Purinergic Receptors in Neurological Diseases With Motor Symptoms: Targets for Therapy.

Since proving adenosine triphosphate (ATP) functions as a neurotransmitter in neuron/glia interactions, the purinergic system has been more intensely studied within the scope of the central nervous system. In neurological disorders with associated motor symptoms, including Parkinson's disease (PD), motor neuron diseases (MND), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's Disease (HD), restless leg syndrome (RLS), and ataxias, alterations in purinergic receptor expression and activity have been noted, indicating a potential role for this system in disease etiology and progression. In neurodegenerative conditions, neural cell death provokes extensive ATP release and alters calcium signaling through purinergic receptor modulation. Consequently, neuroinflammatory responses, excitotoxicity and apoptosis are directly or indirectly induced. This review analyzes currently available data, which suggests involvement of the purinergic system in neuro-associated motor dysfunctions and underlying mechanisms. Possible targets for pharmacological interventions are also discussed.

Activation of type 1 cannabinoid receptor (CB1R) promotes neurogenesis in murine subventricular zone cell cultures.

The endocannabinoid system has been implicated in the modulation of adult neurogenesis. Here, we describe the effect of type 1 cannabinoid receptor (CB1R) activation on self-renewal, proliferation and neuronal differentiation in mouse neonatal subventricular zone (SVZ) stem/progenitor cell cultures. Expression of CB1R was detected in SVZ-derived immature cells (Nestin-positive), neurons and astrocytes. Stimulation of the CB1R by (R)-(+)-Methanandamide (R-m-AEA) increased self-renewal of SVZ cells, as assessed by counting the number of secondary neurospheres and the number of Sox2+/+ cell pairs, an effect blocked by Notch pathway inhibition. Moreover, R-m-AEA treatment for 48 h, increased proliferation as assessed by BrdU incorporation assay, an effect mediated by activation of MAPK-ERK and AKT pathways. Surprisingly, stimulation of CB1R by R-m-AEA also promoted neuronal differentiation (without affecting glial differentiation), at 7 days, as shown by counting the number of NeuN-positive neurons in the cultures. Moreover, by monitoring intracellular calcium concentrations ([Ca(2+)]i) in single cells following KCl and histamine stimuli, a method that allows the functional evaluation of neuronal differentiation, we observed an increase in neuronal-like cells. This proneurogenic effect was blocked when SVZ cells were co-incubated with R-m-AEA and the CB1R antagonist AM 251, for 7 days, thus indicating that this effect involves CB1R activation. In accordance with an effect on neuronal differentiation and maturation, R-m-AEA also increased neurite growth, as evaluated by quantifying and measuring the number of MAP2-positive processes. Taken together, these results demonstrate that CB1R activation induces proliferation, self-renewal and neuronal differentiation from mouse neonatal SVZ cell cultures.

Galanin promotes neuronal differentiation in murine subventricular zone cell cultures.

Neural stem cells of the subventricular zone (SVZ) represent a potentially important source of surrogate cells for the treatment of brain damage. Proper use of these cells for neuronal replacement depends on the ability to drive neuronal differentiation. Several neuromodulators stimulate neurogenesis. Here we examined the effects of the neuropeptide galanin, on neuronal differentiation in murine SVZ cultures. SVZ neurospheres obtained from early postnatal mice were treated with 10 nM to 2 µM galanin. Galanin promoted neuronal differentiation, increasing numbers of NeuN-, vesicular GABA transporter- and tyrosine hydroxylase-expressing neurons. In contrast, galanin neither affected cell proliferation assessed by BrdU incorporation nor cell death evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). Neuronal differentiation was further confirmed at the functional level by measuring [Ca(2+)]i variations in single SVZ cells after KCl and histamine stimulations to distinguish neurons from immature cells. Galanin treatment increased the numbers of neuronal-like responding cells compared to immature cells. Using selective agonists (M617, AR-M1896) and antagonists (galantide, M871) for galanin receptors 1 and 2, we showed that both galanin receptors mediated neuronal differentiation. Early proneuronal effects of galanin included positive regulation of the transcription factor neurogenin-1 (Ngn1). In addition, galanin promoted axonogenesis and dendritogenesis, increasing both the length of phosphorylated stress-activated protein kinase- and Tau-positive axons and the numbers of microtubule associated protein-2 (MAP-2)-labelled dendrites. Moreover, galanin inhibited SVZ cell migration in the transwell assay. Our results show a proneurogenic effect of galanin and open new perspectives for future applications in stem cell-based therapies for neuronal replacement.

Ampakine CX546 increases proliferation and neuronal differentiation in subventricular zone stem/progenitor cell cultures.

Ampakines are chemical compounds known to modulate the properties of ionotropic α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA)-subtype glutamate receptors. The functional effects attributed to ampakines involve plasticity and the increase in synaptic efficiency of neuronal circuits, a process that may be intimately associated with differentiation of newborn neurons. The subventricular zone (SVZ) is the main neurogenic niche of the brain, containing neural stem cells with brain repair potential. Accordingly, the identification of new pharmaceutical compounds with neurogenesis-enhancing properties is important as a tool to promote neuronal replacement based on the use of SVZ cells. The purpose of the present paper is to examine the possible proneurogenic effects of ampakine CX546 in cell cultures derived from the SVZ of early postnatal mice. We observed that CX546 (50 µm) treatment triggered an increase in proliferation, evaluated by BrdU incorporation assay, in the neuroblast lineage. Moreover, by using a cell viability assay (TUNEL) we found that, in contrast to AMPA, CX546 did not cause cell death. Also, both AMPA and CX546 stimulated neuronal differentiation as evaluated morphologically through neuronal nuclear protein (NeuN) immunocytochemistry and functionally by single-cell calcium imaging. Accordingly, short exposure to CX546 increased axonogenesis, as determined by the number and length of tau-positive axons co-labelled for the phosphorylated form of SAPK/JNK (P-JNK), and dendritogenesis (MAP2-positive neurites). Altogether, this study shows that ampakine CX546 promotes neurogenesis in SVZ cell cultures and thereby may have potential for future stem cell-based therapies.