ENDOGENOUS REGULATORS OF GLUTAMATE-ACTIVATED CHANNELS

A basic understanding of many neuropsychiatric disorders has focused on the
synapse as a critical site in the disease process; this has led in several
examples to design of successful therapeutic strategies. In neurology and
psychiatry, much of this emphasis has been on the catecholamine pathways,
however it is increasing apparent that excitatory amino acids acting as
neurotransmitters and neuromodulators also play key physiological roles.
L-glutamate activates several receptor subtypes including the N-methyl-D-
aspartate (NMDA) receptor, and is the major excitatory transmitter in many
brain regions including the limbic system. The NMDA receptor has recently
been shown to underlie a slow excitatory postsynaptic potential at these
synapses. This transmitter system has been implicated in neurodegenerative
diseases such as Huntington's and Alzheimer's disease, in ischemic brain
injury, and in learning and memory. Recent studies, particularly of the
NMDA receptor/channel, suggest that glutamate-activated receptors and ion
channels have a complex pharmacology including several modulatory sites
which dramatically influence the function of the receptor/channel complex;
both endogenous and exogenous agents including psychoactive drugs such as
phencyclidine (PCP) act on these modulatory sites. However, little is
known of the structure or detailed physiological mechanisms of these
ligand-gated ion channels, thus the ability to manipulate this system
therapeutically is presently limited. The long range goal of this project is relate the function of these
receptors and their modulatory sites to their structure; this approach
should allow the design of more effective therapeutic agents as well as
guide molecular biological approaches to these receptors. The objective of
this proposal is to examine in detail a known endogenous regulator of the
NMDA channel as a step toward an understanding of channel function. The
focus will be on two important, unresolved aspects of glutamate receptor
functions: 1. the mechanism of NMDA channel regulation by transition
metal ions including zinc; and 2. the kinetic properties of NMDA channels
evoked by synaptic stimulation. Two preparations will be used: primary
dissociated cultures of rodent hippocampus, and Xenopus oocytes injected
with poly (A) + mRNA purified from rat hippocampus. Single channel and
voltage clamp electrophysiological methods will be used. Agonist-gated
channels will be activated by exogenously applied agonists; as well as by
activation of single presynaptic neurons in the cultures hippocampal
preparation. It is expected that these results will provide important new
information concerning the function and regulation of glutamate receptors
in the CNS.