Cristina Ordóñez

Aging and substitutive hormonal therapy influence in regional and subcellular distribution of ERα in female rat brain.

Estrogens are not only critical for sexual differentiation it is well-known for the role of 17β-estradiol (E2) in the adult brain modulating memory, learning, mood and acts as a neuroprotector. E2 exerts its actions through two classical receptors: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). The distribution of both receptors changes from one brain area to another, E2 being able to modulate their expression. Among the classical features of aging in humans, we find cognitive impairment, dementia, memory loss, etc. As estrogen levels change with age, especially in females, it is important to know the effects of low E2 levels on ERα distribution; results from previous studies are controversial regarding this issue. In the present work, we have studied the effects of long-term E2 depletion as well as the ones of E2 treatment on ERα brain distribution of ovariectomized rats along aging in the diencephalon and in the telencephalon. We have found that ovariectomy causes downregulation and affects subcellular localization of ERα expression during aging, meanwhile prolonged estrogen treatment produces upregulation and overexpression of the receptor levels. Our results support the idea of the region-specific neuroprotection mechanisms mediated by estradiol.

Chronic Levodopa Administration Followed by a Washout Period Increased Number and Induced Phenotypic Changes in Striatal Dopaminergic Cells in MPTP-Monkeys

In addition to the medium spiny neurons the mammalian striatum contains a small population of GABAergic interneurons that are immunoreactive for tyrosine hydroxylase (TH), which dramatically increases after lesions to the nigrostriatal pathway and striatal delivery of neurotrophic factors. The regulatory effect of levodopa (L-Dopa) on the number and phenotype of these cells is less well understood. Eleven macaques (Macaca fascicularis) were included. Group I (n = 4) received 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) and L-Dopa; Group II (n = 4) was treated with MPTP plus vehicle and Group III (n = 3) consist of intact animals (control group). L-Dopa and vehicle were given for 1 year and animals sacrificed 6 months later. Immunohistochemistry against TH was used to identify striatal and nigral dopaminergic cells. Double and triple labeling immunofluorescence was performed to detect the neurochemical characteristics of the striatal TH-ir cells using antibodies against: TH, anti-glutamate decarboxylase (GAD67) anti-calretinin (CR) anti-dopa decarboxylase (DDC) and anti-dopamine and cyclic AMP-regulated phosphoprotein (DARPP-32). The greatest density of TH-ir striatal cells was detected in the striatum of the L-Dopa treated monkeys and particularly in its associative territory. None of the striatal TH-ir cell expressed DARPP-32 indicating they are interneurons. The percentages of TH-ir cells that expressed GAD67 and DDC was approximately 50%. Interestingly, we found that in the L-Dopa group the number of TH/CR expressing cells was significantly reduced. We conclude that chronic L-Dopa administration produced a long-lasting increase in the number of TH-ir cells, even after a washout period of 6 months. L-Dopa also modified the phenotype of these cells with a significant reduction of the TH/CR phenotype in favor of an increased number of TH/GAD cells that do not express CR. We suggest that the increased number of striatal TH-ir cells might be involved in the development of aberrant striatal circuits and the appearance of L-Dopa induced dyskinesias.

Enhanced GDNF expression in dopaminergic cells of monkeys grafted with carotid body cell aggregates

Striatal carotid body cell aggregates (CBCA) grafts improve parkinsonism in animals and patients with Parkinsons disease. As CB cells contain trophic factors, we investigated the long-term effect of striatal CBCA grafts on nigrostriatal dopaminergic cells in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys receiving unilateral (UL-grafted group, n=4) or bilateral (BL-grafted group, n=3) CBCA autotransplant. Two MPTP monkeys were sham-operated receiving only Tyrode. For histological analysis, we also included 3 MPTP-untreated and 3 intact animals. Brain [18]F-luorodopa ((18)F-DOPA)-positron emission tomography (PET) scans were performed to assess dopaminergic function in vivo at baseline, 6 and 12months after surgery. The number of nigral dopaminergic cells was assessed in UL-grafted animals, and the number of dopaminergic cells expressing glial cell line-derived neurotrophic factor (GDNF) in all groups. After 1 year, animals showed a significant recovery of the parkinsonism (San Sebastian et al., 2007) and PET studies revealed a larger striatal (18)F-DOPA uptake in the CBCA-grafted striatum compared to that receiving Tyrode. No differences were found in the number of surviving dopaminergic cells when comparing both subtantia nigra of UL-grafted animals. However, both UL- and BL-grafted animals showed a bilaterally increased number of TH-GDNF immunoreactive nigral neurons compared to intact and MPTP-untreated monkeys, indicating that in addition to the proven long-term motor benefit, CBCA autograft might exert a neuroprotective effect on the surviving dopaminergic cells.

Amyloid-β25-35 Induces Apolipoprotein D Synthesis and Growth Arrest in HT22 Hippocampal Cells

Apolipoprotein D (ApoD) is a secreted glycoprotein that is markedly induced in several pathological and stressful conditions in the nervous system. In the central nervous system, ApoD expression is upregulated during aging, after traumatic brain injury, and in several human neuropathologies such as Alzheimers disease (AD), where it is found associated with amyloid-β (Aβ) plaques. Recent studies have indicated that ApoD has an important function as a neuroprotective and antioxidant protein. The aim of this work is to study the effect of the peptide fragment Aβ25-35, which is believed to play a major role in the neurodegenerative process of AD, in ApoD expression in a mouse hippocampal cell line. In addition, we studied whether direct addition of exogenous human recombinant ApoD protein has neuroprotective effect against Aβ25-35 treatment on neuronal cells. Our results demonstrate that Aβ25-35 induces ApoD expression in hippocampal cells in response to stress-induced growth arrest. This observed relationship between Aβ and ApoD expression could explain the elevated levels of ApoD found in AD brain, where it may be a neuroprotective molecule in the course of AD, probably related to its lipid transport function or a direct antioxidant property. However, the addition of exogenous human recombinant ApoD does not exert any protective effect, most likely due to its major structural modifications.

Levodopa induces long-lasting modification in the functional activity of the nigrostriatal pathway.

Much controversy exists concerning the effect of levodopa on striatal dopaminergic markers in Parkinsons disease (PD) and its influence on functional neuroimaging. To deal with this issue we studied the impact of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and chronic levodopa administration on striatal (18)F-DOPA uptake (Ki) in an animal model of PD. The levels of several striatal dopaminergic markers and the number of surviving dopaminergic neurons in the substantia nigra (SN) were also assessed. Eleven Macaca fascicularis were included in the study. Eight animals received weekly intravenous injections of MPTP for 7weeks and 3 intact animals served as controls. MPTP-monkeys were divided in two groups. Group I was treated with placebo while Group II received levodopa. Both treatments were maintained for 11months and then followed by a washout period of 6months. (18)F-DOPA positron emission tomography (PET) scans were performed at baseline, after MPTP intoxication, following 11months of treatment, and after a washout period of 1, 3 and 6months. Monkeys were sacrificed 6months after concluding either placebo or levodopa treatment and immediately after the last (18)F-DOPA PET study. Striatal dopamine transporter (DAT) content, tyrosine hydroxylase (TH) content and aromatic l-amino acid decarboxylase (AADC) content were assessed. In Group II (18)F-DOPA PET studies performed at 3 and 6months after interrupting levodopa showed a significantly increased Ki in the anterior putamen as compared to Group I. Levodopa and placebo treated animals exhibited a similar number of surviving dopaminergic cells in the SN. Striatal DAT content was equally reduced in both groups of animals. Animals in Group I exhibited a significant decrease in TH protein content in all the striatal regions assessed. However, in Group II, TH levels were significantly reduced only in the anterior and posterior putamen. Surprisingly, in the levodopa-treated animals the TH levels in the posterior putamen were significantly lower than those in the placebo group. AADC levels in MPTP groups were similar to those of control animals in all striatal areas analyzed. This study shows that chronic levodopa administration to monkeys with partial nigrostriatal degeneration followed by a washout period induces modifications in the functional activity of the dopaminergic nigrostriatal pathway.

Sox-2 positive neural progenitors in the primate striatum undergo dynamic changes after dopamine denervation

The existence of endogenous neural progenitors in the nigrostriatal system could represent a powerful tool for restorative therapies in Parkinsons disease. Sox-2 is a transcription factor expressed in pluripotent and adult stem cells, including neural progenitors. In the adult brain Sox-2 is expressed in the neurogenic niches. There is also widespread expression of Sox-2 in other brain regions, although the neurogenic potential outside the niches is uncertain. Here, we analyzed the presence of Sox-2+ cells in the adult primate (Macaca fascicularis) brain in naïve animals (N = 3) and in animals exposed to systemic administration of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine to render them parkinsonian (N = 8). Animals received bromodeoxyuridine (100 mg/kg once a day during five consecutive days) to label proliferating cells and their progeny. Using confocal and electron microscopy we analyzed the Sox-2+ cell population in the nigrostriatal system and investigated changes in the number, proliferation and neurogenic potential of Sox-2+ cells, in control conditions and at two time points after MPTP administration. We found Sox-2+ cells with self-renewal capacity in both the striatum and the substantia nigra. Importantly, only in the striatum Sox-2+ was expressed in some calretinin+ neurons. MPTP administration led to an increase in the proliferation of striatal Sox-2+ cells and to an acute, concomitant decrease in the percentage of Sox-2+/calretinin+ neurons, which recovered by 18 months. Given their potential capacity to differentiate into neurons and their responsiveness to dopamine neurotoxic insults, striatal Sox-2+ cells represent good candidates to harness endogenous repair mechanisms for regenerative approaches in Parkinsons disease.