Glutamate is widely acknowledged as the most prominent excitatory neurotransmitter used by the mammalian central nervous system. This project employs the hippocampal formation of the rat brain as a test system with which to investigate the mechanisms of glutamate transmission. The present proposal focuses on three presynaptic mechanisms: autoreceptor regulation of the release process, alterations of the release process due to eicosanoid production and the involvement of proline. Recent work suggests that glutamate/aspartate release can be enhanced by activation of the NMDA receptor and depressed by activation of either the ACPD or the AP4 metabotropic receptor. The mechanisms by which these forms of autoregulation operate are not understood. Slice and synaptosomal preparations of hippocampal area CA1 will be used to address this problem. These preparations release both glutamate and aspartate in a Ca2+-dependent manner from terminals of the extrinsic Schaffer collateral-commissural-ipsilateral associational pathway. Release of these excitatory amino acids will be quantitated during depolarization of CA1 synaptosomes with agents that work by different mechanisms (elevated K+, 4-aminopyridine, veratridine). In parallel experiments, terminal depolarization, [Ca2+]i and synaptic vesicle cycling will be measured. By studying the effects of receptor ligands on these measures, it will be possible to determine some of the cellular processes involved in autoregulation. Eicosanoids (arachidonic acid and its metabolites) are produced and released in large amounts during neuropathological states, and they may mediate the NMDA recep- tor-dependent enhancement of release. Eicosanoids released from the CA1 area during NMDA receptor activation will be identified, their possible involvement in NMDA receptor-mediated autoregulation will be assessed and their effects on the release process will be determined. Finally, a method will be developed to evoke and quantitate the release of glutamate and aspartate from area CA1 in vitro by stimulation of excitatory afferent fibers. This method will be used to determine the physiological and/or pathological conditions under which autoreceptor regulation of glutamate/aspartate release can be detected. Proline is an excitatory and excitotoxic imino acid that can block memory formation. Na+-dependent, high affinity uptake of proline is expressed by a subset of glutamate pathways. These properties argue that proline plays a role in excitatory transmission. Studies of glutamate synthesis and release and of excitatory synaptic transmission will be carried out to elucidate this role. An important tool will be antibodies directed against the presumed transport site of the cloned transporter. Findings from these studies will be relevant to the treatment of neurological conditions, such as epilepsy, which involve hyperactivity of the hippocampal formation, as well as to the etiology of childhood seizures associated with hyperprolinemia. They may also prove relevant to synaptic mechanisms of memory and learning.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
2R01NS016064-14
Application #
3396652
Study Section
Neurological Sciences Subcommittee 1 (NLS)
Project Start
1980-04-01
Project End
1996-03-31
Budget Start
1993-04-08
Budget End
1994-03-31
Support Year
14
Fiscal Year
1993
Total Cost
Indirect Cost
Name
Duke University
Department
Type
Schools of Medicine
DUNS #
071723621
City
Durham
State
NC
Country
United States
Zip Code
27705
Nadler, J Victor (2011) Aspartate release and signalling in the hippocampus. Neurochem Res 36:668-76
Bradford, S E; Nadler, J V (2004) Aspartate release from rat hippocampal synaptosomes. Neuroscience 128:751-65
Cohen, S M; Nadler, J V (1997) Proline-induced inhibition of glutamate release in hippocampal area CA1. Brain Res 769:333-9
Cohen, S M; Nadler, J V (1997) Sodium-dependent proline and glutamate uptake by hippocampal synaptosomes during postnatal development. Brain Res Dev Brain Res 100:230-3
Cohen, S M; Nadler, J V (1997) Proline-induced potentiation of glutamate transmission. Brain Res 761:271-82
Peterson, C L; Thompson, M A; Martin, D et al. (1995) Modulation of glutamate and aspartate release from slices of hippocampal area CA1 by inhibitors of arachidonic acid metabolism. J Neurochem 64:1152-60
Bowe, M A; Nadler, J V (1995) Polyamines antagonize N-methyl-D-aspartate-evoked depolarizations, but reduce Mg2+ block. Eur J Pharmacol 278:55-65
Zhou, M; Peterson, C L; Lu, Y B et al. (1995) Release of glutamate and aspartate from CA1 synaptosomes: selective modulation of aspartate release by ionotropic glutamate receptor ligands. J Neurochem 64:1556-66
Nadler, J V; Thompson, M A; McNamara, J O (1994) Kindling reduces sensitivity of CA3 hippocampal pyramidal cells to competitive NMDA receptor antagonists. Neuropharmacology 33:147-53
Martin, D; Thompson, M A; Nadler, J V (1993) The neuroprotective agent riluzole inhibits release of glutamate and aspartate from slices of hippocampal area CA1. Eur J Pharmacol 250:473-6

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