A combined behavioral and morphological study on the effects of fetal asphyxia on the nigrostriatal dopaminergic system in adult rats

The influence of anesthetics on substantia nigra tyrosine hydroxylase expression and tau phosphorylation in the hypoxic-ischemic near-term lamb

BackgroundGeneral anesthetics could protect key neurotransmitter systems, such as the dopaminergic system, from hypoxic-ischemic encephalopathy (HIE) by limiting excessive glutamatergic neurotransmission. However, anesthetics may adversely affect inflammation and tau phosphorylation.MethodsA near-term sheep model of HIE by umbilical cord occlusion (UCO) under anesthesia was used. The effect of propofol and isoflurane on the dopaminergic neurotransmitter phenotype in the substantia nigra (SN) was studied using tyrosine hydroxylase immunohistochemistry. The overall microglial response and tau phosphorylation were also measured in the SN, surrounding the midbrain gray matter structures and the hippocampal white matter.ResultsThe isoflurane-treated UCO group had fewer tyrosine hydroxylase-expressing neurons in the SN at 8 h after the insult than the propofol-treated UCO or sham-operated groups (P<0.05). The microglial response was unchanged in the SN region. In the thalamus and the hippocampal stratum moleculare layer, the propofol-treated UCO group had a lower microglial response than the corresponding sham-operated group. Both UCO and the use of anesthetics additively increased tau phosphorylation in the SN region, thalamus, and hippocampus.ConclusionThe choice of anesthetics is important for an emergency C-section. Propofol could potentially protect the dopaminergic neurotransmitter phenotype within the SN at the cost of a widespread increase in tau phosphorylation.

Low Current-driven Micro-electroporation Allows Efficient In Vivo Delivery of Nonviral DNA into the Adult Mouse Brain

Viral gene transfer or transgenic animals are commonly used technologies to alter gene expression in the adult brain, although these approaches lack spatial specificity and are time consuming. We delivered plasmid DNA locally into the brain of adult C57BL/6 mice in vivo by voltage- and current-controlled electroporation. The low current-controlled delivery of unipolar square wave pulses of 125 µA with microstimulation electrodes at the injection site gave 16 times higher transfection rates than a voltage-controlled electroporation protocol with plate electrodes resulting in currents of about 400 mA. Transfection was restricted to the target region and no damage due to the electric pulses was found. Our current-controlled electroporation protocol indicated that the use of very low currents resulting in applied voltages within the physiological range of the membrane potential, allows efficient transfection of nonviral plasmid DNA. In conclusion, low current-controlled electroporation is an excellent approach for electroporation in the adult brain, i.e., gene function can be influenced locally at a high level with no mortality and minimal tissue damage.

High-frequency stimulation of the subthalamic nucleus counteracts cortical expression of major histocompatibility complex genes in a rat model of Parkinson's disease

High-frequency stimulation of the subthalamic nucleus (STN-HFS) is widely used as therapeutic intervention in patients suffering from advanced Parkinson’s disease. STN-HFS exerts a powerful modulatory effect on cortical motor control by orthodromic modulation of basal ganglia outflow and via antidromic activation of corticofugal fibers. However, STN-HFS-induced changes of the sensorimotor cortex are hitherto unexplored. To address this question at a genomic level, we performed mRNA expression analyses using Affymetrix microarray gene chips and real-time RT-PCR in sensorimotor cortex of parkinsonian and control rats following STN-HFS. Experimental parkinsonism was induced in Brown Norway rats by bilateral nigral injections of 6-hydroxydopamine and was assessed histologically, behaviorally, and electrophysiologically. We applied prolonged (23h) unilateral STN-HFS in awake and freely moving animals, with the non-stimulated hemisphere serving as an internal control for gene expression analyses. Gene enrichment analysis revealed strongest regulation in major histocompatibility complex (MHC) related genes. STN-HFS led to a cortical downregulation of several MHC class II (RT1-Da, Db1, Ba, and Cd74) and MHC class I (RT1CE) encoding genes. The same set of genes showed increased expression levels in a comparison addressing the effect of 6-hydroxydopamine lesioning. Hence, our data suggest the possible association of altered microglial activity and synaptic transmission by STN-HFS within the sensorimotor cortex of 6-hydroxydopamine treated rats.

Decomposition of abnormal free locomotor behavior in a rat model of Parkinson's disease

Poverty of spontaneous movement, slowed execution and reduced amplitudes of movement (akinesia, brady- and hypokinesia) are cardinal motor manifestations of Parkinson's disease that can be modeled in experimental animals by brain lesions affecting midbrain dopaminergic neurons. Most behavioral investigations in experimental parkinsonism have employed short-term observation windows to assess motor impairments. We postulated that an analysis of longer-term free exploratory behavior could provide further insights into the complex fine structure of altered locomotor activity in parkinsonian animals. To this end, we video-monitored 23 h of free locomotor behavior and extracted several behavioral measures before and after the expression of a severe parkinsonian phenotype following bilateral 6-hydroxydopamine (6-OHDA) lesions of the rat dopaminergic substantia nigra. Unbiased stereological cell counting verified the degree of midbrain tyrosine hydroxylase positive cell loss in the substantia nigra and ventral tegmental area. In line with previous reports, overall covered distance and maximal motion speed of lesioned animals were found to be significantly reduced compared to controls. Before lesion surgery, exploratory rat behavior exhibited a bimodal distribution of maximal speed values obtained for single movement episodes, corresponding to a "first" and "second gear" of motion. 6-OHDA injections significantly reduced the incidence of second gear motion episodes and also resulted in an abnormal prolongation of these fast motion events. Likewise, the spatial spread of such episodes was increased in 6-OHDA rats. The increase in curvature of motion tracks was increased in both lesioned and control animals. We conclude that the discrimination of distinct modes of motion by statistical decomposition of longer-term spontaneous locomotion provides useful insights into the fine structure of fluctuating motor functions in a rat analog of Parkinson's disease.

The effects of fetal and perinatal asphyxia on neuronal cytokine levels and ceramide metabolism in adulthood

In a rat model of global fetal and perinatal asphyxia, we investigated if asphyxia and long-lasting brain tolerance to asphyxia (preconditioning) are mediated by modifications in inflammatory cytokines and ceramide metabolism genes in prefrontal cortex, hippocampus and caudate-putamen at the age of 8months. Most significant changes were found in prefrontal cortex, with reduced LAG1 homolog ceramide synthase 1 expression after both types of asphyxia. Additionally, sphingosine kinase 1 was upregulated in those animals that experienced the combination of fetal and perinatal asphyxia (preconditioning), suggesting increased cell proliferation. While cytokine levels are normal, levels of ceramide genes were modulated both after fetal and perinatal asphyxia in the adult prefrontal cortex. Moreover, the combination of two subsequent asphyctic insults provides long-lasting neuroprotection in the prefrontal cortex probably by maintaining normal apoptosis and promoting cell proliferation. Better understanding of the effects of asphyxia on ceramide metabolism will help to understand the changes leading to brain tolerance and will open opportunities for the development of new neuroprotective therapies.

Chronic phosphodiesterase type 2 inhibition improves memory in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by progressive cognitive deficits and synaptic dysfunction. Over the last decade phosphodiesterase inhibitors (PDEIs) have received increasing attention as putative cognition enhancers and have been suggested as a novel treatment strategy for AD. Given their ability to prevent hydrolysis of cAMP and/or cGMP, they can stimulate the cAMP/protein kinase A (PKA)/cAMP element-binding protein (CREB) and cGMP/PKG/CREB pathway to enhance synaptic transmission by increasing CREB phosphorylation (pCREB) and brain-derived neurotrophic factor (BDNF) transcription. Based on previous research, we hypothesized that chronic PDE2I treatment would improve AD-related cognitive deficits, by decreasing amyloid-β (Aβ) plaque load, enhancing pCREB and BDNF levels and increasing synaptic density in the hippocampus of 8-month-old APPswe/PS1dE9 mice. Results indicated that chronic PDE2I treatment could indeed improve memory performance in APPswe/PS1dE9 mice, without affecting anxiety, depressive-like behavior or hypothalamus-pituitary-adrenal axis regulation. However, no treatment effects were observed on Aβ plaque load, pCREB or BDNF concentrations, or presynaptic density in the hippocampus, suggesting that other signaling pathways and/or effector molecules might be responsible for its cognition-enhancing effects. Presynaptic density in the stratum lucidum of the CA3 subregion was significantly higher in APPswe/PS1dE9 mice compared to WT controls, possibly reflecting a compensatory mechanism. In conclusion, PDEs in general, and PDE2 specifically, could be considered as promising therapeutic targets for cognition enhancement in AD, although the underlying mechanism of action remains to be elucidated. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.

Effects of birth asphyxia on neonatal hippocampal structure and function in the spiny mouse

Studies of human neonates, and in animal experiments, suggest that birth asphyxia results in functional compromise of the hippocampus, even when structural damage is not observable or resolves in early postnatal life. The aim of this study was to determine if changes in hippocampal function occur in a model of birth asphyxia in the precocial spiny mouse where it is reported there is no major lesion or infarct. Further, to assess if, as in human infants, this functional deficit has a sex-dependent component. At 37 days gestation (term=39 days) spiny mice fetuses were either delivered immediately by caesarean section (control group) or exposed to 7.5min of in utero asphyxia causing systemic acidosis and hypoxia. At 5 days of age hippocampal function was assessed ex vivo in brain slices, or brains were collected for examination of structure or protein expression. This model of birth asphyxia did not cause infarct or cystic lesion in the postnatal day 5 (P5) hippocampus, and the number of proliferating or pyknotic cells in the hippocampus was unchanged, although neuronal density in the CA1 and CA3 was increased. Protein expression of synaptophysin, brain-derived neurotrophic factor (BDNF), and the inositol trisphosphate receptor 1 (IP(3)R1) were all significantly increased after birth asphyxia, while long-term potentiation (LTP), paired pulse facilitation (PPF), and post-tetanic potentiation (PTP) were all reduced at P5 by birth asphyxia. In control P5 pups, PPF and synaptic fatigue were greater in female compared to male pups, and after birth asphyxia PPF and synaptic fatigue were reduced to a greater extent in female vs. male pups. In contrast, the asphyxia-induced increase in synaptophysin expression and neuronal density were greater in male pups. Thus, birth asphyxia in this precocial species causes functional deficits without major structural damage, and there is a sex-dependent effect on the hippocampus. This may be a clinically relevant model for assessing treatments delivered either before or after birth to protect this vulnerable region of the developing brain.

Caloric restriction attenuates age-related changes of DNA methyltransferase 3a in mouse hippocampus

Recent studies have suggested that DNA methylation is implicated in age-related changes in gene expression as well as in cognition. DNA methyltransferase 3a (Dnmt3a), which catalyzes DNA methylation, is essential for memory formation and underlying changes in neuronal and synaptic plasticity. Because caloric restriction (CR) and upregulation of antioxidants have been suggested as strategies to attenuate age-related alterations in the brain, we hypothesized that both a diet restricted in calories and transgenic overexpression of normal human Cu/Zn superoxide dismutase 1 (SOD) attenuate age-related changes in Dnmt3a in the aging mouse hippocampus. For this purpose, we performed qualitative and quantitative analyses of Dnmt3a-immunoreactivity (IR) for the hippocampal dentate gyrus (DG), CA3 and CA1-2 regions in 12- and 24-month-old mice from 4 groups, i.e. (1) wild-type (WT) mice on a control diet (WT-CD), (2) SOD-CD mice, (3) WT mice on CR (WT-CR), and (4) SOD-CR. Qualitative analyses revealed two types of Dnmt3a immunoreactive cells: type I cells--present throughout all hippocampal cell layers showing moderate levels of nuclear Dnmt3a-IR, and type II cells--a subpopulation of hippocampal cells showing very intense nuclear Dnmt3a-IR, and colocalization with Bromodeoxyuridine. Quantitative analyses indicated that the age-related increase in Dnmt3a-IR within the CA3 and CA1-2 in type I cells was attenuated by CR, but not by SOD overexpression. In contrast, the density of type II Dnmt3a immunoreactive cells showed an age-related reduction, without significant effects of both CR and SOD. These changes in Dnmt3a levels in the mouse hippocampus may have a significant impact on gene expression and associated cognitive functioning.

The impact of maternal separation on the number of tyrosine hydroxylase-expressing midbrain neurons during different stages of ontogenesis

Early life stressors have life-long functional and anatomical consequences. Though many neurotransmitters are involved in the functional impact of early life stress, dopamine seems to be important because of its roles in motor control, adaptation to stressful conditions, mood, cognition, attention and reward. Thus, in the present study, we investigated the way that early life stress, in the form of maternal separation (MS), affects the populations of tyrosine hydroxylase-immunoreactive (TH-IR) dopaminergic neurons in rat midbrain structures during ontogenesis. We included in the study the sub-regions of the substantia nigra (SN) and the ventral tegmental area (VTA). In both the control and MS rats, we found that the estimated total number of TH-expressing neurons fluctuated during ontogenesis. Moreover, MS influenced the number of TH-IR cells, especially in the SN pars reticulata (SNr) and VTA. Shortly after the termination of MS, on postnatal day (PND) 15, a decrease in the estimated total number of TH-IR neurons was observed in the SNr and VTA (in both males and females). On PND 35, MS caused a transient increase in the number of TH-IR cells only in the SNr of female rats. On PND 70, MS affected the number of TH-IR neurons in the VTA of females; specifically, an increase in the number of these cells was observed. Additionally, MS did not alter TH-IR cell sizes or the total levels of TH (measured by Western blot analysis) in the SN and VTA for all stages of ontogenesis in both males and females. The results from the study herein indicate that early life stress has enduring effects on the populations of midbrain TH-expressing dopaminergic neurons (especially in female rats), which are critically important for dopamine-regulated brain function throughout ontogenesis.

Central dopaminergic circuitry controlling food intake and reward: implications for the regulation of obesity

Prevalence of obesity in the general population has increased in the past 15 years from 15% to 35%. With increasing obesity, the coincident medical and social consequences are becoming more alarming. Control over food intake is crucial for the maintenance of body weight and represents an important target for the treatment of obesity. Central nervous system mechanisms responsible for control of food intake have evolved to sense the nutrient and energy levels in the organism and to coordinate appropriate responses to adjust energy intake and expenditure. This homeostatic system is crucial for maintenance of stable body weight over long periods of time of uneven energy availability. However, not only the caloric and nutritional value of food but also hedonic and emotional aspects of feeding affect food intake. In modern society, the increased availability of highly palatable and rewarding (fat, sweet) food can significantly affect homeostatic balance, resulting in dysregulated food intake. This review will focus on the role of hypothalamic and mesolimbic/mesocortical dopaminergic (DA) circuitry in coding homeostatic and hedonic signals for the regulation of food intake and maintenance of caloric balance. The interaction of dopamine with peripheral and central indices of nutritional status (e.g., leptin, ghrelin, neuropeptide Y), and the susceptibility of the dopamine system to prenatal insults will be discussed. Additionally, the importance of alterations in dopamine signaling that occur coincidently with obesity will be addressed.

Fetal asphyxia leads to the loss of striatal presynaptic boutons in adult rats

Fetal asphyxic insults in the brain are known to be associated with developmental and neurological problems like neuromotor disorders and cognitive deficits. Little is known, however, about the long-term consequences of fetal asphyxia contributing to the development of different neurological diseases common in the adult or the aging brain. For that reason the present study aimed to investigate the long-term effects of fetal asphyxia on synaptic organization within the adult rat brain. Fetal asphyxia was induced at embryonic day 17 by 75-min clamping of the uterine and ovarian arteries. Presynaptic bouton densities and numbers were analyzed in the striatum and prefrontal cortex at the age of 19 months. A substantial decrease in presynaptic bouton density and number was observed in the striatum of fetal asphyxia rats compared to control rats, while an increase was found in the fifth layer of the prefrontal cortex. These results suggest that fetal asphyxia can have long-lasting effects on synaptic organization that might contribute to a developmental etiology of different neurological disorders and aging.