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Metabotropic glutamate receptor-mediated hippocampal phosphoinositide turnover is blunted in spatial
M M Nicolle1, P J Colombo, M Gallagher
1Mayo Clinic, Department of Pharmacology, Jacksonville, Florida 32224, USA. nicolle.michelle@mayo.edu
Abstract:
Maximal phosphoinositide (PI) turnover was examined in the hippocampus of young and aged Long-Evans rats that were behaviorally characterized for spatial learning in the Morris water maze. The type 1 metabotropic glutamate receptor (mGluR) agonist 1S,3R ACPD was used to stimulate PI turnover and to determine the E(MAX) for each rat. Protein levels in hippocampus for type 1 mGluRs, Galphaq11, and phospholipase Cbeta-1 (PLCbeta-1) were also measured by quantitative Western blotting. The results show that PI turnover mediated by the mGluRs was blunted in the aged rats. The magnitude of the decrement in PI turnover was also significantly correlated with age-related spatial memory decline. The decrease in mGluR-mediated PI turnover occurred without changes in the protein level of either the mGluRs or the G-protein coupled to those receptors, Galphaq11. A significant decrease in the immunoreactivity of PLCbeta-1, however, was observed in the hippocampus of aged rats; PLCbeta-1 immunoreactivity was significantly correlated with spatial learning only when the young and aged rats were considered together. The decrement in mGluR-mediated signal transduction in the hippocampus that is related to cognitive impairment in aging may be attributable, at least in part, to a deficiency in the enzyme PLCbeta-1. That deficiency may also contribute to a blunted response in muscarinic stimulation of hippocampal PI turnover that we previously found in this same study population. An age-related alteration in this signal transduction system may provide a functional basis for cognitive decline independent of any loss of neurons in the hippocampus.
Insights
Aging impairs hippocampal phosphoinositide (PI) turnover, a key signaling pathway. This decline in PI turnover is linked to reduced spatial memory in aged rats, potentially due to lower phospholipase Cbeta-1 (PLCbeta-1) enzyme levels.
Area of Science:
- Neuroscience
- Neurobiology
- Aging Research
Background:
- Aging is associated with cognitive decline, particularly in spatial memory.
- Signal transduction pathways in the hippocampus are crucial for learning and memory.
- Metabotropic glutamate receptors (mGluRs) play a role in hippocampal function.
Purpose of the Study:
- To investigate age-related changes in phosphoinositide (PI) turnover mediated by type 1 metabotropic glutamate receptors (mGluRs) in the rat hippocampus.
- To determine the relationship between mGluR-mediated PI turnover and spatial learning ability in young and aged rats.
- To examine the protein levels of key components of the PI turnover pathway, including mGluRs, Galphaq11, and phospholipase Cbeta-1 (PLCbeta-1).
Main Methods:
- Behavioral characterization of spatial learning using the Morris water maze in young and aged Long-Evans rats.
- Stimulation of PI turnover using the mGluR agonist 1S,3R ACPD to determine maximal turnover (Emax).
- Quantitative Western blotting to measure protein levels of type 1 mGluRs, Galphaq11, and PLCbeta-1 in hippocampal tissue.
Main Results:
- Maximal PI turnover mediated by mGluRs was significantly blunted in aged rats compared to young rats.
- The reduction in PI turnover in aged rats was significantly correlated with their performance in spatial learning tasks.
- While mGluR and Galphaq11 protein levels remained unchanged, PLCbeta-1 immunoreactivity was significantly decreased in aged rats' hippocampi.
- PLCbeta-1 immunoreactivity showed a significant correlation with spatial learning when both age groups were analyzed together.
Conclusions:
- A deficiency in the enzyme phospholipase Cbeta-1 (PLCbeta-1) likely contributes to the age-related decrement in mGluR-mediated signal transduction in the hippocampus.
- This impaired signal transduction may underlie age-related cognitive deficits, specifically in spatial memory, independent of neuronal loss.
- Alterations in this hippocampal signaling system offer a functional basis for age-related cognitive decline.