Dysregulation of epithelial ion transport and neurochemical changes in the colon of a parkinsonian primate.

The pathological changes underlying gastrointestinal (GI) dysfunction in Parkinson's disease (PD) are poorly understood and the symptoms remain inadequately treated. In this study we compared the functional and neurochemical changes in the enteric nervous system in the colon of adult, L-DOPA-responsive, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmoset, with naïve controls. Measurement of mucosal vectorial ion transport, spontaneous longitudinal smooth muscle activity and immunohistochemical assessment of intrinsic innervation were each performed in discrete colonic regions of naïve and MPTP-treated marmosets. The basal short circuit current (Isc) was lower in MPTP-treated colonic mucosa while mucosal resistance was unchanged. There was no difference in basal cholinergic tone, however, there was an increased excitatory cholinergic response in MPTP-treated tissues when NOS was blocked with L-Nω-nitroarginine. The amplitude and frequency of spontaneous contractions in longitudinal smooth muscle as well as carbachol-evoked post-junctional contractile responses were unaltered, despite a decrease in choline acetyltransferase and an increase in the vasoactive intestinal polypeptide neuron numbers per ganglion in the proximal colon. There was a low-level inflammation in the proximal but not the distal colon accompanied by a change in α-synuclein immunoreactivity. This study suggests that MPTP treatment produces long-term alterations in colonic mucosal function associated with amplified muscarinic mucosal activity but decreased cholinergic innervation in myenteric plexi and increased nitrergic enteric neurotransmission. This suggests that long-term changes in either central or peripheral dopaminergic neurotransmission may lead to adaptive changes in colonic function resulting in alterations in ion transport across mucosal epithelia that may result in GI dysfunction in PD.

The selective 5-HT1A receptor agonist, NLX-112, exerts anti-dyskinetic and anti-parkinsonian-like effects in MPTP-treated marmosets.

l-DOPA is the gold-standard pharmacotherapy for treatment of Parkinson's disease (PD) but can lead to the appearance of troubling dyskinesia which are attributable to 'false neurotransmitter' release of dopamine by serotonergic neurons. Reducing the activity of these neurons diminishes l-DOPA-induced dyskinesia (LID), but there are currently no clinically approved selective, high efficacy 5-HT1A receptor agonists. Here we describe the effects of NLX-112, a highly selective and efficacious 5-HT1A receptor agonist, on LID in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated marmosets, a non-human primate model of PD. NLX-112 exhibited modest plasma half-life (~2h) and marked plasma protein binding (96%). When administered to parkinsonian marmosets with l-DOPA (7 mg/kg p.o.), NLX-112 (0.025, 0.1 and 0.4 mg/kg p.o.) reduced LID scores at early time-points after administration, whilst only minimally interfering with the l-DOPA-induced reversal of motor disability. In contrast, the prototypical 5-HT1A receptor agonist, (+)8-OH-DPAT (0.6 and 2 mg/kg p. o.), reduced LID but also abolished l-DOPA's anti-disability activity. Administered by itself, NLX-112 (0.1, 0.2 mg/kg p.o.) produced very little dyskinesia or locomotor activity, but reduced motor disability scores by about half the extent elicited by l-DOPA, suggesting that it may have motor facilitation effects of its own. Both NLX-112 and (+)8-OH-DPAT induced unusual and dose-limiting behaviors in marmoset that resembled 'serotonin behavioral syndrome' observed previously in rat. Overall, the present study showed that NLX-112 has anti-LID activity at the doses tested as well as reducing motor disability. The data suggest that additional investigation of NLX-112 is desirable to explore its potential as a treatment for PD and PD-LID.

Subacute administration of both methcathinone and manganese causes basal ganglia damage in mice resembling that in methcathinone abusers.

An irreversible extrapyramidal syndrome occurs in man after intravenous abuse of "homemade" methcathinone (ephedrone, Mcat) that is contaminated with manganese (Mn) and is accompanied by altered basal ganglia function. Both Mcat and Mn can cause alterations in nigrostriatal function but it remains unknown whether the effects of the 'homemade' drug seen in man are due to Mcat or to Mn or to a combination of both. To determine how toxicity occurs, we have investigated the effects of 4-week intraperitoneal administration of Mn (30 mg/kg t.i.d) and Mcat (100 mg/kg t.i.d.) given alone, on the nigrostriatal function in male C57BL6 mice. The effects were compared to those of the 'homemade' mixture which contained about 7 mg/kg of Mn and 100 mg/kg of Mcat. Motor function, nigral dopaminergic cell number and markers of pre- and postsynaptic dopaminergic neuronal integrity including SPECT analysis were assessed. All three treatments had similar effects on motor behavior and neuronal markers. All decreased motor activity and induced tyrosine hydroxylase positive cell loss in the substantia nigra. All reduced 123I-epidepride binding to D2 receptors in the striatum. Vesicular monoamine transporter 2 (VMAT2) binding was not altered by any drug treatment. However, Mcat treatment alone decreased levels of the dopamine transporter (DAT) and Mn alone reduced GAD immunoreactivity in the striatum. These data suggest that both Mcat and Mn alone could contribute to the neuronal damage caused by the 'homemade' mixture but that both produce additional changes that contribute to the extrapyramidal syndrome seen in man.

Contractile dysfunction and nitrergic dysregulation in small intestine of a primate model of Parkinson's disease.

Bowel dysfunction is a common non-motor symptom in Parkinson's disease (PD). The main contractile neurotransmitter in the GI tract is acetylcholine (ACh), while nitric oxide (NO) causes the relaxation of smooth muscle in addition to modulating ACh release. The aim of this study was to characterise functional and neurochemical changes in the isolated ileum of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated marmoset, an established model of PD motor dysfunction. While NO-synthase inhibitor L-NAME concentration dependently augmented the neurogenically-evoked contractions and inhibited the relaxations in normal tissues, it had no effects on the MPTP ileum. Immunohistochemical analyses of the myenteric plexus showed that ChAT-immunoreactivity (-ir) was significantly reduced and the density of the enteric glial cells as shown by SOX-10-ir was increased. However, no change in TH-, 5-HT-, VIP- or nNOS-ir was observed in the MPTP tissues. The enhancement of the neurogenically-evoked contractions and the inhibition of the relaxation phase by L-NAME in the control tissues is in line with NO's direct relaxing effect on smooth muscle and its indirect inhibitory effect on ACh release. The absence of the relaxation and the inefficacy of L-NAME in the MPTP tissues suggests that central dopaminergic loss dopamine may eventually lead to the impairment of NO signal coupling that affects bowel function, and this may be the result of a complex dysregulation at the level of the neuroeffector junction.

Altered detrusor contractility in MPTP-treated common marmosets with bladder hyperreflexia.

Bladder hyperreflexia is a common non-motor feature of Parkinson's disease. We now report on the contractility of the isolated primate detrusor strips devoid of nerve input and show that following MPTP, the amplitude and frequency of spontaneous contraction was increased. These responses were unaffected by dopamine D1 and D2 receptor agonists A77636 and ropinirole respectively. Contractions by exogenous carbachol, histamine or ATP were similar and no differences in the magnitude of noradrenaline-induced relaxation were seen in detrusor strip obtained from normal and MPTP-treated common marmosets (Callithrix jacchus). However, the neurogenic contractions following electrical field stimulation of the intrinsic nerves (EFS) were markedly greater in strips obtained from MPTP treated animals. EFS evoked non-cholinergic contractions following atropine were also greater but the contribution of the cholinergic innervation as a proportion of the overall contraction was smaller in the detrusor strips of MPTP treated animals, suggesting a preferential enhancement of the non-cholinergic transmission. Although dopaminergic mechanism has been proposed to underlie bladder hyperreflexia in MPTP-treated animals with intact bladder, the present data indicates that the increased neurogenically mediated contractions where no extrinsic innervation exists might be due to long-term adaptive changes locally as a result of the loss of the nigrostriatal output.

Differential toxicity of 6-hydroxydopamine in SH-SY5Y human neuroblastoma cells and rat brain mitochondria: protective role of catalase and superoxide dismutase.

Oxidative stress and mitochondrial dysfunction are two pathophysiological factors often associated with the neurodegenerative process involved in Parkinson's disease (PD). Although, 6-hydroxydopamine (6-OHDA) is able to cause dopaminergic neurodegeneration in experimental models of PD by an oxidative stress-mediated process, the underlying molecular mechanism remains unclear. It has been established that some antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) are often altered in PD, which suggests a potential role of these enzymes in the onset and/or development of this multifactorial syndrome. In this study we have used high-resolution respirometry to evaluate the effect of 6-OHDA on mitochondrial respiration of isolated rat brain mitochondria and the lactate dehydrogenase cytotoxicity assay to assess the percentage of cell death induced by 6-OHDA in human neuroblastoma cell line SH-SY5Y. Our results show that 6-OHDA affects mitochondrial respiration by causing a reduction in both respiratory control ratio (IC(50) = 200 ± 15 nM) and state 3 respiration (IC(50) = 192 ± 17 nM), with no significant effects on state 4(o). An inhibition in the activity of both complex I and V was also observed. 6-OHDA also caused cellular death in human neuroblastoma SH-SY5Y cells (IC(50) = 100 ± 9 µM). Both SOD and CAT have been shown to protect against the toxic effects caused by 6-OHDA on mitochondrial respiration. However, whereas SOD protects against 6-OHDA-induced cellular death, CAT enhances its cytotoxicity. The here reported data suggest that both superoxide anion and hydroperoxyl radical could account for 6-OHDA toxicity. Furthermore, factors reducing the rate of 6-OHDA autoxidation to its p-quinone appear to enhance its cytotoxicity.

Reproducible nigral cell loss after systemic proteasomal inhibitor administration to rats.

Systemic administration of proteasomal inhibitors to rats has been proposed as producing progressive nigral dopaminergic cell loss and impairment of motor function, although this has proved difficult to reproduce. We report reproducible loss of tyrosine hydroxylase-positive cells in substantia nigra and decrease in locomotor activity by proteasomal inhibitor injection in rats up to 10 months after treatment. Dopaminergic cell death was accompanied by the appearance of ubiquitin and alpha-synuclein-positive inclusions in the substantia nigra in these rats. Neuronal loss was also observed in the locus ceruleus, raphe nuclei, and dorsal motor nucleus of the vagus, verifying that proteasomal inhibition produces a relevant model of Parkinson's disease.