The role of dopamine in regulation of thyrotropin-releasing hormone in the striatum and nucleus accumbens of the rat

Striatal Nurr1, but not FosB expression links a levodopa-induced dyskinesia phenotype to genotype in Fisher 344 vs. Lewis hemiparkinsonian rats

Numerous genes, and alterations in their expression, have been identified as risk factors for developing levodopa-induced dyskinesia (LID). However, our understanding of the complexities of molecular changes remains insufficient for development of clinical treatment. In the current study we used gene array, in situ hybridization, immunohistochemistry, and microdialysis to provide a unique compare and contrast assessment of the relationship of four candidate genes to LID, employing three genetically distinct rat strains (Sprague-Dawley (SD), Fischer-344 (F344) and Lewis-RT.1) showing differences in dyskinesia susceptibility and 'first-ever LID' versus 'chronic LID' expression in subjects displaying equal dyskinesia severity. In these studies, rat strains were easily distinguishable for their LID propensity with: 1) a majority of SD rats expressing LID (LID+) and a subset being resistant (LID-); 2) all F344 rats readily developing (LID+); and 3) all Lewis rats being LID-resistant (LID-). Following chronic levodopa, LID+ SD rats showed significant increases in candidate gene expression: Nr4a2/(Nurr1) > > Trh > Inhba = Fosb. However, SD rats with long-standing striatal dopamine (DA) depletion treated with first-ever versus chronic high-dose levodopa revealed that despite identical levels of LID severity: 1) Fosb and Nurr1 transcripts but not protein were elevated with acute LID expression; 2) FOSB/ΔFOSB and NURR1 proteins were elevated only with chronic LID; and 3) Trh transcript and protein were elevated only with chronic LID. Strikingly, despite similar levodopa-induced striatal DA release in both LID-expressing F344 and LID-resistant Lewis rats, Fosb, Trh, Inhba transcripts were significantly elevated in both strains; however, Nurr1 mRNA was significantly increased only in LID+ F344 rats. These findings suggest a need to reevaluate currently accepted genotype-to-phenotype relationships in the expression of LID, specifically that of Fosb, a transcription factor generally assumed to play a causal role, and Nurr1, a transcription factor that has received significant attention in PD research linked to its critical role in the survival and function of midbrain DA neurons but who's striatal expression, generally below levels of detection, has remained largely unexplored as a regulator of LID. Finally these studies introduce a novel 'model' (inbred F344 vs inbred Lewis) that may provide a powerful tool for investigating the role for 'dyskinesia-resistance' genes downstream of 'dyskinesia-susceptibility' genes in modulating LID expression, a concept that has received considerably less attention and offers a new ways of thinking about antidyskinetic therapies.

Adult-onset hypothyroidism increases ethanol consumption

RATIONALE

Only in Europe it can be estimated that more than 20 million of people would be affected by hypothyroidism in some moment of their life. Given that ethanol consumption is so frequent, it would be reasonable to ask what the consequences of ethanol consumption in those individuals affected by hypothyroidism are.

OBJECTIVES

To study the interaction between hypothyroidism and ethanol consumption.

METHODS

We study ethanol consumption in a rat model of methyl-mercaptoimidazole-induced-adult-onset hypothyroidism and thyroid T4/T3 hormone supplementation. Also, we studied the effects of ethanol on motor activity, memory, and anxiety.

RESULTS

We found that hypothyroidism increased the voluntary ethanol consumption and that this was enhanced by thyroid hormone supplementation. Hypothyroidism was associated with motor hyperactivity which was prevented either by T4/T3 supplementation or ethanol. The relationship between hypothyroidism, ethanol, and anxiety was more complex. In an anxiogenic context, hypothyroidism and T4/T3 supplementation would increase immobility, an anxiety-like behavior, while in a less anxiogenic context would decrease rearing, a behavior related to anxiety. Regarding memory, acute ethanol administration did not alter episodic-like memory in hypothyroid rats. Gene expression of enzymes involved in the metabolism of ethanol, i.e., Adh1 and Aldh2, were altered by hypothyroidism and T4/T3 supplementation.

CONCLUSIONS

Our results suggest that hypothyroid patients would need personalized attention in terms of ethanol consumption. In addition, they point that it would be useful to embrace the thyroid axis in the study of ethanol addiction, including as a possible therapeutic target for the treatment of alcoholism and its comorbid disorders.

TRH Analog, Taltirelin Improves Motor Function of Hemi-PD Rats Without Inducing Dyskinesia via Sustained Dopamine Stimulating Effect

Thyrotropin-releasing hormone (TRH) and its analogs are able to stimulate the release of the endogenic dopamine (DA) in the central nervous system. However, this effect has not been tested in the Parkinson’s disease (PD), which is characterized by the DA deficiency due to the dopaminergic neurons loss in the substantia nigra. Here, we investigated the therapeutic effect of Taltirelin, a long-acting TRH analog on 6-hydroxydopamine-lesioned hemi-Parkinsonian rat model. 1–10 mg/kg Taltirelin i.p. administration significantly improved the locomotor function and halted the electrophysiological abnormities of PD animals without inducing dyskinesia even with high-dose for 7 days treatment. Microdialysis showed that Taltirelin gently and persistently promoted DA release in the cortex and striatum, while L-DOPA induced a sharp rise of DA especially in the cortex. The DA-releasing effect of Taltirelin was alleviated by reserpine, vanoxerine (GBR12909) or AMPT, indicating a mechanism involving vesicular monoamine transporter-2 (VMAT-2), dopamine transporter (DAT) and tyrosine hydroxylase (TH). The in vivo and in vitro experiments further supported that Taltirelin affected the regulation of TH expression in striatal neurons, which was mediated by p-ERK1/2. Together, this study demonstrated that Taltirelin improved motor function of hemi-PD rats without inducing dyskinesia, thus supporting a further exploration of Taltirelin for PD treatment.

Relationship between the thyroid axis and alcohol craving

AIMS

A few studies have suggested a relationship between thyroid hormones and alcohol dependence (AD) such as a blunted increase of thyroid stimulating hormone (TSH) in response to thyrotropin-releasing hormone (TRH), lower levels of circulating free triiodothyronine (fT3) and free thyroxine (fT4) levels and down regulation of the TRH receptors. The current study aimed to explore the relationship between the hormones of the thyroid axis and alcohol-seeking behaviors in a sample of alcohol-dependent patients.

METHODS

Forty-two treatment-seeking alcohol-dependent individuals enrolled in a 12-week treatment study were considered. The Timeline Follow Back (TLFB) was used to assess the number of drinks consumed during the 12-week period. Blood levels of thyroid hormones (TSH, fT3 and fT4) were measured prior to and at the end of treatment. Questionnaires were administered to evaluate craving for alcohol [Penn Alcohol Craving Scale (PACS) and the Obsessive Compulsive Drinking Scale (OCDS) and its two subscales ODS for obsessions and CDS for compulsions] as well as anxiety [State and Trait Inventory (STAI)], depression [the Zung Self-Rating Depression Scale (Zung)] and aggression [the Aggressive Questionnaire (AQ)].

RESULTS

At baseline, we found significant positive correlations between fT3 and OCDS (r = 0.358, P = 0.029) and CDS (r = 0.405, P = 0.013) and negative correlations between TSH levels and STAI (r = -0.342, P = 0.031), and AQ (r = -0.35, P = 0.027). At the end of the 12-week study period, abstinent patients had a greater change in TSH than those who relapsed (-0.4 vs. -0.25, F(1,24) = 5.4, P = 0.029).

CONCLUSION

If confirmed in larger samples, these findings could suggest that the thyroid axis might represent a biomarker of alcohol craving and drinking.

Levodopa-induced dyskinesia is associated with increased thyrotropin releasing hormone in the dorsal striatum of hemi-parkinsonian rats

Background

Dyskinesias associated with involuntary movements and painful muscle contractions are a common and severe complication of standard levodopa (L-DOPA, L-3,4-dihydroxyphenylalanine) therapy for Parkinson's disease. Pathologic neuroplasticity leading to hyper-responsive dopamine receptor signaling in the sensorimotor striatum is thought to underlie this currently untreatable condition.

Methodology/Principal Findings

Quantitative real-time polymerase chain reaction (PCR) was employed to evaluate the molecular changes associated with L-DOPA-induced dyskinesias in Parkinson's disease. With this technique, we determined that thyrotropin releasing hormone (TRH) was greatly increased in the dopamine-depleted striatum of hemi-parkinsonian rats that developed abnormal movements in response to L-DOPA therapy, relative to the levels measured in the contralateral non-dopamine-depleted striatum, and in the striatum of non-dyskinetic control rats. ProTRH immunostaining suggested that TRH peptide levels were almost absent in the dopamine-depleted striatum of control rats that did not develop dyskinesias, but in the dyskinetic rats, proTRH immunostaining was dramatically up-regulated in the striatum, particularly in the sensorimotor striatum. This up-regulation of TRH peptide affected striatal medium spiny neurons of both the direct and indirect pathways, as well as neurons in striosomes.

Conclusions/Significance

TRH is not known to be a key striatal neuromodulator, but intrastriatal injection of TRH in experimental animals can induce abnormal movements, apparently through increasing dopamine release. Our finding of a dramatic and selective up-regulation of TRH expression in the sensorimotor striatum of dyskinetic rat models suggests a TRH-mediated regulatory mechanism that may underlie the pathologic neuroplasticity driving dopamine hyper-responsivity in Parkinson's disease.

Effects of pentylenetetrazole-induced kindling on thyrotropin-releasing hormone biosynthesis and receptors in rat brain

It has been postulated that changes in thyrotropin-releasing hormone biosynthesis may be involved in the mechanism of kindling--an animal model of epileptogenesis. To test this hypothesis, a time-course study was carried out to investigate the effects of pentylenetetrazole kindling (40 mg/kg i.p., daily for eight days) on the expression of gene coding for preprothyrotropin-releasing hormone, the thyrotropin-releasing hormone tissue level and thyrotropin-releasing hormone receptor parameters in rat brain. As shown by an in situ hybridization study, a single, convulsant dose of pentylenetetrazole (70 mg/kg i.p.) increased the preprothyrotropin-releasing hormone messenger RNA level in the dentate gyrus of the hippocampal formation and piriform cortex after 3 h and, to a greater extent, after 24 h. Those changes were accompanied with increases in the thyrotropin-releasing hormone level in the striatum, hippocampus, amygdala and piriform cortex. Seven days after single pentylenetetrazole administration, the thyrotropin-releasing hormone level was still significantly elevated in the piriform cortex and striatum. Acute pentylenetetrazole decreased the density (Bmax) of thyrotropin-releasing hormone receptors in the striatum after 3 and 24 h, and increased that density in the piriform cortex and amygdala after 24 h and seven days, respectively. The thyrotropin-releasing hormone receptor affinity (Kd) was decreased in the striatum and increased in the amygdala after only 3 h. Kindled rats showed a moderate increase in the preprothyrotropin-releasing hormone messenger RNA content in the dentate gyrus of the hippocampal formation and piriform cortex after 3 and 24 h; however, a significant decrease in those parameters was found after 14 days. After 3 and 24 h, pentylenetetrazole kindling also elevated the thyrotropin-releasing hormone content in the hippocampus, piriform cortex, and striatum (in the latter structure after 24 h only), whereas in the septum the thyrotropin-releasing hormone level was decreased. After seven days, the thyrotropin-releasing hormone level was still elevated in the hippocampus and piriform cortex of kindled rats, but after 14 days it was significantly lowered in the hippocampus. The kindled rats also showed a significant decrease in the density (Bmax) of thyrotropin-releasing hormone receptors in the striatum (after 24 h, seven and 14 days), and an increase in the piriform cortex (after seven days). The thyrotropin-releasing hormone receptor affinity (Kd) value was increased in the hippocampus after seven and 14 days, and in the piriform cortex after seven days. These results indicate that pentylenetetrazole kindling induces long-lasting alterations in the thyrotropin-releasing hormone biosynthesis and thyrotropin-releasing hormone receptor affinity in discrete regions of rat brain. These region-specific changes, in particular down-regulation of the thyrotropin-releasing hormone biosynthesis in the hippocampus, may be involved in chronic neuronal hyperexcitability associated with kindling.

Inhibition by amphetamine of testosterone secretion through a mechanism involving an increase of cyclic AMP production in rat testes

1. The effect of amphetamine on the secretion of testosterone and the production of testicular adenosine 3':5'-cyclic monophosphate (cyclic AMP) in rats was studied. 2. A single intravenous injection of amphetamine decreased the basal and human chorionic gonadotropin (hCG)-stimulated levels of plasma testosterone. Plasma LH levels were not altered by the injection of amphetamine. 3. Administration of amphetamine in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone. 4. Amphetamine enhanced the basal and hCG-increased levels of cyclic AMP accumulation in vitro in rat testes. 5. These results suggest that amphetamine inhibits the spontaneous and hCG-stimulated secretion of testosterone from the testes through a mechanism involving an increase in cyclic AMP production.

The effects of repeated amphetamine administration on the thyrotropin-releasing hormone level. Its release and receptors in the rat brain

The effects of single and repeated administration of amphetamine (5 mg/kg, i.p., twice a day for 14 days) on the thyrotropin-releasing hormone (TRH) level, release and receptors in the rat striatum and nucleus accumbens were evaluated. Both treatments decreased the TRH level in those structures at 2 h after the drug injection. These effects were accompanied with elevation of the basal release of TRH from the nucleus accumbens and striatal slices at the same time point, whereas the stimulated (K+, 56 mM) TRH release was attenuated following repeated amphetamine administration. Acute amphetamine had no effect on the density and affinity of TRH receptors. Repeated amphetamine increased the Bmax of TRH receptors in the striatum (by ca 49%) and nucleus accumbens (by ca 38%) at 2 h after the last drug injection. At 72 h after the last amphetamine administration, the Bmax of the TRH receptor in the striatum was still elevated (by ca 42%), whereas in the nucleus accumbens it returned to control level. No changes in the affinity of TRH receptors following repeated amphetamine were found. The obtained results indicate that repeated amphetamine evokes long- and short-term up-regulation of TRH receptors in the rat striatum and nucleus accumbens, respectively. Furthermore, it is suggested that these changes may be an adaptive response to the amphetamine-induced alterations in the TRH tissue level and release.

The role of dopamine receptors in the release of thyrotropin-releasing hormone from the rat striatum and nucleus accumbens: an in vitro study

In the present study we examined the influence of dopamine (DA) stimulants: amphetamine (an agent releasing DA), apomorphine (a non-selective agonist of DA receptors), quinpirole (a selective agonist of D2 receptors) and SKF-38393 (a selective agonist of D1 receptors) on the in vitro release of thyrotropin-releasing hormone (TRH) from the rat striatal slices and nucleus accumbens fragments. It was shown that amphetamine, apomorphine and quinpirole (all those drugs added in concentrations of 10(-8)-10(-5) M), concentration-dependently increased the release of TRH, a more potent effect being observed in striatal slices. On the other hand, SKF-38393 (10(-6)-10(-5) M) was ineffective. Furthermore, the increases in the TRH release from the striatal slices, induced by 10(-5) M of amphetamine, apomorphine or quinpirole, were completely blocked by the selective D2 receptor antagonist sulpiride (10(-5) M), but not by the selective D1 receptors antagonist SCH-23390 (10(-5) M). These results indicate that stimulation of D2 receptors is responsible for the TRH release from the striatum and nucleus accumbens in vitro, and that this effect may be involved in the decrease in the peptide content in the striatum following DA stimulants, observed earlier in in vivo studies.

Detection of thyrotrophin releasing hormone in rat brain in vivo using novel antibody microprobes: effects of amphetamine

Antibody microprobes of novel design were used to monitor thyrotrophin releasing hormone (TRH) in rat brain before and after-parenteral administration of amphetamine. Specific antibodies to TRH were bound to the outside of glass microprobes by adsorption to a surface of activated charcoal embedded in epoxylite resin. In male Wistar rats anaesthetised with chloral hydrate a series of antibody microprobes were implanted in forebrain. Amphetamine (10 mg/kg i.p.) caused a highly significant decrease in the binding of 125I-TRH to microprobes, indicating an increase in extracellular TRH localised in the lateral septum. There was also evidence of TRH release in the septo-hypothalamic nucleus. Neither saline, nor amphetamine at 2 mg/kg were able to evoke changes in the release of TRH at any sites.