Augusta Pisanu

Rosiglitazone decreases peroxisome proliferator receptor-gamma levels in microglia and inhibits TNF-alpha production: new evidences on neuroprotection in a progressive Parkinson's disease model

Thiazolidinedione (TZD) class of peroxisome proliferator receptor gamma (PPAR-γ) agonists display neuroprotective effects in experimental Parkinsons disease (PD) models. Neurons and microglia express PPAR-γ, therefore both of them are potential targets for neuroprotection, although the role of each cell type is not clear. Moreover, receptor-dependent as well as receptor-independent mechanisms have been involved. This study further investigated mechanisms of TZD-mediated neuroprotection in PD. We investigated the rosiglitazone effect in the progressive MPTP/probenecid (MPTPp) model of PD. C57BL/6J mice received MPTP (25 mg/kg) plus probenecid (100 mg/kg) twice per week for 5 weeks. Rosiglitazone (10 mg/kg) was given daily until sacrifice, starting on the fourth week of MPTPp treatment, in presence of an ongoing neurodegeneration with microgliosis. Changes in PPAR-γ levels were measured by immunofluorescence and confocal microscopy in tyrosine hydroxylase (TH)-positive neurons and CD11b-positive microglia of the substantia nigra pars compacta (SNc). Chronic MPTPp treatment induced a PPAR-γ overexpression in both TH-positive neurons and microglia (139.9% and 121.7% over vehicle, respectively). Rosiglitazone administration to MPTPp-treated mice, reverted PPAR-γ overexpression in microglia without affecting TH-positive neurons. Thereafter, changes in CD11b and tumor necrosis factor α (TNF-α) immunoreactivity in microglia were evaluated in the SNc. MPTPp progressively increased CD11b immunoreactivity, conferring to microglia a highly activated morphology. Moreover, TNF-α levels were increased (457.38% over vehicle) after MPTPp. Rosiglitazone administration counteracted the increase in CD11b immunoreactivity caused by MPTPp. Moreover, rosiglitazone reverted TNF-α expression to control levels. Nigrostriatal degeneration was assessed by high pressure liquid chromatography (HPLC) measurement of striatal dopamine, and counting of TH-positive neurons in the SNc. MPTPp treatment caused a severe decline of striatal dopamine and a partial degeneration of the SNc. Rosiglitazone arrested the degenerative process in both areas. Results suggest that PPAR-γ expression in microglia and TNF-α production by these cells are crucial changes by which rosiglitazone exerts neuroprotection in PD.

Cannabinoid CB1 receptor agonists increase rat cortical and hippocampal acetylcholine release in vivo

Intravenous administration of the cannabinoid CB(1) receptor agonists (R-(+)-[2, 3-Dihydro-5-methyl-3[morpholinyl)methyl]-pyrrolo[1,2,3-de]-1, 4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate), WIN 55,212-2 (10, 37.5, 75 and 150 microg/kg), and ((6aR)-trans-3-(1, 1-Dimethylheptyl)-6a,7,10,10a-tetrahydro-1-hydroxy-6, 6-dimethyl-6H-dibenzo[b,d]pyran-9-methanol), HU 210 (1 and 4 microg/kg) dose-dependently increased acetylcholine release in dialysates from the prefrontal cortex and the hippocampus of freely moving rats. Administration of the cannabinoid receptor antagonist [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3 carboxamide]HCl, SR 141716A, at a dose that per se did not affect basal acetylcholine release (2. 5 microg/kg), prevented the increase of acetylcholine release by WIN 55,212-2 (150 microg/kg i.v.) or by HU 210 (4 microg/kg i.v.) in both areas. These data demonstrate that, at low i.v. doses, the synthetic cannabinoid CB(1) receptor agonists, WIN 55,212-2 and HU 210 stimulate cortical and hippocampal acetylcholine release.

Intravenous administration of ecstasy (3,4-methylendioxymethamphetamine) enhances cortical and striatal acetylcholine release in vivo.

The effect of intravenous administration of 3,4-methylendioxymethamphetamine (MDMA), in a range of doses (0.32-3.2 mg/kg) that have been shown to maintain self-administration behaviour in rats, on in vivo acetylcholine release from rat prefrontal cortex and dorsal striatum was studied by means of microdialysis with vertical concentric probes. Intravenous administration of MDMA dose-dependently increased basal acetylcholine release from the prefrontal cortex to 57+/-21%, 98+/-20%, 102+/-7% and 141+/-14% above baseline, at doses of 0.32, 0.64, 1.0 and 3.2 mg/kg, respectively. MDMA also stimulated striatal acetylcholine release at the dose of 3.2 mg/kg i.v. (the maximal increase being 32+/-3% above baseline) while at the dose of 1 mg/kg i.v., MDMA failed to affect basal acetylcholine output. Administration of MDMA also dose-dependently stimulated behaviour. The results of the present study show that MDMA affects measures of central cholinergic neurotransmission in vivo and suggest that at least some of the psychomotor stimulant actions of MDMA might be positively coupled with an increase in prefrontal cortical and striatal acetylcholine release.

Δ9-tetrahydrocannabinol enhances cortical and hippocampal acetylcholine release in vivo: a microdialysis study

The intravenous administration of synthetic cannabinoid agonists was recently shown to dose dependently increase acetylcholine release from the rat prefrontal cortex and hippocampus (Eur. J. Pharmacol. 401 (2000) 179]. We report here that the active ingredient of cannabis preparations, Δ9-tetrahydrocannabinol, administered at 10, 37.5, 75 and 150 μg/kg, dose dependently stimulated acetylcholine release from rat prefrontal cortex and hippocampus estimated by means of in vivo brain microdialysis with vertical concentric probes. At these doses, Δ9-tetrahydrocannabinol induced behavioural stimulation. The administration of the CB1 receptor antagonist, ({N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3carboxamide}HCl) SR 141716A (200 μg/kg i.p.) significantly reduced the effect of Δ9-tetrahydrocannabinol (75 μg/kg i.v.) on acetylcholine release from rat prefrontal cortex and hippocampus.

Differential effects of intravenous R,S-(+/-)-3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) and its S(+)- and R(-)-enantiomers on dopamine transmission and extracellular signal regulated kinase phosphorylation (pERK) in the rat nucleus accumbens shell and core

R,S(±)‐3,4‐methylenedioxymethamphetamine (R,S(±)‐MDMA, ‘Ecstasy’) is known to stimulate dopamine (DA) transmission in the nucleus accumbens (NAc). In order to investigate the post‐synaptic correlates of pre‐synaptic changes in DA transmission and their relationship with MDMA enantiomers, we studied the effects of R,S(±)‐MDMA, S(+)‐MDMA, and R(−)‐MDMA on extracellular DA and phosphorylated extracellular signal regulated kinase (pERK) in the NAc shell and core. Male Sprague–Dawley rats, implanted with a catheter in the femoral vein and vertical concentric dialysis probes in the NAc shell and core, were administered i.v. saline, R,S(±)‐MDMA, S(+)‐MDMA, or R(−)‐MDMA. Extracellular DA was monitored by in vivo microdialysis with HPLC. Intravenous R,S(±)‐MDMA (0.64, 1, and 2 mg/kg) increased dialysate DA, preferentially in the shell, in a dose‐related manner. S(+)‐MDMA exerted similar effects but at lower doses than R,S(±)‐MDMA, while R(−)‐MDMA (1 and 2 mg/kg) failed to affect dialysate DA. R,S(±)‐ and S(+)‐MDMA but not R(−)‐MDMA increased ERK phosphorylation (expressed as density/neuron and number of pERK‐positive neurons/area) in both subdivisions of the NAc. The administration of the D1 receptor antagonist, SCH 39166, prevented the increase in pERK elicited by R,S(±)‐MDMA and S(+)‐MDMA, while the D2/3 receptor antagonist, raclopride, increased pERK in the NAc core per se but failed to affect the R,S(±)‐MDMA‐elicited stimulation of pERK. The present results provide evidence that the DA stimulant effects of racemic MDMA are accounted for by the S(+)‐enantiomer and that pERK may represent a post‐synaptic correlate of the stimulant effect of R,S(±)‐MDMA on D1‐dependent DA transmission.

Modulating microglia activity with PPAR-γ agonists: a promising therapy for Parkinson's disease?

A dysregulated response of the neuroimmune system is a main contributor to the progression of neurodegeneration in Parkinson’s disease (PD). Recent findings suggest that protracted activating stimuli including α-synuclein, drive microglia to acquire maladaptive functions and to assume a harmful phenotype that prevail over a restorative one. Based on this concept, disease-modifying drugs should be aimed at targeting suppression of harmful-activated microglia and the associated production of neurotoxic molecules as pro-inflammatory cytokines, while sparing or inducing beneficial-activated microglia. In this study, we review current evidence in support of the beneficial effect of targeting peroxisome-proliferator-activated receptor (PPAR)-γ to achieve neuroprotection in PD. PPAR-γ agonists as rosiglitazone and pioglitazone are currently gaining increasing attention as promising disease-modifying drugs in this disorder. Early in vitro studies, followed by studies in in vivo models of PD, have provided convincing evidence that these drugs inhibit neuronal degeneration likely by selectively targeting the expression of neurotoxic factors in reactive microglia. Potential therapeutic application has been corroborated by recent report of pioglitazone neuroprotective activity in a non-human primate model of PD. All together, preclinical evidence have prompted the translation of pioglitazone to a phase II clinical trial in early PD.

Lesion of medial prefrontal dopamine terminals abolishes habituation of accumbens shell dopamine responsiveness to taste stimuli.

Taste stimuli increase extracellular dopamine (DA) in the nucleus accumbens (NAc) and in the medial prefrontal cortex (mPFC). This effect shows single‐trial habituation in NAc shell but not in core or in mPFC. Morphine sensitization abolishes habituation of DA responsiveness in NAc shell but induces it in mPFC. These observations support the hypothesis of an inhibitory influence of mPFC DA on NAc DA. To test this hypothesis, we used in vivo microdialysis to investigate the effect of mPFC 6‐hydroxy‐dopamine (6‐OHDA) lesions on the NAc DA responsiveness to taste stimuli. 6‐OHDA was infused bilaterally in the mPFC of rats implanted with guide cannulae. After 1 week, rats were implanted with an intraoral catheter, microdialysis probes were inserted into the guide cannulae, and dialysate DA was monitored in NAc shell/core after intraoral chocolate. 6‐OHDA infusion reduced tissue DA in the mPFC by 75%. Tyrosine hydroxylase immunohistochemistry showed that lesions were confined to the mPFC. mPFC 6‐OHDA lesion did not affect the NAc shell DA responsiveness to chocolate in naive rats but abolished habituation in rats pre‐exposed to the taste. In the NAc core, mPFC lesion potentiated, delayed and prolonged the stimulatory DA response to taste but failed to affect DA in pre‐exposed rats. Behavioural taste reactions and motor activity were not affected. The results indicate a top‐down control of NAc DA by mPFC and a reciprocal relationship between DA transmission in these two areas. Moreover, habituation of DA responsiveness in the NAc shell is dependent upon an intact DA input to the mPFC.