Learning and memory deficits consequent to reduction of the fragile X mental retardation protein result from metabotropic glutamate receptor-mediated inhibition of cAMP signaling in Drosophila.

Loss of the RNA-binding fragile X protein [fragile X mental retardation protein (FMRP)] results in a spectrum of cognitive deficits, the fragile X syndrome (FXS), while aging individuals with decreased protein levels present with a subset of these symptoms and tremor. The broad range of behavioral deficits likely reflects the ubiquitous distribution and multiple functions of the protein. FMRP loss is expected to affect multiple neuronal proteins and intracellular signaling pathways, whose identity and interactions are essential in understanding and ameliorating FXS symptoms. We used heterozygous mutants and targeted RNA interference-mediated abrogation in Drosophila to uncover molecular pathways affected by FMRP reduction. We present evidence that FMRP loss results in excess metabotropic glutamate receptor (mGluR) activity, attributable at least in part to elevation of the protein in affected neurons. Using high-resolution behavioral, genetic, and biochemical analyses, we present evidence that excess mGluR upon FMRP attenuation is linked to the cAMP decrement reported in patients and models, and underlies olfactory associative learning and memory deficits. Furthermore, our data indicate positive transcriptional regulation of the fly fmr1 gene by cAMP, via protein kinase A, likely through the transcription factor CREB. Because the human Fmr1 gene also contains CREB binding sites, the interaction of mGluR excess and cAMP signaling defects we present suggests novel combinatorial pharmaceutical approaches to symptom amelioration upon FMRP attenuation.

Neuralized is expressed in the alpha/beta lobes of adult Drosophila mushroom bodies and facilitates olfactory long-term memory formation.

Memory formation involves multiple molecular mechanisms, the nature and components of which are essential to understand these processes. Drosophila is a powerful model to identify genes important for the formation and storage of consolidated memories because the molecular mechanisms and dependence of these processes on particular brain regions appear to be generally conserved. We present evidence that the highly conserved ubiquitin ligase Neuralized (Neur) is expressed in the adult Drosophila mushroom body (MB) alpha/beta lobe peripheral neurons and is a limiting factor for the formation of long-term memory (LTM). We show that loss of one copy of neur gene results in significant LTM impairment, whereas overexpression of Neur in the peripheral neurons of the alpha/beta lobes of the adult MBs results in a dosage-dependent enhancement of LTM. In contrast, learning, early memories, or anesthesia-resistant memory are not affected. We also demonstrate that the role of Neuralized in LTM formation is restricted within the neurons of the periphery of the alpha/beta lobes, and we suggest that this structural subdivision of the MBs participates in the formation of LTM.

Characterisation of the calcium paradox in the isolated perfused pigeon heart: protection by hypothermia, acidosis and alkalosis.

The aim of the present investigation was to examine the conditions inducing a calcium paradox in the isolated perfused pigeon heart. Loss of mechanical and electrical activity, creatine phosphokinase and total protein release were used to define cell damage. Perfusion was performed at 36, 38, 40 and 42 degrees C and calcium deprivation lasted 5, 10, 20 or 40 min. At low temperatures even prolonged calcium depletion failed to induce a calcium paradox. After a 40 min calcium depletion at normal body temperature (42 degrees C) ventricular activity ceased and a major contraction occurred followed by an increase in resting tension. During the 20-min reperfusion period the release of creatine phosphokinase was 267.18 +/- 0.8 IU/g of dry wt and the total amount of protein loss was 109.3 +/- 1.0 mg/g of dry wt, while lower temperatures resulted in a decreased loss of protein and creatine phosphokinase. Using two different Tyrode's perfusion buffers instead of normal bicarbonate ones, a protection of the pigeon heart against the induction of this phenomenon was observed. Furthermore, acidosis as well as alkalosis protected the heart as estimated by the significant recovery of electromechanical activity, and the quite low total protein and creatine phosphokinase losses. The results of this study suggest that the basic mechanisms and damaging effects of calcium overloading are common in mammalian and pigeon hearts.