EphrinB ligands and their Eph receptor tyrosine kinases are known to regulate excitatory synaptic functions in the hippocampus. In the CA3-CA1 synapse, ephrinB ligands are localized to the post-synaptic membrane, while their cognate Eph receptors can be expressed in both pre-and post-synaptic membranes. Previous studies show that interaction of ephrinB molecules with Eph receptors leads to changes in long-term potentiation (LTP), suggesting that reverse signaling through postsynaptic ephrinBs may be required for learning and memory. Our collaborative studies demonstrate that the cytoplasmic domain of ephrinB3, and hence reverse signaling, is not required for ephrinB-dependent learning and memory tasks or for LTP of these synapses. We demonstrate that ephrinB3 null mutants show changes in several synaptic proteins including reduced levels of NMDA receptor subunits. These abnormalities are not observed in ephrinB3lacZ reverse signaling mutants, supporting an Eph receptor forward signaling role for ephrinB3 in these processes. NMDA receptors are important in regulating synaptic functions and plasticity in the adult hippocampus, and Eph receptors have been shown to cluster NMDA receptors to the cell membrane. These studies show that ephrinB3 interacts with EphA4 to regulate plasma membrane levels of NR1 in Cos-1 cells and primary hippocampal neurons. In the absence of ephrinB3, NR1 levels are decreased in synaptosomal membranes, increased in microsomal tissues, but not changed in total extracts. This suggests that ephrinB3 regulates NR1 levels through protein trafficking and not gene transcription. Analysis of protein trafficking confirmed that ephrinB3 specifically interacts with EphA4 receptor to regulate NR1 exocytosis but not endocytosis in both transfected Cos-1 cells and primary hippocampal neurons. We postulate that ephrin-Eph receptor interactions are important mediators of synaptic formation and function, in part, through their regulation of NMDA receptors in the hippocampal synapse. In addition, we find that both ephrinB3KO and ephrinB3lacZ mice show an increased number of excitatory synapses, demonstrating a cytoplasmic-dependent reverse signaling role of ephrinB3 in regulating synapse number. Together, these data suggest that ephrinB3 may act like a receptor to transduce reverse signals to regulate the number of synapses formed in the hippocampus, and that it likely acts to stimulate forward signaling through Eph receptors to modulate NMDA receptor trafficking, LTP and learning.

Carbon monoxide (CO) has been identified as an endogenous biological messenger in the brain. Heme oxygenase (HO) catalyzes the metabolism of heme to CO and biliverdin. CO has been shown to act as a neurotransmitter and neuronal messenger in the brain. We reported recently that CO was involved in central cardiovascular regulation, modulated the baroreflex, may affect glutamatergic neurotransmission, and metabotropic glutamate receptors (mGluRs) may be coupled to the activation of HO in the nucleus tractus solitarii (NTS) of rats. We also reported previously that adenosine can increase the release of glutamate in the NTS. The present study was designed to investigate the possible interaction of CO, adenosine, and mGluRs groups in the NTS. Male Sprague-Dawley rats were anesthetized with urethane, and blood pressure were monitored intra-arterially. Unilateral microinjection of ascending doses of hemin (0.01 to 3.3 nmol), a heme molecule cleaved by HO to yield CO, produced decreases in blood pressure and heart rate dose-dependently. In addition, similar cardiovascular effects were observed in adenosine (2.3 nmol) and several agonists for mGluRs groups such as DHPG (group ¢¹) (0.03 nmol), APDC (group ¢º) (0.3 nmol)and L-AP4 (group ¢») (0.3 nmol). These cardiovascular effects of hemin were attenuatd by prior administration of the adenosine receptor antagonist DPSPX (0.92 nmol). Similarly, pre-treatment of HO inhibitor ZnPP¢Á or ZnDPBG (1 nmol) also attenuated the depressor and bradycadic effects of adenosine. Among the mGluRs agonists, prior administration of ZnPP¢Á (1 nmol), an inhibitor of HO activity, significantly attenuated the cardiovascular effects of APDC and L-AP4, and failed to prevent the cardiovascular responses of DHPG. These results indicated an interaction between CO and adenosine, and group ¢º and ¢» mGluRs may be coupled to the activation of HO in central cardiovascular regulation.

Diss.--Turku--Å̊bo Akademi University, 2003. / Contient cinq articles du même auteur publiés dans des revues scientifiques. Bibliogr. p. 35-43.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 74-91).

Ph.d.

Ph.D.

Thesis (Ph. D.)--University of Missouri--Columbia, 2002. / "December 2002." Typescript. Vita. Includes bibliographical references (leaves 121-148). Also issued on the Internet.

Thesis (Ph. D.)--University of Missouri--Columbia, 2002. / "December 2002." Typescript. Vita. Includes bibliographical references (leaves 117-119). Also issued on the Internet.

Drosophila is a simple and genetically tractable model system for studying neural circuits. This dissertation consists of two studies, with the broad goal of understanding sensory processing in neural circuits using Drosophila as a model system.

NMDA receptor signaling is required for proper synapse formation, maintenance, plasticity and function. Dysregulation of the NMDA receptor has been implicated in pathophysiology of schizophrenia, which has an adult onset of symptoms. NMDA receptor deficient mice were utilized to assess the developmental consequences of NMDA receptor hypofunction. Locomotor activity was elevated throughout development; however, deficits in social interaction and working memory only manifest in adulthood and did not progress with age. Age-dependent deficits in neuron synapse biology were also detected; postsynaptic spine number was normal in juveniles, decreased post-adolescence, and progressively declined in adulthood. To investigate possible molecular mechanisms underlying the observed changes in spine number, protein levels of RhoGTPases and their downstream effectors were examined. Significant changes in Rac1 and downstream effectors were detected at different developmental stages. These studies provide clarification of the temporal sequence of events and mechanisms by which NMDA receptor dysfunction affects neurodevelopment.