Taltirelin improves motor ataxia independently of monoamine levels in rolling mouse nagoya, a model of spinocerebellar atrophy

Quantification of Solid Embryonic Cerebellar Graft Volume in a Degenerative Ataxia Model

Substitution of lost neurons by neurotransplantation would be a possible management of advanced degenerative cerebellar ataxias in which insufficient cerebellar reserve remains. In this study, we examined the volume and structure of solid embryonic cerebellar grafts in adult Lurcher mice, a model of olivocerebellar degeneration, and their healthy littermates. Grafts taken from enhanced green fluorescent protein (EGFP)-positive embryos were injected into the cerebellum of host mice. Two or six months later, the brains were examined histologically. The grafts were identified according to the EGFP fluorescence in frozen sections and their volumes were estimated using the Cavalieri principle. For gross histological evaluation, graft-containing slices were processed using Nissl and hematoxylin-eosin staining. Adjustment of the volume estimation approach suggested that it is reasonable to use all sections without sampling, but that calculation of values for up to 20% of lost section using linear interpolation does not constitute substantial error. Mean graft volume was smaller in Lurchers than in healthy mice when examined 6 months after the transplantation. We observed almost no signs of graft destruction. In some cases, compact grafts disorganized the structure of the host's cerebellar cortex. In Lurchers, the grafts had a limited contact with the host's cerebellum. Also, graft size was of greater variability in Lurchers than in healthy mice. The results are in compliance with our previous findings that Lurcher phenotype-associated factors have a negative effect on graft development. These factors can hypothetically include cerebellar morphology, local tissue milieu, or systemic factors such as immune system abnormalities.

Consensus Paper: Strengths and Weaknesses of Animal Models of Spinocerebellar Ataxias and Their Clinical Implications

Spinocerebellar ataxias (SCAs) represent a large group of hereditary degenerative diseases of the nervous system, in particular the cerebellum, and other systems that manifest with a variety of progressive motor, cognitive, and behavioral deficits with the leading symptom of cerebellar ataxia. SCAs often lead to severe impairments of the patient's functioning, quality of life, and life expectancy. For SCAs, there are no proven effective pharmacotherapies that improve the symptoms or substantially delay disease progress, i.e., disease-modifying therapies. To study SCA pathogenesis and potential therapies, animal models have been widely used and are an essential part of pre-clinical research. They mainly include mice, but also other vertebrates and invertebrates. Each animal model has its strengths and weaknesses arising from model animal species, type of genetic manipulation, and similarity to human diseases. The types of murine and non-murine models of SCAs, their contribution to the investigation of SCA pathogenesis, pathological phenotype, and therapeutic approaches including their advantages and disadvantages are reviewed in this paper. There is a consensus among the panel of experts that (1) animal models represent valuable tools to improve our understanding of SCAs and discover and assess novel therapies for this group of neurological disorders characterized by diverse mechanisms and differential degenerative progressions, (2) thorough phenotypic assessment of individual animal models is required for studies addressing therapeutic approaches, (3) comparative studies are needed to bring pre-clinical research closer to clinical trials, and (4) mouse models complement cellular and invertebrate models which remain limited in terms of clinical translation for complex neurological disorders such as SCAs.

The Thyrotropin-Releasing Hormone-Degrading Ectoenzyme, a Therapeutic Target?

Thyrotropin releasing hormone (TRH: Glp-His-Pro-NH2) is a peptide mainly produced by brain neurons. In mammals, hypophysiotropic TRH neurons of the paraventricular nucleus of the hypothalamus integrate metabolic information and drive the secretion of thyrotropin from the anterior pituitary, and thus the activity of the thyroid axis. Other hypothalamic or extrahypothalamic TRH neurons have less understood functions although pharmacological studies have shown that TRH has multiple central effects, such as promoting arousal, anorexia and anxiolysis, as well as controlling gastric, cardiac and respiratory autonomic functions. Two G-protein-coupled TRH receptors (TRH-R1 and TRH-R2) transduce TRH effects in some mammals although humans lack TRH-R2. TRH effects are of short duration, in part because the peptide is hydrolyzed in blood and extracellular space by a M1 family metallopeptidase, the TRH-degrading ectoenzyme (TRH-DE), also called pyroglutamyl peptidase II. TRH-DE is enriched in various brain regions but is also expressed in peripheral tissues including the anterior pituitary and the liver, which secretes a soluble form into blood. Among the M1 metallopeptidases, TRH-DE is the only member with a very narrow specificity; its best characterized biological substrate is TRH, making it a target for the specific manipulation of TRH activity. Two other substrates of TRH-DE, Glp-Phe-Pro-NH2 and Glp-Tyr-Pro-NH2, are also present in many tissues. Analogs of TRH resistant to hydrolysis by TRH-DE have prolonged central efficiency. Structure-activity studies allowed the identification of residues critical for activity and specificity. Research with specific inhibitors has confirmed that TRH-DE controls TRH actions. TRH-DE expression by β2-tanycytes of the median eminence of the hypothalamus allows the control of TRH flux into the hypothalamus-pituitary portal vessels and may regulate serum thyrotropin secretion. In this review we describe the critical evidences that suggest that modification of TRH-DE activity in tanycytes, and/or in other brain regions, may generate beneficial consequences in some central and metabolic disorders and identify potential drawbacks and missing information needed to test these hypotheses.

Contribution of Thyrotropin-Releasing Hormone to Cerebellar Long-Term Depression and Motor Learning

Thyrotropin-releasing hormone (TRH) regulates various physiological activities through activation of receptors expressed in a broad range of cells in the central nervous system. The cerebellum expresses TRH receptors in granule cells and molecular layer interneurons. However, the function of TRH in the cerebellum remains to be clarified. Here, using TRH knockout (KO) mice we studied the role of TRH in the cerebellum. Immunohistochemistry showed no gross morphological differences between KO mice and wild-type (WT) littermates in the cerebellum. In the rotarod test, the initial performance of KO mice was comparable to that of WT littermates, but the learning speed of KO mice was significantly lower than that of WT littermates, suggesting impaired motor learning. The motor learning deficit in KO mice was rescued by intraperitoneal injection of TRH. Electrophysiology revealed absence of long-term depression (LTD) at parallel fiber-Purkinje cell synapses in KO mice, which was rescued by bath-application of TRH. TRH was shown to increase cyclic guanosine monophosphate (cGMP) content in the cerebellum. Since nitric oxide (NO) stimulates cGMP synthesis in the cerebellum, we examined whether NO-cGMP pathway was involved in TRH-mediated LTD rescue in KO mice. Pharmacological blockade of NO synthase and subsequent cGMP production prevented TRH-induced LTD expression in KO mice, whereas increase in cGMP signal in Purkinje cells by 8-bromoguanosine cyclic 3’,5’-monophosphate, a membrane-permeable cGMP analog, restored LTD without TRH application. These results suggest that TRH is involved in cerebellar LTD presumably by upregulating the basal cGMP level in Purkinje cells, and, consequently, in motor learning.

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.

Thyrotropin-releasing hormone (TRH) in the cerebellum

Thyrotropin-releasing hormone (TRH) was originally isolated from the hypothalamus. Besides controlling the secretion of TSH from the anterior pituitary, this tripeptide is widely distributed in the central nervous system and regarded as a neurotransmitter or modulator of neuronal activities in extrahypothalamic regions, including the cerebellum. TRH has an important role in the regulation of energy homeostasis, feeding behavior, thermogenesis, and autonomic regulation. TRH controls energy homeostasis mainly through its hypophysiotropic actions to regulate circulating thyroid hormone levels. Recent investigations have revealed that TRH production is regulated directly at the transcriptional level by leptin, one of the adipocytokines that plays a critical role in feeding and energy expenditure. The improvement of ataxic gait is one of the important pharmacological properties of TRH. In the cerebellum, cyclic GMP has been shown to be involved in the effects of TRH. TRH knockout mice show characteristic phenotypes of tertiary hypothyroidism, but no morphological changes in their cerebellum. Further analysis of TRH-deficient mice revealed that the expression of PFTAIRE protein kinase1 (PFTK1), a cdc2-related kinase, in the cerebellum was induced by TRH through the NO-cGMP pathway. The antiataxic effect of TRH and TRH analogs has been investigated in rolling mouse Nagoya (RMN) or 3-acetylpyridine treated rats, which are regarded as a model of human cerebellar degenerative disease. TRH and TRH analogs are promising clinical therapeutic agents for inducing arousal effects, amelioration of mental depression, and improvement of cerebellar ataxia.

The ataxic Cacna1a-mutant mouse rolling nagoya: an overview of neuromorphological and electrophysiological findings

Homozygous rolling Nagoya natural mutant mice display a severe ataxic gait and frequently roll over to their side or back. The causative mutation resides in the Cacna1a gene, encoding the pore-forming α₁ subunit of Ca_v2.1 type voltage-gated Ca²⁺ channels. These channels are crucially involved in neuronal Ca²⁺ signaling and in neurotransmitter release at many central synapses and, in the periphery, at the neuromuscular junction. We here review the behavioral, histological, biochemical, and neurophysiological studies on this mouse mutant and discuss its usefulness as a model of human neurological diseases associated with Ca_v2.1 dysfunction.

Emotional behavior in heterozygous rolling mouse Nagoya Ca v 2.1 channel mutant mice

Although rolling mouse Nagoya, a Ca(v)2.1α(1) mutant, exhibits ataxia and elevated serotonin concentrations, heterozygous mice have not been examined in detail. Patients with heterozygous mutations in this orthologous gene exhibit neurological disorders. To examine the emotional behavior of heterozygous mice, we used behavioral tasks and examined Ca(v)2.1α(1) message levels, tryptophan hydroxylase expression patterns, and monoamine concentrations in 2- and 22-month-old mice. Reduced anxiety in the elevated plus maze, light-dark exploration, and marble-burying behavioral tests and reduced depression in the forced swimming and tail suspension tests were observed in 22-month-old heterozygous mice compared to aged-matched wild-type mice. The levels of mutant-type Ca(v)2.1α(1) message, phosphorylation of tryptophan hydroxylase, and serotonin increased in the brainstems of 22-month-old heterozygous mice. No difference was observed between 2-month-old heterozygous and wild-type mice in these analyses. These findings suggest that heterozygous mice show age-related emotional changes due to alterations in the serotonin system associated with mutant-type Ca(v)2.1α(1), and that heterozygous mice may represent a novel model to delineate the interaction between Ca(v)2.1 function and synaptic transmission.

Spinal cord dopamine receptor expression and function in mice with 6-OHDA lesion of the A11 nucleus and dietary iron deprivation

It is suggested that dysfunction of the diencephalospinal dopaminergic (DAergic) pathway may cause restless legs syndrome. We examined the mRNA and protein levels as well as DA receptor subtypes function within the lumbar spinal cord of an RLS animal model. C57BL/6 male mice with or without iron deprivation were lesioned with 6-hydroxydopamine (6-OHDA) in the bilateral A11 nuclei. Locomotor behaviors were observed. DA concentration, mRNA, and protein levels of D1, D2, and D3 receptors in the lumbar spinal cords were analyzed, and the specific binding of D1, D2, and D3 receptors was determined using [(3)H]SCH23390, [(3)H]Spiperone, and [(3)H]PD128907 radioligands respectively. The behavioral tests showed that the locomotor activities were increased significantly in the mice treated with iron-deficiency (ID) diet and 6-OHDA lesions, which were reversed by the D2/D3 agonist ropinirole. DA in the spinal cord was decreased significantly by 6-OHDA lesioning in A11. D2/D3 mRNA and protein levels as well as their binding capacity in the spinal cord were decreased significantly by 6-OHDA lesions. ID with 6-OHDA lesions produced a synergistic greater decrease of D2 binding. Although ID increased D1 mRNA and protein expression in the spinal cord, it did not significantly change D1 receptor binding. The present study suggests that ID and 6-OHDA lesions in A11 nuclei differentially altered the D1, D2, and D3 receptors expression and binding capacity in the lumbar spinal cord of RLS animal model, which was accompanied by changes in locomotor activities.