Properties of glutamate receptors of Alzheimer's disease brain transplanted to frog oocytes

Abstract

It is known that Alzheimer's disease (AD) is a synaptic disease that involves various neurotransmitter systems, particularly those where synaptic transmission is mediated by acetylcholine or glutamate (Glu). Nevertheless, very little is known about the properties of neurotransmitter receptors of the AD human brain. We have shown previously that cell membranes, carrying neurotransmitter receptors from the human postmortem brain, can be transplanted to frog oocytes, and their receptors will still be functional. Taking advantage of this fact, we have now studied the properties of Glu receptors (GluRs) from the cerebral cortices of AD and non-AD brains and found that oocytes injected with AD membranes acquired GluRs that have essentially the same functional properties as those of oocytes injected with membranes from non-AD brains. However, the amplitudes of the currents elicited by Glu were always smaller in the oocytes injected with membranes from AD brains. Western blot analyses of the same membrane preparations used for the electrophysiological studies showed that AD membranes contained significantly fewer GluR2/3 subunit proteins. Furthermore, the corresponding mRNAs were also diminished in the AD brain. Therefore, the smaller amplitude of membrane currents elicited by Glu in oocytes injected with membranes from an AD brain is a consequence of a reduced number of GluRs in cell membranes transplanted from the AD brain. Thus, using the comparatively simple method of microtransplantation of receptors, it is now possible to determine the properties of neurotransmitter receptors of normal and diseased human brains. That knowledge may help to decipher the etiology of the diseases and also to develop new treatments.neurotransmitter receptors ͉ postmortem brain ͉ Xenopus oocytes

Loss of functional GABA A receptors in the Alzheimer diseased brain

“…The microtransplantation method is very convenient for pharmacological and biophysical experiments of human native receptors. However, previous reports mention a large variability in the amplitude of responses among microtransplanted oocytes (10,11,19). Therefore, we determined the response distribution of single brains (SI Results and Fig.…”

“…Lower levels of GABA A Rsubunits α1, α2, α4, δ, and β2 mRNAs in the prefrontal cortex of AD brains (3) and of α1, α5, and β3 mRNAs in the AD hippocampus (2,9) suggest that some receptors may have an altered functional profile in AD. Our initial experiments, evaluating the feasibility of recording the activity of native receptors from frozen brains (10) and of studying glutamate receptors in AD (11), revealed an unexpected and substantial decrease in the amplitude of ionic responses to GABA (i.e., GABA currents) in temporal cortices of AD brains. This reduction was correlated with diminished expression of all GABA transcripts analyzed (α1, α2, α5, β2, β3, γ2) and with decreased α1 subunit protein (11).…”

“…Our initial experiments, evaluating the feasibility of recording the activity of native receptors from frozen brains (10) and of studying glutamate receptors in AD (11), revealed an unexpected and substantial decrease in the amplitude of ionic responses to GABA (i.e., GABA currents) in temporal cortices of AD brains. This reduction was correlated with diminished expression of all GABA transcripts analyzed (α1, α2, α5, β2, β3, γ2) and with decreased α1 subunit protein (11). However, it remains to be determined how those reductions affected the function of GABA A Rs in cellular membranes.…”

Microtransplantation of neurotransmitter receptors from postmortem autistic brains to Xenopus oocytes

“…However, fresh human brain tissues are difficult to obtain, and it was highly desirable to determine whether the frozen postmortem brain tissues that are available from brain banks all over the world could be used to study the function and structure of neurotransmitter receptors and ion channels of the human brain. Initial experiments using tissues from postmortem Alzheimer's brains have already shown that their cell membranes contain functional GABA and glutamate receptors as well as calcium channels (21,22). However, the postmortem intervals (PMIs) of the brains used in those studies were mostly only a few hours in duration (Ͻ5.3 h).…”

The Effect of L-Proline on Two Recombinant AMPA Glutamate Receptors

“…Alteration in the composition, number, subtypes and/or activity of glutamate receptors have also been shown to be associated with mental illnesses, neurodegenerative diseases such as Alzheimer's and in other neurological disorders, such as epilepsy and ischemia (Meldrum 2000;Bernareggi et al 2006;Borbely et al 2009). Glutamate receptors are divided into two major groups based on the pathway that is activated upon binding of glutamate or other agonists to the receptors (Dingledine et al 1999).…”