Francisco Castelán

Cerebellar Bergmann glia: an important model to study neuron–glia interactions

The biochemical effects triggered by the action of glutamate, the main excitatory amino acid, on a specialized type of glia cells, Bergmann glial cells of the cerebellum, are a model system with which to study glia-neuronal interactions. Neuron to Bergmann glia signaling is involved in early stages of development, mainly in cell migration and synaptogenesis. Later, in adulthood, these cells have an important role in the maintenance and proper function of the synapses that they surround. Major molecular targets of this cellular interplay are glial glutamate receptors and transporters, both of which sense synaptic activity. Glutamate receptors trigger a complex network of signaling cascades that involve Ca(2+) influx and lead to a differential gene-expression pattern. In contrast, Bergmann glia glutamate transporters participate in the removal of the neurotransmitter from the synaptic cleft and act also as signal transducers that regulate, in the short term, their own activity. These exciting findings strengthen the concept of active participation of glial cells in synaptic transmission and the involvement of neuron-glia circuits in the processing of brain information.

Temporal coordination of pelvic and perineal striated muscle activity during micturition in female rabbits.

PURPOSE To determine the motor basis of urine expulsion the activity of the pelvic (pubococcygeus) and perineal (bulbospongiosus and ischiocavernosus) muscles was recorded during micturition in anesthetized female rabbits. MATERIAL AND METHODS Virgin female chinchilla rabbits were used for simultaneously recording cystometrograms and electromyograms of the pubococcygeus, ischiocavernosus and bulbospongiosus muscles. The particular contribution of each muscle during micturition was analyzed in another set of experiments in which each was inactivated by bilateral lidocaine injection. Bladder function was assessed using standard urodynamic parameters. RESULTS Cystometrography showed that micturition comprises 2 phases, that is storage and voiding phases. During the latter phase no high frequency oscillations were recorded. On simultaneous electromyography recordings a temporal, coordinated activation of pelvic (pubococcygeus) and perineal (bulbospongiosus and ischiocavernosus) muscles was observed. During specific blockade of each muscle some modifications in urodynamic parameters were found. CONCLUSIONS Our findings indicate a specific role for the pelvic and perineal muscles during feminine micturition.

Glutamate-dependent elongation factor-2 phosphorylation in Bergmann glial cells

Glutamate, the main excitatory amino acid transmitter regulates protein biosynthesis at the transcriptional and translational levels. It is critically involved in the continuous change of the protein repertoire that is inherent to synaptic plasticity. Activity-dependent differential gene expression occurs both in neurons and glial cells. In fact, besides a membrane to nuclei signaling that leads to transcriptional control, a biphasic effect in overall protein synthesis takes place after glutamate receptors stimulation in cultured chick cerebellar Bergmann glia. Therefore, the effect of glutamate receptors activation on translation elongation was characterized. A time- and dose-dependent increase in eukaryotic elongation factor-2 phosphorylation was found. Pharmacological tools established that alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and Kainate, but not N-methyl-d-aspartate trigger this phosphorylation. The removal of external Ca2+ or the pre-treatment with a calmodulin antagonist prevented the glutamate effect. Accordingly, glutamate receptors regulate eukaryotic elongation factor-2 kinase phosphorylation through the involvement of Ca2+/calmodulin/extracellular-regulated protein kinases 1/2. These results demonstrate that glutamate receptors regulate the elongation of peptide chains in glial cells.

Glutamate-dependent phosphorylation of the mammalian target of rapamycin (mTOR) in Bergmann glial cells

Glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, plays an important role in neuronal development and synaptic plasticity. It activates a variety of signaling pathways that regulate gene expression at the transcriptional and translational levels. Within glial cells, besides transcription, glutamate also regulates translation initiation and elongation. The mammalian target of rapamycin (mTOR), a key participant in the translation process, represents an important regulatory locus for translational control. Therefore, in the present communication we sought to characterize the mTOR phosphorylation pattern after glutamate treatment in chick cerebellar Bergmann glia primary cultures. A time- and dose-dependent increase in mTOR Ser 2448 phosphorylation was found. Pharmacological tools established that the glutamate effect is mediated through ionotropic and metabotropic receptors and interestingly, the glutamate transporter system is also involved. The signaling cascade triggered by glutamate includes an increase in intracellular Ca2+ levels, and the activation of the p60(Src)/PI-3K/PKB pathway. These results suggest that glia cells participate in the activity-dependent change in the brain protein repertoire.

Competition in newborn rabbits for thermally advantageous positions in the litter huddle is associated with individual differences in brown fat metabolism

The altricial young of the European rabbit (Oryctolagus cuniculus) are not brooded by the mother, and although they are born into an underground nest, depend importantly on the warmth and insulation provided by littermates for their early growth and survival. Consistent with previous studies, heavier pups occupied more central, thermally advantageous positions in the litter huddle, maintained higher body temperatures, obtained more milk, were more efficient at converting it to body mass, and consequently grew faster than their lighter sibs occupying the periphery of the huddle. In the present study we measured the expression of uncoupling protein 1 (UCP-1), which is essential for the metabolism of brown adipose tissue to generate body heat in response to cold. In nine litters of domestic rabbits maintained for the first four postnatal days at temperatures below their critical thermoneutral temperature, peripheral pups showed greater expression of UCP-1 than intermediate pups, and these greater expression than central pups. This suggests that during early development littermates of the rabbit experience differing degrees of activation of the sympathetic nervous system as a consequence of exposure to different thermal environments associated with different positions in the litter huddle. Whether this is associated with long term differences in the physiological response to cold and perhaps in the manner of responding to other environmental challenges is currently under investigation.

Multiparity causes uncoordinated activity of pelvic- and perineal-striated muscles and urodynamic changes in rabbits.

Temporal and coordinated activation of pelvic- (pubococcygeous) and perineal- (bulbospongiosus and ischiocavernosus) striated muscles occurs during micturition in female rabbits. We have hypothesized that the coordinated activation of pelvic and perineal muscles is modified during the micturition of young multiparous rabbits. Young virgin and multiparous female chinchilla rabbits were used to simultaneously record cystometrograms and electromyograms of the pubococcygeous, ischocavernosus, and bulbospongiosus muscles. Bladder function was assessed using standard urodynamic variables. The temporal coordination of pelvic- and perineal-striated muscle activity was changed in multiparous rabbits. The cystometrogram recordings were different than those obtained from virgin rabbits, as seen in alterations of the threshold volume, the residual volume, the voiding duration, and the maximum pressure. In rabbits, we find that multiparity causes uncoordinated activity of pubococcygeous, ischiocavernosus, and bulbospongiosus muscles and modifies the urodynamics.

Glutamate-Dependent Transcriptional Regulation in Bergmann Glia Cells: Involvement of p38 MAP Kinase

Glutamate (Glu) is the major excitatory neurotransmitter in the Central Nervous System (CNS). Ionotropic and metabotropic glutamate receptors (GluRs) are present in neurons and glial cells and are involved in gene expression regulation. Mitogen-activated proteins kinases (MAPK) are critical for all the membrane to nuclei signaling pathways described so far. In cerebellar Bergmann glial cells, glutamate-dependent transcriptional regulation is partially dependent on p42/44 MAPK activity. Another member of this kinase family, p38 MAPK is activated by non-mitogenic stimuli through its Thr180/Tyr182 phosphorylation and phosphorylates cytoplasmic and nuclear protein targets involved in translational and transcriptional events. Taking into consideration that the role of p38MAPK in glial cells is not well understood, we demonstrate here that glutamate increases p38 MAPK phosphorylation in a time and dose dependent manner in cultured chick cerebellar Bergmann glial cells (BGC). Moreover, p38 MAPK is involved in the glutamate-induced transcriptional activation in these cells. Ionotropic as well as metabotropic glutamate receptors participate in p38 MAPK activation. The present findings demonstrate the involvement of p38 MAPK in glutamate-dependent gene expression regulation in glial cells.

Association between the serum concentration of triiodothyronine with components of metabolic syndrome, cardiovascular risk, and diet in euthyroid post-menopausal women without and with metabolic syndrome

PurposeTo determine the association between the serum concentration of triiodothyronine (T3) with components of metabolic syndrome (MetS), cardiovascular risk (CVR), and diet in euthyroid post-menopausal women without and with MetS.MethodsA cross-sectional study was performed in 120 voluntary women of an indigenous population from Tlaxcala-México. Euthyroid status was assessed measuring the serum concentration of thyrotropin (TSH) and thyroid hormones, while that of estradiol was measured to confirm the postmenopausal condition. MetS was diagnosed using the American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement (AHA/NHLBI) criterion. Estimation of CVR was calculated based on the Framingham scale. Diet components were evaluated based on survey applications. Correlations, logistic regression analyses, ANOVA or Kruskall-Wallis, and chi-square tests were used to determine significant differences (P ≤ 0.05) between women without MetS and women with MetS having different serum concentrations of T3.ResultsTriiodothyronine was positively correlated with insulin but negatively correlated with glucose, high-density lipoprotein cholesterol (HDL-C), and CVR. Compared to women without MetS, women with MetS and low-normal T3 concentration showed a high risk for hyperglycemia and moderate/high risk for CVR. In contrast, a high-normal T3 concentration increased the risk to have a big waist circumference, a high concentration of HDL-C, and insulin resistance. Diet analysis showed a high grade of malnutrition in women from all groups. The intake of calories was positively affected by the T3 concentration, albeit it did not affect the extent of malnutrition.ConclusionsIn contrast to concentrations of TSH, total thyroxin (T4), and free T4, the concentration of serum T3 was strongly correlated with cardio-metabolic variables in euthyroid postmenopausal women. In comparison to women without MetS, a high-normal serum concentration of T3 in women with MetS is positively associated with reduced glycaemia and CVR but negatively related to body mass index (BMI), insulin, insulin resistance, and HDL-C. Although the analyzed population had a nutritional deficiency, both calories and iron intake were positively affected by the T3 concentration. Our results suggest the necessity of health programs monitoring T3 in old people in order to treat hyperglycemia, cardio-metabolic components, and the ageing anorexia.

Effect of multiparity on morphometry and oestrogen receptor expression of pelvic and perineal striated muscles in rabbits: is serum oestradiol relevant?

OBJECTIVE To determine changes in morphometry and expression of oestrogen receptors (OR) in the pubococcygeus and bulbospongiosus muscles, and the concentration of serum oestradiol associated with multiparity. STUDY DESIGN Twelve chinchilla-breed female rabbits were divided into multiparas who had undergone four consecutive deliveries and age-matched virgin nulliparas. Pubococcygeus and bulbospongiosus muscles were surgically removed from each rabbit and processed histologically. Fibre cross-sectional area, number of peripheral nuclei, and expression of ORα and ORβ were measured for each muscle. Serum samples were obtained and the concentration of serum oestradiol was quantified. RESULTS Multiparity increased (p ≤ 0.05) fibre cross-sectional area and the number of peripheral nuclei per fibre in pubococcygeus muscle, but not in bulbospongiosus muscle. Expression of both ORα and ORβ was high (p ≤ 0.05) in both muscles from multiparous rabbits. A rise in serum oestradiol was measured at the end of the second pregnancy, which was absent (p ≤ 0.05) at the end of the fourth pregnancy. The concentration of serum oestradiol was similar (p > 0.05) in nulliparous and multiparous rabbits. CONCLUSIONS Multiparity caused morphometric changes in pubococcygeus muscle but not in bulbospongiosus muscle. As OR expression was high for both muscles, some properties related to fibre composition or muscle physiology could be affected. The finding that serum oestradiol was not elevated at the end of the fourth pregnancy could be related to changes in pelvic and perineal muscles associated with multiparity.

Hypothyroidism affects differentially the cell size of epithelial cells among oviductal regions of rabbits.

Oviductal regions show particular histological characteristics and functions. Tubal pathologies and hypothyroidism are related to primary and secondary infertility. The impact of hypothyroidism on the histological characteristics of oviductal regions has been scarcely studied. Our aim was to analyse the histological characteristics of oviductal regions in control and hypothyroid rabbits. Hypothyroidism was induced by oral administration of methimazole (MMI) for 30 days. For both groups, serum concentrations of thyroid and gonadal hormones were determined. Sections of oviductal regions were stained with the Massons trichrome technique to analyse both epithelial and smooth muscle layers. The percentage of proliferative epithelial cells (anti-Ki67) in diverse oviductal regions was also quantified. Data were compared with Student t-test, Mann-Whitney U-test, or Fischers test. In comparison with the control group, the hypothyroid group showed: (i) a low concentration of T3 and T4, but a high level of TSH; (ii) similar values of serum estradiol, progesterone and testosterone; (iii) a large size of ciliated cells in the ampulla (AMP), isthmus (IST) and utero-tubal junction (UTJ); (iv) a large size of secretory cells in the IST region; (v) a low percentage of proliferative secretory cells in the fimbria-infundibulum (FIM-INF) region; and (vi) a similar thickness of the smooth muscle layer and the cross-sectional area in the AMP and IST regions. Modifications in the size of the oviductal epithelium in hypothyroid rabbits could be related to changes in the cell metabolism that may impact on the reproductive functions achieved by oviduct.