Differential effects of L-trytophan and buspirone on biogenic amine contents and metabolism in Lurcher mice cerebellum

n-Butylidenephthalide exhibits protection against neurotoxicity through regulation of tryptophan 2, 3 dioxygenase in spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 or Machado-Joseph disease (SCA3/MJD) is characterized by the repetition of a CAG codon in the ataxin-3 gene (ATXN3), which leads to the formation of an elongated mutant ATXN3 protein that can neither be denatured nor undergo proteolysis in the normal manner. This abnormal proteolysis leads to the accumulation of cleaved fragments, which have been identified as toxic and further they act as a seed for more aggregate formation, thereby increasing toxicity in neuronal cells. To date, there have been few studies or treatment strategies that have focused on controlling toxic fragment formation. The aim of this study is to develop a potential treatment strategy for addressing the complications of toxic fragment formation and to provide an alternative treatment strategy for SCA3. Our preliminary data on anti-aggregation and toxic fragment formation using an HEK (human embryonic kidney cells) 293T-84Q-eGFP (green fluorescent protein) cell model identified n-butylidenephthalide (n-BP) as a potential drug treatment for SCA3. n-BP decreased toxic fragment formation in both SCA3 cell and animal models. Moreover, results showed that n-BP can improve gait, motor coordination, and activity in SCA3 mice. To comprehend the molecular basis behind the control of toxic fragment formation, we used microarray analysis to identify tryptophan metabolism as a major player in controlling the fate of mutant ATXN3 aggregates. We also demonstrated that n-BP functions by regulating the early part of the kynurenine pathway through the downregulation of tryptophan 2, 3-dioxygenase (TDO2), which decreases the downstream neurotoxic product, quinolinic acid (QA). In addition, through the control of TDO2, n-BP also decreases active calpain levels, an important enzyme involved in the proteolysis of mutant ATXN3, thereby decreasing toxic fragment formation and associated neurotoxicity. Collectively, these findings indicate a correlation between n-BP, TDO2, QA, calpain, and toxic fragment formation. Thus, this study contributes to a better understanding of the molecular interactions involved in SCA3, and provides a novel potential treatment strategy for this neurodegenerative disease.

Attenuating effects of prior oestradiol benzoate priming on 5-HT-mediated lordosis behavior in rats are dose-dependent

The present study was designed to investigate the role of the 5-HT7 receptors in lordosis and compare the lordotic responses with 5-HT1A agent under the influence of different steroid-priming regimens in ovariectomized, non-receptive and receptive rats. 8-OH DPAT, a 5-HT1A agonist and 5-CT, a 5-HT7 agonist inhibited the lordosis differently in non-receptive and receptive rats, however, the response was attenuated in a dose-dependent manner following 5-CT treatment in the first two tests. Treatment with 5-HT1A antagonist, WAY 100 135 caused a protective effect which was evident in the second test only. Priming with 25 microg OB attenuated in the first test in non-receptive rats whereas the same dose repeated a similar pattern in receptive rats. The attenuation of LQ was evident in rats treated with 5-HT7 antagonist, SB 269970-A. This finding shows that WAY 100 135, a 5-HT1A antagonist has potency to attenuate inhibitory influence of 8-OH DPAT by enhancing lordosis behavior acutely in female rats with a low estrous state. Treatment with 5-CT and SB 269970-A as 5-HT7, agonist and antagonist, respectively, have mimicked 5-HT-mediated lordotic response as moderate affinity towards 5-HT1A receptors has been reported. This offers a comparable effect on lordosis as a result of the two 5-HT agents used.

Treatment of spinocerebellar ataxia with buspirone

Preliminary data suggest potential benefit of 5-HT receptor agonists in the treatment of ataxias. We studied the effects of buspirone in a cohort of twenty patients with spinocerebellar ataxia (SCA). Twenty patients were treated in this double-blind, placebo controlled, cross-over trial with either buspirone HCl 30 mg twice daily or placebo for 3 months. Buspirone was not shown to be superior to placebo in the treatment of patients with SCA.

Spontaneous and induced mouse mutations with cerebellar dysfunctions: behavior and neurochemistry

Grid2(Lc) (Lurcher), Grid2(ho) (hot-foot), Rora(sg) (staggerer), nr (nervous), Agtpbp1(pcd) (Purkinje cell degeneration), Reln(rl) (reeler), and Girk2(Wv) (Weaver) are spontaneous mutations with cerebellar atrophy, ataxia, and deficits in motor coordination tasks requiring balance and equilibrium. In addition to these signs, the Dst(dt) (dystonia musculorum) spinocerebellar mutant displays dystonic postures and crawling. More recently, transgenic models with human spinocerebellar ataxia mutations and alterations in calcium homeostasis have been shown to exhibit cerebellar anomalies and motor coordination deficits. We describe neurochemical characteristics of these mutants with respect to regional brain metabolism as well as amino acid and biogenic amine concentrations, uptake sites, and receptors.

Buspirone-induced antinociception is mediated by L-type calcium channels and calcium/caffeine-sensitive pools in mice

RATIONALE

Previous studies have shown that buspirone, a partial 5-HT(1A) receptor agonist, produces antinociceptive effects in rats and mice; Ca(2+) plays a critical role as a second messenger in mediating nociceptive transmission. 5-HT(1A) receptors have been proven to be coupled functionally with various types of Ca(2+) channels in neurons, including N-, P/Q-, T-, or L-type. It was of interest to investigate the involvement of extracellular/intracellular Ca(2+) in buspirone-induced antinociception.

OBJECTIVES

To determine whether central serotonergic pathways participate in the antinociceptive processes of buspirone, and investigate the involvement of Ca(2+) mechanisms, particularly L-voltage-gated Ca(2+) channels and Ca(2+)/caffeine-sensitive pools, in buspirone-induced antinociception.

METHODS

Antinociception was assessed using the hot-plate test (55 degrees C, hind-paw licking latency) in mice treated with either buspirone (1.25-20 mg/kg i.p.) alone or the combination of buspirone and fluoxetine (2.5-10 mg/kg i.p.), 5-HTP (25 mg/kg i.p.), nimodipine (2.5-10 mg/kg i.p.), nifedipine (2.5-10 mg/kg i.p.), CaCl(2) (25-200 nmol per mouse i.c.v.), EGTA (5-30 nmol per mouse i.c.v.), or ryanodine (0.25-2 nmol per mouse i.c.v.).

RESULTS

Buspirone dose dependently increased the licking latency in the hot-plate test in mice. This effect of buspirone was enhanced by fluoxetine, 5-HTP, nimodipine, and nifedipine. Interestingly, central administration of Ca(2+) reversed the antinociceptive effects of buspirone. In contrast to these, ryanodine or EGTA administered centrally potentiated buspirone-induced antinociception.

CONCLUSIONS

Decreasing neuronal Ca(2+) levels potentiated buspirone-induced antinociception; conversely, increasing intracellular Ca(2+) abolished the antinociceptive effects of buspirone. These results suggest that Ca(2+) influx from extracellular fluid and release of Ca(2+) from Ca(2+)/caffeine-sensitive microsomal pools may be involved in buspirone-induced antinociception.

Behavioral and biochemical effects of L-tryptophan and buspirone in a model of cerebellar atrophy

The Lurcher mutant mouse can be considered an adequate model of autosomal dominant spinocerebellar atrophy because of the severe degeneration of its cerebellar cortex and inferior olive. The purpose of this study was to determine whether the motor coordination deficits of Lurcher mutants could be improved after chronic administration of the serotonin (5-hydroxytryptamine; 5-HT) precursor, L-tryptophan, or of the 5-HT(1A) agonist, buspirone. During these treatments, the mice were submitted to behavioral evaluations using the coat hanger and the rotorod tests, as well as an inclined screen and a vertical grid test. At the end of treatments, 5-HT and 5-hydroxindole-3-acetic acid (5-HIAA) were measured in six brain regions. On the coat hanger test, administration of L-tryptophan accelerated movements along the horizontal bar by 44%, while buspirone increased the time spent on the apparatus by 11%. Neither drug had an effect on climbing ability or on the time spent on a rotating beam. Administration of L-tryptophan increased 5-HIAA levels in frontal cortex, neostriatum, thalamus, brainstem, cerebellum and spinal cord, but elevated 5-HT only in neostriatum, brainstem and cerebellum. In contrast, buspirone led to 5-HT increases in cerebellum and augmented 5-HIAA in the spinal cord. The modest test-specific improvements are consistent with some of the clinical data concerning 5-HT pharmacotherapy in patients suffering from cerebellar atrophy.