PGC-1alpha Down-Regulation Affects the Antioxidant Response in Friedreich's Ataxia

BACKGROUND: Cells from individuals with Friedreich's ataxia (FRDA) show reduced activities of antioxidant enzymes and cannot up-regulate their expression when exposed to oxidative stress. This blunted antioxidant response may play a central role in the pathogenesis. We previously reported that Peroxisome Proliferator Activated Receptor Gamma (PPARgamma) Coactivator 1-alpha (PGC-1alpha), a transcriptional master regulator of mitochondrial biogenesis and antioxidant responses, is down-regulated in most cell types from FRDA patients and animal models. METHODOLOGY/PRINCIPAL FINDINGS: We used primary fibroblasts from FRDA patients and the knock in-knock out animal model for the disease (KIKO mouse) to determine basal superoxide dismutase 2 (SOD2) levels and the response to oxidative stress induced by the addition of hydrogen peroxide. We measured the same parameters after pharmacological stimulation of PGC-1alpha. Compared to control cells, PGC-1alpha and SOD2 levels were decreased in FRDA cells and did not change after addition of hydrogen peroxide. PGC-1alpha direct silencing with siRNA in control fibroblasts led to a similar loss of SOD2 response to oxidative stress as observed in FRDA fibroblasts. PGC-1alpha activation with the PPARgamma agonist (Pioglitazone) or with a cAMP-dependent protein kinase (AMPK) agonist (AICAR) restored normal SOD2 induction. Treatment of the KIKO mice with Pioglitazone significantly up-regulates SOD2 in cerebellum and spinal cord. CONCLUSIONS/SIGNIFICANCE: PGC-1alpha down-regulation is likely to contribute to the blunted antioxidant response observed in cells from FRDA patients. This response can be restored by AMPK and PPARgamma agonists, suggesting a potential therapeutic approach for FRDA.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Optogenetic investigation of the LGN koniocellular influence on V1 activity

The lateral geniculate nucleus (LGN) of the primate thalamus is organized into parallel parvo-, magno- and konio-cellular projection streams to primary visual cortex (V1). While magno and parvo cells label positive for Parvalbumin and project to layer-4 of V1, konio neurons project to the superficial layers of V1 and are positive for CamKII and Calbindin [1] [2]. Of the three systems, our understanding of the konio pathway and its contribution to vision is still very limited. Here we used optogenetics in anaesthetized macaque monkeys to investigate the influence of koniocellular LGN neurons on V1. To this end we injected the construct AAV5-CamKIIa-ChR2-eYFP into the LGN of two monkeys. Post-mortem histological and immunohistochemical analysis verified that ChR2 expression was predominantly present in the koniocellular system, which is characterized by its expression of CamKII and a focus on the LGN intercalated layers. In earlier experiments optogenetic stimulation that was applied to neurons in the LGN intercalated layers resulted in activation of the superficial layers in V1, but not layer 4, as determined from current-source-density measurements (CSD) from multi-contact laminar recordings in V1. Preliminary analysis of the cortical LFP also showed a power decrease in the beta frequency range (15-30Hz) for the superficial layers during optogenetic stimulation. In additional control experiments in one monkey, we found that electrical micro-stimulation in a parvocellular layer activated layer 4 of V1 similar to visual flicker stimulation. In contrast, electrical microstimulation in the intercalated LGN layers induced activity in superficial layers of V1 similarly to the optogenetic stimulation. In summary, we show for the first time the effective connectivity of the koniocellular LGN projection to V1 and its influence on the LFP. Methodologically, our results demonstrate that both circuit probing approaches, optogenetics and electrical microstimulation, render results with very similar specificity. Reference 1. Hendry, S.H. and T. Yoshioka, A neurochemically distinct third channel in the macaque dorsal lateral geniculate nucleus. Science, 1994. 264(5158): p. 575-577. 2. Casagrande, V.A., et al., The morphology of the koniocellular axon pathway in the macaque monkey. Cereb Cortex, 2007. 17(10): p. 2334-2345

Theta Rhythmic Neuronal Activity and Reaction Times Arising from Cortical Receptive Field Interactions during Distributed Attention

Growing evidence suggests that distributed spatial attention may invoke theta (3-9 Hz) rhythmic sampling processes. The neuronal basis of such attentional sampling is, however, not fully understood. Here we show using array recordings in visual cortical area V4 of two awake macaques that presenting separate visual stimuli to the excitatory center and suppressive surround of neuronal receptive fields (RFs) elicits rhythmic multi-unit activity (MUA) at 3-6 Hz. This neuronal rhythm did not depend on small fixational eye movements. In the context of a distributed spatial attention task, during which the monkeys detected a spatially and temporally uncertain target, reaction times (RTs) exhibited similar rhythmic fluctuations. RTs were fast or slow depending on the target occurrence during high or low MUA, resulting in rhythmic MUA-RT cross-correlations at theta frequencies. These findings show that theta rhythmic neuronal activity can arise from competitive RF interactions and that this rhythm may result in rhythmic RTs potentially subserving attentional sampling.28(15):2377-2387.e5

Reward-Related Suppression of Neural Activity in Macaque Visual Area V4

In order for organisms to survive, they need to detect rewarding stimuli, for example, food or a mate, in a complex environment with many competing stimuli. These rewarding stimuli should be detected even if they are nonsalient or irrelevant to the current goal. The value-driven theory of attentional selection proposes that this detection takes place through reward-associated stimuli automatically engaging attentional mechanisms. But how this is achieved in the brain is not very well understood. Here, we investigate the effect of differential reward on the multiunit activity in visual area V4 of monkeys performing a perceptual judgment task. Surprisingly, instead of finding reward-related increases in neural responses to the perceptual target, we observed a large suppression at the onset of the reward indicating cues. Therefore, while previous research showed that reward increases neural activity, here we report a decrease. More suppression was caused by cues associated with higher reward than with lower reward, although neither cue was informative about the perceptually correct choice. This finding of reward-associated neural suppression further highlights normalization as a general cortical mechanism and is consistent with predictions of the value-driven attention theory

Functional identification of primate lateral geniculate nucleus projections to visual cortex using optogenetics and electrical stimulation

Optogenetics and electrical stimulation are routinely used to assess neuronal connectivity. However cell-specific approaches, especially in primates, are still very limited. Here we compare the capacities of optogenetics and electrical stimulation to isolate the specific pathways from the lateral geniculate nucleus (LGN) to primary visual cortex (V1) in the macaque visual system. The organization of LGN into three anatomically separate and neurochemically distinct cell projection systems with virtually no cross-talk provides unique conditions to test for cell-specific targeting by electrical and optogenetic stimulation techniques. For the optogenetics experiments, we injected AAV5-CamKIIα-ChR2-eYFP into the LGN of four macaque monkeys. Histological analysis revealed primarily the predicted laminar expression pattern of the optogenetic construct in CamKIIα-rich LGN konio layers, but also showed some expression in parvalbumin positive magno- and parvo cells. We also observed a retrograde tracing mechanism of the AAV5 virus particles that labeled V1 layer 6 cortico-thalamic feedback neurons and retinal ganglion cells. That expression of the construct also allowed modulation of spiking activity in LGN was confirmed in prior electrophysiology experiments. Neurons expressing ChR2 could be identified reliably based on their short latency (<5ms) spiking responses to direct blue light (473nm) stimulation. Parallel laminar-resolved recordings of the V1 local field potential showed that selective activation of LGN konio layers with optogenetics caused selective electrical current inflow in the supra-granular layers of V1 in agreement with anatomical predictions about the koniocellular projection. Electrical stimulation of LGN konio layers revealed the same supra-granular V1 activation pattern. In contrast, electrical stimulation of LGN parvo layers activated also V1 granular layers in a way that closely resembled visual stimulus driven responses. These findings indicate comparable capacities of both stimulation methods to isolate and identify spatially segregated thalamo-cortical circuit mechanisms of the primate brain

Neuron

Electrical microstimulation and more recently optogenetics are widely used to map large-scale brain circuits. However, the neuronal specificity achieved with both methods is not well understood. Here we compare cell-targeted optogenetics and electrical microstimulation in the macaque monkey brain to functionally map the koniocellular lateral geniculate nucleus (LGN) projection to primary visual cortex (V1). Selective activation of the LGN konio neurons with CamK-specific optogenetics caused selective electrical current inflow in the supra-granular layers of V1. Electrical microstimulation targeted at LGN konio layers revealed the same supra-granular V1 activation pattern as the one elicited by optogenetics. Taken together, these findings establish a selective koniocellular LGN influence on V1 supra-granular layers, and they indicate comparable capacities of both stimulation methods to isolate thalamo-cortical circuits in the primate brain