the rat neural circuitry for the regulation of hypothalamic neuroendocrine secretion and for ontogenetically different behavioral displays. The dendritic spine density of Golgi-impregnated neurons from the MePD was evaluated in young rats following acute or chronic restraint stress and in aged animals (24 months old). Compared to the control group, a single 1 h restraint stress session promoted a decreased spine density (p<0.01) whereas a single 6 h restraint stress session or daily 6-h restraint sessions for 28 consecutive days did not lead to the same effect (p>0.05). Aged rats showed no difference in this dendritic spine parameter when compared to young adults (p>0.05). These results indicate that short-term stress (1 h) can affect MePD dendritic spines and that neural plasticity is involved with adaptive responses onwards in restrained rats. On the other hand, brain structural modifications related with ageing appear not to influence the number of certain postsynaptic sites in the MePD of rats.

Neuropathic pain modifies antioxidant activity in rat spinal cord.

Oxidative stress is an important pathophysiological mechanism of many neurological diseases. Reactive oxygen and nitrogen species have been cited as molecules involved in the nociceptive process. In this study, rats were submitted to sciatic nerve transection (SNT) for induction of neuropathic pain, and enzyme activities of SOD and catalase as well as lipid peroxidation (LPO) were measured in the lumbosacral spinal cord. The results show that LPO was not changed after SNT. SOD activity was reduced 7 days after SNT, while the change in catalase activity occurred on the third and seventh days in both sham and SNT animals. Hyperalgesia in SNT group was detected at the same points in time. These results suggest that SNT was not a strong enough stimulus to deplete all antioxidant content in the spinal cord, since increase in LPO was not detected. However, the role of oxidative stress in nociception can not be excluded.