Browsing by Author "Martín, Yasmina B."

Astrocytosis, a process in which astrocytes undergo proliferation and enhancement of glial fibrillary acidic protein (GFAP) expression, has been suggested to play important roles in the maintenance of dependence to amphetamine and its derivatives. It was previously shown that mice with genetic deletion of pleiotrophin (PTN), a neurotrophic factor upregulated in different brain areas after administration of amphetamine, show a longer lasting amphetamine-induced conditioned place preference (CPP) when compared to wild type mice. In this work, we aimed to pursue the possibility of a different astrocytic response induced by amphetamine in PTN-/- and PTN+/+ mice, which could underlie the higher vulnerability of PTN-/- mice to maintain amphetamine CPP. In confirmation of previous studies, we found that PTN-/- mice significantly maintained amphetamine (3 mg/kg)-induced CPP 5 days after the last drug administration compared to PTN+/+ mice. Interestingly, the number of astrocytes in nucleus accumbens (NAcc), cingulate cortex (CG) and caudate putamen (CPu) did not differ between mice that maintained and did not maintain amphetamine-induced CPP independently of the genotype considered. However, we found that PTN-/- mice showed significantly decreased numbers of astrocytes in CG and CPu compared to PTN+/+ mice independently of whether they maintained amphetamine-induced CPP 5 days after the last drug administration or not. The data demonstrate that maintenance of amphetamine-induced CPP depends on the endogenous expression of PTN. The data tend to discard a correlation between activated astrocytes and maintenance of amphetamine conditioning effects and suggest PTN as a potential modulator of activation of astrocytes after amphetamine treatment.

Pleiotrophin (PTN) is a cytokine involved in nerve tissue repair processes, neuroinflammation and neuronal survival. PTN expression levels are upregulated in the nigrostriatal pathway of Parkinson’s Disease (PD) patients. We aimed to characterize the dopaminergic injury and glial responses in the nigrostriatal pathway of mice with transgenic Ptn overexpression in the brain (Ptn-Tg) after intrastriatal injection of the catecholaminergic toxic 6-hydroxydopamine (6-OHDA) at a low dose (5 μg). Ten days after surgery, the injection of 6-OHDA induced a significant decrease of the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra and of the striatal TH contents in Wild type (Wt) mice. In contrast, these effects of 6-OHDA were absent in Ptn-Tg mice. When the striatal Iba1 and GFAP immunoreactivity was studied, no statistical differences were found between vehicle-injected Wt and Ptn-Tg mice. Furthermore, 6-OHDA did not cause robust glial responses neither on Wt or Ptn-Tg mice 10 days after injections. In metabolomics studies, we detected interesting metabolites that significantly discriminate the more injured 6-OHDA-injected Wt striatum and the more protected 6-OHDA-injected Ptn-Tg striatum. Particularly, we detected groups of metabolites, mostly corresponding to phospholipids, whose trends were opposite in both groups. In summary, the data confirm lower 6-OHDA-induced decreases of TH contents in the nigrostriatal pathway of Ptn-Tg mice, suggesting a neuroprotective effect of brain PTN overexpression in this mouse model of PD. New lipid-related PD drug candidates emerge from this study and the data presented here support the increasingly recognized “lipid cascade” in PD.

Midkine (MK), a neurotrophic factor with important roles in survival and differentiation of dopaminergic neurons, is upregulated in different brain areas after administration of different drugs of abuse suggesting MK could modulate drugs of abuse-induced pharmacological or neuroadaptative effects. To test this hypothesis, we have studied the effects of amphetamine administration in MK genetically deficient (MK-/-) and wild type (MK+/+) mice. In conditioning studies, we found that amphetamine induces conditioned place preference (CPP) similarly in both MK-/- and MK+/+ mice. In immunohystochemistry studies, we found that amphetamine (10 mg/Kg, 4 times, every 2 h) causes a similar striatal dopaminergic denervation in both MK-/- and MK+/+ mice. However, we detected a significant increase of Glial Fibrillary Acidic Protein (GFAP) positive cells in the striatum of amphetamine-treated MK-/- mice compared to MK+/+ mice, suggesting an enhanced amphetamine-induced astrocytosis in absence of endogenous MK. Interestingly, the levels of expression of the MK receptor, Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ, in the striatum were not found to be changed by the drug administration or the mouse genotype. In a similar manner the phosphorylation levels of RPTP β/ζ substrates with important roles in survival of dopaminergic neurons, Fyn kinase and TrkA, and of the MAP kinases ERK1/2, were unaffected by the drug or the genotype. The data clearly suggest that endogenous MK limits amphetamine-induced astrocytosis through Fyn-, TrkA- and ERK1/2-independent mechanisms and identify previously unexpected functional differences between MK and pleiotrophin, the only other member of the MK family of growth factors, in the modulation of effects of drugs of abuse.

Genetic deletion of pleiotrophin (PTN) impairs spinal nociceptive transmission suggesting this heparin binding growth factor could play roles in acute pain processing. Despite the high functional redundancy between PTN and midkine (MK), the only other member of this family of growth factors, we now demonstrate that genetic inactivation of MK does not alter acute nociceptive transmission since pain responses of female MK genetically deficient (MK-/-) and wild type (WT+/+) mice were found to be similar in the hot-plate and tailimmersion tests. It has also been shown that morphine administration significantly regulates MK levels within the brain, suggesting MK could play a role in morphine-induced antinociceptive effects. To test this hypothesis, we have now studied morphine-induced antinociceptive effects in female MK-/- and WT+/+ mice. We did not find differences among genotypes using different doses of morphine (2.5, 5 and 10 mg/kg) in the hot-plate test. In contrast, we found that morphine significantly delayed pain responses in MK-/- mice compared to WT+/+ mice in the tail-immersion test. In confirmation of previous results from our group, we also found significantly enhanced morphine-induced antinociceptive effects in PTN-/- mice in the tail-immersion test. In addition, we now demonstrate that enhanced morphine analgesic effects in PTN-/- and MK-/- mice are not caused by a different contribution of descending noradrenergic inhibitory pathways since the α2-adrenergic antagonist yohimbine failed to alter morphine-induced analgesia in all genotypes. The data demonstrate that MK is an endogenous modulator of morphine antinociceptive effects, identify significant differences between PTN and MK in the control of pain processing at the spinal level, and support the hypothesis that inhibitors of the PTN/MK signaling pathway could potentiate opioid analgesia which may be relevant in opiod-refractory pain cases.