Thyroid hormone receptor α<Subscript>1</Subscript>–β<Subscript>1</Subscript> expression in epididymal epithelium from euthyroid and hypothyroid rats

The objectives of the present work were to assess whether epithelial cells from the different segments of epididymis express TRα₁–β₁ isoforms, to depict its subcellular immunolocalization and to evaluate changes in their expression in rats experimentally submitted to a hypothyroid state by injection of 131I. In euthyroid and hypothyroid groups, TR protein was expressed in epididymal epithelial cells, mainly in the cytoplasmic compartment while only a few one showed a staining in the nucleus as well. A similar TR immunostaining pattern was detected in the different segments of the epididymis. In hypothyroid rats, the number of TR-immunoreactive epithelial cells as well as the intensity of the cytoplasmic staining significantly increased in all sections analyzed. In consonance to the immunocytochemical analysis, the expression of TRα₁–β₁ isoforms, assessed by Western blot revealed significantly higher levels of TR in cytosol compared to the nuclear fractions. Furthermore, TR expression of both α₁ and β₁ isoforms and their mRNA levels were increased by the hypothyroid state. The immuno-electron-microscopy showed specific reaction for TR in principal cells associated with eucromatin, cytosolic matrix and mitochondria. The differences in expression levels assessed in control and thyroidectomized rats ascertain a specific function of TH on this organ.     

Differential responsiveness of metabotropic glutamate receptors coupled to phosphoinositide hydrolysis to agonists in various brain areas of the adult rat

The effects of metabotropic glutamate receptor (mGluR) agonists on inositol phosphates (IP) accumulation were investigated in slices of the cerebral cortex, hippocampus, striatum and cerebellum of adult Sprague-Dawley rats. EC₅₀ values for 1S, 3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) did not differ significantly between various brain areas (range 10⁻⁵ M), quisqualate was the most potent in all the brain areas (range 10⁻⁷−10⁻⁶ M), except the cerebellum (10⁻⁵ M), ibotenate was the most potent in the striatum (range 10⁻⁶ M) and the least potent in the cerebral cortex and hippocampus (range 10⁻⁴ M). The efficacy in the four brain areas showed the following trend of ranking order for ACPD and quisqualate: hippocampus > striatum > cerebral cortex > cerebellum, and for ibotenate: hippocampus > cerebral cortex > striatum > cerebellum, although the observed differences reached the level of statistical significance only in the case of ACPD (hippocampus and striatum vs cerebellum) and ibotenate (hippocampus vs cerebellum). Co-incubation of the agonists at maximally effective concentrations in any pairwise combination resulted in no substantial additivity of IP accumulation. D,L-1-amino-3-phosphonopropionic acid (AP3) and D,L-2-amino-4-phosphonobutyric acid (AP4) at 0.5 mM concentration antagonized ACPD-induced IP accumulation by about 70 and 45%, respectively, without differences between brain areas. On the other hand, the antagonistic effects ofl-serine-o-phosphate (SOP) at 1 mM concentration were the highest in the hippocampus (75%) and the lowest in the cerebellum (25%). The comparative data indicate considerable regional receptor heterogeneity, in terms of different ratios of response to the agonists (but not antagonists, except SOP). There is a robust responsiveness of mGluRs not only in the hippocampus and cerebral cortex, but also in the striatum which exhibits the highest affinity to both quisqualate and ibotenate.     

β-Adrenergic Receptors Mediate a Stress-Induced Decrease in IGF-II mRNA in the Rat Cerebellum

1. Exposure to a combined forced swimming–confinement stress resulted in a decrease in insulin-like growth factor II (IGF-II) mRNA levels in the whole brain (without the cerebellum) and in the isolated brain areas of the cerebral cortex, the hippocampus, and the cerebellum.2. In an effort to elucidate the neurotransmitter systems involved in this stress-induced decrease, animals were injected prior to exposure to the stress, with either propranolol, diazepam, or MK-801.3. Administration of diazepam or MK-801 did not affect the stress-induced decrease in IGF-II mRNA in any of the three brain areas examined.4. Administration of propranolol prior to the exposure to the stress inhibited the stress-induced decrease in IGF-II mRNA in the cerebellum. Propranolol had no such effect in the cerebral cortex or the hippocampus.5. Our results suggest that in the cerebellum, the stress-induced decrease in IGF-II mRNA is mediated by ₂-adrenergic receptors.     

Regional distribution and relative amounts of glutamate decarboxylase isoforms in rat and mouse brain.

The levels of the two isoforms of glutamate decarboxylase (GAD) were measured in 12 regions of adult rat brain and three regions of mouse brain by sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting with an antiserum that recognizes the identical C-terminal sequence in both isoforms from both species. In rat brain the amount of smaller isoform, GAD65, was greater than that of the larger isoform, GAD67, in all twelve regions. GAD65 ranged from 77-89% of total GAD in frontal cortex, hippocampus, hypothalamus, midbrain, olfactory bulb, periaqueductal gray matter, substantia nigra, striatum, thalamus and the ventral tegmental area. The proportion of GAD65 was lower in amygdala and cerebellum but still greater than half of the total. There was a strong correlation between total GAD protein and GAD activity. In the three mouse brain regions analysed (cerebellum, cerebral cortex and hippocampus) the proportion of GAD65 (35,47, and 51% of total GAD) was significantly lower than in the corresponding rat-brain regions. The amount of GAD67 was greater than the amount of GAD65 in mouse cerebellum and was approximately equal to the amount of GAD65 in mouse cerebral cortex and hippocampus.     

CYCLIC AMP-DEPENDENT PROTEIN KINASE ACTIVITY AND SYNAPTOSOMAL PROTEIN PHOSPHORYLATION IN THE BRAINS OF AGED RATS

The activity of soluble protein kinase and phosphorylation of endogenous synaptosomal proteins were studied in vitro, in the hippocampus and cerebral cortex of rats 3, 12, or 24 months of age. No between-age differences in the activity of cyclic AMP-dependent or independent protein kinase were detected in either brain region. The degree of stimulation by cyclic AMP and the apparent K_a, for cyclic AMP were similar at all stages. Cyclic AMP stimulated the phosphorylation of synaptosomal proteins from the cerebral cortex, hippocampus, caudate nucleus, and cerebellum of rats at all ages. There were no significant differences across age in the extent of phosphorylation of any membrane proteins in any brain region. The number and staining density of synaptosornal proteins separated by polyacrylamide gel electrophoresis were also similar at all ages. These studies indicate that the cyclic AMP-dependent phosphorylation system in the rat brain does not change during advanced aging.     

Tau Isoforms Expression in Transgenic Mouse Model of Amyotrophic Lateral Sclerosis

Tau is a protein involved in regulation of microtubule stability, axonal differentiation and transport. Alteration of retrograde transport may lead to motor neuron degeneration. Thus alternative mRNA splicing and expression of tau isoforms were studied in a transgenic mouse model harboring the human SOD1 G93A mutation. The studies were performed on cortex, hippocampus and spinal cord of 64- and 120-day-old animals (presymptomatic and symptomatic stage) and wild type controls. Exon 10 was found in all studied tissues. The 2N isoform containing exons 2 and 3 (+2+3) and the 1N (+2−3) predominated over the 0N (−2−3) in brain regions of the studied mice. The 2N expression was significantly lower in cortex and hippocampus of symptomatic animals compared to analogue control tissues. The decrease in 2N expression resulted in lower levels of total tau mRNA and tau protein. No changes in tau expression were observed in spinal cord of studied animals.     

Thyroid hormone receptor α1 is a critical regulator for the expression of ion channels during final differentiation of outer hair cells

Cochlear outer hair cells (OHCs) terminally differentiate prior to the onset of hearing. During this time period, thyroid hormone (TH) dramatically influences inner ear development. It has been shown recently that TH enhances the expression of the motor protein prestin via liganded TH receptor β (TRβ) while in contrast the expression of the potassium channel KCNQ4 is repressed by unliganded TRα1. These different mechanisms of TH regulation by TRα1 or TRβ prompted us to analyse other ion channels that are required for the final differentiation of OHCs. We analysed the onset of expression of the Ca²⁺ channel Ca_V1.3, and the K⁺ channels SK2 and BK and correlated the results with the regulation via TRα1 or TRβ. The data support the hypothesis that proteins expressed in rodents prior to or briefly after birth like Ca_V1.3 and prestin are either independent of TH (e.g. Ca_V1.3) or enhanced through TRβ (e.g. prestin). In contrast, proteins expressed in rodents later than P6 like KCNQ4 (∼P6), SK2 (∼P9) and BK (∼P11) are repressed through TRα1. We hypothesise that the precise regulation of expression of the latter genes requires a critical local TH level to overcome the TRα1 repression. Harald Winter and Claudia Braig contributed equally to this work.     

Differential Regulation of GABAA Receptor Gene Expression by Ethanol in the Rat Hippocampus Versus Cerebral Cortex

Abstract: Previous research has shown that chronic ethanol consumption dramatically alters GABA_A receptor α₁ and α₄ subunit gene expression in the cerebral cortex and GABA_A receptor α₁ and α₆ subunit gene expression in the cerebellum. However, it is not yet known if chronic ethanol consumption produces similar alterations in GABA_A receptor gene expression in other brain regions. One brain region of interest is the hippocampus because it has recently been shown that a subset of GABA_A receptors in the hippocampus is responsive to pharmacologically relevant concentrations of ethanol. Therefore, we directly compared the effects of chronic ethanol consumption on GABA_A receptor subunit gene expression in the hippocampus and cerebral cortex. Furthermore, we investigated whether the duration of ethanol consumption (14 or 40 days) would influence regulation of GABA_A receptor gene expression in these two brain regions. Chronic ethanol consumption produced a significant increase in the level of GABA_A receptor α₄ subunit peptide in the hippocampus following 40 days but not 14 days. The relative expression of hippocampal GABA_A receptor α₁, α₂, α₃, α_2/3, or γ₂ was not altered by either period of chronic ethanol exposure. In marked contrast, chronic ethanol consumption for 40 days significantly increased the relative expression of cerebral cortical GABA_A receptor α₄ subunits and significantly decreased the relative expression of cerebral cortical GABA_A receptor α₁ subunits. This finding is consistent with previous results following 14 days of chronic ethanol consumption. Hence, chronic ethanol consumption alters GABA_A receptor gene expression in the hippocampus but in a different manner from that in either the cerebral cortex or the cerebellum. Furthermore, these alterations are dependent on the duration of ethanol exposure.     

ATP citrate lyase in cholinergic nerve endings

The activity of ATP-citrate lyase in homogenates of five selected rat brain regions varied from 2.93 to 6.90 nmol/min/mg of protein in the following order: cerebellum < hippocampus < parietal cortex < striatum < medulla oblongata and that of the choline acetyltransferase from 0.15 to 2.08 nmol/min/mg of protein in cerebellum < parietal cortex < hippocampus=medulla oblongata < striatum. No substantial differences were found in regional activities of lactate dehydrogenase, pyruvate dehydrogenase, citrate synthase or acetyl-CoA synthase. High values of relative specific activities for both choline acetyltransferase and ATP-citrate lyase were found in synaptosomal and synaptoplasmic fractions from regions with a high content of cholinergic nerve endings. There are significant correlations between these two enzyme activities in general cytocol (S₃), synaptosomal (B) and synaptoplasmic (B_s) fractions from the different regions (r=0.92–0.99). These data indicate that activity of ATP-citrate lyase in cholinergic neurons is several times higher than that present in glial and noncholinergic neuronal cells.     

Developmental changes in regulation of the Na+, K+-ATPase α3 isoform by thyroid hormone in ferret heart

Ferret heart expresses the α1- as well as the α3-isoform of the Na⁺, K⁺-ATPase. We have shown previously that the α3 isoform is differentially upregulated during postnatal cardiac development and that in adult ferrets expression of α3 is not responsive to regulation by thyroid hormone (TH). Since developmental-stage dependent effects of TH have been reported previously, the present study examined whether effects of TH on expression of the Na⁺, K⁺-ATPase isoforms in ferret heart is modulated during development and possible mechanisms were examined. Ferrets of different age groups were treated with TH and the relative abundance of Na⁺, K⁺-ATPase isoforms in ferret myocardium was determined by immunoblotting. Thyroid hormone (T3; 50 μg/100 g body weight on 3 alternating days, s.c.) increased protein levels of the α3 isoform, but not that of α1 or β1, in myocardium of 5-day-old and 3-week-old ferrets. By contrast, in myocardium of 6- and 8-week-old ferrets T3 failed to increase protein levels of α1 and α3. To determine whether elevated plasma levels of TH during development plays a role in the transition, mature ferrets were first made hypothyroid before TH treatment. In these hypothyroid ferrets expression of the α3 isoform remained unresponsive to TH (T4, 0.5 mg/kg for 7 days, s.c.). The transition from TH-responsive to TH-unresponsive appears to be isoform-specific because in skeletal muscle of 8-week-old ferrets and in hypothyroid ferrets the α2 isoform is upregulated by TH. Finally, there appears to be functional thyroid hormone receptors throughout development because in each age group TH effectively induced expression of α-MHC in the myocardium. In conclusion, these findings demonstrate that expression of α3 isoform in the myocardium of newborn ferret is responsive to TH; however, the responsiveness terminates between 3- and 6-weeks of age. Neither elevated endogenous TH level nor a lack of functional thyroid hormone receptor appears to be responsible for the transition from TH-responsive to TH-unresponsive.     

Effect of perinatal thyroid hormone deficiency on expression of rat hippocampal conventional protein kinase C isozymes

Thyroid hormone (TH) is essential for the proper development of mammalian central nervous system. TH deficiency during critical period of brain development results in permanent cognitive and neurological impairments. Hippocampus is a structure involved in various memory processes that are essential for creating new memories, and lesions to hippocampus result in impaired learning and memory. Protein kinase C (PKC) isoforms play an important role in many types of learning and memory, and deletion of specific PKC genes results in deficits in learning. In the present study, we used real-time PCR and Western blot to investigate the conventional PKC expression in developing rat hippocampus with different thyroid status, trying to establish a correlation between TH deficiency and conventional PKC expression in developing rat hippocampus. We found that PKCβI and PKCγ expression decreased significantly both in mRNA and protein levels in hypothyroid group compared with the normal controls, and thyroxine replacement could restore it. As for PKCα, we did not find any difference between different thyroid status. Though the expression of PKCβII also decreased in the TH deficiency group, the change was not significant. Taken together, our data indicate TH deficiency can cause hippocampal PKCβ1 and PKCγ downregulation during rat brain development. Since there are other PKC isoforms in the rat brain, whether these change is related to impaired learning and memory of perinatal hypothyroid rats requires further researches.     

Changes in Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Activity and Alpha 3 Subunit Expression in CNS After Administration of Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase Inhibitors

The expression of Na⁺, K⁺-ATPase α3 subunit and synaptosomal membrane Na⁺, K⁺-ATPase activity were analyzed after administration of ouabain and endobain E, respectively commercial and endogenous Na⁺, K⁺-ATPase inhibitors. Wistar rats received intracerebroventricularly ouabain or endobain E dissolved in saline solution or Tris–HCl, respectively or the vehicles (controls). Two days later, animals were decapitated, cerebral cortex and hippocampus removed and crude and synaptosomal membrane fractions were isolated. Western blot analysis showed that Na⁺, K⁺-ATPase α3 subunit expression increased roughly 40% after administration of 10 or 100 nmoles ouabain in cerebral cortex but remained unaltered in hippocampus. After administration of 10 μl endobain E (1 μl = 28 mg tissue) Na⁺, K⁺-ATPase α3 subunit enhanced 130% in cerebral cortex and 103% in hippocampus. The activity of Na⁺, K⁺-ATPase in cortical synaptosomal membranes diminished or increased after administration of ouabain or endobain E, respectively. It is concluded that Na⁺, K⁺-ATPase inhibitors modify differentially the expression of Na⁺, K⁺-ATPase α3 subunit and enzyme activity, most likely involving compensatory mechanisms.     

Developmental expression of P<Subscript>5</Subscript> ATPase mRNA in the mouse

P₅ ATPases (ATP13A1 through ATP13A5) are found in all eukaryotes. They are currently poorly characterized and have unknown substrate specificity. Recent evidence has linked two P₅ ATPases to diseases of the nervous system, suggesting possible importance of these proteins within the nervous system. In this study we determined the relative expression of mouse P5 ATPases in development using quantitative real time PCR. We have shown that ATP13A1 and ATP13A2 were both expressed similarly during development, with the highest expression levels at the peak of neurogenesis. ATP13A3 was expressed highly during organogenesis with one of its isoforms playing a more predominant role during the period of neuronal development. ATP13A5 was expressed most highly in the adult mouse brain. We also assessed the expression of these genes in various regions of the adult mouse brain. ATP13A1 to ATP13A4 were expressed differentially in the cerebral cortex, hippocampus, brainstem and cerebellum while levels of ATP13A5 were fairly constant between these brain regions. Moreover, we demonstrated expression of the ATP13A4 protein in the corresponding brain regions using immunohistochemistry. In summary, this study furthers our knowledge of P₅-type ATPases and their potentially important role in the nervous system.     

Brain Region–Specific Alterations in the Gene Expression of Cytokines,Immune Cell Markers and Cholinergic System Components during Peripheral Endotoxin–Induced Inflammation

Inflammatory conditions characterized by excessive peripheral immune responses are associated with diverse alterations in brain function, and brain-derived neural pathways regulate peripheral inflammation. Important aspects of this bidirectional peripheral immune–brain communication, including the impact of peripheral inflammation on brain region–specific cytokine responses, and brain cholinergic signaling (which plays a role in controlling peripheral cytokine levels), remain unclear. To provide insight, we studied gene expression of cytokines, immune cell markers and brain cholinergic system components in the cortex, cerebellum, brainstem, hippocampus, hypothalamus, striatum and thalamus in mice after an intraperitoneal lipopolysaccharide injection. Endotoxemia was accompanied by elevated serum levels of interleukin (IL)-1β, IL-6 and other cytokines and brain region–specific increases in Il1b (the highest increase, relative to basal level, was in cortex; the lowest increase was in cerebellum) and Il6 (highest increase in cerebellum; lowest increase in striatum) mRNA expression. Gene expression of brain Gfap (astrocyte marker) was also differentially increased. However, Iba1 (microglia marker) mRNA expression was decreased in the cortex, hippocampus and other brain regions in parallel with morphological changes, indicating microglia activation. Brain choline acetyltransferase (Chat ) mRNA expression was decreased in the striatum, acetylcholinesterase (Ache) mRNA expression was decreased in the cortex and increased in the hippocampus, and M1 muscarinic acetylcholine receptor (Chrm1) mRNA expression was decreased in the cortex and the brainstem. These results reveal a previously unrecognized regional specificity in brain immunoregulatory and cholinergic system gene expression in the context of peripheral inflammation and are of interest for designing future antiinflammatory approaches.     

At Least Three Neurotransmitter Systems Mediate a Stress-Induced Increase in c-fos mRNA in Different Rat Brain Areas

1. Protooncogene c-fos mRNA levels were determined in the rat cerebral cortex, hippocampus, and cerebellum after exposure to a combined forced swimming and confinement stress. The stress resulted in an increase in c-fos mRNA levels in all three brain areas.2. In an effort to elucidate the neurotransmitter systems involved in this stress-induced increase, animals were injected, prior to exposure to the stress, with either diazepam, MK-801, or propranolol.3. In both the cerebral cortex and the hippocampus the stress-induced increase in c-fos mRNA was inhibited by MK-801, suggesting that it is mediated via NMDA receptors. In the hippocampus, propranolol had a similar effect, indicating that -adrenergic receptors are also involved in the stress-induced increase in c-fos mRNA.4. On the other hand, the increase in c-fos mRNA produced by the stress of the injection was inhibited in the cerebral cortex by diazepam or propranolol and in the hippocampus only by diazepam. Furthermore, administration of MK-801 resulted in an increase in c-fos mRNA in the hippocampus of the nonstressed animals. In the cerebellum no one of the three drugs employed affected c-fos mRNA levels in either stressed or nonstressed animals.5. Our results thus show that various forms of stress activate, in different brain areas, neurons with either NMDA, -adrenergic, and/or GABA-A receptors.     

Taurine in the developing cat: Uptake and release in different brain areas

Taurine is an important modulator of neuronal activity in the immature brain. In kittens, taurine deficiency causes serious dysfunction in the cerebellar and cerebral visual cortex. The processes of taurine transport in vitro were now studied for the first time in different brain areas in developing and adult cats. The uptake of taurine consisted initially of two saturable components, high- and low-affinity, in synaptosomal preparations from the developing cerebral cortex and cerebellum, but the high-affinity uptake component completely disappeared during maturation. The release of both endogenous and preloaded labeled taurine from brain slices measured in a superfusion system was severalfold stimulated with a slow onset by depolarizing K⁺ (50 mM) concentrations. K⁺ stimulation released markedly more taurine from the cerebral cortex, cerebellum and brain stem in kittens than in adult cats. The responses were largest in the cerebellum. Both uptake and release of taurine are thus highly efficient in the brain of kittens and may be of significance in view of the vulnerability of cats to taurine deficiency.     

Influence of intermittent hypoxia and pyrimidinic nucleosides on cerebral enzymatic activities related to energy transduction

The effect of intermittent normobaric hypoxia and of biological pyrimidines (uridine and cytidine) on the specific activities of some enzymes related to cerebral energy metabolism were studied. Measurement were carried out on the following: (a) homogenate in toto; (b) purified mitochondrial fraction; (c) crude synaptosomal fraction, in different areas of rat brain: cerebral cortex, hippocampus, corpus striatum, hypothalamus, cerebellum, and medulla oblongata. Intermittent normobaric hypoxia (12 hours daily for 5 days) caused modifications of the enzyme activities in the homogenate in toto (decrease of hexokinase in cerebellum; increase of pyruvate kinase in medulla oblongata), in the purified mitochondrial fraction (increase of succinate dehydrogenase in the corpus striatum) and in the crude synaptosomal fraction (decrease of cytochrome oxidase activity in cerebral cortex, hippocampus, and cerebellum; decrease of malate dehydrogenase in hippocampus and cerebellum; decrease of lactate dehydrogenase in cerebellum). Daily treatment with cytidine or uridine altered some enzyme activities either affected or unaffected by intermittent hypoxia.