Tricarboxylic Acid Cycle Substrates Prevent PARP-Mediated Death of Neurons and Astrocytes

The DNA repair enzyme, poly(ADP-ribose) polymerase-1 (PARP1), contributes to cell death during ischemia/reperfusion when extensively activated by DNA damage. The cell death resulting from PARP1 activation is linked to NAD+ depletion and energy failure, but the intervening steps are not well understood. Because glycolysis requires cytosolic NAD+, the authors tested whether PARP1 activation impairs glycolytic flux and whether substrates that bypass glycolysis can rescue cells after PARP1 activation. PARP1 was activated in mouse cortical astrocyte and astrocyte-neuron cocultures with the DNA alkylating agent, N-methyl- N ′-nitro- N-nitrosoguanidine (MNNG). Studies using the 2-deoxyglucose method confirmed that glycolytic flux was reduced by more than 90% in MNNG-treated cultures. The addition of 5 mmol/L of α-ketoglutarate, 5 mmol/L pyruvate, or other mitochondrial substrates to the cultures after MNNG treatment reduced cell death from approximately 70% to near basal levels, while PARP inhibitors and excess glucose had negligible effects. The mitochondrial substrates significantly reduced cell death, with delivery delayed up to 2 hours after MNNG washout. The findings suggest that impaired glycolytic flux is an important factor contributing to PARP1-mediated cell death. Delivery of alternative substrates may be a promising strategy for delayed treatment of PARP1-mediated cell death in ischemia and other disorders.

The Intraparietal Cortex: Subregions Involved in Fixation, Saccades, and in the Visual and Somatosensory Guidance of Reaching

The functional activity of the intraparietal cortex was mapped with the [14C]deoxyglucose method in monkeys performing fixation of a central visual target, saccades to visual targets, reaching in the light during fixation of a central visual target, and acoustically triggered reaching in the dark while the eyes maintained a straight ahead direction. Different subregions of the intraparietal cortical area 7 were activated by fixation, saccades to visual targets, and acoustically triggered reaching in the dark. Subregions in the ventral part of the intraparietal cortex (around the fundus of the intraparietal sulcus) were activated only during reaching in the light, in which case visual information was available to guide the moving forelimb. In contrast, subregions in the dorsal part of the intraparietal cortical area 5 were activated during both reaching in the light and the dark, in which cases somatosensory information was the only one available in common. Thus, visual guidance of reaching is associated with the ventral intraparietal cortex, whereas somatosensory guidance, based on proprioceptive information about the current forelimb position, is associated with dorsal intraparietal area 5.

Correlation between Hypermetabolism and Neuronal Damage during Status Epilepticus Induced by Lithium and Pilocarpine in Immature and Adult Rats

The correlation between seizure-induced hypermetabolism and subsequent neuronal damage was studied in 10-day-old (P10), 21-day-old (P21), and adult rats subjected to lithium-pilocarpine status epilepticus (SE). Local CMRglc (LCMRglc) values were measured by the [14C]2-deoxyglucose method for a duration of 45 minutes starting at 60 minutes after the onset of SE, and neuronal damage was assessed by cresyl violet staining at 6 days after SE. In P21 and adult rats, LCMRglc values were increased by 275 to 875% in all thalamic, cortical, forebrain, and hypothalamic regions plus the substantia nigra. In addition, at P21 there were also large increases in LCMRglc in brainstem regions. In P10 rats, metabolic increases were mostly located in cortical and forebrain regions plus the substantia nigra but did not affect hypothalamic, thalamic, or brainstem areas. In adult rats, there was an anatomical correlation between hypermetabolism and neuronal damage. At P21, although hypermetabolism occurred in regions with damage, the extent of damage varied considerably with the animals and ranged from an almost negligible to a very extended degree. Finally, in P10 rats, although quite pronounced hypermetabolism occurred, there was no neuronal damage induced by the seizures. Thus, in the present model of epilepsy, the correlation between marked hypermetabolism and neuronal damage can be shown in adult rats. Conversely, immature rats can sustain major metabolic activations that lead either to a variable extent of damage, as seen at P21, or no damage, as recorded at P10.