Reduced inhibitory action of a GABA(B )receptor agonist on [(3)H]-dopamine release from rat ventral tegmental area in vitro after chronic nicotine administration

BACKGROUND: The activation of GABA(B )receptors in the ventral tegmental area (VTA) has been suggested to attenuate the rewarding properties of psychostimulants, including nicotine. However, the neurochemical mechanism that underlie this effect remains unknown. Since GABA(B )receptors modulate the release of several neurotransmitters in the mammalian brain, we have characterised the effect of the GABA(B )receptor agonist baclofen on the release of [(3)H]-dopamine ([(3)H]-DA) from VTA slices of naïve rats and of rats pre-treated with nicotine. RESULTS: In naïve rats, baclofen concentration-dependently inhibited the electrically evoked release of [(3)H]-DA from the isolated VTA (EC(50 )= 0.103 μM, 95% CI = 0.043–0.249), without affecting the basal [(3)H]-monoamine overflow. This effect was mediated by activation of GABA(B )receptors as it was blocked by the selective receptor antagonist CGP55845A. Chronic administration of nicotine (0.4 mg kg(-1), s.c., for 14 days) affected neither the basal nor the electrically evoked release of [(3)H]-DA from VTA slices. However, the inhibitory effect of baclofen (10 μM) on the stimulated [(3)H]-monoamine overflow was abolished in rats pre-treated with nicotine as compared to saline-injected controls. CONCLUSIONS: Our results demonstrate that GABA(B )receptor activation reduces the release of DA from the rat VTA. In addition, a reduced sensitivity of VTA GABA(B )receptors appears to develop after chronic exposure to nicotine. The resulting disinhibition of VTA DA neurones might therefore contribute to the sensitised dopaminergic responses observed in the rat mesocorticolimbic system following repeated administration of nicotine

Ischemic Preconditioning Modulates the Peripheral Innate Immune System to Promote Anti-Inflammatory and Protective Responses in Mice Subjected to Focal Cerebral Ischemia

The development of tolerance triggered by a sublethal ischemic episode (preconditioning, PC) involves a complex crosstalk between neurons, astrocytes and microglia, although the role of the peripheral immune system in this context is largely unexplored. Here, we report that severe cerebral ischemia caused by transient middle cerebral artery occlusion (MCAo) in adult male mice elevates blood counts of inflammatory neutrophils and monocytes, and plasma levels of miRNA-329-5p. These inflammatory responses are prevented by ischemic PC induced by 15 min MCAo, 72h before the severe insult (1h MCAo). As compared with sham-operated animals, mice subjected to either ischemic PC, MCAo or a combination of both (PC+MCAo) display spleen contraction. However, protein levels of Ym1 (a marker of polarization of myeloid cells towards M2/N2 protective phenotypes) are elevated only in spleen from the experimental groups PC and PC+MCAo, but not MCAo. Conversely, Ym1 protein levels only increase in circulating leukocytes from mice subjected to 1h MCAo, but not in preconditioned animals, which is coincident with a dramatic elevation of Ym1 expression in the ipsilateral cortex. By immunofluorescence analysis, we observe that expression of Ym1 occurs in amoeboid-shaped myeloid cells, mainly representing inflammatory monocytes/macrophages and neutrophils. As a result of its immune-regulatory functions, ischemic PC prevents elevation of mRNA levels of the pro-inflammatory cytokine interleukin (IL)-1β in the ipsilateral cortex, while not affecting IL-10 mRNA increase induced by MCAo. Overall, the elevated anti-inflammatory/pro-inflammatory ratio observed in the brain of mice pre-exposed to PC is associated with reduced brain infarct volume and ischemic edema, and with amelioration of functional outcome. These findings reaffirm the crucial and dualistic role of the innate immune system in ischemic stroke pathobiology, extending these concepts to the context of ischemic tolerance and underscoring their relevance for the identification of novel therapeutic targets for effective stroke treatment

Study of GABAB receptor mechanisms on the mesocorticolimbic system of nicotine dependent rats

SIGLEAvailable from British Library Document Supply Centre- DSC:DXN064656 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Cratterizzazione degli effetti neuroprotettivi della leptina in un modello sperimentale di ischemia cerebrale focale nel ratto

Dottorato di Ricerca in Biochimica Cellulare ed attività dei Farmaci in Oncologia XXIV Ciclo,,a.a. 2010-2011La leptina, oltre ad avere effetti sull’ipotalamo per il controllo del peso corporeo, è coinvolta nella regolazione della funzionalità, dello sviluppo e della sopravvivenza neuronale. Studi recenti hanno evidenziato i suoi effetti neuroprotettivi nel danno ischemico cerebrale, ma fino ad oggi il ruolo del fattore di trasduzione ed attivatore trascrizionale (STAT)-3, il principale mediatore della via di trasduzione del segnale di ObR nel cervello, non è stato chiarito. I nostri dati dimostrano che la somministrazione sistemica acuta di leptina è neuroprotettiva in ratti sottoposti ad occlusione permanente dell’arteria cerebrale media (MCAo), come documentato dalla riduzione significativa del volume di infarto cerebrale e del deficit neurologico fino a 7 giorni dopo l’induzione di ischemia. Mediante analisi di immunofluorescenza e tecniche di frazionamento subcellulare abbiamo osservato che la neuroprotezione da leptina è associata con la modulazione dei livelli di fosforilazione di STAT-3 in differenti tipi cellulari nella corteccia cerebrale ischemica. Infatti, poche ore dopo l’insulto la leptina aumenta i livelli di p-STAT3 nel nucleo degli astrociti della penombra ischemica contribuendo così agli effetti benefici di queste cellule sull’evoluzione del danno. L’aumentata espressione di homer-1a che osserviamo negli astrociti fino a 7 giorni dopo l’induzione di ischemia, sottolinea ulteriormente il loro ruolo benefico. Mediante ricostruzione 3D di immagini di microscopia elettronica, combinata con analisi morfometrica, abbiamo osservato che gli astrociti reattivi mostrano un ridotto coverage bilaterale, mentre la percentuale di contatto con le sinapsi glutammatergiche rimane invariata. Inoltre, l’aumento di p-STAT3 indotto dalla leptina nei neuroni dopo 24h di MCAo è associato con un aumento dell’espressione dell’inibitore tissutale delle metalloproteasi della matrice (TIMP)-1 nella corteccia, suggerendo un suo coinvolgimento nella neuroprotezione indotta dall’adipochinaUniversità degli Studi della Calabri

On the role of store-operated calcium entry in acute and chronic neurodegenerative diseases

In both excitable and non-excitable cells, calcium (Ca2+) signals are maintained by a highly integrated process involving store-operated Ca2+ entry (SOCE), namely the opening of plasma membrane (PM) Ca2+ channels following the release of Ca2+ from intracellular stores. Upon depletion of Ca2+ store, the stromal interaction molecule (STIM) senses Ca2+ level reduction and migrates from endoplasmic reticulum (ER)-like sites to the PM where it activates the channel proteins Orai and/or the transient receptor potential channels (TRPC) prompting Ca2+ refilling. Accumulating evidence suggests that SOCE dysregulation may trigger perturbation of intracellular Ca2+ signaling in neurons, glia or hematopoietic cells, thus participating to the pathogenesis of diverse neurodegenerative diseases. Under acute conditions, such as ischemic stroke, neuronal SOCE can either re-establish Ca2+ homeostasis or mediate Ca2+ overload, thus providing a non-excitotoxic mechanism of ischemic neuronal death. The dualistic role of SOCE in brain ischemia is further underscored by the evidence that it also participates to endothelial restoration and to the stabilization of intravascular thrombi. In Parkinson's disease (PD) models, loss of SOCE triggers ER stress and dysfunction/degeneration of dopaminergic neurons. Disruption of neuronal SOCE also underlies Alzheimer's disease (AD) pathogenesis, since both in genetic mouse models and in human sporadic AD brain samples, reduced SOCE contributes to synaptic loss and cognitive decline. Unlike the AD setting, in the striatum from Huntington's disease (HD) transgenic mice, an increased STIM2 expression causes elevated synaptic SOCE that was suggested to underlie synaptic loss in medium spiny neurons. Thus, pharmacological inhibition of SOCE is beneficial to synapse maintenance in HD models, whereas the same approach may be anticipated to be detrimental to cortical and hippocampal pyramidal neurons. On the other hand, up-regulation of SOCE may be beneficial during AD. These intriguing findings highlight the importance of further mechanistic studies to dissect the molecular pathways, and their corresponding targets, involved in synaptic dysfunction and neuronal loss during aging and neurodegenerative diseases