Purine level regulation during energy depletion associated with graded excitatory stimulation in brain.

Objectives: The formation and release of adenosine following graded excitatory stimulation of the brain may serve important physiological functions such as sleep regulation, as well as an early resistance mechanism against excitotoxicity. However, adenosine at high levels may reflect merely the results of obstructed energy metabolism.

Methods: We examined the extent to which levels of adenosine and adenylate energy charge are affected in vivo by graded excitatory stimulations of brain using unilateral intrastriatal injections of glutamatergic agents and head-focused high energy microwaving for accurate and precise measures of purines.

Ryanodine receptor modulation by diadenosine polyphosphates in synaptosomal and microsomal preparations of rat brain.

Diadenosine polyphosphates (Ap(n)As) are transmitter-like substances that act intracellularly via unclear mechanisms. Here we tested hypotheses that diadenosine tetraphosphate (Ap(4)A) modulates ryanodine binding in microsomal and synaptosomal fractions of rat brain, and that Ap(4)A affects modulation of ryanodine binding by divalent cations and caffeine. Using [3H]ryanodine-binding assays, we showed that Ap(4)A produced significant and concentration-dependent increases in [3H]ryanodine binding in microsomes and these actions were reduced by Mg(2+) and potentiated by caffeine.

Brain glycogen decreases with increased periods of wakefulness: implications for homeostatic drive to sleep.

Sleep is thought to be restorative in function, but what is restored during sleep is unclear. Here we tested the hypothesis that increased periods of wakefulness will result in decreased levels of glycogen, the principal energy store in brain, and with recovery sleep levels of glycogen will be replenished, thus representing a homeostatic component of sleep drive. Using a high-energy focused microwave irradiation method to kill animals and thereby snap-inactivate glycogen-producing and -metabolizing enzymes, we determined, with accuracy and precision, levels of brain glycogen and showed these levels to decrease significantly by approximately 40% in brains of rats deprived of sleep for 12 or 24 hr.

Effects of nitrobenzylthioinosine on neuronal injury, adenosine levels, and adenosine receptor activity in rat forebrain ischemia.

Adenosine levels increase in brain during cerebral ischemia, and adenosine has receptor-mediated neuroprotective effects. This study was performed to test the hypothesis that nitrobenzylthioinosine (NBMPR), a selective and potent inhibitor of one adenosine transporter subtype termed ENT1, or es, can protect against ischemic neuronal injury by enhancing adenosine levels and potentiating adenosine receptor-mediated effects, including attenuation of the cellular production and release of tumor necrosis factor-alpha (TNF-alpha). In rats, the phosphorylated prodrug form of NBMPR, NBMPR-phosphate, or saline was administered by intracerebroventricular injection 30 min before forebrain ischemia.

Calcium signaling in the ER: its role in neuronal plasticity and neurodegenerative disorders.

Endoplasmic reticulum (ER) is a multifaceted organelle that regulates protein synthesis and trafficking, cellular responses to stress, and intracellular Ca2+ levels. In neurons, it is distributed between the cellular compartments that regulate plasticity and survival, which include axons, dendrites, growth cones and synaptic terminals. Intriguing communication networks between ER, mitochondria and plasma membrane are being revealed that provide mechanisms for the precise regulation of temporal and spatial aspects of Ca2+ signaling.